a. Calculate the AC/A ratio (accommodative convergence /      accommodation ratio) using the gradient method and the      following values (taken from an emmetropic patient):       Alternating cover test  for distance (6 metre)       = 10 dioptre esophoria for distance with -3.00DS = 25 dioptre esophoria b. A 6 year-old boy with 25 prism dioptres esotropia has a      + 4.00 DS cycloplegic refraction. He has a AC/A ratio of 6.     What is the result of prescribing hypermetropic glasses? Answer to a AC/A = 5 Using the gradient method, AC/A ratio is given as (Deviation without lens - Deviation with lens)/ Lens in dioptres = (25 - 10) / 3 = 5   Answer to b Significant reduction of esotropia. The patient has +4.00DS hypermetropia and a AC/A ratio of 6 (ie. 6 dioptre prism of esotropia with one dioptre of accommodation). Therefore, prescribing the  +4.00DS will reduce the accommodative convergence by 4 X 6 = 24 prism dioptre.  The residual esotropia = 25 -24 = 1 prism dioptre esotropia  which is insignificant.