PRL Treatment of High Ammetropias Looks Promising

By Cheryl Guttman

Crete - The silicone, foldable PRL™ is a promising new posterior chamber lens for the surgical correction of high refractive errors, reports Ioannis G. Pallikaris, MD, Professor of Ophthalmology, University of Crete School of Medicine.

Participating in a multicenter study of this phakic IOL underway at 11 sites, Dr. Pallikaris and his colleague Maria Kalyvianaki, MD, have implanted 14 myopic eyes (mean preop MSE -14.75 D) and 5 hyperopic eyes (mean preop MSE +7.65 D). In their follow-up, which averages six months, the PRL is providing effective and stable correction of the refractive errors with few complications, he reported.

At six months, mean MSE values are -0.75D for the myopes and -1.00 D for the hyperopes. Mean UCVA was counting fingers preoperatively in both groups and has improved to 0.6 in the myopes and 0.4 in the hyperopes.

No intra-operative complications were encountered and the only postoperative complications have consisted of some complaints of halos and glare at night and elevated IOP in 4 eyes of 2 patients, one myope and one hyperope. Night visual aberrations appear to be associated with a scotopic pupil size larger than the optical zone of the PRL. The PRL has not decentered in these cases, noted Dr. Pallikaris.

The IOP elevation in the myope was determined to be steroid-induced, as there were no signs of pupillary block, angle closure, or pigment dispersion, and the IOP returned to normal after the steroid was discontinued. The IOP increase in the hyperope occurred bilaterally 10 days postoperatively, was due to non-patent surgical iridectomies, and responded to YAG laser iridectomy.

“Power calculations for this IOL are performed by the manufacturer based on white-to-white diameter, cycloplegic refraction, anterior chamber depth, and target postoperative refraction, and we noticed they are very accurate. In addition, the <PRL offers the opportunity for a good refractive outcome immediately after surgery> that is being maintained. Encouragingly our short follow-up shows few complications. However, studies with larger numbers of patients and extended monitoring are necessary to prove the long-term safety of this phakic IOL,” said Dr. Pallikaris.

The PRL is a plate haptic phakic IOL available in powers of +3.0 to +15.0 D for hyperopia and -3.0 to -20.0 D for myopia. Overall length is 11.3 mm for the myopic version and 10.8 mm for the hyperopic lens. The optic is 4.5 mm to 5.0 mm in diameter and is shaped to avoid contact with the natural lens. The myopic optic is biconcave and the hyperopic optic is concave-convex.

HANDLE WITH CARE
The silicone material from which the PRL is made has a high refractive index (1.46) and is very thin and flexible. However, because of the delicate nature of the PRL, gentle manipulations during the surgical procedure are mandatory, noted Dr. Pallikaris.
The PRL is introduced in a fully dilated eye through a temporal 3.2 mm clear cornea incision under retrobulbar anaesthesia. Special forceps have been designed for its insertion and a custom, double-ended spatula is used to place the haptics in the posterior chamber.

Once the lens has unfolded in the eye, acetylcholine is injected into the anterior chamber to constrict the pupil and an iridectomy is performed at 12 o’clock.
“That should be performed as peripherally as possible using the probe of a vitreotome. No irrigation is needed, but only injection of Healon GV, aspiration of the peripheral iris, and then a single cut with the vitreotome. The total procedure time normally does not exceed 5 minutes,” noted Dr. Pallikaris.

The implant is not supported in the sulcus angle, but rather fixates on 4 points and floats in the posterior chamber. Due to its hydrophobic nature, the silicone optic avoids contact with the crystalline lens. Ultrasound biomicroscopy studies have shown that it is propelled anteriorly, away from the anterior capsule of the lens into the posterior iris by the flow of aqueous from behind its haptics.

Nevertheless, there is the theoretical potential for transient or even permanent contact with the crystalline lens that could lead to cataract formation, Dr. Pallikaris said adding:
“Partial touch between the PRL and the natural lens might especially occur during accommodation. If a cataract develops, this implant can be removed relatively easily since it is not permanently fixated and phacoemulsification performed."

He added that IOP monitoring and gonioscopic examination are also essential in the follow-up of patients implanted with the PRL due to the potential for posterior chamber devices to cause angle closure or even pigmentary glaucoma.

The PRL is being developed by Medennium, Inc, California. CibaVision has exclusive worldwide rights to market and distribute the PRL.