An alternative approach to spectacle independence

Presbyopia treatment strategies for spectacle independence usually utilise multifocality or monovision through various corneal or lens-based procedures.¹ However, multifocal strategies are sometimes associated with poor visual quality due to photic phenomena and loss of contrast sensitivity.¹ Monovision arrangements, on the other hand, are associated with reduced stereoacuity and insufficient intermediate vision.^1,2 In recent years, researchers have developed novel IOLs and corneal procedures that function by creating an extended depth of focus (EDOF) to provide continuous vision over a range of distances, achieving the range of vision obtained with multifocal and monovision modalities while avoiding some of their limitations.¹

Laser blended vision

Laser blended vision refers to presbyopia correction by excimer laser–induced corneal spherical aberration combined with micro-anisometropia. PRESBYOND Laser Blended Vision (PRESBYOND LBV) involves nonlinear aspheric corneal ablation with the MEL 80 or MEL 90 excimer laser platform (Carl Zeiss Meditec AG, Jena, Germany) to induce controlled spherical aberrations in the cornea, which extend its depth of focus. This is combined with a small anisometropia (up to 1.50 D). The EDOF created by the spherical aberrations allows seamless merging of vision in both eyes, creating a blend zone of binocular vision as opposed to the blur zone seen with monovision therapy (Figure).^1,3 This allows continuous vision at distance, intermediate and near range, with good stereoacuity and contrast sensitivity.^1,4 Spectacle independence is maintained with high patient satisfaction.^1,4

Figure. Blur zone in monovision causes poor intermediate vision (top) while blend zone in PRESBYOND Laser Blended Vision provides overlap in binocular vision and extends depth of field (bottom). Image courtesy of Dr van Zyl

As LBV is essentially a LASIK procedure, it is contraindicated in patients with thin corneas, media opacities, or coexisting ocular pathologies affecting visual acuity.⁵ In such cases, the only alternatives for spectacle-free presbyopia management are lens-based strategies.

EDOF IOLs utilise various mechanisms to create an elongated focal point, extending the depth of field and providing good quality of vision at distance and intermediate range. However, patients usually need glasses due to unsatisfactory near vision with these IOLs, unless they are implanted in a monovision configuration.^6,7 Most manufacturers of EDOF IOLs recommend a small amount of anisometropia of not more than -0.5 D, but this small offset does not allow for sufficient near vision.

Both EDOF IOLs and PRESBYOND LBV involve the creation of an extended depth of focus and provide good near vision when combined with mild anisometropia. This similarity in their working principles was something I thought could be reproduced by bilaterally implanting EDOF IOL in a PRESBYOND-like anisometropic arrangement, thus bringing the benefits of laser blended vision to patients when it would not normally be suitable for them.

Early experience

For this procedure, I used the AT LARA 829MP EDOF IOL (Carl Zeiss Meditec AG) which utilises spherical and chromatic aberration correction to achieve a wide depth of focus (~ 1.90 D) while reducing dysphotopsias and maintaining contrast sensitivity.⁶ Although it is recommended that anisometropia for monovision arrangements be around 0.75D to 1.00D, the reduction in anisometropia results in a reduction in near vision.^7,8 I believed that 1.50D anisometropia, as induced in LBV, would still be tolerated by patients after EDOF IOL implantation, as the extended depth of focus would lead to binocular blending of vision, similar to that seen in LBV. This would achieve similar range of vision as seen with multifocal IOLs but with better contrast, less glares and halos, and better nighttime vision. In the few cases implanted with this strategy thus far, the results have been encouraging. The refractive status and visual acuity outcomes of all patients are summarised in the Table.

Table. BCVA, best corrected visual acuity; postop, postoperative; preop, preoperative; UDVA, uncorrected distance visual acuity; UNVA, uncorrected near visual acuity.

Patients with thin corneas unfit for LBV were good candidates for this surgery. One such patient was a 47-year-old man with moderate hyperopic astigmatism (case 1) who wanted PRESBYOND LBV because his friend had undergone the same procedure in our clinic and was very satisfied with the results. However, on pachymetry, corneal thickness in both eyes was below 460 µm, making him unsuitable for LBV. On anisometropia tolerance testing at 1.50D (blur test as done prior to PRESBYOND), he noticed a cross-blur, so anisometropia was reduced to 1.00D, with which he was comfortable. As his right eye was dominant, emmetropia was targeted in OD and 1.00D postoperative refraction was targeted in OS. Postoperatively, on monocular unaided vision testing, the patient was emmetropic for distance in the dominant eye, with slightly worse distance vision in the nondominant eye, as expected. On binocular unaided vision testing, the patient was emmetropic at distance as well as near. The patient did not need reading glasses even in dim light.

