Optic design modification enhances vision performance without degrading contrast sensitivity
"Studies investigating previous versions of the lens showed accommodation was the result of a combination of factors," said Dr Hovanesian, clinical instructor at the Jules Stein Eye Institute at the University of California in Los Angeles.
"Optic translation may occur," he said. "However, increased vitreous pressure resulting from ciliary muscle contraction also causes central steepening of the lens optic, a phenomenon described as accommodative arch and that has been demonstrated using wavefront studies."
"The accommodating IOL was developed to take advantage of this optic change to ..improve visual function further," he said. "Laboratory studies' clinical trial data show that the new modified optic achieves its goal in providing better near vision without degrading contrast sensitivity."
The optic change involved a 3µm increase in thickness to the 1.5mm central diameter that shortens the spherical radius and imparts some negative spherical aberration tothe mid-peripheral zone of the lens. Optical bench evaluations at an independent laboratory showed that at 1 D of defocus, the modified optic had a flatter overall wavefront and lower total RMS value compared with the predecessor lens (Crystalens AT 45, 360 versus 570 µm) and a greater depth of field.
In addition, objective evaluation of contrast sensitivity based on modulation transfer function analyses showed some improvement with the accommodating IOl, relative to the predecessor lens (0.29 versus 0.51, respectively) although the difference was not statistically significant.
The FDA study compared 60 eyes with the accommodating IOL implanted and 60 eyes with the predecessor lens implanted.
In monocular testing of near uncorrected visual acuity (UCVA), the results at all thresholds favoured the accommodating IOL for providing better near vision.
J3 or better near UCVA was achieved by 100% of eyes with the accommodating IOL implanted compared with only 78% of eyes with the predecessor lens and J2 or better near UCVA was achieved by 80% of eyes with the accommodating IOL compared with only 55% of eyes with the predecessor lens.
"However, measurement of monocular near VA with distance correction is a better measure of accommodation and the results for this testing also consistently favoured the accommodating IOL over the predecessor lens," said Hovanesian.
In the accommodating IOL group, distance corrected near VA with distance correction is a better measure of accommodation and the results for this testing also consistently favoured the accommodating IOL over the predecessor lens.
In the accommodating IOL group, distance corrected near VA was J3 or better in 90% of eyes, J2 or better in 70% of eyes and J1 or better in 33% of eyes. These different levels of vision were achieved at rates of 65%, 32% and 13% respectively in the predecessor lens group.
Contrast sensitivity was tested with and without glare and the results were slightly better in patients who received the latest version of the accommodating IOL, but not significantly different between the two lens groups.
"Certainly there was no evidence that the optic modification led to worsening of contrast sensitivity," Dr Hovanesian concluded.
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