P. 140

An Urban Experience
OPHTHALMOSCOPY Detailed examination of speci c areas of fundus (e.g., optic nerve, chorioretinal scar, coloboma)
Can use handle to attach other heads (e.g.,
• 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 re ection from a distance of ~18-24 inches from the animal’s eye.
• Step 4: Continue to view the tapetal re ection and move to within 1-2 inches of the cornea 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 (remember** - 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 super cial 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, suf cient light is able to
be re ected. If the lens or cornea is normal, all that is visualized is a blurred image of the fundus because these structures normally re ect very little light.
• Viewing Apertures:
- Use large circular aperture when pupil is large and small circular aperture when pupil is small. It this author’s opinion, it is advisable to always dilate the small animal patient prior to funduscopic examination, regardless of the method being used.
- Slit aperture is useful for eliciting the Purkinje images or determining whether the optic nerve head is raised or
transilluminator or otoscopic) 1.
2. Inexpensive
3. Image greatly magni ed
4. Direct upright image 1.
through cloudy media
2. Small  eld of view (the image is often too magni ed)
3. Short working distance (closer to the animal’s head)
4. No stereopsis
5. Inability to examine peripheral retina
fundus 1. Examiners hands both free to manipulate patient’s head when wearing a headset
(FOCAL LIGHT SOURCE AND LENS) the ocular fundus
Examination of
(*recommended technique for the small animal practitioner*) 1. Inexpensive
2. Portable
3. Better visualization through translucent ocular media
4. Large  eld of view
5. Distance from patient’s head
2. Inverted/reversed image
1. No stereopsis
• Use this technique to achieve greater magni cation of
speci c areas of the fundus in small animals.
• Image viewed is upright, highly magni ed, with a small  eld of view, and there is no stereopsis.
• Extremely dif cult technique to use for general fundus screening and visualization is poor with opaci cation
of the ocular media as compared with indirect
Decreased penetration
Examination of the ocular
2. Better visualization through translucent ocular media
3. Large  eld of view
4. Stereopsis
5. Distance from patient’s head
2. Headset more expensive than direct ophthalmoscope MONOCULAR INDIRECT OPHTHALMOSCOPY
1. Inverted reversed

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