Unit 4: Refractive Error
4: Correction
Refractive errors can be corrected by:
- Spectacles
- Contact lenses
- Laser eye surgery
- Lens implants
- Refractive lens exchange
Contact Lenses
There are two main types contact lens:
- Rigid lenses (also called Hard or Gas Permeable lenses)
- Soft contact lenses (these may be disposable on a daily, monthly or annual basis)
Spectacles
- Spectacle lenses correct ametropia
- Single vision lenses correct either distance or near vision.
- Bifocals correct both distance and near vision in one lens (the near correction is usually in the lower half, for reading).
- Varifocal lens gradually increases from distance to near correction, from top to bottom.
Laser Eye Surgery
- Photo-refractive keratectomy (PRK) uses an excimer laser to remove a slice off the anterior cornea, reducing the power (to correct myopia).
- LASIK is a procedure where a corneal flap is cut and the underlying cornea ablated to flatten and reduce the power.
- Laser eye surgery can also correct hypermetropia and astigmatism
