Surgeons having no ophthalmometer at their disposal and using only skiascopic frames for refraction often encounter difficulties in determining the angle of corneal astigmatism.
The same is true in cases of home visits to bedridden patients, where a bulky apparatus can not be taken. In cases like this the surgeon has to rely on the reply of the patient, which, being a subjective and unreliable manner of examination, is frequently the cause of errors in prescribing glasses.
A simple instrument may help the surgeon, in such a case, to find the angle of the corneal astigmatism rather accurately. It consists of a slit about 2 to 3 mm. in width, mounted on the usual graded trial frame and having a pointer on one side. The slit has to be turned slowly by the examiner.
While throwing light into the pupil of the patient by a plain mirror or a retinoscope,
BRENNER I. A Simple Device to Determine the Angle of Corneal Astigmatism. AMA Arch Ophthalmol. 1958;60(3):504-505. doi:10.1001/archopht.1958.00940080522028