Adaptability of Myopic Children to Progressive Addition Lenses with a Modified Fitting Protocol in the Correction of Myopia Evaluation Trial (COMET)

Purpose. The purpose of this study was to evaluate the adaptability of myopic children participating in the Correction of Myopia Evaluation Trial (COMET) to the use of progressive addition lenses (PALs) with a modified fitting protocol of setting the distance fitting cross 4 mm above the pupil center.

Methods. COMET was a multicenter, randomized clinical trial to evaluate whether PALs vs. single-vision lenses (SVLs) slowed the rate of progression in children with juvenile-onset myopia over 3 years. Of the 469 children enrolled, 234 were assigned to SVLs and 235 were assigned to PALs (+2.00 D near addition), which were fit according to a standard study protocol with the fitting cross positioned 4 mm above the pupil center. The children's adaptability to the use of PALs was evaluated by comparing the frequency and reasons for problem visits, visual symptoms, cover test results, and adherence to wearing glasses between treatment groups.

Results. During the first 3 years of follow-up, no differences were observed between children wearing PALs and those wearing SVLs with respect to the number or reasons for problem visits. One week after receipt of the study glasses, children wearing PALs showed a higher frequency of three visual symptoms related to adaptability: looking down from the blackboard and getting items on their desk in focus (p = 0.001), blur when reading (p = 0.003), and difficulty going down steps (p = 0.02). Children wearing PALs were more likely to report at least one adaptation symptom at 1 week: odds ratio of 2.76 (95% confidence interval = 1.28-5.95). By 1 month, these differences disappeared and the frequency of all visual symptoms remained low and similar for both treatment groups over 3 years. Strabismus was observed on cover test in five children (three SVLs, two PALs). None of the children had to be changed from PALs to SVLs, whereas two of the children were changed from SVLs to PALs as a result of binocular vision problems. The children and parents reported adherence to wearing the eyeglasses approached 100% compliance throughout the follow-up period for both groups. Most (98%) of the 235 children assigned to PALs maintained the modified fitting protocol without any problems over 3 years.

Conclusion. These data show that children can safely and comfortably wear PALs for at least 3 years.

Bifocal and progressive addition lenses (PALs) are primarily prescribed for older adults to compensate for presbyopia, the normal loss of accommodative ability with age. A traditional bifocal has two focal lengths, with the upper portion typically used for distance vision and the lower portion, usually demarcated by a lined segment, used for near vision. In comparison, PALs have an intermediate channel, or corridor, which progresses in relative plus power, connecting the distance and full-addition near areas while providing a seamless intermediate zone. PALs initially became available to the U.S. market in the 1960s and began to gain in popularity in the 1980s. In this article, the term multifocal lenses refers to bifocal lenses and PALs.

Multifocal lenses are also prescribed for children to treat certain conditions such as accommodative esotropia,^{1, 2} nonstrabismic accommodative and/or binocular nearpoint dysfunctions,^{3, 4} and progressive myopia.^{5, 6} Children, unlike presbyopic adults, usually have full accommodative ability and could use the distance part of their glasses to see clearly for near-visual tasks. They do not have the same blur/clear feedback as older adults to reinforce using the correct part of the lens for near-visual tasks. When traditional bifocal lenses are prescribed for children, the segment height of the lenses is often set higher than the standard protocol for adults to maximize use of the bifocal portion of the lenses and to ensure that the near addition is not cut off from the lens when using a smaller child-sized frame. For example, most sources advocate fitting a traditional bifocal to bisect the pupil in the treatment of children with accommodative esotropia,^{1, 2, 7} whereas the standard traditional bifocal fitting height for adults is at the lower eyelid margin.^{7, 8}

As a result of their more complex optics, PALs require more precise fitting. Many adults have had difficulty in adapting to this type of lens as a result of induced astigmatism causing peripheral distortions and the narrow distortion-free channel inherent in the lens design.^{7, 8} In addition to peripheral distortions, which are usually perceived as blur, the induced astigmatism of PALs can cause visual disturbances of optical movement known as swim, which is more evident with head movement.^7-9 The narrow intermediate channel and near-zone results in narrow zones of clear vision, requiring more head movement instead of eye movements during near tasks such as reading across the page.^{7, 8, 10} To use the full addition power, the relatively long corridor necessitates greater vertical downgaze eye movements for PALs (14-19 mm) compared with traditional bifocals (7-8 mm).¹¹ Brooks and Borish summarized the results of 29 separate studies (total of 3523 subjects) on adult acceptance of PALs, dating from 1978 to 1994, and concluded that approximately 80% of presbyopes preferred PALs over conventional lens corrections.⁸ They also stated that these studies were done with careful adherence to accepted PALs' fitting principles.

