Estimation of safe exposure time from an ophthalmic operating microscope with regard to ultraviolet radiation and blue-light hazards to the eye.

Hazards from the optical radiation of an operating microscope that cause damage at the corneal, lenticular, and retinal levels were investigated; we considered, in particular, ultraviolet radiation (UVR) and blue light. The spectral irradiance from a Zeiss operation microscope OPMI VISU 200 was measured in the corneal plane between 300 and 1100 nm. Effective irradiance and radiance were calculated with relative spectral effectiveness data from the American Conference for Governmental and Industrial Hygienists. Safe exposure time to avoid UVR injury to the lens and cornea was found to be 2 h without a filter, 4 h with a UVR filter, 200 a yellow filter, and 400 h with a filter combination. Safe exposure time to avoid retinal photochemical injury was found to be 3 min without a filter and with a UVR filter, 10 min with a yellow filter, and 49 min with a filter combination. The effective radiance limit for retinal thermal injury was not exceeded. The hazard due to the UVR component from the operating microscope is not critical, and operation time can be safely prolonged with the use of appropriate filters. The retinal photochemical hazard appears critical without appropriate filters, permitting only some minutes of safe exposure time. The calculated safe exposure times are for worst-case conditions and maximal light output and include a safety factor.

Bilateral retinal phototoxic injury during cataract surgery in a child.

The intense illumination of the operating microscope has been implicated in photic retinopathy in patients and in animal studies. We report a case of bilateral macular phototoxicity occurring in an eleven-year-old child who underwent bilateral cataract surgery for radiation cataracts. We are unaware of other reports of retinal toxicity occurring during pediatric cataract surgery. We hypothesize that this child may have been predisposed to macular injury because of previous chemotherapy and radiotherapy exposure. Ophthalmic surgeons should be aware that light toxicity from the operating microscope might also occur in the pediatric population.

Prevalence of myopia in a group of Hong Kong microscopists.

PURPOSE: To study the prevalence and magnitude of myopia in a group of Hong Kong Chinese microscopists and compare it with that observed in microscopists working in the United Kingdom. METHODS: Forty-seven microscopists (36 women and 11 men) with a median age of 31 years and working in hospital laboratories throughout Hong Kong were recruited to the study. Information about past refractive corrections, microscopy work, and visual symptoms associated with microscope use were collected. All subjects had a comprehensive eye examination at The Hong Kong Polytechnic University Optometry Clinic, including measures of refractive error (both noncycloplegic and cycloplegic), binocular vision functions, and axial length. RESULTS: The prevalence of myopia in this group of microscopists was 87%, the mean (+/- SD) refractive error was -4.45 +/- 3.03 D and mean axial length was 25.13 +/- 1.52 mm. No correlation was found between refractive error and years spent working as a microscopist or number of hours per day spent performing microscopy. Subjects reporting myopia progression (N = 22) did not differ from the refractively stable group (N = 19) in terms of their microscopy working history, working hours, tonic accommodation level, or near phoria. However, the AC/A ratio of the progressing group was significantly greater than that of the stable group (4.59 delta/D cf. 3.34 delta/D). CONCLUSION: The myopia prevalence of Hong Kong Chinese microscopists was higher than that of microscopists in the United Kingdom (87% cf. 71%), as well as the Hong Kong general population (87% cf. 70%). The average amount of myopia was also higher in the Hong Kong Chinese microscopists than the Hong Kong general population (-4.45 D cf. -3.00 D). We have confirmed that the microscopy task may slightly exacerbate myopia development in Chinese people.

Use of the operating microscope and loupes for head and neck free microvascular tissue transfer: a retrospective comparison.

OBJECTIVE: To analyze whether less cumbersome loupes are as equally efficacious as the microscope for magnification for free tissue transfers in head and neck reconstruction. DESIGN: A 7-year retrospective review of 151 consecutive microvascular free tissue transfers compares the operating microscope with loupe magnification. SETTING: A tertiary care medical center. PATIENTS: A total of 151 consecutive patients undergoing microvascular reconstructions. INTERVENTION: Microvascular reconstruction of ablative head and neck cancer defects using either microscopic or loupe-provided magnification. MAIN OUTCOME MEASURES: Medical records were reviewed for demographic data, preoperative radiation status, type of defect and flap, length of procedure, complications, and length of stay. RESULTS: Two teams shared the reconstructions, with all microvascular anastomoses created or directly supervised by one of us (D.A.R.). One team used the operating microscope for magnification (84 cases), while the other used loupes (67 cases). Complication rates were statistically similar for the 2 techniques, the length of procedure tended to be shorter in the loupe group, and the length of stay was statistically similar in both groups. CONCLUSIONS: A review of the literature validates the usefulness of loupe magnification in free tissue transfer surgery. To our knowledge, this is the largest number of head and neck reconstruction cases presented comparing these techniques. Loupes offer the surgeon comfort and easy access to and uncomplicated visualization of the operating field. Furthermore, loupes may decrease operating time and help avoid complicated equipment. Therefore, loupe magnification should be considered in head and neck reconstruction without the fear of increased morbidity.

Evaluation of the safety of recent surgical microscopes equipped with xenon light sources.

