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Cataracts are caused by progressive, usually age-related, degeneration of the lens of the eye, resulting in diminished lens transparency; consequently, patients with cataracts develop blurred, distorted vision. However, they may be treated by extraction of the cataractous lens. Extracapsular cataract extraction removes the lens, but leaves the posterior lens capsule intact. Preservation of the posterior capsule assists in maintaining sterility in the anterior chamber (portion of the eye between the cornea and the lens) by forming a barrier to prevent organisms from reaching the vitreous humor behind the lens. A 1989 study reported a 29 percent bacterial contamination rate of the anterior chamber of the eye following extracataract extraction; the specific organisms and their numbers (quantification) were not determined. To determine the frequency of anterior chamber contamination, and to quantify and identify the species of the organisms involved, 30 patients who underwent uncomplicated cataract surgery were assessed. Aspiration of fluid was obtained from the anterior chamber near the end of the surgical procedure. Organisms were found in 13 aspirates (43 percent). There were 18 positive aspirates obtained from these 13 patients. The most commonly found organism was Staphylococcus species, occurring in 8 of the 18 isolates (44 percent). Despite the high number of patients having viable organisms in the eye, none of the patients developed endophthalmitis, an inflammatory condition of the internal eye in which the eye becomes red, swollen, painful and possibly filled with pus. In most cases the inoculum (concentration of organisms in the aspirated fluid) was small (10 to 20 colony-forming units per milliliter). These findings suggest that although there may be bacteria present in the anterior chamber of the eye after cataract surgery, if the inoculum is low, the bacteria will be cleared without the development of endophthalmitis. (Consumer Summary produced by Reliance Medical Information, Inc.)

When the strong magnetic field created by a magnetic resonance imaging (MRI) scanner is pulsed, radio frequencies are given off. By manipulating the strength of the magnetic field, different body tissues give off different radio frequencies and can be labeled. These frequencies are analyzed by the MRI computer which produces an image of the tissue or section of the body being scanned. Contrast in MRI images depends upon the density and relaxation time of certain protons, primarily found in fat and water. A difficulty in using MRI scanning in ophthalmology is that bone, which does not contain many of these protons, appears black. By using a contrast agent, the relaxation time of one kind of tissue is reduced relative to another type of tissue, and the resulting image is clearer. The use of contrast agents is particularly helpful in diagnosing intra-orbital tumors. Because MRI scanning requires several minutes to perform eye movements can cause poor images; new techniques are being developed to allow scanning times of less than one minute. If a magnetic foreign body in the eye is suspected MRI should not be used. In addition, claustrophobic individuals and patients who have pacemakers should probably not have MRI scanning. Computed tomography (CT) scanning provides better detail of bone than MRI, but MRI tends to give a better image of abnormalities within the skull. (Consumer Summary produced by Reliance Medical Information, Inc.)