Page 75 - The UK Guide to Laser Eye Surgery
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The light sensitive layer of cells (rods and cones) on the inner, back surface of the eye that converts light images into nerve impulses. These are then sent along the optic nerve for transmission to the brain.
See ‘Enhancement’.
Snellen visual acuity test
The Snellen test is the most common test used to determine visual acuity. It uses a white chart with the big black letter E at the top, followed by lines of letters that descend in size. The test gives a result such as 20/40, which means that the person can see an item 20 feet away with the same clarity as a normally sighted person can see at 40 feet. See also ‘Acuity’.
See ‘ReLEx SMILE’.
Images from light sources blur, with spikes radiating out from the centre. Starbursts can be a complication of refractive surgery, but may also occur naturally.
Topography / Tomography
A technology used to determine the shape of the front and back surfaces of the cornea. This is used to detect any abnormalities in the shape of the cornea, most importantly to detect eyes with keratoconus, in which laser eye surgery should not be performed. Topography data can also be used by some laser systems
to plan a topography-guided treatment, which can be used to smooth the shape of the cornea if it is irregular.
Visual acuity
See ‘Acuity’.
Visual field
The extent of an area seen by the eye in
a given position of the gaze. The central visual field is directly in front of the object at which we are looking. The peripheral visual field is ‘side vision’. The fields in each eye partly overlap.
A technology used to determine and measure higher order aberrations. These aberrations affect the finer quality
of the vision. While conventional eye examinations can detect two types of error on the cornea: spherical (myopia and hyperopia) and cylindrical (astigmatism), wavefront diagnostics can detect an infinite set of ocular aberrations – this information can then be used to create a customised treatment plan.

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