Reference values for selected ophthalmic diagnostic tests and clinical characteristics of chinchilla eyes (Chinchilla lanigera)

Objective To establish reference values for the Schirmer tear test I (STT I), the phenol red thread tear test (PRTT), the intraocular pressure (IOP) with rebound tonometry, to determine the corneal sensitivity for healthy chinchillas, and to describe clinical aspects of normal chinchilla eyes. Animals One hundred and twenty‐two eyes of 61 healthy pet chinchillas of different age and gender were investigated. Procedures A full ophthalmic exam including slit lamp biomicroscopy, ophthalmoscopy, measurement of STT I, PRTT, determination of the corneal touch threshold (CTT), and the measurement of the IOP (TonoVet®) was performed. The normal appearance of the lid, the iris, the lens, the fundus, and the optic nerve disc was evaluated. Results The results of the STT I were very low and not reliable, and the measurement was discontinued. The median value of PRTT was 14.0 mm wetting/15 s (mean 14.6 ± 3.5 mm wetting/15 s). The median CTT was 32.5 mm (mean 31.2 ± 7.0 mm) respectively 1.2 g/mm² (mean 1.5 ± 0.9 g/mm²). The median IOP was 3.0 mmHg (mean 2.9 ± 1.8 mmHg). The predominating iris color was brown. The fundus pigmentation varied. Few lens alteration were seen in otherwise healthy chinchilla eyes. Most chinchillas had myelinated discs. Optic nerve cupping was present in 62% of the animals. Conclusion Because of the small amount of tears, the PRT test is recommended for tear measurements in chinchillas. The IOP in chinchillas seems to be quiet is low in comparison to other rodents.     

Correlation between corneal sensitivity and quantity of reflex tearing in cows,horses, goats,sheep, dogs,cats, rabbits,and guinea pigs

Objective Guinea pigs have a very low threshold of corneal sensitivity and at the same time nearly no reflex tearing compared to dogs, cats, and horses. The question arose whether there is a general correlation between corneal sensitivity and the quantity of reflex tearing. Animals studied Totally 160 animals of 8 different species (20 animals per species) were investigated. Procedures The corneal touch threshold (CTT) was measured with a Cochet–Bonnet esthesiometer. The palpebral fissure length (PFL) was measured with a calliper ruler. The Schirmer tear test (STT) was modified by adapting the width of the STT strip to the PFL of every species. For the STT II, 0.4% oxybuprocaine was applied. Results Corneal touch threshold: Cows (1.67 g/mm²), horses (1.23 g/mm²), sheep (1.13 g/mm²), goats (1.44 g/mm²), dogs (2.16 g/mm²), and cats (1.33 g/mm²) show similar CTT values. In contrast, rabbits (6.21 g/mm²) and guinea pigs (7.75 g/mm²) show a significantly lower CTT. Tear Production Difference STT I ? STT II: Rabbits have the greatest decline in tear production with 38.4%, followed by sheep (33.3%), dogs (31.1%), cats (24.7%), cows (23.7%), horses (18.0%), and goats (14.0%). Guinea pigs have no decline, but a slight increase of ?16.0%. Correlation CTT and STT II ? STT I Difference: Pearson’s correlation coefficient shows a small, but significant correlation. The coefficient of determination can only forecast a value with 7.1% certainty. Conclusions The high variance and low reproducibility of results suggest that the measuring devices are inappropriate to assess the evaluated parameters. Therefore, no assured correlation between the corneal sensitivity and the quantity of reflex tearing could be found.     

Tear production in canine neonates – evaluation using a modified Schirmer tear test

Purpose The ability of human newborns to produce tears has been a subject of controversy in the literature since the mid‐20th century, and there has been considerable debate as to whether they are able to produce tears. Recently, it was established that total tear secretion (reflex + basal) in full‐term infants is similar to those of adults whereas both reflex and basal tear production is reduced in premature babies. The objectives of this study were to assess whether newborn dogs have measurable aqueous tear production at the fourth week of life and to evaluate a modified Schirmer tear test (mSTT) as a useful method for measuring neonatal tear production in dogs. Methods Thirty four‐week‐old healthy puppies from six litters were evaluated. A control group was composed of 10 normal adult dogs. The mSTT strips were obtained by cutting a 5 mm‐wide strip in half (making two 2.5 mm‐wide strips). The mSTT1 was performed in puppies and adult dogs. Values were compared using t‐tests. Results In neonates, the average value for the mSTT1 was 13.6 ± 3.07 (range = 7–19 mm/min), which was significantly lower in neonates than in adult dogs (23.25 ± 3.5, range = 17–30 mm/min, P < 0.0001). Conclusions Canine neonates do produce tears by the fourth week of life, which can be successfully measured with the mSTT. This report established for the first time that canine neonates have significantly reduced total (reflex + basal) tear secretion compared to adults.     

