Chapter 5- Pre-operative Workup Part II

The following conditions should be evaluated (continued).

• Contact lenses should be removed for at least 2 weeks before laser surgery. If the contact is a gas permeable or toric lens, they must not be worn for at least three weeks before laser surgery. Time out of contacts is necessary to acquire accurate correction measurements for the Excimer laser.
• Dry eyes almost always occur following laser surgery, and last for two to three months. If there is a pre-existing dry eye condition, treatment should begin before the laser surgery.
• Keratoconus is a thining of the central cornea. This condition can be diagnosed with pachymetry and topography. If the patient is a keratoconus suspect, Excimer laser is contraindicated. Other options are available.
• Nearsightedness can be corrected with the Excimer laser in patients with up to 10 diopters of nearsightedness. If the patient has more than 10 diopters of nearsightedness, other options such as a refractive lens exchange should be considered. A refractive lens exchange involves removing the crystalline lens of the eye and replacing it with an intraocular lens.
• Farsightedness can be corrected with the Excimer laser in patients with up to 4 diopters of farsightedness. If the patient has more than 4 diopters of farsightedness, other options such as a refractive lens exchange should be considered. A refractive lens exchange involves removing the crystalline lens of the eye and replacing it with an intraocular lens.
• Astigmatism can be corrected with the Excimer laser in patients with up to 4 diopters of astigmatism.
• Presbyopia is the loss of accommodation which prevents individuals from seeing well up close after the age of 40-42. The person who has a full distance correction may have difficulty with close vision. However, a person who is nearsighted may remove their glasses and see better. There are several options for correcting presbyopia. The first option is to correct both eyes for distance and wear readers for near. Second is to correct the dominant eye for distance and the non-dominant for near. Thirdly, the natural crystalline lens can be replaced with a multifocal intraocular lens.
• Herpes simplex and herpes zoster are viruses that can affect the eye. Herpes zoster affects the nerve and can affect the inside of the eye as well as surrounding tissues such as the lid. Herpes simplex affects the cornea of the eye. Both of these viruses in the active stage are contraindicated for Excimer laser surgery. If the herpes simplex is inactive, treatment may proceed but anti-viral medications may be necessary as a precaution.
• Corneal thickness is measured by pachymetry. If the thickness is less than 450 microns the individual may not be a candidate for Excimer laser. Advanced Surface Ablation is a safer procedure than LASIK because the cornea is thinned less.
• Corneal endothelial dystrophy is a disease of the inner layer of the cornea and is a relative contraindication to laser surgery.
• Abnormal closure of the eyelids or conditions that allow the lid to turn in or out should be corrected before Excimer laser surgery is considered
• One eyed patient should have all the risks carefully explained to them. Although, the results with the Excimer laser are excellent, rare complications may occur. The patient must weigh the risks and benefit before making a decision to have laser surgery.

References

Buratto,L. and Brint, S.: Custom LASIK: Surgical Techniques and Complications. Thorofare, N.J.Slack. 2003 p161-287. [book]

Mrochen M et al.. Increased higher-order optical aberrations after laser refractive surgery: a problem of subclinical decentration. J Cataract Refract Surg 2001 Mar; 27 (3): 362-369. [pubmed]

Schwiegerling J, Snyder RWl Corneal ablation patterns to correct for Spherical aberration in photorefractive keratectomy. J. Cataract Refract Surg 2000 Feb; 26(2): 214-221. [pubmed]

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