Reports of intraocular pressure (IOP) being higher in myopes than emmetropes and of myopes being over-represented in
glaucoma statistics, are consistent with a role of IOP in the excessive eye growth typically associated with
myopia. We tested the hypothesis, based on these observations, that ocular hypotensive drugs would slow
myopia progression using the chick as an animal model and
timolol as an example of such a
drug. To induce
myopia, chicks (n = 56) were fitted with either monocular translucent diffusers or -15 D spectacle
lenses from day 8. The
drug treatment protocol comprised topical applications of 0.4%
benoxinate, a local anaesthetic (to improve
drug absorption), followed either by 0.5%
timolol or distilled water (control), either daily (1000 hr) or twice daily (1000, 1600 hr).
Refractive errors and ocular dimensions were measured on days 12 and 17. We also verified the ocular hypotensive effect of
timolol in both normal (n = 8) and myopic (n = 12 diffusers; n = 12-15 D
lenses) chicks. Here, we took baseline IOP measurements, instilled
timolol and then monitored IOP over a further 5-9 hr. We found no difference in the amount of
myopia produced in the
timolol and control groups at either measurement time point (e.g. day 17, once per day application, diffusers: -26.9 +/- 3.3 D vs -22.7 +/- 9.1 D;
lenses: -14.9 +/- 3.8 D vs -14.9 +/- 3.6 D). This was in spite of the fact that
timolol did lower IOP in both normal and myopic chicks (27 and 18% reduction, respectively) While
timolol does have an ocular hypotensive effect in the chick, it does not inhibit the development of
myopia in this animal model.