A comparative study of the effect of face form angle on the low contrast visual acuity before and after calculation of its power

In wrap around frame wearers, when a lens is tilted due to Face Form angle of spectacle, there is a change in the sphere power, and a cylinder is induced. This power change can be compensated by calculating the effect of face form angle. Although high contrast visual acuity is normal in both with and without compensating the effect of face form angle on the power of lenses, this raises the question of whether low contrast visual acuity is normal. The aim of this study was to examine and compare the effect of face form angle on the lowest contrast visual acuity with/without calculating the effect of face form angle on wraparound frame wearers. An experimental study was designed in which two similar wraparound frames ‘with face form angle over 16 degrees’ were selected. 4% contrast visual acuity of 21 participants was tested with/without calculating the effect of face form angle on the best correction power. The results of repeated measured ANOVA indicated that the overall comparison was significant (p < 0.005). The greatest difference was found in non-calculating method (mean difference of VA = 0.02 Log). The difference was less in calculating method (mean difference of VA = 0.01 Log) The results indicated that use of wraparound frames with/without calculating the effect of face form angle in myopia between -3.00 and -6.00 D and with the rule astigmatism less than -1.00 D can decrease visual acuity in 4% contrast visual acuity when the face form angle is over 16 degrees.