To investigate the effects of different light intensities and various mydriatic and miotic drugs on pupil accommodation in guinea pigs.

Forty-two-week-old guinea pigs were randomly divided into four groups to assess pupillary responses under varying light intensities (100, 250, 500 lx) and pharmacological interventions (1% atropine, 1% cyclopentolate, 1% tropicamide, or 2% pilocarpine). Baseline pupil size and eccentricity were recorded using a non-contact Python-based imaging system integrating edge detection and pixel-to-distance conversion. Direct illumination effects were measured at sequential time points, followed by drug administration and longitudinal tracking of pupillary changes. The protocol was repeated at 12wk of age for developmental comparisons. Post-experiment, enucleated eyes were analyzed to evaluate in vitro vs in vivo differences.

Significant age-dependent differences in pupil dynamics were observed. Both 2- and 12-week-old guinea pigs exhibited marked pupil constriction under direct illumination (P<0.001), with decreased eccentricity post-constriction (P<0.001). Indirect illumination caused inconsistent pupil size changes (2-week: P=0.68; 12-week: P=0.49). Pharmacologically, atropine, cyclopentolate, and tropicamide induced pupil dilation (P<0.001), whereas pilocarpine caused constriction (P<0.001). All drug groups showed reduced eccentricity (P<0.001). In vivo/in vitro comparisons revealed significant structural differences.

This study investigates pupillary responses in developing guinea pigs, revealing a direct pupillary light reflex (PLR) with light intensity-dependent responses, while indirect PLR was undetectable. The differential effects of muscarinic modulators on pupillary responses underscore the critical role of cholinergic signaling in ocular accommodation, with age-related variations in sensitivity. Additionally, a novel non-contact measurement methodology achieved a precision of 0.01 mm for pupillary quantification, enhancing accuracy in ocular studies.

To quantitatively measure ocular morphological parameters of guinea pig with Python technology.

Thirty-six eyeballs of eighteen 3-week-old guinea pigs were measured with keratometer and photographed to obtain the horizontal, coronal, and sagittal planes respectively. The corresponding photo pixels-actual length ratio was acquired by a proportional scale. The edge coordinates were identified artificially by ginput function. Circle and conic curve fitting were applied to fit the contour of the eyeball in the sagittal, coronal and horizontal view. The curvature, curvature radius, eccentricity, tilt angle, corneal diameter, and binocular separation angle were calculated according to the geometric principles. Next, the eyeballs were removed, canny edge detection was applied to identify the contour of eyeball in vitro. The results were compared between in vivo and in vitro.

Regarding the corneal curvature and curvature radius on the horizontal and sagittal planes, no significant differences were observed among results in vivo, in vitro, and the keratometer. The horizontal and vertical binocular separation angles were 130.6°±6.39° and 129.8°±9.58° respectively. For the corneal curvature radius and eccentricity in vivo, significant differences were observed between horizontal and vertical planes.

The Graphical interface window of Python makes up the deficiency of edge detection, which requires too much definition in Matlab. There are significant differences between guinea pig and human beings, such as exotropic eye position, oblique oval eyeball, and obvious discrepancy of binoculus. This study helps evaluate objectively the ocular morphological parameters of small experimental animals in emmetropization research.