Module 3 Interpupilary Distance

Question 1

What is the distance in millimeters between the pupils of the two eyes when looking straight ahead?

Answer 1

Pupillary distance (PD)
Interpupillary distance (IPD)

Question 2

What is the interpupillary distance as specified for a near viewing situation?

Answer 2

Near pupillary distance

Question 3

What is the device for measuring PD called?

Answer 3

Pupilometer

Question 4

What is the basis of a pupilometer measurement?

Answer 4

Either the pupil centers or the corneal reflections

Question 5

What is a device used to measure PD that is a polarized camera and a marker blocker?

Answer 5

Photocentron

Question 6

What are the steps in measuring the binocular distance PD?

Answer 6

1. Dispenser aligns himself with patient at a distance of 16 inches.
2. Dispenser closes right eye and has patient fixate on open left eye.
3. Dispenser lines up zero point of ruler in front of patient’s right pupil (either outer right pupillary border or left limbus).
4. Dispenser closes left eye, opens right eye and has patient fixate on open right eye.
5. Dispenser reads off measurement directly in line with patient’s left pupil (left pupillary border or left limbus).
6. Dispenser closes right eye, opens left eye and has patient fixate on open left eye.
7. Dispenser checks to make sure zero point is still correct.

Question 7

What are the steps in measuring the near PD?

Answer 7

1. Dispenser places dominant eye in front of patient’s nose at the patient’s near working distance.
2. Dispenser closes non-dominant eye.
3. Patient fixates on dispenser’s open eye.
4. Dispenser places zero point of ruler at the center of patient’s right pupil.
5. Scale marking at center of patient’s left pupil is read.

Question 8

What are the steps in using the pupilometer?

Answer 8

1. Clean instrument with alcohol wipe.
2. Adjust knob to position desired.
   “infinity” is for distance PD
   40 is for near PD
3. Ask patient to put elbows on table and hold pupilometer like a pair of binoculars.
4. Instruct patient to look at green dot/light (or however instrument is set up)
5. Examiner looks into eyepiece and moves sliders with thumbs so that the vertical lines inside the pupilometer are aligned with the patient’s light reflexes on both corneas.
6. Turn the instrument over and record the measurement individually (EX: 33/32)

Question 9

What are the steps for the ruler and penlight method for distance PD?

Answer 9

1. Sit 16 inches from the patient
2. Hold penlight under your left eye
3. Place ruler across bridge of patient’s nose
4. Have patient look directly at light source.
5. Place zero marker of ruler on the pinpoint reflection of the light on the cornea.
6. Move the penlight to a position under your right eye
7. Instruct patient to keep looking at penlight
8. Record measurement on the PD ruler of the reflection of light on the patient’s left eye

Question 10

What are common difficulties and errors in measuring the IPD?

Answer 10

1. Dispenser cannot close one eye

2. Dispenser is visually impaired or blind in one eye

Question 11

What happens if inaccurate PD is recorded?

Answer 11

Prism before patient’s eye

Question 12

What is Prentice’s Rule?

Answer 12

Prism = c x F
Prism = OC displacement (in cm) x lens power (in diopters)
c = centimeter
F = dioptric power of the lens (can also be written as D)

Question 13

How do you measure the IPD for an uncooperative patient/child?

Answer 13

Canthus to canthus method

Can do Monocular PD, tape or lens method