The first microincisional IOL was developed by Acritec (Berlin). Christine Kreiner helped develop the lens, and A. John Kanellopoulos, MD, of Athens, Greece, implanted the first one in 2000. Wayne Callahan, of Thinoptx (Abingdon, Va), designed a special rollable lens that used a Fresnel principle; and Jairo Hoyos, MD, from Barcelona, Spain, implanted the first ultrathin lens. I then modified it into a special 5-mm–optic rollable IOL,1-19 and created a technique to remove cataracts through the smallest incision possible.
On May 21, 2005, I used this technique (deemed the microphakonit technique) while using a 0.7-mm phaco needle tip with a 0.7-mm irrigating chopper for the first time (Figure 1). It was developed with the help of Larry Laks, of Microsurgical Technology (manufacturer of the instruments; Redmond, Wash). The challenge at present is the need for the IOL to pass through sub–1-mm incisions.
THINOPTX ULTRACHOICE 1.0
Thinoptx has patented technology that allows the manufacture of IOLs that are 100 µm thick with ±30.00 D of correction, so they may be implanted through incisions <1.5 mm. The hydrophilic lens can be inserted using a special injector, which rolls and injects the IOL. The surgeon can then move the lens into the capsular bag. The natural warmth of the eye causes the lens to open gradually (Figure 2).
The Ultrachoice 1.0 is manufactured to eliminate most spherical aberrations. Each curve on its back has a slightly different radius. The small change in curvature on each back surface will ensure one focal point. With this technology, each ring has an exposed edge of ≥50 µm. This diffractive implant is only 100-µm thick with a range of correction from -25.00 D to +25.00 D. The second surface of the Ultrachoice 1.0 is designed to assist the front surface in focusing the light at a single point, which by definition is a refractive lens.
A form of aberration occurs due to light rays' traveling longer in the thicker portion of the lens. The error is additive to spherical aberrations, but it is small if the lens manufacturer controls the lens' thickness or compensates for the differences in thickness when measuring the lens. The error is not as much from the IOL's thickness as the fact that most lens benches are calibrated using the back focal length of the lens. A corrective factor for thickness is added to determine the lens power. The bench should be calibrated even with the same lens power if the lens' thickness changes significantly. The Ultrachoice 1.0 is so thin that the error is negated. With a central axis thickness of 50 µm for a meniscus lens and 300 µm for a biconvex or plano optic, there is little error in measuring the lens due to thickness.
AcriTEC IOLs
The single-piece foldable Acrilyc IOL (Acritec) is composed of highly purified biocompatible hydrophobic acrylate with a chemically bonded UV-absorber. This IOL's cartridge is not inserted inside the anterior chamber but rather is kept at the tip of the incision through which the lens is then inserted.
The Acrismart IOL (Acritec) is a one-piece, hydrophobic acrylic lens with a water content of 25%. It is stored in balanced salt solution to facilitate its implantation. The high purity of the lens material (which is exposed to a specific cleaning process), the excellent surface design and the sharp-edge design significantly decrease secondary cataract formation.
CLINICAL EXPERIENCE
My colleagues and I have routinely implanted Acritec IOLs and have also worked with the special 5-mm optic Thinoptx rollable IOL. Jorge Alió, MD, of Alicante, Spain, implanted 46 eyes with the Acrismart IOL.20,21 He inserted the lens through a mean incisional size of 1.5 ±0.3 mm (SD).
Patients' mean uncorrected distance visual acuity improved significantly from 20/100 (0.2 ±0.2 decimal value) preoperatively to 20/32 (0.7 ±0.3) by the end of 6 months postoperatively (P<.000). Patients' best-corrected distance visual acuity improved significantly from 20/50 (0.4 ±0.2) preoperatively to 20/25 (0.9 ±0.2) after 6 months (P<.000). The uncorrected near visual acuity at the end of 6 months was 20/32 (0.6 ±0.2, P<.000). The mean postoperative spherical equivalent was 1.10 ±0.90 D (P<.947).
The safety index was 2.5 for distance and 1.4 for near. There were no intraoperative or postoperative complications. No eye required an Nd:YAG laser capsulotomy for posterior capsular opacification, and no patient reported undesirable complications at the end of 6 months.
Dr. Alió also evaluated the modulation transfer function in eyes implanted with a conventional IOL and two IOLs designed for microincisional cataract surgery. His prospective, nonrandomized consecutive series comprised 30 eyes implanted with one of the following IOLs: a conventional, foldable acrylic lens (Acrysof MA60BM; Alcon Laboratories, Fort Worth, Texas); the Ultrachoice 1.0 (Thinoptx); or the Acrismart 48S. The 0.5 and 0.1 modulation transfer functions following microincisional cataract surgery were calculated 3 months after implantation with the Optical Quality Analysis System for a 5-mm pupil. The differences were statistically analyzed with the Mann-Whitney U test.
The values of 0.5 modulation transfer function for the Acrysof, Ultrachoice 1.0 and Acrismart IOLs were 2.647 cycles per degree (cpd) ±0.833 (SD), 2.601 ±0.986 cpd, and 3.453 ±0.778 cpd, respectively. The mean 0.1 modulation transfer function values for the same IOLs were 8.720 ±3.074 cpd, 8.814 ±4.380 cpd, and 11.418 ±2.574 cpd, respectively. Statistical analysis did not show significant differences in 0.5 and 0.1 modulation transfer function between the conventional and microincisional IOLs.
THE FINAL FRONTIER
Although microphakonit allows sub–1-mm cataract surgery, the hurdle of creating an IOL to fit through the same incision remains. Work continues on a 26% material lens, which will be the forerunner of the sub–1-mm lens (according to an e-mail to me from Wayne Callahan of Thinoptx on Dec 22, 2005). Because such a lens must be extremely thin, its optical zone must be protected to avoid warping inside the eye.
Amar Agarwal, FRCS, FRCOphth, is director of Dr. Agarwal's Group of Eye Hospitals in Chennai, India. He states that he holds no financial interest in the products or companies mentioned. Dr. Agarwal may be reached at +91 44 2811 6233; dragarwal@vsnl.com.
Up Front | May 2006
Microphakonit and Microincisional IOLs
The evolution of the necessary lens technology continues.
Amar Agarwal, FRCS, FRCOphth
