Evaluating pterygium severity: a survey of corneal specialists.

PURPOSE: Accurate and reliable evaluation techniques are essential for clinical and epidemiologic studies. This survey of corneal specialists was designed to lay a foundation for the further development of methods for evaluating and staging pterygium. METHODS: In a self-administered, mailed questionnaire, 213 corneal specialists rated the importance of nine symptoms, nine signs, and nine clinical tests for the severity of primary pterygium. Severity was defined as the present need for surgical intervention. RESULTS: The most important factors for determining primary pterygium severity were the extent of encroachment onto the cornea, decreased visual acuity, restricted ocular motility, and increased rate of growth. Many patient symptoms were rated as moderately to highly important. The questionnaire was shown to have good response reliability by test-retest comparisons. Cronbach's alpha was 0.89, which indicates very good internal consistency reliability. CONCLUSION: The survey identifies the priorities of experts in determining the severity of pterygium. More precise and clearly defined evaluation methods will enhance future clinical and epidemiologic studies of pterygium. The ranked list of pterygium signs, symptoms, and tests can serve as a guide for developing pterygium evaluation methods in the future. There is a need for a method that accurately and precisely quantifies the distance of pterygium encroachment onto the cornea and the pterygium progression rate. Furthermore, there is a need for an assessment of patient symptoms.

Motorist vision policy.

BACKGROUND: The primary purpose of public policy requiring vision testing for driver license renewal is to identify individuals with functional vision impairments and, when necessary, to restrict their driving. This is based on the presumption that poor vision is causally related to poor driving and traffic crashes. METHODS: The AOA Environmental and Occupational Vision Committee performed a synthesis of relevant empirical literature on policy-based research and developed potential options for enhancing traffic safety. RESULTS: Presently, some states require vision testing for driver's license renewal and some do not. Regional and nationwide studies report that vision-related license renewal policies are associated with enhanced traffic safety. However, contemporary vision screening tests may be of limited value in identifying individuals with functional vision impairments. CONCLUSION: The most cost-effective and valid method for identifying, treating and counseling visually impaired drivers is to require a comprehensive eye examination as a condition for driver license renewal for those with a high prevalence or high probability of vision impairment.

Repeatability of visual acuity measurement.

PURPOSE: This study investigates features of visual acuity chart design and acuity testing scoring methods which affect the validity and repeatability of visual acuity measurements. METHODS: Visual acuity was measured using the Sloan and British Standard letter series, and Landolt rings. Identifiability of the different letters as a function of size was estimated, and expressed in the form of frequency-of-seeing curves. These functions were then used to simulate acuity measurements with a variety of chart designs and scoring criteria. RESULTS: Systematic relationships exist between chart design parameters and acuity score, and acuity score repeatability. In particular, an important feature of a chart, that largely determines the repeatability of visual acuity measurement, is the amount of size change attributed to each letter. The methods used to score visual acuity performance also affect repeatability. CONCLUSIONS: It is possible to evaluate acuity score validity and repeatability using the statistical principles discussed here.

Prospective randomized trial of vitrectomy or observation for stage 2 macular holes. Vitrectomy for Macular Hole Study Group.

PURPOSE: To determine the risks and benefits of vitrectomy surgery in eyes with stage 2 macular holes. METHODS: A multicentered, controlled, randomized clinical trial was performed with participation of 16 community and university-based ophthalmology clinics. Thirty-six eyes with stage 2 macular holes and 12 months of follow-up were studied. Pars plana vitrectomy with separation of the posterior hyaloid membrane and intraocular injection of perfluoropropane (C3F8) was followed by postoperative face-down positioning for two weeks. This protocol was compared with observation alone. Outcome variables included anatomic closure of the macular hole, macular hole size, and four standardized measures of vision. RESULTS: At 12 months, 15 (71%) of 21 eyes randomly assigned to observation progressed to stages 3 or 4, compared with three (20%) of 15 eyes randomly assigned to surgery (P < .006). Compared with eyes randomly assigned to observation, eyes randomly assigned to surgery had significantly smaller hole diameters (P < .01) and significantly better visual acuity outcomes, as measured by the Word Reading (P = .02) and Potential Acuity Meter (P = .002) charts. No significant differences were found for the Early Treatment Diabetic Retinopathy Study chart and Contrast Sensitivity test. CONCLUSION: Compared with observation alone, surgical intervention in stage 2 macular holes resulted in a significantly lower incidence of hole enlargement and appeared to be associated with better outcome in some measures of visual acuity.

Reading and eye movements in age-related maculopathy.

