Small-aperture IOL poised to fill unmet need

Approved for use in Europe, the small-aperture IOL IC-8 (Acufocus) is proving to be a very useful implant, particularly for patients who are not good candidates for current multifocal (MF), accommodating or extended depth-of-focus technology.

The small aperture lens approach to vision correction is based on pinhole optics—a novel property not found in other available lenses.

The pinhole optic blocks out-of-focus, stray light, thereby creating a depth of focus with the small aperture of 1.36 mm allowing for a continuum of vision.

The lens is forgiving, with a broad landing zone that makes it virtually immune to up to 1.50 D of astigmatism, while at the same time offering high-quality, sharp vision and less concern with photic phenomena.

The IC-8 is a single-piece, hydrophobic acrylic IOL embedded with an opaque mini-ring. Besides Europe, it is also approved for use in Asia and is currently being investigated in clinical trials in the United States.

A retrospective comparative review of studies assessed the range and quality of vision with small-aperture, accommodating or MF IOLs.¹

The IC-8 IOL was found to enhance vision at all distances, with improved visual acuities and a broad range of continuous functional vision.

Likewise, the patients receiving this implant experienced superior intermediate vision and binocular mesopic contrast sensitivity, which is comparable to the other lenses.

Review of the evidence
The small-aperture IOL was paired with an aspheric monofocal IOL and compared with bilateral implantation of the MF lens Acrysof ReSTOR +3.00 D (Alcon) and MF IOL Tecnis +4.00 D (Johnson & Johnson Vision), and with the accommodative Crystalens AO (Bausch + Lomb).

The IC-8 cohort comprised 105 patients,with the Restor, Tecnis and Crystalens platforms implanted into 25, 22 and 26 study subjects, respectively.

Investigators examined 6-month postoperative monocular uncorrected and distance-corrected vision at distance (4 m for IC-8, 6 m for others), intermediate (67 cm for IC-8, 80 cm for others) and near visual acuities (all 40 cm).

They looked at defocus curves (binocular for IC-8, monocular for others) and compared binocular mesopic contrast sensitivity with and without glare.

Defocus curve
The defocus curves revealed that the small-aperture lens had a 4.50 D continuous expanse of vision compared with 4.50 D for Restor, 4.00 D for Tecnis and 2.50 D for Crystalens – but the latter three were not continuous.

Rather, the others showed a dip in the middle range for intermediate vision (Figure 1).

The IC-8 IOL and Crystalens gave excellent intermediate vision, better than MFs, and MFs produced better near vision. The mean uncorrected near visual acuity (UNVA) for the new lens was 0.18 and 0.19 for the Tecnis. The Restor lens performed better with a UNVA at 0.01; Crystalens had a worse UNVA at 0.26 (P < 0.01).

All four IOL groups had a similar mean uncorrected distance visual acuity (0.02–0.11). The small-aperture lens and Crystalens had a mean uncorrected intermediate visual acuity of 0.08 and 0.07. This was almost a 2-line improvement over Restor and Tecnis (0.24, P < 0.0001).

Symptomology and contrast sensitivity
Unwanted visual effects such as blurring, fluctuating vision and ghosting were of low severity in all the lenses studied, with a very low ghosting score for the IC-8 lens.

Along with the Crystalens, the small-aperture IOL elicited very few reports of halos when both were compared with the two MF lenses, which received higher scores for halo and glare (Figure 2).

With regard to contrast sensitivity, the lenses were binocularly comparable. For contrast sensitivity with and without glare, the IC-8 lens and Restor groups were similar across all spatial frequencies.

The small-aperture lens group was worse than Crystalens at 6 cycles per degree (cpd), but better than Tecnis at 3 cpd, and with no glare (P < 0.05).

Summary findings
When compared with accommodating or MF IOLs, the IC-8 IOL enhanced vision at all distances and provided both improved visual acuities and a broad range of continuous functional vision.

Likewise, the patients receiving this lens experienced superior intermediate vision and binocular mesopic contrast sensitivity comparable to the other lenses.

The IOL has minimal impact on the ability to visualise the retina with optical coherence tomography or on visual fields.

One study recently showed that even with bilateral implantation, patients experience a minimal change in contrast.²

The expanded depth of focus with the small-aperture lens allows refractive surgeons to target roughly -0.75 D without really losing much distance.

The IC-8 lens proved tolerant of up to 1.00 D deviation from the refractive target and it corrects up to 1.50 D of corneal astigmatism free from the concerns that accompany toric technology. One should remember that every degree of rotation is about a 3.3% reduction in the offset of the astigmatism.³

In addition, toric lenses do not come in every power. Even just 0.75 D of residual astigmatism has a significant impact on MF lens performance at all distances.

In studies of the IC-8 IOL versus the standard monofocal implanted contralaterally, even those small-aperture eyes that miss target by 0.50 D to 1.50 D still experience only a slight impact on vision – maybe within 1 line on an EDTRS chart. With the monofocal on the other hand, the result can be as much as 3 lines if the target it missed.

Conclusion
The IC-8 IOL should prove particularly useful for patients with previous refractive surgery and corneal aberrations, extending to those with irregular astigmatism from trauma, a small iris defect or in a pupil that is not completely round, for example.

In eyes with any type of irregularity or an aberrated cornea that could cause a high angle kappa and therefore impact the central ring, the implant should be a ‘shoo-in’.

For those patients who are not good candidates for other premium technology, the IC-8 lens gives surgeons something unique to offer.

This IOL is forgiving in terms of hitting both targets, sphere and cylinder with a broad landing zone; has a very low dysphotopsia rate; and results in high patient satisfaction. In fact, 95% of small-aperture patients reported that they would undergo the procedure again.

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Jay Pepose, MD, PhD
E: jpepose@peposevision.com
Dr Pepose is a professor of clinical ophthalmology at Washington University’s School of Medicine, United States, and director of the Pepose Vision Institute in St. Louis, Missouri. Dr Pepose is an investigator for the IC-8 IOL clinical study.

References

1. Pepose J. Evaluating visual performance of small-aperture, accommodating, and multifocal IOLs. Presented at: AAO 2019; October 11-15; San Francisco, California, US.

2. Ang RE. Visual performance of a small-aperture intraocular lens: first comparison of results after contralateral and bilateral implantation. J Refract Surg. 2020;36:12-19. Doi: 10.3928/1081597X-20191114-01.

3. Novis C. Astigmatism and toric intraocular lenses. Curr Opin Ophthalmol. 2000;11:47–50.