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    A membrane lining the inside of the back of the eye that contains light-sensitive nerve cells that convert focused light into nerve impulses, making vision possible.


A flexible layer surrounding a cell, organelle (such as the nucleus), or other bodily structure. The movement of molecules across a membrane is strictly regulated in both directions.

Tissue that conveys sensation, temperature, position information to the brain.

The sense of sight.


Reticuloendothelial system
A network of phagocytic cells.

Retin-a is a prescription or over-the-counter drug which is (or once was) approved in the United States and possibly in other countries. Active ingredient(s): tretinoin.

Retin-a micro
Retin-a micro is a prescription or over-the-counter drug which is (or once was) approved in the United States and possibly in other countries. Active ingredient(s): tretinoin.

Light-absorbing portion of rhodopsin. The absorption of light causes retinal to change from 11-cis to 11-trans configuration

Retinal detachment
A retinal detachment occurs when the retina, that part of the eye that contains the photoreceptors, detaches from the underlying layers of cells, called the choroid. A retinal detachment my be the result of injury to the eye such as blunt trauma (remember Sugar Ray, the boxer) or it may result from other things like high myopia or age-related macular degeneration. In certain diseases, retinal breaks and tears occur and these may lead to a retinal detachment. Early warning signs include bright dots or lights or some of your side vision may appear dark. A retinal detachment may be treatable if detected early, so see your Ophthalmologist.

Retinal layers
Retinal layers are: Outer nuclear layer - Contains photoreceptors; Inner nuclear layer - Contains bipolar, horizontal and amacrine cells; Ganglion cell layer - Contains ganglion cells; Outer plexiform layer - Contains processes of receptor, bipolar and horizontal cells; Inner plexiform layer - Contains processes of bipolar, amacrine and ganglion cells.

Retinex Theory
Theory of lightness and color perception. Argues that the color of an object is not determined by the composition of the light coming from the object. The color of a unit area is determined by a trio of numbers each computed on a single waveband to give the relationship for the waveband between the unit area and the rest of the unit areas in a visual scene.

Inflammation of the retina.

Retinitis Pigmentosa (RP)

The most common cancer in the eye occurring in early childhood. A parent or doctor may first suspect a problem by detecting whiteness in the normally dark pupil. Occasionally it leads to a wandering eye (strabismus). It does not spread from one eye to the other but about 25% have a tumor in each eye. Immediate medical treatment is necessary. Sometimes the eye(s) must be removed to prevent spreading of the tumor into the brain.

A natural or synthetic substance derived from vitamin A.

Degeneration of the retina.

Retinotectal pathway
Pathway from the retina to superior colliculi.

Retinotopic map
A preservation of the spatial relationships of the photoreceptors in the retina in a higher brain representation.

Retisert is a prescription or over-the-counter drug which is (or once was) approved in the United States and possibly in other countries. Active ingredient(s): fluocinolone acetonide.


A substance used for pain relief that is also being studied for its ability to prevent cancer and to block the growth of new blood vessels to solid tumors. It belongs to the family of drugs called nonsteroidal anti-inflammatory drugs.

Ribonucleic acid. A long-chain, usually single-stranded. The primary function of RNA is protein synthesis within a cell. However, RNA is involved in various ways in the processes of expression and repression of hereditary information. The three main functionally distinct varieties of RNA molecules are: (1) messenger RNA (mRNA) which is involved in the transmission of DNA information, (2) ribosomal RNa (rRNA) which makes up the physical machinery of the synthetic process, and (3) transfer RNA (tRNA) which also constitutes another functional part of the machinery of protein synthesis.

Ribonucleic acid
RNA. The generic term for polynucleotides, similar to DNA but containing ribose in place of deoxyribose and uracil in place of thymine. These molecules are involved in the transfer of information from DNA, programming protein synthesis and maintaining ribosome structure. The 4 main types of RNA are heterogeneous nuclear RNA (hRNA), messenger RNA (mRNA), transfer RNA (tRNA) and ribosomal RNA (rRNA).

A molecule that recognizes a unique hormone. Once that hormone is bound to the receptor, the information carried by the hormone can now exert its biological action.


Recessive gene
A gene that is inferior to another gene that controls the same trait (the dominant gene). The inferior gene does not get expressed in the presence of a dominant gene.

An 8-inch chamber connected to the large intestine that receives solid waste (feces) from the descending colon to be expelled from the body. The rectum connects the colon to the anus. It is the rectum's job to receive stool from the colon, to let the person know that there is stool to be evacuated, and to hold the stool until evacuation happens.

A general disease characterized by painful, often multiple, local inflammations, usually affecting the joints and muscles, but also extending sometimes to the deeper organs, as the heart.

Retinitis Pigmentosa (RP)

Rheumatoid arthritis
Rheumatoid arthritis is a chronic disease that is of unknown cause and is characterized by pain, stiffness, inflammation, swelling and sometimes destruction of joints.

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