NEW APPROACH TO CAPSULE REFILLING

A new approach to capsule refilling which involves the use of a pair of accommodating membranes to cover and seal an anterior and posterior capsulorhexis has produced encouraging results in animal studies. The method appears to provide around 2.5 D of accommodation while leaving the optical axis clear, said Okihiro Nishi MD, Nishi Eye Hospital Osaka, Osaka, Japan.

“Some useful accommodation can be obtained by this refilling technique in young monkeys. This procedure solved two of the persisting problems in lens refilling, leakage of the injectable silicone and capsular opacification,†Dr Nishi told the XXIX Congress of the ESCRS.

The basic concept behind capsule refilling is that the non-accommodating stiffened lens material of a presbyopic patient is replaced by a silicone liquid polymer in an empty but intact capsule. The silicone polymerises and the elasticity of the retained capsule will then alter its shape in response to the natural physiological mechanisms of accommodation. That is, the relaxation of the zonule will cause the capsule and its contents to assume a more spherical shape.

Dr Nishi noted that early research conducted in the 1980s proved the validity of the concept in animal studies, which showed that the eye would alter its shape in response to pilocarpine injections to an amount of around 6 D. However, problems with leakage and capsule opacification have prevented the clinical application of the capsule-refilling approach.

More recently, Dr Nishi has developed a new approach to preventing leakage and capsule opacification that involves the removal of the visually important parts of the capsule and replacing them with foldable silicone membranes.

In a study involving 18 macaque monkeys, refilling the lens in this way resulted in accommodative amplitude of 2.0 D to 3.0 D, regardless of whether the capsule was filled to 80 per cent, 100 per cent or 125 per cent of its capacity. Mean refraction on the other hand was closest to emmetropia in eyes in which the capsule was filled to 80 per cent, with a spherical equivalent of -0.5 D, compared to -6.1 D with 100 per cent refilling and -8.8 D with 125 per cent refilling. The same held true for astigmatism, which was -1.0 D in the 80 per cent refill group, -3.7 D in the 100 per cent refill group and -6.9 in the 125 per cent refill group.

Furthermore, in a series in which rabbit eyes underwent capsule refilling with anterior and posterior accommodating membranes and anterior and posterior capsulorhexis, there was no capsule opacificationat least in the visual axis five to eight weeks after surgery, he noted.

Some of the remaining problems with the capsule-refilling approach include the improvement of the refractive predictability of the procedure. Also requiring elucidation is the impact of capsule opacification outside the optical axis on accommodation, he noted.

“The next step may be applying the procedure for a blind eye of volunteer patients and conducting postoperative examinations such as refraction, accommodation, topography, OCT, UBM, wavefront analysis, optical quality and clinical safety. Precise, exact and thorough examinations for all these parameters are not possible in monkeys but only in humans,†Dr Nishi said.

contact Okihiro Nishi – okihiro@nishi-ganka.or.jp