Samuel Masket, MD,
Shaleen Belani, MD
Contents
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Glare Disability |
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Contrast Sensitivity |
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Measurement of Contrast Sensitivity Function |
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Combination of Glare and Contrast Sensitivity Testing |
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Intraoperative Floppy Iris Syndrome |
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Assessment of Potential Visual Function Following Cataract Removal |
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A Paradigm for the Clinical Evaluation of the Patient with Cataract |
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CHAPTER HIGHLIGHTS |
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Preoperative evaluation of patients with visually significant cataracts is threefold. It includes an appreciation of the severity of the cataract, an assessment of the overall visual prognosis after cataract extraction, and a determination of preoperative conditions that may complicate surgery. The latter, in particular, includes the now well described intraoperative floppy iris syndrome (IFIS) associated with the use of alpha blocking agents, originally described by Chang and Campbell.[1]
Advanced cataract formation produces a characteristic symptom, profound visual loss, which may be deduced from the patient's medical history. Likewise, the physical findings of a well-developed cataract can be determined during a basic ocular examination, which includes simple tests of visual function. Cataracts in earlier stages or in eyes with concomitant disease, however, require a greater degree of diagnostic skill and clinical investigation to determine the visual significance of the cataract and how to best advise and treat the patient in question.
Until recently, the only device used to assess the loss of visual function associated with cataract formation was Snellen acuity testing developed by Dr. Hermann Snellen during the middle of the nineteenth century. Snellen testing employs high-contrast familiar letter optotypes. As such, it is a measure of the optical resolving power of the ocular system. Moreover, Snellen testing is performed under the controlled lighting conditions (generally darkened) of the refracting lane and therefore does not simulate the varied visual challenges of daily life. Patients with certain types of cataract in relatively early stages often note diminished visual function, although good Snellen acuity may be maintained.[2,][3,][4,][5]
Given that “real-life” conditions present a far more complex series of visual clues to interpret than does Snellen testing, there has been an interest in and a need for the development of additional methods for testing visual function. Such devices have been referred to as tests of “functional vision,” which are designed to simulate the visual disability induced by ocular disease and its impact on the visual tasks presented under conditions of daily life. Two general categories of functional vision testing devices have been developed; one system tests for glare disability, or diminution of vision induced by ambient light, and the other evaluates contrast sensitivity function (CSF), which tests visual recognition of varying target sizes against backgrounds of differing contrasts. Although the two testing systems have significant overlaps and a reduction in one function often leads to a diminution of the other, they are distinctly different, but vital, aspects of functional vision evaluation. They are useful in assessing the visual loss attributed to cataract and other ocular diseases when good Snellen acuity is noted despite significant visual complaints offered by the patient. Tests of visual function are designed to aid in the determination of the visual significance of cataract formation; they are not intended to be used as screening devices or to induce patients without functional complaints to have surgery.
Preoperative evaluation of the patient with cataract additionally requires an appreciation of the visual prognosis for surgery, or potential visual acuity. This is particularly valuable for patients with ocular disease occurring in association with cataract formation. Several methods are available to help determine the potential postoperative vision.
During the last decade, the Agency for Health Care Policy and Research, a previous arm of the Department of Health and Human Services, performed a comprehensive review of cataract care and issued a set of guidelines outlining suggested preoperative, intraoperative, and postoperative management of the adult with cataract.[6] They were a framework on which a paradigm (see further on) was constructed for the evaluation of the adult with cataract. Included in the guidelines, among other material, was a review of the ophthalmic literature regarding preoperative functional vision testing. The guidelines recognized that functional vision loss may be noted with certain cataract types and good Snellen acuity. Recently, The American National Standards Institute (ANSI) designated linear sine-wave gratings as the standard for measurement of contrast sensitivity. A survey of members of the American Society of Cataract and Refractive Surgery in 1998 indicated that 65% of the respondent members employed either glare disability testing or CSF in evaluating the patient with cataract.[7]
On the other hand, advanced cataracts, those that prohibit adequate ophthalmoscopy, require to be evaluated for the potential visual benefit of their removal because the integrity of the retina and optic nerve cannot be assessed by routine means.
Finally, the preoperative evaluation should include an assessment of conditions that may complicate surgery. This includes as assessment of pupillary dilation and zonular support. It is especially important to review the medication history for the use of alpha-1 blocking agents as preoperative and intraoperative measures can be utilized to adequately control complications arising from intraoperative floppy iris syndrome (IFIS).
Glare disability
Glare may be considered a subjective visual response to light. In the absence of significant ocular disease, bright light may induce discomfort glare before retinal photic adaptation; visual function, however, is unimpaired by discomfort glare. Conversely, disability glare implies that there is a reduction in visual function caused by the scattering of incoming light by inhomogeneity of the ocular media. As in other ocular diseases that induce partial opacification of the ocular media, cataracts disperse incoming light, creating forward light scatter and a “veiling luminance” that interferes with the perception of the visual object of regard. More commonly, this phenomenon is called glare disability (Figure 3-1).[4] In general, opacities of the anterior segment (cataract being the most typical) are associated with glare disorders, whereas posterior segment abnormalities are less likely to induce disabling glare. The closer the media opacity is to the retinal image plane, the less the geometric opportunity for light scattering and obscuring of the image. Therefore, corneal edema is a more likely source of glare than is macular edema.[8] Cataracts disperse incoming light and are anterior in the path of light. Therefore, patients with cataracts may exhibit marked disability glare while retaining good visual acuity under favorable lighting conditions, such as the darkened refracting lane. Cortical and posterior subcapsular cataracts generally cause daytime glare more readily than do nuclear cataracts, which are more prone to cause nighttime glare. [9] Glare disability, therefore, is a common cataract-related symptom, and testing for glare should be sufficiently sensitive to correlate well with patient complaints and adequately specific to avoid confusion with posterior segment disorders.
