LASERS in Ophthalmology

What is LASER ? L - Light A - Amplification by S - Stimulated E - Emission of R - Radiation

What is LASER ? Substances have the property to “lase” i.e.absorb energy in one form & emit a new form of light energy which is more useful.

LASER history A. Einstein: Laser possible C.H. Townes, A.L. Schawlow: Theoretical basis for lasers T. Maiman: Built first laser C. Zweng: First medical laser trial (retinal coagulation) W.Z. Yarn: First clinical laser surgery.

Basic Laser Components Laser tube and pump

Laser medium and pump Energy (electrical, optical, or chemical) from an external source - the LASER PUMP - interacts with a substance within the optical cavity - LASER MEDIUM – of a laser to cause energy emission. The substance can be a crystalline solid, a gas, a liquid containing a dissolved organic dye, or a semiconductor. When these electrons return to their original state, they emit photons with identical wavelengths characteristic of the particular substance. Mirrors at either end of the laser tube selectively reflect photons traveling parallel to the tube axis, which strike other atoms and cause the spontaneous emission of more photons of identical wavelength. Photons moving in other directions are absorbed or reflected by the sides of the tube. Eventually, the remaining photons pass through the partially reflective mirror at one end of the tube to the laser delivery system in a coherent beam (one in which all photons are in phase and moving in the same direction) of extremely high irradiance (power density measured in watts/cm2).

Types of Lasers

Tissue Interactions

How do Lasers affect the tissue? 1.Laser coagulation. The thermal effect of the laser radiation is used here, it gives a particularly pronounced therapeutic effect in vascular pathology of the eye: laser coagulation of vessels of iris, cornea, retina, trabeculoplasty, and the effects on the cornea with infrared radiation (1,54-2,9 m), which is absorbed by the stroma of the cornea, to change the refraction. Among different lasers which coagulate tissue, currently the most popular and commonly used is an argon laser. 2.Photodestruction (photodiscision). Thanks to the high peak power of the laser radiation the dissection of tissues became possible. It is based on an electro "breakdown" of tissue that occurs due to the release of large amounts of energy in a limited volume. In this case, at the point the laser plasma is formed, and this leads to the creation of a shock wave and of microscopic tearing of tissue. To get this effect we should use infrared YAG-laser. 3.Photoevaporation and photoincision. The effect is based on prolonged heat exposure to the evaporation of tissue. Used for this purpose infrared CO2 laser (10.6 m) to remove surface formations of the conjunctiva and eyelids. 4.Photoablation (photodecomposition). Is based on the d in the removal of biological tissue. It is an excimer laser operating in the hard UV range (193 nm). Application: refractive surgery, treatment of degenerative changes in corneal opacities, inflammatory disease of the cornea, pterygium surgery and glaucoma 5.Laser stimulation. For this purpose, in Ophthalmology used low-intensity red light He-Ne-laser. Found that the interaction of radiation with various tissues from complex photochemical processes are shown anti-inflammatory, desensitizing, resolving effects

Radiation Wavelengths 193 nm - Excimer (Cornea) nm- Argon (Retina) nm- Ruby nm - Diode 1064 nm- Nd Yag (Capsule) 10,600 nm- Carbon dioxide (Skin)

Delivery systems Most ophthalmic laser systems consist of a laser module - a laser medium, laser pump, and cooling system that is typically coupled to a slit-lamp biomicroscope by a flexible fiberoptic cable. Other laser-energy delivery systems include indirect ophthalmoscopes, intraocular probes, and interfaces for operating microscopes. The ophthalmologist views the structures within the patient’s eye and aims and focuses the laser through the optics of the slit lamp; when the laser is fired, the energy is delivered through these optics or through coaxial optics.

Uses Diagnostic Therapeutic

Diagnostic Uses Laser Fluorescence Spectroscopy Scanning Laser Ophthalmoscopy Laser Interferometry Fundus Fluorescein Angiography

Therapeutic Uses Widely Used - Extra-ocular adnexae i. Removal of lid masses ii.Orbitotomies iii. Blepharoplasty, Aesthetics (smoothen wrinkles) iv.Capillary hemangioma, Portwine stain Anterior Segment i. LASIK, PRK, PTK ii. Conjunctival / Corneal Growths, Neovascularisation iii. Cyclophotocoagulation iv. Reopen failed filtering blebs v. Iridoplasty, Gonioplasty vi. Iris cyst, Pupilloplasty vii. Posterior Capsular Opacification

Posterior segment