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Glands
Eye lids
Conjunctiva - Nictitating membrane
Nasolacrimal system (tearing eyes)
Cornea
Uvea
Lens
Inner eye pressure
Retina
Inflammations
Tapetum lucidum
Albino-Cats (Siamese points)
Nystagmus

Note on the Literature:
Mostly the access to the referenced Journals is not for free, one has to pay for the article.
Where a free access to the full text is available, the link is provided.
You may find all those Journals and articles, at least an abstract at:
NCBI, PubMed, where you enter simply the name of the disease.

Disorder in the glands

Chalazion

If the openings of the Meibomian glands are blocked or closed, that may lead to Chalazions or cysts.
The Meibomian glands are located in the edge of the eye lids.

Stye = Hordeolum

Inflammation of Moll's or Zeis' glands.
The Moll's and Zeis' glands are located in the edge of the eye lids.

Prolapse of the nictitating gland
Cherry eye

due to weakness of the conjunctival tissue, it is also called Cherry Eye (due to similar color as the cherries).

Causes:
Likely to be inherited.

Treatment:
A surgical resection of the nictitating gland is not to be recommended, because that may dry out the eyes. Therefore the nictitating gland will be fixed and replaced to its original location.

Breeds, in which the prolapse of the nictitating gland was noticed:
Burmese.

Literature:

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Disorder in the eye lids

Coloboma

A fissure or partly absence of the upper eye lid in the medial third of the lid.
Also often connected with secondary corneal diseases.

Symptoms:
This developmental defect may be a little notch in the upper eye lid, but there can be up to 2/3 parts of the upper lid and conjunctival tissue absent. The defect is mostly symmetric in both eyes.

Causes:
It is a hereditary defect.

Treatment:
Operation, using the techniques of skin grafting, a lobe from the lower eye lid is used to repair the slit, the lobe remains connected with the lower eye lid (is called rotational pedicle) until the defect is completely cured.

Breeds, in which hereditary colobomas have been noticed:
The defect occurs more frequently in Persian, Burmese and domestic shorthaired.

Literature:

Enrolled eye lid - Entropion

The lower eye lids are rolled inwards. Very painful!

Causes:
Mostly acquired due to chronic eye inflammation.
Can be also hereditary.

Treatment:
The method of Hotz-Celsus (elliptic excision) is combined with the resection of a half-moon-like part in the lateral canthus.
Angulus oculi (canthus) lateralis ... outer (mostly pointed) angle
Angulus oculi medialis ... inner (mostly rounded) angle
resection ... excision of a part

Breeds, in which hereditary entropions have been noticed:
Persian, Exotic, and other brachycephalic breeds
Brachycephaly ... short headed

Literature:

Ectropion
Eversion of the eye lids, the eye lids are rolled outwards. Rare in cats, plays a minor role.

Distichiasis

Fine, lash-like hairs grow from the glands located in the edge of the eye lids towards the eye ball. These wrong-positioned lashes grow out from the opening of the glands. Distichiasis may affect the upper and the lower eye lid, one eye or both eyes.
Diagnosis is done with a slit-lamp.
If these additional lashes cause a permanent irritation, they must be removed by operation under full anesthesia (obliteration, freezing, or in severe cases by excision of the edge of the eye lids).

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Disorder in the conjunctiva

Conjunctivitis = inflammation of the conjunctiva

It may be caused by irritation (for example through a foreign body) or by an infection.

Prolapse of the nictitating membrane

Haws syndrome
Is a spontaneous prolapse in both eyes, frequently it may be caused because of a gastrointestinal inflammation due to rotaviruses or parasites.
An exact etiology (also etiology, research and history of the origin) is not known.

Horner syndrome
is a neurological disease resulting from a dysfunction of the sympathetic nervous system, which regulates the function of many glands and of involuntary reflexes. Mostly the disease appears only in one eye. The consequence is, that the cat has a restricted night vision.

Prolapse of the nictitating membrane due to enophthalmus

The involuntary prolapse of the nictitating membrane, i.e. automatic prolapse can be noticed also in cats, when the eye ball recesses into the eye socket (= recessing eyes, Enophthalmus).

It might be seen in extreme Siamese, which have slit-like eyes.

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Disorder in the nasolacrimal system

naso- ... referring to the nose
lacrimal ... Latin; belonging to the tear apparatus

Epiphora = Tearing, crying eyes

Permanent overflow of the lacrimal fluid over the lower eye lid, which may lead to several bacterial inflammations.

