Lasers in ophthalmology

Lasers in ophthalmology , mainly discussing retinal lasers here. Recent advances in retinal lasers.

1. Retinal Lasers Dr. Anuraag Singh 04-08-2018

2. What is Laser? L : Light A : Amplification (by) S : Stimulated E : Emission (of) R : Radiation Term coined by Gordon Gould . Lase means to absorb energy in one form and to emit a new form of light energy which is more useful.

3. LASER history 1917 -Sir Albert Einstein created the foundations for the laser.

4. Concept of laser/light sources in ophthalmology came from????????

5. The concept of ocular therapy using light first was publicized by Meyer- Schwickerath , who took patients to the roof of his laboratory in 1949 and focused sunlight on their retinas to treat melanomas. But ,…required sunny weather Thus, nonsolar sources. Carbon arcs were used; by the mid-1950s, the xenon arc photocoagulator had been developed and was made commercially available by Zeiss. BUT, …Strong visible and infrared emission leads to intense retinal burn

6. A  MASER (microwave amplification by stimulated emission of radiation) is a device that produces  coherent   electromagnetic waves  through amplification by  stimulated emission . The first maser was built by  Charles H. Townes , James P. Gordon, and H. J. Zeiger at Columbia University in 1953

7. 1960 - Theodore Maiman : Built first laser by using a ruby crystal medium .

8. 1963 - C. Zweng : First medical laser trial (retinal coagulation). 1965 - W.Z. Yarn: First clinical laser surgery. 1970- The excimer laser was invented in  by  Nikolai Basov 1971 -Neodymium yttrium aluminum garnet (Nd.YAG) and Krypton laser developed. 1983 : Trokel developed the eximer laser.

9. PROPERTIES OF LASER LIGHT Monochromatic (emit only one wave length ) Coherence (all in same phase -improve focusing ) Polarized (in one plane -easy to pass through media) Collimated (in one direction & non spreading ) High energy (Intensity measured by Watt J/s)

10. LASER PHYSICS Light as electromagnetic waves, emitting radiant energy in tiny package called ‘quanta’/photon. Each photon has a characteristic frequency and its energy is proportional to its frequency. Three basic ways for photons and atoms to interact: Absorption Spontaneous Emission Stimulated Emission

11. Absorption E 1 E 2

12. Spontaneous Emission

13. Stimulated Emission

14. CLASSIFICATION OF LASER Solid State Ruby Nd.Yag Erbium.YAG Gas Ion Argon Krypton He-Neon CO 2 Metal Vapour Cu Gold Dye Rhodamine Excimer Argon Fluoride Krypton Fluoride Krypton Chloride Diode Gallium-Aluminum Arsenide (GaAlAs)

15. TYPES OF OPHTHALMIC LASERS

16. THREE TYPE OF OCULAR PIGMENT Haemoglobin : absorbs blue, green and yellow with minimal red wavelength absorption , Argon Green are absorbed , Krypton yellow. useful to coagulate the blood vessels. Xanthophyl l : Macular area, Lens Maximum absorption is blue. minimally absorbs yellow or red wavelengths. Argon blue is not recommended to treat macular lesions. Melanin: RPE, Choroid absorbs green, yellow, red and infrared wavelengths Pan Retinal Photocoagulation, and Destruction of RPE Effective retinal photocoagulation depends on how well light penetrates the ocular media and how well the light is absorbed by pigment in the target tissue

17. LASER TISSUE INTERACTION LASER TISSUE Thermal Effect Photo-chemical Ionizing Effect Photocoagulation Photoradation Photodisruption Photoablation Photovaporization

18. Thermal Effects (1) Photocoagulation: Laser Light  Target Tissue  Generate Heat  Denatures Proteins (Coagulation) Rise in temperature of about 10 to 20 C will cause coagulation of tissue.

19. How does panretinal photocoagulation work? Sublethally injured RPE cells that surround areas of photocoagulation necrosis and produces significant thinning of the outer retina. By decreasing the oxygen consumption at the photoreceptor–RPE complex , more oxygen is available to diffuse into the inner retina and vitreous. Enhanced oxygen diffusion into the inner retina and vitreous reduces inner retina ischemia and the stimulus for neovascularization .  PRP reduces retinal ischemia and the hypoxia-induced expression of VEGF.

