Presbyopia-correcting IOLs

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Introduction

Intraocular lens implants (IOLs) are used in both refractive lens exchange and cataract surgery to replace the natural lens of the eyes and correct for refractive errors. Over recent years, many improvements in intraocular lenses have allowed for the development of a wide-spectrum of lenses beyond the traditional monofocal lens implants. These developments include presbyopia-correcting IOLs which provide a treatment option for presbyopic patients who do not qualify for laser refractive surgery and do not want to rely on reading glasses.[1] Presbyopia-correcting lenses can be divided into two broad categories: multifocal IOLs and accommodative IOLs. 

Multifocal IOLs

Multifocal IOLs consist of multiple zones of lens power that produce more than one focal point, allowing for enhanced vision at both near and far.[2]  The multifocal IOLs can be further subdivided into diffractive and refractive lenses.

Diffractive IOLs

Diffractive IOLs such as Tecnis and ReSTOR create two distinct images at near and far.[3] ReSTOR was the first diffractive lens approved by the FDA in 2005.[1] Its mechanism of action is based on apodization, in which a near-dominant central area is surrounded by 12 concentric rings of decreasing height that result in diffraction of light at both distance and near.[1] The Tecnis diffractive IOL is an acrylic lens with an aspheric anterior surface and a posterior surface with diffractive rings that focus both near and distance light regardless of pupil size.[1] Diffractive IOLS are typically less limited by pupillary diameter, but can result in poorer intermediate vision.[4]

ReSTOR multifocal IOL. © 2017 American Academy of Ophthalmology

Refractive IOLs

Refractive IOLs such as ReZoom and Array function by creating multiple focal points that allow for viewing at all distances.[3] The Array zonal progressive silicone IOL consists of five concentric zones alternating between distance- and near- dominant.[2] The ReZoom IOL is a second-generation refractive IOL, that enhanced some aspects of the Array design, such as enlargement of the second and third zones, reduction of the fourth and fifth zones and an aspheric transition between zones so that visual disturbances could be reduced.[1] While refractive IOLs produce good quality distance, intermediate, and near vision, they are limited by pupillary diameter because of the zonal design of the lens.[4]

Accommodative IOLs

The only accommodative IOL to be FDA-approved is the Crystalens IOL, a 4.5 mm optic with two haptic plates and four polyimide loops that help fix it into place within the capsular bag.[5] Its placement within the capsular bag allows it to simulate the natural accommodative process in the eye by changing power in response to ciliary muscle contraction.[5] The Crystalens accommodative IOL provides good distance vision and the advantage of fewer visual disturbances compared to multifocal IOLs.[5]

Close-up of Crystalens HD IOL. © 2017 American Academy of Ophthalmology

Outcomes

Patients with diffractive and refractive multifocal lenses have better near vision than those with accommodating lenses and monofocal lenses.[6] In a prospective randomized study comparing Crystalens, ReSTOR, and Tecnis IOLs, the ReSTOR demonstrated better UNVA compared with Crystalens and Tecnis, with the Crystalens accommodating IOL demonstrating better intermediate and low-contrast distance-corrected vision compared to ReSTOR and Tecnis.[7],[8] However, there was no difference in uncorrected distance visual acuity (UDVA) between the three groups.[7]A meta-analysis of 20 clinical trials looking at 11 monofocal and 35 multifocal IOLs, also found that patients with the ReSTOR IOL had significantly better UNVA than all other multifocal IOLs.[9]

When multifocal IOLs are compared to other treatment modalities such as laser in-situ keratomileusis (LASIK) monovision, they demonstrate significantly better UNVA.[10] LASIK monovision, however, produces better uncorrected intermediate visual acuity (UIVA) and UDVA than multifocal IOLs as well as less visual disturbances.[10]

Complications

IOL implantation after cataract extraction or as part of refractive lens exchange is a relatively safe procedure but carries the risks that come with invasive eye surgery. These surgical complications include, but are not limited to infection, increased IOP, corneal edema, posterior capsular opacification (PCO), IOL decentration, and retinal detachment.

The other major side effect experienced by patients after IOL implantation are visual disturbances. Reduced visual quality and visual phenomena such as halos, glare, and starbursts are characteristic of multifocal IOLs due to the light scatter that naturally occurs when transitioning between near and far zones .[11]  Patients with monofocal IOLs experienced less visual distortions and halos compared to patients with multifocal IOLs.[12] In a prospective study of 95 eyes comparing multifocal IOLs to monofocal IOLs, 29% of multifocal patients reported glare while 25% reported halos, compared to 19% and 12% in the monofocal group, respectively.[13] Accommodative IOLs as a whole produce less visual disturbances compared to multifocal IOLs. This can be explained by the design of the accommodative lens which contains a smooth central surface and acts to enhance near vision through movement in conjunction with ciliary muscle contraction. This is in contrast with multiple zones of optical power in a multifocal IOL that can result in scattering of light and visual disturbances. 

