Anatomy and Physiology
Persistent pupillary membrane
Anterior uveal cysts
Anterior uveitis - iritis, cyclitis, iridocyclitis
Equine recurrent uveitis
Anterior uveal atrophy
The uvea (uveal tract) is the vascular tunic of the eye and consists of the iris, ciliary body and choroid. As with most of the other ocular structures, sensory innervation is through the trigeminal nerve.
The iris and ciliary body together often are referred to as the anterior uvea. The choroid is referred to as the posterior uvea.
The iris consists of a delicate network of blood vessels, connective tissue (stroma), muscle fibers (sphincter and dilator), nerves and the posterior epithelium (double layer).
Because the iris lies in contact with the lens, it has a curvature similar to the anterior surface of the lens. If the lens is displaced, a change in the anterior surface of the iris will result.
Anterior endothelium. There is an incomplete layer of endothelial (mesothelial) cells on the anterior surface of the iris.
Stroma. This accounts for most of the mass of the iris and is composed of connective tissue, blood vessels and nerve fibers. Scattered within the stroma are numerous pigmented cells, usually containing melanin.
When one uses the term eye color, it is in reference to the iris and, in particular, the stroma of the iris. When there is abundant melanin in the stroma and epithelial cells, the iris is brown; less melanin results in lighter shades of brown or yellow (especially in cats who have cells containing this type of pigment). Blue or green irides partly are the result of lack of melanin in the stroma combined with melanin in the epithelium and some other ill-defined structural change.
Only in the true albino eye is there no melanin in any part of the iris, giving the 'eye' a pink appearance and allowing visualization of the vasculature and other structures of the iris.
When an individual iris is composed of regions having fundamentally different colors or when one iris is of a different color from that of the opposite eye, the condition is termed heterochromia iridis. This is just a descriptive term and does not denote an abnormal situation in itself.
Note well - the iridal blood vessels in most domestic animals are fragile and bleed profusely when cut. For this reason, surgery on the iris usually necessitates the use of an electroscalpel to reduce or prevent bleeding. This is in contrast to humans and other primates: their iris can be cut with scissors and usually no bleeding will occur.
The anterior surface of the iris often is separated into two concentric zones by an region termed the collarette or minor iridial circle (there is a circularly arranged blood vessel often visible here); the inner or more central zone usually is a different color than the outer or more peripheral zone (usually shades of the same color).
Sphincter muscle. The muscle fibers are arranged circularly (or variations thereof in species with non-circular pupils). Motor innervation primarily is parasympathetic by the oculomotor nerve although some sympathetic fibers have been found.
Dilator muscle. The muscle fibers are arranged radially and are part of the outer epithelial layer (see next section). Motor innervation primarily is sympathetic although some parasympathetic fibers have been found.
Iris epithelium. This consists of a double layer of cuboidal cells which in most animals contain melanin. This is one of the structures that contributes to the color of the 'eye.'
In many animals the epithelial cells extend anteriorly around the pupillary border giving it a fine, beaded appearance. This is called the pupillary ruff.
Corpora nigra or granulae iridica . These are masses of modified iridal tissue attached at the pupillary border and composed of melanotic cells, blood vessels, and fluid-filled spaces. They usually have a lobulated appearance and are present only in herbivores. The dorsal ones usually are larger; the ventral ones may be poorly developed or absent.
Ciliary cleft (filtration or drainage angle). This is a region formed by the junction of the iris and cornea and is composed of pectinate ligament, trabecular meshwork and aqueous humor outflow paths.
Pupil (pupillary aperture). Keep in mind that the pupil is not a structure, but is an opening in the iris. Depending on the angle and amount of incident light, the pupil will appear dark or black, red (reflection from blood vessels in the posterior part of the eye), bright (tapetal reflection), or white or beige (due to opacification of the lens, retinal separation, neoplasia, etc.). When the pupil appears white or beige, this is termed leukocoria. The normal pupillary aperture shape in domesticated animals is as follows:
Dog - round.
Cat - round when widely dilated, vertically oval (ellipsoid) when mid-dilated, and a vertical slit when miotic.
