Research shows IOL design must evolve toward imitating natural lens      

By Michela Cimberle [OSN CORRESPONDENT]
[OSN, Ocular Surgery News Vol. 25, No 8, April 15, 2007]

High ultrasound imaging, Miyake-Apple view reveal problems with all current IOLs and suggest future changes.

None of the currently avaiable IOLs can be considered a perfect reproduction of the natural lens’ original design, and if we want to improbe, “we sgould learn Mother Nature’s lesson better,” according on the surgeon.  

  

In an interview with OCULAR SURGERY NEWS, Philippe Sourdille, MD, discussed what has been learned in studies he has been conducting using the latest techniques for measuring the crystalline lens, IOLs and their influence on the capsular bag.

“The modern imaging of the anterior segment with high frequency ultrasound has created the conditions for a direct and dynamic internal viewing of the crystalline lens and the implanted capsular bag,” Dr. Sourdille said.
Subtle changes concerning anatomy, movements, distances and relations can be observed and precisely measured, documented dynamically in vivo and vitro through the Miyake-Apple view in implantated eye bank eyes.
Such a direct observation of IOL implantation created for Dr. Sourdille “a rethinking of the aphakic IOL configuration,” involving material diameter, shape and sizing.
”The true revolution in IOL technology will be an artificial lens that fits in and moves in the exact way the natural lens does,” Dr. Sourdille said.   



  In vitro measurements of 15 eye bank eyes (age 24 to 78) taken by Dr. Sourdille, along with Liliana Werner, MD, and Nick Mamalis, MD, at the Moran Eye Center at the University of salt Lake City, demonstrated the large individual variations of lens diameters (from 8.14 mm to 9.85 mm).
It was also found that after removal of the lens material, the diameter of the capsular bag increases by 0.1 mm to 0.5 mm, due to the flattening of the bag.
  “Quite often, the implantation of an IOL changes the preoperative diameter of the capsular bag, to an extent that varies according to the IOL design and pre-existing size of the bag,” Dr. Sourdille said.
For example, a one-piece IOL with open loops produces a slight ovalization of the bag with the major axis of the IOL, loop-end-to-loop-end, slightly larger (0.1 mm to 0.6 mm) than the perpendicular axis, according to the design and material, he noted.
  “When you compare the effects of different designs in the same operated capsular bag, you clearly see the difference between a one-piece hydrophilic acrylic IOL, such as the Barrett-designed IOLs from Cornéal and three-piece IOL.
The bag is more stretched and ovalized in the second case,” Dr. Sourdille said.
On the other hand, closed loops will adapt to most capsular bag diameters, but may be sensitive to small diameters.
In this study, the capsular bag of an average 9.5-mm diameter natural lens responded to the implantation of different IOLs with significant variations, which Dr. Sourdille summarized as follow:


1 - After implantation of a Barret-designed IOL, the loop-to-loop end axis measured 9.75 mm, while the perpendicular axis was 9.3 mm (figure 1).

2 - After implantation of a three-piece IOL, the loop-to-loop end axis was 10.3 mm, and the perpendicular axis was 9.86 mm (figure 2).

3 - After implantation of a closed-loop IOL (Quatrix, Cornéal) the loop-to-loop end axis was 10.01 mm and the perpendicular axis was 9.74 mm (figure 3).


In vivo: cascade functional changes

  Marina Modesti, MD, and Dr. Sourdille conducted in vivo measurements at the Fabia Mater Hospital in Rome, in collaboration with Rossella Apolloni, MD. Twenty-nine eyes of 24 patients were scanned with high frequency ultrasound (HiScan, Optikon, 45 mHz and 50 mHz probes) preoperatively, and followed postoperatively for 6 months.
The same surgeon (Dr. Apolloni) operated on all eyes implanted.

The same one-piece acrylic hydrophobic IOL (AcrySof MA60, Alcon) Preoperative lens diameter ranged between 8.20 mm and 10.44 mm, with an average of 9.46+-0.6 mm.   One month after the operation an enlargement of the preoperative diameter was noted in all cases. The new average of 9.95+-0.81 mm, ranging between 8.53 mm and 12.14 mm. Two months postop the bag had begun to shrink, as previously noted by Drs. Strenn and Tehrani. Consequently, the average diameter decreased slightly to 9.79+-0.69 mm (range 8.56 mm to 11.48 mm).  “Our first question is, should the same IOL diameter be used if the individual differences in lens size are superior to 20%? The second question is, what are the consequences of this capsular bag enlargement?” Dr. Sourdille said. Ultrasound technology was able to provide a straightforward answer to the second question. The modifications of the capsular bag diameter were shown to have immediate cascade effects on the reciprocal anatomical and functional relations between structures in the complex architecture of the eye.  “The preoperative distance between the ciliary ring and the equator of the lens, which varied from 0.1 mm to 0.5 mm preoperatively in a large majority of eyes, became virtually nonexistent in 80% of the eyes during the postoperative period,” Dr. Sourdille said (figures 4a and b).

