Objective—To quantitatively and qualitatively compare electroretinography (ERG) recordings in awake, sedated, and anesthetized dogs.
Animals—Six 6-month-old Beagles.
Procedures—A brief ERG protocol for dogs was used. Following 1-minute and subsequent 5-minute dark adaptation, mixed rod-cone responses were recorded bilaterally with a handheld multispecies ERG device with dogs in each of 3 states of consciousness: awake, sedated (dexmedetomidine and butorphanol), and anesthetized (atropine and hydromorphone, followed by propofol and midazolam and anesthetic maintenance with isoflurane). Low- and high-frequency noise levels were quantified via Fourier analysis, and the effect of consciousness state on signal amplitude, implicit time, and noise was analyzed via repeated-measures ANOVA. In addition, 13 veterinary ophthalmologists who were unaware of the dogs’ consciousness states subjectively graded the ERG recording quality, and scores for each tracing were compared.
Results—ERG amplitudes were highest in awake dogs and lowest in anesthetized dogs. Implicit times were shortest in awake dogs and longest in anesthetized dogs. Differences in b-wave amplitudes and a-wave implicit times were significant. Neither low- nor high-frequency noise levels differed significantly among consciousness states. Furthermore, no significant differences were identified among observers’ scores assigned to ERG tracings.
Conclusions and Clinical Relevance—Anesthesia and sedation resulted in significant attenuation and delay of ERG responses in dogs. Chemical restraint of dogs had no consistently significant effect on low- or high-frequency noise levels or on observer perception of signal quality.
Objective—To compare aesthesiometer-determined
corneal sensitivity between diabetic and nondiabetic
dogs and to investigate the correlation between
corneal sensitivity and duration of diabetes or status
of glycemic control, as estimated by use of glycated
blood protein concentrations.
Animals—23 diabetic and 29 nondiabetic normoglycemic
Procedure—A Cochet-Bonnet aesthesiometer was
used to measure corneal touch threshold (CTT) in 5
corneal regions of each dog. At the time of ocular
examination, duration of diabetes mellitus was estimated
from the history, and blood was drawn for
assessment of blood glycosylated hemoglobin and
serum fructosamine concentrations.
Results—Median CTT for central, nasal, dorsal, temporal,
and ventral corneal regions in nondiabetic dogs
(1.6, 2.3, 2.8, 2.8, and 5.1 g/mm2, respectively) was
significantly lower than in diabetic dogs (2.8, 4.0, 5.1,
5.1, and 6.6 g/mm2, respectively). Median regional
CTT in diabetic dogs was not significantly correlated
with estimated duration of diabetes mellitus or blood
glycated protein concentrations. No significant difference
was found in regional CTT between eyes of normoglycemic
dogs with unilateral cataracts.
Conclusion and Clinical Relevance—Diabetic dogs
have significantly reduced corneal sensitivity in all
regions, compared with nondiabetic normoglycemic
dogs. Regional variation in corneal sensitivity is similar
in diabetic and normoglycemic dogs. Neither
glycemic control nor duration of diabetes, as estimated,
is significantly correlated with corneal hyposensitivity.
Corneal nerve dysfunction may be associated
with recurrent or nonhealing ulcers in diabetic dogs
for which no other underlying cause can be found.
(Am J Vet Res 2003;64:7–11)