eye conditions

Eye Conditions in the Domestic Ferret

Several conditions can impact the eyes of domestic ferrets.  The following conditions are the most common:  cataracts, glaucoma, uveitis, infections, nutritional or metabolic conditions, Cancer, toxic (including drug) exposure, and trauma.   These conditions may arise congenitally or occur later in life.
 
Each of the following conditions can cause blindness.   The impact of blindness on the quality of life in a ferret is quite variable.  Ferrets that are born blind may have very different experience than a ferret that was previously sighted and experiences gradual or sudden loss of vision.  
 
Owners of blind ferrets must be cognizant to inform others who interface with their pet.   Some ferrets, particularly those that were sighted at birth but have subsequently lost vision may demonstrate fear responses when approached by strangers or a novel unfamiliar environment.    Having said this, the majority of blind ferrets adapt quite well and live normal high quality lives.   ​

Figure 1:  Anatomy of the Normal (Human) Eye

Trauma 
Trauma is a very common cause of eye injury in the ferret.   Traumatic injury includes scratches, perforating injuries, foreign bodies, and chemical or contact corneal trauma.   All require assessment by a veterinarian and should be considered a MEDICAL EMERGENCY. Untreated eye injury can lead to corneal ulcers,  uveitis, cataracts, and may result in blindness.
 
Treatment
Infections can arise from traumatic injuries to the eye.  Antibiotics are used to prevent and treat infections.   "A corneal ulcer, if it's not full thickness, can be healed," Williams said. "But if the lens has been punctured, the proteins in the lens when released into the rest of the eye cause tremendous inflammation and those animals go blind."
 
Prognosis
Early intervention is the key to maintaining eye function.   However, severe injury, and secondary infection can lead to cataracts, uveutis, glaucoma all of which result in blindness.
 
Cataracts
One of the most common causes of blindness in both humans and ferrets are cataracts.  A cataract is the result of a change in the normally clear eye that causes it to become cloudy, reducing the light that is transmitted to the eye retina.
 
Diagnosis
Cataracts can usually be diagnosed by the ferret owner on visual inspection of the eye.   A follow up professional eye examination by a veterinarian is highly recommended.

Figure 2:  Bilateral Cataracts in a 6.5 year old neutered male ferret [Photo:  F Hoffman – 2013]

Etiology and Pathology
Cataracts are most common in older animals, and may be a biological consequence of normal aging.   In the ferret both the nucleus and the cortex of the lens are involved. (Fox -1998)  Retinal degeneration may also be present. (Fox-1998
Ferrets with certain medical conditions, such as Aleutian Virus Disease (ADV), diabetes mellitus (“sugar” diabetes), or uveitis, may be at increased risk of developing cataracts.    Exposure to environmental toxins, drugs (including high oxygen levels during surgery), can cause cataracts.
 
When a kit is born with a cataract it or develops one at a very young age, it is considered a “congenital” cataract.   Most likely congenital cataracts are due to breeding in the ferret.   However, cataracts may arise due to nutritional or metabolic abnormalities, infectious and environmental toxins (including drugs), either direct or through maternal exposure.  
 
Early cataracts have been observed in domestic ferrets from both small private and commercial breeding facilities.   Development of cataracts at an early age (<5 years ) is not uncommon, and the  incidence has been reported to be as high as 47%. (Montiani-Ferreira -2009).   Early proclivity to develop cataracts is most likely due to a nutritional, genetic, familial, and/or metabolic abnormality.  In more than 30 ferrets bred by a “backyard” breeder, all of the males developed cataracts between the ages of 1.5 and 3.5 years of age, suggesting a “sex-linked” abnormality.
 
Treatment and Prognosis
For ferrets the prognosis of the animal’s eyesight is very poor. In early stage disease the animal will be able to discern light and shape.  As the condition progresses, however, the ferret will experience increasing blindness.  Most ferrets will become totally blind.   
 
Aside from blindness, the cataract may cause the animal to go on to develop a glaucoma, which can cause the eye to deteriorate to the point of requiring surgical removal of the eye.
Estrus in ferrets is photoperiod controlled.  Jills (whole females) who have bilateral cataracts may experience absent or irregular estrous cycles.  [Miller-1997]
 
Surgical removal of cataracts is the treatment of choice for cataract removal in both humans and other animals, such as dogs and cats,   Lens removal is done through either extracapsular surgery [Miller-1997] or phacoemulsification, where the lens is emulsified and broken up by ultrasound and removed by aspiration.  [Montiani-Ferreira -2009]   
 
Surgery should prevent secondary problems occurring, such as glaucoma, lens induced uveitis (not as common in ferrets and more mild than in dogs), subluxation and luxation. When performing surgery, care should be taken to avoid the intrascleral venous plexus.
 
