ABSTRACT
Acknowledgment 251
References 251
1. DEFINITION
Hypotony maculopathy is a change in the structure of the retina and choroid as a result of
lower than normal intraocular pressure (IOP). It is most often seen after filtration surgery.
Hypotony is usually defined as an IOP of 6 mmHg for over 24 hours (1). Lower than normal IOP (“statistical” hypotony) is rarely significant if short term (2). However, pro-
longed hypotony can lead to structural changes in the retina, which may have an effect
on the vision of the patient. This circumstance is called hypotony maculopathy, where
the macula shows changes ranging from fine striae radiating out from the fovea to more
definite choroidal folds, tortuous and engorged retinal blood vessels, and occasionally a
swollen disc (3) (Fig. 26.1). However, there is no leakage from the vessels. Vision is
usually impaired by these changes, although not all patients with hypotony will develop
subsequent maculopathy and vision loss (4). The cause of vision loss is probably due
to mechanical distortion of the photoreceptors due to the wrinkling and folding of
the choroid and retina. With prolonged hypotony there may be permanent changes in
the retinal pigment epithelium and neurosensory retina, leading to permanent visual
loss (5). A further possibility, which may explain the fluctuating vision sometimes
reported, is that hypotony may induce variable amounts of astigmatism as the lid closes
over a soft globe (6,7).