Two studies with small sample sizes, one with 25 children and the second with 32, have recommended the benefits of prescribing PALs over traditional bifocals for treatment of children with accommodative esotropia.^{12, 13} They described the main benefit of PALs, besides cosmetic, as a more natural progression of accommodative response from distance to near to include the intermediate zone without the image jump that is present in traditional bifocals. This was also stated as being more practical for playing sports. In both of these studies, PALs were fit 4 mm higher than the standard (adult) fitting protocol of setting the fitting cross to the center of the pupil, with successful adaptation reported in all 57 children in both studies. Successful adaptation was defined as the children having no complaints about wearing PALs and expressing a preference for wearing PALs over traditional bifocals. In theory, this higher fitting protocol could cause symptoms of distance blur and make adaptation more difficult.

Presently, the standard fitting protocol recommendations set by industry for PALs do not address any special considerations when fitting children. To date, there have been no large-scale studies evaluating adaptation to wearing PALs in children, specifically when a modified fitting protocol is used. Although most adult studies have only looked at the initial adaptation as a result of distortions from the complex design of PALs, for children, it is important to also look at long-term adaptation and possible adverse effects of the decreased accommodation stimulus when wearing PALs.

The Correction of Myopia Evaluation Trial (COMET), a multicenter clinical trial involving 469 ethnically diverse children, 6 through 11 years old with moderate myopia (-1.25 D to -4.5 D) who were randomly assigned to wear either single-vision lenses (SVLs) or PALs for a minimum of 3 years, found the use of PALs compared with SVLs slowed the progression of myopia in COMET children by a small, statistically significant amount only during the first year.¹⁴ The children assigned to wearing PALs were fit according to the study-fitting protocol of setting the distance fitting cross 4 mm higher than the industry standard fitting protocol, which is primarily designed for adults. Therefore, this trial provides an excellent opportunity to evaluate the adaptation to wearing PALs with a modified fitting protocol in this group of myopic children, looking at both initial adaptation during the first month and long-term adaptation over 3 years.

METHODS

Study Design Overview

COMET was designed as a randomized, double-masked, multicenter clinical trial involving four clinical centers: University of Alabama at Birmingham School of Optometry, University of Houston College of Optometry, Pennsylvania College of Optometry, and New England College of Optometry. Before the baseline examination, children and parents agreed to accept random assignment of either SVLs or PALs, attend follow-up appointments semiannually for at least 3 years, and refrain from wearing contact lenses throughout the study. Children agreed to wear their COMET glasses during all waking hours. COMET optometrists, parents, and children were masked regarding lens assignment, and they were encouraged not to try to determine the assignment. The COMET study and protocols conform to the tenets of the Declaration of Helsinki. The Institutional Review Boards of each participating center approved the research protocols. Informed consent (parents) and assent (children) were obtained after verbal and written explanation of the nature and possible consequences of the study. Overall study performance and child safety were reviewed by a Data and Safety Monitoring Committee (DSMC). A complete description of the COMET study design and other baseline characteristics can be found elsewhere.^{15, 16}

Study Population

Of the 469 children enrolled in the COMET, 235 were assigned to PALs and 234 to SVLs. There were 223 (48%) males and 246 (52%) females, with an average age at baseline of 9.3 years ± 1.3, ranging from 6 to 11 years. The average amount of myopia at baseline was -2.39 D ± 0.80 D ranging from -1.14 to -4.59 D. The distribution of the children's ethnic background was diverse with 218 (46%) white, 123 (26%) black, 68 (15%) Hispanic, 36 (8%) Asian, and 24 (5%) mixed.

As part of the inclusion criteria for COMET, these children had never been previously fit with bifocals or PALs and this would be their first experience with multifocal lenses. Additional inclusion/eligibility criteria were: no prior wear of contact lenses; astigmatism less than or equal to 1.50 D in either eye; anisometropia less than or equal to 1.00 D spherical equivalent between eyes; visual acuity with distance correction of 0.20 LogMAR units or better (20/32 Snellen equivalent); no strabismus by cover test at far (4 m) or near (33 cm) wearing distance correction or at 33 cm wearing + 2.00 D over distance correction; birth weight at least 1250 g; no known ocular, systemic, or neurodevelopmental conditions that might affect refractive development; and no use of medications that might affect refractive development.

