Biomedical subjects
Publications and source records attributed to E Marg.
The authors report on a 20-year-old patient who developed hydantoin lymphadenopathy during treatment with diphenylhydantoin. The problems associated with clinical and histological delimination from malignant lymphomata are described by reference to the literature. Hydantoin lymphadenopathy is regarded as a drug-induced allergic and toxic process.
Visual evoked potentials (VEP's) recorded from the scalp are sensitive to retinal image sharpness and thus to changes in the refractive state of the eye. Initially the responses to checkerboard flash or reversal stimuli were computer-averaged in order to raise the signal above the noise, primarily the electroencephalogram (EEG). Recently analogue Fourier signal analysis has been proposed for using the VEP for rapid clinical refraction. We have confirmed that this method can measure the spherical refractive state to within +/- 0.50D. However, because of large slow-wave fluctuations, measurements of changes within +/- 1.00D are not always clear. Despite its promise the method does not appear to be clinically useful at present.
Eighty patient-volunteers were refracted by the computer-assisted Refractor III system and the results were compared with those obtained by the usual manual method. For the distance prescription 95% of the results were satisfactory. For the near add all were satisfactory. Relative validity of the system was also measured objectively by repeatability data. System test differences and test-retest manual-examination data were found comparable, indicating that the validity of the system is similar to that of the manual method. Further developments are expected to improve reliability, simplify maintenance, and extend testing so that the system will be an economical and useful instrument in eye clinics.
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A computer-assisted subjective eye examination was administered to 78 patients as they volunteered. They were also examined in the conventional, manual way, some before and some after the computer-assisted examination. Results of the computer-assisted examination were compared to those obtained by conventional subjective methods. For the distance prescription, satisfactory agreement was obtained for 83% of the patients. The 17% unsatisfactory prescriptions were subdivided into about 6% avoidable errors (caused by errors in software, hardware, or optometric flow charts), about 6% errors of undetermined cause, and 4% fundamental errors (caused by patient's physical and mental impairment or confusion). A similar analysis is made for the near add. With further development of the system it is expected that between 90 and 96% of patients in an optometric clinic can be successfully examined by this computer-assisted method.
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The case of a 19-year-old patient is reported who during treatment with phenytoin (5,5-dephenylhydantoin) developed a Stevens-Johnson syndrome. The symptomatology is regarded as an early allergic reaction to phenytoin. The risks involved in using a high inital dose are discussed with reference to this particular case.
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After a brief introduction to the optical principles and terms, formulas are derived which demonstrate that with conventional methods and designs it is not possible to summate with accuracy the labeled power of three or more ophthalmic lenses in tandem. The effective power of sphero-cylindrical combinations in all currently available eye refractors, when powers of eight to ten diopters are exceeded, may differ from the summated labeled power by a quarter diopter or more, which can be clinically significant. This error can be directly and readily eliminated only in computer-actuated refractors by including a computer program which calculates the effective power and makes the necessary correction.
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