The Modern Presbyopia Exam
It’s time to move towards a more quantitative approach that can better guide treatments for presbyopia
By James A. Katz, MD
Presbyopia is a manifestation of the aging of the eye that is associated with near and intermediate blurry vision, headache, and eye strain or fatigue.
In presbyopia, all of the tissues of the eye increase in stiffness, including the lens, sclera, and the other elastic tissues of the eye, such as the Bruch’s Membrane Choroid Complex. These age-related changes impact the biomechanical movements in the eye and result in a loss of Dynamic Range of Focus which includes the loss of accommodation(central optical power through shifts in lens curvature and shape), extended depth of focus(Extended Range of Focus [ERoF] through multifocality), pseudoaccommodation due to higher order aberration (depth of focus due to Higher Order Aberrations [HOA]), and changes in power due to the pupil size(pin hole effect). The degree to which these combined factors affect vision varies considerably from one individual to another, as does the pace of age-related crosslinking. In other words, while presbyopia changes worsen over time, we cannot just assume that every 50-year-old will need the same add power to read.
In evaluating visual performance in presbyopes, clinicians primarily rely on age and subjective manifest refraction at various distances—which are woefully imprecise ways to describe near function. For example, the font size for digital devices ranges from 8-point to 36-point, with 16- to 20-pt fonts being very common on websites and cell phone screens. People can position their digital devices at a wide range of “near” distances from the viewer, and many allow easy font size adjustment to suit the user. A reading acuity of 20/20 in the real world is rarely needed. Consider that a typical newspaper or paperback book can be read with just 20/50 to 20/60 near vision. On the other hand, contrast is often worse in today’s near-vision environments than it might have been in decades past when most reading took place on a black-and-white, high-quality printed page.
The symptoms and complaints of aging and progressive presbyopia are clearly understood. However, the effects of presbyopia are challenging to measure. In addition, we need more objective and quantitative tools to add to the current qualitative information about vision, age-related changes, ocular rigidity, lens, and biomechanical dysfunction.
A Better Presbyopia Exam
Several devices can provide valuable quantitative information to aid in a presbyopia evaluation, including the dysfunctional lens index (DLI) on the iTrace device (Tracey Technologies), double-pass retinal imaging objective scatter index (OSI) on the OQAS II device (Visiometrics); and the two-dimensional point spread function (PSF) on the HD Analyzer (Keeler).
The same wavefront technology that has revolutionized refractive surgery has the potential to provide much more information to enhance our understanding of presbyopia, as well. Static ray-tracing aberrometry, for example, can provide an Effective Range of Focus (EROF) and show meaningful changes in that EROF. However, change in EROF is captured at just one point in time with static aberrometry, and this technique is less likely to demonstrate low levels of accommodation and pseudoaccommodation or small degrees of change.
A relatively new device called dynamic Hartmann-Schack aberrometry (WaveDyn Vision Analyzer, WaveFront Dynamics) offers a much more robust way of measuring changes in the aging eye. It can be used objectively over time to evaluate the true Dynamic Range of Focus (DRoF). The device employs a moving target that shifts back and forth from far to near, allowing it to measure through focus dynamically (Figure 1). It can also consider changes in dioptric power as the pupil changes during the dynamic measurement (Figure 2).
My expectation is that in the future, a presbyopia exam will consist of more than just an ETDRS card and a biomicroscopy LOCS score but will also incorporate a workup with dynamic aberrometry and other sophisticated diagnostic tools, just as we currently have for laser vision correction and cataract surgery planning.
Impact on Decision-Making
Quantifying the dynamic range of focus becomes increasingly important as our options for correcting presbyopia expand. Historically, we have not had much to offer beyond glasses, contact lenses, and surgical monovision. However, we are entering an era when a variety of treatments may be offered, depending on the stage of presbyopia and objective measures of the eye’s optical, biomechanical, and lenticular health. Clinicians must know how to objectively classify presbyopic changes in a more granular fashion to help guide those treatment decisions.
For example, in the emergence of presbyopia, topical drops to modulate the pupil size may be all that is needed to increase the patient’s depth of focus satisfactorily. As the sclera becomes progressively more rigid with age, a new investigational treatment, Laser Scleral Microporation (LSM, Ace Vision Group), could potentially be used to “uncrosslink” the scleral microfibrils and restore dynamic range of focus. As long as the lens is relatively clear, LSM rejuvenates the eye’s natural biomechanics, which could reverse the effects of the eye’s aging. Once the lens stiffens and opacifies, uncrosslinking will provide less functional benefit. Instead, the crystalline lens must be removed and replaced with a multifocal or accommodating lens implant.
Better diagnostic information can help to define when each of these approaches works best, rather than leaving it up to clinicians to guess what will be effective.
The field of presbyopia is rapidly changing. Clearly, we need a better way to evaluate patients who are suffering from age-related loss of their dynamic range of focus and to guide better decision-making. The degree to which these factors affect vision varies considerably from one individual to another, as does the pace of age-related degradation. In other words, while presbyopia changes worsen over time, we cannot just assume that every 50-year-old will need the same add power to read.
Dr. Katz is President of The Midwest Center for Sight in Des Plaines, IL. He is a consultant for ACE Vision Group; Alcon; Allergan; Bausch + Lomb; Carl Zeiss Meditec; Cassini Technologies B.V.; Centricity Vision; Dompé; Johnson & Johnson Vision; LEGRANDE Health; Novartis; Ocuphire Pharma; RxSight; Sight Sciences; Tarsus Pharmaceuticals; Trukera; Visionary Ventures; Visus Therapeutics. He can be contacted at [email protected].
