Interpupillary Distance

• Distance between centers of the entrance pupils

  • Important for:

    • Alignment of optical instruments (avoids prismatic effects induced)

    • Spectacle design considerations

      • Optical centers match PD’s (if not, induces prism)

    • Documentation of craniofacial abnormalities

  • Measure monocular PD’s for high powered spectacle prescriptions, PALs

• Procedure for binocular PD

  • Sit at eye level with patient ~40 cm away

  • Close your right eye and have patient look into your open left eye

  • Place zero at the temporal limbus of the right eye (DO NOT MOVE)

  • Note position that is aligned with the nasal limbus of the left eye: NEAR PD

  • Close left eye and have patient look into your open right eye

  • Note position that is aligned with the nasal limbus of the right eye: DISTANCE PD

  • Record distance/near

• Procedure for monocular PD

  • Place ruler on the patient’s bridge

  • Close your right eye and have patient look into your left eye

  • Align zero mark with the center of the pupil (CANNOT use pupil margin or limbus)

  • Note the mark centered on the bridge: OD MONOCULAR PD

  • Move ruler and place an easily recognized mark on the center of the bridge (use this as the zero mark)

  • Open your right eye, close your left, and have patient look into your right eye

  • Note mark centered in the patient’s left pupil; subtract the ‘zero’ reading from the last reading: OS MONOCULAR PD

• Use Prentice’s rule to calculate the induced prism from decentration

  • P= dF

• Errors: unsteady positioning, error in parallax, patient’s with fixation disparities and doctor’s PD significantly wide (will overestimate)

Ocular Dominance

• The preferential sighting of a target with one eye

• In monovision CLs fitting, the dominant eye is generally fit with the distance

• Useful when the subjective match in the clarity of the lines of letters cannot be achieved during binocular balance

  • Leave dominant with slightly clearer vision

• Do not leave the VA of the dominant eye worse than the non-dominant eye

• Place prism before the non-dominant eye

• Procedure

  • Instruct patient to fully extend arms and create a triangle with both hands

  • Patient looks through aperture at the doctor’s right eye

    • Eye aligned with the doctor’s is the dominant eye

  • Record ocular dominance