Laser Eye Effects (1968) / Chapter Skim
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Retinal Injury From Laser and Light Exposure
Retinal Injury From Laser and Light Exposure
Pages 20-56
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From page 20... ...
The purpose of this report is the review and discussion of some of the findings presented in the literature relating to permanent injury to the eye caused by laser irradiation and light coagulation. Since this study is concerned with our present knowledge of retinal energy doses capable of producing permanent injury, only those studies are summarized and discussed which give data on exposure times, image sizes of the irradiating beam on the retina, and energy levels.
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From page 21... ...
However, the first scientific description of thermal injury to the eye was reported by Verhoeff and Bell These investigators pointed out that eclipse burns were actually thermal lesions, originating in the retinal pigment epithelium by the transfer of light energy to heat. During World War II, numerous foveal lesions were documented among persons using optical instrumentation to "spot" planes attacking from the direction of the sun'2.
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From page 22... ...
Previous reported absorption values for the human retinal pigment epithelium and choroid include light scattered and reflected by the various structures of the eye 2^ , 25 . This resulted in excessively high absorption values.
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From page 23... ...
Percent absorption in retinal pigment epithelium and choroid for equal intensities and light incident on the cornea. (Human data)
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From page 24... ...
Percent absorption in retinal pigment epithelium and choroid for equal intensities and light incident on the cornea. (Rabbit data)
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From page 25... ...
Percent absorption in retinal pigment epithelium and choroid for equal intensities and light incident on the cornea. (Rhesus monkey data)
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From page 26... ...
0n the other hand, the anatomical and optical characteristics of the eye of the Rhesus monkey are quite similar to the human eye; the foveal region and retinal vascularization are similar to the human eye. However, at long exposure times and/or at energy levels greater than that required for the production of minimal retinal injury, the more intense choroidal pigmentation of the Rhesus eye contributes markedly to the development of retinal thermal lesions.
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From page 27... ...
Minimal lesions usually present slightly darker coloration than the surrounding fundus and moderate to severe lesions show a uniform, greyish area. For minimal and above minimal lesions the size of the lesion is approximately equal to the image size of the exposure light beam or laser beam.
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From page 28... ...
, typical histopathological changes after irradiation are described for these three species together. It should be understood that the similarities of the lesion are mainly in the range of minimal or so-called threshold lesions, since for the production of these minimal lesions, apparently only the retinal pigment epithelium is primarily involved.
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From page 29... ...
Nitro BT tetrazolium studies for cytochemical localization of oxidative enzyme systems represent another useful method * , At long exposure times, minimal lesions already show definite adherence to the underlying retinal pigment epithelium which becomes very obvious during sectioning and preparation of the histological material, for otherwise the neural retinal layers become easily detached during processing of the histological specimen.
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From page 30... ...
The PE cells in these areas are disrupted, and the rods and cones show swelling and distortion. In moderate lesions, disruption of pigment epithelium cells is always present and pronounced, with retinal pigment granules throughout the outer and inner retinal layers.
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From page 31... ...
Such lesions as produced in Maxwellian view in the intact monkey eye and at low energy densities on the retina are frequently not visible by ophthalmoscopy. However, under histological examination, damage could always be demonstrated and consisted primarily of retinal detachment, pigment loss from the retinal pigment epithelium, choroidal damage, micro-lesions with scattered pigment granules, degeneration of the inner and outer segments of the receptor cell layers, pyknotic nuclei, and free blood cells.
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From page 32... ...
Electron-mi croscopy. An electron microscopic comparison of retinal lesions produced by white light and laser radiation.at equal exposure times was conducted to study the details of morphological changes at a cellular level 35~37.
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From page 33... ...
The boundary between exposed and nonexposed retinal pigment epithelium was rather sharply demarcated, showing granulation effect of the photoreceptor outer segments, vacuolization of the endoplasmic reticulum, and disturbances of the infolding of the basal membrane of the pigment epithelium of the exposed cells, while the immediate neighboring cells did not show any pathological changes. In general, the observations support the hypothesis that the intercellular changes are non-specific to this particular insult.
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From page 34... ...
The production of mild ophthalmoscopic visible retinal lesions in the rabbit retina by white light of the Xenon high pressure arc, pulsed ruby laser and q-switched ruby laser as a function of average irradiance and exposure time has been studied by various investi gators 1~7|28-30,3^-37,^l~t> Work conducted by Ham, Geeraets, Guerry and co-workers * '~^" ranged in exposure times from three minutes with the Xenon high pressure arc down to 28.5 ns for the q-switched ruby laser with an overlap of white light and pulsed laser radiation in the microsecond range (200 /usec)
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From page 35... ...
x data for ruby laser, b94.3 nm. (Ham et al., Trans.
