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Today's Practice | Apr 2012

Identifying the Ideal LASIK Patient

Factors to consider in determining a candidate's appropriateness.

There are two perspectives to consider in defining the ideal LASIK patient: the scientific knowledge base and the empiric so-called soft skills of an experienced surgeon. This article discusses the factors to take into account when determining whether a patient is an appropriate candidate for this refractive surgical procedure.


It is well known to refractive surgeons that LASIK candidates should have a minimum corneal thickness of 500 μm. When a LASIK procedure is planned, this limit should be respected. In some countries, it is considered a matter of iatrogenic failure to disregard it.

Corneal steepness should also be considered when determining a patient’s candidacy for LASIK. The cornea should not become too flat after a treatment, as the flatter the cornea is, the more optical problems will result. An advisable limit of corneal flatness is 36.00 to 38.00 D. On the other hand, the corneal steepness should not exceed 50.00 D, as greater steepness could lead to nutritive problems and tear film instability.

As a rule of thumb, the refraction can be added to the steepness to estimate the outcome in respect to corneal curvature. Ideally, a myopic patient should have a keratometry (K) reading of 48.00 D and refraction of -5.00 D; this patient should end up with a K reading of approximately 43.00 D after treatment. The perfect hyperopic patient would have a K reading of 39.00 D on topography and 4.00 D of hyperopia. This patient would also be expected to have a K reading of 43.00 D after treatment.


The planning for astigmatic ametropia is similarly calculated, and the same limits should be obeyed. The estimated treatment should consider the axis of cylinder in an attempt to detect lentogenic astigmatism— that is, astigmatism caused by the lens rather than the cornea. The ideal LASIK candidate should show only corneal astigmatism. If there is remarkable lentogenic astigmatism, one should be aware of the fact that the planned LASIK treatment will produce corneal astigmatism. The surgeon would therefore be responsible for the stability and correct alignment of both ametropias over time, and the fact that the patient will be left with severe iatrogenic astigmatism after lens extraction. This information should be discussed with the patient. The ideal treatment in eyes with lentogenic astigmatism is correction via implantation of a toric IOL.


Exclusion criteria derived from other diseases should be taken into account when determining if a patient is a candidate for LASIK. Patients with rheumatoid arthritis or other collagenosis should be identified. Patients with cataracts should first undergo lens extraction. Great care should be taken to identify patients who have keratoconus, especially the not-so-evident early cases and forme fruste cases. Visualization of the cornea’s back surface is extremely valuable, so it is helpful for the refractive surgeon to have a corneal topography device with this capability.

Patients with diabetes are typically not ideal candidates for LASIK, as there is increased risk of epithelial ingrowth in these cases. This should be explained to the patient, and the option of PRK should be discussed. The measurement of refraction may also be problematic in patients with diabetes; under conditions of high blood sugar, the measurement will over-estimate myopic values, and vice versa. The best time to calculate refractive measurement is when the patient’s blood sugar levels are normal. Therefore, it is advisable to first measure the patient’s blood sugar, and, when the reading is good, to then measure his or her refraction.

It has been suggested not to perform LASIK in patients with glaucoma; however, I do not find this to be a logical recommendation, as every patient who undergoes LASIK has a certain risk of developing glaucoma later on. The better solution is to explain to patients how corneal thickness influences intraocular pressure (IOP) readings.

Patients must be educated that they should inform every ophthalmologist that they visit in their lifetimes that they have undergone LASIK; the ophthalmologist should then be mindful of this when taking IOP readings. Although this seems evident, there may be some doctors who do not measure corneal thickness when taking IOP readings.


In terms of soft skills, there are two important factors to consider: (1) the motivation of the patient, and (2) the patient’s ability to understand the refractive treatment. It is helpful to discuss the patient’s motivation for undergoing LASIK in the visit prior to the surgery to determine whether the patient has unrealistic expectations. Additionally, poor motivation can lead to problems during the healing period, especially in times of discomfort.

Of course, most patients identify freedom from glasses and contact lenses as their primary motivation to undergo LASIK. Perhaps they cannot wear contact lenses due to dry eyes or they cannot manage their use. Other patients may want to save the money that they traditionally expended for glasses or contact lenses. Regardless of the patient’s motivation, it is important to know his or her exact goal in order to detect any hidden problems that may occur postoperatively. For example, a patient who is active in martial arts is not an ideal LASIK candidate, as a punch could hit the cornea and loosen the flap. Another problem might be the requirements of a driver’s or pilot’s license, which may not be fulfilled for a period of time after LASIK. Divers should be prepared to stop these activities for about 2 months following the procedure.

If physical appearance is the patient’s ultimate motivation for LASIK, one should prepare him or her to experience possible discomfort from facial wrinkles, which are more visible without glasses. All patients should be educated about the eventual onset of presbyopia, especially hyperopic patients who undergo surgery later in life and are approaching the age at which presbyopia occurs.


A group of patients that warrants special consideration are those with presbyopia. If the surgeon offers correction for far vision to a presbyopic patient, he or she must be informed of the continued need for reading glasses after surgery. If a multifocal corneal pattern is used, the patient must be prepared for problems with enhancement surgeries and visual impairments caused by the multifocal effects, including glare and contrast sensitivity loss.

If monovision is offered, the method should be demonstrated to the patient with glasses or contact lenses. It is important that the patient completely understand the monovision treatment. He or she must be informed that each eye will have only one focal plane, so there are two distances to be used—far and near. In this context, it is necessary to instruct the patient about the depth of field in his or her near-vision eye. Patients should understand that there is only one focal length for near, but it can be broadened by optimizing the illumination of the place of work.


Performing a comprehensive preoperative evaluation to determine if a patient is an appropriate candidate for LASIK will increase the likelihood of delivering optimal visual results. Additionally, devoting time to understanding patients’ motivations and goals will help manage their expectations and increase their overall satisfaction.

Andreas Frohn, MD, PhD, practices at the Avila Eyeclinic in Siegen, Germany. Dr. Frohn states that he has no financial interest in the companies or products mentioned. He may be reached at e-mail: andreas-frohn@gmx.de.