Cataracts in Dogs

Glaucoma is a condition in which the pressure within the eye becomes elevated. It is often very painful and is a leading cause of blindness in dogs. Glaucoma may be a primary disorder or secondary (the result of other disease within the eye).

dog that has cataractsIn the normal eye, a fluid called aqueous humor is produced by a portion of the eye known as the ciliary body. Normal aqueous humor flow within the eye maintains a stable intraocular pressure (IOP) and also carries nutrients to (and waste products from) those portions of the eye that do not contain blood vessels, such as the lens and the cornea. Aqueous humor leaves the anterior chamber of the eye through the filtration angle. When the outflow of aqueous humor is obstructed, fluid builds up and leads to an elevated IOP. Normal IOP in dogs ranges from 15 to 25 mmHg.

Primary glaucoma can be classified as narrow angle (in which the filtration angle is narrow and does not allow adequate outflow of aqueous humor), open angle (filtration angle appears normal but outflow is likely obstructed by a deeper structure), or goniodysgenesis (in which the filtration angle has not developed normally). Primary glaucoma is often a bilateral disease (both eyes are affected, although often one at a time) and is likely inherited.

Secondary glaucoma occurs as the result of other intraocular disease, such as anterior uveitis (inflammation of the iris, ciliary body and or choroid), lens luxation or subluxation (the lens has moved out of its normal position in the eye), trauma, cataract, or neoplasia (cancer).

Glaucoma may be acute (a sudden rapid rise in IOP with no previous signs) or chronic (progressive but not necessarily apparent immediately). Although patients with chronic glaucoma may not have the pronounced sudden onset of signs, they are still likely painful and develop blindness.

Vision loss may occur more quickly if there is a sudden profound rise in IOP versus a gradual increase. Blindness results when the IOP leads to damage of the cells in the back of the eye that are responsible for vision or direct damage to portions of the optic nerve.

Common name: Cataract, Lens opacity, Cloudy eye
Scientific name: Cataract

Diagnosis

Signalment
Most cataracts in dogs are hereditary. Breeds that are predisposed to primary cataract formation include English Cocker Spaniel, Cavalier King Charles Spaniel, West Highland White Terrier, Miniature Schnauzer, Boston Terrier, Golden Retriever, American Cocker Spaniel, Miniature Poodle, and others. The age of onset of primary cataract formation varies by breed and may occur as early as at a few months of age to several years old. Dogs with hereditary cataracts are usually affected in both eyes. Cataracts that form secondary to other diseases do not necessarily have a breed predilection or typical age of onset.

Incidence/prevalence
Cataracts are common in dogs and are a significant cause of vision loss.

Geographic distribution
There is no known geographic distribution.

Clinical signs (primary, most to least frequent, scientific term, synonyms)
Lens opacity (cloudy appearance to the eye) Vision impairment (dog bumps into furniture, seems startled when approached from behind).

Clinical signs (secondary, most to least frequent, scientific term, synonyms)
If secondary to diabetes mellitus, signs of primary disease may include polyuria (increased urination), polydipsia (increased drinking), and weight loss Blepharospasm (squinting eye) if concurrent uveitis (primary or secondary) If secondary to other systemic disease, may see signs of primary disease process.

Causes (scientific, common term)
Hereditary – most common cause, Diabetes mellitus, Uveitis (inflammation in the iris, ciliary body, and/or choroid) may lead to or result from cataracts, Nutritional deficiency, Radiation, Secondary to other intraocular disease (progressive retinal degeneration).

Organ system affected (most to least affected)
Eye. Other organ systems may be affected primarily (if cataract is secondary to systemic disease such as diabetes mellitus or infectious cause of uveitis).

Diagnostic tests 
Ophthalmic examination using slit-beam biomicroscopy Blood chemistry/complete blood count if suspected systemic cause for uveitis-induced cataract; also as pre-anesthetic screen prior to surgery to correct cataract. Electroretinography (ERG), measures electrical activity in the retina; recommended prior to surgery to rule out concurrent retinal disease (which would affect prognosis for vision). Ophthalmic ultrasound, to visualize position of structures in the eye prior to cataract surgery.

Differential Diagnosis
Lenticular (nuclear) sclerosis, a normal aging change that gives the lens a blue-gray appearance; a veterinarian will be able to differentiate this type of change. Uveitis, Hyperplastic primary vitreous, Leukocoria (white pupil).

Overview

A cataract is an opacity in the lens of the eye that may compromise vision by obstruction of the ocular fundus (portion of the back of the eye necessary for vision). The lens is a transparent structure located toward the center of the eye. The lens is composed of fibers that are mostly protein and water surrounded by a lens capsule. The transparency of the lens is dependent on the specific arrangement and structure of the proteins and lens fibers. Anything that disrupts the arrangement of these lens fibers or affects the proteins composing the lens may lead to cataract formation. Most cataracts are hereditary. However, they also may form secondary to diabetes mellitus, uveitis (inflammation of the inner eye), radiation, toxins, nutritional deficiency, or other intraocular disease processes such as progressive retinal degeneration.

Classification of cataracts is based on age of onset (congenital, juvenile, adult, senile) or on the stage of cataract formation. An incipient cataract is a small opacity seen in one area in the lens with no loss of vision. Immature cataracts are mostly opaque but do not completely obstruct vision. A mature cataract consists of a lens that is completely opaque, resulting in loss of vision. A hypermature cataract also consists of a completely opaque lens, but in some patients vision is partially restored because the lens may shrink and the individual can see partially around it. Cataracts may also be classified according to percentage of the lens that is affected and the specific location within the lens.

Treatment

Home Care
Home care is limited to the recognition of initial signs (such as a cloudy appearance to the eye), progression of vision loss, and/or other clinical signs related to disease elsewhere in the body. Dogs that may have cataracts should be seen by a veterinarian.

Professional Care
Once a cataract has been diagnosed, a veterinary ophthalmologist will determine whether or not treatment is indicated. There is no medical therapy for cataracts once they have formed. If there is no ongoing intraocular disease and the patient is otherwise stable, cataract surgery is the treatment of choice. Further diagnostic testing including electroretinogram and ocular ultrasound may be performed to assess prognosis for restoration of vision following surgery. There are many techniques for cataract removal.

Action
A dog with a cloudy appearance to the eye or signs of visual impairment should be seen by a veterinarian. Since many types of cataracts and other intraocular diseases are progressive (get worse over time), the patient should be examined as soon as possible. Once confirmed, cataract patients should be examined by a veterinary ophthalmologist (a veterinarian who is a Diplomate of the American College of Veterinary Ophthalmology).

Outcome
Prognosis for restoration of vision is dependent on presence of concurrent retinal disease and or lens-induced uveitis. In the absence of concurrent intraocular disease, many dogs regain vision after surgery. Most diabetic dogs that undergo cataract removal surgery have restored vision. Dogs that have cataract surgery may be at increased risk for developing glaucoma.