Presbyopia, the loss of accommodation with age, is a condition we all experience typically beginning in the 5th decade of life. The most common treatment for presbyopia is to wear reading glasses, either bifocals or separate near vision spectacles. Instead of glasses, contact lenses can be used to provide multifocal vision or monovision. Surgical methods for correcting presbyopia also exist. Numerous procedures have been investigated, and many are currently being evaluated in FDA trials.
The monovision approach is the most common surgical method of correcting presbyopia and has been performed for years with corneal (LASIK, PRK, RK, and CK) and intraocular (IOLs) procedures. This is usually the treatment of choice for patients who have been successful with monovision contact lenses, but can also be used after a positive monovision contact lens trial in patients considering this option. When performing a contact lens trial, patients usually tolerate monovision best when the dominant eye is corrected for distance vision and the nondominant eye for near vision, but some prefer the reverse situation. Therefore, if monovision is not accepted during the initial trial period, then reversing the correction for the dominant and nondominant eyes should be tried. Failure is due to contact lens intolerance or the inability to adapt to monovision after a three-week trial. Monovision preserves best spectacle-corrected visual acuity (BSCVA) and contrast sensitivity, but it decreases uncorrected distance vision in the treated eye and reduces stereopsis. If the patient is unhappy with the monovision result, then additional surgery may be performed to correct the residual myopia in the near vision eye.
A novel excimer laser technique for monovision is IntraCOR (Technolas), in which a femtosecond lasercuts concentric rings in the corneal stroma to produce a central steepening in the nondominant eye. Two-year data showed improved near vision, but there was an associated myopic shift that affected distance vision, and patients reported halos. Therefore, this technique may be best utilized in slightly hyperopic presbyopes.
Another method of creating monovision is with corneal inlays, which are placed under a LASIK-style flap. There are currently 3 designs (under FDA investigation in the United States; available outside the US):
- Kamra (AcuFocus) is a small aperture corneal inlay that increases depth of focus with a pinhole effect (3.8 mm lens with a 1.6 mm central opening) and therefore does not interfere with distance acuity. Three-year results showed improved intermediate and near vision without any change in distance vision.
- Flexivue microlens (Presbia) is a hydrophilic corneal inlay for center distance vision. The 3 mm inlay provides near add power in the lens periphery. One-year data showed improvement in uncorrected near vision in all participants, but the uncorrected distance vision declined.
- Vue+ (ReVision Optics) is a hydrogel corneal inlay for center near vision (formerly PresbyLens). The 2 mm ultrathin lens improves near vision by changing the central corneal curvature. All patients had an improvement in near vision, but some had a decrease in distance acuity.
The major concern with placing a foreign material in the cornea is biocompatibility, and historically, such implants have not faired well. However, the latest generation of inlays seems to have overcome this significant obstacle. This approach is also reversible, so if the patient is unhappy with the result, the inlay can be exchanged or removed.
The multifocal approach to presbyopia correction can be performed with intraocular (multifocal IOLs in patients undergoing cataract surgery and refractive lens exchange) or corneal surgery. The advantage of this approach is the preservation of binocular function, but there may be a sacrifice in contrast sensitivity as well as BSCVA, and patients are commonly aware of glare or halo from lights at nighttime. Presbyopic laser ablation profiles which are performed outside the US, have been under investigation for over a decade in the US. The results of PresbyLASIK show an improvement in near vision but distance acuity can be affected. In the future, multifocal phakic IOLs may also be available.
In addition to the compensatory approaches of monovision and multifocality for the correction of presbyopia, the other approach is restoration of accommodation. Techniques that aim to achieve this "holy grail" of presbyopia correction have primarily been based on creating more space between the ciliary body and the lens. The theory is to restore the effective working distance of the ciliary muscle and thereby increase the power for accommodation. Specifically, anterior ciliary sclerotomy involves creating 8 partial thickness radial incisions in the sclera over the ciliary body, and scleral expansion involves placing synthetic implants posterior to the limbus to stretch the sclera. Various refinements in these procedures have been made over the last 2 decades, but regression of effect and complications (hemorrhage, infection, induced astigmatism, regression of effect, and implant extrusion) continue to be concerns.
The surgical correction of presbyopia is an exciting area of investigation that continues to be full of innovation. The most recent attempt at restoring accommodation is being undertaken by LensAR and utilizes a femtosecond laser to soften the crystalline lens. Initial treatments show that this technique can work but the effect has been variable. New accommodating IOL designs are also being developed, any many of these are showing promising results. The future is bright for presbyopia treatment, and I eagerly await FDA approval of these new procedures.