Correcting Presbyopia Modern Options
Jason Higginbotham BSc (Hons) MCOptom FBDOHead of Clinical Affairs
What is Presbyopia?First noticed by the ancient Greeks, Presbyopia was considered to be a deficiency in the eyes energy in focussing rays FROM the eyes onto near objects and that the weaker energy in the old meant that these rays could only be focussed on more distant objects and still be seen. Presbyopia, a natural age-related condition, is the result of a gradual decrease in accommodative amplitude, from about 15 dioptres (D) in early childhood to 1 D before the age of 60 years. An irreversible, normal physiologic condition that affects all primates, it impairs the ability to see clearly at near. If presbyopia is uncorrected, a significant functional visual disability is likely to develop. (AOA.ORG)Beers AP, van der Hiejde GL. Age-related changes in the accommodation mechanism. Optom Vis Sci 1996; 73:235-42.
Hamasaki D, Ong J, Marg E. The amplitude of accommodation in presbyopia. Am J Optom Arch Am Acad Optom 1956; 33:3-14.
Ramsdale C, Charman WN. A longitudinal study of the changes in the static accommodation response. Ophthalmic Physiol Opt 1989;9:255-63.
What is Presbyopia?
In 1922, Duane did extensive research on amplitude of accommodation on some 4200 eyes. AGE AMPLITUDE OF ACCOMMODATION (D)High Amplitude in childhood, but reduction in amplitude begins very early on.Presbyopia begins around the early forties, where the reduction in amplitude becomes symptomatic.Depth of focus seems responsible for what little accommodation remains beyond around 50 years.*With thanks to Leon Davies at Aston University
How does Accommodation work?Scheiner (1619) first suggested and proved some form of active mechanism was at work in the eye to change the total dioptric power of the eyes focussing system.Descartes suggested the lens was responsible. Others also suggested a change in axial length of the eye, axial position of the lens, curvature change of internal refracting surfaces and change in pupil size were responsible.We now know there is an element of a few of these at play lens curvature change and thickness, slight movement of lens axial position and pupil size change.
Myopia studies also now show that there is a change in axial length of the eye to maintain internal ocular volume constants.
Ultimately, there are two main elements of accommodation. These are known as static and dynamic. The static element of accommodation involves things like depth of focus from pupil size, corneal spherical aberration and coma, astigmatic differential focus and so on. The dynamic element of accommodation involves things like the actual change in curvature of the lens surfaces by action from the ciliary body and the lens capsule as well as anterior axial movement of the lens due to pressure from the vitreous for example. 4
Accommodative Apparatus Revisited
Pardue and Sivak 2000
Longitudinal fibres (L)Radial fibres (R)Circular fibres (C)When the ciliary muscle is relaxed, the circular and radial fibres pull the zonules tight and the zonules hold the lens capsule flatter. This keeps the lens in its unaccommodated state.
The longitudinal fibres seem to also produce some effects on the choroid and sclera which in turn can affect the vitreous pressure axially. It appears that during accommodation, there is some anterior axial pressure from the vitreous onto the lens, pushing it forward slightly and increasing positively the effective power of the total optical system.
The suspensory ligaments are known as the zonules and research has shown these are primarily split into anterior and posterior zonules. The anterior zonules are attached from the ciliary processes to the anterior lens capsule and the posterior zonules are attached from the pars plana to the posterior lens capsule.Most sources suggest that the posterior zonules pull on the anterior zonules during negative accommodation or relaxation of the ciliary muscle. This action applies pressure anteriorly and posteriorly and the tension flattens the capsule and thus the lens.5
Accommodative Apparatus Revisited
Lens anatomy is thought to be pivotal in how accommodation works via the recoil of parts of the lens capsule.
Lens Capsule anatomy after Fincham (1926)AnteriorPosteriorThe areas of highest thickness produce changes to the lens thickness and curvature as well as a reduction in equatorial diameter of the lens.
