<unk>  lenses (here unusually thick) are used for pre-operative<unk>  adaptation. Eye care professionals use<unk>  as a component of some eyeglass prescriptions. A lens which includes some amount of<unk>  will displace the viewed image horizontally, vertically, or a combination of both directions. The most common application for this is the treatment of strabismus. By moving the image in front of the deviated eye, double vision can be avoided and comfortable binocular vision can be achieved. Other applications include yoked<unk>  where the image is shifted an equal amount in each eye. This is useful when someone has a visual field defect on the same side of each eye. Individuals with nystagmus, Duane's retraction syndrome, 4th Nerve Palsy, and other eye movement disorders experience an improvement in their symptoms when they turn or tilt their head. Yoked<unk>  can move the image away from<unk> ary gaze without the need for a constant head tilt or turn.<unk>  is measured in<unk>  dioptres. A prescription that specifies<unk>  will also specify the "base". The base is the thickest part of the lens and is opposite from the apex. Light will be bent towards the base and the image will be shifted towards the apex. In an eyeglass prescription, the base is typically specified as up, down, in, or out, but left and right are also used sometimes. Whether a patient needs this type of<unk>  can be determined by a variety of methods.
Prism correction
Vision restoration therapy
Vision therapy
Vision rehabilitation
Piezoelectric surgery
Play therapy
Light therapy
Eyelid revision