Sustained hypertension damages small arteries and arterioles. Eyes of carnivores seem to be much more sensitive than lesser organs to the effects of hypertension: 'The eyes go first'. Pathogenesis may not be fully understood but one version states that arterioles go into spasm followed by necrosis of the endothelium and vessel wall. Blood cells and fibrin can then enter the wall leading to 'fibrinoid necrosis'.
The wall thickens as a result, compressing/occluding the lumen. This can result in infarction, haemorrhage and exudation and hence can resemble an inflammatory process.
Clinical signs may include retinal detachment, retinal haemorrhage, intra- and pre- retinal exudation (visible as grey areas in the retina), papilloedema, vitreal haemorrhage and (in the cat) anterior chamber haemorrhage (hyphaema). The signs are not usually subtle. The retinal detachment is due to the effects of hypertension on the choroidal vessels--'hypertensive retinopathy' is a bit misleading. Iris vessels may be affected in the cat leading to hyphaema.
With old cats going blind, especially with hyphaema, hypertension is top of the list. In the dog hypertension is one cause of asteroid hyalosis--the 'snow storm' in the vitreous.
The eyes may not be symmetrical i.e., one eye 'full of blood' and the other 'normal'. Always look at the fundus in the fellow eye for early signs.
True incidence not known--physicians and pathologists need to look at more eyes.
Diabetic cataracts are often of rapid onset (few days). Cataracts may be the first abnormality noted by owners or at least the one that makes the most impression. Cataracts may still develop suddenly months or years after start of insulin therapy with apparently good control. The risk probably never goes away and diabetics are always at risk of blindness.
Diabetic cataracts are typically:
Slightly 'wet' > crystalline appearance
Water clefts are lines of separation of the lens quadrants along the suture lines. Look for a Y-shaped cleft in the anterior lens. Rapid onset may cause the lens to leak protein leading to lens-induced uveitis giving a hazy eye with some redness, may feel soft.
It is probably best to get diabetic cataracts out as soon as possible rather than waiting for perfect diabetic control or total control of intraocular inflammation. Refer diabetics early if the owners are interested.
In extreme (fortunately rare) cases 'exploding cataracts' may occur where the lens swelling is so severe that the lens can rupture spontaneously, leading to severe inflammation and glaucoma which may be unmanageable. This possibility is a further reason for referring diabetic cataracts early.
In uncomplicated diabetic cataracts the prognosis is the same with surgery as with other causes. Diabetic vasculopathy may be present at the microscopic level but is not a clinical problem in dogs. In the dog diabetes is one cause of asteroid hyalosis--the 'snow storm' in the vitreous.
Lipid has white crystalline or opalescent appearance. Oedema is more of a blueness (sometimes with a 'ground glass' appearance) with less well-defined margins. Most common appearance is paracentral lipid dystrophy:
White marks in the centre of both (usually) corneas
Circular, oval or annular
Shelties and Cavalier King Charles spaniels
No pain, vascularisation or ulceration (fluorescein negative)
Not associated with systemic abnormalities
If the lipid is either more extensive or forms bands following the limbus or is vascularised, then consider hyperlipidaemia or a local mass. Band shaped deposits following but not contacting the limbus is known as arcus lipoides corneae and is associated with hyperlipidaemia due to hypothyroidism. If in doubt look for a local problem, then test for hyperlipidaemia and then for a primary cause (hypothyroidism, Cushing's, diabetes mellitus).
Very variable presentation. Any non-pigmented thickening in or around the eye may be suspicious.
Classical picture is of 'uveitis'--bilateral iris thickening and exudation due to diffuse lymphomatous infiltration in both eyes but can also be...
Focal non-pigmented mass resembling some other kind of tumour
Haemorrhage and inflammation in both eyes (bilateral intraocular haemorrhage quite suspicious)
Typically sheds large amounts of material into the anterior chamber--unlike most tumours. Third eyelid involvement--usually bilateral in dogs resembling cherry eye but sometimes unilateral. Conjunctival and optic nerve involvement is very unusual.
Full physical exam is always needed with any uveitis.
Metastatic Tumours Within the Eye
Carcinoma is most common, hence mostly mammary tumours in the dog but others have been seen.
No particular pattern but locally aggressive. Haemangiosarcoma--may simply look like haemorrhage in the eye rather than a tumour, as it can elsewhere. Haemangiosarcoma tends to have a low cell: blood ratio.
The Lung-Digit Syndrome of the Cat
Primary lung carcinoma can metastasise to the toes presenting as an enlarged toe (often multiple) while the primary is clinically silent. Never remove an enlarged toe from a cat without a chest X-Ray. They may also metastasise to the eye of the cat where they spread over internal surfaces and resemble uveitis (or nothing specifically) rather than a tumour (the lung-eye syndrome).
Unless you have a specific diagnosis, do not remove an eye from an older cat without a chest X-Ray. Consider submitting for pathology if in doubt.
Feline Infectious Peritonitis (FIP)
Pyogranulomatous foci and necrotising vasculitis; anterior or posterior uveitis. Anterior uveitis may include large fibrinous clots in anterior chamber. Posterior may include bullous detachment or retinal vasculitis.
Retinal vasculitis shows as grey sheathing of retinal vessels and is virtually pathognomic in presence of other supporting information.
Feline Leukaemia Virus (FELV)
Anterior or posterior involvement according to textbooks but......all the cases I have seen have been young cats with chronic anterior uveitis:
Adhesions of iris to lens with irregular pupil
Young cats, generally unwell and non-specific ill thrift.
Feline Immunodeficiency Virus (FIV)
Lymphoplasmacytic uveitis is a particular form of uveitis with some association with FIV but the precise pathogenesis is not known. Not all affected cats are positive. Certainly occurs mainly in older male cats with outdoor lifestyle, currently or in the past.
Chronic (even if owners did not notice it)
Keratic precipitates (white spots of exudate on posterior ventral cornea)
Rubeosis iridis (blood vessels on iris surface resembling a road map)
Grey inflammatory nodules in iris
Small areas of iris thinning (look dark)
Cloudy vitreous with cellular infiltration
Grey lesions in retina
Important possible sequelae:
Anterior lens luxation
Corneal oedema and ulceration
Treat with topical steroids, e.g., Predforte or Maxidex one drop QID for two weeks then reducing slowly to maintenance. Reasonable prognosis if seen early.
These may all appear around the eyes:
Tarsal gland adenitis (not a systemic disease as such but presents as multiple nodular thickenings along all four lids with an aggressive appearance).
Sustained scratching at the eyes usually indicates pruritus rather than an eye problem and is usually atopy.