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Electroretinography
and Electrooculography: These two tests
are done to evaluate the function of the
retina. Light is projected onto the retina
and electrical potentials that occur normally
in the eye are recorded using special electrodes
placed near and on the eye. Certain retinal
degenerative diseases are diagnosed only
on testing with electroretinography. Specialized
computer soft ware is needed to analyze
the data.
Low vision aid testing:
There are certain diseases that may lead
to permanent partial loss of vision. These
patients can be sometimes helped to some
extent by using special aids called low
vision aids. There are a variety of these
available and most of them are fine tuned
for a specific function. Most of them have
been made to enable reading fine print.
It is important that the patient should
be motivated to use them. They are used
at a closer range than normal working distance
and hence one needs to get used to the same.
Computers and closed circuit television
are also useful as low vision aids. One
has to test different varieties before choosing
what is appropriate for them.
Ultrasonography:
Ultrasonography is test that permits the
evaluation of the back of the eye in case
of opaque media. In a normal eye one is
able to see the back of the eye using instruments
such as indirect ophthalmoscope. In conditions
of disease and injury the cornea, the lens
or the vitreous cavity can become opaque
and prevent this visualization. In these
circumstances, ultrasound can be used to
scan the eye and get useful information
about the tissues lying behind the opaque
media. This information is needed not only
for proper diagnosis but also to plan the
surgery where indicated.
Special tests for squint
and related disorders
Cover test and prism
tests: An important part of the evaluation
of a patient with squint is the cover test
and prism tests. These tests are conducted
in the office of the eye doctor itself.
Using these tests the eye doctor is able
to classify the type of the squint and to
grade the severity of the same. This information
is needed to plan the treatment including
surgery where needed. With a torch light
and a set of loose prisms the eye doctor
is able to evaluate squint to a great degree.
Orthoptic evaluation:
Orthoptics is the study of how effectively
the two eyes function together (binocular
vision). This testing is done on many instruments
including the synaptophore.. Special instruments
are used to measure the near point of convergence
and near point of accommodation. These points
give a guide as to how difficult it is for
a person to view near objects. Many people
with eyestrain on performing near work may
be helped by exercises after the orthoptic
evaluation.
Corneal topography:
Corneal topography is the detailed mapping
of the surface of the cornea. Advanced computer
analysis of several spots on the surface
of the cornea using the study of the reflected
image is done. Color coded graphs of the
surface map enable the doctor to diagnose
certain conditions such as keratoconus.
Before undergoing excimer laser treatment
for getting rid of glasses, one needs to
perform this test to understand the surface
of the cornea better and plan the treatment
accordingly.
Pachymetry: Pachymetry is the
study of the thickness of the cornea. The
accurate measurement of the thickness is
made possible by using ultrasound or optical
means. Measurement of the thickness is important
in the diagnosis and management of certain
corneal conditions such as keratoconus,
corneal endothelial dystrophy etc.
Specular microscopy: Specular microscopy
is a test that enables the evaluation of
the back most layer of the cornea called
the endothelium. The health of this layer
is important in maintaining the clarity
of the cornea. With age, injury, surgery
and in some diseases this layer may have
reduced number of cells and become abnormal.
Study of this layer is done by counting
the number of cells per square millimeter
as well as study the type of the cells.
This study is important in planning certain
surgeries.
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