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Figure 3-1 Glare resulting from oncoming car headlight hinders the ability to view pedestrians, as the dispersed light veils the objects. Glare loss is inversely related to the distance between the glare source and the object of regard. The pedestrian nearer the headlight is obscured more than is the pedestrian farther from the light. |
Several useful devices for determining and measuring glare disability have been employed in clinical practice (Table 3-1). These devices, which may be in short supply today, are generally designed to test a function of vision with and without the addition of an offending light or glare source. The difference in visual function with and without the glare source is attributed to glare disability. However, each testing system uses a different glare source (central or peripheral point light sources, diffuse background illumination, and so on) and test of visual function (letter optotypes, sine wave gratings, Landolt ring, and so on). The brightness acuity tester (BAT) (Figure 3-2)[10] is in common use because it is readily portable, compact, and relatively inexpensive and may be used in conjunction with the Snellen chart of the refracting lane. The BAT offers three levels of background illumination in a small hemispheric bowl held near the eye. As a result, one possible source of error is pupil constriction by the illuminator; certain patients with cataract will perform better with pupil constriction, thereby giving a false-negative test. Conversely, the third level of brightness is dazzling, inducing false-positive results. Moreover, because no point source of light is used, the BAT does not simulate night-driving conditions.
Table 3-1 -- Automated instruments for measuring glare disability
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Instrument |
Manufacturer |
Test Format |
Glare Light |
|
BAT |
Mentor |
Letter acuity |
Background |
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Eye Con 5 |
Eye Con |
Letters |
Background |
|
IRAS GT |
Randwal Instrument Co |
Sine wave acuity |
4-point |
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MCT 8000 |
Vistech |
Sine wave contrast |
Points or background |
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Miller-Nadler |
Titmus Optical |
Landolt C contrast |
Background |
|
TVA |
Innomed |
Letter acuity |
Point |
From Ocular surgery news, Stack, Inc, Thorofare, NJ.
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Figure 3-2 Brightness acuity tester (BAT). Handheld device allows patient to view distance charts. The bowl presents diffuse background illumination at three levels of light intensity. |
Another popular device is the Miller–Nadler glare testing device (Figure 3-3).[11] This unit relies on a modified tabletop slide projector to provide diffuse background illumination against which the patient views one of a series of 20/400-sized Landolt rings that sit on a constant-contrast background circle. The rings vary in contrast to the background. Because the Miller–Nadler system employs background glare with a contrast test, it may be useful in simulating daytime glare disability but has been faulted for offering only one object size.[12]
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Figure 3-3 Clinical model Miller–Nadler glare tester. The unit is a modified tabletop projector. Glare is induced by the background illumination of the projector. The chin rest support system maintains consistent testing distance. |
As noted in Table 3-1, other automated devices have been developed and marketed. Moreover, simple, albeit noncalibrated, methods may also be used to assess glare disability. One simple means is to measure Snellen acuity indoors and then retest the patient outdoors with the chart positioned in front of the direct sunlight. Another method is to direct a penlight obliquely toward the pupillary margin while Snellen testing is underway; the difference between the Snellen acuity with and without the penlight is attributed to glare disability.[13]
No uniform standards have been established for glare testing devices, a fact that limits their acceptance by rigidly scientific criteria. Nevertheless, it appears that measurement of disabling glare is most useful because it correlates well with cataract symptoms and is reversible with successful cataract surgery.[14–16]
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Contrast sensitivity
Activities of daily living, such as driving an automobile, confront the individual with an ever-changing set of visual targets, luminances, and contrasts that require rapid visual interpretation. CSF evaluates the patient's ability to perceive a variety of coarse, intermediate, or fine details at differing contrasts relative to the background (Figure 3-4). In such fashion, contrast testing seeks to objectively assess the equivalent of the patient's visual function in daily life.
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Figure 3-4 Representative portion of preprinted contrast sensitivity test plates. Note varied orientation of contrast bars. |
Contrast sensitivity testing is somewhat analogous to audiometry, which measures hearing threshold sensitivity to audible tones of differing intensities and audio frequencies. Snellen testing of visual acuity, which is performed only at high contrast, is similar to audiometry performed at only one volume, or much like listening to music in which all notes are played at maximum loudness. Therefore, contrast sensitivity testing is a much more complete form of vision analysis than is Snellen testing.[17] Nevertheless, because different object sizes are tested in both systems, a clear relationship exists between visual acuity and contrast sensitivity. The 20/20 “E” optotype subtends a total of 5′ arc on the retina, with each arm and each space accounting for 1′. As noted in Figure 3-5, a contrast grating pattern correlates to the arm and space of the letter “E.” One dark and one light bar together equal one cycle. Thirty cycles per degree (or 60′) of retinal arc, therefore, correspond to the spacing of a 20/20 optotype. It follows then, that just one point, 30 cycles degree, on a contrast sensitivity curve (Figure 3-6) at high contrast corresponds to the 20/20 line of Snellen testing. The typical human contrast sensitivity curve, noted in Figure 3-6, reveals that the peak contrast sensitivity of the visual system occurs at image sizes near six cycles per degree as subtended on the retina. An object that subtends six cycles per degree on the retina corresponds in size to a 20/100 optotype. This indicates that the human visual system requires higher contrast for perception at higher spatial frequencies. Therefore, it is possible that the eye may perceive small target sizes at high contrast while not recognizing larger objects at reduced contrast levels. This concept offers an explanation for the visual complaints of patients who retain reasonably good Snellen acuity yet express difficulty in “real-life” visual function.
