Photoreceptor function in eyes with macular edema

The irreversible loss of visual acuity in macular edema is usually attributed to permanent loss of photoreceptor cells, although there is hardly any information on changes in photoreceptor function in macular edema. The purpose of this study was to assess photoreceptor function in various stages of macular edema and to relate the findings to visual acuity and angiographic changes.

Directional sensitivity (optical Stiles-Crawford effect) and visual pigment density of foveal cones was measured with a custom-built scanning laser ophthalmoscope (SLO) in 19 eyes of 19 patients. Twelve eyes exhibited macular edema: five of inflammatory origin, and seven of diabetic origin. Seven eyes with an intraocular inflammatory disease without clinical or angiographic evidence of edema were also included (four of which had previous macular edema and one of which had shown development of macular edema at the 1-year follow-up). Results of SLO measurements were related to findings using fluorescein angiography and Snellen visual acuity, both assessed at the time of SLO measurement and 6 months thereafter.

Eyes with macular edema exhibited diminished directional sensitivity of photoreceptor cells in the fovea compared with eyes without (P = 0.02). Visual pigment density of eyes with macular edema was decreased and associated with both initial and follow-up visual function and with the angiographic macular edema grade at follow-up. Abnormal directional sensitivity and pigment density were already present in eyes with slight edematous changes and normal visual acuity.

Eyes with inflammatory or diabetic macular edema showed decreased directional sensitivity and visual pigment density in the macular area. These findings may support a role for SLO measurements in detecting retinal damage due to macular edema.