Horse - round in foals, but becomes oval with longer dimension horizontal as individual matures.
Ruminants - somewhat round in neonates, but becomes oval with longer dimension horizontal as individual matures.
Anterior and posterior chambers of the eye: The iris serves as the major boundary between and anterior and posterior chambers both of which contain aqueous humor and communicate by way of the pupil.
Anterior chamber - bounded by cornea, anterior iris and anterior lens surface.
The anterior chamber is optically clear; when a focused beam of light is passed through, the path appears invisible or has a faint outline due to light reflected from tiny particles suspended in the aqueous. With anterior uveitis (iritis, cyclitis), there is an increase in the protein content to the aqueous humor and the light beam is well outlined. This is termed aqueous flare and is an important sign in the diagnosis of anterior uveitis , but could also form a clot . Cells of various types also will be present. When both conditions are present, it is termed flare and cells.
Exudate into the aqueous humor often will be grossly visible (e.g., blood, purulent material), but in early or non-exudative anterior uveitides, demonstration of aqueous flare essentially is pathognomonic for uveitis.
The aqueous flare phenomenon is based on the Tyndall effect similar to dust particles rendering incoming sunlight visible.
Posterior chamber - bounded by ciliary body, lens and posterior iris. Note well that it is not the vitreous cavity.
The ciliary body supports the lens through the zonules, and is the major site for the production of aqueous.
The anterior portion consists of the ciliary muscle and the ciliary processes; the posterior portion (pars plana) extends posteriorly to the choroid and retina. The junction with the retina is distinct and is called the ora serrata (ora ciliaris retinae).
Because ciliary muscles are scantily developed in most domestic animals, it may be that accommodation is not an important function for these muscles.
The choroid is a highly vascular structure which provides nourishment to the outer retinal layers in those species having well developed retinal vessels (e.g., dog). In species not having extensive or any retinal vasculature, the choroid provides all retinal nourishment (e.g., in the horse).
Because most choroidal diseases also involve the retina, they will be covered in the chapter on the retina.
The choroid can be divided into four layers in most animals:
Suprachoroidea - outer most layer next to lamina fusca of sclera.
Stroma - this layer contains most of the blood vessels and, in melanotic individuals, there is abundant melanin. The blood vessels have some sympathetic nervous control.
Choriocapillaris - thin layer of capillaries with fenestrated endothelium which lies in direct apposition to the retinal epithelium. These vessels are derived from the stromal vessels and are directly responsible for the retinal nourishment.
Tapetum - specialized structure produced by the choroid; it lies between the stroma and the choriocapillaris. This is the structure responsible for the 'eye-shine' seen in many species. It normally is a highly organized tissue which appears to act as a diffraction grating, but whose purpose is obscure. It is not present in the pig, rabbit, most birds and most primates .Tapetal colors normally are different within and between species. In dogs and cats, the tapetum is not fully developed until after four months postnatal (it initially is gray-white to purple). The tapetum usually has a triangular shape and occupies the upper one-third of the ocular fundus. Tiny, regularly spaced, dark spots are end-on views of capillaries (called Stars of Winslow).
Changes in tapetal reflection often indicate overlying retinal abnormalities; thinning of the retina leads to increased reflectivity whereas thickening or distortion results in discoloration (brown to gray).
Congenital diseases or defects are seen frequently. Except for persistent pupillary membrane or major structural alteration, the defects usually have little or no adverse effect on vision.
This is a condition in which there is white fur, blue eyes and deafness. Reported in mice, cats and dogs as well as in humans.
The eyes are not abnormal; the blue eye may not have a tapetum.
This is an increase in melanin content of individual cells. Not pathologic.
This is a localized increase in the number of melanocytes usually with slight protrusion above the surface. Not pathologic, but could be precursor to melanoma. Best to record size and watch for change in size or character. Plural is nevi.
Could also be termed a melanocytoma.
In the fetus, the pupil is closed by a thin, vascular membrane that is mostly resorbed before birth. Normally, any strands remaining at birth are resorbed by 4-5 weeks of age.
