A rapid screen-based screening test for CVD. The lowest pair of letters that can be read in each of the three columns corresponds to your score. The score can then be compared to the severity guide on the right [Rabin…

An album of 20 Pseudoisochromatic Plates first published in 1936 in Russia. The plates test for both red-green and blue-yellow defects and was the first Pseudoisochromatic Plate test to try and differentiate dichromacy from anomalous trichromacy. The plates were well…

The Rayleigh Match was devised by Lord Rayleigh in 1881 as a tool for classifying color vision. It is the color matching method used in Anomaloscopes for red-green CVD. The equivalent for blue-yellow CVD was designed much later and it…

The scattering of photons as light moves through the atmosphere. Rayleigh scattering is stronger for shorter wavelengths of light, so blue light wavelengths will scatter faster than red wavelengths. Some practical examples: We cannot see the stars during the day…

Generally, the receptive field is a spatial area/volume that can excite a given sensor. A Photoreceptor has a receptive field defined by the cone of light that can excite it. A Retinal Ganglion Cell has a receptive field that can…

A property of an allele that means its Phenotype is expressed only if there is no Dominant allele to "take precedence". An individual has two copies of most genes, so for the recessive allele's Phenotype to express, both of these…

A misleading name for Protanopia. The name derives probably from the red-green opponent channel, which is – by definition – skewed permanently to the far green side in Protanopes, typically because they are missing the L-Cones that balance the channel.…

A misnomer for the L-Cone, so called because the Cone is more sensitive to red light than the other Photoreceptors, despite the Peak Sensitivity (560nm) actually corresponding to yellow, not red.

A hypothetical form of colorblindness where the individual sees in Monochromacy (grayscale) because only one class of cone is present (L-Cone / Red Cone). This disease is an intersection of Tritanopia (missing the gene for the S-Opsin) and Deuteranopia (missing…

A misnomer of the L-Opsin.

A misleading name for Protanomaly. The name derives probably from the red-green opponent channel, which is – by definition – skewed permanently to the green side in Protans. “Red Weak” infers that the L-Cones in Protanomals are someone less sensitive,…

An Opponent Channel as well as a category of CVD where that opponent channel is affected. This includes Protan and Deutan defects. The Red-Green Opponent Channel is a reformulation of the Tristimulus values (LMS), which is a balance between the…

How much light is reflected from an object's surface. It is a function of Wavelength, so it is what defines an object's inherent color. The perceived color of an object is the product of its Reflectance and the Illuminant Spectrum.…

The tissue that lines the inside of the back of the eye. It contains the Photoreceptors that react to light.

A small molecule that absorbs a photon to begin the Phototransduction Pathway. Retinal is the Chromophore at the center of every human Opsin. When it is absorbs a photon, it isomerizes (its 'tail' kinks), and this sets off the chain…

A wide category of progressive genetic visual disorders that affects 1 in 4,000 individuals. There are several kinds of retinal dystrophy that are linked to over 300 genes, which makes exact diagnosis difficult.There is currently no cure or treatment options…

A type of neuron located in the retina. It transmits visual information from the retina to the brain, with their axons forming the optic nerve. They are the final cell of the Phototransduction Pathway in the retina and receive a…

The spatial distribution of Rods and Cones on the Retina. These mosaics show the different colors of cones in the Fovea. The Retina on the left is a Color Normal. The Retina on the right is a Protanope (no L-Cones)

A type of PIP that are visible to the Colorblind, but not Color Normals. This is not because the Colorblind have better hue discrimination for some colors, but because they can see a small change in contrast in a field…

An additive, Trichromatic Color Model that is used to describe the mixing of colors of light sources (not pigments). Red Green and Blue are the Primary Colors and are added together in various ways to reproduce a broad array of…

A spatial representation of the RGB Colorspace.

One of 5 classes of visual Opsins in vertebrates, which includes Rhodopsin, the Opsin in Rod cells. The peak wavelengths in this class range from 460-530nm. The other classes include SWS1, SWS2, RH2 & LWS.

One of 5 classes of visual Opsins in vertebrates, to which humans possess none. They are present in most birds, fish and reptiles, but are absent in all mammals. The peak wavelengths in this class range from 470-530nm and are…

The Opsin present in human Rod cells. It is mostly unrelated to color vision or CVD. Human Rhodopsin is a type of Ciliary Opsin, designated with the class Rh1. It was the last class of the vertebral visual opsins to…

The type of photoreceptor cell in the retina that is responsible for Scotopic Vision, i.e. seeing at night. Rods are much more sensitive than Cones and can detect a single photon through the stronger signal amplification in the Phototransduction Pathway.…