Yong Meng Hsien Lecturer & Ophthalmologist, UKM & HCTM, Malaysia yongmenghsien@ppukm.ukm.edu.my Last edited: Feb 202

1. About Light & Laser & Cryo
@Ophthalmology
Dr Yong Meng Hsien
Lecturer & Ophthalmologist, UKM & HCTM
yongmenghsien@ppukm.ukm.edu.my
Last edited: Feb 2022

2. Basic Sciences- Laser
• light amplification by stimulated emission of
radiation
• Components x 3: lasing/ionizing material,
energy source, optical cavity/reflector.
• Mechanism: population inversion, decay,
steady vs excited state, stimulated emission
• Characteristic: monochromatic, coherent/in
phase/directionality

3. Tissue Interaction
• Target Pigments
– Melanin (RPE)/Melanocyte (Choroid)
– Xanthophyll (Macula)
– Hemoglobin (vessels/h’rge)

4. Common Laser
• Argon
• Yellow
• double-frequency Nd-YAG
• Diode (TSCPC/ECP/TTT/portable LIO)
• Diode micropulse
• pulsed Nd-YAG (capsulotomy/vitreolysis)
• double frequency Q-switch Nd-YAG (SLT)
• PDT with verteporfin
• others: excimer (UV), CO2, femtosecond, TTT

6. VR Laser
Argon/diode/micropulse:
• PRP/sectoral/scattered
• Macular laser/grid/focal/sub threshold
• ARC
• Argon photocoagulation
• PDT

7. Laser
• Scatter- sector 400-500#, 200-500um, 0.05-0.1s
• Grid- leakage site (FFA) 50-100um, 0.1s
Disadvantage of threshold laser
• sublethally injured RPE cells adjacent to the areas of the
coagulation necrosis zone.
• collateral expansion (scar expansion up to 300%)
• photoreceptors damage
• CNV
• Subretinal/subfovea fibrosis
• long-term visual acuity decrease in up to 10% of eyes
• tritanopic color vision, dark adaptation, visual field
• decrease sensitivity within the central 12° of visual field (focal/grid)

8. Anterior retinal Cryopexy (ARC)
• Preparation
– cryoprobe 2.5mm
– anesthesia (peribulbar/GA)
– prefer peritomy/rectus muscle isolation
• Rule of 8
– 8mm from limbus (equator)
– 8-12 spots per quadrant (total 32-48)- divided to 3
rows (equator to vascular arcades)
– 8-10 sec duration (-76 degree Celsius)
– 80% success rate (reduce NeoV/IOP/VH)

9. PDT
• Verteporfin (Visudyne)
• Basic: photo-chemical/-radiation/-dynamic therapy with
chromophore/photosensitizer
• MoA: Bind LDL receptor (more in proliferating vessel/CNV)  free radical
 microthrombosis + occlusion @ abn vessel (endothelium)
• Set spot size (greatest linear diameter + 1000 μm if FFA, + 500um if ICG)
• Reconstitute 15mg powder with 7mL water  2 mg/mL solution
• Dose 6mg/m2 BSA + 5% glucose  30ml final solution
• IV over 10min  wait till 15 min
• Diode laser (689 nm) @ 600mW/cm2 x 83 seconds (=50J/cm2)
• Retreatment max 3mthly
• IPCV polyp/CNV/Choroidal hemangioma/retinal capillary
hemangioblastoma
• in wet ARMD subfoveal
– if it is 100% classic or predominantly classic
– or, 100% occult lesions with CNV 4 DD in size and/or with a recent decrease in
VA.

11. PDT Half Dose vs Fluence
• Half dose
– 3mg/m2 BSA
– Infusion 8min, start laser 10min
• Half fluence
– Laser power 300mW/cm2

12. Extrafoveal CNV Argon Laser
• if well demarcated
• confluent burns over the whole lesion and up
to 100 μm beyond its circumference.