20. Thermal Effects (2) Photodisruption : Mechanical Effect: Laser Light  Acoustic Shockwaves  Tissue Damage Contd. …

21. Thermal Effects (3) Photovaporization Vaporization of tissue to CO 2 and water occurs when its temperature rise 60—100 C or greater. Commonly used CO 2  Absorbed by water of cells  Visible vapor (vaporization)   Heat Cell disintegration   Cauterization Incision eg .. Femtosecond laser

22. Photochemical effcts Photoablation : Breaks the chemical bonds that hold tissue together essentially vaporizing the tissue, e.g. Photorefractive Keratectomy , Argon Fluoride ( ArF ) Excimer Laser . Usually - Visible Wavelength : Photocoagulation Ultraviolet Yields : Photoablation Infrared : Photodisruption Photocoagulation Contd. …

23. PHOTOCHEMICAL EFFECT Photoradiation (PDT): Also called photodynamic therapy . E.G. Treatment of Ocular tumours and CNV Photon + Photo sensitizer in ground state (S)   Molecular Oxygen Free Radical S + O 2 (singlet oxygen) Cytotoxic Intermediate   Cell Damage, Vascular Damage , Immunologic Damage

24. Delivery systems Transpupillary: - Slit lamp - Laser Indirect Ophthalmoscopy Trans scleral : - Contact - Non contact Endophotocoagulation.

25. Slit lamp biomicroscopic laser delivery Most commonly employed mode for anterior and posterior segment. ADVANTAGES : Binocular and stereoscopic view. Fixed distance. Standardization of spot size is more accurate. Aiming accuracy is good.

26. Laser indirect ophthalmoscope. Advantages : Wider field(ability to reach periphery). Better visualization and laser application in hazy medium. Ability to treat in supine position.(ROP/EUA) Disadvantage : difficulty in focusing. Difficulty to standardize spot size. Expensive. Un co-operative patient. Learning curve.

27. Retinal lasers- Types and uses

28. Lens Uses Image Spot magnification Field of view Goldmann Macula Equator Periphery Virtual Erect 1.08 36⁰ Volk Supermacula 2.0 Macula Real Inverted 2.15 70⁰ Mainster High magnification Macula Real Inverted 1.34 75⁰ Volk area centralis Macula Equator Real Inverted 1.13 82⁰ Mainster Standard Macula Equator Real Inverted 1.03 90⁰ Panfundoscopic Equator Periphery Real Inverted 0.76 120⁰

29. Lens Uses Image Spot magnification Field of view Volk transequator Equator Periphery Real Inverted 0.75 122⁰ Mainster wide field Equator Periphery Real Inverted 0.73 125⁰ Volk Quadr Aspheric Equator Periphery Real Inverted 0.56 130⁰ Mainster Ultra field PRP Equator Periphery Real Inverted 0.57 140⁰ Volk SuperQuard 160 Equator Periphery Real Inverted 0.56 160⁰

30. Uses- Therapeutic Diabetic retinopathy Diabetic maculopathy Retinal vein occlusion Retinopathy of prematurity Choroidal neovascularization (CNV) Retinal lesions predisposing to detachment and retinal tear Eales ’ disease Central serous chorioretinopathy Retinal artery macroaneurym Coats’ disease Retinal capillary hemangioma Choroidal hemangioma Choroidal melanoma YAG Laser hyaloidotomy Optic disc pit

31. Uses- Diagnostic Scanning laser ophthalmoscopy Optical coherence tomography

32. Uses Diabetic Retinopathy – Pan-retinal photocoagulation. Indications : High risk PDR Early PDR or very severe NPDR in Patients with poor compliance During pregnancy Patients with systemic diseases Pending cataract surgery One-eyed patients

33. Type of laser : PRP with Argon (green-514nm wavelength) Laser delivery system : Indirect ophthalmoscope and +20 D lens Laser parameters : Spot size: 200-500 μ Pulse duration: 100 ms Power: 200-250 mW (goal is to produce grey burn) Spacing: 1-1.5 burn width apart

34. Number of sittings : 3 PRP I: Inferior and nasal retina PRP II: Temporal retina PRP III: Superior retina

35. Complications Transient: headache, blurring of vision, macular edema Persistent: nyctalopia , accomodative defect, reduced contrast sensitivity, photophobia, reduced visual fields PVD induction Inadvertent foveal burns

36. Diabetic maculopathy : Indication: Clinically significant macular edema Basic guidelines All areas of macular thickening must be treated FFA is done to look for points of leakage Focal leak → focal laser photocoagulation Diffuse leak → grid photocoagulation Laser delivery system: Slit lamp

37. Focal laser Direct laser to microaneurysm >500 μ m from centre of fovea Laser parameters: Spot size: 50-100 μ Duration: 50-100 ms Power- titrated to whiten microaneurysm Grid laser Laser to area of diffuse leakage & capillary non-perfusion on FFA Laser parameters: Spot size: 50-200 μ Duration: 50-100 ms Power: titrated to achieve mild burn Laser is done in C-shaped manner within the vascular arcade & avoiding area of papillomacular bundle

