This work investigates two key questions: ; how myopia progression control treatments
impact accommodation and binocular vision function and if accommodation and
binocular vision function prior to myopia control interventions has any association with
the efficacy of treatment. The work is made up of four main studies.
Study 1 was a review and re-analysis of a previously completed study to investigate
whether there are any possible associations between accommodation and binocular
vision status prior to lens wear which may impact the myopia control efficacy of
orthokeratology lens treatment. The data of 26 children were used. The study involved
using an orthokeratology lens in one eye, with the contralateral eye used as a rigid gas
permeable lens wearing control. Given the unusual nature of this modality,
accommodation and binocular vision status was measured at baseline and monitored
throughout the study to ensure that there were no adverse responses to lens wear. In a
novel analysis of pre-existing data, the accommodation and binocular vision profiles of
those participants that responded the best to orthokeratology lens treatment in terms of
inhibiting ocular axial length growth were compared to those that did not respond to
treatment. A similar comparison was made between those participants who progressed
the most to the least in the control eye.
Results from this analysis suggested that accommodation and binocular vision status
prior to orthokeratology lens wear may be associated with treatment effect.
Orthokeratology lens treatment worked best for myopia control when accommodative
facility was higher and closer to population norms, AC/A ratio was lower and closer to
population norms and accommodative lag was higher. None of these associations
reached statistical significance, however further investigation appeared warranted. Interestingly, baseline near phoria did not appear to have an influence on response to
treatment with orthokeratology lens wear. This is different to bifocal spectacle lens wear
studies that show that initial near phoria has an impact on the efficacy of myopia control
Study 2 was a review of clinical records of 37 children and young adult patients seen in
two private optometric practices in Australia. Accommodation and binocular vision
function prior to orthokeratology lens wear was compared to during lens wear in patients
who were fitted with orthokeratology lenses between 2010 and 2012.
The results of this study showed that there was a statistically significant change in mean
near phoria in the exo direction with lens wear. Mean positive relative accommodation
increased, mean negative relative accommodation decreased and accommodative
facility increased. While the mean distance phoria remained unchanged there was a
statistically significant reduction in the standard deviation of this variable. There was a
slight reduction in mean lag of accommodation, but it failed to reach statistical
The study showed that the binocular vision status including accommodative and
vergence measures changed during orthokeratology lens wear. The changes were in a
direction closer to population norms.
Study 3 was a prospective study of the impact of short-term orthokeratology lens wear
on binocular vision in 12 young adults. Measurements of binocular vision status were
taken at baseline and after one month of lens wear.
The results of this study were similar to Study 2. There was no statistically significant
change in mean near phoria. Distance accommodative facility increased. There was a
slight, but not statistically significant, change in mean near accommodative facility Again, while there was no change in mean distance phoria, there was a significant
reduction in the standard deviation of this variable.
Additional variables of interest in this study included stereopsis, which was unchanged,
and fixation disparity at distance and near which were unchanged.
This short-term study showed that orthokeratology lens wear alters binocular vision
status including accommodative and vergence measures. Again, the changes in
binocular vision were in a direction closer to population norms.
Study 4 was a record review of patients seen in the Myopia Control Clinic at the
University of New South Wales, Sydney, Australia. The accommodation and binocular
vision function of myopic children treated with orthokeratology lens wear or low dose
atropine were reviewed. A total of 9 children treated with orthokeratology were followed
for 3 to 6 months. Mean near phoria moved in the exo direction with orthokeratology
lens wear and gradient AC/A ratio moved to more normal values with lens wear. There
was an association between annualised axial length growth and gradient AC/A ratios
and stereopsis, suggesting that baseline accommodation and binocular vision function
may influence treatment.
A total of 19 children were treated with low dose atropine and data were available from 3
to 6 months of treatment. Low dose atropine led to a small but not statistically significant
decrease in amplitude of accommodation. Patients who were the worst responders to
low dose atropine had lower baseline amplitude of accommodation compared to the
best responders. Although speculative, the reduction in amplitude of accommodation
may have a detrimental impact on the accommodation and binocular vision function and
increase blur. Alternatively, those patients with high amplitude of accommodation may
benefit from a subtle change in the accommodation and vergence relationship Both accommodation and vergence measures of binocular vision status appear to
change with orthokeratology lens wear. The changes in binocular vision move in a
direction closer to population norms; this is a novel finding of this thesis and is not
reported elsewhere. Binocular vision that is abnormal has been associated with onset of
myopia and progression. The changes in binocular vision associated with
orthokeratology lens wear may contribute to the myopia progression control effect.
Close monitoring of accommodation and binocular vision during myopia progression
treatment is warranted.