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Commonly Seen Sensory Conditions and Diseases
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6.1. Vision
The sense of vision is the only sense on which studies have been performed in aging psittacines. "Visual acuity is greater in psittacines than in humans," according to T. Lightfoot in Geriatric Psittacine Medicine.37 Their range of vision is much greater than that of humans, and they see a much wider range of visible light, including the ultraviolet (UV) spectrum. If birds go blind in the wild, they are in danger of being attacked by a predator. But in captivity, birds who lose their vision are able to adapt as long as their cages are not moved or rearranged and the furniture in the home is not moved.37
6.1.1. Macular Disease
While macular degeneration has not been reported in birds, other macular problems are seen. Zinc deficiencies can exist in older birds from poor absorption of food antioxidants (Vitamin A, C, and E). These vitamins may help slow down macular degeneration and other aging factors associated with activated oxygen from exposure to light, but this has yet to be established.10,22
6.1.2 Cataracts
Cataracts are commonly seen in aging psittacines and are the leading cause of blindness in older pet birds. In addition to being caused by aging, they are associated with nutritional deficiencies, trauma, toxins, infections, and inflammation of the eyes. 60 Most species will develop them as they mature. Macaws, Amazon parrots, and cockatiels are prone to cataracts. 62 If birds develop them gradually, they are usually able to acclimate to their surroundings; however, if the cataracts develop suddenly, "The bird may exhibit clinical signs such as depression, inactivity, and reluctance to come out of or move around in the cage".62 Cataracts may cause behavioral changes related to decreased vision. 59
In a study of older macaws, Bennet and Harrison report that most birds over the age of 35 have at least one cataract. "For many birds, the cataract remains immature for several years without completely obstructing the birds’ vision. In other cases, the change from an incomplete, immature cataract progressed rapidly to a complete, mature cataract, seemingly skipping the complete, immature stage".6
Nutrition plays an important part in the development of cataracts. "The nucleus of the lens is particularly sensitive to nutritional deficiencies. Nuclear cataracts are associated with deficiencies in fat-soluble Vitamin A and the water-soluble Vitamins B2 (riboflavin) and B3 (niacin)".22 Carotenoids have strong antioxidant qualities, and without these, nuclear cataracts tend to develop. Riboflavin, selenium and Vitamins C and E are also important in the prevention of cataracts; however, supplementation with selenium is "not recommended as cataracts have been correlated with both deficiencies and excesses of this trace mineral".22 Cortical cataracts occur in the cortex of the lens, and they can be prevented with the supplementation of polyunsaturated fatty acids. "Insufficient Omega-3 fatty acids or excesses of trans-fats influence the progression of eye disease. Birds may suffer zinc deficiencies in their old age due to poor absorptions of food. Zinc is necessary for the action of many enzymes, some of which are involved in retina function".10,22
Companion birds must be protected from the damaging effects of bright light, both indoor and direct sunlight outdoors. Light coming through windows can damage the eyes, so owners are advised to make sure their birds are in the shade, both indoors and outdoors. UV lamps are an additional cause of cataracts as they shine directly on the bird and can damage the eyes.22
Birds with cataracts tend to hold their heads to the side so that their good eye is forward. The eyes of older birds should be examined annually to detect early changes in lens opacity (clarity). Because of the small size of the exposed cornea and pupil in psittacines, screening by an avian ophthalmologist is recommended.10,37, 60
Many people believe that exposing the bird to direct sunlight or other forms of light, such as lamps directed onto the cage, will not damage the eyes. This is false!
