Background: The authors prospectively and longitudinally studied changes in optic disc topography during spontaneous reduction of intraocular pressure (IOP) in five monkeys with experimental glaucoma, using a computerized image analyzing system (Topcon IMAGEnet).
Methods: Glaucomatous optic neuropathy was produced in one eye of each animal by repeated argon laser photocoagulation of the trabecular meshwork. The duration of follow-up was 12 months. After laser treatment, IOP fluctuated and tended to increase. Spontaneous reduction in IOP was frequently observed during follow-up. Changes in optic disc parameters (vertical and horizontal cup-to-disc ratios, rim area/disc area, cup volume/disc area) that accompanied a given magnitude of spontaneous reduction in IOP at the early stage of glaucoma (first 4 months of follow-up) were compared with those at the later stage of glaucoma (last 4 months of follow-up).
Results: All optic disc parameters improved significantly during IOP reduction at each stage of glaucoma. Although there was no significant difference between the two stages in the magnitude of IOP reduction, the extent of improvement in each disc parameter was significantly less in the later stage than in the early stage. In both stages, reversal of cupping occurred symmetrically in the vertical and horizontal dimensions. Expansion of the cup occurred symmetrically in the early stage, but this was predominantly vertical in the later stage.
Conclusion: These results suggest that the extent of cupping reversal after IOP reduction may decrease with progressive glaucomatous damage in primate glaucoma.