Adaptive Technology

Electronic magnification systems like closedcircuit TVs (CCTVs) and computers.

Amsler Grid

A test for determining potential changes in central vision and the level of impairment due to those changes. It is often used to detect and follow AMD.


Using both eyes; also, a device designed for use with both eyes.


The term "blindness" or "blind" should be reserved for individuals who are actually blind, meaning that they have no light perception or those who have so little vision that they rely mostly on other senses (this is known as "vision subsitute skills").  Even very slight light perception can serve to increase orientation and mobility in a patient.  

Legal blindness is different.  

Contrast Sensitivity

The ability to detect differences in grayness and background. There are special tests to measure the loss of contrast which are useful in prescribing optical and non-optical devices and strategies for independent function.

Depth Perception

The ability to determine how far away an object is.

Eccentric Viewing

Not looking directly at an object, but rather learning to focus an image onto a healthier part of the retina. This is used when central vision has been diminished.

Functional Blindness

Describes the condition of an individual who has no useful vision. 

Functional Vision

Vision loss defined in terms of the individual’s abilities with regard to activities of daily living such as reading, orientation in space and mobility. Functional vision describes the way an individual is able to live his or her day to day life and does not describe the function of one or both of his or her eyes.

Functional Vision Loss

How vision loss affects the ability to function and perform activities of daily living.

Legal Blindness

In the United States and Canada, “legal blindness” is defined as visual acuity with best correction in the better eye worse or equal to 6/60 (20/200), or a visual field extent of less than 20 degrees in diameter. 

The term “legal blindness” is a arbitrary definition and it has little value for vision rehabilitiation.  Many legally blind people can lead rich and functional lives with the help of low vision rehabilitation.  The definition of legal blindness is important for determining ability to drive and eligibility for government programs.

Low Vision Services

The examination and accompanying education that lead to and determine what devices will be prescribed.


Using one eye; also a device intended for use with one eye.

Orientation and Mobility

Training to help the partially-sighted get around as safely and as independently as possible.

Peripheral Vision

Ability to see objects that are not in the direct line of vision.


Discomfort and/or sensitivity to light.

Severe Vision Impairment

An inability to recognize a friend at arm’s length even when wearing glasses or contact lenses, or an inability to read ordinary newspaper print even when wearing glasses or contact lenses, or reports poor or very poor vision even when wearing glasses or contact lenses, or is blind in both eyes.

Severe visual impairment is a condition where best-corrected visual acuity is less than 6/48 (20/160), including 6/60 (20/200), to 3/60 (20/400), or the visual field diameter is 20 degrees or less (largest field diameter for Goldmann isopter III4e, 3/100 white test object, or equivalent). Severe visual impairment in both eyes is the minimum requirement to be considered legally blind.

Visual Acuity

The ability to see detail (see definition of Legal Blindness).

Visual Impairment

Vision loss defined in terms of the function of the eye. Examples are visual acuity loss or visual field loss. An individual can have visual impairment in one eye, while the other eye is normal.

Visual Field

The space in which objects are visible when the eye is in a fixed position.

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