A cataract is opacity or clouding in the lens of a dog’s eye which may impair a dog’s sight or cause blindness, depending upon the size and location of the cataract. Opacification of the lens obstructs light from passing and being focused on to the retina at the back of the eye resulting in vision loss. A small cataract may not be visible with the naked eye but in some cases there may be some cloudiness seen in the eye. This cloudiness should not be confused with nuclear sclerosis which also causes clouding of the eye and is a natural result of aging. Not all dogs with cataracts will go blind or suffer any other ill effects from this condition.  Size and location may determine this and a consultation with a veterinary opthamalogist should be sought if it is a concern.  It is recommended that Cavaliers with this condition should not be bred.

Retinal Dysplasia (RD)
The retina is the neurological structure in the back of the eye which receives light (images) and converts it to an electrical signal which transmits it to the brain for interpretation. Retinal Dysplasia is a defective development of retina where the 2 primitive layers of the retina do not fit together properly. There are 3 degrees of retinal dysplasia, folds (mild dysplasia) where there are folds in the inner retinal layer, geographic where there are larger areas of defective retinal development and detachment (severe dysplasia) where the retinal layers do not come together at all. Retinal dysplasia is a congenital defect (a dog is born with it) and does not progress as the dog ages.

While in some countries a cavalier with retinal folds may not be bred, in the Netherlands, there are no guidelines regarding breeding with a cavalier who has RD. It’s certainly no problem to breed with the milder form of RD.
When a cavalier has a geographic RD, but also has an excellent heart and mri result, than it’s the breeders choice whether or not to breed the dog. A cavalier with severe RD, should not be bred from.

Progressive retinal atrophy (PRA)
Progressive retinal atrophy (PRA) is a group of genetic diseases seen in certain breeds of dogs. Similar to retinitis pigmentosa in humans, it is characterized by the bilateral degeneration of the retina, causing progressive vision loss culminating in blindness. The condition in nearly all breeds is inherited as an autosomal recessive trai.

Progressive vision loss in any dog in the absence of canine glaucoma or cataracts can be an indication of PRA. It usually starts with decreased vision at night, or nyctalopia. Other symptoms include dilated pupils and decreased pupillary light reflex. Fundoscopy to examine the retina will show shrinking of the blood vessels, decreased pigmentation of the nontapetal fundus, increased reflection from the tapetum due to thinning of the retina, and later in the disease a darkened, atrophied optic disc. Secondary cataract formation in the posterior portion of the lens can occur late in the disease. In these cases diagnosis of PRA may require electroretinography (ERG). For many breeds there are specific genetic tests of blood or buccal mucosa for PRA.

Absent a genetic test, animals of breeds susceptible to PRA can be cleared of the disease only by the passage of time—that is, by living past the age at which PRA symptoms are typically apparent in their breed. Breeds in which the PRA gene is recessive may still be carriers of the gene and pass it on to their offspring, however, even if they lack symptoms, and it is also possible for onset of the disease to be later than expected, making this an imperfect test at best.

There are more forms of PRA.
Generalized PRA is the most common type and causes atrophy of all the neural retinal structures.
Central progressive retinal atrophy (CPRA) is a different disease from PRA involving the retinal pigment epithelium (RPE), and is also known as retinal pigment epithelial dystrophy (RPED).

Distichiasis is quite common in dogs. Distichiasis is a condition in which extra hairs grow out of the eyelash area.
It happens when there are two or more hairs growing out of a Meibomian gland opening. (Meibomian glands are located along the margin of the eyelid.) These hairs are not supposed to be there. In some cases, these extra hairs can be long and stiff and irritate the eye, resulting in a corneal ulcer. The severity of the problem depends on how stiff the hairs are, how long they are, where they’re located, and how many extra hairs there are.

Distichiasis is different from entropion. Distichiasis involves extra eyelashes; entropion is an inward roll of the eyelid that causes eye irritation from normal eyelashes or hair. In some untreated distichiasis, it can cause corneal ulcers, chronic eye and eyelid pain, and excessive tearing. It is quite uncomfortable and/or painful for the animal, depending on the amount irritation. If the excessive hair causes any clinical signs at all, the hair should be permanently removed.

Signs include increased blinking, lots of extra tears that often look like a tear streak, and squinting.
Dogs don’t typically paw at the eye. The more severe cases are the most easily diagnosed, as the milder cases often involve small softer hairs that can easily be missed.

It’s seen most often in puppies or young adults and is typically diagnosed before a dog is three years old.
Any dog can have it, but it’s considered to be one of the most commonly inherited diseases in dogs, and considered by some to be the most common congenital eye problem.