In persistent pupillary membrane, the strands persist beyond several months of age. There may be associated changes in the lens or cornea. This condition is heritable in the basenji in whom there may be concomitant optic nerve defects (Bistner, et al.); it also is seen frequently in the collie and Australian shepherd dog. It is present sporadically in most other canine breeds as well as in other species (Burek, et al.).
The pupillary membrane arises from the iris collarette; this is important in differentiating persistent pupillary membrane from iridal synechiae which usually arise from the pupillary border of the iris.
In most cases, the strands are of no concern. They may go from one region of iris to another, or from iris to cornea, or from iris to lens. Where the strands attach to cornea or lens, a white, gray or brown opacity may be present. Most of these opacities are minor and have no significant effect on vision. Occasionally there will be extensive corneal edema due to endothelial cell destruction, or a large cataract.
Surgical intervention is neither desirable nor necessary; some of these strands contain patent blood vessels and would bleed profusely if cut. In patients with extensive corneal or lenticular disease, a mydriatic may improve vision. Basenjis and other individuals affected with persistent pupillary membrane should not be used for breeding.
This is seen mostly in color dilute animals whose irides are hypomelanotic. The individual may be photophobic. Various degrees of choroidal hypoplasia also may be present.
If you retroilluminate the iris, the hypoplastic regions transilluminate. Direct your light at an angle through the pupil to produce a strong fundus reflection (pupil should be in non-dilated state).
Frequently seen in Siamese cats. Also seen in some horses, particularly in Welsh ponies who have blue irides (Buyukmihci, et al.). In these individuals, the hypoplastic region may bulge forward due to aqueous humor pressure from behind . This may be mistaken for a cyst of the iris stroma, or worse, with a neoplasm. Be careful not to make a misdiagnosis of neoplasia; get a second opinion in all questionable cases.
No treatment is available or necessary. If there is concurrent choroidal hypoplasia and it is substantial, there may be loss of vision, but this is rare.
Tiny cysts of the iris or ciliary body epithelium are seen routinely in histologic preparations of eyes from young animals. Sometimes these cysts are large enough to be seen clinically: in the anterior chamber, at the pupillary border, or in the posterior chamber (Carter and Mausolf). Occasionally the cysts break off and float free in the anterior chamber or vitreous cavity.
Often, however, the cysts are not seen until later life. These may be new or may represent enlargement of congenital cysts. Clinically detectible cysts are most commonly seen in dogs, particularly in golden retrievers, Labrador retrievers and Boston terriers.
Cysts must be differentiated from neoplastic masses. Cysts do not have associated inflammation of ocular tissues whereas a neoplasm usually would. Most cysts will have a rounded, smooth surface. Many cysts will have walls thin enough to allow transillumination .
Most of these cysts are innocuous and do not require treatment. Occasionally a free-floating cyst may become adherent to the cornea and cause edema or melanosis (Bedford). In a few cases, a cyst may become large enough to cause pupillary block glaucoma. Treatment in problem cases would be by surgical excision, by aspiration, of the cyst. Do not, however, attempt this; always refer the patient to a specialist for evaluation and, if necessary, treatment.
Inflammation of the anterior uvea breaks down the blood-aqueous barrier so that protein escapes into the aqueous humor resulting in flare. Blood and other cellular infiltrates also may be present. The following terms are used for description of these conditions. Keep in mind that these conditions are the result of anterior uveal abnormalities and are not diseases in themselves. Thus, your treatment should be aimed at the cause; the exudate will disappear when normal function is re-established.
Hypopyon - pus in the anterior chamber; will gravitate to ventral aspect of chamber; when it forms as a result of a bad corneal ulcer, may build up below the level of the ulcer with a peak resembling hourglass sand.
Hyphema - blood in anterior chamber; often does not clot so that it gravitates to ventral aspect of chamber; may take weeks to resorb if it has clotted.
Fibrin (plasmoid aqueous) - may only be seen as flare , but could also form a clot .
Lipid aqueous - this is a rare condition in which lipoidal material is present in the aqueous humor; often the eye shows no overt signs of inflammation; the material is often glistening and greasy in appearance; affected individuals usually have hyperlipemia; the material will disappear once the primary problem is corrected. At a distance, this condition may be confused with an anteriorly luxated cataractous lens.
