Myopia was certainly a key theme at this year’s AAO conference in Orlando. And with the World Health Organisation using the conference to underline the importance of optometry in the first presentation of their newly published World report on Vision, in which the global threat to eye health from myopia is emphasised, this was perhaps no surprise.
Of the many various methods of myopia management currently being practised, contact lens management is the most commonly used. So many papers presented this year discussed both the effectiveness of the technique and the safety issues raised by introducing long term contact lens correction from an early age.
Safety
Noel Brennan (J&J) and colleagues have looked at the ocular adverse event data from six randomised controlled trials among a total of 663 myopic children (aged between seven and 15 years at baseline) who had been fitted with daily disposable hydrogel (etafilcon A) contact lenses. They had found no microbial keratitis (MK) or serious infiltrative events, and no other serious ocular adverse events in any of these children. A total of 86 non-significant ocular adverse events had been identified in 53 of the children. The crude incidence of ocular adverse events was 10.6 per 100 patient years, and the estimated pooled incidence, using a random effect model, was 8.9 with a 95% CI of 4.5 to 17.4. The most common ocular adverse events were:
• Slit-lamp signs of grade 2 or less requiring treatment (26
children)
• Unspecified conjunctivitis (14)
• Allergic conjunctivitis (13)
Of the 86 adverse events, 37 were classified as highly likely or possibly contact lens-related, giving a crude incidence of 4.5 per 100 patient years for contact lens-related events. There were two non-significant infiltrative events among the contact lens wearers.
Interestingly, these studies also included data on 266 spectacle wearers aged seven to 12 years old, comprising 398 patient years. Among these, there were seven non-significant adverse events in four subjects giving a crude incidence of 1.8 per 100 patient years.
The conclusion — these data suggest daily disposable etafilcon A hydrogel contact lenses are safe for use in children. For suitable myopic patients, risks associated with contact lens wear seem likely to be outweighed by the possible benefit of myopia control. The rate of ocular adverse events among children wearing contact lenses is similar to, if not less than, that among adults.
Benefit versus Risk
Continuing the theme of weighing the benefit of contact lens myopia management and risk of life-long wear, Drs Mark Bullimore and Eric Ritchey (Houston) presented their efforts to give numerical value to these competing factors. ‘Myopia control has the potential to lower the risk of visual impairment later in life by lowering a patient’s ultimate level of myopia, but this benefit has not been quantified, nor has it been compared with the increased risk of visual impairment associated with myopia control modalities. Such a comparison should be expressed in years of uncorrectable visual impairment and based on published, defensible data,’ Bullimore explained in his presentation.
Microbial keratitis – the low risk is easily outweighed by the benefits of contact lens myopia management.
The risk from contact lens wear had been outlined in the seminal paper by Fiona Stapleton in 2008, which had suggested that daily wear is safest (only one to two cases of MK per 10,000 years of wear), with increased risk from occasional overnight wear (two to six cases per 10,000 years) and regular overnight wear (20 to 25 per 10,000 years). Around 15% of cases of MK result in vision loss.
Bullimore’s own work has previously suggested that the incidence of corneal infiltrative events is much lower in eight to 12-year-olds than in adults, with no reported cases of MK in over 2,400 patient years of lens wear (cited in 2017).
Myopia is known to increase the risk of visual impairment. For example, Bullimore reminded delegates that 1.00DS of myopia control should reduce the risk of myopic maculopathy by 40%. Visual impairment risk increases with age. For myopia, ‘each dioptre more, increases visual impairment by 25% (= 1.25 – 1), while each dioptre less, reduces visual impairment by 20% (= 1 – 1/1.25). Using such data for visual impairment as a function of the level of myopia (from Tideman et al, 2016) and the risk data from Stapleton, it has been possible to derive a formula linking visual impairment risk (P), refractive error and age as follows;
PVISUAL IMPAIRMENT = 1 – EXP(–10 0.041(AGE + 2.4Rx – 107))
The conclusion – ‘The benefits of myopia control outweigh the risks associated with daily wear of contact lenses, but increased incidence of microbial keratitis associated with overnight wear and older children will alter this risk-benefit relationship.’ And this was neatly illustrated by the calculation that ‘five dioptres of myopia ≡ 12 years of ageing.’
Myopic Children
The BLINK (bifocal lenses in near-sighted kids) study is one of the several dubiously acronymed, but important, randomised clinical trials looking at influences to slow myopia progression. Researcher Krystal Schulle (Texas) and colleagues presented some incidental data of interest, in that they had recorded the frequency of retinal findings in myopic children at the baseline visit to determine if there is an association with the amount of myopia or eye length.