Reading characteristics were studied in age-related maculopathy (ARM) by monitoring eye movement patterns as subjects read word charts and text charts that contain a wide range of print sizes. Eye movements were monitored with an infrared scleral reflection device and subjects were tested over a wide range of chart luminances. In normal subjects, as print size approaches threshold, reading speed slows mainly because of a decrease in fixation rate, whereas regressive saccades remain infrequent. There is little change in the ratio of number of letters read per forward saccade. With decreased luminance, there is a decreased reading acuity but the relation between reading speed and the size of print relative to the threshold size remains relatively constant. Subjects with ARM show similar fixation rates to normals, but they average fewer letters per forward saccade and make more frequent regressions. ARM subjects are more likely to have reading performance strongly affected by luminance. The number of letters per forward saccade can show a strong dependence on luminance, whereas fixation rates remain relatively unchanged. It is proposed that reduced reading performance in ARM is predominantly the result of a reduced perceptual span, with poor oculomotor control playing a secondary role. Optimal print size may be best predicted from letter chart acuity (r = 0.70) or word reading acuity (r = 0.69). Word reading acuity is the best predictor of peak reading speed (r = -0.74), whereas peak reading speed is poorly correlated with contrast sensitivity (r = 0.26) and scotoma area (r = -0.42).

Low vision magnifiers--their optical parameters and methods for prescribing.

Information provided by manufacturers of low vision magnifiers is usually insufficient to allow the clinician to predict accurately the resolution improvement that patients may be expected to achieve. We have measured and tabulated the key optical parameters of 92 stand magnifiers and 53 hand-held magnifiers. For the fixed focus stand magnifiers, the image location and the equivalent power of the lens system have been determined and the enlargement ratio has been derived. For each magnifier, 3 different eye-to-lens distances (2.5, 10, and 25 cm) have been considered and, for each of these, the Equivalent Viewing Distance (EVD), the eye-to-image distance, and the theoretically predicted field width have been computed. The EVD is useful in predicting resolution performance because, for a given patient, the visual resolution limit will be directly proportional to the EVD. The eye-to-image distances allow the clinician to consider whether the patient will be in satisfactory focus or whether adjustments need to be made to the power of any reading addition. The stand magnifiers are listed in order of the EVD they give when the eye is a moderate (10 cm) distance from the magnifier. For the hand-held magnifiers, the equivalent powers have been measured. The EVD for a hand-held magnifier will be the same as the equivalent focal length of the magnifier if the lens is used so that the image is at or close to infinity. The tables include supplementary information on the size of the magnifier lenses and whether the magnifiers incorporate battery, electric, incandescent, or halogen lighting systems. Examples are presented to illustrate how the tables might be used in the selection of magnifiers to meet the resolution and other needs of individual patients.

Considerations in the subjective assessment of cataract.

The subjective classification of lens opacities is a fundamental component in both the clinical evaluation of the individual patient and in large-scale clinical trials. This procedure has been improved substantially by the implementation of standardized photographic systems depicting various levels of nuclear opacity and color, cortical, and posterior-subcapsular cataract. Comparison can also be made with recently developed objective measurements of opacity and color. Further improvements in reliability and sensitivity to change can be achieved by modifying traditional integer scaling systems by interpolating between photographic standards.

The Lens Opacities Classification System III. The Longitudinal Study of Cataract Study Group.

OBJECTIVE: To develop the Lens Opacities Classification System III (LOCS III) to overcome the limitations inherent in lens classification using LOCS II. These limitations include unequal intervals between standards, only one standard for color grading, use of integer grading, and wide 95% tolerance limits. DESIGN AND RESULTS: The LOCS III contains an expanded set of standards that were selected from the Longitudinal Study of Cataract slide library at the Center for Clinical Cataract Research, Boston, Mass. It consists of six slit-lamp images for grading nuclear color (NC) and nuclear opalescence (NO), five retroillumination images for grading cortical cataract (C), and five retroillumination images for grading posterior subcapsular (P) cataract. Cataract severity is graded on a decimal scale, and the standards have regularly spaced intervals on a decimal scale. The 95% tolerance limits are reduced from 2.0 for each class with LOCS II to 0.7 for nuclear opalescence, 0.7 for nuclear color, 0.5 for cortical cataract, and 1.0 for posterior subcapsular cataract with the LOCS III, with excellent interobserver agreement. CONCLUSION: The LOCS III is an improved LOCS system for grading slit-lamp and retroillumination images of age-related cataract.

New procedures for detecting early vision losses in the elderly.

With the proportion of elderly in the population increasing, and with improving methods for modifying or treating age-related changes affecting the visual system, there is an increasing need for broader and more specific assessments of vision functions in the older patient. As age increases, vision function changes are diverse. Here we discuss methods for the clinical assessment of three of these functions; namely, visual acuity, contrast sensitivity, and disability glare. Visual acuity remains the most useful test of visual function and improved chart designs and scoring methods enhance our ability to detect and monitor change. A variety of different approaches to assessing contrast sensitivity and contrast sensitivity testing should facilitate the diagnostic process and help to predict and explain changes in visual functioning. Disability glare can be expected to become more important in the routine evaluation of the ocular media and for this several new tests have recently become available.

