Matthew L. Severns

Selective loss of pattern discrimination in early glaucoma

A new perimetric pattern discrimination test was compared with conventional automated perimetry (Humphrey program 30-2 or Octopus program 32) in glaucoma patients, glaucoma suspects, and control subjects. The new test is based on the rationale that a greater percentage of retinal ganglion cells should be needed to detect a stimulus by its shape, or pattern, than by its brightness. The pattern discrimination stimulus was apatch of nonrandom dots embedded in a surrounding random dot field of the same average density. Pattern discrimination thresholds were measured by changing the degree of regularity, or coherence, of the stimulus dots. The fully coherent target was a static, 1-s duration, 20 x 20-dot checkerboard. Using a criterion-free relative operating characteristic analysis, we estimated the ability of both the pattern discrimination and conventional tests to distinguish the normal data distribution from the suspect and glaucoma distributions. The pattern discrimination test appeared to produce separations greater than conventional perimetry for glaucoma suspects and separations equivalent to conventional perimetry for glaucoma patients.

Methodologic dependence of electroretinogram oscillatory potential amplitudes

The International Society for Clinical Electrophysiology of Vision (ISCEV) protocol for eliciting oscillatory potentials uses a considerably lower flash intensity and a different preconditioning stimulus than the only oscillatory potential protocol used to predict progression of diabetic retinopathy. To determine if the ISCEV protocol will be useful in predicting progression of diabetic retinopathy, summed oscillatory potential amplitudes were measured by both protocols in a population of diabetics. Summed oscillatory potential amplitudes measured by the ISCEV protocol, although smaller, are highly correlated with the summed oscillatory potential amplitudes measured with the higher-intensity flash. Thus, summed oscillatory potential amplitudes measured with the ISCEV protocol should be useful in predicting outcome in diabetic retinopathy. Different signal processing filters used to extract oscillatory potentials from the electroretinogram waveform have a small, but significant, effect on summed oscillatory potential amplitude. Use of the caliper-square method or the summed peak-to-trough method for measuring oscillatory potential heights had an insignificant effect on measured oscillatory potential amplitude.

Automated estimation of implicit time and amplitude from the flicker electroretinogram.

The electroretinogram (ERG) has been shown to yield sensitive and specific information about the development of neovascularization in ischemic disorders such as diabetic retinopathy and central retinal vein occlusion. However, even though the test is quick, easy to perform, and carries few risks, the ERG is poorly utilized in clinical situations because of the extended training period necessary for test interpretation. We have developed an algorithm that estimates the phase and amplitude of a 30-Hz flicker ERG and that is relatively insensitive to many forms of interference in ERG recordings. These estimates can be directly compared to established criteria for the risk of proliferative retinal disease.

The variability of the b-wave of the electroretinogram with stimulus luminance

We measured the variability of the b-wave of the electroretinogram as a function of stimulus luminance in two young normal individuals. We also estimated b-wave variability by examining residuals from Naka—Rushton curves fit to intensity-response data. The change of variability with amplitude was similar with both techniques. The standard deviation of b-wave amplitude rose with b-wave amplitude at low stimulus intensities. At higher intensities, the standard deviation of b-wave amplitude became constant. The point at which the standard deviation became constant was LogK for the eye, as determined by fitting the data with the Naka—Rushton equation. These changes suggest that the mechanisms underlying the growth of the b-wave with luminance change near LogK.

The Anomaloscope Plate Test: A New Color Vision Test for Screening Congenital Red-Green Defects

Pseudo-isochromatic plate tests provide an easy to use, rapid method for discriminating people with red-green color vision deficiencies from those who have normal color vision. With the exception of the out-of-print AO-HRR plates, pseudo-isochromatic plates do not provide a diagnosis of the red-green anomaly. For diagnosis of color vision defects, an anomaloscope is preferred. However, the anomaloscope is not well-suited for vision screening because a trained operator and a relatively sophisticated, trained subject are required to obtain accurate results. Although simple to administer and to perform, pseudo-isochromatic plate tests suffer deficiencies when used for vision screening. These deficiencies include the need for a standardized source of illumination and wear and fading associated with repeated handling by test subjects. In response to the need for a rapid, easily administered, durable, but accurate diagnostic color vision screening test, we have developed the anomaloscope plate test (APT) for screening red-green color vision deficiencies. This test, which utilizes the principle of the Nagel anomaloscope, presents images in a pseudo-isochromatic plate format. In this manner, a test which has diagnostic capabilities is combined with ease of use on young and untrained subjects.

Anomaloscope plate test field trial: comparisons with four other tests of congenital red-green color vision deficiencies

The anomaloscope plate test (APT-5) is a new test for congenital red-green color defects that combines the color-matching features of an anomaloscope with the spatial features of pseudoisochromatic plates. The APT-5 consists of an array of yellow and red-green light-emitting diodes (LEDs). The red-green LEDs form three different test patterns embedded in a surrounding array of yellow LEDs. The intensity and chromaticity of the test LEDs can be controlled to produce normal, protanopic, protanomalous, deuteranopic and deuteranomalous color matches to the yellow LEDs in the surround.