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Laser in Ophthalmology1
GOOD MORNING
LASER in OphthalmologyLaser is an acronym for Light Amplification by Stimulated Emission of Radiation .
Laser are used in the management of many Ophthalmic conditions , particularly because so many ocular structures can be easily visualized & because of precision of laser delivery .4/14/2011
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• Stringent safety regulations must be applied because of the risk of laser damage to the eyes of patient , the operator and the bystander , so it is recommended to wear safety goggles when entering the Laser room.
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The Physics of Laser :
Energy is applied to a potential light source ,the applied energy excites atoms raising their electrons to a higher energy level.When an electron fall back to the lower energy level , it emits a photon of light.
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In a Laser instrument ,the process of excitation & photon release is controlled & synchronized so that an extremely bright light is emitted in which photons are of identical wavelength , are in phase ( at the same stage of wave cycle at any given point), and travel in parallel.
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Laser- Tissue interaction
1- Photocoagulation: conversion of Laser energy to heat ,with subsequent thermally induced structural changes in the target, e.g. Laser for diabetic retinopathy.2- Photodisruption
High-peak-power pulsed laser to ionize the target & rupture the surrounding tissues e.g. Nd-YAG Laser for peripheral iridiotomy.
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3- Photoablation:
A high powered ultraviolet laser pulses can precisely etch the cornea , e.g. Excimer Laser (193 nm ) used in refractive surgery.
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In summery:
Laser light is coherent : all photons have the same wavelength & in phase.The Laser beam is also collimated i.e. the waves of light are parallel & monochromatic.
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Clinical applications:
1- Diabetic RetinopathyLaser treatment of proliferative diabetic retinopathy( PDR) , and macular edema has revolutionized the progress of these diseases.
In PDR : ischemic retina stimulates the growth of abnormal “ New Vessels” which can bleed & cause retinal detachment ( RD).
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Proliferative diabetic retinopathy
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Diabetic macular edema
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Sever rubeosis iridis
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Laser for diabetic retinopathy
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Pan retinal photocoagulation ( PRP )
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Pan retinal photocoagulation PRP
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Argon or Diode Laser ablation of ischemic areas ( pan retinal photocoagulation) PRP , causes regression of neovascularization.
Certain types of Diabetic macular edema respond to gentle Argon Laser treatment.
Same principle applied in cases of Retinopathy of prematurity ( ROP ).4/14/2011
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Retinopathy of prematurity (ROP)
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2- Glaucoma :
Nd- YAG Laser peripheral iridotomy in angle closure glaucoma.Argon Laser trabeculoplasty in open angle glaucoma.
Diode Laser as a cyclodestructive procedure in Rebuotic glaucoma which occur in response to ischemic retina of PDR , and retinal vein occlusion.
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Laser in Ophthalmology
Argon Laser trabeculoplasty ( ALT)
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3- Posterior capsule opacification:
Posterior capsule thickening , also known as “ After cataract ” , is a common late complication of cataract extraction.
It occur as a result of proliferation & metaplesia of residual lens fibers attached to the capsule , symptoms include poor vision & glare.
The Nd-YAG Laser is used to create a central defect in the posterior capsule.
This does not affect the position or integrity of the Intraocular Lens Implant (IOL) .
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Laser in Ophthalmology
Posterior capsule opacity ( PCO )
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• 4- Age–related Macular Degeneration ( AMD):
• The growth of abnormal vascular tissue from the choroid into the subretinal spaces cause rapidly progressive sight loss.• This tissue can be destroyed by Argon Laser.
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Choroidal neovascular membrane(CNV) in AMD
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5- Retinal Detachment ( RD ) :
A retinal tear or hole without RD can be surround with laser to induce Adhesion & prevent RD.During RD Surgery , Laser is some times used as an alternative to cryotherapy to promote retinal adhesion.
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Retinal hole surrounded by laser
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6- Refractive Errors :
The Excimer Laser , applied with the computer assistance , very precisely remove corneal tissue in the management of low-moderate degree of myopia , hypermetropia & astigmatism combined with creation of hinged flap of cornea ( LASIK).
Larger Refractive Errors can now also successfully treated .
