Over the last two decades there has been a slow but progressive increase in the presbyopic population in Europe. According to Eurostat, 18.9% of the European population in 2009 was aged between 50 and 65, reflecting a 2.3% increase from 1998 in the same age interval.1 The number of wearers of multifocal contact lenses has also experienced a significant growth in recent years, although only about 10% of UK contact lens wearers received a correction for presbyopia in 2008.2 Similarly, a recent international survey has revealed a considerable variance among countries with respect to contact lens fittings for presbyopia, ranging from 79% of all soft lens fittings to patients older than 45 years of age in Portugal to zero in Singapore.3 Interestingly, the same survey revealed that 63% of presbyopes were fitted with non-presbyopic corrections, with the remaining 29% and 8% of presbyopes being corrected with multifocal or monovision fitting philosophies, respectively.

Contact lens correction for presbyopia offers diverse options, including monovision, translating or simultaneous vision contact lenses. The goal of simultaneous vision designs is to provide concurrent clear vision at two or more distances by broadening the lens-eye system depth of focus. Simultaneous vision could be described as the overlapping of multiple individual focal points, each having its own range of clear vision, to provide a single, large expanse of clear vision from infinity to near distance.4 However, this method of correction involves a compromise in which depth of focus for high-contrast targets is gained at the expense of glare and losses in retinal image contrast, particularly manifest when the target contrast is low.5

Simultaneous vision may be achieved through concentric, aspheric or diffractive designs.6 Concentric or annular contact lenses are designed with a central zone, which provides either distance or near power, surrounded by a peripheral annulus granting either near or distance vision, respectively. Aspheric designs are truly multifocal to the extent that they display a gradual transition in lens power between distance and near powers by manufacturing the lens with a front, back or front and back aspheric surfaces. Diffractive designs have multiple echelettes that focus distant images by refraction and near images by diffraction of light. While they are considered to be truly pupil-independent, the design of diffractive contact lenses involves a loss in image contrast caused by the fraction of light that goes into higher diffraction orders.7,8 Diffractive contact lens designs are currently not available for presbyopia correction.

It is relevant to note that a successful simultaneous vision contact lens fit requires good lens centration, with little movement on blinking.9 Besides, a certain pupil diameter is required to allow light passing through the diverse zones of the lens to enter the eye, thus determining retinal image quality.9–11 Age has also been found to influence simultaneous vision contact lens success, not only as a result of an increase in the actual addition of the lens (i.e. larger power gradient across the lens surface)12 but also as a consequence of the associated decrease in pupil diameter (i.e. increase in depth of focus and reduced useful optic zone of the lens) and of a reported major tolerance to defocus4. The last two factors have been found to contribute to an increase in the subjective depth of focus of about 0.027 D per year from the age of 21 to 50 years.13

Ocular dominance has traditionally been considered of relevance in presbyopia correction, both in monovision and multifocal wearing modalities. It is interesting to note that several types of ocular dominance have been described in the literature14 whereby it is not uncommon for different dominance tests to yield different results. Indeed, Ooi and He15 described as, for a given person, ocular dominance changed with different test conditions, at different positions in the visual field and with different levels of attention.

Multifocal contact lens wearing success has been explored from different perspectives: objective retinal image quality analysis,10 psychophysical measures of visual quality (mainly visual acuity and contrast sensitivity evaluation)16,17 and subjective visual satisfaction.18–24

Subjective visual satisfaction and wearing success have been previously studied in different contact lens designs and wearing modalities.18–23 On the one hand, Papas and co-workers18 explored subjective visual satisfaction with a 100 point numerical rating scale, where 0 represented the worst and 100 the best possible response to such variables as ghosting, appearance of halos, lens comfort, vision quality, vision fluctuation, facial recognition and overall satisfaction. Significant reductions were found for all wearing modalities and all subjective vision variables under evaluation. Interestingly, these reductions were not associated with similar reductions in visual acuity, as measured by conventional chart based methods, leading the authors to encourage subjective vision evaluation as a better indicator of lens performance than traditional visual acuity tests. On the other hand, wearing success has been defined as wearers still using their lenses a minimum of 8 hours per day, 5 days per week, at three months after the initial contact lens adaptation19 or as a willingness of patients to acquire a new pair of lenses from their contact lens practitioner.18 Monovision, or some form of modified monovision, was initially identified as the most successful wearing modality for presbyopia,19 although more recent studies reveal bifocal and multifocal contact lenses to offer similar or superior patient satisfaction.20–24 The majority of these studies documented blurred and insufficient quality of vision as the principal reason for contact lens discontinuation.

Even though unsatisfactory vision has been identified as the main reason for multifocal contact lens discontinuation, our literature review revealed a large disparity of criteria to define wearing success and patient satisfaction. Very few studies investigate multifocal contact lens performance during visually demanding habitual tasks,25 opting, instead, for an approach consisting on asking patients for an overall quantification of contact lens performance and a simple description of adverse symptomatology.

In this work, a longitudinal prospective, cross-over and double masked study was designed in order to evaluate visual satisfaction and wearing success with two types of simultaneous vision multifocal contact lenses: Acuvue Bifocal (Johnson & Johnson Visioncare, Jacksonville, FL, US) and Proclear Multifocal (Cooper Vision, Pleasanton, CA, US). Visual satisfaction was assessed by means of several task oriented patient evaluation questionnaires where subjects had to grade satisfaction with the performance of their multifocal contact lens designs during diverse visually demanding habitual tasks at home or at the workplace, including near, distance and intermediate vision activities. Wearing success was defined by the percentage of subjects opting to continue multifocal lens wear after the completion of the study and also by the number of subjects still wearing their lenses six months later.

