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Medical and surgical innovations expected to transform treatment of presbyopia
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Presbyopia is the most common refractive error in the world, impacting about 40% of the population. All of us who are in the presbyopic age group appreciate the fact that it represents a significant functional disability.
Most of us living in the so-called advanced countries manage our presbyopia with glasses or, in a minority of cases, a contact lens. It should be remembered that in many developing countries spectacles of any kind, including simple inexpensive reading glasses, are simply not available. While on a cataract surgery mission trip with my now-deceased good friend John Pearce of England, he made the astute observation that presbyopia-correcting IOLs were not just for the affluent but ideal for emerging countries where readers are not available or unaffordable. An inexpensive widely available bifocal IOL would be a welcome addition for the cataract surgeon treating those with no access to glasses after cataract surgery.
In the advanced countries, significant human and financial capital is being invested to provide the more affluent with both medical and surgical alternatives to reading glasses, bifocals, progressive lenses and presbyopia-correcting contact lenses. I would like to disclose that the medical and surgical treatment of presbyopia has been a special interest of mine for more than 30 years and that I consult widely in this field of invention. I have participated in research and development on each of the products I will mention in my commentary. Here are a few thoughts to add to those of the excellent panel in the accompanying cover story.
First, the optical principle of small-diameter aperture optics is being applied successfully to the medical and surgical treatment of presbyopia. We are all aware that reducing the f-stop on a camera increases the depth of focus. In the eye, creating pupillary miosis with a topical drop can effectively treat presbyopia. Those of us in ophthalmology during the era in which glaucoma was primarily treated with pilocarpine, carbachol, eserine and phospholine iodide are familiar with emmetropic presbyopes or pseudophakes on strong miotics seeing well at distance, intermediate and near. They also enjoyed a relatively seamless range of vision from far through intermediate to near, a distinct advantage of small-diameter aperture optics. To achieve a meaningful improvement of more than two lines at near, the pupil must be reduced to less than 2 mm in diameter.
Much research using small-diameter aperture optics in corneal inlays and IOLs has been performed by AcuFocus, resulting in an FDA-approved device, the Kamra inlay. Optical bench research and patient clinical trials helped select an aperture diameter of 1.6 mm at the corneal plane with a slightly smaller aperture near 1.4 mm needed at the pupillary and IOL plane. Of note, the increased depth of focus created by small-diameter aperture optics allows one to target mild myopia of –0.75 D to –1 D and still retain excellent distance vision. This is the exact same optics that are incorporated into the widely used disposable cameras, and in that application, mild near focus with a small-diameter aperture has been defined as hyperfocality. I find hyperfocality a useful term and hope it becomes familiar and useful to other ophthalmologists and optical scientists.
As an aside, there is much for ophthalmology to learn from research done by our optical colleagues designing cameras, telescopes and microscopes, including the fact that the best possible optical resolution can be obtained using diffractive optics, not refractive optics. Some of the principles learned in advanced optical devices have been applied to create my current favorite presbyopia-correcting IOL, the Symfony from J&J Vision. Significant clinical data support the conclusion that inducing hyperfocality in one eye and leaving the other at emmetropia creates a functional visual system for patients, with significant advantages over the very popular monovision.
While no drops are currently FDA approved, I see a role for medications that induce miosis, allowing patients with early presbyopia to enhance their near vision for 6 to 8 hours whenever they wish by simply instilling a topical drop. I am confident many presbyopes will find this an attractive option. Even more exciting to me, we have a topical drop that in an FDA phase 2 clinical trial has shown promise in actually reversing presbyopia and restoring near vision. Encore Vision, recently acquired by Novartis Pharmaceuticals, has developed a topical prodrug based on the molecule alpha lipoic acid that appears in early laboratory and clinical study to work by increasing the elasticity of the natural lens. I think of the mechanism here as doing the opposite of the collagen cross-linking we do in keratoconus, basically uncross-linking collagen to make it less stiff and more elastic by reducing the sulfhydryl groups that cross-link the human lens with age. So, now we will potentially have treatments that can make collagen stiffer and treatments that can make collagen more elastic. If further study confirms the safety and efficacy of this drop, I believe it will be to presbyopia treatment what Restasis (cyclosporine ophthalmic emulsion 0.05%, Allergan) was to dry eye therapy or timolol and latanoprost were to glaucoma: a disruptive innovation.
Much research and clinical experience have now generated a large number of bifocal, trifocal and multifocal IOLs. I have participated in the research and clinical trials of these lenses starting with the IOLAB center surround IOL and 3M Vision Care diffractive multifocal IOL in the 1980s and continuing with Alcon and J&J Vision. All ophthalmologists are familiar with the strengths and weaknesses of these presbyopia-correcting IOLs, and as we have accessed multiple add powers, trifocal optics and toric models, our patient outcomes have continued to improve. These lenses all require an outcome near emmetropia, including minimal residual sphere, astigmatism and higher-order aberrations, to achieve the best outcome.
While improvements in biometry, intraoperative aberrometry and the ability to perform refractive corneal surgery enhancements have allowed us to meet the demands of most patients, I see the advent of an adjustable IOL as the ultimate solution. For this reason, I remain excited about the progress being made by RxSight because no other technology seems capable of matching the refractive outcomes of an adjustable IOL. This adjustable IOL capability will also be helpful in our monovision patients, allowing us to set them at their exact preferred refractive outcome.
Finally, I have been an active participant in many research projects aimed at developing a true accommodating IOL, including some using electronic-adjusted optics. This area of research has developed one useful FDA-approved IOL in the U.S. labeled as accommodating, the Crystalens and Trulign from Bausch +Lomb, but all of us would like to see a lens implant reach the market with a greater amplitude of accommodation. The biology of the retained lens capsule and its loss of elasticity with healing after cataract surgery has been a significant barrier in development of an accommodating IOL with a satisfactory amplitude of accommodation, but several investigators demonstrating extraordinary perseverance are closing in on this elusive goal.
The day when we can delay symptomatic spectacle-dependent presbyopia, and perhaps even cataract (dysfunctional lens syndrome), from an onset in the 40s to sometime closer to age 60 appears probable within the next decade. In addition, medically and surgically induced hyperfocality with small-diameter optics is an exciting advance, as are other advanced optical methods of inducing increased depth of focus. I am even optimistic that I may have the opportunity to implant an accommodating IOL with 2.5 D or greater of accommodating amplitude, generating 20/20 vision at all distances, during my career. It is an exciting time to be involved in bringing decades of bench research in presbyopia to the patient bedside.
Disclosure: Lindstrom reports financial disclosures with AcuFocus, Alcon, Bausch + Lomb, Encore Vision, J&J Vision and RxSight.