Cataracts

An opacity involving the lens of the eye that prevents light from reaching the retina is termed a cataract. Cataracts can be inherited (juvenile cataracts) or might develop secondary to eye trauma, infections, or metabolic disease, such as diabetes mellitus. As lens opacity increases, the amount of light allowed to reach the retina is diminished, and partial blindness ensues.

Cataracts can also predispose to rotation or luxation of the lens. Such lens movement can disrupt normal fluid flow within the eye and lead to secondary glaucoma. True cataracts must be differentiated from lenticular sclerosis seen in older pets. Lenticular sclerosis is a lens opacity caused by a normal hardening of the lens material due to age. It is a normal aging change seen in some dogs, and rarely leads to loss of sight as can occur with cataracts.

As a result, no specific treatment is required for most cases of lenticular sclerosis. Lenticular sclerosis and cataracts can be differentiated with an ophthalmologic examination performed by a veterinarian.

Treatment for cataracts usually involves surgical removal of the offending lens. A less invasive surgical technique for cataract removal is called phacofragmentation. This procedure employs the use of ultrasound to break up the lens material into small pieces, which can then be drawn or sucked out of the eye using special instrumentation. Once cataracts are removed, vision is effectively restored in the affected pet.

Keratoconjunctivitis Sicca (Dry Eye)

Seen primarily in dogs, keratoconjunctivitis sicca (KCS), or “dry eye,” is a condition affecting the cornea and conjunctiva of the eye resulting from inadequate tear production. Actually, only the water portion of the tear film is deficient; the mucus portion is still produced in adequate quantities. This leads to the characteristic green, mucoid buildup in and around eyes affected with KCS. The lack of adequate tear moisture also predisposes the cornea to damage and ulcers. Long-term sequelae include pigmentation of the corneal surface and blindness.

KCS can have a number of underlying causes. In many breeds—such as Yorkshire terriers, schnauzers, cocker spaniels, bulldogs, and beagles—KCS can be an inherited trait. Other potential causes include canine distemper, certain medications (such as sulfa drugs), hypothyroidism, diabetes mellitus, and autoimmune disease.

Diagnosis of KCS is made using tear flow tests to determine the amount of tear production.

Treatment of KCS involves the use of tear replacement drops, followed by an application of a tear replacement ointment to seal in the drops. These replacements must be applied every 3 to 4 hours to be truly effective. If infection or inflammation is present, antibiotics and anti-inflammatory medications should be instilled into the eyes as well.

Medications designed to stimulate more tear production have been used for treatment in the past with varying success. Also, the drug cyclosporine can be quite effective at stimulating renewed tear production in some dogs with KCS. For more information on cyclosporine, owners should contact their pets’ veterinarians.

In especially advanced cases of KCS, surgical intervention might become necessary. The standard surgical treatment used, called parotid duct transposition, involves repositioning a duct from a salivary gland to the corner of the affected eye(s), thereby providing a constant source of moisture (saliva) to the eye.

Retinal Degeneration and Disease

Retinal degeneration and disease can be a cause of blindness in dogs and cats. For instance, progressive retinal atrophy (PRA) is a hereditary condition that can strike middle-aged to older dogs and produce blindness over a period of several months to years. Breeds that are predisposed to this condition include Gordon setters, Irish setters, poodles, Norwegian elkhounds, Labrador retrievers, collies, cocker spaniels, and malamutes. Characterized by a slow degeneration of the receptor cells composing the retina, PRA in its early stages often leads to nightblindness in affected dogs. These dogs tend to fear or shy away from poorly lit areas. As PRA progresses, it eventually causes the pupils to remain dilated and fail to respond to light, causing complete blindness.

Retinal function may also be partially or completely lost due to underlying disease or injury. For example, glaucoma affecting an eye can place so much pressure on the blood vessels supplying the retina of that eye that secondary retinal degeneration results. Sudden acquired retinal degeneration (SARD) is another nonhereditary condition that can cause blindness in dogs, yet its exact cause remains a mystery. Interestingly, this disease is often accompanied by an increase in thirst and in appetite in those dogs so affected. Infectious diseases, such as ehrlichiosis and Rocky Mountain spotted fever, and fungi can also adversely affect the region of the retina where the optic nerve exits, leading to inflammation and subsequent loss of vision. In addition, neoplasms such as lymphosarcoma can infiltrate the retinas of dogs and cats and inhibit retinal function. Finally, trauma, immune-mediated diseases, and certain toxins can cause retinal injury and lead to blindness.