Anterior uveitis has many causes, however a specific cause in a particular case may not be evident (O'Connor). Thus, most of the time, the condition is treated symptomatically.
Prostaglandins and other inflammatory mediators are elaborated in uveitis and may be the major cause of the inflammatory response.
Some specific causes of anterior uveitis include trauma (including any intraocular surgery), spread of inflammation from sclera or cornea, spread of infection from other organs, and immune-mediated conditions (Bellhorn, et al.; Davidson, et al.; Gwin).
Acute cases often are nongranulomatous and respond well to medication. If the condition continues for more than a week, it should be re-evaluated. Chronic cases have an unfavorable prognosis partly because of secondary damage to the eye.
Nongranulomatous versus granulomatous: It often is useful to determine if inflammation is granulomatous. Certain causative agents characteristically cause a granulomatous response (including fungi, certain bacteria and protozoa), and are more readily diagnosed because the agent is present within the granulomas. Granulomatous uveitis is often characterized by 'mutton-fat' keratic precipitates and a localized, exudative response. Cytologic studies on aspirated samples often are diagnostic if the process is a primary anterior uveitis.Nongranulomatous uveitis often is due to hypersensitivity from a remote focus of infection so that cytologic studies on aqueous or other aspirates are unrewarding.
If the inflammation is the result of systemic disease, it usually will be bilateral. Many of the hypersensitivity cases will be unilateral. In bilateral conditions, it is not unusual for the second eye to develop signs several days after the first.
Blepharospasm or increased blinking.
Increased lacrimation, epiphora.
Disturbed vision, if bilateral.
Enophthalmia - due to retractor bulbi muscle spasm from intraocular pain; this results in protrusion of the nictitating membrane.
Perilimbal conjunctival hyperemia, and chemosis.
Anterior chamber exudates: starts out as aqueous flare, then may lead to fibrin clots, hyphema or hypopyon.
Keratic precipitates:These are particles of various sizes, which are adherent to the corneal endothelium . They are composed of fibrin and cellular debris and differ in quality with the type of uveitis present. They may be individual or groups of inflammatory cells, or microgranulomas (the latter also are called 'mutton-fat' precipitates - epithelioid and histiocytic cells from granulomatous uveitis).Iris changes:Iris surface may be rough and lack luster. The iris may be swollen and have reduced mobility. It may be darker than that of the normal eye.Hypotony:
Vascular congestion - superficial blood vessels in the stroma become congested to give the iris a reddened appearance. In chronic cases, new blood vessels may develop on the surface of the iris (this is termed rubeosis iridis) .
Synechiae - exudate, or fibrovascular tissue in chronic cases, may result in adhesion of the iris to lens or cornea. Posterior synechiae (adhesions of iris to lens) are more common. Focal adhesions will result in an irregularly shaped pupil and an opacity of the lens capsule at the site of adherence. If the entire pupillary margin of the iris becomes adherent to the lens, the pupil is considered to be secluded; if this prevents aqueous from flowing into the anterior chamber, the iris bulges forward (iris bombé) , obliterating the ciliary cleft (drainage angle), and causing secondary glaucoma.If the pupillary space becomes obscured by exudate, fibrovascular tissue or melanin, it is called an occluded pupil.
Anterior synechiae may occur at the base of the iris (peripheral anterior synechiae) due to organization of inflammatory membranes. If these are sufficient in scope, aqueous humor outflow will be hampered and glaucoma may result.In uncomplicated anterior uveitis, the eye is hypotonic due to decreased aqueous humor production; the intraocular pressure can be less than 4 mmHg in acute cases. If the drainage angle is obstructed, secondary glaucoma may result. However, during the acute uveitis, glaucoma may not develop due to the pressure lowering effects of the inflammation. As the uveitis subsides and aqueous humor production increases, glaucoma may then occur, seemingly paradoxically, as a result of treating the uveitis.
