Purpose The purpose of this master thesis was to develop an algorithm for an automatic subjective refractometer with which the refractive status of an eye could be measured. It was an innovation project to Topcon Healthcare Solution Emea Oy, later called a “Company”. This master thesis was focused only on the distance refraction. It did not include binocular vision problems and near vision examination.

Methods Distance refraction was explained by searching information from highly respected optometry text books and evidence-based studies. After that, there was an analysis of what must be considered when different parts of the examination are programmed to an algorithm. The greatest concern was about the Jackson Crossed-Cylinder examination. That examination was opened by mathematical calculations. Especially, the axis examination was carefully explained with the calculations.

Results As results, distance refraction was found to include seven different parts: A starting point, the first spherical adjustment, an examination of astigmatism, the last adjustment of the spherical power, a binocular balancing, a binocular control of accommodation, and finally, the distance refraction of both eyes. Two new proposals of axis examination were made from mathematical calculations about cylinder axis examination. A couple of algorithms about different parts of the distance refraction were made together with the Company’s optometrist.

Conclusions This thesis was to help the Company in planning the automatic refractometer. In addition to that, this thesis was a kind of reminder to every optometrist how the subjective distance refraction should be performed. This thesis gave new information about the cross-cylinder examination, especially the axis examination. All the necessary information to understand obliquely crossed cylinders effects was explained. A couple of tables from calculations explained various features of cylinder axis errors.