The bifixation field as a function of viewing distance

Area of Science:

• Ophthalmology
• Neuroscience
• Vision Science

Background:

• Hering's theory on eye movement and bifixation.
• Hering predicted differences in eye lag based on convergence distance.

Purpose of the Study:

• To test Hering's predictions regarding the bifixation field size and eye lag.
• To investigate eye movements at the limits of bifixation.

Main Methods:

• Subjective index of eye position measurement.
• Two experiments examining bifixation fields at near and far convergence distances.

Main Results:

• Bifixation field is significantly smaller at near convergence distances.
• In most cases, the nasally directed eye lagged behind the temporally directed eye at bifixation limits.
• Results partially contradicted Hering's prediction on eye lag direction.

Conclusions:

• Hering's prediction on bifixation field size was confirmed.
• Eye drift towards tonic vergence state occurs when fusion breaks.
• The nasally directed eye typically lags behind the temporally directed eye at bifixation limits.