Multifocal Contact Lenses: a Review

By Francesca La Forgia, Optician-optometrist

and student of the Expert Certificate in Clinical Optometry

Presbyopia

Presbyopia is not considered an eye disease, but a disorder that affects everyone during the natural aging process. It is an age-related loss of lens accommodation resulting in inability to read/write or to do near work. When we’re young, the crystalline, a lens, is flexible and relatively elastic. It can change its length or shape with the help of tiny muscles that surround it. The muscles that surround the eye can easily reshape and adjust the crystalline to accommodate both close and distant images. With age, the lens and the muscle fibers surrounding the lens slowly lose flexibility and stiffen. As a result, the crystalline becomes unable to change shape and constricts to focus on close images. There is a change also of the quality and quantity of tear film and the internal aberrations of the eye.

Presbyopia usually begins between the ages of 38 and 45 and the prevalence is virtually 100 per cent by 50 to 52 years of age¹. Overall, since 1950 the proportion of older persons (over 60 years) has been rising steadily, passing from eight per cent in 1950 to 11 per cent in 2009 and it is expected to reach 22 per cent in 2050².

Presbyopic patients can use reading glasses, progressive lenses, surgery or have a variety of options for correcting their refractive error with contact lenses². These options can be grouped into three main categories: supplemental spectacle correction over contact lenses, monovision (uses one eye for distance and the other for near) and multifocal contact lenses^3,4.

Many presbyopic lens wearers are currently prescribed monovision, althought this form of correction has major limitations⁵. Binocular high contrast visual acuity is lower with monovision compared to multifocals, contrast sensitivity function is reduced binocularly and stereopsis is also reduced^6,7. Monovision offers limited varieties of opportunity for patients. Why give up to the high quality vision?

When presbyopia is corrected with contact lenses, multifocal lenses are fitted 3.6 times more than monovision lenses². To fit multifocal contact lenses is an opportunity, but the dissatisfaction with the performance of multifocal soft contact lenses due to unwarranted visual compromise does not make it in an attractive option for the potential presbyopic lens wearer⁸. If the wearer is not satisfied in comfort and vision, the dropout is near. The aim and the key factor of the eye care practitioner is to find the best correction, design and materials for his patient.

Designs

There are different designs of multifocal contact lenses: concentric (or annular), aspheric and diffractive².

Concentric design: a small central annular zone which provides either distance or near power, surrounded by a peripheral annulus granting either near or distance vision, respectively.

Aspheric lens design: a gradual change of curvature along one of their surfaces based on the geometry of conic sections. It can be centre-near (the highest plus power is in the geometrical centre and decreases in the periphery) or centre-distance (the lowest plus power in the centre).

Diffractive design: a central zone focuses images at distance by refraction of light and near through diffraction principles created by the zone echelettes. The selection of design is based on various wearer ocular features.

Fitting

The through-focus nature of the image, which influences the “best focus” (distance correction) and the reading addition, varies due to several factors: ocular aberrations (particularly spherical aberration), the wearer’s pupil diameter and lens centration. Visual performance with some designs may show greater sensitivity to these factors⁹.

Between individuals, spherical aberration of the whole eye varies, unlike other high order aberrations, is invariably positive in nature. The aberrations of the internal eye increase progressively with age, due mainly to crystalline lens changes. Spherical aberration, like other optical aberrations, is affected by pupil size. The same aberration in the same eye with a 6mm pupil results in considerably greater defocus than with a 3mm pupil. Spherical aberration results in depth of focus at the retina, in object space it results in depth of field¹⁰. Why such interest for spherical aberration? Spherical aberration provides the multifocal effect¹¹. The same multifocal lens applicated on two different eyes gives back different visual performance.

Very important is to find the appropriate design for the wearer, evaluate the centration and the movement of the contact lens. If a multifocal lens decentres, it will induce unwanted aberrations. Corneal topography may be a useful method to evaluate lens centration¹². With the objective method can be gaining feedback on subjective vision performance, by asking patient if they notice any doubling or splitting of vision¹⁰.

