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Direct Ophthalmoscope
Dr. R S Walpitagamage
Registrar in Ophthalmology
Colombo North Teaching Hospital,Ragama
Sri Lanka

“A physician using a direct
ophthalmoscope is like,
one-eyed Eskimo peeping in to an
igloo from the entry way with a
flash light”

History..
• Charles Babbage 1847
• Hermann von Helmholtz 1851

Introduction
• The direct ophthalmoscope is commonly used for routine
examination of the fundus of the eye, especially when a slit
lamp cannot be used.
– It is small
– Easily portable
– Can also be used to examine the more anterior parts of the eye

• The instrument consists of a system of
lenses which focus light from an
electric bulb on to a mirror where a
real image of the bulb filament is
formed.
• The mirror reflects the emitted light in
a diverging beam which is used to
illuminate the patient's eye.
• Reflected rays from patients retina
refracted by patients crystalline lens
become parallel and enters into the
observed eye through the mirror hole
and the observer views the illuminated
eye.
• The image of the bulb is formed just
below the hole so that its corneal
reflection does not lie in the visual axis
of the observer.
Optics of Direct Ophthalmoscope

Patient’s eye Observer’s eye
Mirror with a hole
Light source
Aperture
Lens
Optics of Direct Ophthalmoscope
Compensation
lens

Detailed structure of direct ophthalmoscope showing
the illumination and viewing optical system

Direct Ophthalmoscope
Patient side
Front
surface
mirror
Crossed
Linear
Polarizing
filter/red free
Filter switch
Our side
Rubber
brow rest
Lens
selection disc
Illuminated
lens indicator
On/Off switch
Aperture
Selection
dial

APERTURES AND FILTERS
Small Aperture: Provides easy view of the fundus
through an undilated pupil. Always start the examination
with this aperture and proceed to micro aperture
if pupil is particularly small and/or sensitive to light.
Large Aperture: Standard aperture for dilated pupil
and general examination of the eye.
Micro Spot Aperture: Allows easy entry into very small,
undilated pupils.
Slit Aperture: Helpful in determining various elevations
of lesions, particularly tumors and edematous discs.

APERTURES AND FILTERS
Fixation Aperture : The pattern of an open
center and thin lines permits easy observation
of eccentric fixation without masking the
macula.
Cobalt Blue Filter: Blue filter used with
fluorescein dye permits easy viewing of small
lesions, abrasions, and foreign objects.
Red-Free Filter: Excludes red rays from
examination field for easy identification of veins,
arteries, and nerve fibers.

How to Conduct an Ophthalmologic Examination
with a Direct Ophthalmoscope
• In order to conduct a successful examination of the fundus,
the examining room should be either semi darkened or
completely darkened.
• It is preferable to dilate the pupil when there is no pathologic
contraindication, but much information can be obtained
through the undilated pupil.
• The following steps will help the practitioner obtain
satisfactory results:
1. For examination of the right eye, sit or stand at the patient’s
right side.
2. Select “0” on the illuminated lens disc of the ophthalmoscope
and start with the small aperture.

3. Take the ophthalmoscope in the right hand and hold it
vertically in front of your own right eye with the light
beam directed toward the patient and place your right
index finger on the edge of the lens dial so that you will
be able to change lenses easily if necessary.
4. Dim room lights. Instruct the patient to look straight
ahead at a distant object.
5. Position the ophthalmoscope about 6 inches (15 cm)
in front and slightly to the right (25º) of the patient and
direct the light beam into the pupil. A red “reflex” should
appear as you look through the pupil.

6. Rest your left hand on the patient’s forehead and hold
the upper lid of the eye near the eyelashes with the
thumb. While the patient is fixating on the specified
object, keep the “reflex” in view and slowly move toward
the patient.
• The optic disc should come into view when you are
about 1 to 2 inches (3-5 cm) from the patient.
• If it is not focused clearly, rotate lenses with your
index finger until the optic disc is as clearly visible as
possible.
• The hyperopic, or far-sighted, eye requires more
“plus”(green numbers) lenses for clear focus of the
fundus; the myopic, or nearsighted,eye requires
“minus” (red numbers) lenses for clear focus.

