How pinhole camera effect in small-aperture implant corrects presbyopia
Figure 1
Figure 2
When paired with multifocal extended depth-of-field technology, the new, small aperture ocular IOL, IC-8, delivers excellent extended depth of focus at near, far and intermediate ranges whilst reducing halo and glare.
A new small-aperture ocular IOL, IC-8 (Acufocus), which is CE Marked and currently under investigation by the United States Food and Drug Administration (FDA) employs the pinhole camera effect to correct presbyopia. By flattening the defocus curve on both the myopic and hyperopic sides, the IOL essentially creates a small amount of myopia, thereby extending the patient’s depth of focus and eliminating visual effects from corneal astigmatism or other irregularities.
This high-technology, one-piece hydrophobic acrylic ocular implant comprises an embedded opaque annular mask with a central aperture. Aligned light rays converge through the 1.36-mm central aperture, while peripheral defocused and, often, aberrated rays are blocked from disrupting the image.
As a result, patients experience a continuous range of vison from near to far, including the increasingly important intermediate range. At 1.5- to 7-feet away, the intermediate range represents a critical zone of activity for most people. It is where we eat most of our meals, do our desk work and watch the majority of our large-screen media. It is where many people earn their livings, including refractive surgeons.
Originally intended to be paired with a monofocal IOL, it has been found that, when paired with a multifocal IOL, the IC-8 is better than previous alternatives at enhancing visual acuity at intermediate distances, and so has the potential to benefit this underserved cohort. Likewise, patients who have had previous refractive procedures are becoming more common.
As they proliferate, so does our necessity for techniques and technologies tailored to support their special needs. The IC-8 has shown good outcomes in these ‘veteran’ surgical patients.
Surgeons are only now beginning to appreciate the additional benefits made possible by combining the small-aperture lens with IOLs that function on completely different optical principles. Experimentation is ongoing, and this novel strategy may ultimately lead us to maximise the full potential of the IOL, providing patients with truly satisfying customised outcomes.Lens attributes
LOW-ADD MIOLS
Low-add multifocal lenses (MIOLs) have been shown to improve intermediate visual acuity and offer surgeons the ability to further individualise patients’ visual outcomes, particularly when mixed with another refractive technology. Combining a multifocal lens with a different type of lens also can act to minimise glare and halo, an intrinsic characteristic of MIOL optics.
It is well known that most types of presbyopia-correcting IOLs-including multifocal refractive and diffractive, and even the newest trifocal technology-sacrifice distance vision to some extent in order to correct near vision and induce a variable amount of dysphotopsias.1 One study of the AcrySof ReSTOR +2.50 D IOL (Alcon) found it provided good intermediate and functional near vision for patients who did not want to accept the higher potential for visual disturbances associated with the +3.00 D version of the same IOL, but wanted more near vision than a monofocal IOL generally provides.2
Another prospective comparative investigation evaluated bilateral cataract surgery using the +3.00 D AcrySof IOL or a +4.00 D power of the implant.3 The +3.00 D IOL provided superior uncorrected distance visual acuity, significantly better uncorrected intermediate visual acuity at 40, 50, 60 and 70 cm, and functional reading acuity at 38.9 cm. Eyes with the +3.00 D IOL had better intermediate vision than those with the +4.00 D model without compromising distance and near visual acuity.
MF EXTENDED DEPTH OF FOCUS
The Lentis Mplus LS-313 MF20 (Teleon; available in Europe but not in the US) is a foldable, one-piece, aspherical multifocal posterior chamber IOL that extends a patient’s depth of focus. Its refractive rotationally asymmetric design helps minimise the loss of light to below approximately 7%, thereby improving contrast and retinal image quality.
An evaluation of the implant, with +2.00 D of near add compared with +3.00 D, found superior visual outcomes from far distance to a near of about 25 cm with the latter lens. The +2.00 D demonstrated excellent visual results from far distance to an intermediate distance of about 50 cm.4Anchor with small-aperture approach
Unlike the aforementioned multifocal implants, the IC-8 IOL functions due to the pinhole effect: by reducing scattered light and permitting only parallel rays to reach the macula, depth of focus is extended and visual disturbances such as glare and halo are reduced. Small-aperture technology can even overcome problems with corneal asphericity and irregularities. Astigmatism up to 1.50 D can be corrected with the lens alone.5
Typically, the IC-8 IOL is implanted in the non-dominant eye, with a monofocal lens in the contralateral eye. To enhance acuity, the small-aperture IOL can be paired with other technologies, such a multifocal, a low-add multifocal or even a trifocal lens. There are many combinations to consider, with the basic idea being that using different types of implants can enhance the sharpness of vision at near, intermediate and distance, and minimise the side effects of the competing technologies.
