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ASSESSING SUITABILITY
Assessing suitability is a complex subject. To some extent it is possible to get an idea of wether a given person is suitable based on a
few key bits of information.
The factors that are important are as follows.
1. The needs and expectations of the patient
We often encounter patients whose expectations are unrealistic or whose personalities do not make then good candidates. Very pedantic and anxious types are generally not good candidates.
Commonly, patients present to us whose only problem is presbyopia. The problem of reading in a person over the age of 45 is discussed in our section on presbyopia. There are options available but usually this is not the best person for vision correction.
2. The refraction
The strength of the current script is very important as there are limits to Lasik.
As a rule, the limitations are as follows.
- Myopes (short sighted) up to about 9 diopters
- Hyperopes (long sighted) up about 4-5 diopters
- Astigmatism up to about 4-5 diopters
3. The corneal thickness
The normal cornea is about 550 microns in central thickness (about half a millimeter).
For life long safety, at least 250-300 microns needs to remain after Lasik. Think of it like floor boards that can’t be too thin or they can break under the weight of a person.
The Lasik flap is about 120 microns and the laser procedure removes about 12 microns per diopter. Thus as an example, a person whose script is say 5 diopters will have 12×5= 60 microns removed + 120 for the flap = 180. Thus if their cornea is the average 550 that will leave 550-180 = 370 which is safe.
4. No underlying eye disease
The most concerning is Keratocconus or a variant of it. Keratocconus is generally an inherited condition in which the cornea progressively thins and which can be made worse by laser procedures. The tests which are performed prior to the procedure are largely aimed at detecting this condition. Keratocconus is discussed in greater detail in another section.
In addition, other corneal conditions such as corneal dystrophies, certain conditions such as Lupus or rheumatoid arthritis and many others could make laser vision correction undesirable. Woman who are pregnant are not suitable and if there is a chance of being pregnant or becoming pregnant then vision correction should be postponed.
All of these issues and others are taken into account at the assessment visit. A number of tests and measurements are also performed at the initial visit to determine suitability.
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