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Editors Selection IGR 22-3

Basic research: Neuroprotection and brimonidine

Comment by Makoto Aihara on:

20899 Agreement between slit lamp examination and optical coherence tomography in estimating cup-disc ratios, Martinez-de-la-Casa JM; Saenz-Frances F; Fernandez-Vidal AM et al., European Journal of Ophthalmology, 2008; 18: 423-428

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Neuroprotection is an alternative the-rapy to protect neurons excluding IOP reduction and will be promising therapy in future. Drugs should be delivered topically or systemically. Some of to-pical IOP-lowering drugs reportedly have neuroprotective effect, but it is difficult that the mechanism may be due to IOP reduction and/or the other direct unknown effect. Brimonidine is one of the candidates of neu-roprotective drugs. Hernandez et al. (531) investigated the effect of intraperitonally injected brimonidine, topically administrated latanoprost, and their combination using ocular hypertension rat glaucoma model induced by episcleral vein occlusion. RGC survival was evaluated in the number of survival neurons and its soma area by retrograde labeling. These three kinds of treatments all indicated significant neuroprotective effect compared to untreated contra-lateral eyes, but no significant differences were present among them (103.7, 94.7 and 94.4% vs 78.9% in no treatment of glaucoma model). The authors concluded that brimonidine had a direct and IOP-independent neuroprotective effect. Topical latanoprost also have a neuroprotective but it was still unknown whether its mechanism was caused by IOP reduction, other function or both. Unfortunately it was not described whether the evaluation of IOP or RGC damage was investigated in a masked manner. The sample sizes of three groups are so small (n = 3 or 4) that more numbers are required to verify the neuroprotective effect. There is a limitation to count the cell number manually and to measure the soma area. The authors concluded that brimonidine treatment perfectly protected, and simultaneous treatment with latan-oprost and brimonidine had no additive effect. However, in this study, latanoprost also showed almost perfect protective rate (94.7%) with sufficient IOP reduction. Thus, synergistic effect of IOP reduction and IOP-independent is not clear. Moreover, the timing and dose of brimonidine treatment initiated in three days after laser treatment and continued for 12 weeks. In future, therapeutic timing of brimonidine should be clarified to obtain clinically relevant information.

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