Surgeon shares experiences with small-aperture lens
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Small-aperture optics, whether through a pinhole IOL, pinhole pupilloplasty or presbyopia-correcting drops, can help patients tremendously.
H. Burkhard Dick, MD, PhD, FEBOS-CR, of Germany, my guest for this column, is a pioneer of pinhole IOLs. Other pioneers who have helped take pinhole IOLs to such a great level include the Trindade family in Brazil and Richard L. Lindstrom, MD, in the United States.
Amar Agarwal, MS, FRCS, FRCOphth
OSN Complications Consult Editor
The options for surgical presbyopia control are ever expanding and obviously not affected by the pandemic. Among the different concepts for extended depth of focus (EDOF) lenses, there is a design whose origins date back more than 400 years.
It was around 1600 when Christoph Scheiner, who was both a cleric in southern Germany and a scientist, made a remarkable observation that he described in his correspondence to other learned minds: If one looks through a very small hole, vision becomes sharper. Even an eye with “weakness” — by later generations called myopia — might suddenly distinguish objects farther away, although at the price of reduced light perception. As Scheiner hypothesized, channeling light through a small hole blocks stray light and unfocused light from the periphery and sharpens vision. This principle of providing an extended depth of focus is now known as the pinhole effect or, better, the small aperture.
The pinhole principle these days is at work in contact lenses, corneal implants and IOLs, but also in the normal eye. With a small pupil, it is primarily the paraxial light rays that reach the retina while light rays from the more aberrated peripheral cornea are blocked.
IC-8 IOL
We were able to gather a lot of clinical experience with the IC-8 (AcuFocus), a one-piece hydrophobic acrylic posterior chamber monofocal small-aperture IOL with an optic that contains an embedded mask with a 1.36-mm central aperture. The mask, which acts as an aperture, is made up of about 3,200 mini-perforations. The IC-8 is usually implanted in the capsular bag of the nondominant eye with a target refraction of –0.75 D (Figure 1). The fellow eye usually receives an aspheric monofocal IOL.
Source: H. Burkhard Dick, MD, PhD, FEBOS-CR
The IC-8 might lead to good results in a difficult segment of patients: the aging “first generation” of refractive patients who underwent early keratorefractive procedures such as PRK and later LASIK, a generation that is now reaching the presbyopia age and in some cases even the cataract age and still cherishes and expects spectacle independence. The greater degree of forgiveness of a small-aperture IOL could be beneficial in post-refractive eyes in which a greater deviation from target refraction can be expected due to the unpredictability of IOL power calculations in such eyes. Beyond patients with a history of corneal refractive surgery, small-aperture IOLs also offer an opportunity to improve vision in eyes with scars, iris damage or corneal irregularities that could be masked by the opaque annulus.
The implantation of the IC-8 does not differ from normal cataract surgery. In all of our cases, topical anesthesia is administered three times, and pharmacologic mydriasis is induced. Two side-port paracenteses are performed. Next, the anterior chamber is filled with ophthalmic viscosurgical device (OVD), and a capsulorrhexis as well as hydrodissection and hydrodelineation are performed. A clear corneal incision of up to 3.25 mm in width is made. Phacoemulsification of the nucleus is performed using the Stellaris Elite phacoemulsification machine (Bausch + Lomb). After aspiration of the nucleus, the residual cortex is removed with bimanual irrigation and aspiration, and the small-aperture lens is implanted just like any other IOL in the capsular bag using the injection system provided by the manufacturer. Finally, after OVD removal, corneal wounds are closed, if needed, with balanced salt solution for watertightness, and antibiotic and steroidal ointment are applied.
The overly satisfied patient syndrome
After having implanted the IC-8 in a significant number of patients in one eye, we were faced with what can be called “the overly satisfied patient syndrome.” Some patients who had the IC-8 implanted in their nondominant eye were so happy about the outcome that they became interested in having the same type of IOL implanted in their dominant eye when the time for surgery seemed ripe. So, we had the opportunity to evaluate the clinical outcomes of a binocular implantation in a small group of six patients. This resulted in an extended depth of focus and better intermediate as well as near vision; monocular implantation, however, led to higher overall patient satisfaction, which may be influenced by the slightly higher symptom score for halos in the bilateral group.
Our generally positive experience was shared by other surgeons in the literature. In an international multicenter study, the small-aperture IOL was implanted in 105 patients. The results can only be described as encouraging: At 6 months, the uncorrected distance visual acuity (UDVA), uncorrected intermediate visual acuity (UIVA) and uncorrected near visual acuity (UNVA) in eyes with the small-aperture IOL were 20/23, 20/24 and 20/30, respectively; 99%, 95% and 79% of patients achieved 20/32 or better binocular UDVA, UIVA and UNVA, respectively. The mean binocular uncorrected visual acuities were unchanged between all postoperative visits. The satisfaction rate among patients was high. Almost 85% said they are now never or only occasionally using spectacles since implantation of the IC-8, and only 6.7% were wearing glasses most of the time. Asked if they would undergo the procedure again, 95% answered in the affirmative. More than half of the patients implanted with the IC-8 will enjoy complete spectacle independence, as Hooshmand and colleagues demonstrated in a series of 126 patients, of whom 98% achieved UDVA of 6/9, 94% achieved UIVA of 6/12 and 91% achieved UNVA of 6/12. Those who still had to resort to spectacles in this group did so only for specific tasks such as near-vision hobbies and reading under less than perfect light conditions.
