keratorefractive surgery


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re·frac·tive ker·a·to·plas·ty

any procedure in which the shape of the cornea is modified, with the intent of changing the refractive error of the eye; for example, if the cornea is flattened, the eye becomes less myopic. See: photorefractive keratectomy, keratophakia, lamellar keratoplasty, thermokeratoplasty, keratomileusis, radial keratotomy.

keratorefractive surgery

Photoreactive keratotomy, see there. Cf Radial keratotomy.

epikeratoplasty

A surgical procedure on the cornea aimed at correcting ametropia. The patient's corneal epithelium is removed and a donor's corneal disc (or lenticule) that was previously frozen and reshaped to produce a new anterior curvature is rehydrated and sutured to Bowman's membrane. The lenticule can be removed and exchanged to provide a different power. There are many problems associated with this procedure, in particular the surface re-epithelialization. Syn. epikeratophakia; refractive keratoplasty and keratorefractive surgery (both terms also include keratomileusis, keratophakia and radial keratotomy). See Intacs; keratomileusis; keratophakia; photorefractive keratectomy; LASIK; LASEK; lenticule.

Intacs

Trade name of an intracorneal implant consisting of two tiny half-ring segments, which are inserted into the cornea to reshape its curvature and correct ametropia. The method is presently used to flatten the cornea by a given amount (the thicker the ring segments the flatter the cornea) in order to correct low myopia. It is an outpatient procedure carried out under local anaesthesia, takes less than half an hour and is reversible. The ring segments are made of clear biocompatible plastic inserted into the stroma and around the optical zone of the cornea.

keratectomy, photorefractive

A surgical procedure on the cornea aimed at correcting ametropia. The epithelium is completely removed over a central diameter of about 7 mm and excimer laser ablation is then carried out on the stroma. A bandage soft contact lens is usually worn afterwards for a few days while the epithelium regenerates. Complications are more common than with either LASEK or LASIK. Useful vision recovers more slowly and pain lasts longer than with the latter procedures. Syn. keratorefractive surgery; laser refractive keratoplasty (LRK); refractive keratoplasty. See corneal ectasia; radial keratotomy.

keratomileusis

A surgical procedure on the cornea aimed at correcting ametropia. An anterior layer of the cornea is sliced off with a microkeratome, frozen, ground to a new curvature and sutured back in the same location. There are many complications and technical difficulties associated with this procedure. Syn. refractive keratoplasty and keratorefractive surgery (both terms also include epikeratoplasty, keratophakia and radial keratotomy). See epikeratoplasty; Intacs; photorefractive keratectomy; keratome; keratophakia; LASEK; LASIK.

keratophakia

A surgical procedure on the cornea aimed at correcting ametropia. A donor corneal disc (or lenticule) that was previously frozen and reshaped is inserted into the host cornea to modify the anterior corneal curvature. There are many complications and technical difficulties associated with this procedure. Syn. refractive keratoplasty and keratorefractive surgery (both terms also include epikeratoplasty, keratomileusis and radial keratotomy). See epikeratoplasty; Intacs; keratomileusis; photorefractive keratectomy; LASIK; LASEK; lenticule.

LASEK

A surgical procedure on the cornea aimed at correcting ametropia. An alcohol solution is applied to the cornea (usually for less than 30 seconds) to loosen the epithelium. A trephine is used to make an incision in the epithelium leaving a hinge of 2-3 clock hours of intact margin. The loosened edges of the epithelium are lifted along the trephine mark and the epithelium is folded or rolled back exposing Bowman's layer. Excimer laser ablation is then performed on the anterior stromal surface and Bowman's layer is ablated away over the treatment area. The epithelial flap is repositioned and a bandage soft contact lens is worn for 3-4 days to minimize discomfort and to protect the epithelium. The method is less invasive than LASIK and appears to give rise to fewer complications. LASEK is an acronym made from the following italic letters 'laser assisted epithelial keratomileusis'. See photorefractive keratectomy; pachometer.

LASIK

A surgical procedure on the cornea aimed at correcting ametropia. A suction ring is applied to the globe and an increase in intraocular pressure to approximately 65 mmHg is induced for a maximum of two minutes. During that time an automated microkeratome advances across the cornea creating a corneal flap of about 8.5 mm in diameter, which contains the epithelium, Bowman's layer and a portion of the anterior stroma. The vacuum is then switched off and the suction ring removed. The corneal flap, which is hinged on one side of the cornea, is turned round onto the conjunctiva and the exposed stroma is ablated with the excimer laser. On completion of the laser ablation, the corneal flap is repositioned and left to adhere without sutures. There are some complications associated with this procedure, but it gives rise to less postoperative pain and more rapid visual rehabilitation than other similar surgical procedures (Fig. L4). LASIK is an acronym made from the following italic letters 'laser in situ keratomileusis' or 'laser assisted intrastromal keratoplasty'. See corneal ectasia; epikeratoplasty; Intacs; keratome; keratomileusis; keratophakia; photorefractive keratectomy.
Fig. L4 LASIK procedure. A, an incision is made into the anterior part of the cornea leaving a hinge of intact margin (shown on the left). B, the corneal flap is rolled back leaving it attached at its hinge. Excimer laser ablation is performed on the expos corneaenlarge picture
Fig. L4 LASIK procedure. A, an incision is made into the anterior part of the cornea leaving a hinge of intact margin (shown on the left). B, the corneal flap is rolled back leaving it attached at its hinge. Excimer laser ablation is performed on the expos cornea
References in periodicals archive ?
The former are important for keratorefractive surgery since they couple mechanical forces between lamellae; the distribution of interweaving, sometimes referred to erroneously in the biomechanical literature as "cross-links" is shown in Figure 2.
Before the development of the excimer laser, incisional techniques were the mainstay of keratorefractive surgery.
Introduction of 193nm argon-fluoride excimer laser into clinical practice in the late 1980s rapidly changed keratorefractive surgery by enabling highly controlled removal of corneal tissue and so modification of corneal curvature.
In the case of excimer laser keratorefractive surgery, all of the longest follow up studies of myopic and hyperopic PRK demonstrate refractive stability.
In keratorefractive surgery, corneal shape is changed either indirectly by weakening the cornea or directly by selective tissue ablation.