Diabetic patients that receive panretinal photocoagulation (PRP) for treatment of diabetic retinopathy develop a thinner retinal nerve fiber layer that may be mistaken for glaucoma . These patients were also found to have an increase in atypical or nonglaucomatous cupping with increasing severity of retinopathy. For instance, these patients may have more sectoral pallor versus the traditional enlargement of the cup:disc ratio.

One explanation is that panretinal photocoagulation may lead to death of the retinal ganglion cells whose axons constitute the optic nerve, that is, damage from laser causes sectoral damage within the nerve. In glaucomatous damage, principle damage originates in the optic nerve itself which may lead to more uniform damage, or cupping.

The authors also note that visual field testing is unreliable in the proiferative diabetic population as panretinal photocoagulation can cause abnormal test results similar to glaucoma.

What does this mean? The study was a prospective study comparing healthy, untreated diabetic patiets and diabetics treated with laser. Nerve fiber analysis, as well as optic disc morphology, was evaluated. The authors found that patients that were treated with PRP had a thinner nerve fiber, as seen in glaucoma patients, but usually did not have typical glaucomatous cupping.  Special attention should be made to the morphology of the optic nerve to help differentiate glaucomatous damage in these diabetic “glaucoma suspects.”

Randall V. Wong, M.D.
Retina Specialist
http://www.TotalRetina.com ^[1]