7. Now examine the disc for clarity of outline, color,
elevation and condition of the vessels.
• Follow each vessel as far to the periphery as you can.
• To locate the macula, focus on the disc, then move the
light approximately 2 disc diameters temporally.
• You may also have the patient look at the light of the
ophthalmoscope, which will automatically place the
macula in full view.
• Look for abnormalities in the macula area.
• The red-free filter facilitates viewing of the center of the
macula.

8. To examine the extreme periphery, instruct the patient
to:
• Look up for examination of the superior retina
• Look down for examination of the inferior retina
• Look temporally for examination of the temporal retina
• Look nasally for examination of the nasal retina.
This routine will reveal almost any abnormality that
occurs in
the fundus.
9. To examine the left eye, repeat the procedure outlined
above but hold the ophthalmoscope in your left hand,
stand at the patient’s left side and use your left eye.

USE OF FIXATION TARGET
• Direct the patient to focus on the center of the fixation target
projected within the light beam.
• Simultaneously check the location of the pattern on the
fundus.
• If the center of the pattern does not coincide with the macula,
eccentric fixation is indicated.
• In this procedure, the crossed linear polarizing filter is
especially useful since it dramatically reduces reflections
caused by the direct corneal light path.

ADDITIONAL EXAMS WITH COAXIAL
OPHTHALMOSCOPE
• By selecting the +15 lens in the scope and looking at the pupil
as in a fundus examination [2 inches (5 cm) distance from the
patient], the examiner may verify doubtful pupillary action.
• One can also easily detect lens opacities by looking at the pupil
through the +6 lens setting at a distance of 6 inches (15 cm)
from the patient.
• In the same manner, vitreous opacities can be detected by
having the patient look up and down, to the right and to the
left. Any vitreous opacities will be seen moving across the
pupillary area as the eye changes position or comes back to
the primary position.

Field of view
• The area of retina which can be seen at any one time is called
the field of view.
• It is governed by the projected image of the sight-hole on the
retina , the hole in the mirror or the observer's pupil,
whichever is the smaller.
• Smaller than the field of illumination.
Direct ophthalmoscope. Image of sight-hole formed by emmetropic eye.
R = retina; P = principal plane.
The image A1 B1 of the sight-hole AB is constructed using a ray through the nodal
point-N, and a ray parallel to the visual axis which is refracted by the eye to pass
through its posterior focal point.

Factors affecting field of view in Direct
Ophthalmoscopy
1. Axial length of observed eye
• The figure shows the field of view (a-b)
– is smaller in a myopic eye-Rm
– larger in a hypermetropic eye-Rh
– than in an emmetropic eye-R.

Ophthalmoscopy
2. Size of the pupil of observed eye
– This figure shows the effect of pupil size on field of view -a b
– The field of view is considerably enlarged when the pupil is dilated;
hence the advantage of instilling a mydriatic prior to fundoscopy.
Small pupil- ab smaller
Large pupil – ab larger

Ophthalmoscopy
3. Distance between the observed eye and the observer
– In order to utilize the maximum available field of view it is necessary
for the observer to be as close as possible to the patient's eye.
– Figure shows that as the distance between the patient and the
observer decreases, the field of view –a b (the projected image of
the sight-hole on the patient's retina) becomes larger.

• Light reflected from the illuminated retina of the patient's eye passes
back, through the hole in the mirror and into the observer's eye.
• The position and size of the image formed in the observer's eye can
be constructed by first constructing the image, xy, of the illuminated
retina XY which is formed at the patient's far point.
• A ray from the top of that image, passing through the observer's
nodal point-No, locates the position of the top of the image- X'Y', on
the observer's retina -Ro.
• R-the patient's retina,
• P- principal plane,
• N- nodal point
• Fa -anterior focal point respectively
• Ro, Po and No refer to the observer’s retina, principal plane and
nodal point.

An emmetropic observer
viewing an emmetropic patient
• The rays of light leaving the patient's eye are parallel and are
therefore focused on the observer's retina without any
accommodative effort or the use of a correcting lens.
• Patient’s eye acts as a simple magnifier 60D/4=15D

viewing a hyperopic patient
• If the patient is hypermetropic, a diverging beam of light leaves his eye and
it behaves an emmetropic observer to accommodate or to use a correcting
convex(plus) lens in order to bring the light to a focus on his retina.

