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Editors Selection IGR 10-3

Differential Diagnosis: Glaucomatous change or due to PRP for Diabetes?

Comment by Robert Fechtner on:

27673 Impact of Panretinal Photocoagulation on Optic Nerve Head Parameters, Cankaya AB; Ozdamar Y; Ozalp S et al., Ophthalmologica, 2011; 225: 193-199

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This study looks again at a question that challenges glaucoma care. How do we follow our glaucoma patients who have the comorbidity of diabetic retinal disease? Can we use our usual tools of intraocular pressure, functional testing and structural testing? Intraocular pressure remains no more or less valuable than in any other glaucoma patient. Functional testing is altered in the presence of diabetic retinopathy. One can question whether it has any value in detecting progression in an eye following pan retinal photocoagulation. Is structural testing, then, a reliable tool for following progression in glaucoma patients with diabetic retinopathy? In this study Cankaya et al. (329) used confocal scanning laser ophthalmoscopy (CSLO) to study the optic nerves of diabetic patients. They performed CSLO on eighty eyes of eighty diabetic patients who did not undergo PRP and 45 eyes of 45 patients who underwent PRP. The eyes treated with PRP had global optic nerve head parameters that differed significantly from the untreated group. They had greater rim area, smaller cup/disc ratio and shallower cup depth. They also had thinner mean peripapillary retinal retinal nerve fiber layer.

What is one to make of these observations? Eyes that require PRP have pre-proliferative or proliferative disease. This can include proliferative structural alteration at the optic nerve and/or vascular changes allowing altered permeability and edema. Following PRP one could postulate that there would be retrograde neuronal degeneration resulting in loss of neuroretinal rim. Yet the rim area was greater. This is somewhat difficult to reconcile with the observation of thinner peripapillary retinal nerve fiber layer.

Two questions remain incompletely answered. How much change should we expect in structural parameter as a result of PRP? Can we detect additional loss of optic nerve and nerve fiber layer from glaucoma in an eye that had PRP in the past? With the known limitations of functional testing in eyes following PRP we benefit from better understanding of the interaction between PRP and structural parameters.

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