How can you tell if a rat has gone blind in one eye? - briefly
Observe the rat’s response to light and moving objects; an absent or reduced pupillary reflex and failure to avoid obstacles on one side indicate unilateral blindness. The affected eye may also remain closed or appear dark and unresponsive.
How can you tell if a rat has gone blind in one eye? - in detail
Observing unilateral visual impairment in a laboratory rat requires systematic assessment of behavior, ocular appearance, and physiological responses.
Behavioral indicators include:
- Hesitation or inability to navigate obstacles when approaching from the side of the affected eye.
- Failure to locate food or water presented directly within the visual field of the compromised eye, while detection remains normal from the opposite side.
- Persistent turning of the head toward the blind side when attempting to locate stimuli, suggesting reliance on the functional eye.
- Reduced use of the affected eye during grooming, reflected by asymmetrical facial cleaning.
Physical examination should focus on:
- Corneal clarity; opacities, ulcers, or scarring often accompany loss of vision.
- Lens transparency; cataracts produce a characteristic cloudiness that can be detected with a slit lamp or simple magnifying lens.
- Pupillary light reflex; illumination of the blind side should elicit little or no constriction, whereas the normal eye maintains a brisk response.
- Presence of ocular discharge or inflammation, which may signal underlying pathology affecting the retina or optic nerve.
Objective testing methods:
- Optokinetic drum test – place the rat on a rotating drum with vertical stripes. Normal tracking occurs when the functional eye faces the moving pattern; absence of tracking when the pattern is presented to the opposite side confirms unilateral blindness.
- Light‑avoidance assay – expose the animal to a bright light source from each side separately. Preference for the dark compartment when the light is directed toward the suspect eye indicates visual deficit.
- Electroretinography (ERG) – record retinal electrical activity following light stimulation of each eye. A markedly reduced or absent ERG wave from one eye confirms retinal dysfunction.
- Direct ophthalmoscopy – visualize the retina and optic nerve head. Degeneration, detachment, or optic neuropathy evident in one eye corroborates functional loss.
Combining behavioral observations with clinical and instrumental evaluations provides a reliable determination of single‑eye blindness in a rat.