The red reflex test is vital, non-invasive test that can identify early warning signs of serious eye conditions in children, such as cataract (white water), glaucoma (blue water) and retinoblastoma (childhood eye cancer) and high refractive errors. Infants or children in whom parents or other observers describe a history suspicious for the presence of leukocoria (a white pupil reflex) in one or both eyes should be examined because small retinoblastoma tumors or other serious lesions may present in a subtle fashion.
The red reflex test uses transmission of light from an ophthalmoscope through all the normally transparent parts of the eye, including the tear film, cornea, aqueous humor, crystalline lens, and vitreous humor. This light reflects off the ocular fundus, the interior surface of the eye opposite the lens which is transmitted back through the optical media and through the aperture of the ophthalmoscope, and is imaged in the eye of the examiner. Any factor that obstructs this optical pathway will result in an abnormality of the red reflex.
An abnormal red reflex can result from corneal opacities, aqueous opacities, iris abnormalities affecting the pupillary aperture (pupil), cataracts, vitreous opacities, and retinal abnormalities including tumors or chorio-retinal coloboma. Unequal or high refractive errors (need for glasses) and strabismus (eye misalignment) may also produce abnormalities or asymmetry of the red reflex. There may be significant variation in the red reflex in children from different racial or ethnic groups resulting from their differing levels of pigmentation of the ocular fundus.