Glossary of Laser Eye Surgery Terms: S – Z

laser eye surgery glossary


Condition in which the eyes are not both directed toward the same point simultaneously. Strabismus occurs when eye muscles are not working together properly. It is most commonly an inherited condition, but may also be caused by disease or injury. If diagnosed early, strabismus can usually be corrected. The condition may be treated with corrective glasses, eye-muscle exercises, surgery or a combination of these approaches. Young children with this condition may need to wear an eye patch over their stronger eye to force their weaker eye to function correctly. Children whose strabismus is not corrected may develop amblyopia. It is usually a contra-indication to laser eye treatment. A full assessment would be required to confirm suitability.


A new laser eye treatment for treating presbyopia, where the reading prescription changes due to age. The procedure uses a different treatment profile to standard laser treatment in order to correct both eyes equally well for distance and near. At present, this laser eye surgery is only available for patients who are hyperopic (long-sighted).


Varifocal glasses combine three different prescriptions (near, intermediate and distance) in one pair of glasses. These are designed for patients who require different prescriptions due to age-related changes within the eye. Refractive surgery has now advanced to be able to treat these prescriptions, enabling patients to focus on close objects without the need for reading glasses.


Visian ICL is a popular brand of Implantable Contact Lens that is has been endorsed by the US Army due to its reliable high standard of vision. Since it was introduced in 2006, the US Military has implanted over 3,000 Visian Implantable Contact Lenses and recommends this as the treatment of choice for their recruits who are unsuitable for laser eye treatment.

20/20 VISION

‘Normal’ visual acuity in American terms. The UK version is 6/6. The upper number is the standard distance (20 feet/6 metres) between an eye being tested and the eye chart; the lower number indicates that a tested eye can see the same small standard-sized letters or symbols as a normal eye at 20 feet/6 metres. If a person does not have 20/20 vision with their glasses/contact lenses before surgery it is not possible to achieve it after laser eye surgery.


The measurement of visual clarity. Best corrected visual acuity (VA) is the measurement of the best vision achieved with glasses or contact lenses. Uncorrected VA is the sharpness of vision without spectacles and contact lenses.


Wavefront refers to the unique way that light travels into and out of the eye. Any deviations from the ideal visual path (wavefront) are known as aberrations and affect the quality of vision.

wavefrontThe wavefront of the eye can be measured using a Zywave Aberrometer. By examining the wavefront a more accurate prescription can be achieved in comparison to a standard eye exam, which only looks at the refractive errors in specific areas of the eye (cornea and lens). Wavefront analysis allows for a complete examination of the visual process by measuring how light travels into and out of the eye. This identifies any irregularities (aberrations) in the visual process, allowing for a truly individual prescription.

The Zernike algorithm and polynomials are used to mathematically reconstruct the wavefront in the form of a topographical chart. This enables the identification of low order aberrations (myopia, hyperopia and astigmatisms) and high order aberrations (more complex visual errors like trefoil, coma etc).

Wavefront analysis is used to provide a bespoke laser treatment that is tailored to refractive errors of each eye, providing a better correction than glasses and contact lens can achieve


The XP Microkeratome can be used to create the flap during the LASIK laser eye surgery procedure. This has now been preceded by a blade free option called IntraLase.


The very latest development in laser eye treatment from Bausch and Lomb is a system called Zyoptix. This is an advanced procedure that delivers a laser eye treatment unique to every individual. The laser has many safety features that help to optimise the success of the treatment. It has a unique integrated diagnostic system; one set of data thoroughly evaluates the structure of the cornea to confirm suitability. The second measures the eye’s anatomy to determine its unique optical characteristics using advanced Wavefront technology. This process enables the eye surgeon to plan a bespoke laser vision correction procedure completely personalised to each patient.


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