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Figure 3-5 Comparison between 20/20 letter “E” optotype and contrast sensitivity bars. Note that the arm and space of the letter subtend 2′ arc and are equal in size to a contrast bar and space at 30 cycles per degree. Therefore, at high contrast the 30 cycles per degree bar is equivalent to 20/20 Snellen acuity. |
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Figure 3-6 CSF curve typical for the normal eye depicted as solid line with surrounding gray area that corresponds to two standard deviations of the normal mean. Note that peak sensitivity occurs near six cycles per degree of subtended retinal arc. The arrow denotes the portion of the curve that corresponds to 20/20 Snellen acuity. |
Given that CSF is analogous to a greatly expanded form of Snellen testing, it stands to reason that reduced contrast function will occur at high spatial frequencies when visual acuity is reduced for any reason, including uncorrected refractive errors and a number of anterior segment abnormalities, for example, keratoconus and pterygium.[18] CSF, therefore, is quite sensitive but not as specific as disability glare testing when evaluating symptomatic cataract.[19] It has been reported that early cataracts reduce contrast sensitivity primarily at high and intermediate frequencies (Figure 3-7),[20,][21] whereas optic neuropathies are purported to reduce contrast sensitivity at low frequencies. Early PSC and cortical cataracts have the greatest effect on reducing CSF at intermediate frequencies, while early nuclear cataracts primarily reduce CSF at high spatial frequencies.[22] Reduced CSF has also been noted and reported in a host of posterior segment disorders, including macular degeneration and diabetic retinopathy.[18]
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Figure 3-7 Typical CSF curve of the presurgical cataract patient. Note that the CSF curve of both eyes falls below the range of the accepted norm (90th percentile). The left eye (broken line) has markedly diminished contrast sensitivity yet the same high-contrast Snellen acuity as the right eye. |
In addition, interest has centered on the effect of monocular cataract on binocular visual function. By means of CSF testing, it has been established that at high spatial frequencies, binocular contrast sensitivity decreases to a level below that of the cataractous eye alone. This demonstrates binocular visual inhibition and indicates that a patient with one cataract may suffer significant visual disability, even when the noncataractous eye has normal monocular vision.[23,][24] Furthermore, this information suggests that correcting only one eye in a patient with binocular cataracts may not fully improve functional vision; often the second eye will require surgery for the patient to gain the benefits of cataract rehabilitation. Moreover, a patient's perceived visual disability with cataract may correlate better with tests of binocular contrast sensitivity than with any of the monocular tests of visual function.[25]
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Measurement of contrast sensitivity function
The determination of a CSF curve for the eye requires measurement of two separate functions: (1) the perceived contrast threshold between the object and the background and (2) the target size of the object subtended on the retina and measured in cycles per degree. Originally used as a research tool in the evaluation of ocular and neural diseases, early contrast testing systems used a series of sinusoidal (sine wave) grating patterns (Figures 3-4, 3-8, and 3-9). Currently, the familiar letter optotype contrast charts (Table 3-2) designed by Terry (Figure 3-10), Pelli-Robson (Figure 3-11), and Regan are used as clinical alternatives to sine wave gratings, and CSF is often measured in a fashion similar to Snellen testing, with the patient reading letter charts of differing contrasts. The Regan charts each employ log MAR optotypes between 20/200 and 20/20 at varying contrasts of 96%, 50%, 25%, 11%, and 4%. The 25% and 11% Regan contrast charts have been found particularly useful in evaluating cataract patients.[26] Because the Regan charts present letter targets of differing sizes at varied contrasts, they can be used to establish a true CSF curve for the eye, whereas the Pelli-Robson and Terry charts offer only one size of letter targets. Both attempt to evaluate the most sensitive part of the contrast sensitivity curve, near six cycles per degree. Without targets of varied sizes, a complete contrast curve for the eye cannot be determined.
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Figure 3-8 A, Sinusoidal grating pattern used in testing contrast sensitivity. B, Luminance versus spatial relationship in sinusoidal grating patterns. |
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Figure 3-9 Computerized contrast sensitivity apparatus used for determining CSF. Contrast patterns are presented on a video display terminal as generated by the computer. |
Table 3-2 -- Letter optotype charts for contrast sensitivity testing
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Pelli-Robson |
Regan |
Terry |
|
|
Contrast range |
1–100% |
4%, 11%, 25%, 50%, 96% |
2.5–80% |
|
Letter sizes |
20/80 |
20/20–20/200 |
20/70 |
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Testing distance |
10 ft |
10 ft |
10 ft |
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Figure 3-10 The Terry acuity standard contrast chart. Letter optotype chart with contrast between letters and background varying between 2.5% and 80%. Letter size is equal to 20/70 optotype viewed at 10 ft. Nighttime driving may be hazardous for the patient who cannot read line 5 or above. This chart is for demonstration purposes only. |
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Figure 3-11 A portion of the Pelli–Robson letter contrast sensitivity chart. Note that the letters are of equal size but differ in contrast. |
When contrast sensitivity is measured with letter charts, the room and chart illumination must be standardized. Self-contained tabletop vision testing devices offer the possible advantage of uniform internal illumination for enhanced reproducibility. Table 3-3 lists the available automated devices for evaluating CSF. Unfortunately, as in the case of glare disability testing, there has been no consensus on the appropriate standards for contrast sensitivity testing, and a number of devices are available to determine CSF, with each of them employing a somewhat different manner.
Table 3-3 -- Contrast sensitivity testing devices
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Device |
Manufacturer |
Format |
Target Type |
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B-VAT II |
Mentor |
Computer screen |
Sine wave |
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CSV 1000 |
Vector Vision |
Illuminated wall chart |
Sine wave |
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Eye Con 5 |
Eye Con |
Computer screen |
Letters |
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MCT 8000 |
Vistech |
Tabletop view box |
Sine wave |
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Optec 1000 |
Stereo Optical |
Tabletop view box |
Sine wave |
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Optec 2000 |
|||
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TVA |
Innomed |
Computer screen |
Square wave |
|
VCTS |
Vistech |
Near-far charts |
Sine wave |
From Ocular surgery news, Stack, Inc, Thorofare, NJ.