Acute anterior uveitis must be differentiated from acute glaucoma and acute conjunctivitis. The following table gives some of the principal differences between these conditions:
Item Conjunctivitis Iritis Glaucoma Congestion Conjunctival vessels Deep ciliary vessels Scleral venous outflow Effect of 1:1000 epinephrine Blanches vessels No effect No effect Pupil Normal response to light Miotic Often dilated; may not respond to light Cornea Clear Edematous Opacification due to edema and structural changes Intraocular pressure Normal Low High Anterior chamber Clear Aqueous flare and sometimes cells Usually clear, may have some aqueous flare
Iridocycloplegia: Atropine is the drug of choice. Apply a 1% solution every 2-3 hours until the pupil starts to dilate, then frequently enough to keep pupil dilated. In horses, may need to use greater concentration initially, as much as 4%, to initiate dilation if the uveitis is severe. You must, however, be careful to monitor the horse for signs of abdominal pain because topical application of atropine can cause colic (Williams, et al.)It is important to keep in mind that your goal is to relieve iris sphincter and ciliary spasm (which are very painful) and effect pupillary dilatation. This can only be done using an iridocycloplegic. Do not use sympathomimetic agents alone as they can significantly increase the pain by stimulating the iris dilator muscle without paralyzing the iris sphincter muscle.Anti-inflammatory medication: This may be the most important part of uveitis therapy; it sometimes is the only medication given. Reduces the immune-mediated uveal response and restores integrity of the uveal capillary bed.
Some people recommend the use of 10% phenylephrine in addition to atropine, or alternating with atropine. This regimen is supposed to be helpful in breaking down relatively new adhesions of the iris to the lens. The efficacy of this treatment combination is not proven.Corticosteroids:Antibiotics: Because many, if not most, cases are not the result of direct infection, an antibiotic probably should not be used. In cases where an infectious agent is found, however, use the appropriate antimicrobial agent.Topical - usually all that is necessary for mild cases, but also used concurrently with systemic administration in severe cases. Initially every 2-3 hours, then three times a day.Nonsteroidal anti-inflammatory medication:
Systemic administration - the best method of treatment for severe cases.
Subconjunctival - use only if condition is severe and systemic therapy is not possible; triamcinolone is good (see therapeutics chapter).Flurbiprofen sodium or suprofen could be used (topically), but usually not necessary if corticosteroids are being used.
Flunixin meglumine (Banamine®) - by Schering (50 mg/ml injectable) - used to reduce prostaglandin synthesis in horses; give about 1 mg/kg body weight IV, or orally (e.g., oral granules can be used for chronic therapy). This should be used in conjunction with topical corticosteroids, at least initially, as it significantly reduces inflammation and pain. Do not use in dogs or cats.
Phenylbutazone - in horses. It may not be as effective as flunixin.
Topical cyclosporine has been used with some success (Gratzek, et al.), but it is unclear whether this has an advantage over the more economic corticosteroid treatment.
Supportive treatment: The patient should have access to darkened area if desired for relief of photophobia; it is not necessary, however, to force them to stay in this area.Warm, moist compresses may provide additional comfort for the patient.Granulomatous uveitis: The diseases causing this are usually serious. When granulomatous inflammation is present, find and treat the exact cause, if possible. Because most will be from fungal infection, an antifungal agent might be appropriate to use in undiagnosed cases in which you suspect or have proven that the inflammation is granulomatous. Corticosteroids may be contraindicated because of the inhibitory effects on the immune response. You must, however, weigh this against the negative consequences of inflammation on the eye and vision.
Often recurrent or relapsing. This is characteristic of uveitis in general, and the client should be forewarned.
Anterior synechiae with corneal opacification, corneal scarring with vascularization, or corneal endothelial degeneration with resulting edema.
Posterior synechiae with cataract.
Corneal mineralization, mostly in horses.
Degeneration or atrophy of ciliary body leading to phthisis bulbi.
Cataract. This is not uncommon and the client should be warned of this.
Secondary glaucoma. This usually occurs only after severe or chronic anterior uveitis in which the drainage angle (ciliary cleft) has become obstructed.
