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Differences between anatomical and physiological interpupillary distance.

BACKGROUND
The interpupillary distance (IPD) is usually measured between the centers of the pupils (anatomical IPD) or between the visual axes (physiological IPD). We have investigated the differences between the two methods of measuring IPD.


METHODS
A millimeter ruler was used to measure the distance between the nasal and lateral limbus of 400 male Arab subjects (anatomical IPD). An Essilor corneal reflex pupillometer was employed to also measure the inter visual axes distance (physiological IPD) of the same group of subjects.


RESULTS
The anatomical IPD is on the average 0.10mm and 0.30mm wider than the physiological IPD at distance and near respectively. The calculated near physiological IPD is significantly different from the measured near physiological IPD.


CONCLUSIONS
Although individual differences between anatomical and physiological IPDs could be clinically significant, generally, there is good agreement between the two. It is preferable to employ the monocular components of the physiological IPD in ophthalmic procedures.