What 'irregular' means
Regular astigmatism is symmetric: the cornea is steeper along one meridian and flatter along the one at right angles, like a football, and a cylindrical spectacle lens corrects it exactly. Irregular astigmatism has no such symmetry: the steepness varies from point to point across the cornea, as in a cone, a scar or a distorted graft. No spectacle lens has a surface that can cancel it. Corneal topography shows it as an asymmetric, distorted map, and the gap between vision with glasses and vision with a rigid lens over the eye measures how much of the blur is irregularity.
How a lens corrects it
Place a rigid lens on the eye, and the tear film fills the space between the irregular cornea and the lens's smooth back surface. Tears and cornea have almost the same refractive index, so light no longer 'sees' the cornea's irregular surface; it sees the lens's regular front surface. The eye's optics become those of a regular cornea. This is why rigid lens over-refraction is the diagnostic test for irregular astigmatism and why rigid optics are the treatment.
Choosing the lens
- Corneal rigid gas permeable lenses: for mild irregularity on a cornea that can support a small lens; sharpest optics, most adaptation
- Hybrid lenses: rigid optics with a soft skirt, for mild to moderate irregularity where comfort and stability matter
- Scleral lenses: for moderate to severe irregularity, scars, grafts and post-surgical corneas; vault the whole cornea, most stable and comfortable, and protective of a compromised surface
- Advanced scleral designs with custom back surfaces and wavefront-guided front optics, considered where appropriate for eyes whose residual aberrations limit vision even in a standard scleral lens
Alongside treatment of the cause
A lens corrects vision over an irregular cornea; it does not treat the cornea. Keratoconus that is progressing is cross-linked. Scars may be treated with a surface laser. Grafts are monitored by the cornea surgeon. The lens fitting and the corneal management run together, and the lens is refitted whenever the cornea changes.
Is this right for your eyes?
Nothing on this page is a diagnosis. Whether this is the right choice for you is decided by a full examination at one of our 4 offices: Pasadena, Huntington Beach, Woodland Hills and Beverly Hills.
About this content: This page was written with the assistance of AI tools and reviewed for medical accuracy by Dr. Arbi Melikian, OD. It is general information, not medical advice, and does not replace an eye examination. Individual results vary. Read our medical disclaimer.