“This, in turn, produced significant changes in the zonular system, resulting in a consistent modification of its functionality. The overall behavior and performance of the IOL was therefore affected,” Dr. Sourdille said.

  As he explained, a permanent relaxation of the zonular fibers, due to the decreased distance between lens equator and the ciliary ring, decreases the zonular system’s capacity. Also, if the capsular bag is compressed against the ciliary ring, the zonular traction will move the IOL posterior. If the capsular bag plane is posterior. If the capsular bag plane is posterior to the ciliary apex, as occurred in 20% of the cases, there will be no possibility of anterior movement, which will prevent any possible pseudo accommodation (figures 5a and b).

IOL DESIGN 


 Regaining accommodation To evaluate pseudo accommodation in these eyes, Dr. Modesti measured the anterior chamber depth during relaxed and active accommodation. She found that the depth remained unchanged in four of 29 eyes (no movement), increased in 16 of 29 eyes (posterior movement) and decreased in nine of 29 eyes (anterior movement). She also found pupil diameter was 40% to 50% smaller in all eyes. “This may be a problem for aspheric or multi-zone IOL optics,“ Dr. Sourdille said.
 He explained that an original aspect of the study was to examine the postop modifications of the sulcus-to-sulcus and ciliary-ring-to-ciliary-ring distances. It is known that sulcus-to-sulcus distance during active and relaxed accommodation varies from 10% to 20% at the accommodating age. It decreases when presbyopia occurs, and even further with cataract and hardening of the lens. “We have been able to observe that some movement does reappear after cataract extraction and IOL implantation in a variable way, related to the IOL size and position,” Dr. Sourdille said.
 Similar variations were noted for ciliary-ring-to-ciliary-ring distance under the same conditions. “The movements of uveal structures involved in accommodation and pseudo accommodation must combine with free zonular and implanted capsular bag movements if we aim to create some unaided near vision postoperatively. Respecting the natural anatomy and its surroundings seems to be the first prerequisite for this,” He said.
 From the first findings of this study. Dr. Sourdille and golleagues were able to conclude that most current IOLs, in regard to their design and overall diameter, do not take into consideration the postoperative structure of the anterior segment anatomy, “While Mother Nature has made the lens round, we have mainly developed implants that tend to ovalize the capsule, with the consequences that were explained above. If we want to recreate optimal conditions for pseudo accommodation we should leave enough room at the right place for the capsulo-lenticular system to move. In other words, we should try to recreate a pre-cataract situation,” He said.


TRANSPARENCY RELATES TO SIZING

 Another major objective of cataract surgery is to maintain the transparency of the entire capsular bag, to prevent the formation of a fibrous system with only the central posterior capsule remaining transparent.
“If the anterior capsule touches the IOL optic, it will always become at least less transparent than it was at the end of the operation,” Dr. Sourdille said.
“Preventing the migration of lens epithelial cells is mandatory, not only at the posterior optic edge, but also circumferentially, at the equator of the capsular bag, and we should also consider a free floating anterior capsule as the only way to maintain transparency.”
 The concept 360 IOL (Cornéal) has six haptics aiming at a circular equatorial contact with the capsular bag and at maintaining a safe distance between the anterior capsule and the optic, he said.
“This lens has succeeded in maintaining distance and transparency over 5 years, but the system is lens-diameter-dependent,” Dr. Sourdille said.
Depending on the individual size of the capsular bag, the haptics, which are only partially compressible, can be either in contact in a capsular bag of corresponding diameter, overlapping in a smaller capsular bag or out of contact in a larger capsular bag.
 When the IOL exactly fits the capsular bag diameter, the haptic ends from a circular barrier that prevents long-term lens epithetial cell migration (figure 7), resulting in overall transparency. If the capsular bag is larger or smaller than the IOL, some epithetial cell migration may occur between the partially open haptics. The anterior and posterior capsule may remainly visible at the equator, along the edge of the lens (figure 6).

“Mother Nature’s lesson, through high frequency ultrasound and clinical observation, proposes that we reconsider our IOL designs according to individual sizing, or producing IOLs that could adapt to different capsule diameters,” Dr. Sourdille concluded.






For more information:
Philippe Sourdille, MD, can be reached at Le Chaigne, 16120 Touzac, France; 33-630-362-846;
e-mail: philippe.sourdille@wanadoo.fr
Dr. Sourdille is a paid consultant for Cornéal Laboratoires.

[OSN, Ocular Surgery News Vol. 25, No 8, April 15, 2007]