Advances in CSF include digital-image-processing software which translates contrast-sensitivity data into modified pictures that represent what the patient actually sees.[27] These images closely represent the quality of vision and can be used to evaluate visual function before and after surgery as well as compare IOL designs with respect to CSF.
In addition to light-scatter, loss of contrast sensitivity induced by cataract formation is also due to optical aberrations induced by lens changes, which can be measured using wavefront aberrometry.[28] Developed primarily for corneal refractive surgery, wavefront aberromety may be a useful method of detecting early lenticular changes in patients with subjective complaints and good Snellen acuity. In one study,[29] higher order aberrations of the whole eye and cornea alone were compared in eyes with nuclear and cortical cataract and eyes without cataract formation. While corneal higher-order aberrations were statistically equivalent between the three groups, patients with lenticular opacities had more higher-order aberrations than normal eyes and the polarity of the aberration depended on the nature of the cataract. In this study, nuclear cataracts induced negative aberrations while cortical cataracts induced positive aberrations. In another study, higher order aberrations were three times greater in eyes with nuclear sclerosis and two times greater in eyes with cortical cataracts compared to normal eyes.[28]
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Combination of glare and contrast sensitivity testing
It has been well established that glare disability reduces the contrast sensitivity of the visual system.[30] Therefore, certain glare testing systems, such as the Miller–Nadler glare tester, evaluate the effect of a glare source on contrast targets to determine glare disability. Testing of CSF or low-contrast visual acuity in the presence of glare is superior to the testing of disability glare with high-contrast targets in assessing cataract patients with essentially normal neuroretinal function.[31] It has become common practice to evaluate visual function when combining the BAT as a glare source with the Regan or Pelli–Robson contrast sensitivity charts.[25] This form of testing has been adopted by the United States Food and Drug Administration as requisite for determining visual function after placement of multifocal lens implants. Conversely, separate glare or contrast tests may have specific value for assessing other neural-visual conditions.[12] Given that high-contrast testing alone is of limited value in simulating the visual complaints of the patient with cataracts, it is likely that clinicians will accept into daily practice the combination of low-contrast visual acuity testing with an added glare source as the most effective means to quantify cataract-induced visual symptoms. A simple and gross system employs a penlight as a glare source in combination with Pelli–Robson contrast charts.[32] Hopefully, standard means for combining glare and contrast testing for the evaluation of patients with symptomatic cataract will be established and widely accepted among academicians, clinical practitioners, and regulating organizations.
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Intraoperative floppy iris syndrome
In 2005, Chang and Campbell[1] described what is now increasingly recognized and commonly known as intraoperative floppy iris syndrome (IFIS). This condition is associated with the systemic use of alpha 1A blocking agents such as tamsulosin (Flomax, Boehringer Ingelheim Pharmaceuticals, Inc.) for the non-surgical management of benign prostatic hyperplasia. It is important to recognize the potential for IFIS in the preoperative evaluation of the cataract patient. Its manifestations include iris floppiness or instability, poor pupillary dilation, progressive intraoperative miosis, and billowing of iris tissue in the presence of routine irrigating currents. Previous reports indicated increased complication rates in the presence of IFIS, including posterior rupture; however, identifying these patients preoperatively and applying preventative strategies can reduce or eliminate these complications. Standard methods for dealing with small pupils, such as pupil stretching maneuvers, do not help in the management or prevention of this condition.
Appropriate strategies include pharmacologic stimulation of the iris dilator muscle and blockade of the pupil sphincter, mechanical enlargement of the pupil with hooks or other devices, altered fluidic parameters during the phacoemulsification process, use of highly cohesive OVDs, or a combination of any or all of these modalities. Since there is considerable heterogeneity in the behavior of the iris in these patients, a tailored approach should be used in each patient.
Pharmacologic stimulation of the weakened iris dilator muscle with preservative-free, buffered intracameral epinephrine in a 1:2500 dilution has been shown to be safe and effective.[33] This approach helps to stabilize the iris, improves pupillary dilation and reduces iris floppiness. There may also be a synergistic benefit of using preoperative atropine 1% 2 days prior to surgery in addition to intraoperative intracameral epinephrine.[34] Atropine sulfate, as the strongest available pupiloplegic agent is a logical approach for pupillary dilation and preventing intraoperative miosis. Intracameral phenylephrine has also been reported to successfully reverse pupillary constriction and stabilize the iris intraoperatively in patients with IFIS.[35]
Though tamsulosin has the highest affinity for the alpha 1A receptor, it is important to perform a thorough medication history on these patients in order to determine if they are on any alpha 1A blocking agents besides tamsulosin. IFIS has also been reported with the use of alfuzosin[36] (Uroxatral, Sanofi-Aventis) and naftopidil[37] for benign prostatic hyperplasia and doxazosin for the treatment of systemic hypertension.[38] It has also been reported in a patient taking labetolol, which has predominantly beta-blocking effects, but some alpha-blocking effects as well.[39]
It is important that patients suffering from benign prostatic hyperplasia do not stop their alpha 1A blocker, especially when preoperative atropine is used, as acute urinary retention or systemic hypertension may ensue. Preoperative identification of patients on alpha 1A blockers and using appropriate strategies to deal with this condition can eliminate its potential complications.
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Assessment of potential visual function following cataract removal
Patients with symptomatic cataract formation and otherwise normal ocular examinations can anticipate amelioration of their diminished vision with successful cataract removal. However, patients with cataract and concomitant ocular disease, for example, macular degeneration, may present a dilemma in management because ophthalmoscopy may be misleading or particularly difficult with advanced cataracts. Often, the patient and surgeon are reluctant to consider cataract surgery when the prognosis for return of visual function is limited. Nevertheless, in some cases of multiple ocular disease, cataract rehabilitation may prove significantly beneficial to the patient. Determination of the expected visual improvement after surgery may allow the patient to arrive at an appropriate decision for or against surgery. Toward that end, a few devices for the determination of potential retinal function or visual return have been brought to the clinical arena (Tables 3-4 and 3-5).