This disease is a panuveitis (entire uveal tract is affected) which is characterized by repeated recrudescence (Rebhun). Most early cases, however, are an iridocyclitis and the disease sometimes is termed recurrent iridocyclitis. Each episode is called an attack and the interval between attacks is highly variable (from one week to greater than a year). Each attack causes further ocular damage until eventually the eye may become blind due to either cataract, retinal degeneration, or phthisis bulbi. Attacks may subside spontaneously without treatment (but treatment reduces the course and damage).
Equine recurrent uveitis is the most important cause of blindness and ocular unsoundness in the horse. It is a disease with which the horse practitioner should be well-versed because of variation and subtlety in expression during periods when the condition is clinically inapparent (quiescent phase). This is important in pre-purchase or insurance exams because most horses probably would appear outwardly normal.
The condition also has been called 'moon blindness' because people used to think the recurrences were related to phases of the moon, which is not the case. Periodic ophthalmia is another term sometimes used, but is misleading because periodic implies periodicity which also is not the case.
It is important to bear in mind that uveal inflammation is by nature recurrent. Any process capable of sensitizing the uveal tract may cause a recurrent syndrome not necessarily related to a specific agent. There is some evidence that the pineal gland also may be involved (Kalsow, et al.).
Bacteria: Leptospira infection (Davidson, et al.; Matthews, et al.). A high or rising Leptospira titer has been shown in some patients and a syndrome similar to the spontaneous form has been produced experimentally with this organism.Other bacteria could be capable of inducing a hypersensitivity reaction.Parasites: Onchocerca cervicalis infection (Cello; Schmidt, et al.). The microfilariae of this parasite have been found in most ocular tissues. Their presence, however, is not a sign of disease. If this parasite is a cause of uveitis, then the microfilariae probably must be dying or dead in order to produce disease. Focal vitiligo of the lateral perilimbal conjunctiva often is seen without other signs of disease. This 'lesion' often yields many microfilariae if biopsied, but the significance of this is unclear.
Viruses: Viral cause has been proposed, but is not founded.
Metabolite deficiencies: Deficiencies in vitamins A, B2 (riboflavin) and C have been suggested, but not proven.
Essentially similar to any other uveitis; can be acute or chronic. Patients with chronic disease, or those having had previous attacks, often will show secondary changes such as posterior synechiae, occlusion or seclusion of the pupil, cataract or corneal scarring . Surprisingly, it is unusual for secondary glaucoma to occur. Instead, phthisis bulbi is a more likely sequela.
If the choroid is involved, you will see secondary retinal inflammation and degeneration. There may be fibrosis or separation of the retina in chronic or relapsing cases.
Peripapillary choroiditis or chorioretinal atrophy is common. These lesions appear alar in shape and are sometimes referred to as the 'butterfly' lesions of equine recurrent uveitis. However, they can be seen in horses who have not had overt uveitis so that they cannot be considered pathognomonic.
Between attacks, the eye may appear clinically normal. More likely, however, the eye will show signs of previous uveitis as mentioned before. Any horse with ocular changes suggestive of previous uveitis must be considered suspicious of having recurrent uveitis even if the eyes are non-inflamed at time of examination.
In order to diagnose equine recurrent uveitis, you must demonstrate (as the name implies), a recurrence. The first time uveitis is diagnosed in a particular individual, it should not be called recurrent although the likelihood of this being so is high. The exception to this would be a history of a previous problem which resolved either spontaneously or with treatment; in these cases a diagnosis of recurrent uveitis is justified.
Treat symptomatically as for any other uveitis (see previous section). Many patients are brought too late for treatment to be of value.
Treatment of each attack must be vigorous; subconjunctival injections of steroids may be indicated.
Proponents of Onchocerca infection as a cause recommend treating for microfilariae also: diethylcarbamazine at 11 mg/kg. Note: it is believed that you should use high concentrations of systemic corticosteroids (e.g., dexamethasone) when treating the microfilariae because an acute inflammatory response will occur as they die. You also may use ivermectin, at the label dose. This may be less likely to result in an exacerbation of inflammation.
