Cataract
A condition of the crystalline lens, in which the normally clear lens becomes clouded or yellowed, causing blurred or foggy vision. Cataracts may be caused by aging, eye injuries, disease, heredity, or birth defects. Surgery is a treatment option. The affected lens is removed and is replaced with a substitute (implant) lens or with a special type of contact lens. Generally the success rate of cataract surgery is over 90%, if the eye is otherwise healthy.Cheiroscope
An instrument used in orthoptics/vision therapy to train binocular skills and accommodation skills. The Keystone Correct-Eye Scope is an example of a Cheiroscope.Ciliary Body
A structure directly behind the iris of the eye and contains the ciliary muscle. (See diagram of the eye)Ciliary Muscle
A band of muscle and fibers that are attached to the lens that controls the shape of the lens and allows the lens to accommodate (change focus).Coloboma
A congenital malformation (birth defect) in which part of the eye does not form due to failure of fusion of an embryonic feature called the intraocular fissure. The resultant coloboma can be likened to a missing slice from a pie that may involve a number of different structures within the eye including the choroid, iris, lens, optic nerve, and retina.A coloboma can occur as an isolated defect in an otherwise normal baby, or it can be part of a multiple congenital malformation syndrome such as the cat-eye syndrome (named after the coloboma which gives the eye something of a feline look). Colobomas are also seen in the aniridia-Wilms tumor association (the concurrence of undergrowth of the iris of the eye and Wilms tumor of the kidney); and the trisomy 13 syndrome (a disastrous disease due to an extra chromosome number 13).
Color Perception Test
A test that measures the ability to identify and distinguish colors.Color Vision Deficiency
Also known as Colorblindness. It is the absence of or defect in the perception of colors. Color vision is based on perception of red, green, and blue. If there is a defect in the perception of one of these colors, a color will be perceived as if it were composed only of the other two colors. Based on the color or colors for which there is defective perception, a person may suffer from red, green, or blue blindness. Color blindness in which all colors are perceived as gray is termed monochromasia. For people with the common, inherited, types of color deficiency there is no cure.Comitant Strabismus
A condition in which the magnitude of deviation remains essentially the same in all positions of gaze and with either eye fixating.Computer Vision Syndrome (CVS)
The complex of eye and vision problems related to near work that are experienced during or related to computer use. Its symptoms include eyestrain, dry or burning eyes, blurred vision, headaches, double vision, distorted color vision, and neck and backaches. The condition is caused by various internal and external factors. Treatment options may include prescription glasses and/or vision therapy.Cone
A receptor cell which is sensitive to light and is located in the retina of the eye. It is responsible for color vision.Conjunctivitis
An inflammation of the conjunctiva, the transparent layer covering the inner eyelid and the white portion (sclera) of the eyeball. Conjunctivitis can be caused by a virus, bacteria, or fungus (infectious conjunctivitis, or "pink eye", may be contagious); by allergies to pollen, fabrics, animals, or cosmetics (allergic conjunctivitis); or by air pollution or noxious fumes such as swimming pool chorine (chemical conjunctivitis). Symptoms include red or watery eyes, blurred vision, inflamed inner eyelids, scratchiness in the eyes, or (with infectious conjunctivitis) a puss like or watery discharge and matted eyelids. Conjunctivitis is usually treated with antibiotic eye drops and/or ointment.Contrast Sensitivity Test
Contrast sensitivity tests measure the degree to which this ability has been lost. Unlike the Snellen visual acuity test, which measures the ability to see objects (or letters) of different sizes, a contrast sensitivity test measures two variables, size and contrast. The ability to detect objects of different sizes at lower contrasts is expressed as a contrast sensitivity function (CSF). The test determines the person's contrast detection threshold, the lowest contrast at which a pattern can be seen.Typically, the best scores of CSF are recorded for medium-sized objects when their contrast is low. The smallest objects can be detected only when their contrast is very high. Imagine an image comprising vertical black and white stripes. If the stripes are very thin, individual stripes will not be visible. Only a gray image is visible. As the stripes then become wider, there is a threshold width from where it is possible to distinguish the stripes.
The fact that larger objects require higher contrast is explained not by how the eye gathers information but by how the brain processes that information. The brain is relatively insensitive to what neurologists call "low spatial frequencies." Contrast sensitivity readings are presented as a curve, which plots the lowest contrast level at which a person can detect an object of a given size. The higher the contrast sensitivity, the lower the contrast level at which an object can be seen.