Acute Osmotic Diabetic Cataract

Vets are generally aware that most canine diabetics end up getting cataracts, but many are unaware that some of these diabetic cataracts can have catastrophic ocular complications if left untreated.  Clients interested in saving vision in their diabetic dogs need early referral to VOR, Adelaide’s only referral service offering cataract surgery, to avoid potential disappointment.

Neglected Cataract-Induced Uveitis

Diabetic cataracts will occur in around 90% of canine diabetics within 12 months of diagnosis.  This is a much higher frequency than in diabetics of other species and reflects the high level of activity in canine lenses of the enzyme sorbitol dehydrogenase.  When excess intraocular glucose passes through the semipermeable lens capsule, much of it is converted by this enzyme to the sugar-alcohol sorbitol.  Unfortunately, sorbitol is too large to pass back out through the lens capsule, creating an osmotic gradient that draws water into the lens.  The excess hydration triggers a degenerative change in the lens fibre proteins with rapid onset osmotic cataract formation.  Worse still, the lens fibres swell inside the lens capsule, leading to cataract intumescence and, in some cases, rupture of the lens capsule.

So, what’s the big deal?  Lens capsule rupture leads to rapid release of lens capsule proteins into the rest of the eye, triggering a rapid onset severe immune-mediated inflammation.  Left untreated this can lead to severe uveitis, secondary glaucoma (making cataract surgery impossible) and sometimes even loss of the eye.  Early aggressive medical therapy and/or rapid cataract extraction help control inflammation.