Ophthalmic Examination in the Adult Patient

Introduction

The adult patient, defined as the second and third quarter of life, can present with a wide variety of inherited or acquired ophthalmic changes that commonly include cataract formation, corneal dystrophy, corneal degeneration, glaucoma, keratoconjunctivitis sicca (KCS), and Golden Retriever Pigmentary Uveitis (GRPU).

Most structural abnormalities (e.g., eyelid conformation and abnormal hairs) and third eyelid gland prolapse will most likely have been identified and corrected at an earlier age. Age-related changes (indolent ulcers, lenticular sclerosis, and benign eyelid masses) begin to emerge in later adulthood and will be discussed in more detail in the article Ophthalmic Examination in the Senior Patient. For more information about keratoconjunctivitis sicca (dry eye) and GRPU, please see the related articles.

Cataracts

Cataracts may be inherited or acquired. Inherited cataracts can arise at any age and may vary in extent between eyes. Acquired cataracts develop secondary to diabetes (dogs), trauma, or uveitis. Despite diligent regulation of blood glucose levels, diabetic cataracts typically affect both eyes, can develop very rapidly and can result in marked inflammation within the affected eye(s) (uveitis).

Evaluation by a veterinary ophthalmologist for the rapid control of lens-induced uveitis (LIU) and/or surgical removal of the lenses (phacoemulsification) is critical. Traumatic cataracts typically develop in one eye and may not progress to affect the entire lens.

All cases of cataracts require continued monitoring for, and treatment of, LIU. Cataract removal is elective and highly successful, however like a three-legged stool, a successful surgical outcome is equally dependent upon the health of the eye, nature of the patient, and compliance of the owner.

Cataract surgery requires strict adherence to the recommended post-operative medical regimen and recheck schedule to achieve the best outcome by minimizing the development of intraocular inflammation and scarring.

Scarring that develops in an eye can result in glaucoma and/or retinal detachment, both of which can be blinding. For more information about cataracts and glaucoma, please see the related articles. (See PHH’s article on Cataracts)

Corneal Degeneration and Corneal Dystrophy

Corneal degeneration and corneal dystrophy refer to calcium or lipid deposits in the cornea(s) and can appear clinically identical. Corneal dystrophy is inherited, slowly progressive, and typically present in the central part of both corneas as white-grey crystalline deposits. The development of these deposits is not associated with prior corneal ulceration or underlying disease.

Over time, the area of deposition enlarges but at the same time, the center often becomes clear – much like an expanding doughnut. Rarely will the deposits become vision threatening.

In contrast, corneal degeneration develops secondary to prior corneal injury or underlying disease (hypothyroidism, Cushing’s disease, diabetes, pregnancy, high blood cholesterol, lipid, or calcium), and may affect one cornea or both at any location.

When corneal degeneration is suspected, the underlying cause of the corneal changes can sometimes be identified through blood tests performed by your veterinarian. These blood tests will help to identify elevations in blood cholesterol, triglycerides, or calcium, and can be useful in diagnosing hypothyroidism, Cushing’s disease, and diabetes.

While uncommon, irritation of the eye by these deposits can occur, and is more often associated with calcium deposition which are often spikey and appear flakey vs the soft deposits of fat. Medication can be prescribed by your veterinarian to help blunt these sharp calcium points and promote thinning of the deposits.

Glaucoma

The tone or pressure of the eye is governed by the fluid within it. The pressure in the eye varies throughout the day and within a normal range. Glaucoma is defined as an elevation of intraocular pressure (IOP) that goes beyond the health of the eye.

While glaucoma is frequently blinding, early detection and treatment can prolong vision in most cases. Glaucoma is more common and more easily blinding in dogs than it is in cats.

Glaucoma can be broadly classified as primary glaucoma or secondary glaucoma. Primary glaucoma is the inherited form of glaucoma that develops secondary to progressive changes that reduce fluid drainage from the eye.

Primary glaucoma will nearly always affect both eyes but not necessarily at the same time. Secondary glaucoma is acquired; caused by changes in the eye that were initiated by scarring (eg. uveitis) or mechanical obstruction within the eye (eg. space-occupying tumor, lens displacement). Secondary glaucoma typically affects one eye only.

While all dogs and cats can develop glaucoma, primary glaucoma is more common in dogs than in cats and tends to be more prevalent in certain breeds such as the American Cocker Spaniel, Basset Hound, Chow Chow, Shiba Inu, Siberian Husky, and Shar Pei. Secondary glaucoma occurs more commonly in cats than in dogs.

Early clinical signs associated with glaucoma (primary or secondary) can be subtle. These signs include conjunctival redness and an enlarged pupil (dilated) that does not become smaller (constricted) in response to a bright light.

Other signs that can manifest very quickly include corneal greying (some people describe this as a ‘blue’ eye), reduced vision, rubbing at the affected eye, sleeping more, eating less, or avoiding social activities.

