Experience can increase prism fusion range

Aim: Differences in near prism fusion ranges (PFR) were assessed in 4 groups of participants who differed in experience of exposure to such testing. The effect of encouragement in the two least experienced groups was also tested.

Methods: The near base in (BI) and base out (BO) fusional amplitudes (FA) were measured in four groups of 10 participants, all with normal or corrected to normal vision. One group was naÏve to such testing, being non-orthoptic students, the other three groups consisted separately of Year One, Two and Three student orthoptists. The two most inexperienced groups, NaÏve and Year One student orthoptists, were also tested a second time with encouragement to try as hard as possible to increase their fusion amplitudes.

Results: Year Two and Year Three students had significantly ( p < 0.001, often over 20∆) larger BO FA than naÏve students or Year One orthoptic students. No such differences were seen for BI measures. Encouragement also significantly ( p < 0.01), but modestly (<6∆), increased BO FA and slightly (about 1∆, p < 0.05) increased BI FA.

Conclusions: Experience did increase PFR but this was mainly in BO fusion amplitudes and was far greater than obtained by encouraging participants. The experience needed to obtain this increase appeared to be the exposure occurring in one year of training to be an orthoptist. Further experiments could help clarify the factors involved in this improvement by tracking any increase throughout this first year and also look for changes in performance in other orthoptic tests.