When the capsule recoils, it produces steepening of both lens surfaces, but primarily the anterior surface. There is thickening of the lens and this seems to be mainly down to anterior movement of the anterior lens cortex, though there is some evidence to show pressure from the vitreous playing a part in this via longitudinal ciliary muscle contraction as well. 6
The Helmholtz Theory of AccommodationThe Helmholtz Theory is sometimes referred to as the relaxation theory of accommodation.It postulates that the elastic capsule surrounding the crystalline lens is the driver of positive accommodation. As the ciliary muscle contracts and moves inwards, the tension on the zonules is released; allowing the lens capsule to recoil and try and take on a more circular shape. This forces the lens into a more steep curvature, with reduction in the equatorial lens diameter and an increase in the lens axial thickness.Other theories exist, but for the purpose of this lecture and in accordance still with modern consensus, the Helmholtz Theory shall be taken as the most likely to be correct.
The Helmholtz Theory of Accommodation
Classic Relaxed versus Contracted diagram of AccommodationSplit MRI images of same eye in relaxed (right half) and accommodated state (left half).
Recent studies have shown that during accommodation, probably from contraction of the longitudinal muscles of the ciliary body, the vitreous pushed the lens forward slightly. This has some effect on the effective power of the lens and total refractive apparatus of the eye. This has some advantage in providing some near vision functionality in pseudophakic patients.8
PseudoaccommodationEssentially, Pseudoaccommodation in phakic patients can be defined as the ability of the unaccommodated emmetropic eye to view near objects.
Ultimately, the primary factor in this is pupil size and thus depth of focus.
Pallikaris et al (2011) described Pseudoaccommodation in pseudophakes as a complex phenomenon that can be attributed to several static (i.e. pupil size, against-the-rule cylindrical refractive error, multifocality of the cornea) and dynamic (i.e. anterior movement of the implant itself) factors.
Methods of Correcting PresbyopiaThree Principal Approaches (Pallikaris et al 2008)1) Provide functional multifocality in the visual system2) Provide binocular divergence with one eye viewing Distant objects and the other eye viewing Near objects (i.e. MONOVISION)3) Attempt to restore normal accommodation to the eyeStatic Surgical and non surgicalStatic Surgical and non surgicalDynamic Surgical only
There are multiple ways of achieving multifocality and monovision; both non surgical and surgical. These are known as Static interventions as they dont produce any dynamic change to the focussing power of the eye.
Attempting to restore accommodation to the eye can only be done with surgical techniques and these are dynamic interventions producing an actual change in focussing ability of the eye.10
Static techniquesSpectacles- Reading glasses, or over refraction readers for CLs- Bifocals- PALs (Progressive addition lenses)- Half eyes or monocles- Intermediate / occupational lensesContact lenses- Monovision- Bifocal or Multifocal - Enhanced monovision multifocalSurgical- Corneal options- IOLs (pIOLs, mIOLs, monovision, etc)- Scleral implants
For the purposes of this presentation, I will assume that delegates are familiar with current spectacle and contact lens options.
However, to recap briefly, apart from normal reading glasses, bifocals and progressive addition lenses, some patients are near full time contact lens wearers. These patients can use ready readers to provide near vision over their contact lenses, or they can use some form of multifocal CL corrections, including enhanced monovision.
Enhanced monovision can be used with either bilateral multifocals with one lens more balanced for distance (smaller add) and the other more balanced for near (larger add) or with the distance lens having the higher add and with the near lens being given maximal plus for distance and a smaller or similar add to the other eye. This depends on ocular dominance and patient requirements.
In all static techniques, some degree of patient tolerance adjustment may be necessary and in many monovision based options, the patients expectations need to be properly managed to avoid disappointment. In many cases, despite lower levels of binocular distance acuity than previous, the increase in near acuity outweighs this for many patients and they are happy with their overall visual outcome.11
Corneal Surgical Static techniquesThere are several corneal techniques which can be used to provide some form of presbyopia correction; these include: Corneal inlays (CIs) / onlays (KAMRA)Laser ablation (LASIK or LASEK)Conductive keratoplasty (CK)Corneal implant lenses (Raindrop lens)Intrastromal Femtosecond Ring Incisions (INTRACOR)
Corneal Inlays / OnlaysKAMRA This uses a circular ultrathin biomimetic stromal implant which has a small central aperture. This is normally implanted in the non dominant eye to improve depth of focus and provide a form of monovision through pseudoaccommodation.
Where a laser is used to excavate some corneal tissue for som