Study Visits

Children received their COMET glasses at a randomization visit after baseline data collection. To identify any initial adverse effects of wearing the study glasses, data were collected at short intervals after the initial dispensing of study glasses to monitor child safety; data on visual symptoms and adherence to wearing their glasses were collected by phone at 1 week for 365 children and at 3 months for 323 children. In addition, the first 152 children enrolled were seen at 1 month, whereas an additional 242 children were contacted by phone at 1 month to monitor for potential adverse effects from the use of PALs. Because no adverse effects were observed for these children, the 1-month contacts were no longer deemed necessary and were discontinued. To monitor any potential long-term adverse effects of wearing the study glasses, data on visual symptoms and adherence to wearing their glasses were collected at routine study visits, held every 6 months after baseline for 3 years. Interim visits were held as needed to address problems with frames, lenses, and/or visual symptoms that occurred between routine visits. Separate visits were scheduled as needed for dispensing new glasses as determined at a routine study or problem visit. If the child played sports, Rec Specs sports goggles with SVLs (Rec Specs USA, Fairfield, NJ) were recommended and provided for these activities.

Procedures/Data Collection

Table 1 provides an overview of the measures of adaptability to wearing PALs. Using questionnaires with child-friendly language, the clinic coordinators collected data regarding visual symptoms and the frequency of wearing study glasses at each visit and phone survey. The questions concerning visual symptoms included six questions derived from the Convergence Insufficiency and Reading Study symptom survey.¹⁷ Children were asked to rate how often they experienced the following symptoms when reading or studying: eyes feeling tired or hurting, headaches, feeling sleepy, double vision, and words wiggling or jumping on the page. An additional seven questions, more representative of adaptation problems, asked children to rate how difficult/blurry or easy/clear the following tasks were when wearing their glasses: 1) in school, getting stuff in focus when looking at the blackboard; 2) looking down from the blackboard getting stuff on their desk in focus; 3) reading; 4) going down steps, stairs, or curbs; 5) trying to see things off to the side (while outside or working at school); 6) looking at things in the distance (TV, movies, outside sports); and 7) using the computer. If the responses indicated that the child was experiencing visual symptoms (e.g., the task was impossible/fairly hard, very/kind of blurry), a problem visit was scheduled with the COMET consulting optometrist, who was unmasked, and able to determine if the symptoms might be related to the lens assignment.

Table 1

Parents and children were asked about the frequency and use of the glasses at school, after school, and on weekends (none of the time, some of the time, about half of the time, most of the time, or all of the time). If the child reported wearing their glasses less than most of the time, additional questions were asked to determine possible reasons for not wearing the glasses, and, if indicated, a problem visit was scheduled. Each child was also asked about the use of Rec Specs and/or study glasses while playing sports.

At each routine study visit, the cover test, using an isolated 20/25 letter target, was done by the COMET optometrist to assess any strabismus or phoria at far (4 m) and at near (33 cm) using the distance prescription and also using a +2.00 D add at near. If strabismus was found, the child was referred to the COMET consulting optometrist for further evaluation. During the dispensing visit, the COMET optician verified the study fitting protocol measurements and proper frame adjustment, and assessed whether the child was using the lower portion of the lenses for reading materials. Regardless of lens assignment, the COMET optician instructed the child to use the top part of the glasses to focus on distant objects and to use the bottom part of the glasses for reading and near tasks. At every visit, the children were encouraged to follow the COMET wearing instructions protocol for using their glasses, which included suggestions for changes in head posture, eye, and/or head movements, if necessary, to see more clearly with their glasses (Cited Here...).

Children remained in their original lens assignment and were fit according to the study protocol unless a change was indicated for the proper care of the child's visual welfare or for retention. The children's eyeglass prescriptions were changed only if there was a 0.50 D or greater spherical equivalent change in at least one eye compared with the most recent prescription or if it was otherwise clinically indicated.

Lenses and Lens-Fitting Protocol

All lenses, SVLs and PALs, were of polycarbonate material with a scratch-resistant coating using the ANZI Z80.1-1995 standards. Rec Specs sports goggles were fabricated using 3.0-mm polycarbonate SVLs and meeting all requirements for sports eyewear. The PALs selected for use in COMET were Varilux Comfort lenses by Essilor Laboratories with a +2.00-D near addition. The Varilux Comfort PALs (Essilor, Dallas, TX) are a soft design lens, in which the change from the near zone to the peripheral area of astigmatic distortion is more gradual compared with a hard design lens. The major reference point (MRP) of this lens, which is usually the optical center of the lens and marks the beginning of the progressive channel, is located 4 mm below the fitting cross. There is a 14-mm corridor, or channel, with 85% of the total add power reached at 12 mm from the fitting cross (see Fig. 1A).

Figure 1

The monocular near pupillary distance (PD) was measured using an Essilor pupillometer set at 35 cm and 2.5 mm was then added to each near PD measurement to obtain the monocular distance PD. The frame selected by the child was adjusted for maximum comfort, with a vertex distance of 12-14 mm and pantoscopic tilt between 10° and 15°. The vertex distance refers to the measurement from the corneal apex to the back surface of the lens. The pantoscopic tilt is the amount of vertical inclination of the frame to position the optical centers of the lenses midway between straight-ahead gaze for distance vision and downward gaze for near tasks. All frames used in this study had adjustable nosepads.

