Accommodating intraocular lenses: a critical review of present and future concepts

Abstract

As opposed to psychophysical evaluation techniques, laser interferometry measures what shift lenses are designed to provide: axial shift on accommodative effort. While under pilocarpine some movement was recorded, no movement at all was found under near-point stimulation with any of the lenses currently marketed. In contrast, magnetic-driven active-shift lens systems carry the potential of sufficiently topping up apparent accommodation to provide for clinically useful accommodation while using conventional lens designs with proven after-cataract performance. Dual optic implants significantly increase the impact of axial optic shift. The main potential problem, however, is delayed formation of interlenticular regenerates. Lens refilling procedures offer the potential of fully restoring accommodation due to the great impact of increase in surface curvature on refractive lens power. However, various problems remain to be solved before clinical use can be envisaged, above all, again, after-cataract prevention. The concept of passive single-optic shift lenses has failed. Concomitant poor capsular bag performance makes these lenses an unacceptable trade-off. Magnet-assisted systems potentially combine clinically useful accommodation with satisfactory after-cataract performance. Dual optic lenses theoretically offer substantial accommodative potential but may allow for interlenticular after-cataract formation. Lens refilling procedures have the greatest potential for fully restoring natural accommodation, but will again require years of extensive laboratory and animal investigations before they may function in the human eye.

Accommodating intraocular lenses: a review of design concepts, usage and assessment methods

“…Typical minimum pupil diameters specified by manufacturers range from 2.3 mm (for example, ShunNippon NVision-K5001/Grand Seiko WR-5100K and grand Seiko Auto Ref/ Keratometer WAM 5500) to 2.9 mm (Shin-Nippon SRW-5000/Grand Seiko WV-500). 69 Several authors have questioned the application of autorefractors in AIOL research 5,47 due to difficulties in data capture associated with miotic pupils 68,71 and the sub-prime optical quality of the eye caused by bright Purkinje images from the anterior optic surface, and the likely presence of some level of posterior capsular opacification. Wolffsohn and colleagues 59 were able to measure static objective refractive change and record the objective accommodative response through undilated pupils in a cohort of mainly elderly subjects, using a commercially-available open-view autorefractor (Shin-Nippon SRW-5000).…”

“…These studies also used a diverse range of metrics to determine that AIOLs are stable over time with no significant difference between measures such as vision, distance and near visual acuity, accommodation, defocus curve fitting and lens position. Meanwhile, the near performance of currently available AIOLs has been reported to decrease over time, 5,59,105 probably as a consequence of capsular fibrosis and shrinkage limiting optic movement. 6,91 To verify the benefit of AIOLs in providing true accommodation, there is a critical need for more randomised, patient and practitioner-masked, clinical trials that involve long-term follow-up.…”

“…Progress in IOL materials and design, use of advanced pre-operative biometry and small incision procedures have allowed near-emmetropic distance refractions to be achievable in the majority of cases. [3][4][5] Problematic refractive errors, including high levels of astigmatism may also be successfully treated with cataract surgery or refractive lens exchange (RLE). Despite such significant accomplishments since IOLs were pioneered 60 years ago, the management of presbyopia remains a challenge for modern surgeons and researchers alike.…”

“…Potentially-accommodating IOLs (AIOLs) that are able to change either their position or shape in response to ciliary muscle contraction are at the forefront of much ongoing research attempting to restore true accommodative function to presbyopic eyes. [5][6][7] Accommodation is the dynamic change in the refractive power of the eye to focus on objects at different distances 8 and is governed by ciliary muscle contraction. The widely-accepted Helmholtzian theory 9 states that as the ciliary muscle contracts, the majority of its mass shifts anteriorly and crucially, inwards, to reduce the diameter of the ciliary muscle collar, 10,11 relaxing tension on the zonular fibres and allowing the elastic capsule to mould the lens into a more convex and dioptrically powerful form.…”

“…45,46 To avoid such disturbing visual effects and restore natural accommodative function, the ultimate goal in ongoing AIOL and presbyopia research is to refill the capsular bag with a substance able to mimic the behaviour of the youthful lens mass. 5,47,48 To date, elastic polymers 48,49 and fluid filled balloons 50 have been trialled in animal eyes but not yet in humans in vivo. Problems such as severe capsular opacification, difficulties removing the lens contents through a small capsulorhexis, plugging of the capsulorhexis following polymer injection, unpredictable post-surgical refractive error and low amplitude of accommodation compared to the pre-operative state have yet to be overcome and it is likely that further years of laboratory and animal investigations are required before human use is plausible.…”