A similar case was that of a 54-year-old man with moderate hyperopic astigmatism and presbyopia who also had thin corneas unsuitable for LBV (case 2). Refractive lens exchange was done after the patient passed 1.5D anisometropia testing. Postoperatively, he had above average binocular unaided visual acuity at distance and near.

Another group of patients unfit for LBV are those with cataracts. A 58-year-old woman with reduced distance vision had been referred to our clinic for cataract removal (case 3). She desired spectacle independence, therefore, the EDOF IOL was bilaterally implanted after 1.5D anisometropia tolerance testing. On binocular unaided vision testing postoperatively, the patient was emmetropic for distance and was able to read the smallest print on the near vision chart.

A 68-year-old man with decreased distance and near visual acuity due to cataract and presbyopia had been referred to our clinic (case 4). He was very active and enjoyed surfing, tennis and cycling. Naturally, he wanted to be as spectacle independent as possible after the surgery. His postoperative unaided binocular vision was emmetropic for distance and above average for near. The patient was very happy to be able to continue being active in outdoor sports without needing glasses.

A 51-year-old man, who had cataract with myopic astigmatism and presbyopia, had requested spectacle independence as he was tired of putting his glasses on and off to read (case 5). His postoperative binocular unaided vision was above average at distance as well as near.

All five patients achieved complete spectacle independence and were very satisfied with the quality of vision achieved, reporting clear vision at all ranges. They were especially happy with the freedom from using glasses. Patients did experience occasional glare but none found it bothersome.

Conclusion

Implantation of the AT LARA 829MP EDOF IOL in 1.00 D to
1.50 D anisometropic arrangement achieved spectacle independence and clear vision at all ranges with good binocularity and preserved visual quality. This strategy can provide an alternate route to spectacle independence for patients for whom laser blended vision therapy is not suitable.

References

1. Russo A, Reinstein DZ, Filini O, et al. Visual and refractive outcomes following laser blended vision with non-linear aspheric micro-anisometropia (PRESBYOND) in myopic and hyperopic patients. J Refract Surg. 2022;38(5):288-297. doi:10.3928/1081597X-20220323-01

2. Labiris G, Toli A, Perente A, Ntonti P, Kozobolis VP. A systematic review of pseudophakic monovision for presbyopia correction. Int J Ophthalmol. 2017;10(6):992-1000. doi:10.18240/ijo.2017.06.24

3. Zheleznyak L, Sabesan R, Oh JS, MacRae S, Yoon G. Modified monovision with spherical aberration to improve presbyopic through-focus visual performance. Invest Ophthalmol Vis Sci. 2013;54(5):3157. doi:10.1167/iovs.12-11050

4. Shetty R, Brar S, Sharma M, Dadachanji Z, Lalgudi V. PresbyLASIK: a review of PresbyMAX, Supracor, and laser blended vision: principles, planning, and outcomes. Indian J Ophthalmol. 2020;68(12):2723. doi:10.4103/ijo.IJO_32_20

5. Patient selection refractive laser treatment. ZEISS. Accessed December 28, 2023.
https://www.zeiss.co.uk/content/dam/Meditec/gb/Chris/Refractive-
Business-Builder/UpdatedFiles/
refractive_lasers_patient_selection.pdf

6. Megiddo-Barnir E, Alió JL. Latest development in extended depth-of-focus intraocular lenses: an update. Asia Pac J Ophthalmol (Phila). 2023;12(1):58-79. doi:10.1097/APO.0000000000000590

7. Cochener B. Influence of the level of monovision on visual outcome with an extended range of vision intraocular lens. Clin Ophthalmol. 2018;12:2305-2312. doi:10.2147/OPTH.S184712

8. Næser K, Hjortdal JØ, Harris WF. Pseudophakic monovision: optimal distribution of refractions. Acta Ophthalmol. 2014;92(3):270-275. doi:10.1111/aos.12148

Dr Lourens van Zyl, MBChB, FCOphth, FRANZCO, FEBO, FRCSI, FWCRS, MMed(RefCatSurg) | E: lourens.vanzyl@crystaleye.com.au

van Zyl is the principal ophthalmologist at Crystal Eye & Laser Centre, Western Australia. He has a special interest in laser eye surgery and advanced vision correction surgery including cataracts.

Financial disclosure: None