Causes:
The lacrimal canaliculi may be bent, crushed or not fully developed (i.e. also missing).
Also the punctum lacrimalis is mostly distorted.
Mostly the upper punctum and canaliculi are affected.
Punctum lacrimalis ... entry for the lacrimal canaliculi.

Treatment:
By operation. Mostly an artificial duct is led to the nasopharynx.

Breeds, in which hereditary epiphora was noticed:
Persian, Exotic, and all other brachycephalic breeds with prominent and too large eyes.
Brachycephaly ... short headed

Literature:

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Disorder in the cornea

Cornea nigra, Corneal sequestrum
or corneal necrosis, necrotizing keratitis, corneal mummification

is a coagulation necrosis in the Stroma of the cornea, that means the protein of the stroma is coagulated and the cells die (necrosis).
Stroma ... a layer of the cornea

Symptoms:
First there appear brown plaques on the cornea, which will become black later on and which are caused due to dying cells of the Stroma. It causes a permanent irritation of the eyes and is painful. It may also be the source for several infections. As the disease progresses, edemas in the cornea are built and superficial vascularization occurs.
Edema ... tissue fluid containing serum between the cells of a tissue
Vascularization ... growth of new vessels

Causes:
A precise reason for the dying of cells in the Stroma is not known, but a corneal sequestrum has also been noticed in conjunction with herpes-virus infections, which seems to play a minor role compared to brachycephaly.
Breeds with shallow orbits and prominent eyes seem to be prone for this disease. The mean palpebral fissure length in Persians is 1 mm larger than in other breeds. Also corneal sensitivity in Persians is lower than in other breeds.

Treatment:
By medication (antibacterials, and with artificial tear fluid), because the growth of the sequestrum sometimes slows down.
By operation, when the sequestrum becomes painful and shows a rapid growth.

Breeds, in which corneal sequestrum has been noticed:

Corneal opacity due to Lysosomal Storage Disorders

Causes:
Opacity of the cornea can be caused by the following storage diseases: Mucopolysaccharidosis I, VI, and VII; GM1- and GM2- Gangliosidosis; α-Mannosidosis, and Mucolipidosis II.

Literature:
Please read the article about GM-Gangliosidosis.

Corneal dystrophy
or corneal lipidosis

Dystrophy ... a disorder and change in the entire organism due to lack or malnutrition, or disorder and change of parts or tissues (for example: disorder due to a disorder in the nutrition of vessels and/or nerves)

Corneal dystrophy is mostly a disorder in the epithelium and/or stroma, both are layers of the cornea.
The dystrophy occurs generally in both eyes, it is not caused by an infection or other systemic disease.

Symptoms:
May be several ones.
Lipid inclusions, connected with calcium, under the surface and appear as whitish, silver or gray plaques, which are not inflammatory and usually not painful. These plaques have variable progress.
There may occur edemas, or bullous changes in the cornea.
Edema ... tissue fluid containing serum between the cells of a tissue

Causes:
The dystrophy is commonly inherited in a family line (familiar).

Treatment:
In lipidosis, which do not progress rapidly, eye drops, which bind the calcium, are given.
Otherwise a surgery is necessary.

Breeds, in which corneal dystrophy has been noticed:
Manx, domestic shorthaired

Literature:

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Disorder in the uvea

The uvea consists of the iris, the ciliary body and the choroid.

Klein-Waardenburg syndrome

Connected with Heterochromia (i.e. odd eyed) in white cats and is also connected with deafness. Differences in pigmentation of the choroid and the pigment epithelium of the retina may also occur simultaneously. The necessary pigmentation of the Stria vascularis is degenerated.

Causes:
Genetic, hereditary, connected to the dominant gene W for white color and heterochromia.

Breeds, in which the Klein-Waardenburg syndrome has been noticed:
Odd-eyed white cats of all breeds.

Chediak-Higashi syndrome

Pale iris coloration. The irises of affected cats appear thin, with a pattern like the weaving of baskets.

Symptoms:
Irides of affected cats are pale yellow-green rather than the bold copper or yellow of unaffected cats.

Breeds, in which the Chediak-Higashi syndrome has been noticed:
The disease has been recognized only in blue-smoke Persians.

Literature:

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Disorder in the lens

Persisting hyperplastic Tunica vasculosa lentis
or persisting pupillary membrane (PPM) or Membrana pupillaris persistens (MPP)

Persisting ... remaining
hyperplastic ... adenoids of mucous membrane

In the pupillary membrane around the lens there are oft residual vessels originating from the embryonic development. The vessels start at the iris and are spanned over the pupil, or even over the cornea and the lens causing cloudiness of the lens.  Usually these embryonic vessels degenerate and disappear within the first weeks after birth. 