The final segment height was obtained by adding 4 mm to the measured segment height with the fitting cross at the center of the pupil. The COMET fitting protocol stated that there must be at least 11 mm available for distance vision and a minimum segment height of 22 mm. If the vertical depth of the frame, which is the B measurement, minus the final segment height was <11 mm, a change to a larger size frame was indicated. The proper position of the PALs was verified at each visit by measuring the fitting cross position laser marks in reference to the center of the child's pupil for each eye. Figure 1B diagrams the COMET fitting protocol for Varilux Comfort PALs in children. With this modification of the standard adult fitting protocol, the center of the child's pupil coincides with +0.40 D of the near addition, as shown in Figure 1A.

Methods of Data Analysis

Adaptability to wearing PALs was evaluated by comparing the frequency of and reasons for problem visits, the frequency and type of visual symptoms, and adherence to wearing glasses between the PAL and SVL groups. Fisher exact test was used to compare the distribution of categorical variables between the treatment groups. The SVL children served as a control group, whereby any statistically significant differences found in adaptability measures between the two treatment groups were assumed to be the result of wearing PALs.

RESULTS

Measures of Safety and Adaptability

Safety concerns and adaptability to using PALs were evaluated by comparing the frequency of signs of possible adverse effects such as an increased incidence of problems with frames/lenses, visual symptoms, injuries, greater difficulty during physical activities, the development of strabismus, or other binocular anomalies between the PAL and SVL groups. Losses to follow-up were few (four PAL children, two SVL children), and the number of losses was not different between the two treatment groups.

Problem Visits and Symptoms

Over the 3-year period, the total number of problem visits was similar for both groups (n = 699 for the PALs group, n = 675 for the SVL group). As shown in Table 2, the frequency of problem visits per child was similar for PAL and SVL children within each year and cumulatively over 3 years. During the first year, over one-third of the children (PALs = 37%, SVLs = 38%) did not need to be seen for a problem visit.

Table 2

In addition, when examining the specific reasons for problem visits over the same 3-year period, there was no difference found between the children wearing PALs and SVLs. The majority of problem visits were the result of problems with frames/lenses only and was equally distributed for both treatment groups over 3 years (PALs = 84%, SVLs = 84%, baseline to 3 years). Problem visits resulting from visual symptoms only was 11% or less for 1-year intervals and similar for both groups over 3 years (PALs = 8%, SVLs = 8%, baseline to 3 years). Problems with frames/lenses and visual symptoms accounted for <3% (baseline to 3 years) of the problem visits for both groups. There were only 1% of problem visits resulting from eye pathology/injury for both groups during the first year and a total of 2% for PAL and 4% for SVL children from baseline to 3 years. The majority of children in both groups (PALs = 75%, SVLs = 76%) had no problem visits resulting from visual symptoms over the 3-year period. As Table 3 shows, when looking specifically at the number of problem visits per child resulting from visual symptoms (combining the two categories of visual symptoms only and problems with frames/lenses and visual symptoms), there was no difference between the two groups.

Table 3

Table 4 presents the results from the questionnaire concerning adaptability to different uses of study glasses at 1 week, 1 month, and 3 years. The frequency of severe symptoms for any use of study glasses, e.g., impossible/fairly hard, was low ranging from 0-8% at 1 week, 1 month, and 3 years for both groups. The only difference in the frequency and type of symptoms reported between the two treatment groups over 3 years was found at 1 week after receipt of study glasses for three symptoms related to adaptation: 1) when the child looks down from the blackboard with glasses on getting items on desk in focus; 2) reading with glasses; and 3) when the child goes down steps or stairs with glasses on (p = 0.001, 0.003, and 0.02, respectively). Although at 1 week after receipt of the study glasses a higher percentage of PAL vs. SVL children reported that trying to see things off to the side with glasses on was impossible/fairly hard (6% vs. 3%), these differences are not statistically significant (p = 0.07). At 1 month, the proportion of children reporting this symptom was identical in both groups. The majority of the PAL children experiencing any of these symptoms at 1 week reported a mild symptom level of just OK, with very few children reporting at the more severe symptom level (impossible/fairly hard or very/kind of blurry). When looking at the frequency of responses for the more severe symptom level, the greatest difference between treatment groups is for reading with glasses on. PAL children were more likely to respond at the more severe level for at least one adaptation symptom at 1 week only: odds ratio of 2.76 with 95% confidence interval of 1.28-5.95. At 1 month and 3 months, the frequency of severe adaptation symptoms was low and similar in both treatment groups.

