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Options for refractive surgery patients continue to improve, expand
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After closing the first half of 1997, it is a good time to review our current refractive surgery alternatives and try to make sense of the options we can offer our patients.
Still a role for RK, AK?
Is there still a role for radial and astigmatic keratotomy (AK)? The answer, of course, is yes, but we hope to see the procedure tempered with some precautions and restrictions. In the first place, RK has a relatively steep learning curve, so it makes sense that it should be restricted to the experienced surgeon. The problem is that with access to laser technology so expensive and time consuming for the general ophthalmologist, we may see more and more practitioners encompassing RK into their practice to serve interested refractive surgery candidates.
Most busy refractive surgeons would agree that the procedure is currently indicated only in older myopes of less than 2 D, in low myopic astigmats and as an enhancement for low degrees of undercorrected cylinder in postoperative photorefractive keratectomy (PRK) or LASIK patients.
PRK, LASIK improvements
In many surgeons’ hands, results with PRK meet those of LASIK, but with a price. Despite refinements in mechanical or chemical debridement of the epithelium, and transepithelial techniques notwithstanding, the procedure is still uncomfortable, and delayed epithelial healing is still responsible for pain and slow visual rehabilitation.
Nonetheless, it can be safely applied in patients with spherical equivalents up to 4 or 5 D and, additionally, it may even be recommended in patients with both myopia and basement membrane disease as it would theoretically reduce the consequences of recurrent erosion syndrome.
Although no definitive data exists to substantiate this fact, I have performed PRK in selected instances of basement membrane disease with definite reduction in symptomatology.
LASIK provides rapid recovery
LASIK certainly has become the procedure of choice of most refractive surgeons, primarily for its ability to provide rapid visual recovery with relatively little discomfort and minimal need for postoperative medication. For these reasons, most busy surgeons now prefer LASIK as the procedure of choice for the correction of ametropias.
It can be argued that LASIK may be "overkill" for low degrees of myopia, but for the surgeon comfortable with the technique, the risks remain low and relatively equal to those of RK.
LASIK should be used with caution in patients with myopia higher than 14 D, as corneal ectasia may result from excessive ablation. The currently acceptable range for LASIK is +5.0 to -14.0 D.
ICR segments may be reversible
Intrastromal corneal ring segments (ICR segments, KeraVision, Fremont, Calif.) are twin semi-circles of optically clear PMMA that are threaded into the corneal stroma, outside of the optical zone. This device supersedes the original 360° ring. Varying thicknesses of the implanted device correlate with reduction of between 1 and 5 D of myopia, presumably due to interruption of transverse corneal lamellae with resultant apical corneal flattening.
Initial studies show slightly lower degrees of efficacy and accuracy than corneal laser ablative procedures for uncorrected postoperative visual acuities. In addition, 5% of patients lost two or more lines of best corrected visual acuity, a statistic double that for laser procedures, according to Summit FDA data.
Although the ICR segment is an incisional procedure, it may be reversible, which would indeed add value to its usage. Nonetheless, only two cases have been explanted, both within the first 5 days because of complications. Further long-term studies are pending.
Lensectomy has a place
Lensectomy still has a prominent place in the correction of very high myopia (higher than 12 to 14 D) as well as hyperopia (higher than 4 to 5 D), especially in patients older than 50 years with early nuclear sclerosis and experience with presbyopia.
Lensectomy should be performed by a skilled cataract surgeon, presumably one with experience in clear corneal cataract extraction and topical anesthesia. The introduction of foldable multifocal intraocular lenses later this year will allow for a more natural postoperative visual rehabilitation.
ICL is exciting
Certainly the most interesting and exciting addition to our refractive surgery menu is the Implantable Contact Lens (ICL, STAAR Surgical, Monrovia, Calif.). This lens is a silicone plate haptic lens, similar to current posterior chamber IOLs, but sized to fit over the crystalline lens in the ciliary sulcus. It is implanted through a 2- to 3-mm incision, preferably through clear cornea. It is vaulted to eliminate contact with the anterior lens capsule.
The ICL can, theoretically, correct any refractive error and is reversible. As of this writing, four surgeons in the United States have implanted the initial cases. Phase I Food and Drug Administration studies should be in full swing later this year. The ICL represents a unique and valuable option to the refractive surgeon and will play an increasing role in the surgical correction of high refractive errors.
LASIK preferred method
My personal preference in the current state-of-the-art technology is laser in situ keratomileusis (LASIK) for all refractive errors from low plus up to about 14 D of myopia. For myopia under 2 D or simple nonmyopic astigmatism, I still do radial keratotomy (RK). Low myopes eventually may benefit from the intrastromal corneal ring segments (ICR segments), but after more data is available.
For myopia higher than 14 D, or lower myopia in older patients, lensectomy with IOL is my procedure of choice; however, I believe a large portion of this group will ultimately be treated with the intraocular contact lens. Needless to say, practitioners looking to refer patients for refractive surgery must find a surgeon or center offering the appropriate modality for all refractive errors.