Variability of control in intermittent exotropia

Abstract

Purpose: Assessing control is thought to be important in the management of intermittent exotropia, including the decision to perform surgery. The purpose of this study was to assess the presence and degree of any change in control occurring over the course of 1 day using a previously described 6-point clinic control scale and to evaluate interobserver and minute-to-minute variability.

Design: Prospective case series.

Participants: Twenty-five patients with intermittent exotropia.

Methods: Interobserver agreement was determined in 17 patients by comparing control scores assessed simultaneously by 2 observers (kappa test). Minute-to-minute variability was observed in the same 17 patients by assessing control twice within 5 minutes. Variability over 1 day was assessed in 5 of these patients plus 8 additional patients (n = 13) by comparing 3 or 4 assessments at least 2 hours apart.

Main outcome measure: Control of intermittent exotropia measured using a 6-point clinic control scale.

Results: Interobserver agreement was high (kappa = 0.94 for distance and kappa = 0.95 for near fixation). Disagreements were no more than 1 level on the control scale; therefore, for further analysis, change in control was defined as >/=2 levels. For minute-to-minute variability, 4 (24%) of the 17 patients tested twice within 5 minutes showed a change in control: 1 (6%) changed from tropia to phoria at distance and 3 (18%) changed from phoria to tropia at near. Of the 13 patients assessed over 1 day, 6 (46%) showed change in control: 2 at distance fixation only, 3 at near only, and 1 at near and distance.

Conclusions: Control of intermittent exotropia can vary throughout the day, even within minutes, including from phoric to tropic and vice versa. The worst level of control was not always later in the day. This suggests that an isolated assessment of control may not categorize severity of intermittent exotropia in an individual patient.

Figure 1

Inter-observer agreement for distance control scores between investigator 1 and 2 (n=34 paired observations). There was excellent agreement between investigators (k=0.94). The dotted line represents the unity line where there was perfect agreement between investigators. No paired observation differed by more than one level on the control scale (points not on the unity line).

Figure 2

Inter-observer agreement for near control scores between investigator 1 and 2 (n=34 paired observations). There was excellent agreement between investigators (k=0.95). The dotted line represents the unity line where there was perfect agreement between investigators. No paired observation differed by more than one level on the scale (points not on the unity line).

Figure 3

Three patients showed change in distance control score over one day. All 3 patients showed changes between tropia (score 3-5) and phoria (score 0-2). No patient was worse at the end of the day.

Figure 4

Four patients showed change in near control score over one day. 2 of these patients showed change from tropia (score 3-5) to phoria (score 0-2). No patient was worse at the end of the day.