When glaucoma is present for longer than a few days, the eye can become enlarged (buphthalmic) and in dogs is associated with blindness. Interestingly, cats can have a buphthalmic eye secondary to glaucoma but remain visual!

As discussed above, the early signs of glaucoma can be subtle and be easily missed. Because glaucoma can be rapidly blinding it is important to diagnose and start treatment early.

If you know your dog or cat to be at risk (susceptible breed, history of glaucoma in siblings or parents, history of glaucoma in the fellow eye) it is important to monitor the eyes for early signs of glaucoma.

One of the earliest indicators of elevated intraocular pressure is a dilated pupil that is poorly or not responsive to direct light stimulation. If you notice the pupil (the black center of the eye) to be dilated, you can perform the pupillary light reflex test. The pupillary light reflex test allows you to monitor the pupil’s response to a focal light source. To perform this, simply shine a bright focal light into the eye that has the dilated pupil.

Do not keep the light shining in the eye for more than a couple of seconds! You should notice the pupil become smaller very quickly in response to the light. This is called a positive direct pupillary light reflex and is a normal response to light.

A positive response does not exclude the possibility of glaucoma, and seeing your veterinarian is still warranted if other signs (described above) are noted.

When the pupil does not constrict in response to a bright focal light, this is called a negative direct pupillary light reflex. A negative or sluggish positive response warrants a call to your local veterinarian to have the IOP measured as quickly as possible.

Glaucoma is painful and very rapidly blinding. Following diagnosis of glaucoma, medication to rapidly lower eye pressure must be initiated to minimize retinal damage or blindness, and prompt referral to a veterinary ophthalmologist is recommended.

Blindness in Adult Dogs and Cats

Uncommonly, adult dogs and cats will become blind for no outwardly apparent reason. Blindness can be caused by many conditions, two of which were discussed above – glaucoma and cataracts. Blindness that occurs because of changes in the retina can occur quickly or slowly.

The two most common reasons for retinal blindness are sudden acquired retinal degeneration syndrome (SARDS) and progressive retinal atrophy (PRA). SARDS, only documented in dogs, is typified by the rapid onset (1 day to 3 weeks) of blindness with 65% of dogs reported as middle-aged to older, overweight, and female.

The cause of SARDS is unknown, but is often accompanied by increased thirst, urination, appetite, weight gain, and an initial rise in a stress hormone called cortisol. The retina of a patient affected by SARDS initially looks normal but, over several months, becomes indistinguishable from other causes of retinal atrophy.

Because the retina initially appears normal, diagnosis of SARDS requires early examination by a veterinary ophthalmologist who will be able to confirm the diagnosis of SARDS by performing a retinal function test.
This test is called electroretinography (ERG).

Unfortunately, there is no treatment for SARDS. In contrast to SARDS, PRA is inherited, slowly progressive (develops fully over 10 to 12 months), and typically develops in 3 to 5 year-old or 7 to 10 year-old age-groups of dogs. PRA can also develop in cats. By the time vision changes are noted, a patient affected by PRA has degenerative changes that include thinning of both the retina (tapetal hyperreflectivity) and retinal blood vessels (vascular attenuation).

While any breed of dog can be affected by SARDS or PRA, Dachshunds and Miniature Schnauzers are overrepresented. As with SARDS, diagnosis of PRA is confirmed via ERG testing.

Golden Retriever Uveitis

Golden Retriever Pigmentary Uveitis (GRPU) is an inherited, complex ocular condition in Golden Retrievers. The disease typically becomes evident between the ages of 4 to 7 years of age, with early signs such as intermittent tearing and redness of the conjunctival tissue, which could be mistaken for allergic conjunctivitis.

As the disease progresses, more severe symptoms develop that including aversion to light (photophobia), low intraocular pressure, darkening of the iris, and pigment deposition onto the lens.

GRU typically affects both eyes and when not treated early, can lead to chronic inflammation and intraocular scarring. Complications from these include glaucoma, cataracts, and ultimately blindness, with nearly half of affected dogs becoming blind due to glaucoma.

Early treatment focuses on controlling inflammation with topical and or oral anti-inflammatory medications and monitoring intraocular pressure.

Early detection and continuous therapy are critical, with lifelong management required to maintain vision and manage symptoms. With early intervention and continued care, the prognosis is excellent for maintenance of vision.

The prognosis becomes more guarded when the disease is detected late and intraocular scarring has already been established. Early detection emphasizes the importance of regular eye examinations to detect and manage this heritable condition effectively.

Conclusion

Understanding and promptly addressing eye health issues in adult dogs and cats can significantly impact their quality of life. Regular ophthalmic examinations are crucial for early detection and effective management of eye conditions.

Owners are encouraged to observe their dogs and cats at every age for any signs of eye discomfort or visual impairment and seek veterinary advice if concerns arise. Advanced treatments and surgical options are available for many conditions, which can help preserve or prolong vision.