Having said this, cataract surgery is not commonly used in ferrets due to the size of the ferret’s lens.  Also, the cost of surgery may be prohibitive.
 
Prevention
It is important to make sure your ferret is getting complete nutrition through a balanced diet.  If a breeding ferret or its offspring develop cataracts, particularly at an early age, the ferret and its offspring should be altered and removed from the breeding program. [Montiani-Ferreira -2009]  
 
Selected References
Fox, JG.  Chapter:  Other Systemic Conditions. in Biology and Disease of the Ferret.  2nd Edition  Ed.  JG. Fox. Williams & Wilkins, Baltimore, USA.  1998.
Miller, P.E. Ferret ophthalmology. Journal of Exotic Pet Medicine (formerly Seminars in Avian and Exotic Pet Medicine)   6:146-151, 1997. 
Montiani-Ferreira, F.  Ferrets: ophthalmology in the BSAVA Manual of Rodents and Ferrets; Keeble, E. and Meredith, A. (Eds.)   BSAVA, Gloucester, UK. 2009
http://wildpro.twycrosszoo.org/S/00dis/Miscellaneous/Cataract_Rabbit.htm
 
Glaucoma
 
Another common eye disease in ferrets is glaucoma.    There are two kinds of glaucoma:

• Primary glaucoma:  caused by a deformed filtration angle, which causes pressure in the eyeball to build up
• Secondary glaucoma:  results from the lens of the eye falling forward, causing blockage of the eye’s natural drainage, which in turn causes a pressure build-up behind the eye.

 
Glaucoma may affect one or both eyes, and occurs at any age.   Primary glaucoma most likely has a genetic link.  Secondary glaucoma occurs when there is a shift in the lens, that can happen due to cataracts or severe eye trauma.

Figure 3:  Eye with Glaucoma (Blocked filtration)

Diagnosis
Unlike dogs and cats that exhibit pain and other signs of corneal edema (swelling) with glaucoma, ferrets are not easy to diagnose.  Because ferrets do not show significant corneal edema, or display the level of pain seen in dogs and cats they are used diagnosed at a very late stage when the disease has progressed.  This is usually when the eye globe becomes so swollen the eye no longer shuts properly.  At this point ocular pressures exceed 70 or 80 millimeters of mercury, and the ferret has lost considerable or complete vision.  [Williams]

Figure 4:  Comparison of normal to swollen eye with cataract and glaucoma  (at Yellow Arrow).  [Photo:  Dr. Jorge Pereiera, Rio de Janeiro Brazil (www.cepov.combr)

Treatment and Prognosis
Glaucoma from any cause can lead to blindness if left untreated.   However, at the point that most ferrets are seen by a veterinarian, they have advanced disease that does not respond well to therapy.    Treatment for advanced glaucoma unfortunately requires removal of the eye (enucleation).   In most cases the ferret is blind at that point, and removal of the swollen eye relieves pain.  
 
Retinal Atrophy

Retinal atrophy is a degenerative condition that gets worse with time.   It is a progressive degeneration of the retina of the eye that causes increasing loss of vision, ending in total blindness.   Often overlooked by both owners and veterinarians, the condition may outrank cataracts as the leading cause of blindness in ferrets. [Kawasaki-1992]
 
Diagnosis
 
Retinal atrophy is diagnosed during a professional eye examination.   It can occur at any age, but particularly in older ferrets.
 
Most pet owners do not recognize that their ferret has the condition.  Because most ferrets have dark eyes, the presence of dilated pupils goes unnoticed.
 
Etiology and Pathology
Some speculate that the condition is hereditary; others believe is may be related to a deficiency of the amino acid, Taurine.
 
The following abnormalities are seen:  

• Abnormal pupillary dilatation (mydriasis).
• Decreased pupillary light reflex.  )
• Examination of the fundus shows attenuation of retinal vessels and hyperreflectivity of the tapetum.

In advanced stages, the pupil will be completely dilated, fixed and will no longer respond to light.
Prognosis and Treatment
 
Currently there is no treatment for retinal atrophy.   Ferrets with this condition start out with normal vision but gradually lose their sight.  
 
Kawasaki, T.  Retinal Atrophy in the ferret. J of Small Exotic Animal Medicine 1992; 3: 137.
 
