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Application of Optical Coherence
Tomography for examination
of the posterior segment of the eye
in the Beagle dog
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Jérémy Silvano, Caroline Dauzat, Anne-Sandrine Augsburger
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Application of Optical Coherence Tomography for examination of the posterior segment
of the eye in the Beagle dog
Jérémy Silvano 1, Caroline Dauzat 1, Anne-Sandrine Augsburger 2 and Roy Forster 1
1. CiToxLAB France, Evreux, France
2. DMV Clinique Vétérinaire, Bois Guillaume, France
Photo 1
Introduction
Optical coherence tomography (OCT) is a non
invasive, noncontact imaging technique capable of
producing high-resolution images of the retina and
optic nerve. These images provide information that
is useful for investigation of the posterior segment
of the eye. Increasingly detailed images can now
be obtained in humans and live animals.
Adapting the instruments initially designed for use in
human patients requires a unique set of adjustments
for each species. The eyes must be positioned and
prepared, and the ocular globe must be immobilized
with specific clips which allow the papilla to be
placed in front of the imaging device. Appropriate
general anesthesia, eye positioning and pupil dilatation were selected to obtain good
quality scans, free from artefacts. Moistening agents appropriate for repeated use and
prolonged transparency of the anatomic structures were also selected.
Method
tatoo
eye
1889649
Left
Right
2237726
Figure 1a
Animal 18899649
Left
Right
2308828
Left
Right
2134617
Six healthy beagle dogs (4 males and 2 females; 2 to 4 years old) were used in this work,
which was performed in accordance with the ARVO Statement for Use of Animals in
Ophthalmic and Vision Research and reviewed by CiToxLAB France ethical committee.
The dogs were anesthetized using an i.v. injection of 45 to 65 µg/kg of Domitor®
(Medetomidine), followed by topical instillation Tetracaïne 1%, a local anesthetic. The
pupils were dilated with a topical administration of Mydriatium 0.5%® (Tropicamide).The
animals were placed in sternal recumbency and the head was maintained horizontally in
order to manage eye movements and facilitate the spatial location and recognition of
eye structures in the slit lamp biomicroscope. An eyelid speculum was used to keep the
eyes wide open and the cornea was kept moistened by instillation, every 3-4 minutes,
of a sterile isotonic buffered solution (Dacryoserum®). Sclera-corneal clips were used
to prevent unexpected eye movements (neuromuscular paralysis was not used) and to
precisely move the eye globe. Ocrygel® (Carbopol) was administered after the end of
the procedure. Two High Definition screens (1920x1080 pixels) were used, one for the
Left
Right
2003189
Left
Right
2009979
Left
Right
measure 1
measure 2
measure 3
Mean
SD
image 1
204
186
189
193
9,6
image 2
199
205
194
199
5,5
7,2
image 1
194
206
193
198
image 2
200
201
198
200
1,5
image 1
165
162
150
159
7,9
image 2
169
170
178
172
4,9
image 1
212
202
208
207
5,0
image 2
201
207
194
201
6,5
image 1
183
177
189
183
6,0
image 2
185
183
181
183
2,0
image 1
191
189
192
191
1,5
image 2
198
202
203
201
2,6
image 1
207
210
204
207
3,0
image 2
180
184
179
181
2,6
image 1
191
195
198
195
3,5
image 2
192
201
201
198
5,2
image 1
194
191
192
192
1,5
image 2
196
183
185
188
7,0
image 1
183
184
177
181
3,8
image 2
194
181
172
182
11,1
image 1
177
169
175
174
4,2
image 2
169
166
177
171
5,7
image 1
190
187
180
186
5,1
image 2
215
213
223
217
5,3
Figure 1b
Left eye
Animal 18899649
Figure 1c
Animal 18899649
Table 1: Individual and mean results of retinal thickness measurement (µm)
Figure 4
Animal 18899649
Most of the images were obtained with x6 magnification, grid pattern, and medium to
low light intensity (due to the tapetum lucidum, a specific choroidal structure found in
cats and dogs, which reflects light). At least 5 photographs of both eyes were taken
and 2 images/eye/animal were retained (Figures 1a to 1d). Three retinal thickness
measurements were performed per image, using IMAGEnet i-base software. In order
to avoid bias in the retinal thickness measurements, these measurements were made
in areas without apparent vessels, with significant contrast, good morphology and
perpendicularly to the nerve fiber layer and choroid (Figure 2). Data from all animals
were pooled.
Results
Visual inspection of the OCT images and comparison of the morphological structures
with routine histological images with healthy beagle dogs allowed us to confirm good
condition of the retina of the animals (Figures 3 and 4). We generated 72 reference retinal
thickness measurements in the 6 dogs. These values gave an average retinal thickness
of 190 microns, with mean standard deviation (SD) of 14 microns (Table 1).
This variability indicates differences in retinal thickness depending on location and
image quality. We obtained a mean intra-animal SD of 4.9 µm, thus indicating good
reproducibility of the marker positioning per animal.
Conclusion
OCT is a powerful tool for non invasive imaging. This experimental work allowed us
to validate appropriate anesthesia, eye positioning and machine settings for use with
this technique. The retinal thickness value obtained is consistent with our reference
histological images, thus demonstrating that OCT can be used successfully for retinal
thickness measurement in beagle dogs. This approach could be a valuable technique in
toxicological studies where ocular toxicity is found.
Figure 3
Left eye
Figure 2: Screenshot
Figure 1d
Right eye
ophthalmologist and one for the handler. A Topcon OCT, SL SCAN-1 (slit lamp SL-D7
biomicroscope equipped with a DV-3 camera, S/N: 700101, Photo 1) enabled capture
and high resolution recording of cross sectional images of the retinal layers.
Right eye
A: Whole Retinal Thickness
NFL: Nerve Fiber Layer
IPL: Inner Plexiform Layer
INL: Inner Nuclear Layer
OPL: Outer Plexiform Layer
ONL: Outer Nuclear Layer
IS: Inner Segments
OS: Outer Segments
RPE: Retinal Pigment Epithelium
Choroid
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