Investigation of Laser-Induced Retinal Damage: Wavelength and Pulsewidth Dependent Mechanisms
Abstract
Although the consequences of excessive light exposure to the eye have been known since ancient times, the actual mechanisms of light damage in biological tissue have only been systematically investigated in this century. The response of tissue to laser or incoherent light depends on the power density, peak power, and wavelength of irradiating energy. At least three light damage mechanisms have been identified. Photochemical damage is produced by short wavelength light (typically < 550 nm) of long exposure duration, low peak power, and relatively low to moderate power density. Because tissue heating is minimal under these conditions, damage is thought to occur as result of excitation of target molecules to excited triplet states, some of which damage tissues directly through proton or electron transfers. The light-activated molecules may also cause damage indirectly by reacting with molecular oxygen to produce oxygen radicals, which are known agents of cellular damage. Thermal damage may be produced by light exposures of any wavelength capable of being absorbed by the tissue, given a sufficiently high power density and/or moderate to high peak power. Heating occurs by direct absorption of photons by a tissue chromophore which converts this photic energy into increased vibrational modes. The target chromophore, as well as surrounding structures depending on local heat conductivity, may then undergo thermal denaturation. At very high peak power, however, the strength of E-, or electrical, field of the absorbed electromagnetic wave may exceed the dielectric properties of the absorbing tissue, causing optical breakdown, ionization, plasma formation, and other phenomena associated with nonlinear (photodisruptive) damage mechanisms.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 30, 1994
- Accession Number
- ADA286066
Entities
People
- Randolph D. Glickman
Organizations
- University of Texas Health Science Center at San Antonio