Astigmatic fan block

1. Jackson cross cylinder is a combination of two cylinders of equal strength but of opposite sign, placed with their axis at 90 degrees to each other and manted on a handle. 2. It is use to refine the axis of the cylinder and power of the cylinder in subjective refraction.  3. To determine principal meridians rotate the arrow situated under the fan to the point at which the patient reports the lines of the fan appear clearest. Continue fine adjustment of the arrow until both of its limbs are equally clear.  This point indicates the negative cylinder axis. 4.  Insert half of the negative cylinder that you found on retinoscopy at the axis found in the previous step. 5. Direct the patient to look at the blocks situated under the arrow. 6. Ask the patient which of the block appear clearer or blacker? If the block with the lines going in the same direction as the cylinder axis appear cleaner,  in add the cylinder power by -0.25, if however, the block with the...

Astigmatic fan block technique is used in subjective refraction for determination of Astigmatism in a patient and to determine correct cylinder axis and power. 1. Astigmatic dial is a combination of fixed dial rotary dial. 2. The inner portion of the dial content a "V" and two sets of mutually perpendicular line. This dial is rotateable. 3. And the outer peripheral dial contains radial lines spaced at 10' interval and arranged after the manner of the rays of the rising sun. 4.  "V" block can be rotated through go. Procedure... 1. Perform retinoscopy and find the power of both eyes. 2. Starting with right eye ( left eye ocluded) remote the cylinder lens found on retinoscopy from the trial frame. 3. Determine the best vision sphere by fogging -unfogging technique or by duocrome test. 4.The expected BVS will be half of the cylinder power. 5. Direct the patient to fan and block chart and while looking at the fan add fogging lens of spherical power until ...