The red reflex refers to the reddish-orange reflection from the eye

Eye

Eyes are organs that detect light and convert it into electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement...

's retina

Retina

The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...

 that is observed when using an ophthalmoscope or retinoscope from approximately 30 cm / 1 foot. This examination usually done in a dimly lit or dark room.

Many eye problems may be detected by this test, such as:

• Cataract
  Cataract
  A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light...
  
  s - show leukocoria
  Leukocoria
  Leukocoria is an abnormal white reflection from the retina of the eye. Leukocoria resembles eyeshine, but leukocoria can occur in humans and other animals that lack eyeshine because their retina lacks a tapetum lucidum....
  
  , or white coloration of the eye which may be from rubella or other maternal infections
• Retinoblastoma
  Retinoblastoma
  Retinoblastoma is a rapidly developing cancer that develops in the cells of retina, the light-detecting tissue of the eye. In the developed world, Rb has one of the best cure rates of all childhood cancers , with more than nine out of every ten sufferers surviving into...
  
   - shows leukocoria
  Leukocoria
  Leukocoria is an abnormal white reflection from the retina of the eye. Leukocoria resembles eyeshine, but leukocoria can occur in humans and other animals that lack eyeshine because their retina lacks a tapetum lucidum....
  
  .

Newborns

Infant

A newborn or baby is the very young offspring of a human or other mammal. A newborn is an infant who is within hours, days, or up to a few weeks from birth. In medical contexts, newborn or neonate refers to an infant in the first 28 days after birth...

 are regularly screened

Screening (medicine)

Screening, in medicine, is a strategy used in a population to detect a disease in individuals without signs or symptoms of that disease. Unlike what generally happens in medicine, screening tests are performed on persons without any clinical sign of disease....

 for retinoblastomas with an ophthalmoscope.

According to Bate's Guide to Physical Exams, retinal detachment

Retinal detachment

Retinal detachment is a disorder of the eye in which the retina peels away from its underlying layer of support tissue. Initial detachment may be localized, but without rapid treatment the entire retina may detach, leading to vision loss and blindness. It is a medical emergency.The retina is a...

would result in the absence of red reflex in the affected eye.

External links

• "Red reflex examination in infants. Section on Ophthalmology. American Academy of Pediatrics." Pediatrics. 2002 May;109(5):980-1. PMID 11986467.