Diagnosis of retinal disease and degeneration is made using history, physical exam findings, and information obtained from an ophthalmic examination of the retinas themselves. In addition, an electroretinogram, which measures the electrical activity taking place within the retinas, will provide a definitive diagnosis of retinal degeneration and retinal blindness. If a disease condition such as glaucoma, infection, neoplasia, or toxicity is suspected, other diagnostic testing procedures specific to these conditions may be required as well to confirm a diagnosis.

Unfortunately, there are presently no known treatments for PRA and SARD, and the prognosis remains grave for the restoration of sight in affected dogs. Other diseases involving the retina may respond favorably to treatments specific for the particular disorder; however, it must be remembered that the longer such treatments are delayed or neglected, the greater the chances are of permanent loss of vision.

Prolapse of the Third-Eyelid Gland (Cherry Eye)

The third eyelid of dogs contains a gland that might occasionally become inflamed and protrude over the edge of the third eyelid, producing a classic “cherry eye” appearance. Certain breeds—such as the cocker spaniel, Lhasa apso, Pekingese, and beagle—seem to be more predisposed to this condition than others.

In the past, treatment for a prolapsed gland of the third eyelid involved complete surgical removal of the gland. However, researchers agree that the gland might play an important role in tear production; hence, complete removal of the gland might predispose a pet to keratoconjunctivitis sicca. As a result, newer surgical procedures involve removal of only a portion of the gland, or actually tacking down the prolapsed portion of the gland to the inner surface of the third eyelid.

Entropion

Entropion is an ophthalmic condition in which the eyelids roll inward, allowing lashes and hair to irritate the surface of the eyes. The condition is inheritable, or it can occur secondary to other types of eye irritation (spastic entropion) or eyelid injury. Congenital entropion has a high incidence in chow chows, shar-peis, English bulldogs, poodles, and rottweilers. Signs of entropion include excessive tearing, squinting, constant rubbing of the affected eye(s), excessive redness to the eye(s), and a noticeable inward roll to the eyelid, especially the lower lid.

If a pet is suffering from entropion, surgical treatment might be essential to prevent lasting damage to the surface of the eye(s). Some puppies afflicted with this disorder might outgrow it as they mature; hence, surgery is usually delayed in these young animals until they are at least 6 months old, unless the damage to the eye is severe.

In the meantime, topical lubricants designed to protect the corneas can be used on a daily basis in these patients. In some pups, especially shar-peis, temporary eversion of the offending lids with sutures implanted in the skin of the lids can also help prevent complications until they outgrow the entropion or are old enough for the surgery.

Entropion surgery involves the removal of a flap of skin just beneath (lower lid) or above (upper lid) the inverted lid. Suturing close the resulting gap of skin will then provide enough tension to roll the lid back out. In many instances, more than one surgery is necessary to achieve just the right amount of eversion.

After surgery is performed, care must be taken to prevent the dog from irritating the incision line and causing swelling. Hospitalization for a few days after the procedure is performed will help reduce this occurrence. Because of the inheritable nature of this disorder, all dogs affected with entropion should be neutered to prevent its passing to future generations. When selecting a new pet, especially one that falls into the high-risk category, owners should examine the pup’s parents closely for any signs of entropion or for evidence that surgical correction has been previously performed.

Ectropion

Ectropion is the exact opposite of entropion; it is the outward rolling of the eyelid(s), which exposes the pink conjunctival lining within. As with entropion, this condition is inheritable, with cocker spaniels, St. Bernards, and bloodhounds having a high incidence. Facial nerve paralysis, such as that seen secondary to otitis media, can also result in ectropic lids.

Mild cases of ectropion usually cause no problems whatsoever in affected individuals. Moderate to severe cases are often accompanied by conjunctivitis, excessive lacrimation, and eye discharges.

Keeping the eye(s) clean and free of discharge on a daily basis using saline solution or medicated drops or ointments will help keep minor cases of ectropion under control. For more extensive involvement, surgical correction designed to release the tension placed on the skin of the eyelid, allowing it to roll back to its correct position, might be required.

Masses Involving the Eyelids

The integrity of the eyelids is vital to protect the eyes from environmental hazards. Any disruption or alteration in the normal lid anatomy can place vision in jeopardy. And certain masses involving the lids can do just that if they become large enough.

