Is Primate Lens Accommodation Unilaterally or Bilaterally Controlled?

Area of Science:

• Neuroscience
• Ophthalmology
• Primate vision

Background:

• Primate vision requires coordinated eye movements and lens focus adjustment for target distance.
• The neural organization controlling lens accommodation (monocular vs. binocular) is debated.

Purpose of the Study:

• To investigate whether premotor neurons controlling lens accommodation project bilaterally to the Edinger-Westphal nuclei.
• To determine if these projections consist of bilateral cells or a mix of ipsilateral and contralateral cells.

Main Methods:

• Recombinant rabies virus (N2c) with distinct fluorescent markers (green/red) was injected into the ciliary muscles of each eye in Macaca fasicularis monkeys.
• Viral tracing mapped neuronal connections to the Edinger-Westphal nucleus and associated premotor areas.

Main Results:

• Preganglionic motoneurons in the Edinger-Westphal nucleus showed the same marker as their ipsilateral injected muscle.
• Premotor neurons in the supraoculomotor area and central mesencephalic reticular formation were often doubly labeled, indicating bilateral projections.
• Some premotor neurons projected only ipsilaterally or contralaterally.

Conclusions:

• Evidence supports both monocular and binocular control of lens accommodation.
• Binocular inputs synchronize accommodation between the two eyes.
• Monocular inputs may allow for adjustments based on individual eye target distances or ciliary muscle capacities.