Chris A. Johnson

A computerized method of visual acuity testing: adaptation of the early treatment of diabetic retinopathy study testing protocol.

PURPOSE To develop a computerized method of visual acuity testing for clinical research as an alternative to the standard Early Treatment for Diabetic Retinopathy Study (ETDRS) testing protocol, and to evaluate its test-retest reliability and concordance with standard ETDRS testing. DESIGN Test-retest reliability study. METHODS Multicenter setting of a study population of 265 patients at three clinical sites. Visual acuity was measured with both the electronic visual acuity testing algorithm (E-ETDRS) and standard ETDRS protocol (S-ETDRS) twice on one eye of each patient. E-ETDRS testing was conducted using the electronic visual acuity tester (EVA), which utilizes a programmed Palm (Palm, Inc, Santa Clara, California, USA) hand-held device communicating with a personal computer and 17-inch monitor at a test distance of 3 meters. RESULTS For the E-ETDRS protocol, test-retest reliability was high (r = 0.99; with 89% and 98% of retests within 0.1 logMAR and 0.2 logMAR of initial tests, respectively) and comparable with that of S-ETDRS testing (r = 0.99; with 87% and 98% of retests within 0.1 logMAR and 0.2 logMAR of initial test, respectively). The E-ETDRS and S-ETDRS scores were highly correlated (r = 0.96 for initial tests and r = 0.97 for repeat tests). Based on estimates of 95% confidence intervals, a change in visual acuity of 0.2 logMAR (10 letters) from a baseline level is unlikely to be related to measurement variability using either the E-ETDRS or the S-ETDRS visual acuity testing protocol. CONCLUSIONS The E-ETDRS protocol has high test-retest reliability and good concordance with S-ETDRS testing. The computerized method has advantages over the S-ETDRS testing in electronically capturing the data for each tested letter, requiring only a single distance for testing from 20/12 to 20/800, potentially reducing testing time, and potentially decreasing technician-related bias.

Frequency doubling technology perimetry for detection of glaucomatous visual field loss

Abstract PURPOSE: To evaluate the ability of frequency doubling technology perimetry to detect early, moderate, and advanced glaucomatous visual field loss. METHODS: In a prospective study, frequency doubling technology perimetry (C-20 full threshold) was performed in the right eye of 254 normal control subjects and 230 patients with early (n = 85), moderate (n = 114), or advanced (n = 31) glaucomatous visual field loss. Previous Humphrey Field Analyzer test results were used to classify glaucomatous visual field loss as early (mean deviation no worse than −6 dB), moderate (mean deviation between −6 and −12 dB) or advanced (mean deviation between −12 and −22 dB). RESULTS: Receiver operating characteristic curves showed 100% sensitivity and specificity (area under the curve, 1.0) for detecting advanced glaucomatous visual field loss, approximately 96% sensitivity and 96% specificity (area under the curve, 0.9751) for detecting moderate glaucomatous visual field loss, and approximately 85% sensitivity and 90% specificity (area under the curve, 0.9261) for early glaucomatous visual field loss. CONCLUSIONS: Frequency doubling technology perimetry demonstrates high sensitivity and specificity for detection of early, moderate, and advanced glaucomatous visual field loss.

Computerized method of visual acuity testing: Adaptation of the Amblyopia Treatment Study visual acuity testing protocol

PURPOSE To report a computerized method for determining visual acuity in children using the Amblyopia Treatment Study visual acuity testing protocol. METHODS A computerized visual acuity tester was developed that uses a programmed handheld device that uses the Palm operating system (Palm, Inc, Santa Clara, California). The handheld device communicates with a personal computer running a Linux operating system and 17-inch monitor. At a test distance of 3 m, single letters can be displayed from 20/800 to 20/12. A C program on the handheld device runs the Amblyopia Treatment Study visual acuity testing protocol. Using this method, visual acuity was tested in both the right and left eyes, and then the testing was repeated in 156 children age 3 to 7 years at four clinical sites. RESULTS Test-retest reliability was high (r =.92 and 0.95 for and right and left eyes, respectively), with 88% of right eye retests and 94% of left eye retests within 0.1 logarithm of minimal angle of resolution (logMAR) units of the initial test. The 95% confidence interval for an acuity score was calculated to be the score +/- 0.13 logMAR units. For a change between two acuity scores, the 95% confidence interval was the difference +/- 0.19 logMAR units. CONCLUSIONS We have developed a computerized method for measurement of visual acuity. Automation of the Amblyopia Treatment Study visual acuity testing protocol is an effective method of testing visual acuity in children 3 to 7 years of age.

