An essay in Ophthalmology about "Refractive procedures". It was made in April 2017

1. Refractive procedures
2017
Mansoura university
Faculty of medicine
Ophthalmology department
 Prepared by:
Kareem Fisal Alnakeeb
 Supervised by:
Dr. Ayman Mohamed Fawzy
Dr. Samy Ali Aboulkhair
Dr. Adel El Layeh

2. page. 1
Introduction
- Refractive surgery encompasses a range of procedures aimed
at changing the refraction of the eye by altering the cornea or
lens, the principal refracting components.
- Myopia, hypermetropia (hyperopia) and astigmatism can all
be addressed, though correction of presbyopia is yet to be
achieved on a consistently satisfactory basis.
• Surface ablation procedures :
It can correct low–moderate degrees of myopia.
• Laser in situ keratomileusis (LASIK) :
It can correct moderate to high myopia depending on initial
corneal thickness,
But for very high refractive errors one of the intraocular
procedures below is necessary.
• Refractive lenticule extraction :
It is a newer technique for the correction of myopia and myopic
astigmatism.
• Clear lens exchange :
It gives very good visual results
But carries a small risk of the complications of cataract surgery,
particularly retinal detachment in high myopes.

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• Iris clip (‘lobster claw’) implant is attached to the iris (Fig. 1)
Complications include :
o subluxation or dislocation due to dislodgement of one or
both attachments (Fig. 2)
o An oval pupil
o endothelial cell loss
o cataract
o pupillary-block glaucoma
o retinal detachment.
• Phakic posterior chamber implant (implantable contact lens, ICL)
It is inserted behind the iris and in front of the lens , and
supported in the ciliary sulcus. (Fig. 3)
Fig.2 inferior subluxation with resultant
inferior endothelial decompensation – note
also an iridectomy to prevent pupillary block
Fig.1 Anterior chamber iris claw
implant with anterior iris attachment
at 3 and 9 o’clock

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-The lens is composed of material derived from collagen
(Collamer) with a power of −3 D to −20.50 D.
-Visual results are usually very
good
But complications include :
o uveitis
o pupillary block
o endothelial cell loss
o cataract formation
o retinal detachment.
• Radial keratotomy :
It is now predominantly of historical interest. (Fig. 4)
Fig.3 emplacement of a posterior chamber
phakic implant between the iris and anterior
lens surface
Fig.4 Radial keratotomy
(Courtesy of C Barry)

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• Surface ablation procedures :
It can correct low degrees of hypermetropia.
• LASIK can correct up to 4 D.
• Conductive keratoplasty (CK) :
It involves the application of radiofrequency energy to the
corneal stroma and can correct low–moderate hypermetropia
and hypermetropic astigmatism.
Burns are placed in one or two rings in the corneal periphery
using a probe.
The resultant thermally induced stromal shrinkage is
accompanied by an increase in central corneal curvature.
Significant regression may occur but the procedure can be
repeated. CK may also be helpful for presbyopia.
Complications are infrequent.
• Laser thermal keratoplasty with a holmium laser can correct
low hypermetropia.
Laser burns are placed in one or two rings in the corneal mid-
periphery (Fig. 5).
As with CK, thermally induced stromal shrinkage is
accompanied by increased corneal curvature.
Correction decays over time but treatment can be repeated.

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• Other modalities include :
✓ clear lens extraction
✓ phakic lens implants ( as described above for myopia )
- intraocular surgical procedures are the only options for high
degrees of refractive error.
• Limbal relaxing incisions/arcuate keratotomy :
involves making paired arcuate incisions on opposite sides of
the cornea (Fig. 6) in the axis of
the correcting ‘plus’ cylinder (the
steep meridian).
The resultant flattening of the
steep meridian coupled with a
smaller steepening of the flat
Fig.6 Arcuate keratotomies
(Courtesy of C Barry )
Fig.5 Thermal keratoplasty
(Courtesy of H Nano Jr)

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meridian at 90° to the incisions reduces astigmatism.
The desired result can be controlled by varying the length and
depth of the incisions and their distance from the optical centre
of the cornea.
Arcuate keratotomy may be combined with compression
sutures placed in the perpendicular meridian, when treating
large degrees of astigmatism such as can occur following
penetrating keratoplasty.
• PRK and LASEK can correct up to 3 D.
• LASIK can correct up to 5 D.
• Lens surgery involves using a ‘toric’ intraocular implant
incorporating an astigmatic correction (Fig. 7). Postoperative
rotation of the implant away from the desired axis occurs in a
small minority of cases.
• Conductive keratoplasty
(see ‘Correction of hypermetropia’ above).
Fig.7 toric intraocular implant in site – markings
incorporated in the lens (arrows) facilitate correct
orientation

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• Lens extraction, either to treat cataract or for purely
refractive purposes.
Acronyms used include clear lens exchange (CLE), refractive
lens exchange (RLE) and presbyopic lens exchange (PreLEx).
Much research effort is being applied to the development of
effective accommodating prosthetic lenses.
○ Implantation of a multifocal, bifocal or ‘accommodating’/
pseudoaccommodative intraocular lens implant (IOL) can
optically restore some reading vision; reading glasses
commonly still have to be used for some tasks.
Although many recipients of multifocal IOLs are very happy
with the visual outcome, dissatisfaction occurs in a significant
minority, mainly due to nocturnal glare and reduced contrast
sensitivity.
Around 10% of patients receiving multifocal IOLs subsequently
undergo higher-risk IOL exchange surgery. In some jurisdictions,
implantation of a multifocal IOL is a contraindication to the
holding of a private or commercial pilot’s licence, or to military
service.
○ ‘Monovision’ consists of the targeting of IOL-induced
refractive outcomes so that one eye (usually the dominant) is
optimized for clear uncorrected distance vision and the other
for near or intermediate vision, in order to facilitate both good
distance and near vision when the eyes are used together.

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○ Some studies show similar levels of functional near vision
using bilateral distance-optimized monofocal IOLs compared to
multifocal IOLs.
• Conductive keratoplasty (see ‘Correction of hypermetropia’
above); there is some evidence that CK can impart a degree of
multifocal functionality to the cornea.
• Laser-induced monovision refers to the use of laser refractive
surgery to optimize one eye for distance and the fellow for near
or intermediate vision (see above under ‘Lens extraction’).
• Corneal multifocality. Several different approaches are under
development utilizing a laser procedure to alter the shape of
the cornea such that a bifocal or transitional effect is induced.
• Scleral expansion surgery. Results have been inconsistent
and unpredictable and this technique has not achieved
sustained popularity.
• Intracorneal inlays (Fig. 8 A–D) commonly provide substantial
benefit in presbyopia, though in the past the biocompatibility
of some materials has been relatively poor, and complications
such as extrusion (Fig. 9) can mandate explantation.
• Laser modification of the natural lens. Research is ongoing
into the use of a femtosecond laser to modulate crystalline lens
elasticity.

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Fig.8 (A) and (B) Refractive inlay
Fig.8 (C) and (D) small aperture inlay – utilizes the pinhole effect
Fig.9 partial extruded refractive inlay
Source : Kanski’s Clinical Ophthalmology Book - A SYSTEMATIC APPROACH - EIGHTH EDITION 2016