Near Point

of Converg

ence

Definition:

Convergence Is the only disjunctive movement that

is under conscious control. It is a fusional movement that may be stimulated by volition, disparate stimulation, and accommodation.

The near point of convergence (NPC) Is the point of intersection of the lines

of sight of the eyes when maximum convergence is utilized.

The near point of convergence distance Is the distance from the near point of

convergence to the midpoint of the line connecting the center of rotation of the eyes.

Clinical use:

The near point of convergence distance is a measurement of the maximum convergence ability of a patient. Patients who have reduced near point of convergence distances may have visual and ocular discomfort when performing near point vision tasks.

Instruments:

Penlight Transilluminator Millimeter ruler RAF near point rule

Clinical procedure

The measurement of the near point of convergence distance should be performed in free space, the clinical procedure is as follows:

1. The patient is seated comfortably with the habitual spectacles prescription in place.

2. A PD ruler is held below the line of sight with the zero point coincident with a line that would pass through the center of rotation of the eye

3. Full room illumination should be used. A small accommodative target or penlight is placed about 40 cm in front of the patient’s midline.

4. The patient is encouraged to maintain fixation on the target and report when it doubles.

5. Slowly move the target (about 5cm/sec) along the midline toward the patient.

6. Note the fixation distance when one eye loses fixation on the target, or the patient reports diplopia. This is the near point of convergence. The eye that maintains fixation is the dominant eye.

7. Measure the distance from the near point of convergence to the center of rotation of the eye for both the subjective and objective near points of convergence.

8.Slowly move the target away from the patient along the midline and ask the patient to report when fusion occurs. This is the recovery distance.

9. This is recorded as break/recovery (e.g., 10cm/15cm).

10. This procedure may be repeated several times to determine the effect of fatigue. When the near point of convergence is repeated five or more times, symptomatic patients often show significant decreased convergence ability with repeated testing, whereas asymptomatic patients demonstrate little change.

The near point convergence can also be determined using a red lens technique. The clinical procedure for this follows:

1. The patient is seated with the habitual Rx in place.

2. A PD ruler is held below the line of sight with the zero point coincident with a line that would pass through the center of rotation of the eye

3. A penlight or transilluminator is held at 40cm from the patient, aimed at the bridge of the nose. A transilluminator is more desirable than a penlight, since the brightness of the light source may be modified for patient comfort. Place a red lens in front of one of the patient’s eyes.

4. Move the light toward the patient at a rate of about 5cm/sec.

5. The patient is instructed, and constantly encouraged to fixate the light and to report when a red light and white light are seen.

6. Note the fixation distance when the patient reports seeing a red and white light or the clinician sees one eye turn out. This is the near point of convergence. Measure the distance from the near point of convergence to the center of rotation of the eye.

7. Slowly move the light away from the patient along the midline, and ask the patient to report when the red and white lights go together. This is the recovery distance.

8. Record the result as before. Clinical significance

Patients with a near point of convergence may express symptoms such as diplopia, frontal headaches, decreased reading comprehension, asthenopia, and, occasionally, fatigue when undertaking near tasks.

Clinical interpretation The near point of convergence is

expected to be 6 to 10cm. Closer than 5cm is considered to be

convergence excess. A remote near point of convergence is

suspected to have convergence insufficiency.