Selective versus nonselective losses in glaucoma.

This article reviews the histopathologic and psychophysical evidence for selective losses to specific subpopulations of optic nerve fibers in glaucoma. Based on this evaluation, the degree to which these losses are selective is drawn into question, and a distinction is drawn between selective tests and selective losses. An alternative hypothesis for early detection of functional losses in glaucoma, the reduced redundancy hypothesis, is presented. This concept takes into account the redundancy or sampling characteristics of specific subpopulations of optic nerve fibers, as well as the relative amount of glaucomatous loss incurred by each optic nerve fiber subpopulation. An example is presented in which an undersampled subpopulation of optic nerve fibers with minimal redundancy is better able to reveal early losses, even though there are greater amounts of relative loss for other optic nerve fiber subpopulations. The design of psychophysical tests for early detection of functional losses in glaucoma should take into account both the relative amounts of loss for various subpopulations of optic nerve fibers and their inherent redundancy or sampling properties.

Age-related changes in the central visual field for short-wavelength-sensitive pathways

The sensitivity of short-wavelength-sensitive (SWS) cone pathways throughout the central 30-deg visual field was determined in both eyes of 62 normal volunteers between the ages of 20 and 72 years. We found an average SWS cone pathway sensitivity decrease with age of approximately 0.15 log unit per decade. The sensitivity reduction was approximately linear, with a slightly larger decrease beyond the age of 50 years. The age-related SWS cone pathway sensitivity reductions also became larger as a function of increasing stimulus eccentricity. Measurements of ocular-media absorption characteristics in each eye revealed that 30-40% of the age-related sensitivity loss could be attributed to reductions in transmission of short-wavelength light by the ocular media. After corrections for preretinal media transmission loss, the decrease in the sensitivity of SWS cone pathways with age was approximately 0.09 log unit per decade. This age-related loss is greater than age-related sensitivity decreases in the middle-wavelength-sensitive and/or long-wavelength-sensitive cones (approximately 0.06 to 0.07 log unit per decade). In the age group older than 60 years, there was an inverse relationship between media-corrected SWS cone pathway sensitivity and media absorption characteristics (i.e., media-corrected SWS cone pathway sensitivity was higher in eyes with lower media transmission of short wavelengths). This relationship was not so evident for younger subjects. A similar inverse relationship between transmission loss in the ocular media and SWS cone pathway sensitivity was found between left and right eyes of the same individual.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of Progressive Glaucomatous Visual Field Loss

In normal individuals, visual field measures are not perfectly repeatable and individual test locations exhibit both short- and long-term sensitivity variations. This physiologic variability is greatly increased in glaucoma and confounds detection of real progressive loss in visual function. Distinguishing progressive glaucomatous visual field loss from test variability therefore represents a complex task. Procedures used for detection of glaucomatous visual field progression may be broadly grouped into four categories: 1) clinical judgment, which consists of simple subjective observation of sequential visual field test results; 2) defect classification systems, whereby specific criteria are used to stratify field loss by discrete score and define progression as score change over time, such as the Advanced Glaucoma Intervention Study scoring system; 3) trend analyses, which follow test parameters sequentially over time to determine the magnitude and significance of patterns within the data, for example linear regression; and 4) event analyses, which identify single events of significant change relative to a reference examination. All of these methods demonstrate distinct benefits and drawbacks, making each useful in specific circumstances, although no single method appears universally ideal. At the present time the best method of detection of progression may be to rely upon confirmation of change at successive examinations and also by correlation of visual field changes with other clinical observations. Alternative analysis methods may become available in the near future to help identify cases of progressive loss.

Effect of dioptrics on peripheral visual acuity

Abstract The peripheral dioptrics of the eye displays a considerable error of refraction caused primarily by oblique-ray astigmatism. It was hypothesised that this refractive error might contribute to the well known reduction in visual acuity in the peripheral visual field. Independent experiments were carried out in two laboratories, using different methods and different targets; sinusoidal gratings and Landolt rings. A third experiment was run in which two subjects from one laboratory were tested in the other. Measurements of visual acuity were obtained between 0° and 60° of eccentricity along the horizontal meridian both with and without correction of refractive error. The results of all three experiments indicate that the existing errors in refraction do not influence peripheral visual acuity.

