Pupillometry in mice: sex and strain-dependent phenotypes of pupillary functioning

Pupillometry is used as a phenotyping assay for investigating pupil responses in normal and genetically engineered mice. The mice used most often in contemporary ophthalmic research have not been adequately investigated by pupillometry.

An infrared-video camera was used to assess pupillary functioning under standard dark-adapted conditions (30 min acclimatization in a ganzfeld chamber) and 30 min after the installation of either 10 microl tropicamide (1.0%) or 10 microl pilocarpine (5.0%) into the conjunctival cul-de-sac. The experiment was self-controlled using a repeated-measures analysis of variance to analyze 60 mice (30 males, 24 weeks of age) from three strains (C57BL/6, 129SvJ, and F1 hybrid).

The dark-adapted pupillary diameter of mice ranged from 2.3 mm (SD = 0.14) in female C57BL/6 to 2.9 mm (SD = 0.05) in male 129SvJ. Under dark-adapted conditions, all mice examined were sexual dimorphic (F = 19.5, dF = 2, 119, p < 0.001) and strain-dependent differences were observed between male C57BL/6-129SvJ and C57BL/6-F1 and female C57BL/6-F1 (F = 82.32, dF = 1, 119, p < 0.001). The mean pupillary diameter 30 min after the application of tropicamide ranged from 2.5 mm (SD = 0.16) in female F1 to 3.0 mm (SD = 0.13) in male C57BL/6. Tropicamide produced a sexual dimorphism in mydriasis for all mice (F = 56.30, dF = 1, 59, p < 0.001); however, strain-dependent differences were not observed (F = 1.31, dF = 2, 59, p < 0.280). The mean pupillary diameter 30 min after the application of pilocarpine ranged from 2.6 mm (SD = 0.28) in female C57BL/6 to 3.2 mm in both male F1 (SD = 0.22) and 129SvJ (SD = 0.04). Pilocarpine produced a sexual dimorphism in mydriasis for 129SvJ and F1 (F = 106.70, dF = 1, 59, p < 0.001) and strain-dependent differences were observed between female C57BL/6-F1 (F = 17.25, dF = 2, 59, p < 0.001).

The experiment demonstrates that mice respond idiosyncratically in their pupillary response under standard dark-adapted conditions and to either tropicamide or pilocarpine depending on strain and/or sex of the mouse. The characteristic responses observed are likely due to subtle differences in the genetic expression of phenotype.