All 294 children (aged from seven to 11 years at baseline, with myopia between -0.75 and -5.00DS) had a dilated fundus exam (1% tropicamide) performed at the BLINK Study baseline visit, and ocular findings were documented in an online data capture system. Retinal findings were classified into three main categories: vitreous, peripheral retina, and other retinal findings. The findings are concerning, in that 30% of children in this cohort (with myopia not yet considered ‘high’) had a documented retinal finding, and 9% had a vitreous or retinal finding that could increase the risk for potential sight-threatening complications such as retinal detachment. The results underline the need for routine dilation and regular follow-up to monitor for retinal changes in all young myopes.
Dual Focus versus Single Vision
A team led by CooperVision’s Baskar Arumumgam and Paul Chamberlain presented data from their now familiar trial looking at the efficacy of their omafilcon A one day dual focus lens (MiSight). This presentation focused on the myopia progression rates of two matched groups of children, one already having been managed with MiSight, the other with single vision spherical daily disposable lenses of the same material. The group has found the myopia progression rates were similar across the two demographically matched populations, even though the previous single vision group had more myopia and longer axial length at the point of refit to dual focus. So, a good argument for introducing the dual focus even at a later stage of correction.
Multifocal Lenses and Vision
Centre-distance multifocal contact lenses (MFCLs) are increasingly being prescribed for myopia control. But has this an impact upon contrast sensitivity, and therefore visual quality? A team from Houston looked at 25 young adults with -1.00 DC or less of astigmatism and spherical equivalent refraction between -0.75 DS and -6.00 DS who were then masked and fitted binocularly, in random order, with three lenses: one single vision contact lens (SVCL) (Biofinity sphere) and two MFCLs (Biofinity D +2.50 add and NaturalVue). Contrast sensitivity (CS) was measured at 1.5, 3, 6, 12, and 18 cycles per degree and the acuity, the area under the log contrast sensitivity function (AULCSF), and the log contrast sensitivity by spatial frequency were analysed.
The AULCSF was smaller for both MFCLs than the single vision CL under photopic and mesopic lighting. At 18cpd, CS with NaturalVue was the same as with the SVCL, likely due to spurious resolution at that particular spatial frequency, but otherwise was reduced compared to the SVCL at all other spatial frequencies, similar to the Biofinity D. Though there were no meaningful differences in high-contrast VA between both MFCLs and the SVCL, these data demonstrate VA alone does not capture the full effect of MFCLs on vision. Perhaps time, yet again, to argue for CS assessment in contact lens practice?
A novel approach to assessing visual performance in MFCLs was presented by a team from SUNY. Centre-distance MFCLs have been reported to induce under-accommodation during near vision, possibly reducing the therapeutic effect. An audio biofeedback signal indicated the level of accommodation adopted by subjects viewing a known working distance, the frequency of which was proportional to the accommodative effort. A target tone corresponding to the tested distance was presented and subjects were asked to adjust their accommodation so that the pitches matched. After a two-minute break, accommodation without biofeedback was measured for 20 seconds at each distance. The training effect was determined to be the difference between the lag of accommodation before and after training. It was found that myopes were more responsive to accommodative biofeedback training than emmetropes. Considering that myopic children wearing MFCL were found to relax their accommodation at near, so increasing peripheral hyperopia, biofeedback training might be applied to change accommodation through MFCL to improve their myopia control efficacy during near vision. Novel indeed.Anatomical Change and Myopia Management
A team from Montreal have looked at choroidal thickness changes with MFCL wear. It seems that the higher the add, and so the greater the peripheral defocus, the bigger the increase in choroidal volume during wear. Evidence of the underlying physiological mechanism perhaps?
Other Matters
And just in case you were now bored by myopia management with contact lenses, a few other mentions:
• A team from Plymouth and Oklahoma have developed a computer-based task using both Vernier alignment and field matching techniques, where keratoconus patients placed seven target circles with mouse clicks in relation to a reference circle and reference line, to complete a square at 50cm viewing distance. In so doing, the team feel they have found a more accurate way of assessing visual distortion than is possible with standard acuity targets.
• A team from Aston have found that ionic high-water content contact lenses have the highest affinity with nicotine (from solution or fumes), whereas silicone hydrogels showed the lowest. Another consideration when selecting lenses for the more stubborn smoker.