Optimum parameters for short-wavelength automated perimetry.

PurposeTo determine the optimum parameters for short-wavelength automated perimetry (SWAP) and to recommend these for standardization of the procedure. MethodsWe used a variety of stimulus and background configurations to determine the optimum background spectral distribution and luminance, and the optimum target spectral distribution, maximum luminance, and duration. We measured threshold versus intensity curves to determine which combination provided (a) the greatest isolation of the short-wavelength sensitive mechanisms and (b) the largest dynamic range for perimetry. We also evaluated the effect of lens absorption and cataract on these two factors. ResultsA broad-band yellow background at 100 candela/m2 with a narrow-band 440-nm (27-nm half-bandwidth), 1.8° diameter (Goldmann size V) stimulus presented for 200 ms was optimum at all retinal eccentricities. Specific recommendations for how to modify existing perimeters are given. ConclusionAgreement regarding the optimum parameters for SWAP should lead to standardization of the test that will facilitate comparison of results from different centers. Normative data can be collected at several sites and incorporated into statistical analysis packages currently available with various perimeters. This will greatly improve the clinical utility of this test.

Clinical trial of lutein in patients with retinitis pigmentosa receiving vitamin A.

OBJECTIVE To determine whether lutein supplementation will slow visual function decline in patients with retinitis pigmentosa receiving vitamin A. DESIGN Randomized, controlled, double-masked trial of 225 nonsmoking patients, aged 18 to 60 years, evaluated over a 4-year interval. Patients received 12 mg of lutein or a control tablet daily. All were given 15,000 IU/d of vitamin A palmitate. Randomization took into account genetic type and baseline serum lutein level. MAIN OUTCOME MEASURES The primary outcome was the total point score for the Humphrey Field Analyzer (HFA) 30-2 program; prespecified secondary outcomes were the total point scores for the 60-4 program and for the 30-2 and 60-4 programs combined, 30-Hz electroretinogram amplitude, and Early Treatment Diabetic Retinopathy Study acuity. RESULTS No significant difference in rate of decline was found between the lutein plus vitamin A and control plus vitamin A groups over a 4-year interval for the HFA 30-2 program. For the HFA 60-4 program, a decrease in mean rate of sensitivity loss was observed in the lutein plus vitamin A group (P = .05). Mean decline with the 60-4 program was slower among those with the highest serum lutein level or with the highest increase in macular pigment optical density at follow-up (P = .01 and P = .006, respectively). Those with the highest increase in macular pigment optical density also had the slowest decline in HFA 30-2 and 60-4 combined field sensitivity (P = .005). No significant toxic effects of lutein supplementation were observed. CONCLUSION Lutein supplementation of 12 mg/d slowed loss of midperipheral visual field on average among nonsmoking adults with retinitis pigmentosa taking vitamin A. Application to Clinical Practice Data are presented that support use of 12 mg/d of lutein to slow visual field loss among nonsmoking adults with retinitis pigmentosa taking vitamin A. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT00346333.

Frequency-doubling technology perimetry.

The FDT perimeter is a compact and relatively inexpensive perimeter whose transportability, tolerance to refractive errors, and rapid test times (less than 1 minute per eye) make it a suitable candidate for visual field screening. It is a uniform finding that the C-20-1 screening protocol of the FDT perimeter provides good sensitivity and specificity for the detection of moderate and severe losses in glaucoma. Sensitivity can be increased by use of the C-20-5 screening protocol. In addition, the FDT perimeter demonstrates good sensitivity and specificity for detecting the presence of neuro-ophthalmic disorders, though it may have a limited ability to determine whether a field defect is hemianopic. There is only limited evidence that the FDT can appropriately detect retinal disease. Despite some evidence that the current FDT perimeter may be suitable for staging and monitoring the progression of visual field damage, the large targets used in the test make this of limited practicability. The development of a frequency-doubling test with smaller targets spaced over narrower intervals would improve the ability of FDT perimetry to determine the spatial extent of visual field defects.