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Fundus Examination: How to get a good look (ophthalmic exam – part 2)
Elizabeth A. Giuliano DVM, MS, DACVO
Associate Professor, University of Missouri
Columbia, MO, USA
OVERVIEW:
Examination of the Fundus is the most challenging aspect of the complete ophthalmic exam for
most practitioners. First, proper ophthalmoscopic techniques can be difficult to master. Second,
the normal anatomical relationships of the fundic structures are often not fully understood,
making interpretation difficult. Finally, the large variation in normal fundus appearance,
especially in the canine species, adds to the complexity of this important diagnostic tool. This
lectures aims to answer the following frequently asked questions and provide practical tips to
help ensure good ophthalmoscopic skills.
1. “What is Ophthalmoscopy?”
2. “What technique should I be using to get a good look at the posterior segment of my canine or
feline patient?”
 Provide an overview of techniques with indications, advantages, and disadvantages of
each method
3. “What am I looking at?”
 Building a fundus
4. “OK, I can get an image in focus, but what does it mean?”
 Is it normal or abnormal? If abnormal, is it an addition or a subtraction?
The fundus is composite picture formed by the 3 basic tunics of the vertebrate eye
(neurosensory, vascular, and fibrous) superimposed on one another.
As viewed
ophthalmoscopically, those components are the retina, choroid, and sclera. Normal fundic
findings can be highly variable and are influenced by the animal's species, breed, age, and coat
color. Ability to routinely and reliably evaluate the posterior segment of the eye is essential in
any patient with a visual disturbance or for which the differential diagnose includes systemic
infectious disease, vascular disorder, hypertension, or central nervous system disease. Indirect
ophthalmoscopy should be mastered by the veterinary practitioner and routinely employed for
posterior segment examination in the small animal patient. In this author’s opinion, proper
technique for direct ophthalmoscopy is more difficult than indirect technique. The high
magnification afforded by direct ophthalmoscopy often precludes accurate interpretation of the
disease process in question. Once the clinician has mastered the techniques necessary to
perform a good ophthalmoscopic exam, it is essential that the practitioner then become familiar
with the wide variation in normal fundus findings routinely seen between species, within species,
and from breed to breed.
EXAMINATION (follow these steps prior to performing direct or indirect
ophthalmoscopy):
 Ophthalmoscopy is part of the complete ophthalmic examination and should be
performed after the minimum ophthalmic data base has been acquired (see Lecture
#SA263).
 In the initial stages of the complete ophthalmic exam, retroilluminate the patient. With the
patient at eye level and using a Finoff transilluminator (or a direct ophthalmoscope set at
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0 diopters) at arm's distance, establish both tapetal reflexes. Look for anisocoria
(unequally sized pupils) and any opacities present in the ocular media (e.g., cataract).
Pupillary dilation is essential for ophthalmoscopy. First, make certain the animal does not
have glaucoma. Then, dilate the pupils with 1-2 drops of tropicamide (Mydriacyl®).
Complete pupillary dilation will occur in 10-15 minutes and will last 8-12 hours in the dog.
Perform your examination in a darkened room.
COMPARISON OF OPHTHALMOSCOPIC TECHNIQUES:
OPHTHALMOSCOPIC
TECHNIQUE
DIRECT
OPHTHALMOSCOPY
INDICATIONS
ADVANTAGES
Detailed examination
of specific areas of
fundus (e.g., optic
nerve, chorioretinal
scar, coloboma)
Can use handle to
attach other heads
(e.g., transilluminator
or otoscopic)
Examination of the
ocular fundus
1. Portability
2. Inexpensive
3. Image greatly
magnified
4. Direct upright image
BINOCULAR
INDIRECT
OPHTHALMOSCOPY
MONOCULAR
INDIRECT
OPHTHALMOSCOPY
(FOCAL LIGHT
SOURCE AND LENS)
Examination of the
ocular fundus
(*recommended
technique for the small
animal practitioner*)
1. Examiners hands
both free to
manipulate patient’s
head
2. Better visualization
through translucent
ocular media
3. Large field of view
4. Stereopsis
5. Distance from
patient’s head
1. Inexpensive
2. Portable
3. Better visualization
through translucent
ocular media
4. Large field of view
5. Distance from
patient's head
DISADVANTAGES
1. Decreased penetration
through cloudy media
2. Small field of view
3. Short working distance
(closer to the animal's
head)
4. No stereopsis
5. Inability to examine
peripheral retina
1. Inverted reversed image
2. Headset more expensive
than direct
ophthalmoscope
1. No stereopsis
2. Inverted/reversed image
DIRECT OPHTHALMOSCOPY
 Use this technique to achieve greater magnification of specific areas of the fundus in small
animals.
 Image viewed is upright, highly magnified, with a small field of view, and there is no
stereopsis.
 Extremely difficult technique to use for general fundus screening and visualization is poor
with opacification of the ocular media as compared with indirect ophthalmoscopy.
 Step 1: Turn the ophthalmoscope on; adjust the rheostat to the desired light intensity.
 Step 2: Darken the room.
 Step 3: With the instrument set to 0 diopters, hold it your brow, and view the tapetal
reflection from a distance of ~18-24 inches from the animal's eye.
