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Chapter Outline


Visual Acuity Near and Far Testing	Depth Perception Testing
Visual Fields by Confrontation Testing	Colour Vision Testing

Educational Aims

After studying this chapter, you should be able to:

Discuss the automated testing technique
Explain the various testing techniques for visual acuity
Understand and demonstrate the various visual acuity testing techniques

Key Terms / Abbreviations


Abbreviation	Explanation
F	Far
L	Left
N	Near
R	Right
SAQA	South African Qualifications Authority
US	Unit Standard
VA	Visual Acuity
LVA	Left Visual Acuity
RVA	Right Visual Acuity


Term	Definition
Amblyopia	P Also called a lazy eye is a type of poor vision that happens in just 1 eye. It develops when there's a breakdown in how the brain and the eye work together, and the brain can't recognize the sight from 1 eye.
Astigmatism	A common and generally treatable imperfection in the curvature of the eye that causes blurred distance and near vision. Astigmatism occurs when either the front surface of the eye (cornea) or the lens, inside the eye, has mismatched curves. Astigmatism is a common vision problem caused by an error in the shape of the cornea. With astigmatism, the lens of the eye or the cornea, which is the front surface of the eye, has an irregular curve. This can change the way light passes, or refracts, to your retina. This causes blurry, fuzzy, or distorted vision.
Automated Vision Screener	Instrument-based vision screening using automated devises.
Colour blindness	Or deficiency is defined as the inability to distinguish certain colours. This usually happens between greens and reds, and occasionally blues.
Deuteranopia	A type of red-green colour blindness characterized by the inability to distinguish red and green pigments. If a person cannot see green, it is absolute deuteranopia; if a person can see some shaded of green it is a partial deuteranomalia.
Glaucoma	Glaucoma is a group of eye conditions that damage the optic nerve, the health of which is vital for good vision. This damage is often caused by an abnormally high pressure in your eye. Glaucoma is one of the leading causes of blindness for people over the age of 60.
Hyperopia	Farsightedness (hyperopia) is a common vision condition in which you can see distant objects clearly, but objects nearby may be blurry. The degree of your farsightedness influences your focusing ability.
Macular degeneration	Macular degeneration, also known as age-related macular degeneration (AMD), is caused by deterioration of the retina and can severely impair vision. There is a wet and dry form of the disease. It causes blurred or reduced central vision, due to thinning of the macula. The macula is the part of the retina responsible for clear vision in your direct line of sight.
Myopia	Near-sightedness (myopia) is a common vision condition in which you can see objects near to you clearly, but objects farther away are blurry. It occurs when the shape of your eye causes light rays to bend (refract) incorrectly, focusing images in front of your retina instead of on your retina.
Presbyopia	The gradual loss of the eyes' ability to focus on nearby objects. It's a natural, often annoying part of aging. Presbyopia usually becomes noticeable in the early to mid-40s and continues to worsen until around age 65.
Protanopia	Blindness to red is known as protanopia, a state in which the red cones are absent, leaving only the cones that absorb blue and green light. Absolute Protanopia is total inability to see red and partial protanomalia is the ability to distinguish some shades of red.
Stereopsis	Stereopsis (from the Greek words meaning "solid", and opsis meaning "appearance, sight") is a term that is most often used to refer to depth perception and 3-dimensional vision based on information from two eyes. When a visually normal human being looks at an object, each eye sees it from a slightly different angle, and sends those pictures back to the brain. The differences between the two images are integrated into a single one, and the differences are used to show what is nearer, etc., creating the 3D effect.
Strabismus	Strabismus (crossed eyes) is a condition in which the eyes do not line up with one another. In other words, one eye is turned in a direction that is different from the other eye. Under normal conditions, the six muscles that control eye movement work together and point both eyes at the same direction.
Suppression	Of an eye is a subconscious adaptation by a person's brain to eliminate the symptoms of disorders of binocular vision such as strabismus, convergence insufficiency and aniseikonia. The brain can eliminate double vision by ignoring all or part of the image of one of the eyes.
Tritanopia	A condition where a person cannot distinguish between blue and yellow colours. Impaired blue and yellow vision is the main symptom that is associated with this condition. However, people with Tritanopia have normal red and green vision. Tritanopia is often referred to as colour blindness. Tritanopes: do not see either blue or yellow.