Table 4

The four symptoms related to adaptation at 1 week (p ≤ 0.07) were explored further using a longitudinal assessment based on the 1-week cohort. Each child's responses at 1 week and at 1 month were compared with baseline and rated as improved, worsened, or remained the same. By ranking the questionnaire choices from 1-5 (1 = impossible/very blurry, 2 = fairly hard/ kind of blurry, 3 = just OK, 4 = pretty easy/almost clear, 5 = really easy/very clear), a change to a higher number would be rated as improved, whereas a change to a lower number would be rated as worsened. The results in Figure 2 show a greater frequency of worsened for PAL children at 1 week for reading, going down steps, and seeing things off to the side (p = 0.003, 0.02, and 0.02, respectively), which is no longer significant at 1 month. The 1-week cohort responses for getting items on desk in focus showed no significant difference at 1 week, with a greater frequency of worsened for PAL children at 1 month (p = 0.05), which was not significant at 3 months. Table 4 shows the results in Figure 2 are based on only one PAL child responding at the more severe level for getting items on desk in focus at 1 month. Therefore, this figure is picking up a more subtle shift of worsened from really easy to pretty easy or just OK.

Figure 2

Other symptoms measured were related to reading (eyes feel tired or hurting when reading, headaches when reading, feeling sleepy when reading, double vision when reading, and words wiggling or jumping on the page) and showed no difference between groups over 3 years. Reading with glasses on was the most improved symptom in the PALs group at 1 month relative to l week (p value of 0.008). Most symptoms (approximately 90%) improved or remained the same at 3 years as compared with baseline in both groups.

Cover Test

The cover test was performed at baseline and at 6-month intervals for 3 years to monitor binocular vision. These measurements were taken at far (4 m) and near (33 cm) through the distance correction and also with +2.00 D over the distance correction at near. Ten children (7 SVLs, 3 PALs) were found to have strabismus during the follow-up period. For five of these children, the strabismus was not present when tested with their respective lens assignment; four SVL children showed strabismus (exotropia) at near with the +2.00 D over the distance correction and one PAL child showed strabismus (esotropia) when tested at near with the distance correction. The other five children (3 SVLs, 2 PALs) showed intermittent strabismus with their respective lens assignment: exotropia at far (2 SVLs, 1 PAL), esotropia at near (1 SVL), and exotropia at near (1 PAL). The strabismus was resolved by vision therapy for two children (1 SVL, 1 PAL), no treatment for two children (1 SVL, 1 PAL), and a change in lens assignment from SVLs to PALs for one child.

The distribution of cover test phoria results (at far, near, and near with +2.00-D addition) were similar for both treatment groups at baseline, 1 year, 2 years, and 3 years. At baseline and 3 years, the average near phoria (mean ± standard deviation in prism diopters [Δ]) with the distance correction was slightly esophoric: 1.2 ± 4.2Δ for PALs, 1.5 ± 4.3Δ for SVLs at baseline; and 0.8 ± 5.3Δ for PALs, 1.3 ± 5.0Δ for SVLs at 3 years. The average near phoria with the +2.00-D addition was exophoric at baseline and 3 years as follows: baseline: -3.8 ± 3.7Δ for PALs; -3.6 ± 4.0Δ for SVLs; and 3 years: -4.6 ± 4.8Δ for PALs, -4.0 ± 4.7 Δ for SVLs. The majority of children in both treatment groups remained close to their baseline phoria measures over 3 years. None of the children assigned to PALs required a change in lens assignment, whereas two of the children assigned to SVLs had to be changed to PALs as a result of binocular vision problems (one mentioned previously and one showing convergence excess without strabismus).

Physical Activity

Questionnaires regarding which glasses (COMET glasses, Rec Specs, or none) the child wore when playing sports were used to evaluate possible adverse effects of wearing PALs during physical activity. The number of children wearing their COMET glasses only for sports was similar for both treatment groups over the 3-year period, ranging from 44-53% of those children who played sports. The percentage of children playing sports who wore Rec Specs only ranged from 12-23%, whereas those children wearing either COMET glasses or Rec Specs ranged from 23-33% during the 3-year period. Only 6-10% of the children who played sports reported not wearing any lenses when playing sports.