 Step 4: Continue to view the tapetal reflection and move to within 1-2 inches of the cornea
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of one of the animal's eyes. Providing the lens and cornea are normal, the patient’s fundus
should be coming into focus. The dioptric settings may be adjusted slightly so that the
fundus comes into clear focus for the examiner (if the examiner normally wears corrective
eyewear and removes his/her glasses to perform direct ophthalmoscopy, his/her own
refractive error will need to be adjusted for).
Attempt to systematically view the fundus. Find a blood vessel and follow it to the optic
nerve. Using the optic nerve as a “reference point”, scan the fundus for abnormalities of
color, clarity, size, and shape. Change the diopter settings to focus in and out of raised
or depressed areas.
It is often helpful to view the animal's left eye with your left eye and the animal's right eye
with your right eye.
Other: On most ophthalmoscopes, the red diopter numbers are “negative” (representing
the power of diverging lenses). Higher red numbers push the focus point deeper into the
eye. The black (or green in some models) numbers (representing the power of
converging lenses) are “positive” and bring the focus point more superficial in the eye,
enabling visualization of nearer objects.
More positive dioptric settings may be "dialed-in" so that opacities in more anterior
structures become visible. In general, the posterior lens is in focus at +8D, the anterior
lens at +12D, and the cornea at +20D. The lens or cornea will only be visualized using
direct ophthalmoscopy if an opacity is present in those structures and thus, sufficient light
is able to be reflected. If the lens or cornea is normal, all that is visualized is a blurred
image of the fundus because these structures normally reflect very little light.
Viewing Apertures:
Use large circular aperture when pupil is large and small circular aperture when pupil is
small.
Slit aperture is useful for eliciting the Purkinje images or determining whether the optic
nerve head is raised or depressed.
Grid aperture can be used to directly measure the size of lesions or to relate the size of
a lesion to that of the optic nerve.
Green light is red-free and permits differentiation of melanin pigment from blood. With
red-free light, blood looks black and pigment still looks brown.
Blue light filter excites fluorescein dye.
INDIRECT OPHTHALMOSCOPY
 This technique can be performed using a hand-held lens and a bright focal light source
(monocular indirect ophthalmoscopy), or for those with a stronger interest in
ophthalmology, an indirect headset can be purchased and will provide stereopsis
(binocular indirect ophthalmoscopy).
 Indirect ophthalmoscopy is recommended to the small animal practitioner as the
PREFERRED METHOD to visualize the fundus of the small animal patient. The image
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is significantly less magnified than that seen with direct ophthalmoscopy, has a much
larger field of view, and is better for routine screening of the eye.
Indirect ophthalmoscopy provides the examiner with an inverted, reversed image.
Monocular indirect ophthalmoscopy is inexpensive and required equipment consists only
of a bright focal light source and a 28 or 20 diopter lens. It is performed as follows:
Step 1: Begin at arms length from the patient. An assistant is required to restrain the
patient and to help hold the eyelids open.
Step 2: Darken the exam room.
Step 3: With a focal light source such as a transilluminator or penlight held close to your
lateral canthus of your dominant eye or at your cheek and standing at arms length from
the patient, visualize the tapetal reflection (you will see a red reflex in animals with poorly
developed or no tapetum).
Step 4: Hold a 20- or 28-diopter condensing lens in your other hand between the thumb
and index finger, and use your ring finger and pinky to elevate the upper lid. Initially, hold
the lens to one side of the eye until the tapetal reflection is established, and then rotate
the lens such that the eye can be observed through it. Initially, hold your lens close to
the corneal surface (about 1/2 inch from the eye) and then slowly pull the lens towards
you until the image of the fundus fills the lens (usually about 1-2 inches away from the
animal's eye, depending on the diopter power of the condensing lens you are
using). When the image is lost (usually because you or the animal moved), immediately
rotate the lens away from the patient’s eye (the left ring finger and pinky continue to hold
up the upper lid), re-establish the tapetal reflex, and again, rotate the lens back into place
in front of the eye so the fundus comes into view. The fundus should appear as a virtual
image in front of the lens. (Hint: look at the image which is in front of the lens and not at
the lens or the eye).
Step 5: Maintain alignment with your light source, lens, and patient’s eye and then move
yourself up, down, left, or right to examine all quadrants of the patient’s fundus. (Hint:
remember that the image is inverted, so you must move in the opposite direction to the
image). If the image is lost, move the lens out of the light beam and start again.
Indirect ophthalmoscopy is relatively easy to master providing you PRACTICE OFTEN!
Various lenses are commercially available for in indirect ophthalmology and will provide
varying magnification and field of view. The less the magnification, the greater the field
of view.
INTERPRETATION OF FINDINGS
When viewing the fundus, be systematic: ASSESS:
1. Reflectivity (Uniformly or focally increased? Uniformly or focally decreased?)
2. Vascularity (Attenuated? Engorged? Tortuous? Out of focus due to elevation or
depression?)
3. Optic nerve (Color? Degree of myelination? Raised? Depressed?)
4. Pigmentation of tapetal versus nontapetal areas
Ask yourself: Normal versus Abnormal? If Abnormal  is it due to an addition or subtraction?
References available upon request