There’s more to that expression than meets the eye – pun most definitely intended. A clear iris, white non-vascular sclera (the whites of the eye) are indicators of good health.
Systemic disease such as infection, inflammatory illnesses, endocrine disorders like diabetes and cancer can manifest as a condition known as uveitis, which lead to pain in the affected eye, squinting, corneal edema (the colored portion of the eye is blue and cloudy) and the whites of the eye become vascular.
If you notice changes like this, please bring your animal companion to your family veterinarian for further evaluation. Often the pressure of the eyes will be checked, the eyes will be stained to rule out corneal ulcers and labwork should be performed to look for signs of systemic disease including infectious causes.
Waiting isn’t advised as you could miss underlying illness and the inflammation in the eyes can lead to the formation of serious eye diseases such as glaucoma.