One of the major consequences of the aging population is presbyopia. It is expected that the population aged >60 years will reach 22% of the whole world population in 2050.1 At this age, the prevalence of presbyopia is considered to be essentially 100%.
Population aging has important implications in the field of contact lenses (CLs) because it is necessary to provide satisfactory solutions for presbyopia correction with CLs. Recently, Morgan et al.2 carried out a study to determine worldwide patterns of fitting CLs for the correction of presbyopia. They concluded that there were low levels of prescribing of presbyopia-correcting CLs for patients aged >45 years. The authors also showed that when presbyopia is corrected with CLs, multifocal lenses are fitted 3.6 times as much as monovision lenses. It could be due to multifocal CLs provide better stereoacuity than monovision.3–7 Taking into account this low level of prescription of presbyopia-correcting CLs, Morgan et al.2 pointed out that clinical and laboratory research in CL field should be accelerated in order to fully meet the needs of presbyopic CL wearers.
Recently, CooperVision (Fairport, NY) has introduced the Proclear multifocal toric into the market. This multifocal CL is manufactured for a monthly replacement and designed to correct both astigmatism and presbyopia. To the knowledge of the authors, no studies of this multifocal toric CL have been published in the peer-reviewed literature.
The goal of this study was to assess visual function in presbyopic subjects with astigmatism who were fitted with the Proclear multifocal toric. In order to characterize visual function, distance, and near visual acuity (NVA), distance and near contrast sensitivity (CS), defocus curve, and stereopsis were assessed.
A crossover study was carried out at the University of Valencia with a sample of 20 presbyopic subjects with astigmatism. Inclusion criteria were age between 45 and 65 years, spherical equivalent error between + 3.00 and −3.00D, astigmatism between 0.75D and 2.75D, normal binocularity and the desire to no longer wear any form of spectacle correction for distance and near vision. Exclusion criteria included ocular disease, amblyopia and/or strabismus, and a history of ocular surgery or inflammation. All subjects had a complete eye examination, which included refraction, measurements of pupil size under photopic (85 cd/m2) and mesopic conditions (3 cd/m2) using the Colvard pupillometer (Oasis, US), screening for ocular and systemic diseases, slit-lamp biomicroscopy, and examination of the fundus. All subjects were free of any ocular pathology, showed a photopic pupil diameter ≥3.00 mm, and had best-corrected monocular visual acuity (VA) of 20/20 (0 logMAR). The study followed the tenets of the Declaration of Helsinki and was approved by the institutional review board. Informed consent was obtained from all patients after the nature, and possible consequence of the study had been explained.
Patients were fitted with the CooperVision (Fairport, NY) Proclear multifocal toric CL (Fairport, NY). We followed the fitting nomogram suggested by the manufacturer for the initial lens selection.8 The Proclear multifocal toric CLs are available in two versions; one of them is the Proclear multifocal toric “D” with a spherical central zone for the correction of distance vision and an aspherical annular zone for the correction of intermediate and near vision. The other version is the Proclear multifocal toric “N” with a spherical zone for the correction of near vision and aspherical annular zone for the correction of intermediate and distance vision. The front surface of the Proclear multifocal toric “D” and Proclear multifocal toric “N” CLs is aspheric, with the anterior surface having a toric generated surface for the purpose of correcting vision in eyes with astigmatism. The lens is manufactured from Omafilcon A that has a water content of 59%. The lens has a total diameter of 14.4 mm, and the base curves are 8.40 and 8.80 mm. The cylinder powers available are from −0.75 to −5.75D and the add powers are from +1.00 to +4.00D.
The subjects were also fitted with toric single vision distance soft CL (DCL) (Proclear toric, CooperVision, Fairport, NY) combined with reading spectacles. These CLs maximized distance visual acuity (DVA), and the near spectacle prescription was selected to provide best VA at 40 cm. Subjects were randomized to multifocal toric CL or DCL for the first month. After 1 month of wear, subjects returned to be fitted with the other lens.
The near add and the eye dominance were determined following the clinical protocol of the study of Richdale et al.4 For assessing the eye dominance, the patient was asked to create a small viewing hole with his or her hands and to isolate a 20/40 letter on the Snellen chart within the viewing hole. The examiner then covered each of the patient’s eyes to determine which eye was used to sight the letter. The near add was determined by positive relative accommodation +0.50D.
The lens fit assessment process was carried out according to the clinical protocol of the study by Chamberlain et al.9 Following this clinical protocol, after a settling period of 5 minute standard high-contrast DVA logMAR and standard lens fit assessment of centration, movement and corneal coverage using a 5 points system10 were undertaken. Toric lens fitting characteristics were reported in terms of “rotation” (the angle between the vertical lens scribe marking and 6 o’clock position) and “stability” (the maximum excursion of the lens in degrees following version to the right, left, up, and down). If lens rotation was > 5 degrees, the lens was removed, a new lens with a different axis, which compensated for this rotation, was applied, and the assessment process was repeated.