Retinal examination
A question that naturally arises when ophthalmologists implant a small aperture in the center of a mask into the anterior segment that blocks light from entering the eye: How about the reverse? Will it affect the eye care provider’s ability to take a look at the posterior segment and to visualize the retina? This is a particularly crucial issue in patients with additional posterior segment pathology such as diabetic retinopathy or disease of the macula (Figure 2). In our experience, the small-aperture lens does not pose a major obstacle to retinal diagnostics or retinal surgery. We have been able to perform epiretinal membrane peel and pars plana vitrectomy of diabetic retinopathy. Yet, it has to be acknowledged that performing these procedures is not as easy as it would be with an ordinary monofocal IOL, but any experienced posterior segment surgeon should be capable to perform these interventions after some adjustments.
XtraFocus pinhole implant
While our clinical experience with small-aperture IOL optics is based on the IC-8, it should be mentioned that there is another product on the market employing the pinhole principle. It is, however, not an IOL because the device, the XtraFocus pinhole implant (Morcher), does not have any refractive power. It is rather a diaphragm to be placed in the sulcus of pseudophakic eyes, ie, in patients who have severe corneal alterations or irregularities and are dissatisfied with their vision (Figure 3). It is a device made of a black hydrophobic acrylic material with an overall diameter of 14 mm, with a 6 mm occlusive portion and a central aperture of 1.3 mm. It has an optic-haptic angulation of 14° to prevent iris chafing and a concave-convex design to prevent contact with the primary IOL already implanted in the capsular bag.
Summary
As always in refractive surgery, careful patient selection is key to success and mutual satisfaction. Patients should also be counseled on lifestyle and vision requirements to manage their expectations after surgery. Patients who require intermediate and near vision and patients with irregular pupils because of iris trauma or with abnormal corneas after keratorefractive procedures are definitely good candidates for the small-aperture IOL.
Last but not least, the positive effect of the IC-8 on preexisting astigmatism should be noted. The lens is remarkably tolerant of astigmatism — in our experience up to 1.5 D of cylinder and sometimes even of higher corneal irregularities.
As every cataract surgeon knows, when implanting a toric IOL, the success is highly dependent on a stable position and avoiding rotation. A rotation of 5°, for instance, results in a reduction of the toric IOL’s effectiveness to 83.5%; with a 30° rotation, the toric effect of the IOL is completely lost. Because of the optical properties of the small aperture, rotation of the IC-8 is basically irrelevant. The symmetric nature of the small aperture mitigates the influence of the astigmatism axis and eliminates the need for alignment. As Robert Ang, our colleague from the Philippines who has published on the matter, said: “You don’t have to worry about alignment if you are using an IC-8. It provides surgeons with a good solution for addressing low levels of preexisting astigmatism and reduces the influence of residual or induced corneal astigmatism.” We couldn’t agree more.
- References:
- Ang RE. Clin Ophthalmol. 2018;doi:10.2147/OPTH.S172557.
- Dick HB. Curr Opin Ophthalmol. 2019;doi:10.1097/ICU.0000000000000576.
- Dick HB, et al. J Cataract Refract Surg. 2017;doi:10.1016/j.jcrs.2017.04.038.
- Dick HB, et al. J Refract Surg. 2018;doi:10.3928/1081597X-20180716-02.
- Hooshmand J, et al. Eye (Lond). 2019;doi:10.1038/s41433-019-0363-9.
- Schojai M, et al. J Cataract Refract Surg. 2020;doi:10.1097/j.jcrs.0000000000000068.
- Srinivasan S. J Cataract Refract Surg. 2018;doi:10.1016/j.jcrs.2018.07.002.
- For more information:
- H. Burkhard Dick, MD, PhD, FEBOS-CR, can be reached at University Eye Hospital, University of Bochum, In der Schornau 23-25, 44892 Bochum, Germany; email: burkhard.dick@kk-bochum.de.
- Edited by Amar Agarwal, MS, FRCS, FRCOphth, director of Dr. Agarwal’s Eye Hospital and Eye Research Centre. Agarwal is the author of several books published by SLACK Books, sister company of Healio publisher Ocular Surgery News, including Phaco Nightmares: Conquering Cataract Catastrophes, Bimanual Phaco: Mastering the Phakonit/MICS Technique, Dry Eye: A Practical Guide to Ocular Surface Disorders and Stem Cell Surgery and Presbyopia: A Surgical Textbook. He can be reached at 19 Cathedral Road, Chennai 600 086, India; email: aehl19c@gmail.com; website: www.dragarwal.com.
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