Table 3-4 -- Devices for determination of potential visual acuity
|
Guyton-Minkowski Potential Acuity Meter (Mentor) |
Reduced Snellen chart |
|
Lotmar Visometer (Haag-Streit) |
Laser interferometer |
|
Rodenstock (Rodenstock) |
Laser interferometer |
|
IRASInterferometer (Randwal) |
Laser interferometer |
Table 3-5 -- Methods for determination of retinal function-integrity
|
Blue-field entoptoscopy (Mira) |
Foveal capillary net |
|
Visual evoked potential |
Evoked cortical responses |
|
Electroretinography |
Electroretinography |
|
B-scan ultrasonography |
Imaging |
|
Pinhole acuity |
Potential acuity |
|
Penlight entoptic phenomena |
Purkinje images |
|
Maddox rod |
Gross macular function |
|
Two-point discrimination |
Gross retinal function |
|
Color perception |
Gross macular function |
Testing devices for the determination of potential visual acuity attempt to project visible targets through the cataract, in order to reach the retina for subjective interpretation. One system, the Guyton–Minkowski potential acuity meter (PAM),[40] is temporarily attached to a slit lamp and uses a reduced Snellen chart that is projected through a pinhole aperture onto the macular region; refractive errors may be compensated for by the apparatus. The principle of using a pinhole aperture to assess the potential visual acuity after proposed cataract surgery has been further adapted in the potential acuity pinhole test.[41] In this method, the increased depth of focus afforded by pinhole apertures is combined with bright light from a transilluminator to assess potential vision in the presence of a cataract. It is reported to be more accurate than the PAM.[42] The second type of potential acuity apparatus uses laser-generated interference stripes or fringes that are projected onto the retinal surface through the ocular media; the width of the fringes, corresponding to acuity, is variable.[43–46]Refractive errors need not be corrected with interferometry testing because projection of the laser images on the retina is not affected by ametropia.
The potential acuity devices – whether the Snellen chart, the PAM or the interferometry fringes – are subjective methods that require an alert and cooperative patient, in addition to a skilled and compassionate examiner. Moreover, these tests are of greatest value when the cataract has not advanced past the 20/200 level, because very dense lens opacities may yield false-negative results. A clinical rule of thumb indicates that a predicted improvement of four lines of vision by the acuity tester suggests a good prognosis for cataract surgery. Typically, if a patient's best corrected visual acuity is recorded at 20/70, a 20/30 potential acuity response is considered indicative of significant visual improvement with surgery. Caution must be exercised in interpreting the results of potential acuity testing because some cases of maculopathy may yield a false-positive response, whereas extremely dense cataracts may produce false-negative results.
In addition, simple and less expensive clinical tools may be useful in determining the visual prognosis after cataract removal in cases of suspected macular disease. One method is the yellow filter test suggested by Koch.[47] In this system, when a transparent yellow filter is placed over reading material, it is noted to worsen vision in the presence of a significant cataract but might be noted to improve vision if the macular degenerative process is more significant than the cataract.
Occasionally, a cataract or other media opacity may be sufficiently dense to preclude any view of the posterior segment; in such cases, the prognosis for return of vision cannot be assessed by the aforementioned testing devices. A number of alternative means to determine gross potential acuity in patients with markedly advanced cataracts have been developed over time and may be useful. Two-point discrimination, penlight-generated entoptoscopy, gross color perception, blue-field entoptoscopy, and Maddox rod testing are among the available tests of certain value (see Table 3-5). Standard B-scan ultrasonographic imaging and electrophysiologic studies, such as electroretinography and the visual-evoked potential, may provide useful information when considering an eye with totally opaque media, but these methods may be too costly for routine use in determining indication for cataract surgery.
In two-point discrimination testing, two light sources of equal intensity are held about 25inches (or 62cm) from the patient. If the patient can correctly identify the two lights, retinal function is assumed to be grossly intact. No information is learned about macular potential. This test is most useful in cases of fully mature cataracts or otherwise dense ocular media. Similarly, gross color perception may be useful as a tool to establish general retinal integrity; the cobalt blue light source or the green filter (red-free source) of the slit lamp may be useful for this purpose.
Tests of entoptic phenomena have also been used to assess the function of the retina. A penlight or transilluminator may be placed over the closed lid or directly on the globe to stimulate perception of the Purkinje vascular tree images. Although some patients may observe and describe the retinal vasculature, optic nerve, and macular region accurately, other patients, even with intact retinas, cannot observe the Purkinje images. Therefore, the test is most useful in comparing the two eyes of one patient, assuming that one eye is normal and the involved eye has opaque media. In patients with one normal eye and one eye with densely opaque media, testing for an afferent pupillary defect may also be beneficial, because at virtually all stages of development cataracts do not induce abnormal pupillary reactions.
Blue-field entoptoscopy is more specific for macular function and is based on the ability of the patient to observe the flow of white blood cells in the parafoveal capillaries. Blue light is absorbed by the red blood cells but not the white blood cells. As a result, with proper filters and an appropriate bright light source, the patient can observe “flying corpuscles” or white blood cells if the fovea is functionally intact. Unfortunately, the test requires a special apparatus, relies on a carefully discerning patient as observer, and may yield false-negative results with dense cataracts.
A Maddox rod may be used as a simple test of macular function in patients in whom the ocular media is not totally opaque. The Maddox rod is held in front of the eye to be tested, and a light source is held approximately 14inches (or 35cm) away. If the patient observes an unbroken red line, one may assume macular integrity. A discontinuity of the red line suggests a macular lesion. A totally opaque cataract or vitreous will not allow perception of the Maddox rod.
