Ординатура / Офтальмология / Английские материалы / Jaypee Gold Standard mini Atlas Series Lasik_Aragawal, Jacob_2009

MISCELLANEOUS TOPICS/ 177

Figure 4.2A

Figure 4.2B

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Figure 4.2C

Figures 4.2A to C: (A) Posterior chamber implantable collamer lens. Toric ICL (Figure & Text Courtesy: Alaa El-Danasoury);

(B) The currently used ICL (model V4); note the 4 laser marks engraved on the haptic: 2 orientation marks on the leading right and trailing left footplates and 2 alignment marks on either sides of the optic; (C) An eye with limbal pigmentation and high ICL vault (about 800 µm, red arrow); the ICL was oversized because the actual the white-to-white measurement (green arrow) was overestimated by the Orbscan II as Orbscan measurement included the limbal pigmentation (yellow arrow).

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cylinder axis to correct the patient’s astigmatism. It is recommended that rotation is less than 22.5° from the horizontal. The cylindrical power ranges from 1.0 to 6.0 D with the same range of spherical power as the myopic ICL.

High myopia and high myopic astigmatism remain the most common indications for ICL and toric ICL; LASIK being more commonly performed for low and moderate amounts of myopia. Patients who suffer from high astigmatism and high myopia are usually not suitable candidates for corneal-reshaping procedures because there is an increased risk of corneal ectasia, associated with low visual quality and unpredictability. A sufficient anterior chamber depth (ACD) is an important factor to prevent endothelial cell loss after phakic IOLs implantation. ICL is the farthest phakic IOL from the endothelium; its is estimated that an anterior chamber depth of 2.7 mm from the endothelium to the anterior surface of the crystalline lens is the lower limit for safe ICL implantation.

Estimating the proper size and power for the ICL to be implanted in a given eye is key factor for successful ICL surgery.

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cost effective. In 100 consecutive ICL surgeries we found no statistically significant difference in the white-to-white measurements using calipers and Orbscan II. The same finding was also reported by Choi and co-workers. In cases with limbal pigmentation it should be noted that Orbscan may overestimate the white-to-white measurement; and in this particular case, calipers measurements are more reliable.

Many surgeons prefer to perform two peripheral iridotomies one or two weeks before the surgery using a Nd:YAG laser to prevent postoperative pupillary block. Peripheral iridotomies are performed superiorly 90° apart. Before surgery pupil must be widely dilated; in our practice; 1% cyclopentolate hydrochloride (Cyclogyl; Alcon labs, Inc. Fortworth, TX, USA) and 2.5% phenylepherine hydrochloride (Mydfrin; Alcon labs) instilled every 15 minutes for 1 hour before surgery usually result in efficient pupillary dilation. We routinely perform ICL surgery under topical anesthesia (0.5% bupivacaine hydrochloride). It is advisable to double check the white to white measurement with calipers before starting the surgery.

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incision can vary from 2.6 to 3.2 mm depending on the surgeon preference; in our first cases we used a 3.2 mm incision; today we are use a 2.8 mm incision; this enables a smooth injection and shown to have negligible effect on postoperative astigmatism.

The anterior chamber is filled with viscoelastic before the lens is slowly injected using the MicroSTAAR injector, (Staar, Nidau, Switzerland). It is worth mentioning that the injection should be slow enough to allow the leading foot plate to unfold in the anterior chamber before the trailing footplate is injected out of the cartridge. This will prevent the lens from unfolding upside down in the anterior chamber. Once the lens unfolds in the anterior chamber the marks on the distal and proximal footplates are checked for proper orientation. The foot plates near the main incision are then tucked under the iris using an ICL manipulator; we use a Battle ICL manipulator (Rhein medical, Inc. Tampa, Fl, USA) that has a small oval tip with a rough lower surface that gives the surgeon good control on the foot plate. Keeping the lower surface of the manipulator tip flat on the footplate makes manipulation easier. All manipulations should be as peripheral as possible with no instruments touching the optic or crossing the pupillary zone. The distal footplates

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Implantation of toric ICL is basically the same as spheric ICL with the exception that the axis of the cylinder of the lens has to be aligned correctly to correct the preoperative astigmatism. If the surgeon is using a custom made lens; the longitudinal axis of toric ICL, marked with laser marks has to be aligned horizontally (0° rotation from the horizontal meridian), in case the surgeon is using an alternative lens that has the same spherocylindrical power and different axis orientation, the lens will need to be rotated to compensate for this axis difference, the manufacturer recommends the rotation to be less than 22.5° from the horizontal axis. In our practice we use alternative lenses with axis difference less than 15° and we center our incision on the axis of implantation to minimize rotation of the toric ICL inside the eye. More than half of toric ICLs we implanted over the last year were alternative lenses to speed the delivery time.

Marking the horizontal axis is best done while the patient is sitting at the slit-lamp biomicroscope prior to surgery. During surgery a Mendez ring (Katena Products, Inc. Denville, New Jersey, USA) can be used to measure the required rotation from horizontal. It is also advisable to recheck the alignment of the laser marks that mark the axis of the cylindrical power on the lens haptic after implantation and before constricting the pupil.