To understand the clinical application of Conoid of Sturm, we need to understand its basic optics.
In simple words, we can say ” Conoid of sturm is just a representation of how rays are refracted through two different powered meridians” (eg: a sphero- cylindrical lens). So, instead of one focal point, they form two focal lines.
Static Retinoscopy can be done in two ways; using a working distance (WD) lens in front of the patient’s eye or without it.
A working distance lens is used to compensate for the distance between the examiner and the patient’s eye. Usually, the working distance is taken as arm length i.e 66cm (+1.50DS)
Before constructing a Visual Acuity Chart, we need to know and decide what kind of chart we want to construct. There are different kinds of charts for visual acuity measurement.