Effects of Ionizing Radiation on the Conjunctiva, Cornea, and Lens
The human eye is exposed to a wide range of radiant energy aside from the visual spectrum, including ultraviolet, infrared, microwave, and ionizing radiation. Of these, ionizing radiation can cause some of the most significant and long-lasting ocular dama
- PDF / 2,148,000 Bytes
- 11 Pages / 547.08 x 765.36 pts Page_size
- 6 Downloads / 239 Views
CONTENTS 21.1 21.2 21.2.1 21.2.2 21.2.3 21.2.4 21.3 21.3.1 21.3.2 21.3.3 21.3.4 21.3.5 21.4
Introduction 201 Anatomy 202 Conjunctiva 202 Cornea 202 Lens 202 Tear Film 203 Radiation Effects 203 Conjunctiva 203 Cornea 204 Crystalline Lens 204 Dry Eyes: Diagnosis and Treatment Radiation-induced Cataracts 208 Summary 210 References 210
206
21.1 Introduction The human eye is exposed to a wide range of radiant energy aside from the visual spectrum, including ultraviolet, infrared, microwave, and ionizing radiation. Of these, ionizing radiation can cause some of the most significant and long-lasting ocular damage to the lens, conjunctiva, and cornea. Ionizing sources include cosmic (30 Mrem/year) and terrestrial sources (60 Mrem/year), as well as man-made sources (60 Mrem/year). These last include X-rays, radioactive isotopes, diagnostic and therapeutic radioactive sources, and release from nuclear power stations. Control of these man-made exposures with shielding of the globe, when possible, can minimize or eliminate the acute and chronic effects of radiation exposure. The energy of ionizing radiation can be transmitted in a variety of ways, ranging from X-ray photons H. J. INGRAHAM, MD
Department of Ophthalmology, Geisinger Medical Center, Danville, PA 17822-2120, USA E. D. DONNENFELD, MD 2000 North Village Avenue, Suite 402, Rockville Center, New York, NY 11570, USA D. H. ABRAMSON, MD 70 East 66th Street, New York, NY 10021, USA
to heavy particles, and is dissipated in the same way regardless of how it is carried. Charged ions or radicals are created in the tissue; the depth of penetration is directly related to the wavelength of the ionizing source. Tissue destruction occurs through direct cell killing, DNA changes with the creation of abnormal or lethal mutations, direct blood vessel damage with secondary tissue necrosis, or through malignant transformation of the cell (LERMAN 1980). The degree of tissue injury is related both to the intensity of the ionizing source and to the particular sensitivity of the species and the tissue concerned. As a general rule, increasing doses of ionizing radiation result in more severe effects with a shorter latency period. In the therapeutic use of ionizing radiation, damage to normal tissue is minimized through fractionation, a treatment that gives a therapeutically equivalent radiation dose by dividing it into daily sessions; this allows for cellular repair in normal tissues between doses. The human eye is composed of two vital structures which allow light to enter the eye and focus on the photo receptors of the retina (Fig. 21.1). These two anterior segment structures are the cornea and the lens. The cornea is a transparent, avascular structure, which functions as a watch crystal does on a watch. It allows light to pass through and provides structural support for the eye. Once the light has passed through the cornea, it next passes through the anterior segment to the lens. The lens is a biconvex, avascular, colorless, almost transparent structure, which also focuses the light
Data Loading...