Imaging with B-scan ultrasonography may be helpful to determine the presence of vitreous hemorrhage or retinal detachment in cases of mature cataract. However, little to no information about macular function can be learned from imaging, whereas simple clinical testing (light projection, two-point discrimination, etc.) may offer an impression sufficient to determine an indication for surgery.
Electroretinography, which estimates overall rod function, is of little value in determining postoperative vision potential. Although evaluation of visual-evoked potential is more specific for macular function than is electroretinography, simpler clinical tests are generally as valuable in establishing a surgical indication, given the high success rate and low complication rate associated with modern cataract surgery.
Scanning laser ophthalmoscopy, a relatively new testing tool, is capable of imaging the retina in the presence of a significant cataract.[48] However, the cost of the device makes it impractical to use for the sole purpose of presurgical screening.
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A paradigm for the clinical evaluation of the patient with cataract
At present, there is no single, specific, valid, objective test of visual function to indicate the presence of an operable cataract. Rather, new testing tools add to the battery of ocular function tests and, when combined with a careful analysis of patient symptoms, physical findings, and assessment of potential visual function, they offer a rational means of determining an indication for cataract surgery.
Above all, and central to the issue of appropriate indications for cataract surgery, is the patient's history of visual disturbance and what impact the visual deficit has on the patient's daily tasks of life. A history of significant functional impairment may make it appropriate to remove a posterior subcapsular cataract despite distance Snellen acuity of 20/25 or better, if near vision is reduced or disabling glare is present. Conversely, an asymptomatic sedentary individual with a dense uniocular brunescent nuclear cataract may not perceive a significant benefit from surgery if visual symptoms are not noted. An old clinical adage suggests that it is impossible to help an asymptomatic patient; that concept remains valid today. Written entries in the patient's medical record should clearly state the patient's symptoms and the effect they have on activities of daily living. An activities-of-life scale, with written record for documentation, has been proposed as a means of evaluating the subjective significance of a patient's cataract.[49] Moreover, the patient's symptoms should correspond to the vision loss associated with cataract formation, whereas the progressive inability to see traffic signs under night lighting or against background glare could certainly be induced by evolving cataracts.
The objective ocular examination of the patient with cataract must be comprehensive to establish the absence or presence of concomitant ocular and systemic disease that might also produce visual symptoms or bear on the prognosis for recovery of vision. In addition, contraindications for surgery, such as untreated active blepharitis or uncontrolled intraocular pressure, should also be ascertained.
Best (spectacle) corrected acuity for distance and near vision should be determined; meaningful refractive changes might be significant because nuclear cataracts often induce a myopic shift. Given that cataract extraction with lens implantation is the most common procedure performed under Medicare coverage and accounts for $3 billion of health care expenditures, patients, third-party payers, and regulatory agencies have an understandable interest in the appropriateness of cataract surgery. As a result, certain agencies (e.g., State Professional Standard Review Organizations) have set limits of visual acuity (generally 20/50 spectacle corrected distance acuity) as appropriate for cataract surgery. However, it has long been well established that Snellen visual acuity alone is not an adequate means to establish indication for surgery.
Consideration of compromised near vision is often overlooked by review organizations. Posterior subcapsular cataracts are noted for their deleterious effect on reading acuity well in advance of marked reduction in distance acuity. Unfortunately, there are no governmentally ordained minimum requirements for near vision. Conversely, posterior subcapsular (and cortical) cataracts tend to induce symptoms of daytime glare with attendant visual disability. Although no specific glare testing device has received the tacit approval of review organizations, the clinician can employ any of the appropriate methods (see Table 3-1) to measure glare disability to establish documentation for proposed cataract surgery deemed necessary by patient symptoms. Daytime glare disability is best simulated by tests that use a diffuse background glare source.
Nuclear cataracts ordinarily reduce distance vision more than they do near vision. As a result, patients who are visually symptomatic with nuclear cataracts are more likely than patients with posterior subcapsular cataract to fall within review organizations' guidelines for surgical indications. This may be particularly true for some patients with opalescent (oil droplet appearance on retinoscopy) nuclear cataracts who may experience early loss of distance acuity. However, in some cases, advanced nuclear brunescence may be observed without a marked loss in Snellen acuity; the patients, however, are likely to complain about difficulty with nighttime vision, particularly while driving. Moreover, color perception may be significantly hampered by dense brunescent nuclear cataracts. If patients offer significant complaints regarding visual function in the presence of a nuclear cataract yet retain better than 20/50 Snellen acuity, it is likely that CSF will be reduced. In addition, tests of glare disability that simulate nighttime glare (peripheral or paracentral light spots rather than diffuse background illumination) are likely to demonstrate significant abnormality. Combinations of glare and contrast testing are certain to be best in documenting loss of vision function associated with nuclear cataracts.
Assuming that the patient's history suggests a significant visual deficit and that the physical findings support the presence of cataract formation commensurate with the functional vision loss, cataract surgery may be entertained. The patient must be the final arbiter in the decision to have cataract surgery. Moreover, it is essential to determine the prognosis for return of vision with the proposed cataract surgery. Tests of potential visual acuity must be entertained when the ocular findings include other pathologic features, particularly macular degeneration or optic neuropathy. When pupillary reactions are normal (no afferent defect) and the view of the fundus is sufficient to determine the lack of pathologic condition, specific tests of potential acuity are not necessary. However, if optic neuropathy is suspected, visual field studies should be performed. Moreover, in cases of macular degeneration, in which subretinal neovascularization may be considered, fluorescein angiography may be a useful diagnostic adjunct, although its quality is limited by media opacification. When employed in cases of questionable prognosis, specific tests of potential visual function may provide important information for clinician and patient. Given that the PAM, laser interferometers, and the potential acuity pinhole test can bypass some corneal disease, irregular astigmatism, and refractive errors, they are otherwise useful guides when the relative visual significance of a cataract is difficult to measure in view of concomitant disease of the posterior pole. In cases of extraordinarily dense or mature cataracts, one might consider the use of B-scan ultrasonography in addition to tests of entopic phenomena and so on.