Symptoms:
In affected cats these vessels cause cloudiness of the lens or even may affect the vitreus body and the retina. Depending on the development of the disease, it is scaled from 1-6, a scale between 2-6 shall not be used for breeding any more.
Sometimes these vessels can be so fine, that one cannot detect them without a magnifying glass.

Causes:
Not known.

Treatment:
There is no therapy, in some rare cases an operation of the cloudy lens might bring some improvement.

Literature:
In dogs PPM is hereditary in some breeds, in cats there are no clear statements and very few literature.

Cataract

Opacity of the lens (cloudiness), which may lead to complete blindness.
The cataract may occurs in one or both eyes.

Symptoms:
As the lens is behind the iris, one can notice white spots in the pupil, which may cover the entire pupil, depending how severe the disease is.

Causes:
There are several disorders, which may cause cataracts, such as diabetes mellitus, chronic eye inflammations, injuries, or a disorder in the retina.
Primary cataracts (congenital hereditary) are rare.
Mostly the cataract is secondarily acquired.

Treatment:
There is no treatment by medication, only by surgery.
The lens is removed, and - as in humans - is replaced by an artificial lens. To remove the lens the technique of phacoemulsification is used.
Phacoemulsification ... the lens is destructed via ultra sound and its fluid remnants are removed.
The cat must wear a plastic collar after surgery to prohibit the cat from scratching its eyes, also eye drops have to be administered during several weeks.

Breeds, in which hereditary cataracts have been noticed:
The authors suggest an autosomal recessive trait. (Literature see below)
Persian, Himalayan, British Shorthair, Birman

Literature:

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Disorder in the inner eye pressure

Too high inner eye pressure

The aquaeus humour regulates the eye pressure. If the drainage is disturbed (for example having a glaucoma), the pressure is elevated, thus also elevating the pressure on the retina and consequently on the optic nerve, which might affect the vision severely.
See also Glaucoma.

Glaucoma

A glaucoma is the elevation of the inner eye pressure (higher than 25 mmHg) in one or both eyes. When the drainage for the aquaeus humour in the iridocorneal angle is blocked, the inner balance in the eye chambers is disturbed and the inner eye pressure is elevated.

Primary glaucoma

Causes:
A quite common cause for primary glaucoma is a degenerated or disordered iridocorneal angle, which is hereditary.

Secondary glaucoma

Secondary means, that the glaucoma was acquired due to other diseases.

Causes:
A very common cause is the change in the lens' position (lens luxation, dislocation), where the lens is partly or fully disrupted from its zonular ligament and moves "freely" in the eye. This also causes a change in the vitreus and consequently can lead to a block in the iridocorneal angle, thus causing an increase of the inner eye pressure.
Also chronic inflammations inside the eye, injuries and tumors can cause secondary glaucoma.

Congenital glaucoma

This is a primary disorder in the iridocorneal angle. The trabecular meshwork is degenerated or missing or is blocked by embryonic membranes. Already at birth the drainage of the intraocular fluid is blocked.

Causes:
Mostly hereditary.

Symptoms in all glaucoma:
At the beginning the cat owner recognizes rather diffuse signs.
Tearing eyes, slightly reddened eyes, the cat squeezes its eyes and is partly afraid of light. Some cats try to scratch their eyes with the paws. Other cats become abasic due to pain, sleep very long and show loss of appetite.
The cornea becomes cloudy like milk and the pupils are not narrowed, when light rays hit the eyes.
Glaucoma are very painful!

Treatment:
Inspection is done with a gonoscope (device for inspection of the iridocorneal angle).
First various eye drops and/or pills are administered to reduce production of the intraocular fluid and to increase its deduction in the iridocorneal angle.
In case of lens dislocation the lens is removed from the eye by surgery.
In other cases the destruction of the ciliary body (where the intraocular fluid is produced) with laser therapy (Cyclophotocoagulation) or by freezing (cyclocryotherapy) can bring a reduction in the production of the intraocular fluid and thus can lower the inner eye pressure. Surgery is made under full anesthesia.
Cyclophotocoagulation (CPC): The area of ciliary body, where the intraocular fluid is produced, is coagulated from outside through the sclera. Thus production of the intraocular fluid is reduced and the inner eye pressure is lowered.

