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Ophthalmoscopy
Hashem Mohammadian
8533027
Ophthalmoscopy
Ophthalmoscopy is a test that allows a health professional to see
inside the back of the eye (called the fundus) and other structures
using a magnifying instrument (ophthalmoscope) and a light source. It
is done as part of an eye examination and may be done as part of a
routine physical examination
The Ophthalmoscope and Hermann von Helmholtz
In 1850, Hermann von Helmholtz invented the ophthalmoscope and
revolutionized ophthalmology. The ophthalmoscope, the most
important invention for ophthalmologist clinicians, is an instrument
that allows the ophthalmologist to look inside a person’s eye and
see the details of the living retina. Ophthalmoscopes allow
physicians to diagnose eye diseases and prevent blindness.
The Ophthalmoscope and Hermann von Helmholtz
Helmholtz's instrument operated by using a mirror to shine a beam of light into
the eye. The observer would look through a tiny aperture (opening) in the
mirror. Helmholtz found that looking through the lens into the back of the eye
only produced a red reflection. By attaching a condenser lens he obtained a
clearer inverted image, which was then magnified five times. He called this
combination of a mirror and condenser lens an indirect ophthalmoscope. It was
used regularly for eye examinations until 1920.
The modern ophthalmoscope is a hand-held instrument. It contains a small
battery-powered lamp that directs the beam of light by way of a mirrored
prism. The observer looks through a tiny hole in the prism. The instrument
magnifies the image and can be focused by a series of revolving lenses. The
lens needed to focus the image gives the doctor an approximation of the
glasses lens prescription needed to correct the patient's vision
A new type of ophthalmoscope that can project a laser
beam is used in eye surgery to correct a detached
retina. Another, larger type of ophthalmoscope, called
the binocular ophthalmoscope, is used in clinical
research. It provides an image of the eye that is
magnified fifteen times
The fundus contains a lining of nerve cells (the retina) ,which detects
images seen by the clear, outer covering of the eye(cornea). The
fundus also contains blood vessels and the optic nerve .
View of the retina through an
ophthalmoscope
‘
There are two types of ophthalmoscopy.
Direct ophthalmoscopy .Your health professional uses an
instrument about the size of a small flashlight with several lenses that
can magnify up to about 15 times. This type of ophthalmoscopy is
most commonly done during a routine physical examination .
Indirect ophthalmoscopy .Your health professional wears a light
attached to a headband and uses a small handheld lens. Indirect
ophthalmoscopy provides a wider view of the inside of the eye and
allows a better view of the fundus even if the lens is clouded by
cataracts.
Cataracts
A cataract is a painless, cloudy area in the lens of the eye. A cataract blocks
light from reaching the retina (the nerve layer at the back of the eye) and
may cause vision problems.
Cataracts are common in older adults and are associated with aging.
Smoking and exposure to excessive sunlight are additional risk factors.
Cataracts can also occur after an eye injury, as a complication of eye
disease, after the use of certain medications, or because of certain medical
conditions, such as diabetes. Some babies are born with cataracts or
develop them shortly after birth. These are called congenital cataracts.
Cataracts in adults are treated with surgery if vision problems are interfering
with the person's quality of life. Surgery to remove congenital cataracts is
usually done during the first 3 months of a child's life.
Why It Is Done
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Ophthalmoscopy is done to:
Detect problems or diseases of the eye, such as cataracts .
Help diagnose other conditions or diseases that damage the eye .
Evaluate symptoms, such as headaches .
Detect other problems or diseases, such as head injuries or brain
tumors.
Direct ophthalmoscopy
• This is the most common type of examination to look at structures
inside the eye .
• Your eyes may be dilated, and you will be seated in a darkened
room and asked to stare straight ahead at some distant spot in the
room .
• Looking through the ophthalmoscope, your health professional will
move very close to your face and shine a bright light into one of your
eyes. Each eye is examined separately .
• Try to hold your eyes steady without blinking.
Indirect ophthalmoscopy
• This type of ophthalmoscopic examination gives a more complete
view of the retina than direct ophthalmoscopy. It is usually done by
an ophthalmologist.
• Your eyes will be dilated, and you will be asked to sit in a reclining or
semi-reclining position in a darkened room .