Chalazions are masses involving the eyelid that originate from the small meibomian glands that line the edge of the lid. They result from a buildup of secretion within the glands due to blockage of the ducts leading from the gland. Chalazions appear as yellow to white swellings beneath the conjunctiva on the inner lid margin. Puncturing or incising these to remove the trapped contents will afford a cure.

Hordeolums are pus-filled masses caused by infections within the meibomian glands or hair follicles lining the lid margin. As with chalazions, these can be punctured and expressed to help speed healing.

Topical or systemic antibiotics are also used to eliminate infection. Tumors that affect the eyelid can be very serious due to the inability to remove them surgically without disrupting the integrity of the lid. Sebaceous gland adenomas are common lid tumors, especially in older dogs. Others include adenocarcinomas, papillomas, and melanomas. As an alternative or adjunct to surgical removal, radiation therapy, chemotherapy, or cryotherapy (freezing) can be used as well, depending upon which type of tumor is involved.

Ruptured Eardrums

Eardrums can tear or rupture as the result of direct trauma from a foreign body (a twig, cotton-tip applicator, etc.), sudden pressure changes, or, most commonly, as a secondary complication due to otitis externa. Although a serious and painful condition, a torn eardrum will heal quite quickly provided the underlying cause of the perforation is eliminated. Medications designed for use in the ears must be used with caution if a dog or cat suffers from a ruptured eardrum. Not only can their application be painful, but also, as mentioned previously, certain antibiotics and solutions, if allowed direct access into the middle- and inner-ear chambers, can cause damage to the auditory nerve endings, resulting in deafness. As a result, be certain to follow a veterinarian’s recommendations closely.

Deafness

Veterinarians are often confronted by frustrated pet owners claiming that their pet is going deaf! Now, whether this is a valid claim or rather an actual ploy conceived by a defiant subject will not be known until a thorough ear examination is performed. A pet’s apparent inability to perceive sounds can result for a number of reasons.

First, there might be impedance to the sound waves traveling through the ear. An external ear canal clogged with wax and debris can certainly be the culprit, as can constrictive swelling of the ear canal caused by otitis externa. Torn or ruptured eardrums can also diminish the effective transmission of sound waves to the middle and inner ears. Interestingly, some researchers feel that a dog’s eardrums are not altogether necessary for efficient conduction of sound waves; rather, sound waves permeating the bony, air-filled tympanic bullae directly fulfill a major portion of this conductive function. Regardless, researchers do know that sound waves must pass through the middle-ear cavity before reaching the inner ear, and that fluid or inflammation secondary to otitis media can lead to diminished hearing.

Besides interference with the transmission of sound waves, deafness in dogs and cats can also be caused by developmental defects or damage involving the actual nerve endings within the inner ear. Congenital nerve deafness has been reported in some breeds, including dalmatians, collies, and rottweilers. Nerve deafness can also be inherited in some cats. This type of induced deafness is seen primarily in white cats with blue eyes. Certain drugs, such as the aminoglycoside antibiotics, are well known for their adverse effects on the hearing function in dogs and cats. Chronic, untreated bacterial and fungal infections within the middle and inner ears can undoubtedly lead to nerve deafness, as can certain viral organisms.

Diagnosis of nerve deafness is based on history and special hearing tests. One such test, the brainstem auditory evoked response test (BAER), measures the brain’s response to auditory stimuli and is quite helpful in the detection of hearing defects, determining the extent of any defect, and pinpointing its location.

Unfortunately, no known treatment exists for true nerve deafness. Hearing aids designed especially for dogs are now commercially available, and may help improve hearing in select instances. Most deaf pets will adapt to their condition with time. However, because of inherent dangers associated with environmental hazards, deaf dogs and cats should not be allowed outdoors unless closely supervised or maintained on a leash and harness.

Aural Hematomas

Fractures or trauma to the cartilage supporting the pinna of the ear can lead to the accumulation of blood and serum within the affected flap. These aural hematomas cause the pinna to swell, sometimes to enormous sizes. In the majority of cases, the fluid accumulation occurs on the inside portion of the earflap.

Researchers don’t know what precipitates many cases of aural hematomas, but they do have a few suspicions. Since these hematomas are often accompanied by otitis externa, many feel that the trauma induced by scratching and shaking the head predisposes to aural hematomas, especially in those dogs with pendulous ears. Still others suspect that an overactive host immune system is the culprit behind this disorder. Regardless of the cause, aural hematomas are painful and irritating, and need to be surgically drained as soon as possible after initial appearance.

Date: 2014-12-28; view: 946