Why are my dog’s eyes cloudy?

Q: When Toto, my 10-year-old terrier, looks at me, his eyes appear cloudy. At last week's wellness exam, his veterinarian said his eyes are healthy and he has no cataracts or other problems. So why do his eyes reflect a cloudy white-blue-gray haze?

A: It sounds like Toto has a condition called nuclear sclerosis, which is not a disease but a normal consequence of aging that starts in dogs around age 7.

Nuclear sclerosis, also called lenticular sclerosis, is hardening (sclerosis) of the center (nucleus) of the lens (lenticular). Most dogs with nuclear sclerosis have normal vision, though some have a bit more trouble focusing on nearby objects because the hard lens doesn't change shape easily. Compare the condition to a middle-aged person who needs reading glasses.

In nuclear sclerosis, the lens remains transparent, so light travels through it to the retina to produce a normal image. Contrast this to a cataract, an opaque area of the lens that blocks light transmission to the retina. A cataract impairs vision, even causing blindness if it grows to encompass the entire lens.

In addition to nuclear sclerosis, senior dogs sometimes develop iris atrophy. The iris contains muscles that dilate the pupil in dim light and constrict it in bright light. If the iris atrophies with age, you may see tiny holes in it or an irregular border between the iris and the pupil. If Toto's irises have atrophied and he can't fully constrict his pupils, you may see him squint when he goes outdoors on sunny days.

Lee Pickett, V.M.D. practices companion animal medicine in North Carolina. Contact her at vet@askthevet.pet.