Participants were scheduled for a clinical evaluation after 1 month wearing each one of the CLs. Each patient was given a comprehensive eye examination, including medical and ocular history, VA, refraction, and slit lamp biomicroscopy. The clinical measurements of visual function were monocular and binocular high contrast DVA under photopic conditions (85 cd/m2), monocular and binocular high contrast NVA, monocular and binocular distance CS under photopic conditions (85 cd/m2) and under mesopic conditions (3 cd/m2) without and with glare, and monocular and binocular near CS under photopic conditions (85 cd/m2). The through-focus binocular logMAR VA (defocus curve) (range from −4.00 to +2.00D in 0.50D steps), with randomized letter sequences and randomized lens presentation in order to reduce memory effects11 was also evaluated. The near range of clear vision was quantified by the curve fitting method and was defined as the range of defocus that maintains best VA plus 0.04 logMAR.5 All measurements were taken using the Optec 6500 vision testing system (Stereo Optical Co). Stereopsis was measured with Random dot test. All examinations were performed by the same experienced CL practitioner. The order of the testing was randomized between subjects after wearing the CL for a month in each condition (multifocal and DCL) at two measurement sessions.
Data were analyzed using SPSS for Windows v.17.0 (SPSS, Chicago, IL). Normal distribution of variables was assessed using the Kolmogorov-Smirnov test. Hypothesis testing for VA and CS was performed by repeated measures analysis of variance (ANOVA). Different ANOVAs were performed for far and near results, thus not assuming the same performance for the lens at both distances. When differences were found, a Tukey multiple comparison test was performed to control the type I error rate.
Twenty participants (4 men and 16 women) with a mean age of 50.4 ± 7.8 years (from 45 to 63 years of age), a mean spherical refraction of −0.51 ± 2.01D (range: +3.00 to −3.00D), a mean of cylinder refraction of −1.36 ± 0.78D (range: −0.75 to −2.75), and a mean near spectacle addition of +1.84 ± 0.76D (range: +1.00 to +3.00D) were included in this study. Mean pupil diameter was 3.46 ± 0.23 mm and 5.32 ± 0.36 mm under photopic (85 cd/m2) and mesopic conditions (3 cd/m2), respectively.
Repeated measures ANOVA revealed statistically significant differences for VA values, both for far and near vision (p < 0.001 in both cases), thus post hoc tests (Tukey) were then performed to look for those differences among measures. Post hoc test revealed differences between monofocal and multifocal values for VA both at far and near, and both monocular and binocular (always with better values for the monofocal group, as can be seen in Table 1). At distance, differences were not found for monocular DVA between the multifocal toric CL “D” and multifocal toric CL “N.” However, at near the multifocal toric, it can be seen that differences were on the order of 1 to 2 letters of logMAR VA; hence, they could be considered not clinically significant.
Monocular and binocular distance log10 CS under photopic and under mesopic conditions, without and with glare are shown in Fig. 1. Repeated measures ANOVA also revealed statistically significant differences for CS values for far (p < 0.001) and near (p < 0.001). Post hoc Tukey test revealed that under photopic conditions (Fig. 1), binocular CS was better with DCL than with multifocal toric CL only at 18 cycles/degree (cpd). Similarly, differences in monocular CS between DCL and multifocal toric CL “D” were only found at 18 cpd (p = 0.005). Between DCL and multifocal toric CL “N,” there were differences at 6, 12, and 18 cpd. No differences were found between multifocal toric CL “D” and multifocal toric CL “N.”
Under mesopic conditions without glare (Fig. 2) and with glare (Fig. 3), there were differences between both groups in binocular and monocular CS for all spatial frequencies. Differences in monocular CS between the multifocal toric CL “D” and multifocal toric CL “N” were not found at any spatial frequency. Fig. 4 shows binocular and monocular near CS under photopic conditions. There were differences between both groups in monocular and binocular near CS for all spatial frequencies. Monocular near CS was better with the multifocal toric “N” than with the multifocal toric “D” at all spatial frequencies except for 1.5 cpd.
Mean values of stereopsis obtained with multifocal toric CLs and with the DCL combined with reading glasses were 62 ± 12 sec of arc and 59 ± 12 sec of arc, respectively (paired t-test, p = 0.06). The depth of focus curve for the multifocal toric CL is shown in Fig. 5. The near range of clear vision was 1.55 ± 0.33D.
