The Future of LASIK

Microbial keratitis occurs because of intraoperative introduction of organisms into the lamellar interface. Introduction of laser devices to make lamellar flaps will reduce the amount of instrumentation that is required and should minimize this risk. If technology permits the development of intrastromal keratomileusis, then tissue can be ablated without the creation of a lamellar flap, which should completely eliminate the risk of microbial keratitis.

Keratectasia occurs in patients who are predisposed to this due to abnormal topography or excessively thin corneas, or in patients in whom inadequate posterior corneal tissue is preserved. Further work is required to understand which types of patients are predisposed to developing keratectasia, but this clearly is an achievable goal. Laser microkeratomes again offer exciting possibilities, in that flap thickness can presumably be determined with great precision, which should eliminate the risk of ablating too deeply into the corneal stroma.

Retinal and optic nerve complications such as submacular hemorrhages and ischemic optic neuropathy are presumably related to the increase in intraocular pressure that is produced by the vacuum required by the mechanical microkeratome. Once again, laser microkeratomes hold the promise of eliminating these risks.

Refractive issues such as irregular astigmatism, decentered ablations, and underand overcorrections will be addressed in the next section, but again these problems seem solvable.

Dry eye after LASIK is due primarily to corneal denervation caused by the cutting of corneal nerves. Altered corneal contour may contribute to this problem as well. It is still somewhat unclear if there is long-term reduction in tear production in all patients who undergo LASIK. Elimination of this problem will require development of nerve-sparing techniques for making the flap, which is again a potential advantage of intrastromal ablation. Another option would be the development of growth factors to stimulate corneal nerve regeneration.

2. Quality of vision: This is certainly the area of greatest ongoing interest in LASIK and in refractive surgery overall. Several areas need to be addressed, but they fall into two large categories: accurate measurement and delivery of laser energy, and accurate prediction of postoperative wound healing.

The steps required to improve quality of vision and eliminate optical complications have been described in part in Chap. 9. Several key steps are required.

First, accurate measurement of wave front aberrations must be performed. However, we also believe that accurate measurement of the corneal contribution to wave front aberrations will be essential. If the causes of wave front aberrations are intraocular, then correction of these will require the induction of aberrations on the corneal surface. Depending upon the magnitude of these aberrations, the cornea may or may not be amenable to maintaining these corrections.

Registration of the measurement to the treatment will be essential. This will require linkage of the wave front measurement to the laser delivery and will include issues such as torque and rotation of the eye. We must remember that tracking systems that are driven by the pupil can be deceived in part by parallax. Ultimately, real-time measurement of ongoing treatment is desirable, but this is unlikely with current technology owing to the difficulty of obtaining intraoperative measurements. Factors such as corneal hydration and temporary flap irregularity are major barriers to achieving this goal.

Finally, we need to understand better the role of the LASIK flap and wound healing in altering postoperative aberrations. Will we develop new flap-making techniques that

either eliminate new aberrations or are predictable in generating known changes? What will be the role of PRK and its associated wound-healing response?

3. Lifelong refractive adjustments: The ultimate procedure will provide a lifetime (or close to it) of excellent vision. The refractive error of most people varies from their teens throughout the remainder of their lives. There is a trend toward myopia between the ages of 20 and 40, and a shift toward hyperopia between ages 40 and 60. In addition, the aberrations of the eye change owing to both corneal and lenticular factors. Patients who obtain “super vision” will naturally wish to maintain this quality of vision throughout their lifetimes. Therefore a truly adjustable procedure is required.

For lifelong adjustments, LASIK as currently practiced has the major disadvantage of being a subtractive procedure. As a result, many patients might eventually run out of tissue that could be safely ablated. A better option would therefore be an additive, e.g., lamellar surgery with implantation of an intracorneal lens. This lens could be replaced or modified in situ as needed to maintain quality of vision. Periodic replacement of the lenses would introduce the risks of reopening a lamellar flap and predisposing the patient to the vagaries of corneal wound healing. Therefore the ideal solution would be a material that could be modified in situ, presumably using some form of laser technology to adjust or modify the optical characteristics of the synthetic lens. Recent advances in intracorneal lenses offer at least the possibility of the exchangeable implant, and early work with a new type of silicone intraocular lens suggests that at least one modification of a lens might be obtainable using external laser irradiation.

Conclusion: LASIK is currently state-of-the-art for the correction of a wide range of refractive errors. New advances offer the promise of improved safety, enhanced postoperative quality of vision, and the opportunity for lifelong adjustment of refractive errors and ocular aberrations. The Holy Grail of lamellar refractive surgery lies in the attainment of these goals.