Once the diagnosis of a visually significant, surgically remediable cataract has been established, the patient (and family members, as appropriate) should be counseled in regard to the findings and prognosis for return of vision. It is almost exclusively a patient-oriented decision whether to have surgery, as is the timing for the procedure. Assuming the patient chooses corrective surgery, it is then incumbent on the practitioner to ascertain the social and supportive needs of the patient during the perioperative period. Can the patient comply with the instructions for postoperative use of eyedrops or other medications? How will the patient be transported for surgery and postsurgical care? What assistance might the patient need for preparing meals early after surgery? These are a few of the pertinent questions.
When planning surgery for any given patient after determining that it is appropriate for and commensurate with the needs of the patient, a careful assessment of the eye to be operated on should be performed and a surgical plan established. The patient may wish to share in deciding the expected postoperative refraction, which is a particularly important consideration in cases of high preoperative ametropia. Presurgical planning should also consider corneal astigmatism and wound placement and construction. Size and type of intraocular lens might also be affected by the desired spherical and astigmatic results of surgery.
The comprehensive examination should also uncover potentially complicating factors, such as medication allergies, uncontrolled intraocular pressure, corneal endothelial compromise, a narrow chamber angle, a poorly dilating pupil, pseudoexfoliation, lens subluxation, posterior capsular defects (as in patients with posterior polar cataracts), a vitreoretinal pathologic condition with lattice peripheral retinal degeneration, and open retinal tears. In the days just before surgery, an external examination is helpful to rule out conjunctivitis or active blepharitis.
Requirements for presurgical medical evaluation may vary from region to region. However, elderly patients with cataract are subject to a range of general medical disorders. It may be beneficial to include the primary care physician in surgical planning, giving careful consideration to certain conditions, including diabetes, systemic hypertension, cardiovascular disease, pulmonary disorders, hyperthyroidism, anticoagulation, and long-term corticosteroid use.
In summary, the presurgical evaluation of the patient with a symptomatic cataract can be a significant and cognitive exercise. Depending on the density of the cataract and the degree of visual symptoms, the clinician must decide what tests are appropriate and necessary to fully evaluate the patient. After a thorough examination process, the patient can be informed of the findings and can make an educated selection from the options for care. If surgery is indicated and entertained, the patient's general medical and social conditions must also be explored before determining the best course of action.
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References
[1]. Chang D.F., Campbell J.R.: Intraoperative floppy iris syndrome associated with tamsulosin. J Cataract Refract Surg 2005; 31:664-673.
[2]. Hess R.F., Woo G.C.: Vision through cataracts. Invest Ophthalmol Vis Sci 1978; 17:428-435.
[3]. Cinotti A.A.: Evaluation of indications for cataract surgery. Ophthalmic Surg 1979; 10:25-31.
[4]. Jaffe N.S.: Glare and contrast: Indications for cataract surgery. J Cataract Refract Surg 1986; 12:372-375.
[5]. Koch D.D.: Glare and contrast sensitivity testing in cataract patients. J Cataract Refract Surg 1989; 15:158-164.
[6]. Cataract Management Guideline Panel: Cataract in adults: management of functional vision impairment. Clinical Practice Guideline, Number 4, Rockville, MD, US Department of Health and Human Services, Public Health Service, Agency for Health Care Policy and Research, February 1993. AHCPR Pub No. 93–0542
[7]. Koch D.D., Liu J.F.: Survey of the clinical use of glare and contrast sensitivity testing. J Cataract Refract Surg 1990; 16:707-711.
[8]. Carney L.G., Jacobs R.J.: Mechanisms of visual loss in corneal edema. Arch Ophthalmol 1984; 102:1068-1071.
[9]. Neumann A.C., McCarty G.R., Steedle T.O., et al: The relationship between cataract type and glare disability as measured by the Miller–Nadler glare tester. J Cataract Refract Surg 1988; 14:40-45.
[10]. Holladay J.T., Prager T.C., Trujillo J., et al: Brightness acuity test and outdoor visual acuity in cataract patients. J Cataract Refract Surg 1987; 13:67-70.
[11]. Hirsch R.P., Nadler P.M., Miller D.: Clinical performance of a disability glare tester. Arch Ophthalmol 1984; 102:1633-1636.
[12]. Elliot D.B., Bullimore M.A.: Assessing the reliability, discriminative ability, and validity of disability glare tests. Invest Ophthalmol Vis Sci 1993; 34:108-119.
[13]. Maltzman B.A., Horan C., Rengel A.: Penlight test for glare disability of cataracts. Ophthalmic Surg 1988; 19:356-358.
[14]. Masket S.: Reversal of glare disability after cataract surgery. J Cataract Refract Surg 1989; 15:165-168.
[15]. Cink D.E., Sutphin J.E.: Quantification of the reduction of glare disability after standard extracapsular cataract surgery. J Cataract Refract Surg 1992; 18:385-390.
[16]. Rubin G.S., Adamsons I.A., Stark W.J.: Comparison of acuity, contrast sensitivity, and disability glare before and after cataract surgery. Arch Ophthalmol 1993; 111:56-61.
[17]. Jindra L.F., Zermon V.: Contrast sensitivity testing: a more complete assessment of vision. J Cataract Refract Surg 1989; 15:141-148.
[18]. Masket S.: Glare disability and contrast sensitivity function in the evaluation of symptomatic cataract. Ophthalmol Clin North Am 1991; 4:365-380.