Schirmer Tear Test in Clinically Normal Asian Elephants

Veterinary Research Communications -     

Daytime profile of the intraocular pressure and tear production in normal dog

Objective  To evaluate the circadian rhythms of intraocular pressure (IOP) and tear production in dog exposed to a natural photoperiod.
Animals studied  We used 12 clinically healthy Beagles dog housed under natural photoperiod at indoor temperature and humidity.
Procedure  Intraocular pressure and Schirmer tear test (STT) I were measured every 4 h over a 48-h period in both eyes in each animal. Statistical analysis of the data was performed by one-way repeated-measures anova , Student's t -test, and single cosinor method.
Results  On each day, there was a highly significant effect of time on both parameters. A statistically significant difference of STT I values was observed comparing left and right eyes ( P  < 0.0001). Robust daily rhythms were observed for both parameters, IOP values showed diurnal acrophase (left eye: 09:33 ± 00:50 h; right eye: 09:25 ± 00:22 h), while STT I values showed nocturnal acrophase (left eye: 20:27 ± 00:46 h; right eye: 20:00 ± 00:05 h).
Conclusion  This study has demonstrated circadian rhythms in both IOP and STT I.     

Effect of topical 1% tropicamide on Schirmer tear test results in clinically normal horses

Objective  To observe the effect of topical 1% tropicamide on equine tear production as measured by Schirmer I tear test.
Materials and methods  Fourteen adult horses received one drop of 1% tropicamide ophthalmic solution in one eye and the opposite eye served as the control. The tear production in both eyes was tested at 1, 2, 4, 6, and 24 h after 1% tropicamide administration.
Results  Measurements made 1 h after treatment revealed a significant reduction in Schirmer tear test values in tropicamide treated eyes ( P  = 0.002). The observed decrease in tear production was maintained up to 4 h after treatment ( P  = 0.002). Although tropicamide-induced decrease in STT values was observed in the treated eyes, the contralateral eyes did not show significant changes in Schirmer tear test results.
Conclusion  Single dose of topical 1% tropicamide resulted in statistically significant reduction in Schirmer tear test values in clinically normal horses.     

Reference values for selected ophthalmic diagnostic tests of the ferret (Mustela putorius furo)

PURPOSE: To perform selected ophthalmic diagnostic tests in healthy ferrets with the aim of establishing normal physiological reference values for this species. METHOD: A total of 15 healthy, unrelated ferrets were used to test most of the parameters in this investigation. Eight of the 15 ferrets were used for central corneal thickness evaluation. Ages varied from 1.5 to 6 years of age. Selected diagnostic ocular tests were performed including Schirmer tear test, tonometry using an applanation tonometer (Tonopen), central corneal thickness using an ultrasonic pachymeter (Sonomed, Micropach, Model 200P +) and culture of the normal conjunctival bacterial flora. RESULTS AND DISCUSSION: Staphylococcus sp. and Corynebacterium sp. were isolated from healthy conjunctival and eyelid margins, suggesting they are normal constituents of the conjunctival flora of the ferret. Results for selected ocular diagnostic tests investigated here for the ferret eye were as follows: intraocular pressure: 14.50 +/- 3.27 mmHg; Schirmer tear test: 5.31 +/- 1.32 mm/min; central corneal thickness: 0.337 +/- 0.020 mm. No statistically significant differences between ages or genders were found for any of the results. The reference data for the ocular tests obtained in this investigation will help veterinary ophthalmologists to more accurately diagnose ocular diseases in the ferret. Knowledge of these reference values will be particularly useful to diagnose discrete or unusual pathological changes of the ferret eye.     

Effect of lacrimal punctal occlusion on tear production and tear fluorescein dilution in normal dogs

OBJECTIVE: To evaluate effects of lacrimal punctal plugs positioned in either the upper, lower, or combination of upper and lower lacrimal canaliculi on plug retention and tolerance; tear production, as measured by the Schirmer tear test; and the dilution of fluorescein within the tear film in normal dogs. MATERIAL AND METHODS: Lacrimal punctal plugs were positioned in the lower, upper, or combination of lower and upper plugs in six laboratory-quality Beagles under topical anesthesia. Retention of plugs was evaluated daily from 8 to 23 days by visual inspection and slit-lamp biomicroscopy. Schirmer tear tests (STT 1 without topical anesthesia) were performed at 48-h intervals. Dilution of fluorescein was determined at 5- and 45-min post-fluorescein instillations once weekly. RESULTS: Lacrimal punctal plugs of 0.4 and 0.6 mm in diameter were retained for 14 (lower plugs: 100%) and 23 days (75%), and for the upper plugs at 8 days less often (75%), and were infrequently locally nonirritating. Combination of lower and upper plugs seemed to adversely affect retention of either plug. When loss of the plugs occurred, a next larger size plug was necessary suggesting some stretching of the lacrimal canaliculi occurred. Pre- and postplug placement STT results indicated no change with lower and combination lacrimal punctal plugs, but decreased levels following upper lacrimal punctal plugs. Tear fluorescein levels at 5 and 45 min in control eye (no punctum plugs) were 3.39% and 0.14%, respectively. With lower, upper, and the combination of lower and upper lacrimal puncta plugs, tear fluorescein levels at 45 min were higher than the controls (lower: 0.76%; upper: 0.45%, and combination 0.56%). CONCLUSION: Lacrimal punctal silicone plugs are retained for 8-23 days in the lower, upper, and combined lower and upper canaliculi at high rates. Effects on STT levels appear limited. Fluorescein within the tear film persists longer with all different positioned lacrimal punctum plugs than in the control eyes.