Rods induce transient tritanopia in blue cone monochromats.

Transient tritanopia is a cone-cone post-receptoral interaction between short-wavelength (S) cones and medium (M) and long (L) wavelength cones. Blue cone monochromats have rods and S cones of normal sensitivity but lack functional M/L cones. All blue cone monochromats tested (n = 8) show significant amounts of transient tritanopia mediated by rods. Attempts to find a similar rod-S cone interaction while silencing the L/M cones in normals yielded only a small amount of S cone sensitivity loss. The results suggest an exaggerated influence of rods on the S cone pathway in the retina of blue cone monochromats.

Topography of the multifocal electroretinogram.

The functional topography of the human retina was characterized using the multifocal electroretinogram (ERG), with particular attention to the form of the decline in response with retinal eccentricity. Population response variability was examined and compared to standard full field ERG variability. Burian-Allen contact lens electrodes were used to record the cone multifocal ERG from 50 young eyes (28.3 years +/-5.9 years). Responses were recorded in 8 min from 103 retinal locations within the central +/-22 degrees. The spatial distribution of local responses showed an exponential fall-off with eccentricity. The exponential slope parameter was highly similar across individuals. Excluding responses to the central element, the fall off with eccentricity approximated a power function with an exponent of -0.6, which compares to the -0.74 exponent for the human cone density profile. The inter-individual variance in response density is greatest at the central fovea, reducing towards more peripheral locations. The logarithm of response density, however, shows approximately equal variance across eccentricity, making log density a more appropriate way to view response topography. The population range (+/-2 S.D.) of response density is 0.42 log unit, similar to that of standardized ganzfeld electroretinography. The response exponential decay provides a potentially useful addition to element-by-element comparison, in deciding whether an eye's response is within normal limits.

Clinical vision characteristics of the congenital achromatopsias. I. Visual acuity, refractive error, and binocular status.

Visual acuity, refractive error, and binocular status were determined in 43 autosomal recessive (AR) and 15 X-linked (XL) congenital achromats. The achromats were classified by color matching and spectral sensitivity data. Large interindividual variation in refractive error and visual acuity was present within each achromat group (complete AR, incomplete AR, and XL). However, the number of individuals with significant interocular acuity differences is very small. Most XLs are myopic; ARs show a wide range of refractive error from high myopia to high hyperopia. Acuity of the AR and XL groups was very similar. With-the-rule astigmatism of large amount is very common in achromats, particularly ARs. There is a close association between strabismus and interocular acuity differences in the ARs, with the fixating eye having better than average acuity. The large overlap of acuity and refractive error of XL and AR achromats suggests that these measures are less useful for differential diagnosis than generally indicated by the clinical literature.

Clinical vision characteristics of the congenital achromatopsias. II. Color vision.

Twelve X-linked (XL) achromats and 43 autosomal recessive (AR) achromats were tested using the Farnsworth D-15, Nagel anomaloscope, Sloan achromatopsia test, and Berson test using standard procedures. All of the tests identify achromatopsia, but very few differentially diagnose the various types. AR achromats were subclassified as complete (rods only) or incomplete (residual cone function present) by additional psychophysical testing. Complete and incomplete ARs do not perform differently on any clinical color vision measure, indicating that (1) rods predominantly mediate vision in both groups and (2) these tests are not useful for distinguishing between the groups. Both groups show considerable interindividual variation on all measures. Only one of the measures, the Berson test, designed to distinguish XLs from ARs, does so reliably. XLs and ARs do not differ significantly on the Nagel anomaloscope or most of the Sloan plates. The confusion angles of the D-15 do differ for the two groups, but the variability in each group makes the measure unreliable for classifying individuals. The Berson test is recommended to distinguish the XL from AR achromats.