The performance of various multifocal contact lens designs has been previously explored in terms of objective and subjective quality of vision. Although this approach may be useful, particularly for the development of new and better lens designs, multifocal lenses are actually put to the test when their wearers need to do a specially demanding visual task, mostly if it is a habitual task, either at home or at the workplace. For this reason, it was thought that a task oriented evaluation of multifocal lens performance, investigating visual satisfaction for each habitual task, could provide valuable information for practitioners to decide between different contact lens designs, as well as offering a better estimation of long term wearing success.

Ocular sensory dominance may not always be well defined. Indeed, although many contact lens manufacturers recommend determining sensory dominance (Proclear Multifocal) or either sighting or sensory dominance (Acuvue Bifocal) in order to select the eye for distance vision, difficulties may arise when subjects have undefined ocular dominance. These cases are often solved by trial and error. It is also relevant to observe that our elder group of subjects (> 55years) had an average pupil diameter of 5.28mm. Although pupil diameter was measured in predefined illumination conditions, which will vary in real daily life situations, it may be assumed that average pupil diameters of about 5mm may limit the percentage of light entering through the most peripheral area of the Proclear Multifocal lens, for both “D” and “N” designs. The obvious visual implications of this limitation are discussed below.

The study of the characteristics of the sample under evaluation revealed that participants devoted many hours per day to particularly demanding tasks in terms of vision, such as computer work, which involves mostly intermediate vision, or reading and driving, which favour near and distance vision, respectively. As expected, visual satisfaction with multifocal contact lens wear was lowest for those tasks with a higher visual demand.

As for observation distance, visual satisfaction was found to increase in those tasks requiring intermediate vision or a combination of distance and near vision. It may be speculated that the depth-of-focus enlargement associated with the simultaneous vision lens designs under evaluation offers a better compromise for intermediate vision, that is, the retinal image corresponding to an object located at an intermediate distance is sharper. Besides, pupil coverage of intermediate vision zones of the multifocal lens design (as determined for the Proclear Multifocal lens design) is superior to that of distance and near vision areas. Tasks involving a combination of distance and near vision are probably solved by taking momentarily advantage of the asymmetrical multifocal lens design as an alternating monovision solution. On the contrary, sustained distance or near vision tasks would require a more permanent unilateral suppression which, with a lens design allowing for a relatively good binocular vision of intermediate distances, may prove difficult to accomplish. These last considerations, however, are only valid for the Proclear Multifocal lens design and not for the Acuvue Bifocal lens which, notwithstanding fine adjustments in negative power in the dominant eye and addition power in the non-dominant eye, was not adapted following a modified monovision philosophy. As no interaction could be disclosed between “type of lens design” and “observation distance” at Q1 or Q7, further evaluation of these findings is required to draw definite conclusions.

The fact that visual satisfaction with the Proclear Multifocal lens tended to increase towards the end of the trial period (Figure 3) may be interpreted as a partial adaptation to the modified monovision provided by this lens design, not implemented in the Acuvue Bifocal lens. Indeed, success with monovision has been related to patient perseverance, that is, monovision performance seems to improve with time.27

There is a lack of agreement in the literature about the definition of wearing success, thus preventing direct comparison between studies. The present research, for example, would reflect a success rate between 88% and 5%, according to either the percentage of subjects opting for multifocal lens wear continuation after the initial trial, or those still using their lenses in a daily basis six months later. Nevertheless, if wearing success is defined as regular or sporadic lens wear six months after the completion of the initial trial, our success rate reaches 50%, in concurrence with previous studies.19,20

The main reason for multifocal lens wear discontinuation was found to be insufficient quality of vision. This finding has been extensively reported in the literature (see, for example, Papas et al., 2009; and Sheedy et al., 1991).18,21 Particularly demanding visual tasks such as driving at night were found to be the most challenging for this modality of contact lens wear, in agreement with a previous study by Chu and co-workers.28

Finally, a number of limitations of the study should be considered when interpreting these findings. Indeed, the visual requirements of our study sample are probably more demanding than those of a population of subjects from a similar range of ages. Although higher visual demand levels would lead to a better appreciation of multifocal designs limitations, it could be speculated whether wearing success was not actually underestimated, that is, whether other occupational groups with lesser visual demands would exhibit more positive results.

Additionally, multifocal contact lenses wear requires a higher level of commitment to adaptation by the patient than monofocal designs, being often associated with patients with a higher motivation.29 Although subjects with initial manifest poor motivation were excluded from the study, all participants opting for the continuation of multifocal lens wear were provided with free pairs of lenses and solutions for six months after the completion of the initial trials. This type of reward modulated selection may have given rise to a larger number of participants choosing to continue lens wear, probably including less motivated subjects, than if free lenses had not been awarded. This limitation could have been avoided if all participants in the study had received a similar type of compensation, either free contact lenses or another type of reward, with independence to whether they decided to continue lens wear or opted for lens discontinuation.

In conclusion, the results from the present study have revealed an effect of visual demand, observation distance and contact lens design on visual satisfaction of multifocal contact lens wearers. A thorough exploration of each patient's habitual tasks in terms of visual demand, observation distance and time dedication may prove beneficial when selecting lens design in order to increase future visual satisfaction and wearing success. Although the specific characteristics of our study sample probably precluded higher levels of wearing success and, as it is often the case in contact lens research, the findings of the present study are difficult to extrapolate to other, current or future, multifocal lens designs, this research may contribute to increase our understanding of such a complex issue as multifocal contact lens fitting and selection.

The authors have no conflicts of interests to declare.