Learn about hazy eyes in dogs and cats here!

Pet health care questions and answers about puppies and dogs

All About Hazy Eyes In Dogs And Cats
Dogs and cats often need veterinary medical care when the owner notices a hazy appearance to the eyes.  Usually when we say hazy eyes we are referring to the cornea, the transparent "window" at the very front of the eye.  And just like a real window the cornea can be affected by a number of problems that interfere with the unimpeded passage of light.  Anything that creates a space between the many layers of specialized, flattened cell remnants that make up the cornea will diffract, absorb or reflect light back into the environment.  The dog or cat's ability to see is then compromised.
A cat with focal corneal haziness

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Hazy Eyes In Dogs And Cats: Is There A Problem?

     Have you ever wondered what makes some dogs’ eyes seem hazy or cloudy?  Or have you had to visit your veterinarian when an eye suddenly took on a hazy gray color to the cornea?  If so, you aren’t alone.  A very common query heard by veterinarians goes like this:  "What's that hazy look in her eyes, Doctor?  Is she getting glaucoma or cataracts?"  The answer to the question is unique for each patient because there are a variety of ocular disorders, some innocuous and some rather critical, that are first noticed and described as hazy or cloudy eyes.

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The corneas are OK but there is a damaged lens in each eye The corneas are OK but there is early haziness in the lens
Inflammations in this cat's eye and surrounding tissues is consistent with an infection from either a viral or bacterial agent.  Chlamydia bacteria and Herpes Virus infections are common in cats This dog has bilateral cataracts... sometimes due to dehydration of the lens structure within the eye. The corneas are OK but there is early haziness developing in the lens called nuclear sclerosis This dog's lens has become loose and slipped forward into the anterior chamber behind the cornea.  This is a serious condition and needs immediate veterinary care.

Terms to know:
cornea... is the clear, circular front portion of the eye through which light passes into the eye. pupil... is not truly a "structure" but rather is the black variable opening created by the the iris as it opens widens or constricts the opening for light to pass onto the retina. nuclear sclerosis of the lens differs from a cataract by its slightly transparent appearance and will permit some degree of visualization of the retina at the back of the eyeball.  A cataract is so dense no reflection of the back of the eye will be visible.
anterior chamber... is the space within the eye just behind the cornea and in front of the lens.  It is filled with a thin, clear nourishing fluid.
posterior chamber... is the tiny space between the back of the iris and front of the lens.

lens.. is attached to the iris and is the clear structure the inhabits the area just behind the pupil.  It can change shape to permit sharp focusing of light onto the retinal tissues at the back of the eye,

The vitreous is located behind the lens and posterior chamber.  The largest chamber in the eye it is filled with a thin gel-like substance.  Light passes through the vitreous onto the retina at the back wall of the eye.
iris... is the colored elastic tissue that supports the lens and is what gives the eye what we call color.  Brown eyes result from brownish colored iris tissue; blue eyes is from blue colored iris tissue. cataract... is an abnormal lens that has lost it's transparency. retina... is a multilayered tissue at the back of the eye wherein light energy is converted to nerve impulses that ultimately trigger visual perceptions in the brain.

For a nice diagram of the eye look here

     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. 

The corneas are OK but there is a damaged lens in each eye

Cataracts... refers light reflecting
 back from lens opacity inside the eye

A cat with focal corneal haziness

A cat with focal corneal haziness probably secondary to an earlier Herpes virus infection

A dog cornea showing edema and stretching of the corneal tissue

A dog cornea showing edema and
 stretching of the corneal tissue

A dog's eye afflicted with a deep corneal ulcer

A dog's eye afflicted with a deep corneal
ulcer and surrounding inflammation

     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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Be suspicious of any of the following behavioral changes in your dog because they could be our only hints that the dog is losing his vision:

  Sleeping more than usual and taking less interest in activities.
  Acting tentative about going up or down stairs...
  Reluctance to jump off the bed or couch…
  Not seeing or alerting at the squirrels and chippies on the lawn…
  Taking an unusually long time to visually recognize you…
  High-stepping with front legs…
  Acting insecure, more clingy, always at your feet…

     The few paragraphs about hazy eye issues presented here only begin to describe the disorders of the cornea, lens and aqueous humor that create a hazy appearance to the eyes of a dog or cat. It is up to you to assume the worst if you see any changes in the normal appearance or function of your dog’s eyes.  After a thorough physical exam and possibly some blood and urine tests your veterinarian can make a proper evaluation of the causes of the ocular changes.  Only then can you take the appropriate action to preserve your pet’s vision.  

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