Harrison and McDonald state that, "Exposure to UV light and other direct forms of light will lead to cataracts, macular degeneration, and other forms of age-related eye disease".10,22 They recommend the owner administer antioxidants, such as Vitamins A, C, and E to aid in slowing down the development of these ocular diseases and other age-related illnesses related to exposure to light.22
Although wild birds will sometimes have eye damage from exposure to bright sunlight, most of the time they find shelter from it in trees and other shady places, so the time they spend in direct sunlight is limited. Between that and the action of the nictitating membrane, their eyes are protected from the damaging effects of bright light most of the time. The brightness of the light is as much of a problem as the ultraviolet rays. Because of this, companion birds must also be protected from the damaging effects of bright light, both indoor and outdoor direct sunlight. Light coming through windows can also damage the eyes. Owners are advised to make sure their birds are in the shade, both indoors and outdoors.22
Cataracts often develop secondary to infection or trauma or may be age-related; they are seen as lens opacities. "If found early in their development, they may be limited to the swelling of the lens fibers, but advanced cataracts involve the entire lens. Eventually, they progress to phacolytic uveitis (breakdown and inflammation of the iris and lens), and blindness results.10,37,60
In large psittacine birds, surgical removal of cataracts is successful in many cases. The bird's general health and the degree to which the cataracts affect its quality of life should be evaluated before surgery. The home environment must be altered for any bird with decreased vision. Early cataracts, especially if uveitis is present, may be painful. NSAIDs, either in as ocular drops or systemic medications (meloxicam or celecoxib) or both, can be used to reduce inflammation and pain.37
6.1.3 Additional Degenerative Ophthalmic Conditions:
- Keratoconjunctivitis sicca (dry eye syndrome)
- Corneal ulcerations
- Nictitating membrane abnormalities
- Conjunctival granulomas
- Lymphoma
- Lid laxity
- Iris atrophy, leading to darkening of the normally light-colored iris. Sometimes, when the iris atrophies, pupil constriction is seen, causing light sensitivity and retinal damage
- Nuclear sclerosis of the lenses. The nucleus of the lens becomes dense, and fiber production and compression occur.
- Retinal degeneration, often the result of nutritional, congenital, traumatic, or viral conditions. Genetic retinal disease is seen in commercial poultry flocks but not in psittacines.
- Blindness, as a sequela to pituitary tumors, usually adenomas.
- Blindness, following an acute neurological episode that causes impairment of the Central Nervous System. These episodes are a consequence of atherosclerosis and atherothrombotic stroke (a stroke which occurs when an artery in the brain becomes blocked because of a blood clot or fatty deposits in the blood).
- Glaucoma, usually found in the larger raptor species. It is difficult to diagnose in psittacines because of the small size of the cornea.6,37
6.2. Hearing
The sense of hearing in psittacines is neither better nor worse than in humans, just different. Birds can distinguish some ranges of frequencies more accurately than humans can. "These vocalization ranges are comparable to the sounds made by their own species; however, they do not differentiate between the intensity and volume of sounds as well as humans do".37 Birds’ hearing loss appears to be less related to aging and more related to loss of function of their hair cells (sensory receptors of both the auditory system and the vestibular system in the ears of all vertebrates); these are able to regenerate.37
6.3. Olfaction
In the past, it was believed that birds possessed very poor senses of smell and taste. This was attributed to their need to eat quickly due to the danger of predation. But studies have shown that there is a higher percentage of functional olfactory receptors in many species of birds compared to mammals. Early research has shown that some psittacine species have a more highly developed sense of smell than was previously thought. It is not known whether the senses of smell and taste decrease in birds as they age; however, if this is the case, the geriatric bird could be limited in his ability to recognize food, people, and other birds.37
6.4. Integument
There is anecdotal evidence that damage to the beak can affect feather grooming and thus affect the appearance of the feather coat. Cutaneous tumors are the most common skin lesions as noted in the ZEPS survey in the table above; these were associated with a history of self- trauma, although the underlying causes was not always evident.54
According to Reavill and Dorenstein, older lovebirds (over the age of 6) "tend to develop a high number of inflammatory skin lesions (22.8%)."54 These are primarily the nonspecific syndromes of lovebird dermatitis or chronic ulcerative dermatitis. The most commonly affected areas were the patagium, neck, and back. These areas will develop pruritus, and this leads to the self-mutilation. Although researchers suspect a viral etiology, it has not be identified. Polyfolliculitis may be a part of these lesions. Both syndromes are chronic and often return.54
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