Assessment of Intraocular Pressure by Applanation and Rebound Tonometry in Guinea Pigs of Different Ages

© 2018 Elsevier Inc. 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.