Edinger--Westphal stimulated accommodative dynamics in anesthetized, middle-aged rhesus monkeys

Area of Science:

• Ophthalmology
• Neuroscience
• Physiology

Background:

• The Edinger-Westphal nucleus (EW) controls accommodation, crucial for focusing vision.
• Understanding the dynamics of accommodation (focusing) and disaccommodation (unfocusing) is vital for visual science.
• Age-related changes in accommodative amplitude are known, but velocity dynamics require further investigation.

Purpose of the Study:

• To investigate the relationship between stimulus amplitude and the peak velocity of Edinger-Westphal (EW) stimulated accommodation and disaccommodation.
• To compare accommodative and disaccommodative peak velocities across different stimulus amplitudes in rhesus monkeys.
• To assess if age affects these dynamic parameters of accommodation.

Main Methods:

• Anesthetized, middle-aged rhesus monkeys were used.
• Accommodative responses were stimulated via the Edinger-Westphal (EW) nucleus.
• Responses were measured using infrared photorefraction at a 30Hz sampling rate.

Main Results:

• Peak velocity for both accommodation and disaccommodation showed a linear increase with stimulus amplitude.
• Accommodation peak velocity continued to rise even with supramaximal stimulus amplitudes.
• Disaccommodation peak velocity plateaued at maximal stimulus amplitudes, not increasing further.
• Older monkeys achieved similar peak velocities to younger ones for equivalent accommodative amplitudes.

Conclusions:

• Accommodative and disaccommodative peak velocities are amplitude-dependent in rhesus monkeys.
• While maximal response amplitude declines with age, the peak velocities for a given response amplitude remain comparable between younger and older individuals.
• These findings contribute to understanding the neural control of accommodation and its age-related dynamics.