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Photorefractive keratectomy ( PRK )
IndicationsStable myopia up to 6D with astigmatism no more than 3D
Hypermetropia up to 2.5D
Main complication
Subepithelial haze which
usually resolves after 1-6
months
Reshaping of cornea by excimer laser ablation of
Bowman layer and anterior stroma
Technique
Laser in-situ keratomileusis (LASIK)Indications - similar to PRK but corrects higher degrees of myopia
Thin flap of cornea fashioned
Bed treated with excimer laser
Flap repositioned
Complications
Wrinkles in flap
Cellular interface proliferation
Technique
7- Miscellaneous uses :A- ablation of intraocular & adnexal tumors.
B- Division of intraocular post- inflammatory adhesions.
C- Destruction of aberrant lashes.
D-Removal of superficial corneal scars & calcific band keratopathy ( Excimer laser ) .
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Vitreous Body
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The transparent vitreous body, or hyaloid is one of the most delicate connective tissues in the body.
A. It occupies the posterior or larger compartment of the eye, filling the globe
between the internal limiting membrane of the neural retina and the posterior lens capsule.
B. The structure is composed of a framework of extremely delicate collagen filaments closely associated with a large quantity of water binding hyaluronic acid.
Anatomy of vitreous
Features:Virtually acellular viscous content of the globe.
Framework of collagen fibrils reinforced with hyaluronic acid molecules
98 % water.Volume = 4-5 ml in emmetropic eye.
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Anatomy o the vitreous body
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Attachments:
Vitreous base3-4 mm annular attachment
Very strong
Extends across ora serrata.
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The ora serrata
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Ageing changes:
Dissociation of hyaluronic acid from fibrils
Fibril degeneration & reduced elasticity.Drainage of hyaluronic acid into retrovitreal space ( producing posterior vitreous detachment PVD).
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Vitreous opacities:
1- Muscae volitantes: remnants of hyaloid system.2- Syneresis: the Weiss ring ( posterior vitreous detachment PVD )
3- Hemorrhage
4- Asteroid hyalosis
Appears in 1 in 200 eyes
Composed of calcium soaps adherent to fibrils
Does not settle at rest
More common in diabetic people.
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Asteroid hyalosis
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5- Synchisis scintillans
6- Inflammatory cells: Pars planitis, Chorioretinitis7- Neoplastic
8- Amyloid
9- Tobacco dust in retinal detachment :pigment cells.
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Amyloid deposit in the vitreous
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Tobacco dust ( pigment cells in the vitreous)
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Vitreous degeneration
1- Syneresis:Vitreous liquefaction
Aggregation & condensation of collagen fibrils
Associated with floaters
Causes:
Myopia , senescence , trauma , inflammation , hereditary e.g. Stickler’s disease
2- Detachment
Collapse of vitreous gel
Associated with floaters and photopsia
Causes:
Senile , myopia , post inflammatory, postvitrous hemorrhage , and diabetic retinopathy.
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Posterior vitreous detachment (PVD )
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Vitreous hemorrhage ( VH )
1- causes:Proliferative retinopathy: DM , retinal vein occlusion, sickle cell retinopathy and retinopathy of prematurity.
Posterior vitreous detachment PVD
Trauma
Disciform macular degeneration
Blood dyscrasias
Subarachnoid hemorrhage ( Terson’ s syndrome)
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Vitreous Hemorrhage
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2- Complications
SyneresisInflammation & fibrosis : leads to traction detachment
Haemosiderosis
Synchisis scintillans:cholestrol crystals ; settles inferiorly at rest.
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Indications for Vitrectomy
1- Anterior segment conditions:Incarceration of vitreous in cataract section
Vitreous touch causing bullous keratopathy
Accidental vitreous loss during surgery
Lensectomy e.g. for secondary cataract in childhood arthritis
Malignant glaucoma
Glaucoma drainage surgery in aphakic eye.
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2- posterior segment conditions:
Diabetic disease:
Persistent hemorrhage, rubeosis with poor view, tractional RD involving macula.
Trauma: foreign body retrieval , dislocated lens, vitreous hemorrhage, giant tears
Complicated RD:gaint tear, proliferative vitreoretinopathy, large retinal breaks.
Endophthalmitis
Vitreous biopsy e.g. Amyloid.
Idiopathic macular hole.
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Thank you