PRESENTING SIGNS

Dogs with cataracts due to diabetes mellitus can present in two different ways. Firstly, they can present with sudden onset blindness, where the owner was unaware that the dog was suffering from any clinical disease, but on examination was found to have the typical signs of diabetes mellitus. In these cases the patient can be quite ill, and clearly the blindness is not life threatening and so must take second priority. The other way patients can present is with, again, a rapid deterioration of vision in a known diabetic patient. These can be both poorly and well-stabilized patients, although more likely in the former. With both presentations the owners will have noticed that the dog suddenly became disoriented and started bumping into things, and at the same time they noticed that the eyes looked cloudy (or ‘with a film over them’).

CASE HISTORY

If the patient has presented due to the visual loss only, in addition to the ophthalmic problems it will have the typical history associated with diabetes mellitus – polydipsia and polyuria, weight loss despite polyphagia, and possibly even dehydration, weakness and collapse and so on if in a state of diabetic ketoacidosis. Known diabetics might have recently had a period of instability or another illness – urinary tract infection most commonly – and a few days to weeks afterwards the owner noticed the clouding and vision loss. Sometimes there will be a more gradual loss of vision, particularly in very well stabilized patients, and the progress of the cataract might have been noted for several weeks. However, it is far more common for the dog to progress from normal vision to total blindness within a very short space of time – just days.

CLINICAL EXAMINATION

General clinical examination will reveal the typical signs of diabetes in non-diagnosed patients, while those currently on treatment might have symptoms attributable to other disease processes which have affected their insulin metabolism. Thus they should be carefully examined for evidence of urinary tract infection, dental disease and signs of hyperadrenocorticism or hypothyroidism for example.

Ophthalmic examination will reveal reduced or absent menace responses and poor vision. Pupillary light reflexes are often normal, but occasionally are slightly sluggish. Some conjunctival hyperaemia or episcleral congestion can be present. The iris might be uniformly dark. However, the most striking abnormality is the presence of bilaterally symmetrical total mature cataracts. Frequently the lenses appear slightly ‘swollen’ (intumescent) and water clefts along the suture lines are apparent (Figure 40.1). Fundus examination is rarely possible. If intraocular pressure can be measured it is frequently slightly below normal (e.g. 8–12 mmHg). Lens-induced uveitis is very common in sudden onset cataracts, particularly those induced by diabetes mellitus. Schirmer tear test readings should be recorded and the cornea stained with fluorescein to check for ulceration.

Figure 40.1 Typical sudden onset cataract in a diabetic dog. Note the total opacity with ‘water clefts’ along the anterior suture lines and swollen appearance to the lens. The iris is very dark, suggesting some lens-induced uveitis.

CASE WORK-UP

Obviously the patient needs to be worked up for the diabetes and this should be stabilized as much as possible. Once the diagnosis is made via urine and blood glucose measurements, and the patient started on insulin therapy, discussions about referral for cataract surgery can be considered. Most ophthalmologists will only consider surgery when the patient is stable, with blood glucose curves and fructosamine assays used in addition to clinical parameters to assess this. Clearly full laboratory evaluation should be undertaken to ensure that they are free from other metabolic disease (such as hyperadrenocorticism) and severe dental disease is a contraindication for elective cataract surgery – this should be treated prior to elective phacoemulsification. However, some patients are difficult to stabilize, and since the surgical success is higher before complications such as severe lens-induced uveitis (with lens capsule rupture) have occurred, early surgical intervention is occasionally advocated. It is sensible to discuss the patient with your ophthalmologist as soon as the cataracts are diagnosed so that liaison can take place for the best outcome for the patient.

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