The phenol red thread tear test in large Psittaciformes

OBJECTIVE: To develop a standard method for measuring tear production in large Psittaciformes using the phenol red thread (PRT) tear test. To establish mean PRT tear test values in clinically normal pet birds and to assess the reproducibility of the test. ANIMALS: Two geographically distinct populations of healthy, large Psittaciformes (pilot study and study population). Species groups include: cockatoo (17), macaw (22), Amazon (10), African gray (1), eclectus (1) and pionus (1). PROCEDURE: The PRT was placed under the upper eyelid and both eyelids were held closed throughout the test. The PRT tear test was repeated after 2 months in the pilot study and after approximately 5 min in the study population. RESULTS: The mean PRT tear test values for the pilot study were OD=28.2 mm/15 s (+/- 6.3 mm), OS=24.1 mm/15 s (+/- 6.6 mm) and OD=25.4 mm/15 s (+/- 3.3 mm), OS=25.5 mm/15 s (+/- 5.2 mm), for the first and second visits respectively. The mean PRT tear test value for the study population was: OD=19.8 mm/15 s (+/- 4.3 mm), OS=20.1 (+/- 3.9 mm) and OD=20.0 mm/15 s (+/- 4.5 mm), OS=19.1 mm/15 s (+/- 3.3 mm), for the first and second tests respectively. There was poor repeatability between tests. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the PRT tear test is a practical method for measuring tear production in large Psittaciformes, although adaptations to the established diagnostic method are necessary to overcome some anatomical differences present in birds. Good reproducibility of the PRT tear test could not be demonstrated in a clinically normal population of birds but geographic location appears to significantly influence results.     

Schirmer tear test, phenol red thread tear test, eye blink frequency and corneal sensitivity in the guinea pig

OBJECTIVE: To establish reference values for Schirmer tear tests (STT) I and II, phenol red thread (PRT) tear test and eye blink frequency, and to determine corneal sensitivity for normal guinea pigs. ANIMALS STUDIED: One hundred and eight eyes of 54 adult Duncan-Hartley guinea pigs. PROCEDURE: Schirmer tear test (STT) I and then STT II were performed in 36 guinea pigs. PRT and STT I were compared in 18 adult Duncan-Hartley guinea pigs. Corneal sensitivity was determined in 23 guinea pigs by evaluating the corneal touch threshold (CTT) of five different regions using a Cochet-Bonnet esthesiometer. Eye blink frequency was measured in 10 guinea pigs over a period of 20 min and in 17 guinea pigs over a period of 10 min. RESULTS: Mean STT I was 0.36 mm +/- 1.09 mm (wetting/min) and mean STT II was 0.43 mm +/- 1.29 mm (wetting/min). There was no significant difference between mean STT I and mean STT II (P = 0.79). The mean PRT-value was 16 +/- 4.7 mm (wetting/15 s), and the mean STT I-value in the same guinea pigs was 0.6 +/- 1.83 mm (wetting/min). Corneal sensitivity was significantly higher in the center than in the four limbal regions. The mean CTT for central, ventral, nasal, temporal and dorsal regions was 2, 1.7, 1.7, 1.7 and 1.6 cm or 3.7, 5.2, 5.6, 5.7 and 6.4 g/mm(2), respectively. Eye blink frequency was between two to five (mean 3.4 +/- 1.04) blinks per eye over 20 min in guinea pigs in their home environment, while in handheld and restrained guinea pigs eye blink frequency showed a variation between 0 and 17 blinks per eye (mean 3.24 +/- 3.64 blinks per eye) over 10 min. CONCLUSIONS: As there were no significant differences between STT I and STT II results, reflex tear secretion in the guinea pig may not exist. The most likely explanation is a lower corneal sensitivity in the guinea pig than in other species, such as cats, dogs and horses. Because of the small amount of tears, PRT is the preferred test for tear measurement in the guinea pig.     

Measurement of phenol red thread tear test in Arabian and throughbred horses

Objective To determine physiologic levels of tear production in Arabian (AH) and throughbred horses (TH) by using phenol red thread test (PRT). Animals studied The study was performed on 16 AH and 14 TH, ranging from 2.5 to 24 years of age, housed in a stable situated in the Sanliurfa of Turkey. Procedures For the measurement of PRT, the strip was placed under the lower eyelid approximately one‐third the distance from the temporal to nasal canthus and left for 15 s. The length of the wet area was measured in mm and compared among breed, sex, and age groups and between eyes of both sides. Results The mean length of the wet area was in AH and TH were 30.22 ± 0.99 mm ranging from 16 to 41 and 31.00 ± 1.4 mm ranging from 14 to 47, respectively. There were no significant differences in tear production among breed, sex, or age groups. The values measured for left eyes were significantly higher than those for right eyes (P < 0.05). Conclusions Phenol red thread test measurement is easily used, with no pain, and a comfortable method. PRT can be used in equine ophthalmology on a routine basis to the measurement of tear production. These normal PRT values help diagnosis keratoconjunctivitis sicca in horses.     

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.     

Measurement of tear production in black‐tufted marmosets (Callithrix penicillata) using three different methods: modified Schirmer’s I,phenol red thread and standardized endodontic absorbent paper points

Objective: To report normal tear production of healthy adult black‐tufted marmosets and propose a novel alternative for the measurement of the aqueous portion of tear production in animals with small eyes. Animal studied: Black‐tufted marmosets (Callithrix penicillata). Procedures: Tear production of 19 animals was evaluated by the following methods: modified Schirmer’s I, phenol red thread and the novel use of standardized endodontic absorbent paper points. These methods and results were compared. Additionally, blink frequency and palpebral fissure length were measured. Results: Modified Schirmer’s test I, mean = ?0.46 ± 3.41 mm/min; Phenol red thread, mean = 13.27 ± 5.41 mm/15 s.; Standardized endodontic paper points, size 30, mean = 9.32 ± 3.09 mm/min; Mean palpebral fissure length = 7.83 ± 0.72 mm. Blink frequency, mean = 20.27 ± 5.92/5 min. Conclusions: Normal parameters for blink frequency, palpebral fissure length and tear production measurement are presented. The palpebral fissure of black‐tufted marmoset is very small and tear production is one of the lowest reported for all animal species. A novel and practical alternative for tear production measurement using standardized endodontic absorbent paper points is presented and is indicated for animals with small eyes.