Contact Lenses Versus Spectacle Lenses

Contact Lenses Versus Spectacle Lenses

 

There is some evidence in the literature that

rigid gas permeable (RGP) contact lenses have a

beneficial effect on myopia development .

A more recent study could not find a difference

between contact lens wearers and spectacle

wearers (–1.33 vs –1.28D progression in 2 years

[24]). In this study, 105 children aged 6–12 years

wearing contact lenses were compared with 192

children wearing spectacles. Because this is a

potentially important issue, another major

study is underway (the CLAMP study, Contact

Lens and Myopia Progression study). Why

myopia should be inhibited with hard contact

lenses, but not with soft ones is also an interesting

question [13]. It is clear that hard contact

lenses flatten the cornea for several days, and

that this mimics a reduction of myopia. Therefore,

vitreous chamber depth measurements are

necessary to confirm that there was really

growth inhibition.

                  The observation from animal models that

refractive state is locally controlled, also in the

peripheral retina (see Sects. 1.2.2.1 and 1.2.2.2),

suggests another possible explanation: spectacle

lenses could produce more hyperopic refractions

in the peripheral retina than hard contact

lenses and this could stimulate more eye

growth.

              Until now, only very limited data have

been published on the peripheral refraction of

human eyes with hard contact lenses compared

to spectacle lenses [61]. This study found that,

on average, there was 0.43 D more hyperopia at

22° off-axis with spectacle lenses, compared to

hard contact lenses (p=0.026). The question

merits further studies in a larger sample.

 

                       Lowering the retinal image brightness in the

chick eye by light neutral density filters has no effect on

refractive development as long as the filters are weak (1

no attenuation, 2 0.5 log units, 3 1.0 log units). If the filters

are more dense (4 2.0 log units attenuation) some

myopia develops, similar to when the filters are completely

black (5).However, frosted diffusers that attenuate

the light only a little (0.38 log units) cause much

more myopia (6). This result suggests that low retinal

image brightness interferes with eye growth. Furthermore,

if the chicks are kept in low light (2.0 log units

less than controls), even clear occluders cause some

myopia,suggesting that eye growth becomes more sensitive

to minor image degradation

 

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