Is Hirschberg enough? - A comparative study of corneal light reflex test and alternate prism cover test in measuring comitant horizontal strabismus.

ObjectiveTo determine the mean difference in deviation in prism dioptres as measured by corneal light reflex test and alternate prism cover test in comitant horizontal strabismus to improve practice patterns.Materials and methodsStudy settingInstitute of Ophthalmology, Mayo Hospital, Lahore, Pakistan; Sardar Trust Eye Hospital, Lahore; The Eye Associates, Lahore, Pakistan.Study designCross-sectional study.ResultsThe study included a total of 69 patients (36 males, 33 females) aged between 16 to 68 years (mean 23.5 years), of which 48 (70%) had exotropia and 21 (30%) had esotropia. The angle of deviation for exotropia ranged from 12 to 87 prism dioptres (PD) (mean 44.23 ± 19.20 PD), while for esotropia it was from 10 PD to 104 PD (mean 47.19 ± 29.10 PD). The average difference between the angle of deviation as measured by the corneal light reflex test i.e. the Hirschberg test, compared to that by the alternate prism cover test (APCT) for severe deviations was significant (-value < 0.05). The difference was also significant for severe exotropia and esotropia, as well as moderate esotropia.ConclusionThere is a statistically significant difference between the measurements obtained by the corneal light reflex test and those by the alternate prism cover test, with the corneal light reflex test being substantially less accurate. Moreover, this relationship varies with the angle of the deviation, with overestimations more likely to occur with mild deviations and underestimations with severe deviations.