Inherited retinal degenerations (IRDs) are a major cause of severe visual impairment worldwide. Promising treatments for these diseases include gene-based, cell-based, and small molecule therapies. A hurdle to initiating clinical trials for IRDs is the lack of prospective natural history studies that have provided quantitative descriptions of changes in retinal structure and function over time. The long-term goal of our research is to develop quantitative methods for describing changes in retinal structure and function in IRDs and to use these methods in future prospective natural history studies and clinical trials for IRDs. Dyschromatopsia is common to all IRDs affecting the central retina. Color vision screening tests (e.g., Ishihara, D15) are poorly suited to quantitating the severity of dyschromatopsia in IRD. In contrast, the anomaloscope, a quantitative color test that uses a 2 deg stimulus is difficult for participants with central scotomas, unstable fixation, or poor visual acuity. The Cambridge Color Test (CCT) is based on the principles employed by all pseudoisochromatic tests (e.g., Ishihara), but this computerized system also provides detailed quantitative analysis of color vision. We have implemented a low vision version of the CCT (LvCCT) to quantitate color vision in participants with reduced visual acuities and central scotoma. Based on these preliminary data, we hypothesize that the CCT and LvCCT are sufficiently sensitive and robust to detect and quantitate clinically meaningful changes in color vision in IRDs. To examine this proposal, we will explore the following aims:
Specific Aim 1 : Examine the sensitivity of the CCT and LvCCT to disease severity in IRD patients by comparing color vision status with changes in retinal structure and function.
Specific Aim 2 : Examine the effects of eccentric fixation and reduction in visual acuity on the color discrimination thresholds obtained with the CCT and LvCCT.
Specific Aim 3 : Establish normal ranges for the CCT and LvCCT and determine the inter-session and intra-session variabilities for these two tests. This study was recently approved by the NEI IRB. We have started to enroll normal volunteers to anwer Specific aims 2 and 3.