Page 128 - The Indian Optician Digital Edition May-June 2023
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TABLE 1 - IPAD BASED CONTRAST STEREOACUITY
OD OS OU
PRE 1.76 ± 0.90 1.80 ± 0.91 1.91 ± 0.95
POST 1.82 ± 0.91 1.85 ± 0.91 1.99 ± 1.00
P-VALUE 0.17 0.02 0.24
monovision correction, or bifocal and multifocal subsequent square, the contrast is reduced in
correction based on alternating or simultaneous increments of 0.3 log MAR units. The first three
image principles. The purpose of bifocal and sequences present the same set of contrasts
multifocal contact lenses is to bring objects at again, resulting in two presentations for each
different distances into sharp focus. Compared of the 24 contrasts. If the subject does not
to spectacles, contact lenses are closer to the respond correctly to two targets in a row, the
eye, provide a wider field of view, have less rest of that sequence is skipped, and the next
distortion, and are more consistent to use since sequence begins.
they are not easily removed throughout the
day. They serve as a platform for bifurcation The contrast sensitivity is measured in
and multifocality. log MAR units, and the score expresses the
reciprocal of the threshold contrast using the
METHODOLOGY Weber contrast ratio. After providing appropriate
instructions to the patient, the test is performed,
This study is prospective and observational, and the results are recorded upon completion.
involving 38 subjects aged between 40 and
60 who met the inclusion criteria and had IPAD-BASED STEREO ACUITY TEST
no ocular disease. A detailed ocular and
systemic history was obtained, followed by a This test can be performed at multiple
comprehensive slit lamp examination. Visual distances, allowing for testing of up to ten
acuity assessments for distance and near levels of stereo acuity at each distance. It uses a
were conducted using Snellen's visual acuity random dot stereogram viewable with anaglyph
chart and the N-notation visual acuity chart, spectacles, and habitual refractive error
respectively, and were converted to a log MAR correction is applied. The test has applications
value. Objective refraction was performed in visual screening programmes and the design
using either streak retinoscopy or an auto- and use of 3D displays are suggested. For depth
refractometer. Subjective refraction was perception evaluation, the test is performed at
also conducted, including a duo chrome test 40 cm with a red filter in front of the right eye
and binocular balancing, followed by direct and a green filter in front of the left eye. The
ophthalmoscopy for fundus evaluation. After patient must identify the cut portion of a circle
the primary evaluation, iPad-based stereo acuity presented on the screen and match it with the
and contrast sensitivity tests were conducted side option bar. After each correct answer, the
using the subject's existing refractive correction. test proceeds to the next level, and the final
result is displayed on the screen.
IPAD-BASED CONTRAST
SENSITIVITY TEST After the pre-workup and questionnaire with
existing refractive correction, the patient is
The blinking square contrast sensitivity test counselled for a multifocal soft contact lens trial,
involves showing the patient target squares at and oral consent is taken. Contact lens fitting
various contrast levels in different quadrants measurements, such as keratometry readings,
of the screen. The patient is then instructed horizontal visible iris diameter, and pupil
to touch the quadrant with the target square. diameter in dim and room illumination, are
The test is divided into six squares, starting taken. To fit multifocal soft contacts correctly,
with a high-contrast square, and with each identifying the dominant eye is crucial, and an
124 | THE INDIAN OPTICIAN | MAY-JUNE 2023 OPTOMETRY
