Monovision or multifocals?

Patient suitability and tolerance should determine presbyopia correction method.

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Rigorously assessing patients’ suitability for specific presbyopia options, and managing expectations, are critical for successfully offering monovision or multifocal intraocular lenses, said Mitchell A Jackson MD at the ASCRS Virtual Annual Meeting 2020. Communicating effectively with patients starts with using language they can better understand, Dr Jackson said. “Terms like ‘monovision’ or ‘micro-monovision’ seem like you are going to be a cyclops. We prefer terms like ‘blended vision’ and ‘natural vision’ for multifocality. These relate better to the patient’s experience and help set expectations on the limits of their vision.” Blended vision In assessing patients for “blended vision”, Dr Jackson first considers occupation. Favourable jobs that require frequent viewing distance changes include teaching, performing arts, public speaking, sales and flight attendant. Unfavourable occupations requiring prolonged distance or near vision or good stereoacuity include commercial driver, surgeon, seamstress and pilot. Personality is considered, with perseverance a more important trait than motivation, Dr Jackson said (DuToit R et al. Optom Vis Sci. 1998;27:119-125). Introverted men do not adapt well (Erickson DB, Erickson P. Percept Mot Skills. 2000). Prior wearers of contact lenses adapt most easily, Dr Jackson noted. “Actually, if blended vision is not given these patients will be extremely unhappy because it is what they are used to.” He typically does a contact lens trial for six weeks or more before surgery. The longer they have done it the more likely they are to tolerate it. Still, patients should be prepared for an adaptation period for night vision. It is worth considering prescribing spectacles for night driving and low-light tasks. Eye dominance is also important, with about 75-to-80% preferring the dominant eye for distance – though up to 25% may strongly prefer the dominant eye for near, so it’s important to figure that out, Dr Jackson said. Monovision is most successful in patients with alternating dominance, which allows for better blur suppression. To determine dominance Dr Jackson typically uses a motor eye technique, sometimes as simple as asking a patient to close one eye and look at his finger across the room. “They don’t know what you are testing for and usually the unclosed eye is dominant,” he said. The amount of myopia induced in the near eye depends to an extent on occupation and frequent activities, with -1.00 dioptre affecting stereoacuity very little but giving poor near vision, out to -2.00 dioptres delivering J2 to J1 near, but stereoacuity about half of normal at about 158 arc seconds (Hayashi K et al. J Refract Surg. 2010 Sept 1:1-7.) Dr Jackson usually targets about -1.5 dioptres for the near eye and plano for the distance eye, which must be perfect. He recommended correcting astigmatism with a monofocal toric lens, and using lenses such as Crystalens, Trulign or Envista to extend the depth of the blended vision zone. Options for correcting distance vision after surgery, such as contact lenses or laser vision correction, should be in place. Natural vision While “natural vision” attempts to replicate some of the range of natural youthful vision, it actually imposes a static multifocal solution in place of a dynamic accommodating system, Dr Jackson said. “There are good, but not perfect, options available – EDOF, trifocals and low-add bifocals. But perfect, not good, candidates are needed,” he added. Because stable tear film is essential for good multifocal lens performance, a “perfect” candidate starts with pristine ocular surface in terms of osmolarity, MMP-9 presence, low ocular surface disease index and functional meibomian glands. No macular pathology should be present, Dr Jackson said. Because multifocal IOLs depend on precise refraction, corneal topography, tomography and epithelial mapping should show the possibility of correcting any residual refractive error with PRK, LASIK or SMILE®, Dr Jackson added. Corneal astigmatism should be corrected, preferably with a toric IOL if it exceeds 0.77D. Multifocal lenses should not be implanted in patients with an angle alpha or kappa of greater than 0.7 mm, or with corneas with a higher-order aberration RMS greater than 0.38 microns. For optimal predictive precision, Dr Jackson recommended using fourth-generation IOL formulae, such as the Barrett, Barrett True K, Hill-RBF or Holladay 2. Selecting a proper refractive target is also critical for success, and this can vary by patient and lens, Dr Jackson said. For example, in a study he conducted with fellows, Dr Jackson determined that optimal vision was achieved in patients receiving bilateral extended depth of focus lenses with the dominant eye targeting emmetropia and the non-dominant eye between -0.21 and -0.63D (Jackson M et al. Clin Ophthalmol 2020;14:455-62). For the trifocal PanOptix lens, he targets plano dominant and one click below plano for the non-dominant eye. And always, realistic patient expectations should be reinforced in terms of near, intermediate and distance vision, glare and low light performance, and adaptation time, Dr Jackson concluded.