ACCOMMODATION

Surgical restoration of accommodation in elderly patients has already been successfully achieved in a few isolated cases, but a lot more research needs to be done before the technique can be successfully extended to the majority of presbyopic or older patients, according to Adrian Glasser PhD.

Addressing delegates at the XXXI ESCRS Congress in Amsterdam, Dr Glasser, professor of optometry and vision sciences and biomedical engineering, Benedict/ Pitts Professor College of Optometry, University of Houston, said that the results of some trials have shown that it is possible to obtain a significant accommodative response in some patients implanted with accommodating intraocular lenses (IOLs).

“I am going to be a little controversial here and say that I do believe that accommodation has actually successfully been achieved with accommodating IOLs, albeit only in a very limited number of individual cases. Most presbyopes would be satisfied with 1.0 D to 2.0 D of accommodation. While 1.0 D will help, 3.0 D would likely be quite satisfactory and probably more than 5.0 D is not necessary for most patients. I believe the biggest obstacle remains the biological challenges associated with the postoperative healing response of the eye,” said Dr Glasser.

Age-related variation in shape and size of isolated human donor lenses
Courtesy of Adrian Glasser PhD

DYNAMIC PROCESS
Defining accommodation as an increase in the optical power of the eye due to ciliary muscle contraction, Dr Glasser emphasised that it is an active and dynamic process and is not simply the ability of a distance corrected eye to see clearly at near. He noted that age-related changes occur in just about every aspect of the accommodative anatomy including the crystalline lens, capsular bag and ciliary muscle. The critical factor, however, seems to be increasing stiffness of the lens as the patient ages to the point where the shape of the lens can no longer be changed by the accommodative mechanism, said Dr Glasser.

With some studies showing that the ciliary muscle continues to contract even in presbyopic eyes, a lot of research has focused on the potential of intracapsular accommodative IOLs to mimic the accommodative effect of the crystalline lens, with generally disappointing results thus far, said Dr Glasser. Numerous challenges exist in trying to manufacture an IOL that can successfully restore dynamic accommodation, he said. “The considerable variation in the size and shape of individual human lenses at all ages of life is just one obvious hurdle to be overcome in trying to manufacture an artificial replacement,” he said. (See attached image which shows the agerelated variation in shape and size of isolated human donor lenses.)

DIMINISHING PCO
Another key problem for intracapsular accommodative IOLs is the likelihood of postoperative lens epithelial cellular proliferation, said Dr Glasser, noting that techniques such as maintaining an open capsule to aqueous fluid exchange or ensuring a tight fit of the lens in the capsular bag may help to diminish the incidence of PCO and fibrosis. Another approach is to bypass the capsule altogether by using accommodative IOLs specifically designed to be placed into the sulcus. Dr Glasser added that customising the fit of the IOL into each individual capsular bag may ultimately be necessary for dynamic accommodation to be achieved.