PRL Treatment of High Ammetropias Looks Promising
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.
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
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 oclock.
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.