Spatial adaptation to text on a video display terminal.

We employed vertical sinusoidal test gratings to search for spatial adaptation to lower-case text presented on a standard video display terminal. The parameters of the contrast sensitivity test were selected on the basis of waveform analysis of horizontal spatial luminance profiles of the text. We found that subjects exhibited a small (4-5 dB), but significant, frequency-specific spatial adaptation consistent with the frequency spectrum of the stimulus. The theoretical and practical significance of this finding is discussed.

Artificial pupils and Maxwellian view.

When control of the pupil size is required, the simplest method is to use a physical artificial pupil or aperture that is placed in the spectacle plane. In some clinical applications (e.g., the potential acuity meter) an optical artificial pupil is imaged in the plane of the natural pupil by a Maxwellian view optical system. We compared visual performance with physical and Maxwellian artificial pupils by measuring the effects of the pupil diameter (0.5-5 mm in range) and defocus (5-D myopia to 4-D hyperopia) on minimum angles of resolution (MAR's) and on angular blur disk diameters. For pupil diameters down to ~ 2.0 mm there were no meaningful differences between the visual resolution that is obtained with the physical and the Maxwellian pupils. At the smallest diameter (0.5 mm) the physical artificial pupils caused the MAR to increase because of the diffraction limitation on resolution, and defocus no longer affected MAR. With the small Maxwellian pupils vision did not become diffraction-limited so that maximum resolution could still be obtained. MAR was still affected by defocus. The angular blur disk diameters measured with the smaller Maxwellian pupils were slightly but significantly larger than those found with physical artificial pupils. For physical artificial pupils, field-of-view restrictions may result from vignetting with the eye pupil. Thus small physical artificial pupils can act as pinholes causing resolution to become impaired but insensitive to defocus. Also vignetting by the eye pupil can restrict the field of view. Small optical artificial pupils from Maxwellian viewing do not impair resolution, and the resolution may remain sensitive to defocus. The eye pupil does not cause any field restriction, although, if small, it may filter higher spatial frequencies out of the retinal image.

A new test for the evaluation of disability glare.

We describe a new glare test that uses low contrast letters and a variable surround glare source. The test is easy to administer clinically and all test targets, luminance levels, glare geometry, and viewing conditions are well controlled. We found the most useful index of disability glare to be the difference in visual acuity scores for the low contrast chart in the no-glare and high-glare conditions and refer to this as the disability glare index (DGI). We tested a group of normal subjects who were divided into younger (age 15 to 41 years) and older (age 50 to 82 years) groups. The mean DGI value for the older group (10.2 +/- 4.8) was significantly higher than that for the younger group (2.3 +/- 1.9). The DGI is a better discriminator between the two groups than either high or low contrast visual acuity. We attribute the significantly higher DGI values in the older group to increased intraocular light scatter. We find DGI is poorly correlated with high contrast visual acuity (r = 0.33). Our findings suggest that this test of disability glare is sensitive to relatively modest changes in the ocular media. It is a potentially useful tool in detection and assessment of subtle media disturbances and in monitoring changes in the ocular media over a period of time.

Visual performance at video display terminals--effects of screen color and illuminant type.

A limited set of illuminants and phosphor colors are commonly used in video display terminal (VDT) working environments. This study attempts to identify any combinations of such conditions that influence performance on a visually demanding counting task. Experiments were performed to test whether the phosphor color, ambient lighting spectrum, or temporal frequency characteristics of the display and ambient lighting could alter performance. Under conditions where potentially contaminating variables such as reflectance level and screen glare patterns were equalized, no significant differences in performance were produced by the particular sets of stimulus conditions tested. The results suggest that displays and illuminant types that are in common use allow substantially equivalent visual performance.

Human electroretinogram responses to video displays, fluorescent lighting, and other high frequency sources.

Time-averaged human electroretinogram (ERG) responses were determined for several workplace visual stimuli which are temporally modulated at rates exceeding the perceptual critical fusion frequency (CFF). A clearly identifiable synchronous response was in evidence for a video display terminal (VDT) stimulus operating with a refresh rate as high as 76 Hz. A directly viewed fluorescent luminaire with controllable driving frequency elicited a synchronous response at rates as high as 145 Hz. In addition, an intense stimulus created by modulating the light from a slide projector produced responses at least as high as 162 Hz. The implications of these high-frequency responses are representing a potential basis for visual symptoms are discussed.

Face recognition in age-related maculopathy.

