Myopia in brief

A special two-hour symposium on the Sunday morning of the conference was opened by Bernard Gilmartin (Aston University) who looked at eye growth in myopia.

There was a significant change in vitreous chamber depth and increase in myopia between six and 14 years of age as the eye grew and the crystalline lens thinned, with most change between six and nine years. The two major issues in ocular growth were the role of peripheral vision and what elements of the blur signal were computed.

Clinical trials based on accommodative lag in children showed that eye growth was triggered by a small hyperopic defocus, with substantial defocus causing an increase in axial length. The accommodative effort could be optimised at near to reduce this effect by using progressive spectacle lenses, or possibly progressive contact lenses which would also help with peripheral vision. Magnetic resonance imaging showed the myopic eye to be flatter at the back in addition to growing posteriorly and there were differences in nasal and temporal stretching.

A presentation on epidemiology by Dr Nicola Logan (Aston University) highlighted that myopia is being driven by education and urbanisation. Rates of myopia varied across the globe from 25-35 per cent of the population in Europe to more than 70 per cent in East Asia, but only 12 per cent in Australia. In the UK, the prevalence was 5 per cent among seven-year-olds, 38 per cent in 13-year-olds and 52 per cent in 20-year-olds. Two per cent of the population had high myopia ( >6D), which had been shown to be more prevalent in a university population.

Risk factors included genetics, intense near work, female gender, urban living and possibly diet. Incidence might be altered with a significant change in the environment, bearing in mind the low prevalence in Australia compared to Hong Kong.

Dr Pauline Cho (Hong Kong Polytechnic University) looked at the effectiveness of myopia control. Eighty per cent of those undergoing orthokeratology in Hong Kong are children, sometimes as young as three years. Studies with children had shown significant differences in increases in axial length and vitreous chamber depth between an ortho-k group and controls (after one year, change in axial length 0.27mm for spectacle wearers compared to 0.14mm with those fitted with ortho-k lenses).

Dr Cho concluded that orthokeratology was an effective option for myopia control in children. However, there were large variations in the amount of axial length increase, so it was not possible to predict what the outcome would be in each case, or, since the effect was transient, what would happen if lens wear ceased.

Judith Morris (City University) provided some practical tips for fitting high myopes with contact lenses. An enlarged globe, large flatter corneas, possibly reduced blink rate and hypoxia from thicker lens designs were among the factors to consider. Flexibility was key with these patients, such as suggesting over-spectacles if a favoured contact lens type was out of range. Lens designs might need to be modified to optimise fit and vision, such as increasing total diameter to improve stability. RGPs should be lenticulated for higher powers and designs amended to improve centration.