Measuring Rod- and Cone-Photoreceptor-Specific Vision in Inherited Retinal Diseases Using a Commercial Perimeter

The primary pathology in most inherited retinal diseases (IRDs) is located within photoreceptors. Standard automatic perimetry (SAP) can measure photoreceptor disease severity but cannot distinguish between rods, long/middle-wavelength (L/M)-sensitive, and short-wavelength (S)-sensitive cones. Herein we developed a protocol that can provide photoreceptor-specific sensitivities.

A commercial (unmodified) perimeter was used to develop a clinical protocol that includes five profiles along the vertical meridian, utilizing different chromatic stimuli presented in the dark-adapted state or on adapting backgrounds. Data were recorded by the Perimetry for IRD (PERIRD) consortium in control participants and patients with IRDs.

The protocol was developed by evaluating the relationship between chromatic thresholds and adapting backgrounds using a threshold-versus-intensity paradigm. Five conditions were selected: two-color dark-adapted, red-on-blue, and blue-on-yellow tests in addition to white-on-white SAP. Prediction intervals from control eyes were defined, and physiological ranges over which rod-, L/M-, and S-cone-specific results can be obtained were estimated. Testing in complete achromatopsia, blue-cone monochromacy, and enhanced S-cone syndrome confirmed classic patterns expected from cone diseases. Patients with incomplete achromatopsia showed partially retained L/M- or S-cone function. Patients with retinitis pigmentosa demonstrated use of photoreceptor-specific function to interpret different disease subtypes and stages. Total test time for the protocol was usually under 30 minutes.

Photoreceptor-specific function can be measured over a large dynamic range using a turnkey commercial perimeter and a relatively short, practical protocol that may be introduced into the clinic, translational work, and clinical trials.