0521779407-18 CUNY1086/Karliner 0 521 77940 7 June 13, 2007 8:1
1276 Refractive Disorders (Ametropias)lens implant-based procedures that either replace the crystalline
lens or add a lens implant that has added convex power
Keratorefractive methods of correcting hyperopia include:
■LASIK (laser in situ keratomileusis) – After creating and lifting a thin
corneal flap, laser ablation is performed in the peripheral cornea,
causing effective steepening of the central cornea. Regression over
time may occur.
■PRK (photorefractive keratectomy) and LASEK (laser subepithelial
keratectomy) – Peripheral corneal photoablation causes relative
steepening centrally. As with LASIK, regression over time may occur.
■Thermokeratoplasty – using laser or non-laser approaches, thermal
treatment is applied to the peripheral cornea, causing collagen con-
traction and central steepening. Regression of effect is a frequent
occurrence with this method, particularly with correction of higher
degrees of hyperopia.
Lens procedures that increase the net effective convex power of the
crystalline lens:
■Phakic intraocular lens implantation – an artificial lens is placed in
the anterior or posterior chambers, but the natural crystalline lens
is left intact
■Clear lens extraction with intraocular lens implantation – the
undoubted effectiveness of this method of correcting higher degrees
of hyperopia must be balanced against the uncommon but poten-
tially serious complications of an intraocular surgical procedure.
However, the risk of postoperative retinal detachments is lower in
lens extraction performed in hyperopes than in myopes.
■Astigmatism
➣Optical correction – Regular astigmatism corrected with lenses.
Irregular astigmatism requires correction with a rigid contact
lens that can “float” over the tear film, thus neutralizing the
underlying irregular cornea.
➣Surgical correction – Regular astigmatism can be corrected using
the same metbods used to correct myopia and astigmatism, with
modification. Irregular astigmatism is more difficult to correct
and may require special techniques such as “custom corneal
ablation,” in which a small- or variable-diameter beam excimer
laser is directed in a topographically or wavefront-guided fashion
to “smooth” the irregular corneal surface.
■Presbyopia
➣Optical correction – Convex (“plus”) lenses can assist with view-
ing near objects. Early presbyopes (e.g., those in their early 40s)