Facts on File Encyclopedia of Health and Medicine

matched to the correct procedure, had the opera-
tion performed by a competent and experienced
eye surgeon, and had an uncomplicated course of
recovery. Some people are able to completely
eliminate the need for corrective lenses. Many
people do still require corrective lenses, though at
much improved refractive correction and perhaps
only for specific applications such as near or
midrange vision.
Doctors do not know what, if any, long-term
consequences may result from refractive surgery,
as most of the laser techniques predominantly in
use today have been available only since the
1990s. Routine eye care and ophthalmic examina-
tions are especially important for people who have
had surgery on their eyes, to detect complications
from the surgery as well as eye conditions such as
GLAUCOMA, AGE-RELATED MACULAR DEGENERATION
(ARMD), and CATARACT.
See also AMBULATORY SURGERY; CORNEAL TRANS-
PLANTATION; OPERATION; PHOTOTHERAPEUTIC KERATEC-
TOMY(PTK); SURGERY BENEFIT AND RISK ASSESSMENT.

retina The innermost layer of the EYE. The retina
receives light images and converts them to NERVE
impulses the OPTIC NERVEconveys to the BRAIN. The
retina is two tissue-thin layers that together are
less than^1 ⁄ 2 millimeter in thickness. The outer pig-
ment layer provides a completely light-absorbing,
nonreflective lining. The inner sensory layer con-
tains the photoreceptors (rods and cones) respon-
sible for vision. Rods detect only shades of gray
though can register images of very low intensity.
Cones detect color and detail.
Laid out flat, like a disk, the retina measures
just under 2 inches in diameter. The primary work
of vision takes place in an area about the size of a
postage stamp called the macula. Most of the
retina’s 120 million rods and 6 million cones
reside in the macula. A section of the central
retina no larger than a pencil eraser, the macula,
contains almost no rods and an abundance of
cones and handles detail vision. A pencil-point
depression within the macula, the fovea, has the
highest concentration of cones.
The optic nerve enters the retina somewhat to
the NOSE-side at the back of the eye, along with
the ARTERYand VEINthat manage the retina’s BLOOD
supply. Vitreous humor, a gelatinous substance,

fills the inner eye and holds pressure against the

retina, keeping it smoothly and tightly adhered to

the choroid.

The ophthalmologist can examine the surface of

the retina using OPHTHALMOSCOPY. Under illumina-

tion the retina appears reddish orange. The optic

nerve disk appears as a pale, pinkish circle. The

macula, of similar size, appears as a darker and less

distinct circular area with a depression, the fovea,

in its center.

CONDITIONS THAT CAN AFFECT THE RETINA

AGE-RELATED MACULAR COLOR DEFICIENCY

DEGENERATION(ARMD) COLOR DEFICIENCY

NIGHT BLINDNESS RETINAL DETACHMENT

RETINITIS PIGMENTOSA RETINOBLASTOMA

RETINOPATHY traumatic injury

For further discussion of the retina within the

context of eye structure and function please see

the overview section “The Eyes.”

See also ELECTRORETINOGRAPHY; FLASHES; LENS;

VISION IMPAIRMENT; VITREOUS DETACHMENT.

retinal detachment A separation of the RETINA

from the choroid, the layer of the EYE’s structure

that nourishes and attaches the retina. Retinal

detachment may occur as a result of TRAUMA TO THE

EYE, AGE-RELATED MACULAR DEGENERATION (ARMD),

VITREOUS DETACHMENT, RETINOPATHYof DIABETES, or

surgery on the eye. Retinal detachment may also

occur spontaneously, a circumstance more com-

mon in people with moderate to severe MYOPIA

(nearsightedness).

Prompt treatment to reattach the

retina is necessary to save vision.

Symptoms and Diagnostic Path

Retinal detachment does not cause PAINor discom-

fort. Detachment may be gradual, in which case

symptoms are progressive, or sudden, in which

case loss of vision may be the only symptom.

Symptoms of retinal detachment include

• seeing flashing lights or multiple FLOATERS
  
  
  • the perception of a curtain or shadow dropping
    across the VISUAL FIELD, often from top to bot-
    tom though sometimes from the side
  
  
  
  

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