Although recent surgical microscopes for neurosurgery are equipped with xenon light sources to obtain bright fields of vision, the safety of a xenon beam, which has strong energy intensity in a long ultraviolet light, for cortical neurons has not been evaluated. Cranial windows were made in the parietal bones of gerbils. The skull of each gerbil was covered with warmed saline (0.5 mm in depth) to maintain the brain temperature. Ultraviolet irradiation (365-nm) was performed for 30 minutes at energy levels of 9.6, 4.4, 1.3, and 0.3 mwatts/cm(2), and neuronal damage was observed in 90 +/- 4%, 42 +/- 23%, 9 +/- 6%, and 0 +/- 0% of pyramidal cells in the parietal cortex 24 hours later. With the use of a logistic regression curve, the energy level causing 50% of neuronal damage was estimated to be 5.4 mwatts/cm(2). By increasing the thickness of the saline layer over the skull surface (1 mm and 2 mm), neuronal damages were significantly attenuated (21 +/- 18% and 10 +/- 8%, respectively, 4.4 mwatts/cm(2). Because the highest energy levels of 365-nm ultraviolet rays emitted from surgical microscopes measured in the present study (0.379 mwatts/cm (2)) were much closer to the dose causing 0% damage than to the dose causing 9% damage, the risk of neuronal injury occurring during microsurgery could be negligible. However, care should be taken in patients who take medicine classified as photosensitizing agents, such as diphenylhydantoin, which are thought to concentrate ultraviolet energy. The use of saline over the cortical surface may be beneficial for reducing the detrimental effects of 365-nm ultraviolet light.

Study of filtered light on potential retinal photic hazards with operation microscopes used for ocular surgery.

There have been numerous reports of retinal photic injury from operation microscopes used during cataract surgery. The risk of injury has been associated with the intensity of the light directed into the eye, short-wavelength emission, user technique, exposure time, and direct axial lighting. We evaluated use of light transmission filters to modify a tungsten-halogen light source spectrum to reduce the risk of retinal photic injury. A two-light source filter combination was found with a color profile acceptable for intraocular surgery that reduces the risk of retinal photic injury by a factor of approximately 2.5.

Microscope-induced retinal phototoxicity in cataract surgery of short duration.

OBJECTIVE: Microscope-induced retinal phototoxicity has been described after prolonged cataract surgery, usually in operations lasting longer than 100 minutes. The purpose of this study was to compare the features of microscope-induced retinal phototoxicity occurring in patients who underwent cataract surgery of short duration and long duration. DESIGN: A retrospective nonrandomized comparative trial. PARTICIPANTS: Thirty-four patients, whose medical records documented the development of phototoxic lesions in the retina as a result of cataract surgery, were divided into two groups: group A with 14 patients whose operating time was 30 minutes or less, and group B with 20 patients whose operating time was greater than 30 minutes. INTERVENTION: All patients underwent either phacoemulsification or extracapsular cataract extraction (ECCE) with implantation of an intraocular lens. RESULTS: The mean operating time was 23.1 minutes (range, 11-30 minutes) in group A, and 60.8 minutes (range, 34-123 minutes) in group B. Phacoemulsification was done more often in group A (P = 0.001) and ECCE in group B (P = 0.0003). A final refraction of +/- 1 D was achieved by 12 eyes (86%) in group A and by 12 eyes (60%) in group B (P = 0.11). The correlation between final refraction and duration of the operation was significant; the closer the final refraction approached to emmetropia, the shorter the duration of surgery (r = 0.53; P = 0.001). Diabetic retinopathy was more common in group A (P = 0.03). CONCLUSIONS: Phototoxic lesions of the retina may occur during cataract surgery even when the duration of the operation is short. The most relevant associated factors found in this study were correction approximating emmetropia and diabetic retinopathy.

Protecting the retina during MemoryLens insertion.

BACKGROUND: To determine the light-scattering power of the folded MemoryLens(R). SETTING: Department of Ophthalmology, University of Utah, Salt Lake City, Utah, USA. METHODS: The focusing power of 10 unfolded MemoryLenses (Mentor Ophthalmics) was measured using an optical bench. The IOLs were then unfolded in a 37 degrees C distilled water bath and reexamined within 15 seconds of removal from the bath. Resolutions were read after the lenses were dried for 1 hour and cooled to room temperature and again after they were rehydrated and reheated in the water bath. RESULTS: In the rolled state, all lenses diffused the illumination of the light source. After the IOLs were unfolded in the water bath at 37 degrees C, they gave readings of acceptable to high resolution. After the lenses were air dried for 1 hour and cooled to room temperature, the resolution of all lenses decreased. However, after the IOLs were rehydrated and reheated for 1 more hour, resolution was similar to that of the original hydrated lenses. CONCLUSION: When folded, at a low temperature, or dehydrated, the MemoryLens may provide protection from the operating microscope by scattering light.

Posterior corneal rings in monkeys.

Contact wide-field specular microscopy was performed on 27 monkeys of known ages. The induction of posterior corneal rings as a result of applanation pressure to be age-dependent. There was a total absence of these folds in animals under two years of age, and they usually occurred only in animals older than four years of age.