During an ocular evaluation the doctor quickly categorizes
the potential causes for hazy appearing eyes into three main
types. The problem could originate in the cornea, the lens
or the aqueous humor that is the transparent fluid that
fills the two chambers behind the cornea and in front of the
lens. Interestingly, the cornea and lens are each composed
of about 65 percent water and 35 percent soluble proteins.
Easiest to recognize are the superficial problems
associated with the cornea, the glass-like dome of
transparent tissue at the front-central portion of the eye.
The cornea, only about 3/4mm thick, is actually a
specialized extension of the "white of the eye" called the
sclera, and assists in maintaining the globe's shape,
intraocular pressure and diffraction of light entering the
eye.
Any disruption of the surface epithelium (often called a
corneal ulcer) will alter the cornea’s normal state of
dehydration. Other common causes of haziness are immune
mediated infiltrates of the cornea, trauma, viral
infections, liver trouble, chronic irritation and
intraocular stresses such as glaucoma.
Once the surface layer is damaged or
stretched the cornea loses its ability to maintain the water
and protein ratios within it, and the cornea will
over-hydrate and swell. The influx of water separates the
delicate cells layers and throws the corneal proteins into
disarray. Light no longer passes unimpeded through the now
hazy-blue or whitish cornea. A call to the veterinarian
should be made right away!
Corneal opacities occur secondary to inflammation in the
structures that manufacture the nourishing fluid inside the
front portion of the eye. This constantly flowing
specialized fluid bathes the cornea, iris and lens and
assists in maintaining normal intraocular pressure.
Inflammation from infections, bleeding, trauma or immune
issues can result in blockage of the aqueous humor flow
within the eye.
Since it is such a nourishing fluid it is an excellent
medium for bacteria and viruses, the end result of which may
appear as a hazy, dull appearance to the dog’s eye.
During an exam if the cornea is clear and transparent and
there is no evidence of inflammation in the aqueous humor
just behind the cornea, the doctor can easily inspect the
colored structure called the iris and then past the iris
opening called the pupil.
Just beyond the pupil is the lens, suspended by
specialized tissue that automatically changes the lens
shape, a function called accommodation, so that light rays
are focused on the "screen" at the back of the eye called
the retina. |
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Cataracts... refers
light reflecting
back from lens opacity inside the eye |
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A cat with focal
corneal haziness probably secondary to an earlier
Herpes virus infection |
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A dog cornea
showing edema and
stretching of the corneal tissue |
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A dog's eye
afflicted with a deep corneal
ulcer and surrounding inflammation |
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A variety of pathological disorders can adversely impact the
lens. Trauma, metabolic problems such as diabetes mellitus
and immune mediated disorders are a few. If any stress to
the lens affects how the lens proteins are arranged or
upsets the normal state of dehydration, the lens becomes
opaque.
The lens, much like the cornea, is composed of approximately
65 percent water and 35 percent protein but each structure’s
architecture and function are quite different. They both
highly depend on a healthy outer layer of specialized
epithelial cells. Interestingly, most of the work these
outer membrane cells do is to pump water out of the lens and
cornea (maintaining that 65 percent water concentration),
and allow nutrients in which keeps a normal lens and cornea
in a state of relative dehydration.
Probably the most commonly noticed change in the dogs' eyes
that prompts us to call them hazy is the condition referred
to as nuclear sclerosis of the lens. Occurring in most
older dogs this gradual increase in the water content
of the lens and relative decrease of soluble proteins blocks
the light on its way to the retina. We see the reflected
and diffracted light brighten the lens substance.
As aging progresses the epithelial surface is less able
to perform its various jobs, the haziness becomes more
intense and we then classify (there are several methods of
classification) the lens as having a cataract. In the right
patient with the right kind of lens cataract, veterinary
ophthalmologists may be able to remove the lens and restore
a useful level of sight.
There is a wide variety and degree of damage occurring when we
notice a hazy eye is present. Surely if your dog displays a sudden
haziness to one or both eyes an immediate exam is obligatory! And
do not let a “full schedule” keep you from a timely office visit.
Case in point: glaucoma. The only change you might notice in an eye
affected by a sudden pressure increase will be a slight haziness to
the cornea. Without vigorous treatment initiated in the early
stages of glaucoma permanent damage to the eye can result.
Fortunately, most veterinary clinics prioritize “eye trouble” so
same day evaluation can be done.
Many dogs with some opacity to the lens or cornea adapt to their
gradually darkening world and function very well. But there are
times when, with or without hazy eyes, dogs may lose their sight for
a number of reasons unrelated to the lens or cornea. Subtle changes
in the dog’s behavior may be the only hints you have that vision is
being impaired.
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Sleeping more than usual and taking less interest in activities.