Retinal Lasers in Ophthalmology Dr. Atul Dhawan (M.S., F.E.R.C.) Vitreo-Retina Consultant Dr. Agarwal’s Retina Foundation Chennai
INTRODUCTIONLASER is an acronym for:• L : Light• A : Amplification (by)• S : Stimulated• E : Emission (of)• R : RadiationTerm coined by Gordon Gould.Lase means to absorb energy in one form and to emit a new form oflight energy which is more useful.
Incandescent vs. Laser Light1. Many wavelengths 1. Monochromatic2. Multidirectional 2. Directional3. Incoherent 3. Coherent
These three properties of laser light arewhat can make it more hazardous thanordinary light. Laser light can deposit alot of energy within a small area.
Two things to produce laser1. Population inversion2. Stimulated emission
Stimulated emission• Suppose an electron is in a higher energy level and a photon comes along with an energy equal to the difference between the electrons energy and a lower energy. What will happen is that the photon will stimulate the electron to fall into the lower energy state, thereby emitting a photon. This is pictured below.• The emitted photon will have the same energy as the original photon, and viewed as waves we will then have two waves emerging from the atom in phase with the same frequency. Such waves will constructively interfere, leading to a more intense wave.
Types of Lasers LASERS Gas Solid State Metal EXCIMER Dye Diode Vapour Argon Ruby Copper Argon Fluoride Krypton Nd Yag Gold Helium NeonCarbon Dioxide
Factors effecting retinal photocoagulation• Degree of scattering• Absorption of energy by ocular pigments• Spot size• Power used• Exposure time
Ocular pigments• Melanin: RPE, Choroid Argon Blue, Krypton Pan Retinal Photocoagulation Haemoglobin: Absorb blue,green and yellow but poor for red light. Argon Green are absorbed, Krypton yellow. These laser are found to be useful to coagulate the blood vessels.• Xanthophyll: Macular area Maximum absorption is blue
THREE BASIC LIGHT TISSUE INTERACTIONS(1) Photocoagulation: Laser Light transfer energy Target Tissue[absorption by ocular pigments] Generate Heat[transfer to tissue by thermal conduction] Denatures Proteins (Coagulation)Rise in temperature of about 10 to 20 0C will cause coagulation of tissue.
PHOTOCHEMICAL EFFECTPHOTORADIATION :• Hematoporphyrin Derivatives administerd i.v. are selectively taken up by metabolically active tissue. subsequently irradiated by rhodamine dye laser[630 nm] 72 hours injection .This leads to formation of singlet oxygen which is cytotoxic.e.g. Treatment of ocular tumour and CNV
THREE BASIC COMPONENTS A Laser Exciting Optical Cavity Medium Methods (Laser Tube)• e.g. Solid, • for exciting • around the Liquid or Gas atoms or medium molecules in which act as the medium a resonator e.g. Light, Electricity
MODES OF LASER OPERATIONContinuous Wave • It deliver their energy in a (CW) Laser: continuous stream of photons. • Produce energy pulses of a few Pulsed Lasers: tens of micro to few mili second. Q Switches • Deliver energy pulses of extremely Lasers: short duration (nano second). A Mode-locked • Emits a train of short duration Lasers: pulses (picoseconds).
IntroductionVascular obstructive disease of retina is a common vascular disorder, second only toDiabetic Retinopathy in incidence RVO Central retinal vein Branch retinal vein obstruction obstructionIschemic non ischemic
Venous Occlusion Causes elevation of venous and capillary pressure Stagnation of blood flow Hypoxia of involved retina Damage of capillaries endothelium Extra vasation of blood More pressure Further more stagnation Viscous cycle starts
C.R.V.O StudyQn. What is the natural history of eyes with perfused CRVO (<10 DD CNP areas) ?Ans. 1/3rd of eyes with perfused CRVO became non- perfused by 3 years Majority of eyes classified as indeterminate were non-perfused
C.R.V.O StudyQn. Does early PRP prevent NVI in non- perfused CRVO (>10 DD area CNP) ?Ans. Prophylactic PRP does not prevent Neovascularisation of iris or angle Careful monitoring of INV/ANV and prompt PRP is needed
C.R.V.O StudyQn. Does early PRP is more effective than delaying the Tt until ant. Segment neovascularization is first seen in preventing NVG?Ans. NO
C.R.V.O StudyQn. Does macular grid PHC improve V.A. in macular oedema due to perfused macular edema ?Ans. Grid PHC not recommended in perfused macular oedema.
PRP Protocol• 500 or 1000 µ size, duration 0.2 sec• Burns 0.5 – 1 burn width apart• More than 2 DD from center of the fovea till equator or beyond in all quadrants, nasally >500 µ from disc• Around 2000 spots• Avoid retinal hemorrhages or large retinal vessels
Treatment Recommendations – Non-perfused CRVO Nonperfused CRVO Nonperfused CRVO with TC-INV without INV/ANV or any ANV Panretinal PHCNo PRP unless monthly followup not possible Follow up every 2-4weeks If INV/ANV increases Supplemental panretinal PHC
Neovascularisation B.R.V.O In BRVO• Areas of CNP >5DD (NVD or NVE : first 3 yrs) – 60% do not develop NVE• 40% develop : NVE• 60% of NVE Vit. hge
• For this reason it is recommended that laser photocoagulation should be delayed till NVE develops.
