The most common vision problems are refractive errors, more commonly known as nearsightedness, farsightedness, astigmatism and presbyopia.
Keratoconus is a vision disorder that occurs when the normally round cornea (the front part of the eye) becomes thin and irregular (cone) shaped. This abnormal shape prevents the light entering the eye from being focused correctly on the retina and causes distortion of vision. Nystagmus is a vision condition in which the eyes make repetitive, uncontrolled movements, often resulting in reduced vision. These involuntary eye movements can occur from side to side, up and down, or in a circular pattern. Coloboma is an eye abnormality that occurs before birth. Colobomas are missing pieces of tissue in structures that form the eye. Coloboma occurs in approximately 1 in 10,000 people. Because coloboma does not always affect vision or the outward appearance of the eye, some people with this condition are likely undiagnosed. Chromosomal abnormalities are a group of conditions that are the result of a problem with one of the 23 pairs of chromosomes. Chromosomes are the structures within the body’s cells that contain genes. Normally, people have 23 pairs of chromosomes. A chromosomal abnormality can affect the number of chromosomes, the structure of certain chromosomes, or the composition of chromosomes. If the material found in chromosomes is balanced so that the expected amount is found in each cell, no abnormalities occur. Astigmatism is a vision condition that causes blurred vision due either to the irregular shape of the cornea, the clear front cover of the eye, or sometimes the curvature of the lens inside the eye. Nystagmus is a vision condition in which the eyes make repetitive, uncontrolled movements, often resulting in reduced vision. These involuntary eye movements can occur from side to side, up and down, or in a circular pattern. Refraction is the bending of light as it passes through one object to another. Vision occurs when light rays are bent (refracted) as they pass through the cornea and the lens. The light is then focused on the retina. The retina converts the light-rays into messages that are sent through the optic nerve to the brain. The brain interprets these messages into the images we see. When light travels through water or a lens, for example, its path is bent or refracted. Certain eye structures have refractive properties similar to water or lenses and can bend light rays into a precise point of focus essential for sharp vision. Most refraction in the eye occurs when light rays travel through the curved, clear front surface of the eye (cornea). The eye's natural (crystalline) lens also bends light rays. The process of vision begins when light rays that reflect off objects and travel through the eye's optical system are refracted and focused into a point of sharp focus. For good vision, this focus point must be on the retina. Presbyopia. An age-related vision condition in which there is a gradual loss of the eye’s ability to focus on near objects. Pterygium. An abnormal growth of tissue on the conjuctiva, the clear membrane that covers the white of the eye, and the adjacent cornea, the clear front surface of the eye. Ptosis.  Listen. The most common vision problems are refractive errors, more commonly known as nearsightedness, farsightedness, astigmatism and presbyopia. Refractive errors occur when the shape of the eye prevents light from focusing directly on the retina. Vision occurs when light rays are bent (refracted) as they pass through the cornea and the lens. The light is then focused on the retina. The retina converts the light-rays into messages that are sent through the optic nerve to the brain. The brain interprets these messages into the images we see. Red-green color vision defects are the most common form of color vision deficiency. This condition affects males much more often than females. Among populations with Northern European ancestry, it occurs in about 1 in 12 males and 1 in 200 females. Color vision deficiency (sometimes called color blindness) represents a group of conditions that affect the perception of color. Red-green color vision defects are the most common form of color vision deficiency. Affected individuals have trouble distinguishing between some shades of red, yellow, and green. When coloboma occurs as a feature of a genetic syndrome or chromosomal abnormality, it may cluster in families according to the inheritance pattern for that condition, which may be autosomal dominant, autosomal recessive, or X-linked. Coloboma occurs in approximately 1 in 10,000 people. Because coloboma does not always affect vision or the outward appearance of the eye, some people with this condition are likely undiagnosed.
http://www.aoa.org/patients-and-public/eye-and-vision-problems http://ghr.nlm.nih.gov/condition/coloboma http://health.cvs.com/GetContent.aspx?token=f75979d3-9c7c-4b16-af56-3e122a3f19e3&chunkiid=101103 http://www.aoa.org/patients-and-public/eye-and-vision-problems https://nei.nih.gov/healthyeyes/problems http://www.allaboutvision.com/eye-exam/refraction.htm http://www.aoa.org/patients-and-public/eye-and-vision-problems/glossary-of-eye-and-vision-conditions https://nei.nih.gov/healthyeyes/problems http://ghr.nlm.nih.gov/condition/color-vision-deficiency http://ghr.nlm.nih.gov/condition/coloboma
what vision abnormality occurs