One proposed method of control is the daily application of a topical corticosteroid on an indefinite basis in those individuals with known recurrences. The most often used steroid is dexamethasone. This is an untested and potentially very dangerous thing to do. If the horse develops an unrelated corneal ulcer on this regimen, the client may not recognize this change and continue using the steroid. The risk of fungal infection of the cornea would be high in such a case.
Another method of control is the use of oral aspirin. The initial dose is 25 mg/kg body weight twice a day for 2 weeks. After this it is increased to 30 mg/kg and given once a day indefinitely. There is no proof this is effective.
Prognosis must be considered guarded to poor because of the recurrent nature of the disease.
A condition known as the Vogt-Koyanagi-Harada or uveomeningoencephalitic syndrome is seen in human beings. It is characterized by moderate to severe uveitis (anterior and posterior ), secondary retinal separation, poliosis (whitening of hair), vitiligo (loss of cutaneous melanin ), dysacousia and meningitis. Not all patients have all symptoms and the degree of symptomatology differs from patient to patient.
A syndrome similar to this syndrome is recognized in dogs (Kern, et al.). Because not all human symptoms are expressed in the signs the affected dogs show, the syndrome in dogs should be referred to as Vogt-Koyanagi-Harada-like if there is a desire to use the eponym.
Dogs with the Vogt-Koyanagi-Harada-like syndrome have various degrees of uveitis involving iris, ciliary body and choroid. Retinal separation is seen as a complication of choroiditis. Vitiligo seems to be present in almost every affected dog. Poliosis occurs less frequently, but still is relatively common. Meningitis or signs of meningeal irritation have been seen in at least one dog. Dysacousia has not been recognized in affected dogs.
Many breeds of dogs have been affected. However, the Akita, Siberian husky, Alaskan malamute and Samoyed are most commonly affected.
Treatment is as for uveitis in general. Systemic corticosteroids seem especially important. The treatment must be continued for months beyond the point at which the signs subside.
Prognosis is poor overall. The uveitis tends to recur and may result in permanent blindness due to cataract and retinal degeneration after long term separation or inflammation. Even vigorous therapy may not control the situation. In patients in whom inflammation is controlled, useful vision may be retained and melanosis of the skin may recur.
The cause of this syndrome is unknown in people or dogs. It is hypothesized that there may be an immune response mediated against the patient's melanin. Viral initiation has been put forth as a possibility.
This frequently occurs in previously normal irises as the individual gets older. In this case it is called senile iris atrophy. The effects on the pupillary border are most visible: the border will appear ragged and the sphincter muscle may be severely affected causing a loss of the pupillary response to light. This is important to remember when evaluating pupillary responses in an elderly patient. The stroma also is affected, but the changes often are not appreciable. If you retroilluminate the iris by an ocular fundus reflection, you may be able to demonstrate a thin stroma. Senile iris atrophy is most common in miniature poodles and other small breed dogs.
Degeneration may lead to a darkened appearance to a light-colored iris due to exposure of the posterior epithelium which is heavily melanotic . Be careful not to confuse this with melanosis, which has other implications.
Iris atrophy also may occur in irises which were hypoplastic.
Rarely, there may be primary atrophy of the iris unrelated to age. This is called essential iris atrophy and is seen most frequently in the Chihuahua and miniature schnauzer. The iris takes on a marked 'moth-eaten' appearance.
No treatment is available nor necessary.
Severe anterior uveitis or chronic glaucoma may result in destruction of the anterior uvea, particularly of the ciliary body. This eventually leads to phthisis bulbi or an enlarged, hypotonic globe.
There is no treatment.
Small islands of hypermelanosis form and spread to involve most of or the entire anterior surface of the iris. Can be unilateral. Although this condition is itself not harmful, it must be watched carefully because it may be the result of chronic inflammation, or it may herald the onset of annular or diffuse iris melanoma. If there is any question, you should get consultation from a specialist because the diffuse melanomas may be fatal.
Severe contusions to the eye can cause separation of the iris, or iris and ciliary body, from the sclera. Trauma severe enough to do this also may cause retinal separation.
This often leads to hypotony or phthisis bulbi. It also may be called recession of the chamber angle. It is not treatable.