Presbyopia correction is currently an important area of CL practice and, due to population aging, will be even more so in the future. Among CLs options for presbyopia, the multifocal CL is preferred for most wearers,2,4 probably because stereopsis is better than with monovision.3–7 Recently, a new multifocal toric CL has been introduced to correct both astigmatism and presbyopia. However, to the best of our knowledge, no studies of the correction of astigmatism and presbyopia with this simultaneous vision multifocal CL have been conducted.
The results of the current study in terms of binocular and monocular DVA and NVA show that multifocal toric CLs provides good outcomes for distance and near vision (about 20/20); however, there were statistically significant differences between multifocal toric CLs and DCLs for binocular DVA and NVA. We think that these differences could are not clinically meaningful, as the difference was in the order of 1 to 2 letters of log MAR VA (Table 1). Unfortunately, we could not make comparisons with other studies because to our knowledge, this is the first study that evaluates the visual performance of this lens. However, it seems valuable to compare our results with those obtained in other studies with other simultaneous vision multifocal CLs (without toric surface, that is for patients without astigmatism or with low astigmatism). Ferrer-Blasco and Madrid-Costa7 with the Proclear multifocal CL showed similar results to those obtained in the current study (−0.007 and 0.012 logMAR for distance and near vision, respectively). These authors6 also reported similar results with the Focus Progressives CL and with the PureVision multifocal CL. Similarly, previous studies12,13 with the Focus Progressives CL agree with our results (about 0 and 0.05 logMAR for distance and near vision, respectively). However, Gupta et al.5 reported worse results with the high addition PureVision CL (0.08 ± 0.10 and 0.27 ± 0.09 logMAR for distance and near vision, respectively).
To properly assess the visual function of the subjects fitted with these multifocal CLs, in the current study, the distance CS, under photopic and mesopic conditions with and without glare, and near CS were evaluated. Previous studies have shown that the creation of simultaneous retinal images either by multifocal intraocular lenses or multifocal CLs, reduces CS under photopic and mesopic conditions compared with that obtained with monofocal lenses or with monovision.5,14–26 The reduction of CS occurs because of the multifocal principle. According to this principle, the incoming light distribution is divided into two or more foci.15 Our results are in agreement with this, because if we compare our results of distance and near CS wearing multifocal CL with those obtained wearing the control CL (single DCL), we find reduced CS over that obtained with DCL in all conditions studied (Fig. 1 to 4). This reduction of CS was mainly at high spatial frequency (12 and 18 cpd) and as has been pointed out,27 the high spatial frequencies are closely linked to VA and visual performance. Although, comparing our results with those of the study of Hohberger et al.28 in which the authors reported the age-related curves for CS in normal subjects, one could observe that despite of the reduction of CS provided by the multifocal CL, mean binocular distance CS under photopic conditions was within normal limits for this age range. Gupta et al.5 assessed distance and near binocular CS with PureVision multifocal CL, and they reported similar results to those obtained in our study.
To our knowledge, this is the first study to assess CS with simultaneous vision multifocal CL when the luminance level was reduced. However, this parameter has been widely studied with simultaneous vision multifocal intraocular lenses. Studies that evaluated CS with simultaneous vision multifocal intraocular lenses found a reduction in CS when the luminance level was reduced, particularly for higher spatial frequencies.14,15,18–20,23–26 This trend agrees with classic data on the effect of the luminance level on contrast sensitivity.29 Consistent with studies with simultaneous vision multifocal intraocular lenses, we observe that in our study the patients with simultaneous vision multifocal CL also had worse CS under mesopic conditions with and without glare (Figs. 2, 3).
For this study, the CLs were available in two design versions. One of them is the “D” design, with a spherical central zone for the correction of distance vision and an aspheric annular zone for the correction of intermediate and near vision. The other version is the “N” design, which has a spherical zone for the correction of near vision and aspheric annular zone for the correction of intermediate and distance vision. The fitting nomogram suggested by the manufacturer indicates to fit the “D” design (center-distance) for the dominant eye, which emphasizes distance vision, and the “N” design (center-near) for the non-dominant eye, which emphasizes near vision. By this strategy, patients should gain good binocular distance and near visual vision. Our binocular visual results support this. However, we considered it interesting to analyze each design separately. When distance CS for both designs (Figs. 1D, 2D, and 3D) is compared, it is possible to observe that differences were not found between the two lenses at any luminance level studied. However, near CS was better with the “N” design than with the “D” design (Fig. 4D). Probably, these differences can be accounted for by two things: the sample chosen for our study and the design of the CL. Most of our subjects were incipient presbyopes (60% of the participants were <50 years of age); hence, most of them used a CL design with a low add (60% of the subjects had a near add lower than 1.50D). For the low add, the central zone diameter of “N” design (center-near) is about 1.7 mm. The pupil diameter in our sample was 3.46 ± 0.23 mm and 5.32 ± 0.36 mm under photopic and mesopic conditions, respectively. Together, the pupil diameter of the patients in our sample and the design of the CL for low adds may explain why for incipient presbyopes the near portion of the “N” design may have a limited effect for distance vision. For that reason, both designs “D” and “N” obtained similar distance visual quality. However, for near vision, the measurements were taken under photopic conditions (the mean pupil diameter under this conditions was 3.46 ± 0.23 mm), and the pupil size also becomes smaller due to the accommodative reflex.30–32 Therefore in this situation, the “D” design (this design has a central zone with a diameter of about 2.3 mm for distance vision) offers mainly distance power. Hence, this design does not provide as good near visual quality as the “N” design (center-near).
