Geriatric eyes: Old dogs new tricks (Proceedings)
Although age may not be a disease, the associated changes of age often compromise the ocular tissue and decrease vision. A quick review of the normal aging process will be discussed.
The eyelids often have increased flaccidity and laxity in advanced age. This may result in entropion, often of the lateral aspect of the upper eyelid. Loss of orbital fat pad may result in enophthalmos and protrusion of the third eyelid. This too can lead to entropion, typically of the lower lids. Decreased tear production and especially when associated with decreased blink reflex result in relative areas of dryness of the central corneal surface. Intraocular pressures tend to decrease with age, and this fact is well documented in cats. It is not unusual for aged cats to have normal intraocular pressures between 8 and 10 mmHg. Iris thinning is common and may involve either the sphincter muscle or the stromal muscles. If the sphincter is involved, dilated pupils are the consequence. If the stromal area of the iris is involved, multiple pupil appearance is the consequence. The lens continues to grow throughout life by adding surface epithelial layers below the lens capsule. Because the lens cannot increase in size substantially, this results in sclerosing of the nuclear lens. This is referred to either nuclear or lenticular sclerosis. It then becomes very prominent in aged dogs, but the starts at approximately age six. Lenticular sclerosis coupled with iris sphincter atrophy makes the cloudy change more obvious, and this should be distinguished from pathological cataract formation. The retinal thinning is documented to occur in older animals, and although this may not compromise vision in a significant way, it does make for changes in the funduscopic examination. The most extreme conditions are going to be present in dogs and cats greater than 16 to 17 years of age.
Pathological Conditions Of Older Dogs And CatsEyelid
Eyelid tumors are common in older patients and start at approximately ten years of age. Most of these tumors are benign adenomas or melanomas, although size alone may cause some discomfort to the patient. Various surgical modalities have been advocated, including laser ablation, cryosurgery and excision techniques.
A slight decrease in tear production is not unusual with the aging process. KCS is common in middle-aged to older patients. The most common form is a decrease in serous tear production, as exhibited by low Schirmer tear test values. The second change in tear film is the loss of the mucin secretion, the results of which can be documented by an increase in the tear film breakup time. Management of keratoconjunctivitis sicca involves the use of topical anti-inflammatories coupled with the use of lacrimomimetics and supportive therapy. Supportive therapy includes topical systemic antibiotics. In addition, it is essentially to use tear supplements, ranging from tear drops to gels to ointments.
The most common corneal age-related disease is that of degeneration. Corneal degeneration is typified by a lipid mineral deposit in the stroma of the cornea. This differs from corneal dystrophy as a primarily genetic condition. Corneal degeneration can lead to pinpoint epithelial erosions. A large slough of crystalline deposit can take place, resulting in large areas of ulceration and loss of tissue integrity. Deep ulcers cause pain and serous discharge and lead to retraction of the globe. Medical management of corneal degeneration includes potassium EDTA drops to help reduce the corneal mineralization and lubricating ointments for comfort. Anecdotal evidence suggests that cyclosporine may be helpful in preventing further build up of degenerative material. Surgical intervention is often necessary. Techniques include superficial keratectomy and conjunctival grafting. Another technique is chemical cautery of the ulcer with trichloroacetic acid. This procedure is typically done under sedation and requires frequent irrigation.
Iris thinning is a normal aging process. In the most extreme cases with marked iris atrophy of the sphincter muscles will result in fixed and dilated pupils. This permits too much light to reach the retina, resulting in photophobia-like symptoms in bright light. To date, there are no surgical options for managing this situation, and avoidance of bright light conditions works best. Dogs with long hair can be groomed to leave hair over the face to provide some shade effect.
In aged patients, zonular instability can result in lens subluxation and luxation. This also is a complicating factor during routine cataract surgery in older patients. With extreme instability of the zonules, liquified vitreous strands may appear in the anterior chamber. Cataracts are a common age-related change and are distinct from lenticular sclerosis. Lenticular sclerosis generally does not block the fundic reflex but gives a circular haze in the center of the lens, where cataracts block the fundic reflex and appear as black spots. Advanced cataract changes can benefit from surgical intervention. With proper patient selection, success rates approach 90% in returning patients to normal vision.
Vitreal degeneration is a common process and involves liquefaction of the vitreous humor. Mineralized lipid deposits may also be noted. Various terms, including asteroid hyalosis, liquified vitreous and vitreal degeneration, have been used to describe this condition. If severe enough these opacities may interfere with vision. Retinal changes may be more common in aged dogs and include genetic diseases that are programmed to occur in older years. Supportive therapy may be of some help. Various vitamin mixtures are available.
Cataract surgery has made significant strides over the last five to ten years. This advancement has been due to improvement in surgical equipment, improved surgical techniques, a better knowledge base concerning cataract surgery and improved anesthetic protocols, including paralytic agents. The development of viscoelastic products, along with affordable artificial lens, reduce surgical trauma. Cataract surgery success rate is based on three factors. The first being the proper selection and preparation of the patient. The second is the surgical team and equipment, to include the skill sets and the dedication to detail. The third part of the success rate is the aftercare, which is provided primarily on an outpatient basis. Frequent postoperative examinations to coach the client through this important period of time are essential.
The actual cataract surgery itself generally requires about 30 minutes of anesthesia per eye. Phacoemulsion units allow the removal of the cataract through small puncture wounds. The incision needs to be enlarged slightly to accommodate the implantation of the foldable artificial lenses. The recovery period is four to six weeks, and the expectation is the return to normal vision. Long-term postoperative medical supportive therapy is recommended