1 - Asimellis Flashcards
Ophthalmic lasers provide good examples of 3 fundamental laser applications based on (4)
Total output energy
Output power
Photon energy
Spectral transmission
Vitreolysis
- purpose/what it is
- aka/layman’s term
A non-invasive procedure that can relieve the visual disturbance caused by symptomatic floaters via vaporization
Floater laser removal
Floaters
- part of what happens in __
- cause __ light scattering
Aging eye
Foward light scatter
Vitreolysis -laser/pulse type —state —lasing medium —wavelength
Low-energy nanosecond pulsed Nd:YAG -solid state -Nd:YAG crystal medium -1064 nm (near IR) —frequency doubled is 532 (green)
Photocoagulation
- describe
- temperatures
- what happens to the tissue
Tightly focused energy interacts with tissue, slowly heats blood/tissue, destabilizing proteins and other biomolecules (bloodless in/excision)
As a blood clot forms, tissue coagulation of 50-100 C is photocoagulation
Shrinks the tissue due to water removal; the tissue is burned and neutered
Floaters
-most serious type
Weiss ring
- created by PVD around optic nerve
- often position selves right above macula
Vitreolysis
-other option
Vitrectomy (surgical replacement of the vitreous with an inert, translucent balanced salt solution via pars plana)
CPC = cyclophotocoagulation
- describe
- purpose
Cyclodestructive procedure that ablates the ciliary body epithelium
Lower IOP by decr fluid production (by detachments of CB)
CPC = cyclophotocoagulation
-variations:
—less invasive
—more precise
Transscleral CPC = less invasive
Endoscopic CPC = more precise
CPC = cyclophotocoagulation
-considerations (2)
A single tx may not achieve adequate IOP control, repeat tx may be needed
Occassionally results in excessive lowering of pressure
Retinal lasers
-laser used for PRP in pts with diabetic ret or retinal ischemia/NV
FD:YAG (532nm)
PRP
- purpose
- part of retina that absorbs the light
- effect of absorption on retina
Retinal ischemia, retinal NV, NPDR
Pigment epi (RPE)
Denatures tissue protein via thermal burns (“bombards the retina”)
-scarring “welds” the retina to underlying tissue
PRP
-pathophys of how it helps with ischemia
Improves oxygenation
Destroys largely unused, ischemic extramacular retina -> reduces area of ischemic tissue -> reduces total VEGF production -> reducing impetus for NV
PRP for diabetic ret study
-results
Early PRP reduces risk of severe visual loss by ~23%
PRP
-retinal laser considerations
Anatomic effects - want to avoid complications due to dispersion of thermal energy within retina and choroid
Multispot pattern - greatly mitigated, but not eliminated these issues
The femtosecond laser
- wavelength and pulse
- energy
- focus in eye
1053m (IR), 10^15 sec pulse (ultrashort)
Each photon = 1.17eV
-recall 3.5eV is threshold for biological tissue damage (UV)
IR can be focused anywhere within or behind the cornea (very low absorption from ocular tissue)
The femtosecond laser
-2 major advantages vs longer pulses (e.g. nanosecond)
Reduced pulse energy necessary to induce ablation (due to power density)
Significant reduction of heat-affected zone -> improved contour/sharpness for laser-processed structures
The femtosecond laser
-example of a sx it’s used for
Cataract removal = “femtosecond laser assisted caratact surgery”
Laser vision correction
- microns per D
- residual bed
- SE
~15 microns per D
Residual bed ~300 microns
Weakend cornea = HOA
Laser vision correction
-myopia correction calculation
Munnerlyn formula:
Ablation depth = (optical zone)^2 * (myopia correction/3)
Laser vision correction
-type of laser usually used
Excimer (photoablation)
Excimer laser
- state
- lasing medium
- wavelength
- energy
Gas
Excited dimer - a noble gas and halide (EXCited diMER)
Depends on the molecules used, usually in UV (193nm)
6.4eV
Steps of LASIK
Flap creation via femtosecond laser (~120nm)
Lift flap
Excimer laser ablation of tx area
Steps of SMILE
2 lamellar cuts (creates a lenticule)
Lenticule separation and removal
Other ophthalmic laser procedures
-PTK (phototherapeutic keratoplasty)
—should be limited to __
Anterior corneal pathology only
-deeper scars need deeper ablations, may result in haze or hyperopic shift
Other ophthalmic laser procedures
-ASP (anterior stromal puncture)
—indication
—laser type
RCE
Nd:YAG
Other ophthalmic laser procedures
-LSL (laser suture lysis)
—one of the most frequently employed techniques for post-op IOP control is __
Partial release of the flap by LSL
Other ophthalmic laser procedures
-oculoplastic surgery
—laser
CO2
Other ophthalmic laser procedures
-briefly, what is photomydriasis/photomiosis
Extension/reposition of the pupil
Laser coagulates are applied on iris circularly/within a region opposite to pupil displacement
Other ophthalmic laser procedures
-anterior synechiolysis/synechiarrhexis
Elimination of iridolenticular synechiae after ct extraction with Nd:YAG
Future of ophthalmic lasers
-one that he hit on
Blue femtosecond laser