This is a specific bilateral inflammation of the entire uveal tract in human beings. The cause is not known, but it almost invariably follows a perforating wound to the globe in which uveal tissue is involved. Sometime after the injury, the injured eye becomes inflamed and at approximately the same time the opposite, or sympathizing, eye also becomes inflamed.
Proper therapy of perforating wounds and the use of corticosteroids have reduced the incidence of this disease.
This phenomenon does not appear to occur in nonhuman animals.
Iris neoplasms often can be detected before they become extensive. Any iris mass should be observed for a short period before invasive procedures are used for treatment. If there is no significant change, or no signs of aggression, you should elect to not treat. Small iris neoplasms could be excised using electrocautery by a specialist. Larger neoplasms should be treated by removing the eye.
Primary neoplasms of the iris (and ciliary body) usually have low metastatic potential. When treatment is indicated, removal of the eye frequently is curative.
Ciliary body and choroidal neoplasms seldom are diagnosed until they cause serious damage to the eye. They may not become evident until they grow large enough to obliterate the anterior chamber by pushing the iris forward, become visible through the pupil, erode the sclera, result in glaucoma, or cause retinal separation, detachment or degeneration. Some of the signs which may help you in diagnosing or suspecting a ciliary body or choroidal neoplasm include:
Continuing uveitis only partially responsive to treatment.
Focal equatorial cataract which progresses - this may indicate a ciliary body neoplasm in that quadrant; the mass may either physically disturb the lens or cause a change in the local metabolism.
Focal thinning of the sclera posterior to the limbus.
Retinal separation or detachment.
Shallowing of the anterior chamber.
Chronic glaucoma of an undetermined cause.
Blind, painful eye. Any eye which is blind and painful and whose ocular media are opaque should be suspected of harboring a neoplasm. Enucleation would be indicated in these cases.
Melanoma : This is the most common primary intraocular neoplasm in most species (Acland, et al.; Collinson and Peiffer; Duncan and Peiffer; Friedman, et al.). It occurs usually in the anterior uvea of middle-aged and older animals. Be aware that uveal melanomas do not behave like skin melanomas. In contrast, uveal melanomas generally are rare to metastasize in our patients, grow slowly and are effectively cured by excision (enucleation or exenteration).
Adenoma and adenocarcinoma : Adenomas and adenocarcinomas occur with some frequency especially in the dog. Adenocarcinomas are especially noteworthy as they are somewhat aggressive and may metastasize (Bellhorn). They should be treated by enucleation or exenteration. Adenomas usually occur in elderly animals and are best left alone unless they enlarge to become a problem. Because you cannot determine clinically which is which, the criterion you may want to use is whether the tumor is causing problems for the patient. If there is intractable uveitis and pain, the eye should be removed; if the eye appears comfortable, leave it alone.
Medulloepithelioma: This is embryonic or neonatal in onset and is derived from the primitive ciliary epithelium. The ciliary epithelium is multipotential, and these tumors may be composed of immature retina, brain tissue, glandular spaces, striated muscle fibers, cartilage and bone. These neoplasms usually are diagnosed in young animals (less than a year). Enucleation or exenteration usually is sufficient, but they can be aggressive and metastasize. It is seen occasionally in the dog (Langloss, et al.) and is seen about as often as melanomas in the horse (Bistner). It also appears to be the most common primary intraocular neoplasm seen in captive cockatiels (Schmidt, et al.).
Metastatic neoplasms to the uvea: Because the uveal tract is rich with blood vessels, hematogenous spread of remote neoplasms is not uncommon. Mammary or other adenocarcinoma (Bellhorn), transmissible venereal sarcoma (Barron, et al.) and lymphosarcoma (Carlton) are most commonly seen. The presence of metastases in the eye always is a poor sign and no treatment is available in most cases. However, removal of the eye and histologic examination may be important in establishing a diagnosis and prognosis.
Retinal epithelial tapeta: Note that in fish, birds and some mammals (such as the American opossum), the tapetum is the result of material within the retinal epithelium.
Sign of granulomatous uveitis: For example, if you recognize 'mutton-fat' keratic precipitates, you can be almost certain that the inflammation is granulomatous.