Evaluation of the Phenol Red Thread Tear Test in Falconiformes

Abstract

Falconiformes are active searchers and hunters that require visual precision to catch their prey and survive in the wild. Despite this, ocular disease is likely to be underdiagnosed in these species, at least in part because of limited proven diagnostic methods and lack of published scientific data. Tear film deficiency is recognized as an important ocular surface disease in dogs but has not been well evaluated in birds. To evaluate the phenol red thread (PRT) tear test as an alternative method to the Schirmer tear test (STT) for determining tear production in Falconiformes, we assessed the PRT tear test twice for each eye in 21 birds from the genus Falco. The mean PRT test values for the right (OD) and left (OS) eyes were OD=30.2±4.6 mm/15 s and OS=29.1±3.7 mm/15 s, with an overall PRT test value for both eyes (OU) of 30.6±4.2 mm/15 s. Good reproducibility was seen with the PRT test as shown by the strong positive correlation between the first and second tests in the birds. The PRT test method provides repeatable results that are easy to obtain, easy to read, and achieved under the same conditions as the STT.

Reference values for selected ophthalmic tests of the blue-and-yellow macaw (Ara ararauna)

“…In a colony of screech owls (Megascops asio), low STT values have been described and correlated with a small or even absent orbital lacrimal gland (Harris et al 2008). Therefore, to establish a standard test for lacrimal assessment in birds can be difficult due to large anatomical and physiological differences in the tear production apparatus and lacrimal drainage between species (Smith et al 2015).…”

“…Despite that macaws tolerated tonometry without chemical restraint, factors such as excessive vocalization, stress from physical restraint and the very restless temperament of A. ararauna (Smith et al 2015) prompted us to use inhalation anesthesia (as previously described), which allowed us to also assess the direct influence of anesthesia on IOP. Inhaled anesthetics are described as drugs of choice for birds, given their safety and fast anesthetic induction and recovery, and of these, isoflurane has been the most used (Nicolau et al 2002, Lichtenberger & Ko 2007.…”

“…Although the ophthalmic examination used in birds is the same as for other animal species, ocular disease is likely to be underdiagnosed in some species, at least in part because of limited proven diagnostic methods and lack of published scientific data (Smith et al 2015). Tear production and IOP measurements should be routine in the ocular examination (Williams 2012).…”

A novel strip meniscometry method for measuring aqueous tear volume in dogs: Clinical correlations with the Schirmer tear and phenol red thread tests

“…The Schirmer tear test (STT) has long been the gold standard used to quantify the aqueous component of the tear film . The phenol red thread test (PRT) also quantifies the aqueous tear film and entails a shorter testing time (15 seconds) than that required for the STT (60 seconds for veterinary application) . The effectiveness of both tests for lacrimal quantification in humans and veterinary patients has been previously discussed …”

Application of phenol red as a marker ligand for bilirubin binding site at subdomain IIA on human serum albumin

“…Moreover, PhRed is used to detect and map the gastric distribution of Helicobacter pylori during endoscopy [6], as phenol red thread (PRT) test in the diagnosis of patients with ocular sicca syndrome [7] and in veterinary for measuring tear production in birds [8][9][10]. PhRed exhibits a structural similarity to some nonsteroidal estrogens and causes significant stimulation of cells proliferation and specific protein synthesis in estrogen-responsive cells [11].…”