The results obtained in our study could vary with different pupil sizes and with other add power and/or designs of CLs. To confirm this, further studies should be carried out in order to assess distance and near CS for different pupil diameters and with different add powers and multifocal CLs designs. Ultimately, the relation between pupil diameter and the performance of different designs of multifocal CLs could be established.
It is logical to think that patients fitted with multifocal CL may also be interested in obtaining an optimal visual performance at intermediate distances. Hence, it would be also interesting to know the visual performance of this multifocal CL at different intermediate distances. In order to do that, previous studies have shown that the defocus curve is an effective method to assess the clear range of vision in patients with simultaneous vision multifocal intraocular lens or CL.5,14,33 Gupta et al.5 showed that the design of multifocal CLs, the combination of aspheric surfaces with near addition, creates a multifocal effect that improves the near range of clear vision. In this previous study, the near range of clear vision was greater with multifocal CL (1.59 ± 0.70D) than with monovision (1.21 ± 0.77D). Hence, the authors suggest that the simultaneous retinal images created by multifocal CLs improve the results of this range over the alternate interocular blur suppression created by monovision. The results of the current study are in agreement with these results because in our study the near range of clear vision was 1.55 ± 0.33D. Although it should be taken into consideration that Gupta et al.5 evaluated the PureVision multifocal CL and we assessed Proclear multifocal toric CL.
Regarding stereopsis, the results obtained in the present study with the Proclear multifocal toric CL (62 ± 12 sec of arc) were slightly worse than those reported by Ferrer-Blasco and Madrid-Costa7 with the Proclear multifocal CL (54.8 ± 20.23 sec of arc). However, we should consider that disparity values of the Random dot stereo test are computed for fixed distance of observation (40 cm) and interpupillary distance of the patients (6.0 cm). Therefore, changes from both distance of observation and/or interpupillary distance could produce different outcomes. Hence, to properly compare the two studies, we can analyze the differences between multifocal CLs and the control lens (DCL with reading spectacles). We can observe that this difference is about 3 sec of arc for both studies and did not reach statistical significance. Hence, the results of stereopsis found in our study with the Proclear multifocal toric CL were similar to those reported with the Proclear multifocal CL.7 Analyzing the previous literature3–7,12,34–37 about stereopsis with multifocal CLs, one can observe that there is variability among results (from 21 to 164 sec of arc). The different methods used to measure stereopsis, the use of different optical principles (refraction or diffraction), the design of the lens (concentric or aspheric and addition power), and hence the image created on the retina make these differences plausible.
The results of the current study suggest that the toric generated surface for the purpose of correcting vision in eyes with astigmatism, and presbyopia has no effect on the visual results analyzed in this work. However, this statement should be taken with caution because Chamberlain et al.9 have recently suggested that the conventional approaches to measure VA do not fully replicate the “real world” experience of soft toric CLs wearers. For example, these authors found that a monofocal soft toric CL wearer suffered a reduction of about 1 line in NVA after diagonal eye versions (these movements of the eye may be required in daily activities such as driving); hence, a conventional statics measurement of VA may overestimate the real visual experience of the wearers. Therefore, further studies with dynamic methods of assessing visual performance should be performed for multifocal toric CLs wearers.
In conclusion, the results of this study suggest that the multifocal toric CL studied is a good option to compensate both presbyopia and astigmatism, providing an optimal distance, intermediate, and near visual quality without compromising the stereopsis.
Optometry Research Group
Department of Optics
University of Valencia
The authors have no proprietary interest in any of the materials mentioned in this article. This research was supported in part by a Ministerio de Ciencia e Innovación Research Grants (SAF2008-01114 and SAF2009-13342) and a scholarship Jose Castillejo to Robert Montés-Micó.
Received November 11, 2011; accepted June 25, 2012.
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