The choice of material can influence tear stability that already reduces with age. The aim is to select a material which maintains a stable tear film and provides more consistent vision as well as reducing symptoms of dryness and discomfort.

Not only for presbyopia

High myopia is a risk factor of many eye diseases, which include the cataract, myopic retinopathy, and retinal detachment. A number of optical and pharmacological modalities have been widely investigated for restriction of myopia progression. More recently, numerous multifocal soft contact lenses and extended depth of focus soft contact lenses (collectively referred to as myopia control contact lenses) were found effective in slowing myopia. As opposed to overnight orthokeratology, myopia control contact lenses are worn during the day and the hypotheses proposed to explain the efficacy of these lenses are generally based on the premise that the stimulus for eye growth is a defocused retinal image with hyperopic blur either centrally or peripherally¹³.

Adaptation, but also communication!

Be professional is essential for the best fitting, but we don’t forget the efficient communication.

Adaptation to multifocal contact lenses is not an immediate process because the brain needs time to integrate effectively those images presented for each of the distance. Visual performance may improve with time. Functionality of any of the simultaneous image designs should also be governed by blur adaptation, which is believed to occur at the cortical level¹⁴. All of us has different tolerance of defocus blur that is related to personality factors¹⁵. We need to explain it!

Authors have suggested ways of opening a discussion with long-term contact lens wearers about how their visual and lifestyle needs change over time¹⁶. What are the expectations? Give importance on wearer habits is useful for a great satisfaction of the patient and consequently of the practitioner.

The freedom to choose every day between multifocal contact lenses or glasses should be presented to patients as a factor for improving their quality of life.

References

1. Kleinstein RN. Epidemiology of presbyopia. In: Stark L, Obrecht G eds. Presbyopia. New York: Professional Press,1987. P 14-15.

2. Pérez-Prados R, Piñero DP, Pérez-Cambrodí RJ, Madrid-Costa D. Soft multifocal simultaneous image contact lenses: a review. Clin and Exp Optom, 2016.

3. Llorente -Guillemot A, Garc í a -Lázaro S, Ferrer Blasco T et al. Visual performance with simultaneous vision multifocal contact lenses. Clin Exp Optom, 2012.

4. Bennett ES. Contact lens correction of presbyopia. Clin Exp Optom 2008.

5. Evans B. Monovision: a review. Ophthalmic Physioln Opt, 2007.

6. Rajagopalan AS, Bennett ES, Lakshminarayanan V. Visual performance of subjects wearing presbyopic contact lenses. Opt Vis Sci, 2006.

7. Richdale K, Mitchell GL, Zadnik K. Comparison of multifocal and monovision soft contact lens corrections in patients with low -astigmatic presbyopia. Opt Vis Sci, 2006.

8. Kim E, Bakaraju RC, Ehrmann K. Power Profiles of Commercial Multifocal Soft Contact Lenses. Optom Vis Sci, 2017.

9. Plainis S1, Atchison DA, Charman WN. Power profiles of multifocal contact lenses and their interpretation. Optom Vis Sci, 2013.

10. Dave T. Understanding multifocals and getting them to work. Optician, 2015.

11. Wagner S, Conrad F,Bakaraju RC et al. Power profiles of single vision and multifocal soft contact lenses. Cont Lens Anterior Eye, 2015.

12. Lampa M, So K, Caroline P et al. Assessing multifocal soft contact lens centration with the aid of corneal topography. Poster presentation at Global Speciality Lens Symposium, 2012.

13. Sankaridurg P. Contact lenses to slow progression of myopia. Clin Exp Optom, 2017.

14. Mon-Williams M, Tresilian JR, Strang NC et al. Improving vision: neural compensation for optical defocus. Proc Biol Sci, 1998.

15. Woods RL, Randall Colvin C, Vera-Diaz FA and Peli E. A relationship between Tolerance of Blur and Personality. Optom Vis Sci, 2010.

16. Bharuchi S, Donne S. Conversations in practice: managing the long-term wearer. O ptician, 2014.