Presbyopic daily disposable contact lenses have until recently been under-represented in the eye care professionals’ fitting armamentarium, with fittings proportionally lower for this indication than for spherical corrections. Dailies AquaComfort Plus Multifocal contact lenses will help address this issue, increasing the possibilities of fitting presbyopes with daily disposable lenses.
Presbyopia
The changes to the eyes occurring in presbyopia, have been elegantly reviewed by Charman.1 Between the ages of 30 and 70, there is a hyperopic shift of about +0.04D sphere per year, accumulating to +1.00 to +2.00D by age 70, and an against-the-rule shift in astigmatism of about 1.00DC. The amplitude of accommodation declines until 52 years of age,2 and presbyopia is generally considered as starting when the amplitude of accommodation has fallen below 3.00D, at about 40 years of age. According to Charman, with increasing longevity, most people in the developed world can look forward to spending almost half of their lives as presbyopes – in the UK 42 per cent of the population are over 45 years old. In an increasingly near-focused world, with tasks such as reading, working on computers and with mobile devices, there are greater near visual demands to correct presbyopia in order to allow people to work and play normally.
Presbyopia correction
The effective correction of presbyopia involves extending the depth of focus of the eye to include two or more distances at which clear vision is required. One of the simplest ways to do this is with a pinhole, but while this works for distance vision, it has limited benefit with intermediate and near acuity,3 and reduces retinal illumination.
Spectacle corrections for presbyopia take advantage of the fixed position of the spectacle lenses, which allows the eyes to rotate and look through the different areas of the lenses. The simplest form is reading glasses for emmetropes or as a second pair for ametropes, bringing the advantages of a wide field of view, and the inconvenience of finding and putting on the appropriate glasses for the task and then removing them for distance vision. Bifocals, attributed to Benjamin Franklin in 1784,4 have the distance correction in the top section of the lens, and the reading prescription in the bottom, allowing alternation between the two by changing the direction of gaze or head position. They offer the convenience of having both corrections in place at the same time, and the inconvenience of having to adopt an unusual head position to see objects not opposite the appropriate area of the lenses.
Bifocals correct for two specific distances, but not for the continuum of intermediate distances between them. For this, multifocals provide intermediate focus steps, and varifocals correct distance and near vision, with all intermediate distances represented in a corridor between the two. The complexity of varifocal optical surfaces means that this corridor is relatively narrow, and there are areas of distortion to either side of it which can be visually uncomfortable. Accurate positioning of the lenses and frames is critical for good performance. Varifocal spectacles wearers often ‘chase’ the focus by using head movement rather than eye movement.
As contact lenses are positioned on the front of the eye, and move with it, they present a different set of challenges compared to spectacles. One of the simplest approaches is to use contact lenses to correct the distance vision, rendering the wearer effectively emmetropic, and then simply supplying reading glasses for near vision use. If multiple corrections are to be achieved through the contact lens alone, as with a multifocal, the area that can be used is restricted to about 8 or 9mm in diameter, and this strongly influences the approaches that can be taken.
Alternating bifocal contact lenses, similar in principle to spectacles where the position of the lens relative to the eye is changed to allow viewing through different portions, tend to be used in rigid gas permeable lens designs. These are smaller than the corneal diameter, and so can be carried upwards on the lid in downgaze to allow viewing for near through the bottom of the lens. Prism is used to orient the lenses with the reading portion at the bottom and, sometimes in conjunction with truncation, to present a thicker edge to the lower lid, so the lens will ride up on it during down gaze and present the reading portion for use. In fact, with so little space in which to position the optical powers, at least some of the time the wearer is looking through both distance and near portions of the lenses simultaneously. Monovision uses a distance correction for one eye, usually the dominant one, and a near-vision correction for the other eye. As a result, there can be a loss of stereoacuity.5,6
[CaptionComponent="183"]A more common strategy for contact lenses, particularly soft ones, is to view through both distance and near portions simultaneously. Two images are seen at any time, one in focus and one not, and the visual system selects to view preferentially the image which is most in focus. Such a system uses the same amount of incident light to create two images instead of one, with an expected loss in contrast and a need for higher levels of illumination. De Gracia et al7 used a beam splitter to examine this effect independently of pupil size, and found that the maximum disruption of the clear image occurred when the other image was blurred by between 0.50D and 2.00D – above this it improved again up to a 4.00D blur, when they speculated that the higher blur allowed for better contrast for the clear image. As presbyopic requirements call for additions of up to about 2.50D, especially when people are using computer screens at a slightly longer working distance, this makes the task of design more interesting. One bifocal makes use of alternating concentric distance and near zones, which confers some independence of pupil size.
