Ablation depth of cornea for Lasik eye
surgery and amount of correction needed
Laser vision correction changes the corneal contour by removing
small amounts of tissue. As a result, the cornea is thinned. The average corneal thickness is 0.540 mm, and the absolute minimum
of residual thickness is 0.250 mm.
If the depth of the ablation
leaves less than 0.250 mm of residual corneal tissue, the risk
of the cornea shape ectasia, or blowing out is greatly increased. Most surgeons of Lasik choose
a flap depth between 0.120 mm and 0.180 mm and leave 0.270 mm -
0.275 mm of residual cornea in order to provide a safety margin
to allow for retreatment of Lasik eye surgery.
Ablation depth of cornea is proportional to amount of correction needed
Ablation depth cornea = Ablation squared diameter X Correction diopter
|
Required Correction |
Ablation Depth of Cornea (mm) |
Diopters |
Diameter 5mm |
Diameter 6mm |
Diameter 7mm |
|
|
– 1.00 |
– 0.0083 |
– 0.0120 |
– 0.0163 |
|
– 2.00 |
– 0.0167 |
– 0.0240 |
– 0.0327 |
|
– 3.00 |
– 0.0250 |
– 0.0360 |
– 0.0490 |
|
– 4.00 |
– 0.0333 |
– 0.0480 |
– 0.0653 |
|
– 5.00 |
– 0.0417 |
– 0.0600 |
– 0.0817 |
|
– 6.00 |
– 0.0500 |
– 0.0720 |
– 0.0980 |
|
– 7.00 |
– 0.0583 |
– 0.0840 |
– 0.1143 |
|
– 8.00 |
– 0.0667 |
– 0.0960 |
– 0.1307 |
|
– 9.00 |
– 0.0750 |
– 0.1080 |
– 0.1470 |
|
– 10.00 |
– 0.0833 |
– 0.1200 |
– 0.1633 |
|
– 11.00 |
– 0.0917 |
– 0.1320 |
– 0.1797 |
|
– 12.00 |
– 0.1000 |
– 0.1440 |
– 0.1960 |
|
|