Quesenberry, K.E. Basic Approach to Veterinary Care in Ferrets, Rabbits and Rodents - Clinical Medicine and Surgery Second Edition; Ed.  Quesenberry, K.E. & Carpenter J.W.  WB Saunders, Philadelphia, Pennsylvania, USA  2004
 
van der Woerdt, A. Ophthalmologic Diseases in Small Pet Mammals, in Ferrets, Rabbits and Rodents - Clinical Medicine and Surgery Second Edition; Ed.  Quesenberry, K.E. & Carpenter J.W.  WB Saunders, Philadelphia, Pennsylvania, USA  2004
 
Uveitis

Uveitis is broadly defined as an inflammatory state of the eye.  Technically it is the inflammation of the uvea, which consists of the middle, pigmented, vascular structures of the eye and includes the iris (color part surrounding the pupil), the ciliary body and choroid.
 
Uveitis requires an urgent referral, thorough examination by a veterinary professional and treatment of the inflammation.
 
In ferrets, uveitis can occur at all ages. 
 
Etiology
 
This condition is most often a result of eye trauma in the eye.   It is often a secondary result of  infection due to a penetrating wound that becomes infected, are a viral infection such as the Aleutian's disease virus [Hadlow-1982], and more recently in a ferret infected with Cryptococcus gattii. [Ropstad -2011]   
 
Treatment and Prognosis
Uveitis can lead to cataracts and glaucoma.
 
Early treatment with anti-inflammatory drugs, such as topically applied cortisone (usually in the form of eye drops), is important to halt the process.    If there is an underlying cause, such as Aleutian Disease Virus, or other systemic condition, the systemic condition must be addressed as well.   
 
Left untreated, the ferret’s eye can become very painful, and the inflammation can be damaging to the retina of the eye, leading to blindness.
 
Hadlow WJ. Ocular lesions in mink affected with Aleutian disease.  Vet Pathol. 1982 Jan;19(1):5-15.
 
Ropstad EO, Leiva M, Pena T, et al. Cryptococcus gattii chorioretinitis in a ferret. Veterinary Ophthalmology 14(4:262-6 2011.
 
Lymphoma

Lymphoma is a cancer of the lymphocyte, one type of white blood cell that normally combats infections.  It is similar to leukemia but is found as a solid tumor mass.   It is a very common type of cancer in most species, including the ferret, and lymphoma is the most common hematologic cancer in ferrets.  Lymphoma most often affects ferrets from 6 to 12 months of age, or 3 to 5 years of age.   [Mitchell & Tully 2009] Younger ferrets develop develop lymphoblastic disease (similar to leukemia), and older adults develop lymphosarcoma. (Mayer-2006); Hrapkiewicz & Medina -2007)
 
When it occurs as retrobulbar (behind the eye) lymphoma, it can grow as a mass, pushing against the eye ball even to the point of dislodging the eye from its socket.    
 
Diagnosis
A ferret presents with a bulging eye.   Unlike glaucoma, however, it is not the eye ball itself, but a mass behind the eye that is causing the enlarged appearance.   Lymphoma affects individual organs or circulating blood. [Lloyd – 1999]  
 
A complete physical examination of the ferret may reveal other enlarged lymph nodes or spleen.  In addition, the ferret may show increased white count, with increased lymphocytes, on a standard Complete Blood Count (CBC), or on blood marrow sampling. 
 
Ultrasound should be used to determine if a mass near the eye is lymphoma, followed by a needle biopsy, to determine what cells are present.    A measure of the pressure inside of the eyeball should also be done to see if it is elevated and to rule out glaucoma.    In lymphoma, the pressure is behind the eye, so the intraocular pressure may be normal.
 
Treatment and Prognosis
It is very important to differentiate retrobulbar lymphoma from glaucoma because both the treatment and the prognosis are very different for these conditions.   While glaucoma can cause blindness, lymphoma left untreated is life-threatening. 
 
The treatment for retrobulbar lymphoma is removal of the tumor and damaged tissues, and perhaps chemotherapy.    In severe cases where the eyes have bulged to the point that they can no longer spring back into the sockets, removal of the eye (enucleation) may become necessary.
 
If the lymphoma has spread to the rest of the body, long-term survival is very poor.  However, if the tumor is isolated, and the remainder of the physical examination is normal, follow up chemotherapy can be considered and may significantly prolong quality of life.
 
Selected References
 
Hrapkiewicz, K. and Medina, L. (Eds.)   Ferrets.  Clinical Laboratory Animal Medicine: An Introduction 3rd Edition Blackwell, Iowa, USA. 2007
 
Lloyd, M. Neoplasia. in Ferrets Health, Husbandry and Diseases.  Blackwell Science Ltd., Oxford, UK.  1999.
 
Mayer, J.   Update on ferret lymphoma. North American Veterinary Conference (NAVC) Proceedings.  20:1748-9. 2006.
 
Mitchell, M.A. and Tully, T.N. (Eds.) Ferrets.  in Manual of Exotic Pet Practice.  Saunders, Philadelphia, USA. 2009