Patients with age-related maculopathy (ARM) complain frequently of difficulty with face recognition. The authors attempted to quantify the level of impairment by comparing face recognition with clinical tests of visual function, namely contrast sensitivity, grating acuity, letter-chart acuity, and word-reading acuity. For face recognition, we used 32 black-and-white photographs that had been cropped to remove the outline of hair so that identification was predominantly dependent on the facial features. The observer's distance from the screen on which the photographs were projected was varied. The angular size of the faces was indicated by the equivalent viewing distance (EVD). Four male and four female models were used, and for each model, there were four photographs with different facial expressions--happy, sad, angry, and afraid. For each photograph, the subject's task was to name the model and identify the facial expression. Threshold EVD (50%) was determined for correct identity recognition and expression recognition. For eight subjects all experimental procedures were repeated at a lower luminance level. For ARM subjects, increasing task complexity (grating/letters/words) substantially decreased resolution. Face-recognition abilities were most closely related to word-reading acuity when comparisons were made either across subjects or across luminances within subjects. Contrast sensitivity was associated poorly with face-recognition thresholds. In some subjects with more advanced ARM, identity recognition was substantially poorer than expression recognition.

Use of the Humphrey Lens Analyzer for off-axis measurements of spectacle lenses.

Automated focimeters can be used to make quick, precise measurements of off-axis power and prismatic effects corresponding to an eye rotating behind a spectacle lens. An automated focimeter, the Humphrey Lens Analyzer, was assessed in this regard. The Humphrey Lens Analyzer can be used to give a valid measure of off-axis power of lenses with low power, but not of lenses with moderate to higher power (greater than 3 D). For 3 D spherical lenses discrepancies of the order of 0.1 D occur at 30 degrees rotation, and 6 D spheres give discrepancies of 0.5 D at the same rotation. Small discrepancies were found for measurements of prism. The Humphrey Lens Analyzer was also used in a mode where the lens being tested is rotated about the center of curvature of its back surface. This is the mode often used to assess aberrations and prism of progressive-addition lenses. In this mode, the instrument provides reasonable accuracy in estimating off-axis power corresponding to eye rotation for lenses with low power, but not for lenses with moderate to higher power (greater than 3 D). However, it provides accurate values of the variation in off-axis surface power for low powered lenses with aspheric front surfaces. There were considerable systematic errors associated with the measurement of prism. A simple raytracing method was developed to predict the results of measurements with the Humphrey Lens Analyzer. Predictions of off-axis power were good when lenses were rotated about a position corresponding to the center-of-rotation of an eye, but were poorer when lenses were rotated about the center of curvature of their back surfaces. Predictions of primatic efforts were good in both situations. A method by which the Humphrey Lens Analyzer should provide an accurate measurement of off-axis powers corresponding to eye rotation behind a spectacle lens is described, but has not been tested.

Clinical grading and the effects of scaling.

In clinical practice, there has been a need to grade the magnitude or the severity of the functions and qualities that are assessed in the examination. It is popular to use a four-step grading scale to categorize the severity of clinical findings. The authors discuss clinical grading scales and their influence on the clinician's ability to detect change. These principles have been applied to grades or measures derived from either objective measuring instruments, subjective tests, or techniques in which the clinician makes subjective judgments. A hypothetical data set was used to show the problems associated with using grading scales that are too coarse. The authors presented a mathematic model that helps to estimate the benefits of using use of a finer scale. Data were presented from two separate studies, one on visual acuity measurement and the other on grading nuclear opacity, to show the advantages of using finer scales to enhance the sensitivity of clinical measurement. High levels of concordance between independent observations indicated that the grading scale was too coarse and that these scales needlessly reduced the clinician's ability to detect change in the parameter being assessed. For moderate sensitivity, the size of the scale increments should not exceed one standard deviation of the discrepancy so that the concordance of paired comparisons would not exceed 37%. For fine clinical sensitivity, the size of the scale increments should not exceed one third of the standard deviation of the discrepancy, in which case the concordance of paired comparisons would not exceed 13%. The theory and evidence presented here could prompt re-evaluations of common methods of clinical grading.

Location of nonlinear processes within the pupillary pathway.

The pupil oscillates in synchrony with a slow beat produced by adding two lights flickering at slightly different frequencies. This behavior shows that nonlinear processes are present within the pathway. To localize these processes, a light of one frequency was presented to one eye, while a light of a different frequency was presented to the other. No pupil oscillations were seen in response to the beat in these dichoptic conditions, but when both lights were superimposed and presented to the same eye a powerful pupillary response was produced. We conclude that the nonlinearity giving rise to the pupil's beat response occurs before the pathways from the two eyes join and hence is neural rather than muscular in origin. Furthermore, the lack of a pupil response in the dichoptic conditions suggests that the signals from the two eyes may combine linearly.