Can eye growth be manipulated pharmacologically?
There is significant incentive to come up with a drug that could be used to either prevent the development or slow the progression of human myopia. Attention to date has been mostly directed at three drug groups, dopamine analogs, anti-muscarinics and prostaglandin analogs. That dopamine analogs influence eye growth is perhaps not surprising as in the retina, DA modulates contrast sensitivity and image contrast is altered by defocus. However, the data are not overly promising. There is also the added problem with this drug group in terms of efficacy for treating human myopia, in that any drug mediating its effects through changes in retinal function is likely to be problematic in terms of side-effects. Anti-muscarinic drugs hold more promise as they appear to directly inhibit scleral growth. The selective drug, pirenzepine, was previously in clinical trial. However, there are many other possible candidates including retinoic acid analogs. In our guinea pig studies we are also studying the effects of the prostaglandin analog latanoprost on myopia progression. This drop, commonly used to lower intraocular pressure (IOP) in patients with glaucoma, may directly inhibit scleral growth. Since longer eyes tend to experience more tension on the scleral walls for a given IOP, lowering IOP might reduce the tension on the scleral wall and as a result slow the axial elongation of the eye associated with myopia progression.