Clinical method for measuring adaptation of tonic accommodation and vergence accommodation

Area of Science:

• Ophthalmology and Vision Science
• Neuroscience
• Biomedical Engineering

Background:

• Tonic accommodation and vergence influence accommodative vergence and vergence accommodation, crucial for clear, single vision.
• Existing clinical methods are limited, primarily measuring tonic vergence (phoria) and accommodative convergence (AC/A ratio).
• Accurate clinical assessment of tonic accommodation and vergence accommodation (CA/C ratio) is needed for diagnosing binocular vision abnormalities.

Purpose of the Study:

• To develop a fast, accurate clinical method for evaluating tonic accommodation (accommodative phoria) and vergence accommodation (CA/C ratio).
• To validate the new method against established laboratory measures.

Main Methods:

• A novel 0.2 cycles per degree (cpd) Difference of Gaussian (DOG) target was used to open the accommodation loop, preventing reflex accommodation while maintaining binocular fixation.
• Dynamic retinoscopy combined with the DOG target was employed to measure tonic accommodative aftereffects and vergence accommodation responses.
• Pinhole Maxwellian view was also utilized to open the accommodation loop for comparison.

Main Results:

• The 0.2 cpd DOG target effectively opened the accommodation loop, yielding response values similar to the pinhole Maxwellian view.
• The method allowed for clinical measurement of the decay rate of tonic accommodative aftereffects and changes in accommodative resting focus due to vergence accommodation.
• Clinical CA/C ratio measurements showed a high correlation (r = 0.92) with laboratory-based objective infrared optometry and eye trac monitoring.

Conclusions:

• A fast and accurate clinical method using dynamic retinoscopy and a DOG target has been established for measuring tonic accommodation and the CA/C ratio.
• This technique provides valuable clinical data for assessing binocular vision abnormalities.
• The findings support the clinical utility and accuracy of the developed method for evaluating key parameters of the accommodation and vergence system.