Seeing red? That’s a good thing! Though many individuals groan upon seeing their eyes shining red in a photo (“I look like a demon!”), they should be happy to note that their eyes are in good health. And if there is only the red eye effect in one eye but not that other? That can indicate a disease of the eye.

What the Red Eye Effect Is

The red eye effect is caused by a combination of factors: the position of the camera lens, the position of the flash, and the scenery’s lighting. In a typical point-and-shoot camera, the lens of the camera will be close to the flash. Combine these factors with low light and individuals in the photo are more likely to have the red-eye effect. This effect is less likely in digital single-lens reflex (DSLR) cameras, as these flashes are further away from the lens or have an attachment to move the flash even further above the lens.

The red eye effect occurs only in the pupil; instead of a brown iris and black pupil, one will see a brown iris and red pupil. Because light from the flash is too quick for the pupil, it cannot close in time and thus the light goes through the pupil. It then reflects off the fundus—the interior surface of the eye that includes the retina—and out of the eyeball through the pupil. The choroid, which is the vascular layer of the eye, blood causes the red color. Not seeing red in one pupil when it appears in the other could indicate a disease of the eye.

Lack of Red Eye Can Indicate Eye Disease

Seeing anything but a glowing red eye can indicate serious eye diseases in individuals—specifically children—especially when the other eye has a red glow. Yellow, white, or gold Leukocorias (glows) in eyes can be indications of more serious childhood eye diseases. The following are eye diseases that can cause an abnormal glow in the eye from flash photography. While some are more serious than others, individuals should make an appointment with an ophthalmologist for official diagnosis and treatment.

  • Amblyopia
    Also known as lazy eye, this disorder can cause an abnormal glow because one eye looks straight into the lens whereas the other does not. The red glow is caused when the eye looks straight into the lens; if the eye does not, there will not be a glow. Amblyopia decreases vision in an eye that otherwise looks normal. If caught early, it can be treated/corrected with glasses or surgery.
  • Cataract
    One of the main cataract symptoms includes clouding of the eyes’ lens that results in decreased vision. It can occur in one eye or in both. While cataracts generally appear in older individuals, they can also appear because of trauma, exposure to radiation, eye surgery, or a cause of diabetes, smoking, or alcohol.
  • Congenital Cataract
    A congenital cataract is a clouding of the eye’s lens that has been present since birth.
  • Choroidal Melanoma

Choroidal melanoma is a cancer of the choroid, which is the vascular layer of the eye that sits below the retina. This cancer is a primary cancer of the eye. It begins in the choroid and is not a cancer that spread from elsewhere into the eye. 

  • Coats’ Disease
    Coats’ Disease is a rare congenital disease that can cause partial or full blindness due to the blood vessels of the eye developing abnormally. It is nonhereditary. Usually only one eye is affected, and occurs predominantly in young males.
  • Coloboma
    A coloboma is a hole in part of the eye’s structure, such as the iris or choroid. Present from birth, this hole is a result of a developmental defect. It can appear in one or both eyes, and most cases of coloboma affect just the iris. The severity of this hole can range from no issues to leaving an individual blind.
  • Norrie’s Disease
    Norrie’s Disease is a genetic disorder of the eye that generally leads to blindness; it may also result in mental challenges and/or hearing loss later in life. With Norrie’s disease individuals may develop cataracts or leukocoria or suffer another developmental issue in the eye.
  • Persistent Hyperplastic Primary Vitreous (PHPV)
    PHPV is a rare congenital developmental anomaly of the eye. The vitreous (a clear gel) that forms the eye during fetal development remains in the eye; it loses its clarity and becomes scarred.
  • Retinoblastoma
    Retinoblastoma, though a rare form of cancer, is the most commonly found in children and is the most common malignant eye cancer of children. Developing from immature cells in the retina, retinoblastoma is survivable but may cause vision loss or require the eye to be removed. There are two forms of the disease, heritable and non-heritable. In two-thirds of all cases, retinoblastoma affects just one eye.
  • Retinal Detachment
    In this disorder, the retina peels away from its support tissue. Only part of the retina may detach but if left untreated the entire retina can detach and cause vision loss or blindness. If not repaired within 24 to 72 hours after initial injury, there could be permanent damage to the eye.

There are hundreds of success stories in treating these eye diseases—all because someone spotted the glow in a “bad” photo! Having regular visits to an optometrist can ensure that eyes remain in good health. Children will receive eye examinations in school but they should begin seeing the family optometrist or pediatric eye doctors for eye exams beginning around five years old.

Hannah Nava loves writing about any topic, and eye health is no exception. She currently writes on behalf of the LASIK eye surgery specialists at EyeCare 20/20. When not marrying words, Hannah enjoys reading science fiction, fantasy, and dystopian works; sipping margaritas (always frozen); and trying to make the world a happier place. Tweet her @hannahmnava or connect with her on LinkedIn.