While not common, corneal edema may occur in some patients. A lens with too much vaults can cause this. Make sure to re-evaluate your SAG value. It should be the minimum SAG that vaults with very little or preferably no apical bearing (100-150 microns after settling). Another cause may be that the periphery of the lens is impinging into the conjunctiva. If this occurs flattening the PC's while maintaining the appropriate SAG is indicated. Lens awareness can occur if there is too much edge lift. Excessive edge lift is caused by either the PC's being too flat or the lens SAG being too low. If excessive edge lift is observed you should first determine if the SAG is appropriate. Often when the SAG is increased, the edge will improve.
If the lens SAG is correct then a steeper periphery is indicated. The two most common causes for SPK are either from preservatives in the solution or excessive bearing on the apex. Because these lenses have very little or no movement, tear exchange is very slow to occur. Therefore, it is very important that a benign saline be used when inserting. This will eliminate any possibility of chemical irritation. On rare occasions metabolic debris accumulation can be an issue. Usually the patient will complain of decrease acuity after eight to ten hours wear. If this occurs have the patient remove, clean and re-insert during mid-day. Excessive redness can be a sign that the lens is fitting too tightly. Patients may complain that their wearing time is limited to only a few hours a day. Recheck the SAG value to make sure it is at minimum apical vault and adjust as necessary. If the SAG is appropriate then re-design with a flatter periphery.
- Lens Diameter should be at least 2mm larger than limbal area of the eye.
- Your 1st trial lens should be flat fitting. That way, you can very accurately adjust the SAG up.
- Central bearing, edge lift and or limbal bubbles indicate a flat fit.
- Increase Sag value if there is a central bearing (0.1mm for every 1.0mm of bearing)
- Deep central pooling or central bubbles indicate a steep fit.
- Decrease Sag value if you have a steep fit.
- Ideal fluorescein pattern will be aligned at 150 microns of clearance after settling.
- Edge should not impinge or lift excessively off of the sclera.
*Your goal is to find the minimum SAG Value that vaults the cornea with no apical bearing (150 microns after settling /250 microns at insertion).