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Rollable IOL enhances cataract surgery through 0.9-mm incision
The ThinOptX lens provided the missing link for the ultra-small incision procedure.
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Since 1998 we have been performing cataract surgery through an incision of 0.9 mm using a technique we call phakonit. The only problem with this technique was that we did not have an IOL that would pass through such a small incision.
In October 2001 one of us (Amar Agarwal) performed the first case of phakonit using a rollable IOL at our hospital in Chennai, India. We used the Rollable IOL from ThinOptX. This lens allowed us to complete the procedure without widening the ultra-small incision.
Performing phakonit
In standard phacoemulsification, we cannot use an incision of less than 1.9 mm because of the diameter of the infusion sleeve. The titanium tip of the phaco hand piece itself is only 0.9 mm in diameter, but it is surrounded by the infusion sleeve that allows fluid to pass into the eye. The sleeve also cools the tip to prevent corneal burns.
To allow us to use a smaller incision we removed the sleeve from the phaco tip. The tip was passed into the eye with no infusion sleeve through an incision of 0.9 mm. An irrigating chopper held in the left hand was used to pass fluid into the eye through a side port incision. The assistant injected balanced salt solution continuously at the incision site to cool the unsleeved phaco tip. Thus the cataract was removed through a 0.9-mm opening.
We named this technique phakonit because phacoemulsification is done with a needle opening via an incision using the phaco tip.
A specially designed 0.9-mm keratome, an irrigating chopper, a straight blunt rod and a 15º standard phaco tip without an infusion sleeve are required to perform phakonit. Viscoelastic is injected with a 26-gauge needle through the presumed site of side port entry. This inflates the chamber and prevents its collapse when the keratome enters the chamber. A straight rod is passed through this site to achieve akinesia, and a clear corneal temporal valve is made with the 0.9-mm keratome. Katena makes this keratome and the other instruments for phakonit. A continuous curvilinear capsulorrhexis is performed, followed by hydrodissection and checking the rotation of nucleus.
After enlarging the side port, a 20-gauge irrigating chopper connected to the infusion line of the phaco machine is introduced with the foot pedal on position 1. The phaco probe is connected to the aspiration line, and the sleeveless phaco tip is introduced through the 0.9-mm incision.
Using the phaco tip with moderate ultrasound power, the center of the nucleus is directly embedded, starting from the superior edge of the rhexis with the phaco probe directed obliquely downward toward the vitreous. The settings at this stage are 50% phaco power, 24 mL/min flow rate and 110 mm Hg vacuum.
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When nearly half of the center of the nucleus is embedded, the foot pedal is moved to position 2, which helps hold the nucleus due to vacuum rise. To avoid undue pressure on the posterior capsule, the nucleus is lifted a bit. With the irrigating chopper in the left hand, the nucleus is chopped with a straight downward motion from the inner edge of the rhexis to the center of the nucleus and then to the left in the form of an inverted L shape.
Once the crack is made, the nucleus is split to the center, then rotated 180º and cracked again so it is completely split into two halves.
The nucleus is then rotated 90º and embedding done in one half of the nucleus with the probe directed horizontally. Repeating the chopping technique, three pie-shaped quadrants are created in one half of the nucleus. Similarly, three pie-shaped fragments are created in the other half of the nucleus. With a short burst of energy in pulse mode, each pie-shaped fragment is lifted and brought level to the iris, where it is further emulsified and aspirated in pulse mode.
Thus the whole nucleus is removed. No corneal burns are made, and cortical cleanup is done with a bimanual irrigation-aspiration technique.
Thin IOL optics
ThinOptX, maker of the Rollable IOL, has patented technology that allows the manufacture of lenses with powers of +30 D to –30 D, with a thickness of only 100 µm. The ThinOptX technology, developed by Wayne Callahan, Scott Callahan and Joe Callahan, is not limited by material choice, but is achieved instead by an evolutionary optic design and a unique nanoscale manufacturing process. The lens is made from off-the-shelf hydrophilic material similar to IOL materials already on the market. The basic advantage of the lens is that it is ultra-thin.
