LASIK: The Final Answer to Refractive Errors

Dr. Mahipal S Sachdev

Senior Consultant Ophthalmology

"Invention" of spectacles was a great achievement at a time when patients with refractive error were severely handicapped or practically blind. Spectacles enjoyed high degree of popularity for a long time, but now their disadvantages viz., cosmetic blemish, restricted field of clear vision, aberrations, obstruction in sports and physical discomfort, are apparent.

A question that always haunts the mind of the ophthalmologists and patients: why depend on prosthesis when it is possible to restore natural vision with all its inherent advantages (not just cosmetic) finds no answer.

Extensive research and technical advancement have produced following alternatives:

1. Contact Lenses
2. Refractive Keratotomy (RK)
3. Excimer LASER (PRK)
4. LASIK (Laser Assisted In-situ Keratomileusis)

CONTACT LENSES

These are small polymer lenses, which are placed directly over the cornea. They are of two main types - soft and semi soft. Soft contact lenses are pliable and therefore very comfortable, but require utmost meticulous care and maintenance. Infections and allergy (GPC: giant papillary conjunctivitis) are the likely complications. Semi soft lenses (or Rigid Gas Permeable) are rigid and thus, initially, slightly uncomfortable to wear, but they do not require too much care. Complications like infection and allergy are uncommon with these lenses. However, in the Indian context infection, GPC, mishandling, dust and pollution associated conjunctivitis continue to be major causes of contact lens intolerance. Patient compliance is generally not satisfactory relating to the lens care and maintenance schedules.

NB:

• High degree of astigmatism can not be corrected by contact lenses.
• Extended wear lenses are not suitable for Indian conditions.
• Hard lenses are obsolete and should never be used as they prevent oxygen supply to the cornea.

REFRACTIVE KERATOTOMY (RK)

This is an operation where 4 to 8 (rarely 16) incisions are made on the cornea using a diamond knife. This results in flattening of the cornea and thus correction of myopia. This adventurous surgery is fraught with complications, viz. perforation of the globe, infections, glare, over or under correction and weakening of the globe making it prone to rupture even by trivial trauma. Although less expensive, RK is not recommended because of its inherent risks. In fact refractive surgery has suffered a serious set back because of the complications caused by RK.

EXCIMER LASER (PRK)

Using a computer controlled LASER (mostly Argon Fluoride 193nm) the surface of the cornea can be reshaped imparting it a predetermined curvature. This leads to correction of both myopia and hypermetropia, and also moderate amount of astigmatism. The procedure is short and simple and being computer controlled is highly accurate. The patients suitable for PRK are the ones above 18 years of age, with refractive error between 1 to 6 D and whose error has been stable for the last 1 years. There should not be any other complicating factor or disease in the eye. PRK, although a little expensive, is relatively safe in comparison to RK. The complications are postoperative pain (due to removal of epithelium during surgery), prolonged healing time and need to use steroids, slight corneal haze and late regression of the effect seen in some patients. It is not useful for high refractive errors and high astigmatism.

LASIK (Laser Assisted In-situ Keratomileusis)

It seems that the final answer to the refractive errors is here. LASIK combines all the advantages of the above procedures and virtually eliminates all their disadvantages. In LASIK an ultra-thin flap of cornea is raised and then Excimer Laser is delivered to reshape the corneal stroma into desired curvature. The flap is repositioned back. The steps are detailed below.

Patient Selection

• Refractive error: 2 to 25 diopter of myopia or up to 8 diopter hypermetropia
• Astigmatism of up to 8 diopter
• Minimum age 18 to 21 years
• Refraction should have been stable for 12 months
• Contraindications: keratoconus, corneal inflammatory diseases, herpetic keratitis and autoimmune diseases.

Preoperative Preparation

• Refraction under cycloplegia
• Corneal Topography
• Pachymetry for corneal thickness
• Informed consent

Procedure

LASIK is performed under topical anesthesia (lignocaine 4%) and the only cooperation required of the patient is to fixate at a blinking light. The steps are:

1. After the anesthesia an eyelid speculum is applied to retract the eyelids. The patient fixates his gaze at blinking light.
2. A suction ring placed around the cornea and serves as a platform for the microkeratome.
3. The automated microkeratome dissects through the superficial layers of the cornea and the corneal flap is folded back.
4. Excimer laser ablates the stromal bed to resurface it into desired curvature. What makes the Excimer laser so well suited for corneal ablation is its ability to remove tissue with accuracy up to 0.25 micron with each pulse. Often, only 50 microns of tissue are removed to achieve the proper amount of correction. The Excimer produces a non-thermal light beam that eliminates the possibility of thermal damage to surrounding tissues.
   During this step a clicking sound is heard and an odor of ablating tissue (similar to charring hair) is smelt.
5. The corneal flap is then repositioned and allowed to dry for a few minutes. The flap self seals itself without the need of sutures.
6. The eye is patched after instilling antibiotic drops for 1-2 hours and the patient is advised to report back the next day. Analgesics are prescribed for 2-3 days.

Comparison of PRK and LASIK

Conclusion

LASIK is major advance in the field of refractive surgery, which combines efficacy, safety, precision and accuracy. This technique is taking us on the path that, in the past, ophthalmologists feared to tread, towards the goal of unaided natural clear vision.

(Also read Excimer Laser)