Amblyopia
An amblyopic eye often referred to as a lazy eye, in which the eye has reduced vision. Often there is no known reason.
Astigmatism
This is explained as an error of refraction, which prevents light from coming to a point of focus on the retina. Usually caused when the cornea (FRONT SURFACE) of the eye is shaped like a rugby ball whereas it should be like a football. Results in blurred vision.
Cataract
The partial or complete loss of transparency of the lens. The eyes internal lens becomes misty which prevents light from reaching the back of the eye and therefore interrupts vision.
Cerebral visual impairment or Cortical visual impairment (CVI)
Visual difficulty caused by damage to the visual cortex or visual pathways, the connection to the brain and the ‘vision’ part of the brain is damaged. Can be associated with the learning disability or acquired through brain damage.
Coloboma
This is normally a developmental defect of the iris (and other parts of the eye) which makes the pupil look keyhole shaped.
Corneal Opacities
Loss of transparency of the cornea (the front surface of the eye). Corneal opacity occurs when the cornea becomes scarred. This stops light from passing through the cornea to the retina and may cause the cornea to appear white or clouded over, resulting in impairment of vision.
Glaucoma
An eye disease associated with increased pressure within the eye,which can cause damage to the retina initially often causing loss of peripheral vision. Eye pressure may be tested during an eye examination often using a machine, which fires a puff of air against the eye and records the internal eye pressure. A test of the visual fields is also normally carried out. It is important to have a regular eye test by a qualified optician, especially if there is a family history of glaucoma.
Hypermetropia (farsighted or longsighted)
Inability to focus on near objects which will appear blurred. Usually corrected by prescription spectacles.
Kerataconus
Occurs when the cornea thins causing the central part of the cornea to bulge forwards in the shape of a cone.
Microphthalmus
The underdevelopment of the eyes, the eyeball is abnormally small and often deeply set in the orbit.
Monocular vision
Consequence of either having vision in one eye only or of a long standing squint.
Myopia
Inability to focus on distant objects which will appear blurred. Usually corrected by prescription glasses or contact lenses.
Nystagmus
Involuntary repetitive movement of the eyes. Caused by poor vision or by muscle defects.
Presbyopia
The inability to focus on close objects such as reading material,caused by the hardening of the internal lens making it difficult for the lens to reshape (increase power) when trying to focus close up. Known as loss of accommodation, usually occurs after the age of 40. First signs are pushing away reading matter to focus clearly. Can be corrected with reading glasses
Presbyopia
The loss of central vision. Central vision is used in tasks like reading and facial recognition.
Peripheral vision
The loss of peripheral vision will give problems with tasks like mobility and in identifying movement and the approach of people and objects.
Strabismus
This is another name for a squint. It refers to eyes that are not straight.
Explanation of Optical Terms
Plastic lenses – Lenses made of a plastic resin material sometimes known as CR39.
Polycarbonate lenses – Tougher than traditional plastic lenses made of a polycarbonate material,often used in rimless spectacles, less likely to break. Used in Safety eyewear.
Hi index Lenses – Plastic lenses made of a denser resin enabling the lenses to be thinner and lighter than traditional plastic lenses. There are differing degrees shown by their index number, ie A standard lens has a
index number of 1.52. Hi index lenses start from 1.6 1.67 1.7.
Bifocal lenses – Lenses that incorporate the distance and reading prescriptions in one lens. The top part of the lens is for distance vision the lower part for reading vision. There is a dividing line between the two. There are many different types of bifocals with different sizes and shapes of reading segments
Multifocal Lenses – Lenses which gradually change power as you look down the lens from distance to reading. Commonly known as Varifocal lenses. There are many different lenses such as Varilux and Progressive Graduate.