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Making Contact

is expected to be below normal. children who went on to develop
The insufficiency also creates an myopia relative to those who remained
accommodative lag, or a depth of field, to emmetropic, may be precursors of
reduce the associated over-convergence juvenile onset myopia. Additionally,
without inducing blur. high NRA values have been found to

An individual with a higher-than-normal be associated with accommodative
lag of accommodation will experience insufficiency and convergence excess.
blur to avoid double vision and If there is higher esophoria and higher
localize accommodation in front of
convergence. This will give a lower lag of accommodation with prolonged
positive relative accommodation (PRA) near vision with contact lenses, then
value and shift the negative relative accommodative convergence (AC) and
accommodation (NRA) to a higher accommodation (A) in the AC/A will
value. also be affected. Since a higher AC/A
ratio is known to be associated with
In younger eyes, the higher lag of reduced accommodation, Gwiazda et al.
accommodation can create points suggests that a significantly high AC/A
behind the retina called hyperopic ratio could speed up the development
retinal defocus. Over time, these can of myopia in children with significantly
serve as a stimulus to increase the
axial length and contribute to myopia reduced accommodation.
progression. Moreover, axial length has
been shown to temporarily increase Hence, the use of contact lenses in all
with accommodation after just 10 to 30 children with myopia. In particular, those
minutes of near work. with complaints of diplopia or blurry
vision should be assessed to discover
CONVERGENCE any undiagnosed binocular vision
Myopes wearing contact lenses for near dysfunction at near (accommodative
work converge more than when they insufficiency, high accommodative lag,
are wearing glasses. This is because the low PRA values or high NRA values, or
increasing base-in prismatic effects convergence excess with low NFV) that
found with glasses, (which help reduce can interfere with visual comfort during
convergence demands when converging extended, visually demanding tasks and
on a near target), are no longer available
to contact lens wearers. contribute to the progression of myopia.
For people wearing contact lenses with Notwithstanding the consortium of
esophoria at near, there is a greater use therapeutic options, such as orthokera-
of the negative fusional vergence (NFV) tology, bifocal glasses and atropine,
to correct the esophoria, producing as well as recommendations to blink
lower NFV values. There is also an frequently or lubricate the eyes, to apply
associated increase in the lag of the 20/20/20 rule (looking 20 feet away
accommodation, due to the relaxation from near, every 20 minutes, for 20
of accommodation to reduce the seconds) with prolonged near vision,
accommodative convergence; this, in and to spend more time outdoors,
turn, reduces PRA, as stated earlier. “performance” lenses in the form of

This agrees with the findings from Goss, low-power plus lenses (up to +0.75)
that differences in accommodation and worn over distance contact lenses for
convergence function, such as higher near activities are very beneficial in
esophoria values at near, more plus reorganizing the visual space at near for
on the binocular cross-cylinder test, single, clear, comfortable and efficient
and lower PRA values that he noted in vision in these young developing eyes. n
E
1 Woodman EC, Read SA, Collins MJ, et al. Axial elongation following prolonged near work in myopes and emmetropes. Br J Ophthalmol. 2011;95(5):652-656
2 Goss DA, Rainey BB. The relationship of accommodative response and near-point phoria in a sample of myopic children. Optom Vis Sci 1999,76:292–294
3 García A, Cacho P, Lara F. Evaluating relative accommodations in general binocular dysfunctions. Optom Vis Sci 2002, 79 (12):779–787
4 Gwiazda J, Thorn F, Held R. Accommodation, accommodative convergence, and response AC/A ratios before and at the onset of myopia in children. Optom Vis Sci
2005, 82(4):273–278

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