Subsequent to my previous report on this subject,7 it has been my practice to measure the angle of misalignment of all sufficiently cooperative patients with intermittent exotropia while they look through a window and fixate on a distant outdoor target (typically a flag on top of a building a quarter mile away), in addition to performing the routine strabismus measurements. Also, I obtain a measurement at 6 m after 1 hour of monocular occlusion. For this study, I will refer to the former measurement as the "outdoor measurement" and to the latter measurement as the "postocclusion measurement." All consecutive patients I operated on for intermittent exotropia between 1985 and 1996 who had either outdoor sensitivity or VA-D were included in this study, subject to the following exclusion criteria: the presence of an A or V pattern requiring treatment, untreated amblyopia, simultaneous oblique muscle surgery, the use of adjustable sutures, a history of strabismus surgery, lateral incomitance of more than 10 prism diopters (Δ),13,14 follow-up of less than 1 year, insufficient cooperation for obtaining the previously mentioned measurements, or unwillingness to be randomized. Because I wanted to limit this study to patients in whom accurate measurements could be obtained with the prism and alternate cover test while fixation was well maintained on the outdoor target, the lower age for inclusion was 3 years. Also, because I frequently use adjustable sutures on postadolescent patients, and because I wanted to eliminate the confounding variable that would be introduced by adjustable sutures, I set the upper age limit for inclusion at 18 years. Finally, I excluded patients if it was known at the time of surgery that follow-up would be performed by the referring physician. Patients were considered to have intermittent exotropia if the deviation was intermittently manifested at either distance or near. Consequently, patients who had a constant exotropia at distance but an intermittent exotropia at near were included. Because outdoor sensitivity and VA-D have been reported in all forms in patients with intermittent exotropia, regardless of the distance or near discrepancy,6,7 this study includes patients in whom the distance measurement initially exceeded the near measurement, as well as those in whom the distance measurement initially equaled the near measurement. Patients with the convergence insufficiency type of exotropia (near exotropia exceeded distance exotropia by >10Δ) were also excluded because they seem to have a different and poorer prognosis.7,15,16 All patients were treated surgically with symmetrical lateral rectus muscle recessions according to a popular surgical formula.2 Because this formula is graduated in 5Δ increments, deviations were rounded to the closest 5Δ step for the purpose of quantifying surgery. Consequently, I considered an increase of 3Δ or more with the outdoor measurement or postocclusion measurement to be clinically important because it would result in an alteration in the amount of surgery performed. The patients were randomized to 1 of 2 groups when they were scheduled for surgery and after they gave informed consent. The study group underwent surgery for either the outdoor measurement or the postocclusion measurement, whichever was larger. The control group underwent surgery for the measurement obtained at 6 m prior to monocular occlusion. If patients had been treated with minus lens therapy or base-in prism prior to surgery, they were put in their appropriate cycloplegic spectacle correction without prism, and it was with those spectacles that the measurements for this study were obtained. For patients with myopia, the full cycloplegic correction was dispensed. For patients with hyperopia, spectacles were prescribed if there was any substantial astigmatic refractive error, anisometropia greater than 0.5 diopters (D), or hyperopia greater than 2 D. In most cases, hyperopic patients with intermittent exotropia were given spectacles that incorporated approximately 1 to 1.5 D less than the full cycloplegic hyperopic correction. Outcome determination was made at the earliest examination date performed at least 1 year after surgery (range, 12-15 months). An outcome was considered satisfactory if there was between 10Δ of exophoria and 5Δ of esophoria. Any intermittent or manifest tropia of any amount, either esotropia or exotropia, was considered an unsatisfactory outcome. Patients who underwent a reoperation, who needed prisms after surgery, or who needed manipulation of their accommodation with plus or minus lenses to meet the previously mentioned criteria were considered to have an unsatisfactory outcome. Patients for whom the angle of strabismus increased with either the outdoor measurement or the postocclusion measurement were subsequently retested again at 6 m after occlusion had been removed for several minutes. This subsequent measurement was obtained to determine if the increase in the angle of exotropia was merely a result of repeated dissociation and testing.