14. CSCR Argon Laser
• Indications:
– persistence >6 months
– contralateral persistent visual defect from CSCR
– multiple recurrences
– occupational needs.
• Technique
– mild burns to the leakage site (usually <10 burns,
50–200μm, 0.1 sec)

15. Supra Scan Quantel Medical
-577nm Yellow Laser & Multispot-
• Setting
– PRP: 200-600mW x 200um x 20ms x lens magnification 2x
(400um)
– 2000-6000 spots for neoV
– Macular laser: 100-200mW x 100um x 10ms x lens
magnification 1x (area centralis)
• Advantages of yellow (577) vs green (532)
– Well absorbed by melanin & oxyHb, not by xanthophyl
– Less duration (higher power)- less thermal
effect/scar/inflam/CMO, less painful
– Less dispersion, more penetration (cataract), less glare

16. Subthreshold MicroPulse Laser Treatment (STMPL)
-Quantel Medical, 577nm Yellow Laser-
• Setting
– Monospot/multispot (no spacing=confluent)
– 160um x 0.2s (200ms) x 5% (duty cycle)
– Titrate power at periphery  50% reduction
• Features
– Train of laser pulse with ON time of 0.1ms then OFF
time of 1.9ms (5% duty cycle) x 100 pulse (in 200ms)
– No thermal effect/damage (OFF time allows heat
dissipation
– No lateral damage/spread

17. SMD (sub-threshold micropulse
diode)- PRP
• Diode > penetration, <scattering, mobile unit
• OcuLight SLx (IRIDEX), IQ 810 (IRIDEX) and the FastPulse (Optos
• 500μm aerial spot size, 0.20 second exposure duration, and a 15% duty
cycle
• with an initial power setting of 2,000mW.
• Around 1000 shots/session
• Laser “on” time was 100μs to 300μs and “off” time was 1,700μs to
1,900μs within
• an exposure duration of 0.1s to 0.3s. Power was initially adjusted upward
until a burn was barely visible and then
• adjusted to half that value for treatment. The overall number of burns
required was approximately 5,250 over
• three to four treatment sessions, with an average response time of 13
weeks

18. Glaucoma Laser
• Iris:
– LPI
– Laser iridoplasty
– Laser pupilloplasty
• CB
– TSCPC
– ECP
– Cyclocryo
• TM
– SLT/ALT/micropulse
• Others
– Laser suturelysis
– Nd YAG ant hyaloidotomy

19. Laser PI- Indications
(therapeutic & prophylactic)
* fellow eye: 50% chance for AACG in 5yr
Contraindications:
• Poor view (cornea/AC)
• PAS
• Patient factor (uncoorperate)

20. Laser PI- method
• consent/equipment/laser/CL (Abraham/Wise)
– Abraham: 66D planoconvex lens @decentered 8-mm hole, area
reduce 4x, energy at site 4x (Wise lens +102D/>magnification)
• Pre op: Alcaine/Pilo 1%/Alphagan
• Technique:
– location: peripheral 3rd (ant to arcus/thin iris/crypt/11 or 1 clock
nasal position)
– size: 200-500um
– Argon: 300-900mW, 50um, 0.05sec, angled beam 20-30#
– Nd/YAG: 1.7-6mJ, 2 Pulses per burst
– end point: Aq/pigment gush, AC deepening, Ant capsule seen
• Post op: IOP check 1h (>8 mmHg spike/>30), topical steroid
QID, TCA 1wk then 1mth (Dilate >8mmHg/gonio)
• Cx: double vision/glare, IOP spike, corneal burn, bleed,
inflam, failed Rx

21. Laser Iridoplasty
• IndiC pull/shrink peripheral iris  widen angle
(plateau iris, blocked trabec/tube, angle
closure- to clear view for LPI)
• Argon laser/Abraham lens
• 2-5 rule: 20–50 burns over 360* (with 2 spot
sizes between burns) of 200–500μm spot size,
0.2–0.5 sec duration, 200–500 mW power.
• Post procedure topical steroid (prevent PAS)

