Accurate phakic IOL biometry essential

The human eye is not geometrically round and biometry is required for proper sizing of phakic IOLs, Dr Liliana Werner told delegates in a presentation titled 'Phakic IOLs: a report from the pathology lab'.

Dr Werner presented some cases submitted to the Berlin Eye Research Institute (BERI) where she is director for preclinical research.

She noted that phakic IOLs are increasing in popularity and said that more accurate sizing in the future could reduce postoperative complications in the future.

It was the conclusion drawn from a wide ranging analysis of phakic IOL explanations. Dr Werner related three cases where an Icare IOL was explanted due to endothelial cell loss. These three cases represented 2.65% of the 113 Icare lenses implanted by Dr Ralph Gerl, Germany.

In each case, Dr Gerl sized the device by measuring white-to-white with the IOL Master (Carl Zeiss Meditec) and surgical callipers. He then added 0.5 mm to 1 mm depending on the gonioscopy.

Dr Werner noted that all these cases were for significant myopia (range -7 to -10.5 D) and that the Icare had four haptics that provided a large surface of contact with the anterior chamber angle.

"Perhaps that large contact, combined with the strength of the IOL, contributed to the problem, " said Dr Werner. The Icare was withdrawn in March 2007.

The next cases looked at ICLs (V4). Two implanted by Dr Alberto Villarrubia led to cataract formation. The two cases represented 1.4% of the 216 ICLs implanted by Dr Villarrubia since 2003, though significantly they represented 6% of 2005, when they occurred.

Dr Villarrubia used white-to-white measurements plus 0.5 mm to size the IOL, but he also accounted for corneal curvature, AC depth and the age of the patient.

A further 10 ICLs (7 V4 and 2 toric) were submitted by Dr Tobias Neuhann of Germany, nine of which caused cataract formation. Strength ranged from 12.5 D to 25 D. Again, Dr Neuhann used white-to-white measurements, initially with the Orbscan, later with IOL master. He has since moved to sulcus-to-sulcus with high frequency ultrasonography.

"There are a number of possible causes of cataract following IOL implantation such as surgical trauma like the possible cataractogenetic effects of Nd:YAG laser or accidental contact of the anterior capsule during different surgical steps, " said Dr Werner.

It could also be caused by intermittent microtraumas, she said, "Such as increased crystalline curvature during accommodation or rotation of the phakic lens postoperatively. Finally, there is risk with the increase in the overall size of the crystalline lens throughout life. "

Dr Werner cited a study on the ICL by Dr F. Trindale (Ophthalmology Times, 2000) which found that the lens could cause constant trauma in the centre or the periphery of the anterior capsule. Similarly it could disrupt the blood-aqueous barrier through friction with the iris or through ciliary sulcus fixation. Dr Trindale concluded that proper sizing and position of the ICL are crucial.

An FDA study of the Visian implantable collamer (STAAR Surgical) found that a significant risk factor in people over 40 with greater than 12.0 D of myopia preoperatively.

Dr Werner finally went through a series of possible measurements for phakic IOL sizing and found that there were no reliable rules of thumb. Each eye is unique and even within an eye measurements vary along different meridians.

Dr Werner concluded that variation of diameter and orientation measures were sufficient to require biometry for proper IOL sizing, though she noted that some IOL design were probably more forgiving because they are flexible and can build different degrees of vaults.