This year, researchers have presented data on the impact and management of multifocal contact lenses; several new contact lens designs and their advantages (including a revival of interest in scleral contact lenses); the latest research on rigid gas permeables and orthokeratology; how wearing contact lenses affects the progression of myopia; and the results of a large epidemiological study of contact lens wearing habits.
Myopia Control
In a study sponsored by CooperVision, researchers at the University of Houston found that multifocal contact lenses and single-vision contact lenses produce different types of peripheral defocus, which might give clinicians a way to impact the progression of myopia in children. (Peripheral myopic defocus has been hypothesized to slow the progression of myopia.)
Twenty-five subjects (mean age 23.8 ±1.3, r: 22 to 27) with myopia (mean -3.62 ±1.56 D, r: -0.05 to -6 D) took part in the study. The researchers measured the refractive error of the right eye while wearing a Biofinity single-vision soft contact lens and while wearing a Biofinity multifocal “D” lens, a soft, center-distance lens with a +2.50-D add. They took measurements centrally and along the horizontal meridian at 20, 30 and 40 degrees from the line of sight, both while viewing a near target at 30 cm, and at distance, under cycloplegia. Lens type and measurement starting location were randomized.
The data showed:
• At distance, the single-vision spherical lens produced a peripheral mean spherical equivalent refractive error that was significantly more hyperopic than that found with the multifocal lens (p<0.001).
• The multifocal lens produced peripheral myopic defocus at all locations tested. The largest difference in defocus between the two types of lens was 2.35 D (temporally); the smallest difference was 1.06 D (all locations p<0.05).
• Regardless of lens type, accommodating to a near target caused a greater myopic shift in the periphery than closer to the center of vision (p<0.01).
• Compared to the spherical lens, when focused at near the multifocal produced different types of defocus at different locations tested: a more myopic defocus at three locations (r: 0.91 to 0.38 D—all p<0.05); a more hyperopic defocus at two locations (r: 0.27 to 0.42 D—both p<0.05); and no difference at two locations.
Although the peripheral defocus caused by the two types of lenses was somewhat similar when focused at near, when focused at distance the spherical lens produced peripheral hyperopia, while the multifocal lens produced peripheral myopia. The authors note that if it is confirmed that peripheral myopic defocus helps to slow axial length growth in children, wearing center-distance multifocal contact lenses could be an effective way to slow myopia progression.5455
A large prospective study was conducted in Yokohama, Japan, to determine how wearing glasses vs. contact lenses affected progression of myopia and/or hyperopia in different age groups over a five-year period. Approximately 270,000 eyes were included in the study; 13,977 eyes ranging in age from 4 to 88 years who were seen at the Okada Eye Clinic in Yokohama for glasses, and 273,042 eyes ranging in age from 10 to 91 years who were seen at the same clinic for contact lenses. (Anyone undergoing cataract surgery or orthokeratology, or who had had a change in refraction greater than 5 D within a one-year period during the course of the study, was excluded.)
The data showed that:
• In the 10-to-14 and 15-to-19 age groups, individuals of both sexes who wore glasses had a significantly greater shift toward myopia than those wearing contact lenses (p<0.001).
• In contrast, men in the 25-to-34 age group and women in the 20-to-24 age group who wore glasses showed significantly less shift toward myopia than those of the same age who wore contact lenses (p<0.05).
• Among those of either sex in all age groups 50 years and older who wore glasses, a shift toward hyperopia was significantly greater than among those of similar age wearing contact lenses (p<0.05).
The authors note that a further prospective study is needed.5478
Managing Keratoconus
Scleral contact lenses have recently re-emerged as a potential approach for managing diseases such as keratoconus. In addition to refractive correction, the lenses serve to mitigate the higher-order aberrations caused by the surface of the diseased eye, in part by generating a tear-film lens.
Noting that this does not totally eliminate the aberration problem, researchers at the University of Houston compared the visual outcomes with scleral contact lenses that were either designed to correct lower-order aberrations alone or customized to correct both lower- and higher-order aberrations. (The rigid nature of scleral lenses makes them ideal for this type of customization.)
At the time of abstract submission, six eyes of three subjects had been tested and analyzed. A fitting lens set was used to determine the optimum lens design for each eye in terms of corneal vault, limbal clearance and blood flow at the margin of the lens. Then, two more scleral lenses were created for each eye, one designed to correct the lower-order aberrations, and one designed to correct for lower- and higher-order aberrations. After a 30-minute period to allow the lens to settle on the eye, visual acuity and residual ocular aberration through the 10th radial order were measured.
