Definition
A degenerative opacity of the lens that leads to loss of vision.
Clinical Signs
May observe the following:
- Initially the start of a cataract will be seen as a white dot behind pupil.
- The progression of a gray or milky white discoloration of the lens.
Etiology
Cataracts, a white/gray cloudy discoloration of the otherwise normally clear lens of the eye, can occur due to trauma, inflammation, systemic disease, congenital or genetic disorders (e.g., inherited retinal dystrophy in the rat, a recessive genetic inherited disorder1), and aging. They can begin as a small partial clouding of the lens and progress so that it covers the entire lens leading to blindness. Cataracts are typically bilateral, but may progress more in one eye than the other depending upon the cause.
A transient form of cataracts has been known to happen frequently in rodents when they are placed under anesthesia. It is believed to be due to the changing composition and temperature of
the aqueous humor of the eye while open and unblinking. This does resolve once the animal recovers.2 It is recommended that veterinary surgeons protect the rat’s eyes from drying out, while under anesthesia, by using an ophthalmic ointment. Also, when surgical scrub solutions are used it is important to protect the rat’s eyes from being contaminated.3
Cataracts occurring with age may be due to changes as seen in protein destruction and clumping, accumulation of water and edema, and the disruption of normal fibers in the lens.
Additional causes and factors that can contribute to the early formation of cataracts are long term use of corticosteroids or phenothiazines, hypertension, diseases such as diabetes, and microphthalmia.
Figures
Case Histories of Cataract Formation
- Fig. 1: Cataracts in male rat (Boomer)
- Fig. 2: Cataracts in hairless rat
- Fig. 3: Cataract in 20-month-old Siamese rat
- Fig. 4: Cataracts in aging male rat (Jerry)
- Cataracts Visit Lisa Jenny’s page for photo of rat showing initial cataracts
Diagnostics
Visualized by ophthalmoscopy
Treatment
Rats, having poor vision to start with, adapt well. Treatment should be directed at correcting underlying conditions if possible.
Nursing Care
- Provide for safe environment. Reduce chances of falls from heights by keeping cage levels to a minimum.
- Allow the rat to become familiar with cage surroundings. Prevent redesigning or moving interior cage accessories around.
- Keep water bottles and food dishes in same familiar area of cage.
Outcome
- Underlying conditions corrected
- No advancement of condition noted
Prevention
- Early treatment of conditions or illnesses associated with the formation of cataracts may prevent or delay their onset.
References
- LaVail, M., Sidman, R., & Gerhardt, C. (1975). Congenic strains of RCS rats with inherited retinal dystrophy. J Hered., 66(4), 242-4. Retrieved February 7, 2012, from http://www.oxfordjournals.org/our_journals/jhered/freepdf/66-242.pdf
- Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery. (1997). Philadelphia: W.B. Saunders Company.
- Guidelines for the Use of Anesthetics, Analgesics and Tranquilizers in Laboratory Animals. (n.d.). Research Animal Resources. Retrieved February 7, 2012, from www.ahc.umn.edu/rar/anesthesia.html
