Astigmatism fan chart

The astigmatism fan chart has line differences in 10 degrees intervals. Some charts have correcting cylinder axis marked in chart written at top of each spoke of line (Figure 1) and some charts just only represent the actual representation of line orientation in degree (Figure 2). We can easily find out whether correcting the cylindrical axis is marked or the line orientation in degree. If the 12 o’clock (vertical) line is marked as 180 or zero, it means the axis of correcting cylinder is written. If the 12 o’clock (vertical) line is marked as 90, means it represents line orientation in degrees. In this case, correcting cylindrical lens axis will be 90 degrees perpendicular (if the axis is less than 90 add 90 to it or if more than 90 then subtract 90)

Before reading procedure read optics behind Astigmatism fan test

Astigmatism charts

Astigmatism fan test Procedure:

• It is the monocular procedure. Occlude LE of the patient.
• Step 1: Determine the patient’s Best vision sphere and record visual acuity.
• Step 2: Add plus power (equal to half of approximated cylinder power depending upon patient visual acuity shown in Table 1). At this point, the patient should have one set of lines in the chart more clearly compared to others, if not add more plus power. Or fog patient using plus power until all lines in the astigmatic fan chart appear to blur and slowly reduce plus power in 0.25 D step till one set of lines becomes clear compared to the other.
• Step 3: Read the correcting cylindrical axis from the chart. Add a minus cylinder lens with an axis similar to mention in the chart and simultaneously keep questioning about equal clarity of lines. The examiner continues adding a minus cylinder lens until the patient report all line are equally clear.
• Step 4: The examiner adds an extra 0.25DC to see the reversal. At this point a set of lines which is 90 apart or perpendicular from the line was clear in step.
• Step 5: Remove the extra 0.25 DC which was added in step 4. Note down the final power of the patient.
• Repeat the same procedure for the other eye.

Vision with COLC on retina	Astigmatism (D)
6/6	Less than 1
6/9	1.00
6/12	1.50
6/18	2.00
6/24	3.00
6/36	4.00
6/60	High