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The study authors note that gain in vision appeared to be subject-dependent, and that given time to adjust to the lenses, the subjects’ vision might improve even further.5466
Researchers at the Osaka University Graduate School of Medicine in Japan explored the visual performance of a new design of silicone-hydrogel soft contact lens. The lens is designed to correct a refractive vertical asymmetry in eyes with keratoconus.
Fifty eyes of 37 individuals with mild keratoconus were involved in the study. Lenses used in the study featured six different asymmetrical refractive power distributions (2, 4, 6, 8, 10 and 12 D) designed to create vertical irregular astigmatism. Eyes were measured using corneal anterior OCT, wavefront aberrometry and subjective refraction; visual acuity and visual clarity (using the visual analog scale) were also checked. A lens was chosen and fitted for each eye based on those measurements. The eye was then retested with the lens on, using wavefront aberrometry and over-refraction, and visual acuity and visual clarity were rechecked.
With the specially designed lenses, monocular visual acuity improved from -0.03 ±0.13 to -0.08 ±0.08 LogMAR (p<0.01); visual clarity improved from 61.2 ±20.7 to 73.8 ±18.5 (p<0.01); vertical coma was reduced from -0.49 ±0.36 µm to -0.35 ±0.38 µm (p<0.05); and overall higher-order aberrations were reduced from 0.66 ±0.39 µm to 0.61 ±0.39 µm (p<0.05). The authors note that the new design’s correction of refractive vertical asymmetry caused a significant improvement in visual performance.5487
Ortho-K and RGPs
A researcher at Fudan University in Shanghai, China, conducted a study using SD-OCT to determine how orthokeratology affects the epithelium, and whether this could account for the refractive changes produced.
The study included 60 patients who had worn orthokeratology lenses for at least one night (mean age 10.6 ±2.38 years), divided into six groups based on duration of wear. Eleven eyes with no history of contact lens use served at controls. A pachymetry module measured epithelial topography in the central 6 mm of the cornea. In addition, average epithelial thickness was measured for the central 3 mm; within a ring from 3 to 5 mm in diameter; and within a ring from 5 to 6 mm in diameter. Then Munnerlyn’s formula was used to determine the refractive change that would be expected as a result of these changes.
The data showed that orthokeratology caused significant epithelial thinning of the central cornea in all wearers. However, in the 3 to 5 mm ring no significant difference was found between wearers and controls. In the 5 to 6 mm ring, thickness increased for some of the groups, but only one group increased significantly (compared to controls). Notably, the refractive changes measured in wearers significantly exceeded the refractive change predicted by the formula.
The author concludes that the lenses can cause significant remodeling of the corneal epithelium, but that these are not sufficient to account for the refractive change. The author hypothesizes that changes in stromal thickness or bending of corneal tissue may also play a role.3113
Researchers in Germany evaluated the value and safety of rigid gas permeable contact lenses for correcting aphakia in infants after removal of congenital cataract. The authors performed a retrospective study of 75 infants who received RGPs after undergoing this surgery between 1987 and 2011. Subjects were divided into four groups: bilateral aphakia; monolateral aphakia with early surgery; monolateral aphakia with late surgery; and aphakia with additional ocular pathologies.
The data showed that the infants tolerated the RPG lenses well. Those treated bilaterally achieved visual acuities up to 1.0; in contrast, monolateral cases frequently developed amblyopia. Also, functional results were better after early surgery than late surgery.
The authors note that as long as the parents are compliant and collaborative, RGPs may be preferable to IOL implantation following congenital cataract surgery in infants. 5474
Quelling Light Sensitivity
A study conducted in Syracuse, N.Y. found that artificial pupil contact lenses (APCLs) provided significant relief to veterans suffering from light sensitivity, photophobia and light-induced headache (triggered even by levels as low as normal room lighting). Eighteen otherwise normal patients exhibiting these symptoms were seen at the Veterans Administration hospital in Syracuse. (Most of these individuals had been treating their symptoms, both indoors and outdoors, with dark wrap-around sunglasses that eliminated up to 90 percent of light entering the eye.)
The patients were fitted binocularly with 4.5-mm APCLs that cut the visual field beyond 70 degrees, reducing light entering the eye by about 30 percent (See sample, left). The subjects were examined and given questionnaires when fitted with the lenses and one month later.
