Comparative morphology of the eye in primates

Area of Science:

• Primate Ophthalmology
• Comparative Anatomy
• Visual Ecology

Background:

• Relative cornea size correlates with mammalian visual ecology and activity patterns.
• Nocturnal mammals typically have larger corneas for visual sensitivity, while diurnal mammals have smaller corneas for visual acuity.
• Previous studies suggested, but did not quantify, similar patterns in primates, with competing hypotheses on diurnal anthropoid or lemur visual system divergence.

Purpose of the Study:

• To quantify the relationship between eye morphology and activity pattern in primates.
• To determine if primates exhibit eye morphology variations comparable to other mammals.
• To investigate divergence in visual systems between diurnal anthropoids and lemurs.

Main Methods:

• Collected data on eye and cornea size for 147 specimens across 55 primate species.
• Analyzed relative cornea size in relation to activity patterns (diurnal, nocturnal, cathemeral).
• Compared eye morphology between primate suborders (haplorhines and strepsirrhines) and with nonprimate mammals.

Main Results:

• Diurnal primate species have significantly smaller relative cornea sizes than nocturnal or cathemeral species within both haplorhine and strepsirrhine suborders.
• Strepsirrhines exhibit relative cornea sizes consistent with nonprimate mammals of similar activity patterns.
• Diurnal anthropoids possess smaller relative cornea sizes than most nonprimate mammals, indicating a derived trait.

Conclusions:

• Primate eye morphology varies with activity pattern, aligning with functional expectations for visual ecology.
• Significant differences in eye morphology exist between haplorhines and strepsirrhines.
• The smaller relative cornea size in diurnal anthropoids likely evolved for enhanced visual acuity in their lineage.