Reliability of binocular vision measurements used in the classification of convergence insufficiency

Near Point of Convergence Norms Measured in Elementary School Children

PURPOSE

Convergence insufficiency (CI) is the most prevalent of binocular dysfunctions. A prime finding in the diagnosis of CI is the near point of convergence (NPC).

METHODS

The NPC was measured six different times on the same 539 children, once in the fall and once in the spring, over the course of 3 years. At each evaluation, the NPC was performed three consecutive times. An accommodative target was used in the testing and the breaks and recoveries were carefully measured and recorded to the nearest centimeter. Normative data for the break and recovery finding were calculated.

RESULTS

We found that the NPC measures receded significantly over three consecutive tests. The recession was not considered clinically significant for either the break or recovery measures. When various break and recovery findings were compared with reported symptoms, it was discovered that one of the break findings statistically predicted the symptomatic group from the asymptomatic group.

CONCLUSIONS

The NPC break and recovery does not change appreciably with multiple administrations of the test in the same test period. The criteria for a NPC break score to differentiate the more symptomatic and less symptomatic, elementary school children on the average should be 5 cm, or less. The NPC break and recovery criteria described here should be tentatively used as one of the benchmarks in the diagnosis of convergence insufficiency.

Influence of target type and RAF rule on the measurement of near point of convergence

PURPOSE

This study was designed to investigate if the use of different target types or the RAF rule affected the measurement of near point of convergence (NPC).

METHODS

The subjects comprised three groups: (1) 20 children aged 6-9 years (2) 17 children aged 11-13 years (3) 14 adults aged 20-30 years. Five targets were used to measure the NPC: (1) pencil tip, (2) fingertip, (3) penlight, (4) N5 letter and (5) vertical line target on the RAF rule.

RESULTS

There was no significant difference in NPC measurements between the pencil tip, fingertip and N5 target in free space. The penlight resulted in significantly more remote NPC break and recovery points compared with the fingertip and pencil tip (p < 0.05). The RAF rule influences the NPC obtained (p < 0.001). The greatest difference in NPC measurements was observed when comparing the RAF line target and the finger in free space; the former resulted in NPC values of 1.9 times (95% CI 1.6-2.2 times) as much as those obtained with the finger.

CONCLUSIONS

Use of the penlight and RAF rule resulted in a more distant NPC break point compared with other targets. The effect of the RAF rule was more apparent for more receded NPC points.

An enhancement to the Maddox Wing test for the reliable measurement of horizontal heterophoria

PURPOSE

To attempt to improve the reliability of the Maddox Wing (MW) test for the measurement of horizontal heterophoria at near.

METHODS

Horizontal heterophoria measurements at 30 cm using the MW instrument were made on a group of 58 normally-sighted binocular young adult subjects. The procedures were repeated at each of five weekly visits. The standard tangent scale card provided by the instrument's manufacturer was used as the control condition vs four alternative cards designed to enhance accommodative stimulation and improve operational reliability.

RESULTS

A statistically-similar mean near phoria value was recorded using each of the five cards. However one of the alternative card designs produced a small but statistically significantly less variable result than the others: this design featured a much smaller typeface (4pt) than that used for the digits on the standard card, and the horizontal row of numbers was flanked by two periods of a low spatial frequency (< 2 c deg(-1)) square wave grating.

CONCLUSIONS

It is suggested that for improved reliability of near phoria measurement when using the MW instrument a more appropriately detailed design of tangent card would promote enhanced accommodation, an operational consideration likely to be especially relevant when examining children.

Statistical normal values of visual parameters that characterize binocular function in children

A wide range of visual parameters used to evaluate binocular function were evaluated in a paediatric population (1056 subjects aged 6-12 years). Mean values are provided for these ages in optometric tests that directly assess the vergence system, horizontal phorias for near and far vision (measured by a modified version of the Thorington method), negative and positive vergence amplitude for near and far vision (step vergence testing), vergence facility (flippers 8 Delta BI/8 Delta BO), and near-point of convergence (penlight push-up technique and red-lens push-up technique), as well as stimulus accommodative convergence/accommodation ratio and stereoacuity (Randot test) which provide an overall evaluation of the vergence, accommodative and oculomotor systems. A statistical comparison (anova and Bonferroni post hoc test) of these values between ages was performed. The differences, although statistically significant, were not clinically meaningful, and therefore we identified two trends in the behaviour of these parameters. For all parameters, except for vergence facility, we established a single mean reference value for the age range studied. The difference between the means for vergence facility indicated the need to divide the population into two age ranges (6-8 and 8-12 years). This study establishes statistical normal values for these parameters in a paediatric population and their means are a valuable instrument for separating children with binocular anomalies from those with normal binocular vision.