Mirror with a hole
Light source
Aperture
Lens
Convex lens
viewing a hyperopic patient

An emmetropic observer viewing a hyperopic patient- with correcting convex lens
• The retina of a hyperopic eye will be magnified less than 15x
because of the reverse Galilean telescope created by the
optics of the eye and the lens of the direct ophthalmoscope
• The image formed on the observer's retina is smaller when a
hypermetropic eye is viewed
• Field of view is wider in hypermetropia.
• Thus, when examining very hypermetropic eyes a small image
of a wide field of view is seen and the whole fundus can be
scanned quickly.

viewing a myopic patient
• An emmetropic observer viewing a myopic eye receives a converging beam
of light which is brought to a focus in front of his retina.
• X’ is a blur circle and the observer sees a blurred image unless he uses a
correcting concave(minus) lens.

Mirror with a hole
Light source
Aperture
Lens
Concave lens
viewing a myopic patient

An emmetropic observer viewing a myopic patient- with correcting concave lens
• If the subject eye is myopic, the extra plus power of the eye's optics
and the minus power dialed into place in the ophthalmoscope
together form a Galilean telescope, increasing magnification and
decreasing the field of view.
• The enlargement of image size seen when a myopic eye is examined,
coupled with the reduced field of view as compared with an
emmetropic eye results in the observer seeing a magnified but
restricted view of the myopic fundus.
• Also, in axial myopia the eye itself is bigger than an emmetropic eye.
• Thus it is difficult to examine a myopic fundus using the direct
ophthalmoscope because the field of view is so small compared with
the size of the fundus.

If the subject is having an astigmatism..
• It is impossible to secure a perfect view of the fundus of an
astigmatic eye because the only correcting lenses in the
ophthalmoscope are spherical.
• It is thus only possible to correct one meridian at a time.
• If the degree of astigmatism is high, the difference in image
size due to the disparity of dioptric power of the eye in the
two principal meridians causes distortion of the image and the
optic disc appears oval.

If the observer has a refractive error..
Two possibilities,
1. The observer can remove his spectacles and rack up the
appropriate lens in the ophthalmoscope to give a clear view
of the patient's fundus.
– The appropriate lens is the algebraic sum of his own and the
patient’s refractive error
2. The observer can use the instrument with his glasses on.
– However, his field of view will be restricted as the sight-hole in the
mirror will be further from his eye.

Direct ophthalmoscopy in summary…
Observer Patient
Myopic
Hyperopic
Emmetropic Emmetropic
Myopic
Hyperopic
Astigmatism Astigmatism
• Use minus lens
• Larger image
• Small field of view
• Difficult to examine
• Use plus lens
• Smaller image
• Larger field of view
• Easy to examine
• Difficult to correct
• Image distortion
1.Use spectacles with
reduce field of view
2.Remove spectacles
Add relevant lens power

Past questions(MD Ophthalmology module-3)
• 2017 April & 2005 July- Compare and contrast the optical
principles of Indirect Ophthalmoscope and Direct
Ophthalmoscope using Ray Diagrams. (70%)
• 1990 Nov- Describe optical principal of direct and indirect
ophthalmoscopy with diagrams and discuss their clinical
advantages.

Direct Ophthalmoscopy
Advantages over Indirect
• Relatively easy to perform and no
need of well trained person to
examine and interpret
• Higher magnification 15 times(5 in
indirect)
• Possible to examine through undilated
pupil
• Less discomfort to the patient
– No need of supine position
– Less intense light
– No indentation
Disadvantages over indirect
• No 3D view(stereopsis)
– Uniocular examination
• Relatively difficulty to examine with
eye movements
– Difficult to perform in babies-ROP
• Impossible to perform procedures like
indirect laser
• Difficult to examine patients with high
spherical/astigmatism
– More image distortion
• Relatively small area of retina can be
examined 50-70%
– Difficult to see the peripheries as no
indentation is used

SHAHANA
NETHRADHAMA
SCHOOL OF
OPTOMETRY

INDIRECT
OPHTHALMOSCOPY
Examination of both the peripheral
fundus and the posterior pole is
possible with indirect
ophthalmoscopy.