38. Retinal vein occlusion Indication: Macular edema V/A: <20/40 (after 3 months) Large segment of capillary non-perfusion(>5 DD) Neovascularization Contraindication: Macular ischemia

39. Type of laser: Grid laser - for macular edema Laser parameters: Spot size: 50-200 μ m Duration: 50-100 ms Power: titrated to achieve mild burn Sectoral photocoagulation - for neovacularization Laser parameters Spot size: 200-500 μ m Pulse duration: 100 ms Power: 200-250 mW Area: beyond 2 DD from centre of macula upto equator

40. Retinopathy of prematurity Indications: Stage I, Zone I with plus disease Stage II, Zone I with plus disease Stage III, Zone I with plus disease Stage III, Zone I without plus disease Stage II, Zone II with plus disease Stage III, Zone II with plus disease Type of laser: PRP (with LIO)

41. Laser parameters: Spot size:200-500 μ m Power: 300-400 mW Duration: 300-400 ms Aim is to ablate the entire avascular retina from the ridge upto the ora serrata in a near confluent burn pattern getting as close to the ridge as possible.

42. Complications : Premature infants are prone to develop apnoea. Conjunctival chemosis . Subconjunctival hemorrhage due to excessive scleral indentation. Rarely cataract formation. Intense photocoagulation may lead to anterior segment ischemia and necrosis resulting in hypotony and phthisis bulbi .

43. Choroidal neovascularization (CNV) Conventional(direct) laser: Type of laser: 532 nm frequency doubled YAG or argon green (514 nm) Technique: The membrane is first delimited by moderate intensity non-confluent laser spots extending to at least 100 μ of the surrounding normal retina Subsequently, intense confluent burns are applied to the membrane per se until uniform whitening is observed

44. Laser parameters Extrafoveal Characteristics Border Membrane Treatment area Spot size 100-200 μ 200 μ 100 μ beyond hyperfluorescence on FFA Duration 100-200 ms 200-500 ms Intensity Moderate Intense

45. Juxtafoveal Characteristics Border Membrane Treatment area Spot size 200 μ 200 μ Confined to hyperfluorescence on FFA Duration 200-500 ms 200-500 ms Intensity Moderate Intense

46. Subfoveal Characteristics Border Membrane Treatment area Spot size 200 μ 200 μ Confined to hyperfluorescence on FFA Duration 200 ms 200-500 ms Intensity Intense Intense

47. Photodynamic therapy: Dosage : 6 mg/m2 of verteporfin infused intravenously The amount of dye calculated is given over 10 minutes ( infusion phase ) and then a further 5 minutes are allowed for the dye to accumulate ( accumulation phase ). After this 15 minute interval, the choroidal membrane complex is exposed to low energy diode laser light (689 nm) for 83 seconds.

48. This activates the dye accumulated with the neovascular complex and results in its closure. Spot size is 1000 more than the greatest linear dimension (GLD) of the choroidal membrane identified in the early angiographic frame (for classic membranes) Complications: Visual disturbances Photosensitivity reactions Overdosing- macular infarction In case of extravasation- backache and allergic reactions

49. Transpupillary Thermotherapy: Advantage over conventional laser : Compared to the 40⁰ temperature elevation with conventional laser photocoagulation, TTT causes a 10⁰ rise of temperature, so minimizing collateral damage Type of laser : Slit lamp with a modified diode(810nm) laser Laser parameters Initial treatment Spot size: 3mm Duration: 60 s Power: 800mW

50. If a change in colour of retina is noted, then the power is reduced by 20% until no colour change is seen for entire 60 sec duration. Transscleral Diode Laser Photocoagulation Procedure: Under aseptic conditions and peribulbar anesthesia Lateral rectus muscle bridled after doing a limited peritomy temporally Intermuscular septa on either side dissected and then the diopexy probe was introduced

51. Test burns are applied to the temporal retina and the time taken to obtain a visible burn noted The probe is then gently guided to the submacular area under indirect ophthalmoscopy Control burn is applied to the region of the membrane as determined by site of leakage seen on early phase of FFA Conjunctiva closed with 6-0 vicryl interrupted sutures Subconjunctival gentamicin plus dexamethasone injection given.