Small-aperture plus EDOF technology
The ongoing prospective, multicentre Mosiac study was undertaken to evaluate visual outcomes from the combination of the IC-8 IOL and the Lentis LS-313 MF-20.6 Our group presented 5-month follow-up data on 13 patients with bilateral implantation of the IC-8 IOL with the Lentis LS-313 MF-20 with +2.00 D of near add. We looked at parameters including:
- Uncorrected and corrected (binocular) far, intermediate and near visual acuity;
- Defocus curves;
- Salzburg Reading Desk; and
- Photic phenomena (halo and glare simulator).
Included were the 26 eyes of 13 patients with cataracts whose average age was 68.5±10.8 years. The targeted refraction for the IC-8 IOL eyes was –0.43±0.18 D with an achieved refraction of 0.42±0.41 D.
The achieved refraction was within ±0.50 D 62% of the time. The targeted refraction for the MF-20 eyes was –0.15±0.16 D and the achieved refraction was –0.33±0.42 D. The achieved refraction was within ±0.50 D 85% of the time.
We found that patients had excellent binocular visual acuity at far and intermediate distances, as well as functional vision at near. Furthermore, they had functional reading acuity at near and intermediate distances, and there was a comparatively low incidence of photic phenomena (see Figures 1 and 2). The combination of the small-aperture implant with a low-add multifocal lens like the Lentis LS-313 MF-20 is a good treatment option for patients who are motivated to achieve spectacle independence.Implications and conclusion
Multifocal lens designs can exhibit pronounced peaks and troughs, but the IC-8 IOL provides uninterrupted functional vision over 3.00 D of defocus.7 The small-aperture principle has the ability to produce a high-quality full range of vision without blurry zones, and it is more forgiving of refractive error misses or surprises.
The implant has been shown to provide good visual outcomes in post-LASIK and post-RK eyes8, making it an attractive option for patients who previously could not find an appropriate presbyopia-correcting IOL. Likewise, patients with corneal irregularities can benefit from the technology’s ability to reduce aberrations.
When paired with multifocal extended depth-of-focus (EDOF) technology, the IC-8 delivers excellent EDOF at near, far and intermediate ranges whilst reducing halo and glare. It can enhance the physician’s ability to customise successful visual outcomes for each patient, even for those who have undergone previous refractive surgeries. Based on the simple, proven and ancient understanding of the pinhole’s effect on light ray alignment, this IOL is a versatile tool to help cataract patients achieve their paramount postoperative visual goals.
Disclosures:
1. Gundersen KG, Potvin R. Comparative visual performance with monofocal and multifocal intraocular lenses. Clin Ophthalmol. 2013;7:1979-1985.
2. de Vries NE, Webers CA, Montés-Micó R, Ferrer-Blasco T, Nuijts RM. Visual outcomes after cataract surgery with implantation of a +3.00 D or +4.00 D aspheric diffractive multifocal intraocular lens: Comparative study. J Cataract Refract Surg. 2010;36(8):1316-1322.
3. Linz K, Attia MS, Khoramnia R, et al. Clinical evaluation of reading performance using the Salzburg Reading Desk with a refractive rotational asymmetric multifocal intraocular lens. J Refract Surg. 2016;32(8):526-532.
4. Venter JA, Pelouskova M, Bull CE, et al. Visual outcomes and patient satisfaction with a rotational asymmetric refractive intraocular lens for emmetropic presbyopia. J Cataract Refract Surg. 2015;41(3):585-593.
5. Calvo-Sanz JA, Sánchez-Tena MA. Characterization of optical performance with defocusing curve: Analysis of two refractive intraocular lens models with high and medium addition. J Optom. 2018 Oct 31.
6. https://www.healio.com/ophthalmology/cataract-surgery/news/online/%7B2809ee76-e466-43fe-b70b-dd94ff661925%7D/video-edof-iol-using-pinhole-effect-lessens-ocular-effects.
7. Dick HB, Elling M, Schultz T. Binocular and monocular implantation of small-aperture intraocular lenses in cataract surgery. J Refract Surg. 2018;34(9):629-631.
8. Dick HB. Small-aperture strategies for the correction of presbyopia. Curr Opin Ophthalmol. 2019;30(4):236-242.
GERD U. AUFFARTH, MD, FEBO
E: auffarthg@aol.com
Prof. Auffarth is chairman and medical director of the Department of Ophthalmology of the University Clinic of Heidelberg, Heidelberg, Germany, director of the David J. Apple, MD International Laboratory of Ocular Pathology, and director of the International Vision Correction Research Center in Heidelberg. He receives research grants and lecture fees from Alcon, Johnson and Johnson, Zeiss, Hoya, Oculentis, Rayner, Acufocus, KOWA and Biotech.
