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Is it Cataract or Nuclear Sclerosis? Understanding the Differences

  • Normal age-related change
  • Caused by compression of lens fibers towards the lens center as the lens continues to grow throughout life 
  • Results in a blue, grey, or hazy central lens appearance
  • > 50% of dogs experience NS by 7-11 years old 
  • Most cats experience NS by 10-13 years old 
  • Horses experience NS by their late teens
  • NS is very slowly progressive, not painful, and mildly affects vision

  • Abnormal color change of the lens (usually white) 
  • Causes
    • Dogs: genetics (develop by 1—4 years old in purebreds), diabetes mellitus, uveitis, lens instability, trauma, senility, retinal degeneration, radiation therapy, electrocution, exposure to ketoconazole, and hypocalcemia
    • Cats: uveitis, genetics
    • Horses: uveitis, genetics
    • Rabbits: infection with E. cuniculi

  • Always DILATE the pupil.
  • Use 1 drop of Tropicamide 1% OU for 10—15 minutes OR
  • 1 drop of Atropine 1% OU for 30 minutes (remember, atropine tastes bitter – give a treat with this!)
  • Examine in a DARK room.
  • Nuclear sclerosis hardens the center of the lens.
  • You will see an opalescent pearl with a clear periphery.  This is NOT visible without dilation.

  • Use RETROILLUMINATION (attempt to look at the retina with a Finoff or a penlight and a lens) – you should be able to see the fundus with fine detail, at least until NS is VERY severe (at that point, it may be hazy, but you will still see it).

  • This is the same as attempting to diagnose NS.
  • Cataracts come in stages of severity – they will ALL obscure your view of the fundus.  This means:
  • An incipient cataract affects <15% of the lens, and obscures <15% of the fundus.
  • An early immature cataract affects 15—49% of the lens, and obscures 15—49% of the fundus.
  • A late immature cataract affects 50—99% of the lens, and obscures 50—99% of the fundus.
  • A mature cataract affects 100% of the lens, and obscures 100% of the fundus.
  • A hypermature cataract is mineralized and resorbing (this is its own special category!)

  • NS often causes far-sightedness, or a diminished ability to see normally up close.
  • Clinical signs – sniffing for treats on the floor, running after a toy and slowing down to find it, climbing stairs slowly, being startled when being petted.
  • Using a mild dilating agent (Tropicamide 1%) 1—3 times daily (beginning with once daily in the morning) can help some animals learn to use the clear periphery of their lens.
  • Cataract surgery is an option for severely affected animals (even when no cataract is present!)
  • Cataracts impair all vision.  Without treatment, cataracts can result in uveitis, glaucoma, and retinal detachment.
  • Animals treated with a topical non-steroidal anti-inflammatory are 65 times less likely to experience a painful complication than animals treated with no medication.
  • Animals treated with cataract surgery are 255 times less likely to experience a painful complication than animals treated with no medication, AND, they get to see again!
  • Cataract surgery is at least 90% successful in most patients.

About the Guide: Elizabeth A. Lutz, DVM, MS, DACVO (Ophthalmology)


Dr. Elizabeth Lutz received her Bachelor of Arts degree from the University of Pennsylvania, and her Doctorate of Veterinary Medicine from Cornell University. She completed a rotating internship in small animal medicine and surgery followed by a specialty internship in ophthalmology at Long Island Veterinary Specialists. Dr. Lutz finished a research fellowship in comparative ophthalmology followed by her Residency in Comparative Ophthalmology at The Ohio State University, and holds a Master of Science in Comparative Veterinary Medicine from The Ohio State University, with an emphasis in Comparative Ophthalmology. Dr. Lutz achieved board-certification in veterinary ophthalmology through the ACVO. Her clinical interests are diverse, and include the medical and surgical management of glaucoma, lens surgery, corneal surgery, the novel treatment of tear film diseases, exotic animal ophthalmology, and equine ophthalmology.


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