Westbury Animal Hospital
713.723.3666 · 4917 S. Willow Dr. Houston, Texas 77035 

Red Eye

Are your pet’s eyes red, watering, or itchy? This phenomenon stems from a variety of causes ranging from just allergies to something much more serious.

How do we evaluate eyes?

We start with a physical exam looking at the cornea, lens, retina, and everything around and in between. This includes vision and other ocular nerves and reflexes.

Diagnostic tools   

Schirmer Tear Test

This tests for adequate production of the aqueous (watery) layer of the tear film. The tip of the paper strip is placed under the eyelid and through capillary action, the tears run up the strip. After 60 seconds, the strip is removed, and the length of tear travel is measured. A dog’s normal tear production is at least 15mm, and low tear production is not a concern in cats.  


Fluorescein Stain

The Fluorescein Stain tests for scratches, ulcers, or perforations of the eye. A drop of eye flush is added to the paper dye strip and touched to the eye, allowing the dye to run across the eye. The liquid dye only attaches to the second layer of the cornea, so if there is no abnormality then the dye runs right off. If there is a scratch past the cornea’s first layer, it will fluoresce using an ophthalmoscope and cobalt blue light.



Tonometry measures the pressure inside the eye similar to people having their eyes checked for glaucoma. First, a drop of Proparacaine (local analgesic) is applied onto the eye to numb the surface.   The Tonometry Pen gently taps the eye multiple times to measure a pressure, and this is repeated to record multiple pressures. Normal pressures are about 10-25 mmHg. Increased pressures may indicate glaucoma while decreased pressures may indicate uveitis (inflammation).




Treatment depends on the patient history, physical exam, and diagnostics. For example, a dog with a “red eye” but normal diagnostics may have allergic conjunctivitis and is treated with topical steroids/antibiotics. Meanwhile, a patient with “red eye” who was scratched by a cat may go home with topical antibiotics and oral pain/anti-inflammatory medications. Additionally, a patient with “red eye” having glaucoma, pain, and no vision may need to have the eye removed and analyzed for evidence of cancer. In some cases, patients may need referral to a board-certified ophthalmologist for more advanced diagnostics and treatments.




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