Other pupil-independent designs such as diffractive phase plates8 or birefringent materials with two refractive indices9 are either not widely available, or still theoretical. Existing designs need to take into consideration a complex mix of factors such as pupil size in the steady state, and with accommodation, lens centration and alignment with the visual axis, optic zone size/position and the effects of the transitions between distance and near zones. The most commonly used designs are concentric, either with the distance vision zone in the centre, surrounded by an annulus for reading (CD) or the other way round (CN).
While distance and near visual acuities were comparable between monovision and multifocal corrections, the latter provides better stereoacuity, and showed improvements in visual acuity over a 15-day adaptation period.10 Sixty-eight per cent of monovision wearers who were transferred to multifocals preferred to continue with them after six months, compared with 25 per cent who preferred their monovision correction.6 Because the visual demands have to be matched to the presbyopic lens characteristics, and the clear image is often using a portion of the available light, assessment of performance for different tasks becomes more critical, especially in scotopic conditions. For early presbyopes, multifocals performed better than monovision for driving during the daytime and at night, for watching television, and for changing focus from distance to near.11 CD designs have a constant area in the centre given over to distance vision, surrounded by an area which will vary with pupil size for near. CN designs have the opposite arrangement, which might be expected to have an advantage by increasing usage of the distance periphery when the pupils are relatively dilated for distance use, and moving the emphasis to near when the pupils constrict with accommodation and convergence. Both visual acuity and depth of focus under near conditions are better with smaller pupils and binocular use with this type of lens.12
A key consideration for a presbyopic population is a greater tendency to ocular dryness symptoms with age. Soft contact lens wearers with dryness symptoms are reported as having aqueous tear deficiency (30 per cent) and contact lens induced tear instability (25 per cent).13 Asymptomatic wearers have significantly longer pre-lens tear break-up times (TBUTs) (9.8 seconds vs 6.6), better lens wetting and fewer deposits on their lenses. Successful contact lenses for this age group should therefore aim to support these characteristics in performance.
The potential
Presbyopes are less frequently fitted in daily disposable (DD) lenses than in other modalities,14 probably because of less availability of suitable lenses. The general trend in daily disposable lens fitting worldwide comprises 26 per cent of all fits, from 0 per cent in Colombia and Costa Rica to 58 per cent in Denmark.15
In Europe, an estimated 5 per cent of contact lens wearers are using multifocal lenses,16 which can be expected to change if a higher proportion of presbyopes are fitted with contact lenses. High-fitting nations are Portugal 78 per cent, Belgium 67 per cent, Spain 57 per cent with, at the other end of the spectrum, low-fitters such as Singapore, China and Jordan with 0 per cent, Romania 1 per cent, and Lithuania 2 per cent. The UK falls in the middle of the range at 22 per cent.17
DD lenses have other advantages in terms of management, as they have the highest compliance with recommended replacement interval when considered against two-weekly and monthly replacement lenses.18 When used between four and five days per week or less, for instance for social and sporting use, the costs of wearing daily disposable multifocal lenses is lower than that for (compliant) monthly or two-week lens wearers.19
Dailies AquaComfort Plus Multifocal
Dailies AquaComfort Plus Multifocal contact lenses extend the options for fitting daily disposable contact lenses for presbyopia. They use the proven centre-near design of Air Optix Aqua Multifocal contact lenses, with LO ADD for wearers needing up to +1.25D of spectacle add, MED ADD for up to +2.00D and HI ADD for up to +2.50D (Figure 1). The LO ADD has a parabolic front surface effectively providing a centre-near add, and the MED and HI ADDs are achieved with bi-aspheric curves.20.
The 8.7mm back surface is also aspheric, to provide a harmonious fit over the progressively flattening cornea and limbus, out to a lens diameter of 14.0mm. Sphere powers stretch from +6.00 to -10.00D in 0.25D steps (Table 1).
A study on early presbyopes with the similarly designed Air Optix Aqua Multifocal contact lens, gives impressive results over monovision.11 Wearer satisfaction ratings for distance and intermediate vision, daytime driving, night-time driving haloes or glare and observing road signs were 90 per cent or more, and satisfaction with changing focus from distance to near and with night-time driving were also high at 87 per cent and 89 per cent respectively.
