Treatment of Diabetic Cataracts in Dogs

My patient is a 7-year old male Terrier that has been treated for diabetes mellitus for the past 2 years. He has been difficult to regulate with NPH insulin given twice a day but seems to be in reasonable control now. 

The dog is clinically good, with relatively normal thirst, very alert and happy, no other problems related to the diabetes or other diseases.

When I first examined the dog, he already had developed moderate cataracts in both eyes but his owners felt that his vision was still good. However, over the last few months, the dog's vision has slowly deteriorated, and he now has mature cataracts in both eyes. I am no longer able to do a fundic exam on the dog. He is still getting around okay but definitely can't see as well as before.

Is surgical removal of one of the cataracts a good idea? Initially the owners were not interested in this so we haven´t discussed it thoroughly, but they seem to be changing their minds as the dogs vision diminishes.

My Response:

Prevalence of cataracts in diabetic dogs
Cataracts are a very common complication of diabetes mellitus in dogs, but are rare in diabetic cats (1). In one study of diabetic dogs, half had developed cataracts within 6 months of the diagnosis of diabetes, while 75% and 80% of the dogs developed cataracts by 12 and 16 months, respectively (2). Therefore, this indicates that the vast majority of diabetic dogs will eventually develop cataracts unless their glycemic control is very good to excellent. Obviously, that is difficult to achieve in many dogs with diabetes because cataracts are a very common complication (2,3).

Preoperative workup for cataracts
If the owners are at all interested in learning about surgical options, I would strongly suggest that they contact an ophthalmic surgeon and have a consultation. Diabetic cataracts are always associated with some level of lens-induced uveitis. It is the uveitis and its effects that can "make or break" the surgery. Therefore, any uveitis should be treated prior to surgery to minimize the inflammation that is inevitable after surgery.

It is also a good idea to refer prior to complete opacification of the lenses so that more thorough evaluation of the posterior structures is possible. If the retina is not visible, then further, costly diagnostic testing such as ocular ultrasound and electroretinogram (ERG) will be necessary to determine if the eye will have vision after cataract surgery. There is, after all, no point to performing this surgery if the eye is going to be blind anyway.

Should cataract surgery be done on both eyes?
It is important to remember the old proverb that states "In the land of the blind, the one-eyed man is king (4)."  A dog need only have one cataract removed to have vision restored. Doing both eyes is an option to discuss with the ophthalmologist, as some dogs may need all the vision they can get (5)

Do we have any medical options to prevent these diabetic cataracts?
Kinostat™ is an aldose reductase inhibitor that is now in clinical trial for the prevention of diabetic cataracts in dogs (6).  In one study, cataract formation and progression was observed in 64% of the dogs receiving placebo. In contrast, cataract formation in the dogs treated with Kinostat™ was significantly inhibited with only 28% developing cataracts

These initial results suggest that Kinostat™ is beneficial in arresting the onset and progression of cataracts in dogs with diabetes mellitus. To my knowledge, this product is not yet commercially available, but hopefully will be soon.

References:

1. Salgado D, Reusch C, Spiess B. Diabetic cataracts: different incidence between dogs and cats. Schweizer Archiv fur Tierheilkdunde 2000;142:349-353.
2. Beam S, Correa MT, Davidson MG. A retrospective-cohort study on the development of cataracts in dogs with diabetes mellitus: 200 cases. Veterinary Ophthalmology 1999;2:169-172.
3. Basher AW, Roberts SM. Ocular manifestations of diabetes mellitus: diabetic cataracts in dogs. Veteterinary Clinics of North American: Small Animal Practice 1995;25:661-676.
4. Wikitionary, org. In the land of the blind, the one eyes man is king. From Latin in regione caecorum rex est luscus, credited to Desiderius Erasmus's Adagia (1500).
5. Klein HE, Krohne SG, Moore GE, Stiles J. Postoperative complications and visual outcomes of phacoemulsification in 103 dogs (179 eyes): 2006-2008. Veterinary Ophthalmology 2011; 14:114-20. 
6. Kador PF, Webb TR, Bras D, et al. Topical KINOSTAT ameliorates the clinical development and progression of cataracts in dogs with diabetes mellitus. Veterinary Ophthalmology 2010;13:363-368.