Measures of Appropriate/Proper Use of COMET Glasses

As a result of the nature of the treatment intervention, SVLs vs. PALs, it was imperative not only to monitor the children for adherence with wearing the study glasses, but also to reinforce and monitor whether they were correctly using the near addition of these glasses. Questionnaire results regarding adherence to wearing COMET glasses indicated compliance with wearing glasses most or all the time ranging from 93-100% for both treatment groups throughout the 3 years. These results were consistent when comparing the parents' reports and the children's reports. With only a few exceptions, all of the children in the PAL group (99-100%) were observed to correctly use the lower portion of their lenses for reading, recorded at 6-month intervals. The distribution of the final fitting adjustment, measured at 6-month intervals, showed that at least 98% of the children wearing PALs successfully maintained the modified fitting protocol.

DISCUSSION

Adaptability

Every child assigned to PALs was able to wear these lenses throughout the 3-year study. In addition, this study found no adverse effects for 98% of the children when using the modified fitting protocol of setting the distance fitting cross 4 mm higher than the center of the pupil, supporting the results reported in the two previously cited studies by Smith¹³ and Jacobs et al.¹² Compared with those previous studies, this study was more comprehensive with a larger sample size and extensive data collection, including information on visual symptoms, problem visits, compliance, and verification of proper fit and proper use of glasses over regular intervals for 3 years. The additional strength of this study is having a group randomized to wearing SVLs for comparison to help differentiate which findings were the result of wearing PALs.

Adaptation to PALs requires changes in head posture, head movement, and eye movements to minimize perception of blur and peripheral distortions.⁹ Presbyopic adults gradually lose their accommodative ability, starting out with lower add powers, which are increased over many years. In contrast, the children in this study were randomly assigned to PALs with a +2.00 D near addition. For children, adaptation to PALs also involves making changes in their normal accommodative response at near, which will affect the accommodative stimulus for convergence posture at near. Although it is outside the scope of this article to look at the actual accommodative responses of children wearing PALs, the data on visual symptoms and cover test results over 3 years was used to detect the development of accommodative/binocular vision problems and/or strabismus.

With the exception of a greater frequency of three symptoms related to adaptation at 1 week, the children wearing PALs did not experience more problems or symptoms when compared with the children wearing SVLs. Two of these three adaptation symptoms were related to near tasks (i.e., getting items on their desk in focus, reading). Reading has been described as the most critical task for adapting to PALs in adults.¹⁰ The third adaptation symptom, difficulty going down stairs, steps, or curbs, is a common symptom expressed by adults when wearing multifocal lenses. To see the floor or steps while wearing PALs, one must lower their head and look through the distance portion of the lenses, whereas when wearing SVLs (distance correction), one can keep their head erect and lower their eyes to look through the lower part of the lenses. This information was not included in the COMET wearing instructions. Of these three symptoms, reading with glasses was reported most frequently as the most severe at the 1-week visit, with 6% (10 of 177) of PAL children vs. <1% (1 of 187) of SVL children reporting very/kind of blurry and the most improved at the 1-month visit (only one PAL child reporting at the severe symptom level). Children wearing PALs did not show any difference for other symptoms related to reading or using the computer compared with children wearing SVLs. It seems that the reduced clarity of reading materials was related to the initial adaptation to PALs, and this perceived blur did not persist long enough to cause other symptoms to develop. Based on subjective questionnaire results, the children's distance vision was not compromised with this fitting protocol, not even during the early adaptation period.

In the clinical setting, it is common practice to tell a first-time adult PAL wearer that the adaptation process may take up to 2 weeks. The few studies that specify the length of adaptation for PALs have shown that the adaptation period is within 2 weeks for the majority of adults.^{18, 19} In this study, some children experienced adaptation symptoms at 1 week, which were no longer evident at 1 month. Although data was not obtained at 2 weeks, the results appear to be consistent with adult studies. As their first experience with multifocal lenses, the majority of the children wearing PALs did not report having any adaptation symptoms at 1 week or any time during the study.

It is important to mention that the symptoms data were self-reported, as was the case for the majority of adult adaptation studies. A few recent adult studies have looked at more objective measures of performance during computer-simulated tasks using PALs vs. SVLs, confirming the increased demand for eye and head movements with PALs, resulting in overall decreased oculomotor reading efficiency.^20-22

The results of this study show no difference between treatment groups in the number of children wearing their study glasses when playing sports. Despite having Rec Specs available, many children chose to wear their PALs when playing sports, with 45-52% of PAL children who played sports wearing PALs only and 23-33% wearing PALs or Rec Specs. As a result of the increased physical activity of children compared with presbyopic adults, including playing sports, the question is raised as to whether PALs are safer than traditional bifocals, as suggested in both the Smith¹³ and Jacob et al.¹² studies. Although Rec Specs are known to provide the best protection from eye injury during sports, in situations when the child does not wear Rec Specs, this study raises the issue as to whether PALs are as safe as SVLs when playing sports, or in general for playing in gym class or on the playground.