A second consideration for this older age group is a contact lens which will sustain wetting and comfort during wear. Dailies AquaComfort Plus contact lenses incorporate three different moisturising agents which have an affinity for water. The first two are incorporated into the packaging solution in the blister. Hydroxypropyl methyl cellulose is a large molecule which increases viscosity of the packaging solution and provides for a ‘cushioning effect’ upon lens insertion. It washes away in the tears shortly after the lens is placed on the eye. Polyethylene glycol (PEG) is a much smaller molecule which diffuses into the matrix of the lens material, and is then released in the early stages of wear. Polyvinyl alcohol (PVA) is the material from which the lens is actually made (nelfilcon A). In production, a small part of this is not cross-linked to form the lens gel and is trapped as a viscous liquid in the lens matrix. The action of blinking causes it to release from the lens during wear.21 Morris22 argues this system is biomimetic as it mirrors the production of mucus from the surface of the conjunctiva, to be spread across the surface in order to stabilise the tears. In fact with this system the pre-lens non-invasive TBUT is longer, indicative of tear stability.23
Conclusion
Dailies AquaComfort Plus Multifocal contact lenses provide a significant expansion of the options for fitting the presbyope. Its combination of proven optics and a three-part blink activated moisturising system fit well with the needs of a population requiring convenience, comfort and good vision at all distances.
References
1 Charman WN. Developments in the correction of presbyopia I: spectacle and contact lenses. Ophthalmic Physiol Opt, 2013.
2 Millodot M and S Millodot. Presbyopia correction and the accommodation in reserve. Ophthalmic Physiol Opt, 1989; 9(2): p126-32.
3 Garcia-Lazaro S, et al. Visual function through 4 contact lens-based pinhole systems for presbyopia. J Cataract Refract Surg, 2012; 38(5): p. 858-65.
4 Optometrists Co. The ‘inventor’ of bifocals? Website, 2013; www.college-optometrists.org/en/college/museyeum/online_exhibitions/artgallery/bifocals.cfm.
5 Erickson P and EC McGill. Role of visual acuity, stereoacuity, and ocular dominance in monovision patient success. Optom Vis Sci, 1992; 69(10): p. 761-4.
6 Situ P, et al. Successful monovision contact lens wearers refitted with bifocal contact lenses. Eye Contact Lens, 2003; 29(3): p. 181-4.
7 de Gracia P, et al. Experimental simulation of simultaneous vision. Invest Ophthalmol Vis Sci, 2013. 54(1): p. 415-22.
8 Freeman MHS. J A New Diffractive Bifocal Contact Lens, in BCLA. 1987.
9 Fiala W. Birefringent multifocal lenses: theory and application to the correction of refractive error. Optom Vis Sci, 1990; 67(10): p787-91.
10 Fernandes PR, et al. Adaptation to multifocal and monovision contact lens correction. Optom Vis Sci, 2013; 90(3): p228-35.
11 Woods J, CA Woods, and D Fonn. Early symptomatic presbyopes – what correction modality works best? Eye Contact Lens, 2009; 35(5): p. 221-6.
12 Plainis S, et al. Through-focus performance with multifocal contact lenses: effect of binocularity, pupil diameter and inherent ocular aberrations. Ophthalmic Physiol Opt, 2013; 33(1): p. 42-50.
13 Young G, et al. Soft contact lens-related dryness with and without clinical signs. Optom Vis Sci, 2012; 89(8): p 1125-32.
14 Efron N, et al. An international survey of daily disposable contact lens prescribing. Clin Exp Optom, 2013; 96(1): p. 58-64.
15 Morgan P, et al. International Contact Lens Prescribing in 2012. Contact Lens Spectrum, 2013; 28(January): p 31-38.
16 Based on third-party industry report, 12 months ending August 2013, Alcon data on file.
17 Morgan PB, et al. An international survey of contact lens prescribing for presbyopia. Clin Exp Optom, 2011; 94(1): p. 87-92.
18 Dumbleton, K, et al. Compliance with lens replacement and the interval between eye examinations. Optom Vis Sci, 2013; 90(4): p 351-8.
19 Efron SE, et al. A theoretical model for comparing UK costs of contact lens replacement modalities. Cont Lens Anterior Eye, 2012. 35(1): p 28-34.
20 Plainis S, DA Atchison, and WN Charman. Power profiles of multifocal contact lenses and their interpretation. Optom Vis Sci, 2013. 90(10): p 1066-77.
21 Mahomed ATB. Contact lenses and comfort enhancers: in vivo and in vitro release of soluble PVA, in EVER – European Association for Vision and Eye Research. 2004.
22 Morris C. High technology contact lens materials and their biomimetic properties – Part 2. Optician, 2008; 235(6146): p. 14-16.
23 Wolffsohn JS, OA Hunt, and A Chowdhury.Objective clinical performance of ‘comfort-enhanced’ daily disposable soft contact lenses. Contact Lens Anterior Eye, 2010; 33(2): p. 88-92.
The authors are affiliates of Alcon Vision Care. Dr Inma Pérez-Gómez is head of professional affairs, EURMEA, Dr Dwight Akerman is head of global professional affairs and Jonathon Bench is head of professional affairs, UK and Ireland