B.R.V.O Recommendations 1. Vision 20/40 or less 2. Wait for 3-6 months: Clearance of Hges : Good FFA 3. Evaluation of FFA: Macular oedema Vs Ischaemia 4. Recommend grid treatment : Macular oedema FFA proven 5. Macular Non perfusion : No laser
Photocoagulation• Flat new retinal vessel: direct laser to vessel• Elevated neovascularization: laser the feeder vessel• NVD: Pan retinal photocoagulation• Capillary non perfusion area: scatter laser
HISTORY• First recognized by von Graefe in 1866 & named central recurrent retinitis• Different names given by diff. persons• ICSC given by Gass et al in 1967s
Idiopathic central serous chorioretinopathy (ICSC)• Patient is usually of Type A personality• Organ transplantation , pregnancy• Less common in high degree of myopia• Young 20—50 yrs• Male : Female 10 : 1 [ Age 30 – 50 yrs ]• Male : Female 2 : 1 [ Age > 50 yrs ]• WHITE > BLACK
SYMPTOMS• Sudden onset Blurring of vision• Metamorphopsia, micropsia• Seeing a dark patch (central scotoma )
Signs• Ophthalmoscopy—circumscribed round or oval area of retinal elevation at post. pole , outlined by a glistening reflex• Foveal reflex—Absent / attenuated
FFA• Pin-points site of RPED & site of leakage of serous fluid from RPE into SR space• In 95% of cases one area of leakage of dye are seen -INK BLOT APPEARANCE• Only in 10% cases the classic “smoke stack pattern” is seen due to convection currents & high sp. gr. of SR exudate
FFA• Majority of leaking sites are within 1 DD of fovea, but foveola is affected in < 10%• Incidence of leakage sites is greatest in upper nasal quadrant >lower nasal >lower temporal• 25% of leaks in PM bundle
TYPES OF ARMD• NON EXUDATIVE – (dry / non neovascular) – slowly progressive – 90% of ARMD• EXUDATIVE – (wet / neovascular) – less common – 88% of legal blindness due to ARMDBoth may occur in combination
Exudative AMDDrusen and AMD - progressionAtrophic AMD
Classical CNV•Well defined memb. fills with dye in “LACY”pattern in early phase, fluoresces brightly duringpeak dye transit then leaks into subretinal spaceand around CNV within 1—2 min•Fibrous tissue of CNV stain to give late Hyperf.•Subdivided into 3, with relation to foveola
Classical CNV 1. EXTRA-foveal >200 um from FAZ center 2. JUXTA-foveal <200 um from FAZ but sparing the foveola 3. SUB-foveal Involving foveola either by nearby extension or direct origin underneath(70% of CNV extend to subfoveal position within 1 yr)
Occult CNV • Poorly defined membrane gives late leakage Occult divided into two By MPS1. Fibrovascular RPED2. Late leakage of fluorescein from undetermined source
TREATMENT OF ARMD1. PHOTOCOAGULATIONFor complete oblitn of CNVFocal—Extra, Juxta, selected subfoveal CNVFor recurrent CNV similar parametersArgon Green laser(514 nm) recommended by MPS. Diode infrared if covered by thin haemorrhage
Disadvantages of laser T/t• Only for well defined CNV• Significant fall in VA depending on site• High recurrence rates• Benefit occurs after long period (months)• Breach of Bruch’s membrane can trigger similar pathgenesis as the ds. itself.
PHOTODYNAMIC THERAPY• Photochemical injury to the target• Drug is conc. in rapidly dividing cells & NV tissue• T1/2 of dye 5—6 hrs• Excreted in stools (urine not discolored)
• Singlet oxygen & free radicals damage cellular str. by platelet activation, vessel occlusion, destruction of fibrovascular tissue
PDT Photosensitizers— working at wave length• Benzoporphyrin derivatives (vertiporfin)-690• Tin ethyl etiopuritin (Purlytin)-664 nm• Lutetiutexaphyrin (Lu-tex)-732 nm
Eligibility criteria for PDT1. Lesions involving FAZ2. Lesion size < 5400 um3. CNV > 50% of the lesion4. Classic component >50% of CNV5. > 200 um from disc edge6. VA 20/200—20/40
C/I of PDT S/E of PDT Extravasation• Allergic to the dye Rash• H/O porphyria Headache• Severe liver disease VA reduction• Severe Heart disease Decreased fields Dry eye• Uncontrolled HT Conjunctivitis Cataract Hemorrhages
Procedure of PDT1. 15 mg visudyne powder + 7 ml dist. water2. Dark green soln (protect from light)3. Store at 20-25o C, use within 4 hrs4. Dose 6 mg/m2 . Dilute in 5% DNS to make 30 ml soln5. Inject 3 ml/min over 10 minutes6. Rinse IV line by 5 ml of 5% DNS7. After 15 min (the vessels fill completely)
Procedure of PDT8. Diode laser 689 nm9. 50—60 J/cm2 at intensity of 600 mw/cm210. Duration—83 seconds11. Spot size—GLD + 1000 um (GLDgreatest linear dimension of lesion by FFA)12. Protective dark glasses, hat, clothing & avoiding sunlight/bright light for 5 days