Optic disc changes following trabeculectomy
- Royal Victorian Eye and Ear Hospital, East Melbourne, Victoria 3002, Australia amvbrooks{at}bigpond.com.au
The reversal of optic disc cupping following pressure reduction by medical or surgical means has long been recognised, particularly in congenital and juvenile glaucoma. Less clear cut is whether this reversal is accompanied by any improvement in visual function. The matter is, obviously, an important one and there are some reports suggesting that an improvement may occur. If so this presumably is due to recovery of neuronal function which has only temporarily been interrupted. Although it is of great importance to know how extensive this process may be, only studies conducted with great care and rigour are likely to tell this conclusively.
The precise pathological mechanism underlying any reversal is also important. Presumably there is reversal of bowing of the lamina but definitive proof of this is difficult. If there is in fact any recovery of function this may be due to a neuronal change although it is doubtful how this would occur, except by reversal of changes which are still transitory.
In a paper in the current issue of the BJO(p 956), Kotecha and coworkers have attempted to solve some of these contentious problems. They have identified “significant” increases in rim volume at 2 years following surgical operations which produced a fall in pressure of around 30%. Some change in maximum cup depth was demonstrated. This was “significant” at 1 year but not at 2 years. The changes seem small. A change in rim volume suggests something more than just a lessening of bowing of the lamina. Although all patients had 24-2 threshold Humphrey visual field tests, no results of these are given so there is no comment regarding visual function. Perhaps a later paper will tell us more.
The results given hardly seem likely to be the basis for much recovery of lost visual function in glaucoma but they do suggest that a reduction in intraocular pressure to the low normal range will halt the glaucomatous process evident at the optic nerve head. However, it may still be too early to paraphrase the slogan of a recent US presidential election “It's the economy stupid” to “It's the pressure stupid.”
