Maria Teresa Peña

A comparative study of corneal sensitivity in birds of prey

OBJECTIVE To determine and compare the corneal sensitivity in healthy wild diurnal and nocturnal birds of prey (BP) indigenous to Catalonia (Spain), and to establish if age is a determining factor in corneal sensitivity in those species. METHODS Ophthalmic examination was performed in 105 BP. Only birds with no ocular abnormalities were included in the study (n = 81): 21 diurnal BP (Falco tinnunculus: 16 fledglings, 5 adults) and 60 nocturnal BP (20 Athene noctua [9 fledglings, 11 adults], 20 Strix aluco [15 fledglings, 5 adults], and 20 Otus scops [6 fledglings and 14 adults]). Corneal touch threshold (CTT) was determined for each eye in five different corneal regions. Five attempts to cause a blink reflex were made in each region, and when three or more reflexes were positive, the pressure was deemed the CTT. Statistical analysis was performed using a Students t-test for independent data or an anova model. The results between species and age groups were compared using the Generalized Estimated Equations model. RESULTS There were no significant differences between any of the corneal regions (P = 0.25), or between the right (CTT = 4.9 ± 1.7 cm) and left (CTT = 4.8 ± 1.7 cm) eye in any of the species (P = 0.692). No difference was found between diurnal and nocturnal species (P = 0.913). Considering all the species, a significant difference was found between the mean CTT of fledglings (5.4 ± 1.2 cm) and adults (4.1 ± 2 cm), P < 0.001. A significant difference was found between fledglings and adults of A. noctua (P < 0.001) and S. aluco (P = 0.002). CONCLUSIONS There is no significant difference in CTT between the different corneal regions in all the species studied. Corneal sensitivity is similar between diurnal and nocturnal birds of prey. Age is a determining factor in the CTT of A. noctua and S. aluco, with fledglings having a significantly higher CTT.

Cryopreservation (-20 °C) of feline corneoscleral tissue: histologic, microbiologic, and ultrastructural study.

OBJECTIVE To evaluate microbiological, histologic, and ultrastructural characteristics of short-term cryopreserved (STC) feline corneoscleral tissue (<1 year) and to compare it with long-term cryopreserved (LTC) tissue (>7 years). ANIMALS STUDIED Twenty healthy feline globes were obtained from 2003 to 2013. PROCEDURE After a decontamination protocol, globes were enucleated and stored at -20 °C in broad-spectrum antibiotics. Corneoscleral tissue was evaluated at different storage periods: <1 year (10 eyes) and >7 years (8 eyes). Two eyes were used as controls. Microbiologic study included direct (blood, McConkey, and Sabouraud agars) and enrichment (brain-heart infusion broth) cultures. Cryopreservation artifacts were evaluated by hematoxylin-eosin. Corneoscleral collagen organization and number of normal and dead keratocytes were established by transmission electron microscopy. RESULTS Although microbiologic cultures were positive only in STC [direct (20.8%); enrichment (37.5%)], significant differences between periods were only found in enrichment cultures (P = 0.006). Cryopreservation artifacts were most commonly observed in LTC tissues (P < 0.001). Normal keratocytes were predominant in STC corneas (STC 58.3%, LTC 12.5%) and apoptotic ones in LTC (STC 41.7%, LTC 75%), whereas necrotic keratocytes were only seen in LTC (LTC 12.5%) (P = 0.046). No structural differences were detected in collagen organization between STC and LTC (Pcornea = 0.147; Psclera = 0.362). CONCLUSIONS Cryopreservation of feline corneoscleral tissue seems to reduce bacterial contamination over time. Apoptosis is the main cause of death of cryopreserved feline keratocytes. Based on the lack of significant structural differences between STC and LTC samples, these cryopreserved tissues could potentially be used for tectonic support for at least 10 years without structural or microbiological impediment.

Evaluation of corneal anaesthesia after the application of topical 2 per cent lidocaine, 0.5 per cent bupivacaine and 1 per cent ropivacaine in dogs

The objective of this study was to describe and compare the efficacy and duration of topical anaesthesia induced by 2 per cent lidocaine (L), 0.5 per cent bupivacaine (B) and 1 per cent ropivacaine (R) in the dog using 24 clinically healthy beagles with normal ocular examination. Dogs were randomly divided into three groups: 2 per cent lidocaine (n=8), 0.5 per cent bupivacaine (n=8) and 1 per cent ropivacaine (n=8). The baseline corneal touch threshold (CTT) was measured using a Cochet-Bonnet aesthesiometer. Following baseline CTT measurement, a single drop of the assigned anaesthetic was applied to each eye and the CTT was measured bilaterally within one minute after administration and every five minutes until the basal CTT value was restored. Data were analysed with non-parametric analysis of variance models and Dunnets test for post hoc analysis. One per cent ropivacaine was the most effective drug (LCTTmax=3 cm, BCTTmax=2 cm, RCTTmax=0 cm; P<0.001), and had the shortest latency (LLatency=5 minutes, BLatency=5 minutes, RLatency=1 minute; P<0.001) and the smallest AUC (LAUC=80 cm×minute, BAUC=68.25 cm×minute, RAUC=36.88 cm×minute; P<0.001). There was no statistical difference in the duration of corneal anaesthesia between the groups (P=0.09) and all topical anaesthetics tested reduced corneal sensitivity, although 1 per cent ropivacaine had the maximal and quickest anaesthetic effect. This drug could be used for specific diagnostic procedures where quick and short, but effective, corneal anaesthesia is needed.

ASSESSMENT OF INTRAOCULAR PRESSURE BY APPLANATION AND REBOUND TONOMETRY IN GUINEA PIGS OF DIFFERENT AGES

Abstract Fifty‐two guinea pigs (Cavia porcellus) with normal ophthalmic examinations were included in this study to determine whether there are differences in the intraocular pressure (IOP) according to age, while assessing the clinical usefulness of 2 different tonometry methods for this species. The animals were divided into 2 groups according to age: young (4 weeks old, 29 animals) and adult (3 to 36 months, 23 animals). Tonometry was performed oculus utro (OU) in the central cornea according to the manufacturer’s recommendations. Only measurements with low standard deviation (SD < 5%) were included. Rebound tonometry was performed first OU; following topical anesthesia, applanation tonometry was then performed OU. The time required to obtain an IOP value was recorded for each eye. Descriptive statistics were calculated and Lin Concordance Coefficient (LCC) was performed to describe concordance between methods. Mean TonoVet IOP readings were 8.53 ± 1.28 mmHg and 13.20 ± 1.28 mmHg for young and adult animals, respectively (p < 0.05). Tono‐Pen VET readings could not be obtained in young animals, but yielded a mean of 10.93 ± 3.61 mmHg in adults. No differences were found between the left and right eyes (p > 0.05) nor between sexes (p > 0.05). TonoVet readings were obtained faster than Tono‐Pen VET readings (less than 1 min vs 3.38 ± 1.27 min, respectively [p < 0.05]). Lin Concordance Coefficient between methods was 0.37 (95% CI: 0.19 to 0.53), documenting a poor concordance between the 2 methods. This study found that normal IOP values are lower in young animals compared with adult animals. Moreover, the results obtained from this investigation demonstrated that TonoVet tonometry is a rapid and well‐tolerated procedure when performed on guinea pigs of any age, whereas Tono‐Pen VET tonometry is a more time‐consuming technique that can only be used on guinea pigs older than 3 months.