22. SLT
• Frequency doubled/q-switched/Nd:YAG/532nm
• Fixed pulse duration 3ns, spot size 400µm (entire width of TM)
• pulse energies ranging from 0.2–1mJ
• IndiC: OAG, PDS, PEXG
• less tissue disruption & repeatable
• preop- topical alcaine/pilocarpine/alphagan, Latina gonio lens
• Start at 0.5mJ at the 3 o’clock  titre till aim for a “champagne“
cavitation bubble  reduced by 0.1mJ at adjacent sites  until no
bubble formation  continue at this energy level
• 180˚ treatments of approximately 50 (48–53 spots) applications
@inferiorly from the 3-9 o’clock position.
• review IOP 1hour  topical steroid  IOP 6/52
• If need second SLT treatment  180 ˚ from 9-3 o’clock positions
(superiorly).
• SE: bleed/inflam/IOP spike/PAS, treatment failure

23. Other trabeculoplasty
• Argon/Diode ALT- 500nm
– Argon: #80–100(360*), 50μm spot size, 0.1 sec duration, 500–
1000 mW (light blanch of ant pigmented TM)
– Diode: 100μm spot size, 0.1–0.2 sec duration, 800–1200 mW
• Titanium:saphire TLT- 790nm (penetrate more deeply into
TM)
– #100, 30–120 mJ, 200 μm spot size
• Micropulse MLT- 810nm (short burst diode with less
thermal injury)
– MLT: #65–130, 2mW, 300 μm spot size, 2ms (0.3 ms on, 1.7 ms
off).

24. TSCPC/cyclodiode
• cyclo destructive procedure
• indiC: intractable high IOP esp NVG/PAS with poor visual
potential, unfit surgical candidate
• specific Cx: phthisis bulbi, SO, scleral thinning
• G probe (1-2mm from limbus, heel to limbus), illumination for
dark CB
• 270degree/3quadrant, 6#/quadrant, avoid 3&9 clock hour
(neurovascular bundle)
• setting: 200mW, 2000ms  pop sound (microablation of CB
epiT)  reduce power
• post op: topical steroid + analgesic, TCA 1day  1wk  IOP
6wk
• SE: fail Rx/reRx, hypotony/hypoypon/hyphaema, phthisical,
inflam/SO, scleral thin/necrosis, malignant glaucoma
• Alternative: ECP

26. ECP
• Intro: cyclodestructive
• Indication:
– refractory glaucoma
– early glaucoma for combine cataract op
– to reduce eyedrop dependence
• Equipment: Uram unit (endoscope/laser)
• Methods:
– Pre med: dilating drop, topical/intracameral LA
– Incision: >1.5mm/phaco wound @limbal or pars plana (PS)
– CB laser: distance 1-3mm, slow continuous  whitening/shrinkage 
270degree
• Post op:
– topical AB/steroid
– review IOP 1wk  6wk
• Cx:
– hypotony/pththisis/SO
– ciliary block glaucoma
• VS TSCPS- precise/time/recovery/Cx

27. Laser suturelyisis (LSL)
• Hoskins (no magnification) or Ritch
(magnification)
• 200mW/0.1 sec/50 μm

31. Laser for Diagnosis
• FAF
• FFA
• ICG
• OCT

32. Fundus autofluorescence (FAF)
• lipofuscin @RPE fluoresce when stimulated
with 488nm light
• SLO with barrier filter which blocks
wavelengths below 495nm
• Indirect measure of the activity of PRC & RPE

33. OCT
• diode laser (810nm)
• coherence interferometry for cross sectional
images

34. Anterior Segment
• Eye lashes/Eyelid
– Argon laser ablation
– cryoT
• Cornea
– CXL
– Ant stromal laser micropuncture

35. Argon laser ablation
• Indication: lashes d/o (trichiasis/distichiasis)
• Methods:
– 1st crater: 50um x 0.2s x 1000mW (on root)
– 2nd crater: 200um x 0.2s x 1000mW (on follicle)
– 1-2 sessions

36. Lash CryoT
• double freeze-thraw cycle @ -20degree Celsius
• Cx:
– necrosis
– madarosis (depigmentation)
– tylosis (lid margin notching)
– meibomian gland injury/dysfx

37. Others