ASTIGMATISM: Material Selection
Ed Bennett OD, MSEd, FAAO, FSLS
Material Selection
Material Selection – based upon oxygen permeability – has been divided into three categories, all pertaining to fluoro-silicone/acrylate materials:1
- Low (25 – 49). These materials have the benefit of rigidity and flexural resistance. They are a viable option for daily wear myopic patients.
- High Dk (50 – 99). These materials are best indicated for daily wear hyperopic patients (i.e., a +3D lens has approximately twice the center thickness of a -3D lens; hence, a material with twice the Dk of a -3D lens is necessitated. Likewise, corneal multifocal and keratoconic/post-surgical patients benefit as well.
- Hyper Dk (≥ 100). These materials are indicated for all extended wear – including overnight wear of orthokeratology designs – and scleral lenses.
Clinical Pearls:
- Your CLMA member laboratory does an excellent job of matching material with design and often removes this decision from the table as it pertains to the final contact lens order. When in doubt, ask your laboratory consultant.
- What about bitoric lenses?. As bitorics are thin lens designs, the criteria mentioned above apply. However, it should apply to the power in the most plus power meridian. For example, if the final powers were +1.00/-3.00D, the thicker meridian is plus power and therefore a high Dk material would be recommended.
References
- Bennett ES, Young R. Material Selection. In Bennett ES, Henry VA. Clinical Manual of Contact Lenses, 5th ed., Wolters Kluwer, Philadelphia, PA, 2020:108-133.