Introduction: changes in the peripheral refractive error profile in

Introduction:

Myopia has emerged as a major ocular health issue
recently because of its increasing prevalence worldwide1
and its progressive nature in children.

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

 

Myopia or near-sightedness is caused due to increase in
axial length or corneal curvature. The increase in axial length is governed by
different etiological factors2, among all near work3
and peripheral retinal image formation4 have been formulated to be
leading factors.

 

Animal studies5, 6
have shown that elimination of signals from the fovea did not interfere with
emmetropization, but  inducing hyperopic
defocus on the peripheral retina promoted development of axial myopia in infant
monkeys. This experiment led to the proposal, peripheral retina defocus leads
to alternation of retinal shape causing axial elongation and myopia progression
7-9.
Donder10 and Helmholtz11 considered myopia to be an
acquired anomaly associated with over-exertion in near work.  It was observed that during near work myopic
children shows lag of accommodation 12
which results in a reduced power of the eye thus causing relative hyperopic
defocus at near, Since it is known from animal studies5, 6
that a hyperopic defocus leads to the development of myopia, the Lag of
accommodation might be a risk factor for the development and/ or progression of
myopia.12, 13

 

As peripheral hyperopic
defocus triggers myopia progression, the treatment modality for Myopia should
be potentially focused on modifying peripheral refraction to counterbalance the
known stimulus that triggers eye elongation and subsequent progression of myopia.
The conventional myopic spectacle lens increases hyperopic defocus in periphery
so to change RPR profile studies have tried adding tints(radiant refracting
lens) or pantascopic tilt which resulted in myopic defocus at peripheral
retinal plane14, 15
although study  has shown that these
changes are only for distance , hyperopic defocus still persists near work.16

 

Conventional soft and
rigid gas permeable (RGP) contact lenses reduces relative peripheral hyperopia,
and can even results in relative peripheral myopia, particularly in high myopia17, 18.

Commercially available multifocal
contact lenses (MFSCL) intended for presbyopic correction served as myopia
control lenses in some studies 19, 20
. The peripheral add power area has shown to induce significant changes in the
peripheral refractive error profile in myopic eyes as compared to distance
power in the periphery19. Walline JJ et al., 21
in their study found 50% reduction in myopia progression and 29% reduction in
axial elongation during the 2-year treatment period with MSCL.

 

 

Reverse geometry contact lenses for corneal reshaping tend
to have promising result in retarding eye elongation 22-24. Ortho k lenses alter ocular
growth pattern by inducing relative peripheral myopic refractive error (RPRE)
whereas the central refraction is fully corrected. Studies comparing
conventional RGP and ortho k lenses have found ortho k lenses have significantly
reduced myopia in the central 20° VF in myopic children25.

Majority of studies have measured RPR
only in horizontal meridian using different modalities of myopia correction,
Atichson et al.,26 found that in vertical meridian myopes
had peripheral myopic  defocus. Study on
size and shape of myopic eye by Verkicherla et al.,9
reported difference in peripheral refraction along horizontal and vertical
meridian. On measurement for near peripheral refraction in myopia by Calver et
al.,27
showed peripheral hyperopia in low myopes and peripheral myopia in high myopes.
However there is a lacunae in all the previous study as none of them have
measured horizontal and vertical meridian PRP for distant and near with all the
modalities such as single vision glasses, Anti-myopia lenses, spherical soft
contact lens, multifocal contact lens and ortho-K. So, the aim of our study is
to measure horizontal and vertical meridian PRP for distant and near with
different corrective modalities.

 

Methodology:

Subjects: All participants will be drawn from L V Prasad Eye
Institute, Hyderabad. Their informed consent will be obtained prior to the
experiment and experiment protocol will be approved by institute’s ethic
committee.

Inclusion criteria:

·        
Age -18 to 25 years

·        
Myopia of at least -1.00D , astigmatism of no
more than -1.00D

·        
Best corrected logMAR visual acuity of 0.0logMAR
for distance and 0.4logMAR for near.

 

Exclusion criteria:

·        
No ocular pathology

·        
Contraindications/ intolerance to contact lens
wear

 

Experimental Procedure:

One eye from each
subject will be investigated (eye with the more myopic refraction will be used).
Comprehensive eye examination will be performed, which includes subjective non
cyclopelgic refraction, slit lamp examination, axial length measurement with
lens star and undilated fundus examination.

 

Peripheral refraction
will be measured in both horizontal and vertical meridians using —- open
field binocular auto refractometer at a distance of 3mtrs and 40cms. The
subject will be seated with the head stabilized in a chin-rest so that the eye
will be aligned with the central target. 
Subjects will be asked only to and rotate their eyes to view a series of
fixation targets. Refractive error will be measured 3 times on-axis, and 3 times
at each eccentricity in 5° increments out to 35° both nasally and temporally
horizontally and out to 15° vertically. Readings will be averaged for each
subject in all positions. The axis of the auto refractor will be aligned with
the centre of the entrance pupil during all measurements. For near Maltase
cross will be given as a target placed 40cms away from corneal apex.

 

Each subject will have
to participate for 2 days, Day 1 will consist of measurements with glasses,
anti –myopia lenses, Single vision soft contact lens and multifocal contact
lenses.

Subjects will be fitted
with Ortho K lenses and advised to sleep with lenses on at least for 8 hours,
the next day lenses will be removed and measurement will be performed. All the
tests will be performed in randomised order.

 

Material / Instrument required:

·        
Open field autorefractometer

·        
Lenstar biometry

·        
Anti- myopia lenses (Essilor)

·        
Single vision SCL (B& L , J & J)

·        
Multifocal SCL (central distance design – low
add à B
& L)

·        
Ortho K lenses (Paragon CRT)

x

Hi!
I'm Owen!

Would you like to get a custom essay? How about receiving a customized one?

Check it out