Some of the optical characteristics of the ThinOptX IOL are as follows. The front surface is a curve that approximates a radius. The back surface is a series of steps with concentric rings. The back surface can be concave, convex or plano. The combination of steps with the front radius corrects for spherical aberrations. The convex and plano back designs are used for positive-power lenses. The concave or meniscus back surface designs are used for negative-power lenses.
Lines intersecting the lens represent parallel light. The light is bent at the intersection of the lens surface in accordance with Snell’s Law. When light strikes the lens surface, it is bent toward the central axis. The light travels to the back edge of the lens and again is bent toward the central axis. All the parallel light rays entering the back of the lens come to focus at approximately the same point. Therefore, the lens is a refractive lens, not a diffractive lens.
The thin edge of the ThinOptX lens helps to prevent glare or halos, even under low-light conditions. The lens is also designed to eliminate spherical aberration. Its thinness also eliminates optical errors caused by lens thickness. The thinness is one of the reasons the ThinOptX lens can be manufactured in 0.125-D increments.
Lens insertion technique
The lens is removed from the bottle, held with forceps, then placed in a bowl of saline solution that is approximately body temperature. This makes the lens pliable. Once it is pliable, it is taken with the gloved hand and held between the index finger and the thumb. The lens is then rolled in a rubbing motion. It is preferable to do this in the bowl of saline so that the lens remains rolled well. It is better to do this without gloves, as the rolling is much better.
The lens is then carefully inserted through the incision. The tip of the haptic should have a pointed shape, which allows the lens to penetrate the corneal wound. One can then move the lens into the capsular bag. The teardrop on the haptic should point in a clockwise direction. The smooth optic lenticular surface will be facing posteriorly. The natural warmth of the eye causes the lens to open gradually. Viscoelastic is then removed with bimanual irrigation-aspiration. The tips of the foot plates are extremely thin, allowing the lens to be positioned with the foot plates rolled to fit the eye.
Commentary and suggestions
Rolling the lens without gloves under the saline gives us excellent rolling. This might be improved by having an instrument that would roll the lens.
We found that the length of the lens was all right, but its current width is too great. To address this, we tried cutting the lens vertically on either side. This way the lens became smaller and easily maneuverable. The optic size was reduced. When we rolled this cut lens and implanted it, it gave us what we wanted.
Now, ThinOptX has made a special lens, the Rollable IOL, with a 5-mm optic for phakonit.
We were worried about whether the cut edges of the lens would produce any glare problems for the patient. The next day the patient had no glare, and the lens reacted very well in the eye. A smaller optic size in a lens with the current length might be considered by the manufacturer.
We checked the patient’s topography and astigmatism because there is no point in having a lens go through a 1-mm incision if we still have problems of astigmatism. Phakonit is more difficult to perform than phaco, so the surgeon must be convinced that it makes sense to shift to a smaller incision. When we saw the patient there was no induced astigmatism. In phaco with a foldable IOL we still get a bit of astigmatism. Topography also confirmed this result. However, we need to do more cases to document topographic changes in phakonit compared to phaco.
We need an instrument that will roll the lens and an injector without a cartridge. Currently we are using forceps, which can tear the lens. Alternatively, the manufacturer might supply the lens already rolled.
Ideally, the rollable lens should be an accommodating or multifocal type of IOL, so that we not only minimize astigmatism but also solve the problem of presbyopia.
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For Your Information:
- ThinOptX, makers of the Rollable IOL, can be reached at PO Box 784, Abingdon, VA 24212; (276) 623-2258; fax: (276) 623-5661; e-mail: ThinOptX@naxs.net.
References:
- Agarwal S, Agarwal A, et al. Phacoemulsification, Laser Cataract Surgery & Foldable IOLs (Second ed.). Delhi, India: Jaypee Brothers; 2000.
- Boyd B F, Agarwal S, et al. LASIK and Beyond LASIK: Wavefront Analysis and Customized Ablations. Panama: Highlights of Ophthalmology; 2000.