Being a randomized clinical trial, the lens assignment for each child was independent of the magnitude or direction of that child's baseline phoria results. Children with less than optimal lens assignments such as children with large exophoria at near assigned to PALs or children with large esophoria at near assigned to SVLs were monitored and were seen for further assessment only if they were having symptoms or other problems.

Although strabismus was one of the exclusion criteria for enrollment in COMET, i.e., no children had strabismus at the baseline visit, 10 children exhibited strabismus at one or more follow-up visits. Every child with strabismus was referred to the COMET consulting optometrist for further assessment. For five of these children, the strabismus was observed to occur only at near with the nonassigned near lens. The other five children showed strabismus with their respective lens assignment: three at far (2 SVLs, 1 PALs) and two at near (1 SVLs, 1 PALs). As a result of the intermittent nature of the strabismus observed in these children, it is difficult to ascertain whether the condition was present before enrollment in COMET or developed during the course of the study. Although it is unlikely that the strabismus observed at far in three children is related to lens assignment, a less-than-optimal lens assignment may have contributed to the intermittent strabismus observed at near. It is important to note that the incidence of strabismus found in this study was low (2% overall, 1% with respective lens assignment), of an intermittent nature, and resolved without treatment for seven children, vision therapy for two children, with only one child requiring a change in lens assignment. Children wearing PALs did not develop symptoms or signs of binocular and/or accommodative problems with greater frequency than children wearing SVLs during the 3-year period.

Clinical Implications

The results of this study present evidence to allow clinicians to prescribe PALs for children with greater confidence of successful adaptation. The two studies of children wearing PALs, using a modified fitting protocol, were limited to children with accommodative esotropia. Based on the Smith study,¹³ Brooks and Borish⁷ recommend using the modified fitting protocol of 4 mm higher than the pupil center when fitting PALs for children. Although it is almost universally recommended that bifocals are fit to bisect the pupil for children with accommodative esotropia, the recommendations are not so clearcut for other conditions when bifocals may be prescribed for children. Even in two recent studies involving multifocal lenses for myopic children, one using bifocals²³ and the other using PALs,²⁴ each study used a modified fitting protocol of only 1 mm higher than the standard for adults. In the bifocal study, the improper use of bifocals (looking over the top of the bifocal for near tasks) was observed in one-third of the children for at least one follow-up visit.²³

The results from COMET demonstrate that most children with mild to moderate myopia are able to successfully adapt to PALs with a modified fitting protocol 4 mm higher than the adult standard protocol. This higher fitting protocol will help ensure that children are getting the full benefit of the near addition. Just like with adults, it is important to demonstrate and reinforce the proper use of PALs to children, including possible changes in head posture, head movements, and eye movements, as well as providing information about possible initial adaptation symptoms. These results indicate that PALs do not interfere with children's visual demands in the classroom, using the computer, or for physical activities such as playing sports.

ACKNOWLEDGMENTS

COMET was supported by National Eye Institute Grants EY11805, EY11740, EY11752, EY11754, EY11755, and EY11756, and by Essilor of America, Marchon Eyewear, Marco Technologies, and Welch Allyn. Figure 1A was provided by Essilor of America. Figure 1B was illustrated by Howard T. Chang, MD, PhD.

Patricia M. Kowalski

4735 Anglia Street

Manlius, New York 13104

e-mail: [e-mail]

APPENDIX A

COMET Wearing Instructions

All children were instructed to wear either the COMET study glasses or the COMET sports glasses at all times. Children were to wear the COMET study glasses during all waking hours except when engaged in sports, swimming, or bathing. When engaged in sports, the COMET sports glasses were to be worn. When swimming, the child could wear goggles with or without correction. Parents and children were reminded that spectacle wear was expected at school, at home, and during the summer months. All children received the following written instructions:

1. Tip chin down to view distant objects clearly if necessary.

2. Lower the eyes to use the near addition while reading.

3. If objects to the side do not appear clear, move head sideways until object clarity improves.

4. If objects in front do not appear clear, move eyes or head up or down until object clarity improves.

5. Return immediately for any frame adjustments.

6. Do not adjust frames or reinsert lenses at home. All frame adjustments must be done by one of the research staff.

7. Do not use super glue on any part of the frame or lens. If the frame breaks, return to the study center for an immediate replacement.

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APPENDIX B

The members of the COMET study group are as follows:

Study Chair's Office, New England College of Optometry, Boston, Massachusetts: Jane Gwiazda (Study Chair/Principal Investigator); Kenneth Grice (Study Coordinator, until July 1999); Christine Fortunato (Study Coordinator August 1999-September 2000); Cara Weber (Study Coordinator October 2000-August 2003); Rosanna Pacella (Research Assistant October 1996-October 1998); Thomas Norton (Consultant, University of Alabama at Birmingham).