Patient Satisfaction

Intraocular lenses produce high levels of satisfaction and freedom from spectacles. ReSTOR IOLs produced high levels of patient satisfaction, with 93.1% of patients reporting a positive change in vision, 88.2% reporting better postoperative vision, and 78% reporting resolution of their vision problems.[14] In addition, spectacle-free rate improved significantly from just 6.4% preoperatively to 87.2% after ReSTOR implantation.[14] Another prospective study using the ReSTOR IOL after bilateral refractive lens exchange, found that all patients reported satisfaction with their visual outcomes, but rated intermediate vision lowest.[15] A study comparing the Tecnis diffractive IOL to the ReZoom refractive IOL found higher levels of patient satisfaction and less visual disturbances in the Tecnis group, but less reported problems with intermediate vision in the ReZoom group, despite no differences in near or distance uncorrected vision between the two groups.[3] This may be explained by the nature of the two lenses, with diffractive lenses producing clear images at near and far with less-than-optimal intermediate vision, and refractive lenses improving vision at all distances. The Crystalens accommodative IOL produced good patient satisfaction with patients reporting adequate vision at all distances in order to complete activities of daily living, with the exception of needing reading glasses for fine newspaper print.[16]

Despite the high level of patient satisfaction with IOLs, studies have demonstrated that patients are no more satisfied with IOLs than with other correction strategies. In a meta-analysis of 20 clinical trials comparing multifocal and monofocal lenses, patients with multifocal IOLs were 3.6 times less likely to require spectacles compared to patients with monofocal IOLs.[9] However, there was no difference in patient satisfaction between patients in the monofocal and multifocal groups.[9],[12] A prospective study comparing refractive lens exchange with multifocal IOL implantation to LASIK-induced monovision, found no significant difference in patient satisfaction or spectacle dependency between the two groups.[10]  Although the new generation multifocal IOLs are an effective means of presbyopic correction, patients seem to be no more satisfied with them than other corrective modalities.

References

  1. 1.0 1.1 1.2 1.3 1.4 Lichtinger A, Rootman DS. Intraocular lenses for presbyopia correction: past, present, and future. Curr Opin Ophthalmol. 2012 Jan;23(1):40-6.
  2. 2.0 2.1 Hoffman RS, Fine IH, Packer M. Refractive lens exchange with a multifocal intraocular lens. Curr Opin Ophthalmol. 2003 Feb;14(1):24-30.
  3. 3.0 3.1 3.2 Barisic A, Dekaris I, Gabric N, Bohac M, Romac I, Mravicic I, Lazic R. Comparison of diffractive and refractive multifocal intraocular lenses in presbyopia treatment. Coll Antropol. 2008 Oct;32 Suppl 2:27-31.
  4. 4.0 4.1 Montes-Mico R, Ferrer-Blasco T, Charman WN, Cervino A, Alfonso JF, Fernandez-Vega L. Optical quality of the eye after lens replacement with a pseudoaccommodating intraocular lens. J Cataract Refract Surg. 2008 May;34(5):763-8. doi: 10.1016/j.jcrs.2008.01.017.
  5. 5.0 5.1 5.2 Doane JF. Accommodating intraocular lenses. Curr Opin Ophthalmol. 2004 Feb;15(1):16-21.
  6. Mesci C, Erbil HH, Olgun A, Yaylali SA. Visual performances with monofocal, accommodating, and multifocal intraocular lenses in patients with unilateral cataract. Am J Ophthalmol. 2010 Nov;150(5):609-18. doi:10.1016/j.ajo.2010.05.023.
  7. 7.0 7.1 Pepose JS, Qazi MA, Chu R, Stahl J. A prospective randomized clinical evaluation of 3 presbyopia-correcting intraocular lenses after cataract extraction. Am J Ophthalmol. 2014 Sep;158(3):436-46.e1.
  8. Ang R, Martinez G, Cruz E, Tiongson A, Dela Cruz A. Prospective evaluation of visual outcomes with three presbyopia-correcting intraocular lenses following cataract surgery. Clin Ophthalmol. 2013;7:1811-23
  9. 9.0 9.1 9.2 Cochener B, Lafuma A, Khoshnood B, Courouve L, Berdeaux G. Comparison of outcomes with multifocal intraocular lenses: a meta-analysis. Clin Ophthalmol. 2011 Jan 7;5:45-56.
  10. 10.0 10.1 10.2 Barisic A, Gabric N, Dekaris I, Romac I, Bohac M, Juric B. Comparison of different presbyopia treatments: refractive lens exchange with multifocal intraocular lens implantation versus LASIK monovision. Coll Antropol. 2010 Apr;34 Suppl 2:95-8.
  11. Venter JA, Pelouskova M, Bull CE, Schallhorn SC, Hannan SJ. Visual outcomes and patient satisfaction with a rotational asymmetric refractive intraocular lens for emmetropic presbyopia. J Cataract Refract Surg. 2015 Mar;41(3):585-93.
  12. 12.0 12.1 Nijkamp MD, Dolders MG, de Brabander J, van den Borne B, Hendrikse F, Nuijts RM. Effectiveness of multifocal intraocular lenses to correct presbyopia after cataract surgery: a randomized controlled trial. Ophthalmology. 2004 Oct;111(10):1832-9. Erratum in: Ophthalmology. 2004 Nov;111(11):2022.
  13. Jacobi PC, Dietlein TS, Luke C, Jacobi FK. Multifocal intraocular lens implantation in prepresbyopic patients with unilateral cataract. Ophthalmology. 2002 Apr;109(4):680-6.
  14. 14.0 14.1 Cochener B, Fernandez-Vega L, Alfonso JF, Maurel F, Meunier J, Berdeaux G. Spectacle independence and subjective satisfaction of ReSTOR multifocal intraocular lens after cataract or presbyopia surgery in two European countries. Clin Ophthalmol. 2010 Mar 4;4:81-9.
  15. Alfonso JF, Fernandez-Vega L, Valcarcel B, Ferrer-Blasco T, Montes-Mico R. Outcomes and patient satisfaction after presbyopic bilateral lens exchange with the ResTOR IOL in emmetropic patients. J Refract Surg. 2010 Dec;26(12):927-33.
  16. Hantera MM, Hamed AM, Fekry Y, Shoheib EA. Initial experience with an accommodating intraocular lens: controlled prospective study. J Cataract Refract Surg. 2010 Jul;36(7):1167-72.