• Your health professional will hold your eye open, shine a very bright
light into it, and examine it through a special lens .
• Your health professional may ask you to look in different directions
and may apply pressure to your eyeball through the skin of your
eyelids with a small, blunt instrument to help bring the edges of your
fundus into view .
How It Feels
Direct ophthalmoscopy
• During direct ophthalmoscopy, you may hear a clicking sound
as the instrument is adjusted to focus on different structures in
the eye. The light is sometimes very intense, and you may see
spots for a short time following the examination. Some people
report seeing light spots or branching images. These are
actually the outlines of the blood vessels of the retina.
Indirect ophthalmoscopy
• With indirect ophthalmoscopy, the light is much more intense
and may be somewhat uncomfortable. Pressure applied to your
eyeball with the blunt instrument also may be uncomfortable.
After-images are common with this test. If the test is painful, let
the health professional know.
Risks
• In some people, the dilating or anesthetic eyedrops can cause:
• Brief episodes of nausea, vomiting, dry mouth, flushing, and
dizziness .
• An allergic reaction .
• A sudden increase in pressure inside the eyeball (closed-angle
glaucoma)
• Call your health professional immediately if you have severe and
sudden eye pain, vision problems (halos may appear around light),
or loss of vision after the examination.
Specialist Ophthalmoscope
Professional Ophthalmoscope
Pocket Ophthalmoscope
Binocular indirect
ophthalmoscopes
Binocular indirect ophthalmoscopes are used by an ophthalmologist to look
into a patient's eye.
• a binocular ophthalmoscope employs a telecentric ocular lens in
front of a viewing mirror assembly in order to provide parallel light
rays from the lens to the viewing mirror assembly and from there to
two direction changing mirrors that direct the light to the viewer's
eyes .
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the need for angular adjustment of the mirror assembly with the forward
and backward movement is avoided without loss of image quality
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provides for advantages in magnification, in that, by having the ocular
lens in front, one can decrease the focal length (and increase
magnification) without decreasing the working distance
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one can get a higher magnification with a wider field by using higher
power (short focal length) ophthalmoscopic lenses
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The ophthalmoscope employs an illumination system that directs light along
an optical path through the telecentric ocular lens, providing uniform
brightness for different magnifications. In general, a binocular
ophthalmoscope employing a pair of objective lenses mounted on opposite
sides of the viewing mirror assembly along respective optical paths from the
assembly, a pair of prisms mounted outside of the objective lenses, and a
pair of ocular lenses between the prisms and the viewer's eyes.
The prisms have reflective surfaces that are positioned to redirect the
optical paths so as to exit the prisms along the paths that are generally
parallel to the viewing direction.
The reflective surfaces also cause the optical path to cross its path within
the prism so as to increase the length of the path. The reflective surfaces
also cause the image to invert vertically and horizontally
. This arrangement provides the magnification advantages associated
with having an objective lens and an ocular lens and employs the
prisms both to change the direction of the optical path at the width of
the viewer's eyes and to provide for the necessary inversion of the
image created by the use of an additional lens
. In preferred embodiments the prisms are pentaprisms that each have
a "roof configuration", i.e., a pair of reflective surfaces at a 90
degree angle with each other in the vertical direction so as to
provide a vertical inversion of the image.
• The assembly includes first and second stages that are movable
along a viewing direction and carry respective first and second
mirrors.
• The first mirror could be in the viewing mirror assembly of a
binocular ophthalmoscope and the second mirror could be in the
illumination system.
• The second stage is mounted for both movement with the first stage
and movement relative to the first stage. This permits the first and
second mirrors to desirably be moved as a unit along the direction of
sight and also permits for the fine tuning adjustments of the relative
positions of the two mirrors by movement of the second mirror
relative to the first.
STRUCTURE AND OPERATION
diagram of a prior art binocular
ophthalmoscope
diagram showing the positions of images of the
observer's pupils and the illumination source in
the patient's pupil
a diagram of a prior art illuminating system
for a binocular ophthalmoscope
perspective view of a pentaprism component
perspective view of an adjustable
mirror assembly which can be used
in binocular ophthalmoscopes
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