The goal in any surgery is to maximize the normal restoration
of the anatomy and physiology of the organ or tissue involved.
Knowing the procedure implied in cataract or presbyopia surgery
this achievement seems totally impossible. The first registry found
on accommodation is dated since the year 1609 when Steiner
demonstrated for the first time that accommodation is an active
process [1].
Many approaches in order to achieve a functional vision for all
distances as if we had again 20 years old have been proposed an
studied: Multifocal glasses [2] and contact lenses [3], Multifocal
Intraocular Lenses [4-18], Lasik correction for presbyopia [19-28],
Scleral Ciliary Surgery [29], corneal inlays [30-32], monovision
[33,34] and accommodative intraocular lenses [35,36]. In this
summary a description of the accommodative intraocular lenses
(AIOLs) is presented.
Accommodation is a dynamic process in which optical changes
involves modifications in the dipodic power of the eye and provides
the ability to focus at different distances [37]. With the normal
physiological degradation of every cell, tissue and organ, presbyopia
and lens/cataract appears as something inevitable.
No system is capable to function at 100% capacity for long
time. The assumption is that using only 50% of the accommodating
potential will enable comfort and prolong function of the human
accommodating system Donders FC [38]. In this topic, the obvious
question that arises: Is there any evidence of pseudophakic
accommodation available?
The capsular bag seems to be a un adequate location for AIOL´s
due to its unavoidable decadence and fibrosis once the crystalline
lens is emptied [39]. The forces generated at the zonular anterior
capsule system are those to be used for AIOL´s [40]. The capsular
bag is a basal membrane of the lens epithelium, once the capsular
bag is emptied, there are no functions and no anatomical reasons
for it to exist. The development of fibrin and atrophy is unavoidable
as it has no function to accomplish and no anatomy to support [40].
There has been a poor methodology to study near vision:
Inadequate distances, non homologated near vision charts and
correct artifacts in the clinical investigation. To this we can add
a commercial bias, investigator´s vanity in order to assure good
results and poor monitorization of the investigation. The following
studies that we present are examples of what was expected of AIOL
and that the conclusions are determinant in terms of functionality
of this type of AIOL.
A. Comparing two AIOLs with a monofocal IOL Both IOLs
restored distance visual function after cataract surgery with
limitations in near visual outcomes. Eyes with the dual-optic
IOL had significantly better ocular optical quality [41].
B. Three-Dimensional Evaluation of Accommodating
Intraocular Lens Shift and Alignment in vivo Quantitative 3-D
anterior segment OCT allows full evaluation of the geometry of
eyes Implanted with A-IOLs preoperatively and postoperatively
[42].
Three basic approaches can be take in account for the
implantation of an AIOL
1. Change in axial position Single or dual optic
2. Change in shape or curvature of residual anatomy after
cataract surgery [40] The structural source of kinetic energy
in the capsular bag is the anterior capsule The role of the
posterior capsule is possibly minimal in accommodation and
null in AIOL´s The generated forces might be axial or at the
frontal plane (centripetal and centrifugal)
3. Change in refractive index or power
Conditions for a new AIOL
A. Must be independent from the capsular bag
B. Outcomes tested by homologated opt metrical standards
for near (40cm) and intermediate (70 cm) vision
C. Accommodation should be measured by subjective and
objective tests
D. Pseudo accommodation should be identified in the
outcomes
E. Outcome proved in large, multicentrical series and in long
term study observation
Direct competitors of AIOLS are Multifocal IOLs (MFIOLs), but
we must understand that mutlifocality is not physiological, besides
this, mutifocality always will disperse light between the different
foci, not using the 100% of it. Other issue is that multifocal optics
will always require some degree of neuroadaptation. Over the
coming years, once AIOLs are developed adequately, MFIOLs will
be unable to compete, as it happened with pseudophakic glasses
and IOLs. Let´s wait and put our maximum effort in achieving the
maximum satisfaction for patients in this new challenge as it has
been during the history ophthalmology.
Professor, Chief Doctor, Director of Department of Pediatric Surgery, Associate Director of Department of Surgery, Doctoral Supervisor Tongji hospital, Tongji medical college, Huazhong University of Science and Technology
Senior Research Engineer and Professor, Center for Refining and Petrochemicals, Research Institute, King Fahd University of Petroleum and Minerals (KFUPM), Dhahran, Saudi Arabia
Interim Dean, College of Education and Health Sciences, Director of Biomechanics Laboratory, Sport Science Innovation Program, Bridgewater State University