Intraocular pressure in zebrafish: comparison of inbred strains and identification of a reduced melanin mutant with raised IOP.

PURPOSE: The goal was to establish an accurate method for measuring intraocular pressure (IOP) in living adult zebrafish and to determine the average IOPs of genetically different strains and mutants. The overall purpose was to develop the zebrafish system for studies of IOP and glaucoma. Elevated IOP and anterior segment dysgenesis are two known risk factors for glaucoma. Because albino mammals have increased IOP and are prone to anterior segment anomalies, the study was focused on a reduced melanin zebrafish mutant, brass.
METHODS: Servo-null electrophysiology was used to measure IOP in anesthetized adult zebrafish. A pulled-glass microelectrode was used to penetrate the cornea into the anterior chamber, and pressure transduction was recorded. IOP, histology, and visual behavioral assays were used to assess the brass mutant.
RESULTS: Significant differences in IOP were detected between genetically distinct zebrafish strains. IOP averages were highest in the long fin (LF) strain (20.5 +/- 1.2 mm Hg) and lowest in the Oregon AB (AB) strain (10.8 +/- 0.3 mm Hg). In brass mutants, which show a reduced melanin phenotype, IOPs were elevated and mild iris hypoplasia was noted. No defects were observed within the retina or in visual function.
CONCLUSIONS: In the present study, an accurate method was developed for measuring IOP in adult zebrafish. Both the ability to measure IOP in the genetically powerful zebrafish model and the conservation of elevated IOP and anterior segment anomalies between albino mammals and hypopigmented fish are important. They strongly support the use of zebrafish for studying the complex genetics of elevated IOP and glaucoma.