Optical Terminology Explained

Optical Prescription

Most people have a small degree of visual impairment. For many this presents no significant problems and they do not need to have spectacles.

However for many the amount of impairment that they have results in blurring of vision, discomfort and problems with everyday life.

These optical errors are due to the structure of eye and the natural aging process and does not necessarily mean that the eye itself is unhealthy.

Some of the most common terms are listed below.

•	Distance Vision is blurred
•	Near Vision is clear

•	Distance vision is generally good
•	Near Vision is more difficult or blurred
•	Younger people often have good distance vision
•	As you get older distance vision becomes more difficult

•	The front of the eye is not spherical like a football but is more the shape of a rugby ball
•	Both distance and near vision can be blurred
•	Even small amounts of astigmatism can cause discomfort when reading or using a computer

•	Affects people from the mid forties
•	The muscles and lens in the eye become less flexible due to aging
•	Near vision becomes more difficult and spectacles are needed for close work

•	Commonly found in young children
•	When one eye turns and does not work properly with the other
•	If one of a pair of muscles is weak a squint can occur
•	A squinting eye may not develop properly leading to a 'lazy' eye
•	Often an operation, followed by exercises, can remedy the squint
•	Early diagnosis is important.

•	Usually hereditary with around 8% of boys and 1% of girls having vision which is colour deficient.
•	Colour vision deficiency cannot be cured
•	Those with colour deficiency should give consideration to future career options.

While 95% of patients have perfectly healthy eyes the Optometrist will look for other conditions which can affect the eye.

•	With age the lens inside the eye becomes cloudy
•	In many people this does not affect their vision but, where it does progress, the following symptoms may occur
•	A reduction in the standard of vision even with spectacles
•	Haze around lights especially at night
•	Glare in bright sunlight
•	Becoming less longsighted or more short sighted
•	When cataracts begin to restrict vision they can be removed and the lens of the eye replaced with a small plastic lens inside the eye. This is now a relatively straightforward procedure with a very high level of success.

•	Glaucoma is the result of the pressure within the eye increasing until, if undetected, it causes a loss of vision.
•	In chronic Glaucoma, by far the most common type, there are no symptoms until visual loss is experienced.
•	Glaucoma affects 2% of the population over 40 and if a person has a close relative who suffers from the condition they then have a higher risk of developing the condition.
•	During a routine eye examination all people over 40 will have the pressure measured to ensure that it is within normal limits.
•	Where Glaucoma is diagnosed treatment can reduce the pressures and prevent the onset of visual loss.

•	ARMD is the greatest cause of visual loss in people over 60
•	There are two types of ARMD
•	Dry - The most common form of the condition where the macula (the area at the centre of the retina at the back of the eye which is responsible for detailed vision) gradually breaks down as part of the aging process. There is no treatment for this condition but it tends to progress slowly
•	Wet - The rarer form of ARMD where there are changes in the blood vessels in the macula area. This form tends to move quickly and where detected early it is possible in some cases to arrest the progress

•	It can affect the lens of the eye with the result that the optical prescription can change over a short period of time
•	Cataracts can form earlier and more quickly
•	Changes in the blood vessels at the back of the eye can affect the vision

It is for this reason that all diabetics are advised to have regular eye examinations.