[19]. American Academy of Ophthalmology: Contrast sensitivity and glare testing in the evaluation of anterior segment disease (ophthalmic procedures assessment). Ophthalmology 1990; 97:1233-1237.
[20]. Adamsons I., Rubin G.S., Vitale S., et al: The effect of early cataracts on glare and contrast sensitivity: a pilot study. Arch Ophthalmol 1992; 110:1081-1086.
[21]. Drews-Bankiewicz M.A., Caruso R.C., Datiles M.B., et al: Contrast sensitivity in patients with nuclear cataracts. Arch Ophthalmol 1992; 110:953-959.
[22]. Chua B., Mitchell P., Cumming R.: Effects of cataract type and location on visual function: The Blue Mountains Eye Study. Eye 1994; 18:765-772.
[23]. Pardhan P., Gilchrist J.: The importance of measuring binocular contrast sensitivity in unilateral cataract. Eye 1991; 5:31-35.
[24]. Taylor R.H., Mission G.P., Moseley M.J.: Visual acuity and contrast sensitivity in cataract. Eye 1991; 5:704-707.
[25]. Elliot D.B., Hurst M.A., Weatherill J.: Comparing clinical tests of visual function in cataract with the patient's perceived visual disability. Eye 1990; 4:712-717.
[26]. Regan D.: The Charles F. Prentice Award Lecture 1990: specific tests and specific blindnesses: keys, locks, and parallel processing. Optom Vis Sci 1991; 68:489-512.
[27]. Ginsburg A.: Contrast sensitivity: determining the visual quality and function of cataract, intraocular lenses and refractive surgery. Curr Opinion in Ophthalmology 2006; 17:19-26.
[28]. Sachdev D., Ormonde S., Sherwin T., et al: Higher-order aberrations of lenticular opacities. J Cataract Refract Surg 2004; 30:1642-1648.
[29]. Kuroda T., Fujikado T., Maeda N.: Wavefront analysis in eyes with nuclear or cortical cataract. Am J Ophthalmol 2002; 134:1-9.
[30]. Abrahammson M., Sjostrand J.: Impairment of contrast sensitivity function (CSF) as a measure of disability glare. Invest Ophthalmol Vis Sci 1986; 27:1131-1136.
[31]. Elliot D.B., Hurst M.A., Weatherill J.: Comparing clinical tests of visual loss in cataract patients using a quantification of forward light scatter. Eye 1991; 5:601-606.
[32]. Williamson T.H., Strong N.P., Sparrow J., et al: Contrast sensitivity and glare in cataract using the Pelli–Robson chart. Br J Ophthalmol 1992; 76:719-722.
[33]. Shugar J.: Use of epinephrine for IFIS prophylaxis. J Cataract Refract Surg 2006; 32:1074-1075.
[34]. Masket S., Belani S.: Combined Pre-Operative Topical Atropine Sulfate 1% and Intracameral Non-preserved Epinephrine HCL 1:2500 for Management of Intraoperative Floppy Iris Syndrome. J Cataract Refract Surg 2007.In press
[35]. Manvikar S., Allen D.: Cataract surgery management in patients taking tamsulosin staged approach. J Cataract Refract Surg 2006; 32:1611-1614.
[36]. Settas G., Fitt A.W.: Intraoperative floppy iris syndrome in a patient taking alfuzosin for benign prostatic hypertrophy. Eye 2006; 20:1431-15143.
[37]. Oshika T., Ohashi Y.: Incidence of intraoperative floppy iris syndrome in patients on either systemic or topical alpha(1)–adrenoceptor antagonist. Am J Ophthalmol 2007; 143:150-151.
[38]. Muqit M., Menage M.: Intraoperative floppy iris syndrome. Ophthalmol 2006; 113:1885-1886.
[39]. Calotti F., Steen D.: Labetalol causing intraoperative floppy-iris syndrome. J Cataract Refract Surg 2007; 33:170-171.
[40]. Minkowski J.S., Palese M., Guyton D.L.: Potential acuity meter using a minute serial pinhole aperture. Ophthalmol 1983; 90:1360-1368.
[41]. Hofeldt A.J., Weiss M.J.: Illuminated near card assessment of potential acuity in eyes with cataract. Ophthalmol 1998; 105:1531-1536.
[42]. Meliki S.A., Safar A., Martin J., Ivanova A., et al: Potential acuity pinhole: A simple method of measure potential visual acuity in patients with cataracts: comparison to potential acuity meter. Ophthalmol 1999; 106:1262-1267.
[43]. Faulkner W.: Laser interferometric prediction of postoperative visual acuity in patients with cataracts. Am J Ophthalmol 1983; 95:626-636.
[44]. Tabbat S.E., Lindstrom R.L.: Laser retinometry versus clinical estimation of media: a comparison of efficacy in predicting visual acuity of patients with lens opacities. J Cataract Refract Surg 1986; 12:140-145.
[45]. Goldstein J., Hecht S.D., Jamara R.J., et al: Clinical comparison of the SITE IRAS hand held interferometer and Haag–Streit Lotmar visometer. J Cataract Refract Surg 1988; 14:208-211.
[46]. Bernth-Petersen P., Naeser K.: Clinical evaluation of Lotmar visometer for macula testing in cataract patients. Acta Ophthalmology 1982; 60:525-532.
[47]. Koch P.: Testing useful for cataract/macular disease patients. Ophthalmology Times 1992; 17:1, 30.
[48]. Kirkpatrick J.N., Manivannan A., Gupta A.K., et al: Fundus imaging in patients with cataract: role for a variable wavelength scanning laser ophthalmoscope. Br J Ophthalmol 1995; 79:892-899.
[49]. Mangione C.M., Phillips R.S., Seddon J.M., et al: Development of the “activities of daily vision scale.” A measure of visual functional status. Med Care 1992; 30:1111-1126.