52. Retinal lesions predisposing to detachment and retinal tear Indications: Presence of symptoms- Floaters, flashes and blurring of vision Focal vitreo -retinal adhesions Presence of non-traumatic retinal detachment in fellow eye Large tear(>2 DD), posterior tear, superior tear, U-shaped or flap tear Family history of retinal detachment

53. Purpose: To induce a sterile inflammation which stimulate proliferation of the RPE → indirectly improves adhesion between the RPE and the neurosensory retina. Laser delivery system: Slit lamp with contact lens or LIO Principle: The entire perimeter of the break should be surrounded by laser application. Particular attention to the anterior margin and horns of a tear should be paid.

54. In the presence of a rim of fluid or in subclinical detachment, laser is applied to the attached retina immediately around the detachment. If applied to the area of detachment, it may cause further progression of the detachment. Laser treatment of an inflamed retina is avoided as there is a risk of producing a retinal break Laser parameters : Two-three rows of confluent burns Spot size: 200-500 μ m Mild to moderate burn intensity

55. Eales’ disease: It is an idiopathic, inflammatory peripheral vasculitis characterised by retinal periphlebitis and capillary non-perfusion leading to hypoxia Indications : Neovascularization elsewhere Neovascularization disc Neovascularization iris Laser delivery system: LIO, Slit lamp

56. NVD → PRP Single NVE → sectoral scatter photocoagulatio NVI → PRP Laser parameter: Spot size: 200-500 μ Pulse duration: 100 ms Power: 200-250 mW

57. Central serous chorioretinopathy Focal laser photocoagulation (extra-foveal leakage) Indications: Non-resolving or recurrent CSCR with V/A: <6/12 Well defined leakage on FFA, atleast 500 μ away from centre of fovea Laser parameters: Spot size: 100- 200 μ Duration: 100-200 ms Power: 100-200 mW

58. Photo dynamic therapy (PDT)- foveal leakage Standard/conventional PDT Dose : 6mg/m2 infusion of vertiporfin over 15 min followed by delivery of laser 692nm 15 min after commencement of infusion Total light energy : 50J/cm2, delivered in 83 sec (photosensitisation time) Complications : CNV development Post-treatment visual loss Potential choroidal ischaemia Safety enhanced PDT Dose : 3mg/m2 infusion of vertiporfin over 8 min followed by delivery of laser 692nm 10 min after commencement of infusion Total light energy : 50J/cm2, delivered in 83 sec (photosensitisation time)

59. Retinal artery macroaneurym : These are solitary, saccular or fusiform dilation (diameter:125 -250μ) of the retinal arteriole involving usually, the first three divisions. Two forms: acute & chronic Acute form: sudden loss of vision due to retinal or vitreous hemorrhage Chronic form: gradual loss of vision due to leakage and exudation into the macular area Laser photocoagulation is required for chronic forms

60. Laser parameters : Spot size: 200-300 μ Duration: 200-500 ms Power: 200mW Direct treatment : laser is focused directly on the macroaneurysm so as to obtain slow and gentle whitening In indirect treatment : laser burns are placed around the aneurysm

61. Coats’ disease : Idiopathic retinal telangiectasia associated with intraretinal and subretinal exudation and frequently exudative retinal detachment, without signs of vitreoretinal traction Indication: Severe vascular anomalies with macular exudation Exudative retinal detachment Vascular anomalies posterior to equator Neovascularization Type of laser: LIO/ Slit lamp

62. Laser parameters: Spot size: 200-500 μ Power: 200 mW Duration: 200-500 ms End point: whitening of lesion

63. Retinal capillary hemangioma : Vascular hamartoma Indication: All capillary hemangiomas except those touching the optic nerve head Type of laser: Argon green or frequency doubled YAG Laser parameters: Spot size: 200-500 μ Duration: 0.2- 1.0 s Power: titreted to produce mild-moderate whitening of lesion. Small lesion → direct treatment Large lesion → treatment of feeder vessel

64. Choroidal hemangioma : Vascular hamartoma Manifest in two forms: diffuse & circumscribed Indication: Serous retinal detachment Aim of treatment: achieve resolutioon of serous retinal detachment and not tumor obliteration Conventional laser: entire tumor surface is covered with laser spots

65. PDT: 6 mg/m2 of verteporfin dye is injected intravenously Laser parameters Spot size: 6000 μ (maximum) Laser used 689 nm Type of laser delivery: Slit lamp Lens used: Mainster wide field lens In peripapillary choroidal hemangioma , laser spot is applied at a distance of 200 μ from the optic disc edge Large lesion(>2 mm) radiant exposure of 100 J/cm2 with exposure of 186 seconds Small lesion(<2 mm) radiant exposure of 75 J/cm2 with exposure of 125 seconds