Coordinating Center, Department of Preventive Medicine, Stony Brook University Health Sciences Center, Stony Brook, New York: Leslie Hyman (Principal Investigator); M. Cristina Leske (Co-Principal Investigator, until September 2003); Mohamed Hussein (Co-Investigator/Biostatistician, until October 2003); Elinor Schoenfeld (Epidemiologist); Lynette Dias (Study Coordinator June 1998-present); Rachel Harrison (Study Coordinator April 1997-March 1998); Jennifer Thomas (Assistant Study Coordinator December 2000-April 2004); Cristi Rau (Assistant Study Coordinator February 1999-November 2000); Elissa Schnall (Assistant Study Coordinator November 1997-November 1998); Wen Zhu (Senior Programmer); Ying Wang (Data Analyst January 2000-present); Ahmed Yassin (Data Analyst January 1998-January 1999); Lauretta Passanant (Project Assistant February 1998-present); Maria Rodriguez (Project Assistant October 2000-present); Allison Schmertz (Project Assistant January 1998-December 1998); Ann Park (Project Assistant January 1999-April 2000); Phyllis Neuschwender (Administrative Assistant, until November 1999); Geeta Veeraraghavan (Administrative Assistant December 1999-April 2001); Angela Santomarco (Administrative Assistant July 2001-August 2004).

National Eye Institute, Bethesda, Maryland: Donald Everett (Program Director, Collaborative Clinical Trials Branch).

Clinical Centers

University of Alabama at Birmingham School of Optometry, Birmingham, Alabama: Wendy Marsh-Tootle (Principal Investigator); Katherine Niemann (Optometrist September 1998-present); Kristine Becker (Ophthalmic Consultant July 1999-March 2003); James Raley (Optician, until April 1999); Angela Rawden (Backup Optician, until September 1998); Catherine Baldwin (Primary Optician and Clinic Coordinator October 1998-present); Nicholas Harris (Clinic Coordinator March 1998-September 1999); Trana Mars (Backup Clinic Coordinator October 1997-March 2003); Robert Rutstein (Consulting Optometrist).

New England College of Optometry, Boston, Massachusetts: Daniel Kurtz (Principal Investigator); Erik Weissberg (Optometrist June 1999-present); Bruce Moore (Optometrist, until June 1999); Robert Owens (Primary Optician); Justin Smith (Clinic Coordinator January 2001-present); Sheila Martin (Clinic Coordinator, until September 1998); Joanne Bolden (Coordinator October 1998-September 2003); Benny Jaramillo (Backup Optician March 2000-June 2003); Stacy Hamlett (Backup Optician June 1998-May 2000); Patricia Kowalski (Consulting Optometrist, until June 2001); Jennifer Hazelwood (Consulting Optometrist, since July 2001).

University of Houston College of Optometry, Houston, Texas: Ruth Manny (Principal Investigator); Connie Cross-Noe (Optometrist, until May 2003); Sheila Deatherage (Optician); Charles Dudonis (Optician); Sally Henry (Clinic Coordinator, until August 1998); Jennifer McLeod (Clinic Coordinator September 1998-August 2004); Julio Quiralte (Backup Coordinator January 1998-present); Karen Fern (Consulting Optometrist).

Pennsylvania College of Optometry, Philadelphia, Pennsylvania: Mitchell Scheiman (Principal Investigator); Kathleen Zinzer (Optometrist, until April 2004); Timothy Lancaster (Optician, until June 1999); Theresa Elliott (Optician, until August 2001); Mark Bernhardt (Optician June 1999-May 2000); Dan Ferrara (Optician July 2000-July 2001); Jeff Miles (Optician August 2001-present); Abby Grossman (Clinic Coordinator August 2001-November 2003); Mariel Torres (Clinic Coordinator July 1997-June 2000); Heather Jones (Clinic Coordinator August 2000-July 2001); Melissa Madigan-Carr (Coordinator July 2001-March 2003); Theresa Sanogo (Backup Coordinator July 1999-March 2003); JoAnn Bailey (Consulting Optometrist).

Committees

Data and Safety Monitoring Committee: Robert Hardy (Chair); Argye Hillis; Don Mutti; Richard Stone; Sr. Carol Taylor.

Executive Committee: Jane Gwiazda (Chair); Donald Everett; Leslie Hyman; Wendy Marsh-Tootle.

Steering Committee: Jane Gwiazda (Chair); Donald Everett; Mohamed Hussein; Leslie Hyman; M. Cristina Leske; Daniel Kurtz; Ruth Manny; Wendy Marsh-Tootle; Mitchell Scheiman; Thomas Norton.