Biomedical subjects
Publications and source records attributed to S G Waller.
Refractive changes in patients after radial keratotomy who are exposed to high altitudes have been reported previously. Hypoxic environments may cause corneal curvature changes in surgically altered corneas that result in refractive error shifts. We report a patient who experienced a partially reversible myopic shift in a previously stable corneal transplant after prolonged exposure to high altitude.
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PURPOSE: To evaluate whether supplementing incisional keratotomy bulk or gape with a biocompatible material enhances the refractive effect. SETTING: Refractive Surgery Laboratory, Massachusetts Eye and Ear Infirmary, Boston. METHODS: Collagen punctal plugs were implanted into astigmatic keratotomy (AK) incisions in the right eyes of five rabbits and six adult cats. The left eyes had AK only and served as controls. RESULTS: Some of the postoperative corneal topographic measurements suggested an enhanced refractive effect. At 1 month, histology demonstrated no remaining implant material and no inflammation in or near the incisions. CONCLUSIONS: Implanting a biocompatible material into AK incisions in two live animal models appears to be safe and may enhance the effect of the incisions. Further study is needed to quantify the magnitude and duration of any refractive effect.
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By analysis of outpatient records at the Massachusetts Eye and Ear Infirmary, the clinical course of 10 consecutive patients who underwent epikeratoplasty for keratoconus was reviewed to determine their clinical and functional status 5 years after surgery. Eight of 10 patients (80%) had clear, intact lenticules at 12 months. During a mean follow-up of 67 months (range = 35-101 months), each maintained long-term stability of best corrected vision, refractive astigmatism, and keratometric astigmatism. The mean uncorrected visual acuity improved from 20/660 to 20/134, whereas the mean spectacle corrected acuity improved from 20/260 to 20/30. All but one patient had a spectacle acuity equal to hard contact lens acuity. However, no patients were corrected to 20/20 at the end of the follow-up period. Refractive and keratometric astigmatism stabilized by 12 months (mean = 3.62 and 3.05 D, respectively), and decreased slightly during the longer period of follow-up (mean = 2.94 and 2.17 D, respectively). Epikeratoplasty is a useful method of visual rehabilitation in highly selected cases of keratoconus in which there is no central opacity, preoperative hard contact lens acuity is worse than 20/40, the average keratometry is < 60 D, contact lens intolerance is present, and in which the patient will tolerate some degree of reduced contrast sensitivity and < 20/20 high contrast acuity.
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Epidemics of viral conjunctivitis are a major public health problem in the Far East. No treatment has been shown to shorten the duration of illness. We studied the clinical course of epidemic keratoconjunctivitis in 74 patients during an outbreak of nearly 3,000 cases in late 1988 at a U.S. military base in the Philippines. Patients were randomly assigned to treatment with trifluridine, dexamethasone, or artificial tears, and examined in a double-masked fashion. There was no significant difference between the results of the three treatments. No bacterial cultures were positive. The prompt use of patient isolation, identification of nonadenoviral red eyes, and symptomatic treatment without steroids, antiviral, or antibiotic medication is recommended in cases of epidemic keratoconjunctivitis. This is the largest series of cases of epidemic keratoconjunctivitis with laboratory confirmation reported from the Philippines.
PURPOSE: Conventional wisdom in ophthalmology is that the force required to perforate an eye during retrobulbar injection is noticeably greater with a specially designed blunt needle than with a standard hypodermic needle. A search of the literature showed no measurements of scleral perforation pressure with specific needle tips. The authors investigated this concept. METHODS: A computerized search for eye perforations of the surgical records over a 5-year period at Wilford Hall United States Air Force Medical Center was conducted. A double-masked trial by experienced ophthalmologists, using preserved eye bank eyes and several commercially available needles, subjectively assessed the force required to perforate the globe. The authors designed and built a portable transducer system to objectively measure the perforation pressure of human globes with the needles. Measurements were done with preserved and unpreserved human cadaver eyes. RESULTS: No globe penetrations or perforations were found in this consecutive series of over 4000 retrobulbar anesthesia procedures. A subjective difference between the hypodermic and blunt needles was detected. Objective measurements showed a significant difference between the hypodermic and blunt needles, and between types of blunt needles. The difference was present with both eye bank eyes and fresh cadaver eyes. CONCLUSIONS: Blunt-tipped needles do require greater force to penetrate the eye. The noncutting edge, blunt-tipped needles have higher scleral perforation pressures than those with cutting edges.
Amygdalin, the gentiobioside derivative of mandelonitrile commonly referred to as Laetrile, is presently under intensive investigation as a potential cancer chemotherapeutic agent. Because of this interest, we investigated the activity of beta-glucosidases that cleave glucose from amygdalin and from prunasin (mandelonitrile monoglucoside) in tissues from germ-free rats and in normal and neoplastic human tissues. Rat and human small intestinal mucosa contain high levels of activity of glucosidases that act on both of these cyanogenic glucosides. Release of glucose from these compounds was not detected in any of the human neoplastic tissues examined in the present study. These observations are consistent with reports of cyanide toxicity through the oral use of amygdalin or prunasin and pose serious questions concerning the alleged tumoricidal effect of amygdalin.
BACKGROUND: Adequate centration of keratorefractive surgical procedures is essential for a successful outcome. An accurate technique to mathematically describe the centration and topography of the ablation zone after photorefractive keratectomy (PRK) would be valuable in assessing the effects of these variables on subsequent visual results. METHODS: A vector center of mass formula and computerized videokeratography were used to study the postoperative treatment zone centration and topography of 17 consecutive highly myopic patients (-6.00 to 12.00 diopters [D]). Each had undergone PRK using either a single 6.0 mm (n = 11) or three-stepped ablation zone (n = 6), with good visual results. RESULTS: Calculations disclosed mean ablation zone decentration relative to the pupil center for all patients to be 0.20 +/- 0.16 mm using the vector center of mass formula. Areas of uniform central corneal dioptric power (mean diameter 3.4 +/- 0.8 mm) and surrounding transition zones of declining dioptric power (mean slope 1.61 +/- 0.44 D/mm) were also determined. CONCLUSION: A new vector center of dioptric power distribution that analyzes centration and transition zone topography offers a rigorous but straightforward means to assess the effects of refractive corneal surgery procedures on central corneal topography.