Vision Glossary

Accommodation

The ability to focus from one object to another at different distances.
Look up:  near point of accommodation ??  Google J

Astigmatism 


An irregularity of the shape of the cornea.  Also referred to as “out-of-round.”
Unlike myopia and hyperopia where poor vision is due to lens function, astigmatism causes
poor vision for both near and distance. 
Best demonstrated by squeezing a half tennis ball.

Cataract 


The opacification of the crystalline lens.  The lens turns milky, most often with age. 
Result is like looking through a dirty window. 
Easily remedied with lens removal and implant of synthetic replacement. 
Most successful of all operations today, often performed under local anaesthetic.

Cone cells, or cones


These are cells in the retina of the eye which only function in relatively bright light. 
There are about 6 million in the human eye, concentrated at the fovea.
They gradually become more sparse towards the outside of the retina. 
Cones are less sensitive to light than the rod cells in the retina (which support vision at low light levels), but allow the perception of color. 
They are also able to perceive finer detail and more rapid changes in images because their response times to stimuli are faster than those of rods.

Concave lens


A lens thinner at its center than at the edges, for correcting myopia or short-sightedness.

Conjunctivitis


A condition which usually affects both eyes, usually one at a time. 
Extremely contagious, and drops are usually prescribed to give comfort and prevent
further bacterial infection. 
It is not dangerous but must be correctly diagnosed.

Convex lens

A lens which is thicker in the center than at the edge, used to correct hyperopia or farsightedness. 

Convergence


The ability to move both eyes in at the same degree as the object moves closer.

Cornea 


The transparent layer that forms the front wall of the eye, covering the iris.

Dark Adaptation 


The time taken for the rods of the retina to become active.

Diabetes 


Changes often occur in the retina, at the back of the eye where the blood vessels become fragile and leak.  Untreated diabetes can result in blindness.

Divergence 


The ability to move both eyes out as object moves away.

Fundus 


See retinal fundus.

Glaucoma


Fluid comes into the eye at one point and leaves at another. 
If the fluid is not moving out at the same rate that it is flowing in, pressure begins to build up.
This will kill off the fibres of the optic nerve and cause irreparable loss of sight.
Chronic glaucoma has no symptoms to indicate warning, therefore this is an essential
part of the visual examination. 
The disease can be hereditary and it is important that family members are screened.

Hyperopia - "Farsightedness"

The ability to see far, however, requires intense focusing in order to see.
The closer the object the greater the difficulty in focusing.
These patients complain of headaches, teary eyes and poor concentration.

Intra-ocular pressure

The pressure of the viscous fluid inside the eye.
The measurement is recorded in mm of mercury.

Low vision 

Abnormal vision despite the best visual correction.

Myopia - "Short-sighted" 


Can see up close but poor distance vision. 
A farsighted eye is too “short,” causing light to converge behind the retina and blurring near vision.

Macular Degeneration


Breakdown of the macular, the back wall of the eye, often through age,
resulting in central blindness which spreads outward.

Ophthalmologist
  Note the spelling!!!!   In particular, the letter "h" and the letter "l."
A specialist of eye surgery and pathology.

Presbyopia


The inability to focus on close objects due to the ageing process. 
The lens loses its flexibility, and one has to hold reading material further away in order to focus.

Radial Keratomy

An operation initially performed with a scalpel and now utilises a Laser.
Fine cuts are made in the cornea to collapse it to reduce myopia.

Retinal Detachment


This is a real optometric emergency, where visual disturbances like flashing lights
and a "curtain" coming down over the eye is noticed.

Retinal fundus


The interior lining of the eyeball, including the retina (the light sensitive screen),
optic disc (the head of the nerve to the eye), and the macula (the small spot in the
retina where vision is keenest).
The fundus is the portion of the inner eye seen during an eye examination
by looking through the pupil.

Fundus is the Latin word for the bottom.
In medicine, fundus refers to the bottom or base of an organ.

Retinitus Pigmentosa


Untreatable inherited disease of the eye, which begins with night blindness and
progresses through tunnel vision to blindness.

Rod cells, or rods


These are photoreceptor cells in the retina of the eye that can function in less intense light
than can the other type of photoreceptor, cone cells. 
Since they are more light-sensitive, rods are responsible for night vision. 
Named for their cylindrical shape, rods are concentrated at the outer edges of the retina
and are used in peripheral vision.

Stye


A common bacterial infection of a little canal within the lid.   
Does not respond well to antibiotics.
The best treatment is to hold hot compresses against it.
The bump is a collection of fluid in a little sac inside the lid.

Ultra Violet


Light travels in wavelengths measured in nanometers. 
The short wavelengths below 400 nm are called Ultra Violet. 
UVA causes ageing through a breakdown of the tissue and UVB causes burning.
Sunglasses must provide 100% protection from UV rays.

Source:  Spectacle World via public domain Listings at www.viperlib.com