Variability of Control in Intermittent Exotropia

Abstract

Purpose-Assessing control is thought to be important in the management of intermittent exotropia (IXT), 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 inter-observer and minute-to-minute variability. Design-Prospective case series. Participants-25 patients with intermittent exotropia.Methods-Inter-observer 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 one 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 IXT measured using a 6-point clinic control scale.Results-Inter-observer agreement was high (k=0.94 for distance and k=0.95 for near fixation). Disagreements were no more than one level on the control scale; therefore, for further analysis, change in control was defined as 2 or more 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, 3 (18%) 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 IXT can vary throughout the day, even within minutes, including from phoric to spontaneously 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 IXT in an individual patient.Intermittent exotropia (IXT) is a common form of childhood strabismus 1, 2 characterized by intermittent divergent misalignment that is often greater at distance fixation. Severity and progression of IXT are currently assessed by determining angle of deviation, stereoacuity, ability to control the deviation and parental reports of frequency. 'Control' may be defined as an estimate of the proportion of time the deviation is manifest and the ease of re-establishing fusion after dissociation. Although the natural history and indications for surgical intervention are poorly defined, 3 it is commonly held that poor control of the exodeviation is a sign of deterioration. 4 On this basis, surgery has been recommended by some authors when the exotropia occurs more than 50% of waking hours or when there is a gradual loss of fusional control as evidenced by an increasing frequency of the exotropia. [4][5][6] Others have suggested that early surgery results in superior sensory outcomes 7, 8 but the timing of surgery for IXT has not been subjected to a randomized clinical trial and prior to such a trial, outcome measures such as control need to be rigorously studied.Until recen...

Long-term results of the surgical management of intermittent exotropia

“…25 Control is an important patient-oriented outcome because it indicates the amount of time that exotropia is manifest in a patient's everyday life; it has also been assessed by the use of control scales or parental report by other authors. 26 Our data confirm several previously described findings. In our cohort, for an excellent motor result, the determined success rate of 64% falls well within the limits defined by previous authors; yet, when one considers sensory outcomes, our success rate of 38% falls below most previous studies.…”

Presenting features and early management of childhood intermittent exotropia in the UK: inception cohort study

“…Although objective measurements of control can be subject to variation depending on time of day and states of attention,25 the NCS incorporates a parental rating of frequency of strabismus, which may make it more useful in serial assessment of the severity of the condition. Children with higher scores on the NCS were more likely to have surgery.…”

Variability of Stereoacuity in Intermittent Exotropia

“…11 Control was scored using a previously described scale for both distance (3 meters) and near (1/3 meter) fixation. 19 Control assessment followed the standard testing procedure reported previously, 11,19 commencing with observation for spontaneous tropia over a 30 second time period (score 5 = constant tropia, score 3 = tropia for <50% of observed time). If no spontaneous tropia was observed, recovery of phoria was rated as the poorest of 3, 10-second periods of occlusion (score 2 = >5 second recovery, score 0 = <1 second recovery).…”