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All patients reported substantial benefit from wearing the lenses regularly. Light sensitivity scores dropped 50 percent, with major reductions in headaches. Not needing to wear sunglasses (except in outdoor bright light conditions) allowed subjects to re-engage in normal activities and improved interactions with family and co-workers. The lenses also eliminated the chronic dark-adaptation problems associated with wearing dark sunglasses.
The authors note that the use of APCLs improves upon currently available treatment options, and that these results suggest that peripheral light may be a key cause of these symptoms.5307
Working with Multifocals
Researchers in Sydney, Australia, working with financial support from Allergan, conducted a study designed to compare the effect of different commercial contact lens designs on accommodation, facility and phoria in myopic wearers. Forty non-presbyopic subjects wore three different types of contact lenses daily, bilaterally, for a minimum of eight days each with a one-week washout period between lens types. Each subject was randomly assigned a single-vision control lens and two of four possible multifocal lenses (Proclear Distance, Proclear Near, Air Optix Aqua and PureVision).
Participants were seen at baseline and once after each lens-wearing period. Researchers assessed static accommodative response and the spherical equivalent using the Eyemapper. Subjects were tested in a fogged state and at four vergences (-2 D, -3 D, -4 D and -5 D) with five repeats in each condition. Accommodative facility was measured using ±2 D flippers, and phoria was measured using a Howell card. Data was averaged for the four exams, to minimize inter-visit variability.
The data showed:
• All lenses produced a myopic shift at +1 D fogging.
• Accommodative response function was relatively linear with the single-vision (control) lenses.
• All center-near multifocals (Air Optix, PureVision and Proclear Near) produced accommodative lead at -2 D, with optimal responses at -3 D and a lag at -4 D and -5 D. In contrast, the center-distance lens (Proclear Distance) produced lag at every test vergence.
• In terms of accommodative facility, all multifocals did worse than the single-vision lenses. The former measured between 14.4 and 16.5 cycles/min; the latter measured 19.2 cycles/min (p<0.05).
• No difference in distance phoria was found between lens types.
• Near phoria was significantly different with the Proclear Near multifocal (5.6 exo, p<0.05).4251
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Subjects ranged in age from 25 to 30 years; subjective spherical refraction was -2.43 ±3.56 D (r: +2.50 to -9.50); subjective astigmatic refraction was -0.48 ±0.44 D (r: 0 to -1.25). BCVA (logMAR) was -0.21 ±0.07 (r: -0.1 to -0.34). Results of the comparison are shown in the chart above.
The authors note that there was good agreement between subjective and objective measurements, except in patients with high refractive errors. They conclude that the autorefractor may be acceptable for over-refracting individuals wearing multifocal contact lenses, except if a patient is highly myopic or hyperopic.5481
Epidemiology
A second large prospective study conducted by the Japanese research group noted earlier was a five-year study involving 204,975 eyes of 103,001 men and women age 9 to 96 who were prescribed contact lenses at the Okada Eye Clinic in Yokohama between January 2007 and December 2011. The study was conducted to find out how the number of lenses prescribed, and the nature of the prescriptions, changed in different groups. (Anyone who had undergone cataract surgery or orthokeratology, or who had a change in refraction greater than 5 D within a one-year period during the course of the study, was excluded.)
After five years, the data showed:
• The most contact lenses were prescribed to those between the ages of 20 and 24 (19.22 percent of men and 17.58 percent of women), followed by ages 25 to 29 (17.53 percent of men and 15.6 percent of women) and ages 15 to 19 (16.46 percent of men and 15.29 percent of women). All told, about half of the contact lenses were prescribed to individuals in these groups (i.e., between the ages of 15 and 29).
• In terms of which levels of refractive error were associated with the highest rates of contact lens wear, those with refractions from -2.75 to -4.5 D had the most contact lens wearers (40.76 percent of men and 40.97 percent of women with this refraction wore contact lenses), followed by those with refractions between -4.75 and -6.5 D (25.87 percent of men and 24.51 percent of women with this refraction wore contact lenses) and -0.75 to -2.5 D (20.89 percent of men and 23.19 percent of women with this refraction wore contact lenses).
• About 10 percent of those studied had myopia ≤-6.75 D (11.71 percent of men and 9.79 percent of women); about 2.5 percent had myopia ≤-8.75 D (2.85 percent of men and 2.24 percent of women). Less than 1 percent of those in the study had hyperopia ≥+0.75 D (0.27 percent of men and 0.84 percent of women).5477 REVIEW
Dr. Asbell is a professor of ophthalmology and the director of cornea and refractive surgery at the Mount Sinai School of Medicine.