 Indirect ophthalmoscopy should be used:
• When examining a patient with symptoms of
shadows, hazy vision, flashes of light, and
floaters, which may suggest retinal tear,
detachment or other retinal abnormality.
• When following a patients with systemic
diseases that have retinal manifestations, such
as diabetes, high blood pressure,
cardiovascular disease, sickle cell disease,
infectious and autoimmune diseases.
• In patient with cataract or following cataract
extraction.
• For older patients who are at greater risk of
developing glaucoma and age related macular
degeneration.

PRINCIPLE
 Indirect ophthalmoscopy(IDO)involves
making the eye highly myopic by placing
a high power convex lens (+13D to
+30D) infront of the eye so that real,
inverted and laterally reversed image is
formed in front of lens
 The technique is called indirect because
the fundus is seen through condensing
lens.

 Two method of indirect ophthalmoscopy:
1. Monocular indirect ophthalmoscopy.
2. Binocular indirect ophthalmoscopy.

MONOCULAR IDO
 Monocular IDO is handheld technique
which produces real and erect image.
 It consist of:
 Illumination rheostat at its base
 Focusing lever for image refinement
 Filter dial with red free and yellow filters
 Forehead rest for steady proper observer
head positioning.
 Iris diaphragm lever to adjust illumination
beam diameter.

OPTICS
 An internal relay lens system re-invests,
initially inverted image to real, which
then magnified. This image is focusable
using focusing lever.

ADVANTAGES:
 Increased working distance from patient
 Increased field of view at low magnification
 Erect, real imaging similar to direct
ophthalmoscopy
DISADVANTAGE:
 Limited illumination
 Fixed magnification
 No stereopsis
INDICATION:
 Need for increased field of view, small pupil,
uncooperative children, patients tolerance of
bright light, basic fundus screening.

BINOCULAR IDO
Viewing fundus by allowing stereoscopic
examination.
CHARACTERISTICS :
 Magnification of image depends upon
the dioptric power of convex lens ,
position of the lens in relation of the
eyeball and refractive state of eyeball.
 With a stronger lens image will be
smaller but brighter and field of vision
will be more.

PREREQUISITES
i. Indirect ophthalmoscope
ii. Dark room
iii. Convex lens
iv. Pupil of the patient should be dilated.

TECHNIQUE:
 The patient’s pupil must be dilated.
 The procedure is explained to the patient and
made to lie in supine position,instructed to
keep both eye open.
 The examiner throw the light into the patient’s
eye from an arm distance with BIO or that
mounted on the spectacle frame.
 Keeping eyes on the reflex the examiner then
interposes the condensing lens(various
power ranging from +15D to +40D) in the
path beam of light close to the patient’s eye
and then slowly move the lens away from the
eye until the image of retina is clearly seen.

 The examiner moves around the head of
the patient to examiner different
quadrants of fundus.
 Examiner has to stand opposite to the
clock hour position to be examined
 By asking the patient to look in extreme
gaze and using scleral indenter,
peripheral retina upto ora serrata can be
examined.

Field of illumination
 More in myopia and less in
hypermetropia as compared to
emmetropia.

Image formation
 Emmetropia
 Myopia
 Hypermetropia

EMMETROPIA
 Emmetropic eye, rays from fundus are
parallel, brought to a focus by the
condensing lens.
 Image formed at the principal focus of
lens.
 Hence, size of image remains the same,
no matter the position of lens.

MYOPIA
 Rays are convergent
 Image formed in front of the eye
 Final image by condensing lens within
its own focal length
 Image is smaller when lens is nearer to
anterior focus of the eye and larger
when away.

HYPERMETROPIA
 Rays are divergent and appear to come
from behind the retina.
 Image by condensing lens in front of its
principle focus
 Image is larger when lens is nearer to
the anterior focus of the eye and smaller
when away

Relative position of images
 In emmetropia: at the principal focus
 In myopia: nearer to the lens than its
principal focus
 In hypermetropia: farther away from the
principal focus

Factors affecting field of
view
 Patient’s pupil size
 Power of condensing lens
 Refractive error
 Distance the condensing lens held from
the patient’s eye

ADVANTAGES
 Wide range of view
 High contrast
 Stereoscopic view
 Variety of lens options
 Excellent depth of focus
 Lesser distortion image

DISADVANTAGES
 Inverted and inversed image
 Low magnification
 Dilation required
 Difficult to master

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