66. Choroidal melanoma: commonest primary malignant intraocular tumors , arising from choroidal melanocytes. Indication: Tumor size: <15 mm basal diameter & thickness <5mm Type of laser: Argon laser photocoagulation

67. YAG Laser hyloidotomy : Indications: Premacular haemorrhage secondary to diabetic retinopathy, aplastic anemia , Terson’s syndrome, Valsalva retinopathy, vasculitis , ruptured retinal artery macroaneurysm , retinal vascular occlusions Persistent premacular haemorrhage beyond 4 weeks Size of harmorrhage : >3 DD Absence of retinal proliferation(If present PRP is done first)

68. Type of laser: Slit lamp Technique: The cone angle is set at 10⁰ and laser energy is focused above the inferior extent of the haemorrhage to facilitate gravity-aided drainage of blood into the vitreous cavity Begin with an energy of 1.5 mJ using single pulse. 5-6 spots required to create a dehiscence and 8-10 spots of lower energy to achieve drainage of the blood.

69. Complications: Non-resolving vitreous haemorrhage Creation of retinal holes Retinal detachment

70. Optic disc pit: Indication: Associated serous macular detachment Laser photocoagulation along the temporal margin of optic disc.

71. Recent advances PASCAL(Pattern scanning laser) Semi-automated laser delivering device Allows for a pattern of 4-56 burns to be applied in <1 sec using a scanning laser with shorter pulse duration Indicactions : Diabetic retinopathy(PDR &NPDR) Choroidal neovascularization(CNVM & SRNVM) Age-related macular degeneration Retinal vein occlusion(BRVO &CRVO) Retinal tear, holes Retinal detachment

72. Laser source: Nd:YAG laser Delivery system: Slit lamp or LIO Laser parameters Spot size: 200 μ Duration: 20 ms Power: 300-750 mW

73. Advantages : Safe Relatively painless Less time consuming Well tolerated More number of spots in single sitting Requires less number of sitting

74. Navigational lasers 532-nm pattern-type eye-tracking laser integrates live colour fundus imaging, red-free and infra-red imaging, FFA with photocoagulator system. After image acquisition and making customized treatment plans by physicians including marking areas which will be coagulated the treatment plan is superimposed onto the live digital retina image during treatment The physician controls laser application and the systems assist with prepositioning the laser beam.

75. Advantages over conventional lasers : Fast Painless Better documentation Wide field viewing system allows for better accuracy

76. Sub-threshold micropulse laser The familiar " grayish " endpoint of conventional threshold photocoagulation is typically associated with thermal elevations of 20-30°C, which cause coagulation necrosis and characterize the treatment as a supra-threshold photocoagulation. The spreading and decaying thermal wave inevitably reaches the tissues surrounding the burn and this causes the laser burn to expand. Using a micropulse mode, laser energy is delivered with a train of repetitive short pulses (typically 100 to 300 microseconds “on” and 1700 to 1900 microseconds “off”) within an “envelope” whose width is typically 200 to 300 milliseconds. Micropulse power as low as 10% to 25% of the visible threshold power has been demonstrated to be sufficient to show consistent RPE-confined photothermal effect with sparing of the neurosensory retina on light and electron microscopy.

77. Sub-threshold micropulse laser Tissue-sparing protocols are designed to produce only subtle thermal elevations with effects that are invisible during treatment and remain so thereafter. The inner retinal temperature must remain below the threshold of coagulative damage for the retina to maintain its natural transparency.

78. Sub-threshold micropulse laser Lower energy per pulse reduces peak power, lowers the risk of hemorrhage , decreases the temperature buildup per pulse, and ultimately results in improved confinement of photothermal effects. Absence of chorioretinal laser damage may permit high-density therapy with confluent applications over the entire edematous area and retreatment of the same areas. This may be particularly useful for the as-needed treatment of macular edema .

79. Subthreshold micropulse laser therapy with yellow (577 nm) laser Now, it is possible to deliver a subthreshold micropulse laser that is above the threshold of biochemical effect but below the threshold of a visible, destructive lesion thereby preventing collateral damage. The 577 nm wavelength occurs outside the absorption spectrum of retinal xanthophylls, potentially allowing for treatment close to the fovea.

80. Subthreshold micropulse laser therapy with yellow (577 nm) laser It also has the highest oxyhaemoglobin to melanin absorption ratio and therefore, is the most effective laser for vascular structures. The combined absorption by both melanin and oxyhemoglobin of 577 nm causes lesser scatter compared to 532 nm or other yellow wavelengths (561/568 nm). This leads to energy concentration to a smaller volume allowing use of lower powers and shorter pulse durations.