Breeds, in which glaucoma have been noticed:
Burmese, Siamese
Extreme breeds with very short noses, like Persians and Exotic, are more prone to glaucoma due to a congenital degeneration in the iridocorneal angle.

Literature:

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Disorder in the retina

Taurine deficieny

Cats display retinal abnormalities, when taurine (an amino acid) is deficient in their diet.
Taurine is a growth factor in the development of the retina.

Progressive retinal atrophy (PRA)
formerly called generalized PRA

PRA is a group of hereditary conditions, that result in a progressive degeneration of the retina and loss of vision. They are the veterinary equivalent of the retinitis pigmentosa in man.
There are different types of PRA.
The initial signs in typical PRA are a loss of rod photoreceptor responses, which leads first to night blindness. This is then followed by a slower loss of cone responses and a progressive deterioration in daytime vision. As the condition progresses, the owners may notice a more dilated pupil and increased reflection from the eye. Secondary cataracts accompany the loss of vision in the later-onset and more slowly progressive forms of PRA.

Breeds, which are likely to inherit PRA:

For detailed description please read the article about PRA.

Hypertensive retinopathy

is the damage of the retina due to high blood pressure (hypertension). A disorder in the blood pressure is mostly seen in changes in the eyes. About 70% of the cats show dilated and fixed pupils, or sudden blindness or vision deterioration, and very often without any other clinical signs.
There may be several causes for high blood pressure, disease of the kidneys,  of the thyroid gland, of the parathyroid gland, or too salty food, but also heart diseases, disorder in the CNS or diabetes mellitus can be a cause for retinopathy.
The high blood pressure dilates the blood vessels in the retina, which become inflamed and swollen. There are hemorrhages into the retina, which may extend to the front parts of the eye and may elevate the inner eye pressure thus causing also painful glaucoma.
CNS ... central nervous system

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Common inflammations

Uveitis

Inflammation of the Uvea. Depending where the inflammation is located, there are different types of uveitis:

Iritis = inflammation of the Iris

Iridocyclitis = inflammation of the middle part, for example of the ciliary body

Choroiditis = inflammation of the choroid

These inflammations might result in cataracts or glaucomas.

Conjunctivitis

See above at the conjunctiva.

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Degeneration or missing of the Tapetum lucidum

Can be noticed in white or extremely white spotted cats (Van-cats), and mostly in blue-eyed cats, but also in odd-eyed cats.
Degeneration of the tapetum lucidum leads to a severe dysfunction of night vision abilities.

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Albino-Cats

Albinism

In Albinism the pigments are completely absent, thus giving the iris a reddish or pink hue. The lack of pigments in this disease causes also a deficiency in vision in Albinos, because the iris is not able to function properly as diaphragm. The light rays also enter through the iris and hit the rods in the retina, which are much less sensible for light, thus blending the eyes and disturbing the development of proper vision abilities.
The eyes appear to be red, when light rays hit the eyes, because of the reflection by the underlying blood vessels.

Disruption in the Chiasma in Albino-cats - Strabism

In Siamese cats (whose color genetically belongs to the Albino-series of the gene C) the wiring on the chiasma may be disrupted and less nerve fibers cross than normally, as several scientists have reported. To compensate this defect in the chiasma the cats are likely to have strabism. You may read the following articles:
Article in OMIA (Online Mendelian Inheritance in Animals)
Article of Dmitry G. Diykov, Visual Cortex Defects in Albinos, The Internet Journal of Ophthalmology and Visual Science. 2005. Volume 3 Number 2.

Strabism

A defect in the senso-motoric of the eye to focus the visual line of both eyes to the same point.

Cats with Siamese points are prone for strabism.

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Nystagmus = ocular tremor

Voluntary, rhythmic movements of the eye ball; ocular tremor; with slow movement followed by a rapid movement into the opposite direction (the nystagmus is specified according to this opposite direction!), or regular-pendular movement (undulant nystagmus).
It is differentiated between fine, medium and coarse strokes, rapid and slow nystagmus, horizontal, vertical, diagonal and rotatory nystagmus; pendular (=oscillating or oscillatory nystagmus), rotatory, spontaneous, positional nystagmus.
In terms of physiology it is differentiated between optokinetic nystagmus, fixation, fatigue-induced, end-position nystagmus; in terms of pathology it is differentiated between vestibular nystagmus and amblyopic nystagmus, darkness tremor (ocular or optical nystagmus).

Nystagmus has been noticed especially in Siamese cats, in some single cases also in Oriental cats.

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