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More options coming for patients with presbyopia
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Myopia followed by presbyopia are the two most common refractive errors. Myopia is reaching an epidemic prevalence as high as 95% in some Asian countries and has grown from 25% of the population in the U.S. in 1979, when I finished my ophthalmology residency and 2 years of fellowship training, to more than 40% today, 40 years later. Presbyopia is estimated to affect 110 million people in America, about 30% of the population. Worldwide, as many as 2 billion are affected by presbyopia. Astigmatism of 1 D or more also affects about 30% of the population. Hyperopia is rarer, milder and usually latent until after age 40.
As a personal rule of thumb, 0.5 D of uncorrected refractive error (when accommodation is lost or relaxed) reduces a patient’s vision about one line on a Snellen chart. Thus, the plano emmetrope who corrects to 20/20 will drop to 20/30 uncorrected with –1 D of myopia or astigmatism. For the presbyope with no accommodation, such as a pseudophakic patient, the J1 potential emmetrope will drop one line for every 0.5 D of presbyopia — for example, to J3 with 1 D of presbyopia.
I have found it extremely rare for patients with 0.5 D or less of refractive error to seek treatment, whether it be optical, medical or surgical. At 1 D or more of any refractive error, most patients are unhappy with their uncorrected vision. The lower the refractive error, the more risk averse the typical patient. This, in my opinion, is why no surgical treatment has significantly penetrated the emmetropic low presbyopia market. Surgery is just too much for most patients who see 20/20 or better at distance and intermediate until they manifest significant presbyopia, say 2 D or more. As the emmetropic presbyope ages, latent hyperopia also begins to manifest itself, and uncorrected distance and intermediate vision begin to blur as well.
At age 45, my manifest refraction was plano in both eyes. I did not need readers until age 48. By age 55, my manifest refraction was +0.50 in both eyes, my reading add was +1.50, and I was dependent on readers for near and some intermediate. I tried a monovision contact lens. I could use it, but it was too big a hassle for me to manage its use daily. At age 60, I was still just using readers, now a +2.00 add. At age 65, my distance manifest refraction in both eyes was +1.00 of hyperopia, and I began to use a progressive bifocal because my distance without correction was also blurry to me. I tried multifocal contact lenses and did not like the reduced quality of vision and night vision symptoms. Monovision contact lenses still did not work well either, as I was developing a mild dry eye secondary to early meibomian gland dysfunction. Laser corneal refractive surgery, an intracorneal lens or refractive lens exchange seemed to be too much, so I acquired a couple pairs of progressive bifocals, which I adapted to easily. At age 71, I am +1.25 in both eyes for distance and require a +2.50 add for near. My manifest refraction and reading add have not changed in the last 4 years. I keep waiting to start to drift less hyperopic as my natural lens develops nuclear sclerosis and a higher refractive index, but it has not happened. Along with this progressive hyperopia, most emmetropic presbyopes experience some loss of contrast sensitivity as we develop early nuclear sclerosis or cortical lens change. However, I still see 20/15 and J1+ with correction and note no issues with night driving.
At present, the handicap and annoyance of dependence on glasses for distance, intermediate and near tasks are pushing me to consider a refractive lens exchange. I, for one, want an adjustable IOL so I can end up plano in both eyes or with mild monovision within 0.125 D of my preferred refractive target and no astigmatism without requiring a laser corneal refractive surgery enhancement. I would love an adjustable accommodating IOL with 3 D or more of accommodative amplitude, but I do not think it will be available in time for me. As I look back at my own natural progression from an emmetrope with good distance, intermediate and near vision to just needing low-powered reading glasses to one needing glasses to see clearly at every distance, I have a few observations that affect my care of patients.
I did not consider mild presbyopia with good retained uncorrected distance and intermediate vision enough of a handicap to cause me to seek surgical correction, even though for me it would have been free. I would, however, have been interested in the drops that are discussed in the accompanying cover story and are now in early clinical trials. I would have definitely been interested in a drop that uncross-linked my aging lens, making it more elastic and restoring some natural accommodation. I would have also found an improvement of two to three lines at near for 4 to 8 hours with a miotic useful in several social and sports settings, especially during daylight hours. I believe both of these medical therapies will be popular with patients and look forward to having them available.
I think these drops will be synergistic, and it will be safe for patients to use both treatments simultaneously. This might well tide patients over until they are 55 or 60, at which time they will become better candidates and be more highly motivated for a refractive lens exchange, especially once that adjustable accommodating IOL that I personally want becomes available. If the government-paid Medicare eligibility age slowly drifts upward toward or even over age 70, as I expect it to do as our federal government becomes ever more fiscally challenged, and the age patients request lens replacement surgery drifts down toward age 60, which is also likely to occur as technology advances, we might see the day when cash-pay refractive lens exchange replaces cataract surgery with lens implantation as the most common surgical procedure performed by the comprehensive ophthalmologist. The glasses, contact lenses and topical medical therapy for presbyopia will also all be cash pay, making the treatment of presbyopia a potential bonanza for the comprehensive ophthalmologist and the industry that supports us in a decade.
Disclosure: Lindstrom reports he consults for Alcon, Bausch Health, Allergan, J&J Vision, Novartis and Orasis.