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Julien Fars, Jan J Kremers, Cord R H Huchzermeyer; Discriminating anomalous trichromacy and cone degeneration in retinitis pigmentosa patients. Invest. Ophthalmol. Vis. Sci. 2020;61(7):5066.
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We performed red-green color matches using an anomaloscope, as well as measurements of photoreceptor-isolating temporal contrast sensitivities in a cohort of patients with retinitis pigmentosa (RP) and a color-normal control group. Primary goal was the identification of anomalous trichromats, necessary for performing further experiments based on the silent-substitution paradigm. Secondary goal was to correlate the results from the color matches and the photoreceptor-isolating temporal contrast sensitivities.
We examined 17 normal subjects (27±8 years, 7 females, 10 males) and 14 RP patients (39±15 years, 5 females, 9 males). Of the RP patients, two were male patients with X-chromosomal RPGR mutations, and two were heterozygous female carriers. Anomaloscope examination was performed using the Rayleigh Equation. Color matching midpoint (AQ mean) and color matching range (AQ range) were used for analysis.We used a dedicated LED stimulator to measure temporal contrast sensitivities for L-cone and M-cone-isolating stimuli in the perifovea using triple silent substitution.
The L- to M-cone-sensitivity ratio is close to one at low temporal frequencies, when color perception is mediated by the color-opponent parvocellular pathway and reflects the relative densities of L- to M-cones in the photoreceptor mosaic (usually > 1) at high temporal frequencies.Many RP patients displayed reduced sensitivities to L- and M-cone isolating stimuli. The majority of RP patients had normal color matching midpoints and ranges. There was a non-significant tendency toward smaller AQ means (pseudoprotanomaly) and larger ranges (decreased color discrimination) mainly in patients with RPGR mutations, indicating that cones are affected in these patients. It is unlikely that all these patients were anomalous trichromats, especially the female patients. When excluding the outliers, the L-cone-driven temporal contrast sensitivities were neither correlated with AQmean nor with AQrange. The LM ratios and anomaloscope parameters are not correlated either.
Abnormal anomaloscope settings may be attributed either to congenital anomalous trichromacy or to cone degeneration. Therefore, additional genotyping of the opsin genes is necessary to distinguish these two conditions. Color matches and temporal contrast sensitivities are based on different mechanisms.
This is a 2020 ARVO Annual Meeting abstract.
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