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Up Front | Feb 2009

Does One Diameter IOL Fit All Capsular Bags?

A system in which axial length and dioptric power determine overall IOL length resulted in a better fit.

Most IOLs companies manufacture a given IOL model with one overall diameter for implantation in the capsular bag. The diameter of the crystalline lens is not the same in all eyes, however, and a single IOL diameter may not ideally fit all capsular bags. In addition to individual variation, axial length and age are also well-known factors in determining crystalline lens diameter. This variability in the size of the capsular bag can be a cause of postoperative IOL complications, including decentration, tilt, and refractive instability.

This situation leads to a number of questions. Postoperatively, what is the anatomical position of the IOL and capsular bag in different-sized eyes implanted with IOLs of the same diameter? Could increasing IOL diameter, as a function of the increasing axial length of the eye, improve the anatomical and functional result of bag implantation? Could experimentation improve the adaptability of such an IOL system?

In an attempt to answer these questions, two studies were performed,1 one experimental and one clinical, using the Quatrix Evolutive IOL (Croma, Korneuburg, Austria), an IOL with an overall diameter that varies linearly from 10.3 to 10.8 mm.

EXPERIMENTAL STUDY
With colleagues at the University of Utah (Liliana Werner, MD, PhD; and Nick Mamalis, MD, of the John Moran Eye Center), we conducted analyses using 25 eye bank eyes. The eyes, from donors aged 18 to 77 years, were stored in culture medium to avoid tissue swelling. All eyes were prepared according to the Miyake-Apple posterior photography technique to document the exact diameter of the lens and the ciliary ring, as well as the anteroposterior position of the lens equator relative to the ciliary ring (at the ciliary plane or posterior to the plane).

implantation
After phacoemulsification, we implanted the capsular bags with different IOLs—one-piece and three-piece designs, and in different diameters—and we measured the modifications that the IOLs induced in the shape and size of the bags. In five cases, we also performed anterior segment optical coherence tomography (OCT) with the Visante OCT (Carl Zeiss Meditec, Jena, Germany) to analyze the capsular wrapping of the IOL immediately after implantation.

In capsular bags of different diameters, we compared the standard 11-mm Quatrix IOL with the Quatrix Evolutive (both from Croma), an IOL designed with an increase in overall diameter from 10.3 to 10.8 mm with increasing dioptric power.

Preoperatively, the crystalline lens diameters, measured with calipers under the microscope, varied from 8.14 to 9.88 mm (Figure 1). The position of the lens equator relative to the ciliary ring (ciliary apex) was documented. In 80% of eyes, the lens was smaller than the ciliary ring and was sitting in the ciliary plane. When the lens was larger than the ring (20% of eyes), the lens equator was situated behind the ciliary apex, in a retrociliary position.

After crystalline lens removal, three of three-piece IOL models consistently enlarged and ovalized the capsular bag, frequently causing central capsular folds. These IOLs also moved the bag into a retrociliary position (Figure 2).

In the same capsular bag (9.34 mm diameter), we compared the effect of a 13-mm diameter, one-piece Barrett hydrophilic acrylic IOL (Croma) with that of a 12-mm diameter AcrySof one-piece hydrophobic acrylic IOL (Alcon Laboratories, Inc., Fort Worth, Texas). In both cases there were no folds, no ovalization of the capsular bag, and comparable bag diameters (Barrett, 10.02 mm; AcrySof 9.93 mm; Figure 3).

The main part of the study was dedicated to direct comparisons in the same capsular bags of Quatrix standard 11-mm IOLs and Quatrix Evolutive IOLs (Figure 4). The Quatrix Evolutive IOLs demonstrated improved adaptability to different bag sizes. In no case was there any retrociliary displacement of the Quatrix Evolutive IOLs.

OCT performed immediately after implantation demonstrated excellent capsular wrapping of the IOLs, with close contact between the optic and posterior capsule (Figure 5).

CLINICAL STUDY
Simultaneously, a clinical study by Marina Modesti, MD, and Rossella Apolloni, MD, of the Fabia Mater Hospital in Rome, revealed clinical information about the sizes of cataractous lenses and the changes induced by IOL implantation. They measured the vertical diameter of the lens and the surrounding anatomical elements preoperatively with high frequency ultrasound in one eye each of 24 consecutive cataract surgery patients (aged 54–82 years) and compared these with postoperative measurements at 1, 2, and 12 months. The same model 12-mm diameter, one-piece acrylic hydrophobic nonangulated IOL was used in all eyes.

Preoperatively, the mean lens diameter was 9.46 ±0.6 mm (range, 8.20–10.44 mm). The lens diameter was smaller than the ciliary ring in 80% of eyes, and the lens was sitting in the ciliary plane in 80% of cases. The distance between the equator of the lens and the ciliary ring was 0.52 ±0.33 mm (range, 0.00–1.20 mm).

At 1 month postoperative, the mean capsular bag diameter was 9.95 ±0.81 mm (range, 8.53–12.14 mm). This indicates consistent enlargement of the bag as compared with the preoperative status. The distance between the equator of the bag and the ciliary ring became virtually zero: 0.02 ±0.06 mm (range, 0.00–0.20 mm).

At 12 months, in nine of 24 eyes (37.5%) the IOL was in a central position, in seven of 24 eyes (29.2%) the IOL was tilted, and in eight of 24 eyes (33.3%) the IOL was posterior to the ciliary ring.

DISCUSSION
We cannot compare directly the results of the experimental and clinical studies. However, we can conclude that an IOL manufactured with only one diameter did not anatomically fit all possible capsular bags in 24 consecutive cataractous eyes. The clinical consequences of tilt and decentration are well known, and they become more significant when IOLs contain multifocal, aspheric, and toric corrections. Retrociliary positioning of the capsular bag also paves the way to a tendency toward a hyperopic result.

The Quatrix Evolutive, which features linear variation of the overall IOL diameter according to dioptric power, demonstrated improved adaptability to the capsular bag as compared to the standard Quatrix, with no retrociliary positioning and no deformation of the capsular bag. The concept behind the lens (ie, longer eyes receive larger IOL diameters and shorter eyes receive shorter diameters) improves the anatomical situation and may avoid unexpected refractive results.

This was clinically confirmed in a recent randomized, prospective, bilateral, masked study.2 In 80 eyes (40 patients), investigators compared the standard Quatrix with the Quatrix Evolutive. Correlation of IOL diameter with dioptric power and axial length resulted in better capsular bag fitting in the Evolutive group.

With an A-constant of 119, the spherical equivalent in the Evolutive group was 0.30 D. No case of hyperopization was noted. The A-constant has now been modified to 119.3 (using the SRK-T IOL power calculation formula) to move the refractive result closer to emmetropia.

CONCLUSION
Adaptability of the IOL diameter should be taken into consideration in future IOL designs. If it is impossible to customize all IOLs, at least we should be able to propose an IOL system that will sit in the ciliary plane in all cases—without tilt, backward movement, or decentration.

More prospectively, we must consider certain anatomic prerequisites for an IOL to provide restoration of accommodation. Sufficient space must be provided between the capsular bag equator and the ciliary ring, and the anterior capsule must be transparent and supple to facilitate zonular action. To support these needs, IOLs with adaptable diameters must be developed.

Philippe Sourdille, MD, practices at the Clinique Sourdille, Nantes, France. Dr. Sourdille states that he is a paid consultant to Croma. He may be reached at tel: +33-630-362-846; e-mail: philippe.sourdille@wanadoo.fr.

Feb 2009