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Options abound in refractive surgery spectrum
Careful evaluation will match each patient with the appropriate refractive surgical procedure.
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In the past decade we have seen the convergence of refractive surgery with cataract surgery, which makes sense because the most commonly performed refractive procedure is phacoemulsification with IOL implantation. Corneal-based refractive surgery has evolved, with precise treatments with excellent outcomes. We are also learning more about phakic IOLs and newer devices such as intracorneal inlays. The key to success is to select the best refractive surgical procedure for each patient.
LASIK, PRK, phakic IOLs
LASIK and PRK have a long track record for success with excellent visual outcomes and very low risk as long as the patient is a strong candidate. The newer femtosecond lasers are able to create LASIK flaps that are far more accurate and predictable than using a bladed microkeratome. There are, however, the rare patients in whom a microkeratome may be preferred, such as those with corneal scars and perhaps some patients with prior radial keratotomy. Femtosecond lasers have improved considerably in both speed and quality of the flaps created, with complete treatments under 30 seconds with minimal issues with opaque bubble layers. Patients who meet topographic, tomographic and pachymetric criteria can do well with femtosecond laser-created LASIK flaps.
While the approved range of treatment for the current generation of excimer lasers is very wide, having a more conservative approach may be safer and produce better quality vision. Limiting the upper range of myopic treatments, which flatten the central cornea, to the –9 D or –10 D range will result in better residual bed thickness as well as better quality vision. Hyperopic treatments are more challenging because the cornea must be steepened by peripheral corneal ablation, which limits the upper range to about the +3 D or +4 D range to keep maximum visual quality even though the laser may be approved for higher treatments. PRK can be a good option for patients who want an alternative to LASIK, but it works far better in myopic ablations compared with hyperopic treatments.
For ultra-myopic patients, phakic IOLs can be an option, although there can be downsides. Anterior chamber phakic IOLs, which are fixated to the iris, can induce corneal endothelial cell loss, and they require a large incision for implantation. Posterior chamber phakic IOLs, which are placed behind the iris but in front of the crystalline lens, can induce cataracts in as many as 40% of patients within 5 years, according to a recent Swiss study.
Images: Devgan U
Cataract surgery with IOL implantation
If the patient has any degree of cataractous changes, it does not make sense to do LASIK or phakic IOLs. These are typically patients in their 60s who already have a degree of nuclear sclerosis. Even though they can be corrected to 20/20 with a refraction, LASIK surgery should be avoided because these patients will be able to achieve the same correction or even better correction with cataract surgery.
Cataract surgery can correct an immensely large range of dioptric powers while maintaining excellent visual quality. With IOL powers available from –10 D to +40 D, the refractive errors that can be addressed range from about –30 D to +15 D at the spectacle plane. While the risks of IOL surgery are low, be aware that very myopic patients may have additional risks with retinal detachment, and all patients with extreme eyes may have less accurate IOL calculations.
No IOL can currently produce the range of accommodation that is present in younger patients. For this reason, performing a refractive lensectomy and IOL implantation should be limited to patients with at least some degree of presbyopia. We can use monovision in order to improve near vision, but this may come at the expense of depth perception. With education, patients can understand that for their daily lives, a mild degree of residual myopia is a blessing because it enables excellent vision for daily activities. While a perfect plano result with 20/20 distance vision in both eyes sounds good on paper, it may not be the best choice if the patient spends most of the day doing near tasks. And any residual myopia can be addressed with spectacles that are intended for driving or nighttime vision.
Multifocal IOLs have also evolved considerably in the past 10 years. Newer multifocal IOL designs bring the near focal point out so that computer use is facilitated. An IOL with a +2 D add at the spectacle plane will give a near point of 0.5 m, which is 50 cm or 20 inches. A +3 D add at the spectacle plane will bring it in closer to 0.33 m, which is 33 cm or 13 inches. In order to minimize nighttime halos induced by these multifocal IOLs, it may be preferable to choose one that has the near rings only in the center of the optic. This way, when the pupil dilates for night driving, the optics favor the distance vision. With any multifocal IOL, the patient must agree to sacrifice some degree of visual quality in exchange for less reliance on glasses.
Intracorneal implants
Another option to address myopia is an intracorneal implant. These can be refractive, corneal shaping or small aperture based, and they are placed in the corneal stroma in the center of the visual axis. These are newer devices, and more data and long term follow-up are being gathered.
The ultimate solution would be a truly accommodating IOL that would restore a full range of vision from near to far and everything in between, with the highest quality of vision. That holy grail of refractive surgery is still years away.
- For more information:
- Uday Devgan, MD, is in private practice at Devgan Eye Surgery, Chief of Ophthalmology at Olive View UCLA Medical Center and Clinical Professor of Ophthalmology at the Jules Stein Eye Institute, UCLA School of Medicine. He can be reached at 11600 Wilshire Blvd. #200, Los Angeles, CA 90025; email: devgan@gmail.com; website: www.DevganEye.com.
Disclosure: Devgan reports no relevant financial disclosures.