51 Hypertensive retinopathy
The presentation in cases of hypertensive retinopathy is variable. Owners might have noticed a sudden or gradual onset blindness, a change in appearance of the eye(s) such as dilated pupils, a clouding or redness, sudden onset hyphaema, or a general change in the pet’s demeanour, perhaps with increased drinking and urination together with some weight loss. Cats are presented more commonly than dogs and they are normally older – 10 years or more.
In some patients there will be no previous history, with the pet presented suddenly with the ocular complaint. On questioning the owner it might be apparent that some abnormalities have been developing for a while – polydipsia, polyuria and weight loss despite a good appetite being the most frequent. The pet might be less active and sleep more, but this is frequently attributed to increasing age. Some animals might already have known systemic disease such as hyperthyroidism, renal insufficiency or cardiac disease for which they are being treated. Occasionally the hypertension is picked up on a routine check-up – on a senile health check for example – or if the pet is presented for vaccination and a thorough ophthalmic examination is performed.
General clinical examination might reveal abnormalities, but might be normal. Patients might be thin, with poor coats, small, hard kidneys, an elevated heart rate and cardiac murmur or a palpable thyroid gland for example.
Ophthalmic examination can be similarly variable. One or both eyes can be affected. Some patients will be blind, with no menace response and dilated poorly responsive pupils. Remember that cats can retain a brisk pupillary light reflex despite advanced retinal disease, so these should not be relied upon in this species. Dazzle reflexes are usually reduced. The conjunctiva is occasionally slightly hyperaemic but no ocular discharge or corneal ulceration is usually present. Some hyphaema or vitreal haemorrhage might be present, both of which render fundus examination impossible (see Figure 36.2). However, it is unusual for both eyes to have severe haemorrhage simultaneously and so some fundus evaluation should be possible.
If any opacification of the ocular media is present, indirect ophthalmoscopy will be more rewarding than direct ophthalmoscopy. The retina might be completely detached in one or both eyes, and can be seen as a grey veil floating behind the lens (see Figure 49.1). In less advanced cases, the fundus will show various changes – some small blister-like areas of bullous detachment (seen as elevated, out-of-focus dull patches within the tapetal fundus) or retinal haemorrhages – both within the retina itself (flame shaped) and pre-retinal (dark puddle-like areas). The retinal blood vessels are frequently engorged and tortuous with some perivascular cuffing and haemorrhage (Figure 51.1). The vessels often have variable diameter along their length, giving the appearance of a string of sausages. Variable amounts of vitreal haemorrhage can also be present. Although bilateral, the condition is not symmetrical.
Routine haematology and biochemistry is essential, together with appropriate tests for hyperthyroidism in cats, but also sometimes hypothyroidism in dogs. Blood pressure should be measured as outlined in Table 51.1. Normal readings are provided in Table 51.2.
• Sometimes the measurement will be more accurate if the owner is present (the patient might be less stressed).
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