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From page 36... ...
the average irradiance measured 2-5 MW/cm^ for the production of mild lesions. The ophthalmoscopic and histological appearance of those lesions in comparison with those produced with the normal pulsed ruby laser and the Xenon light source were different as described in the previous chapter on the histology.
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From page 37... ...
. These investigators, however, used the normal pulsed ruby laser instead of a white light source.
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From page 38... ...
The primary injury then creates secondary degenerative changes involving the receptor cell layer with degeneration, loosing of the outer segment-pigment epithelial junction, fluid infiltration, and finally complete retinal detachment. This assumption can well be compared with the electron microscopic findings as described by Fine and Geeraets 35 which presented similar observations at the primary site of injury in the retinal pigment epithelium and outer segments of the receptor cell layer with secondary degeneration of the first neuron.
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From page 39... ...
They added other techniques to those used previously and mentioned in this report under "Histological Findings". Energy levels for the production of minimal visible retinal lesions produced with normal pulsed ruby laser are not contained in the report by these investigators since exposure times, exact image size, and exact energy were not clearly defined.
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From page 40... ...
Beside their work with effects of normal pulsed laser action on rabbit eyes, the authors have conducted studies with q-switched ruby laser on the rabbit retina and the Rhesus monkey. The authors defined clinical visible threshold lesion as just barely visible changes by ophthalmoscopy within kS to 60 minutes after exposure.
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From page 41... ...
Their retinal dose for minimal lesions produced by the normal pulsed ruby laser was given as 0.l6 i/cm^, which is about 5 times lower than the threshold given by other investigators. The same investigators gave a threshold dose for lesions produced with q-switched pulses of 80 ns duration and equal image size of 250 uon the retina as .0045 j/cm .
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From page 42... ...
Preliminary data for energy densities and power densities of neodymium laser radiation were obtained in chinchilla and dutch rabbit eyes. With exposure times of 200 /us and image size of the exposure beam of approximately 800 /j in diameter on the retinal pigment epithelium, the energy density for an RD 50 lesion (lesion produced in 50% for exposures at this energy level)
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From page 43... ...
The calculated retinal dose for this exposure was 7.9 j/cm^ No ophthalmoscopic visible lesion developed within the next 18 hours. Another exposure was made in the 10 o'clock meridian, increasing the retinal dose to 9.2 j/cm^.
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From page 44... ...
No visible lesion developed over the next 15 minutes and did not appear over another 15 hours of observation. Accordingly, a second exposure to a calculated retinal dose of 12.2 j/cm2 was given to the midperiphery.
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From page 45... ...
For long exposure times it has been shown l that the energy required for producing irreversible retinal injury decreases with the image size of the exposure beam on the retina. DISCUSSI0N AND C0NCLUSI0NS The reported data on energy density incident on the retina for the production of ophthalmoscopically visible, minimal lesions, utilizing white light, are in fair agreement among several independent research groups if exposure times and retinal spot sizes are taken into account.
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From page 46... ...
In recently published data by these investigators 5 , tne required power density for q-switched ruby laser lesions of the retina were even of a wider range depending on "calculated" image sizes on the retina. In this report the power density for an 8 ft in diameter lesion in the rabbit eye was given with 36000 MW/cm2.
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From page 47... ...
Some support for this viewpoint comes from in vitro observations on cellular death for chick retinal epithelial cells in tissue culture when exposed to a q-switched ruby laser beam at 30 ns 73. The LD 50 dose (50% change of cellular death from this energy density)
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From page 48... ...
absorption of radiant energy by the retinal pigment epithelium and choroid in the human and chinchilla rabbit eye are similar and occur primarily in the range 400-950 nm, the peak absorption occurring at approximately 575 nm.
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From page 49... ...
6. Electron-microscopic findings for mild lesions produced in microsecond ranges by white light or by ruby laser showed identical changes in PE and receptor outer segments.
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From page 50... ...
9. The primary site of retinal injury after exposure to neodymium and ruby laser wavelengths is in the retinal pigment epithelial cell and immediate adjacent structures; there is also the possibility of harmful effects on structures of the ocular media and neural retina for wavelengths in the infrared because of greater absorption.
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From page 51... ...
14. Required energy for production of retinal lesions in the human eye appears to be significantly greater than energy levels causing retinal injury in the rabbit eye.
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From page 52... ...
J., Light Reflectance from the Retinal Pigment Epithelium. (Unpublished data)
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From page 53... ...
H., Minimal Cellular Damage to Rabbit Retinae Following Exposure to Focussed Long-pulse Ruby Laser.
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From page 54... ...
Light Coagulator: A Funduscopic and Histologic Study of Chorioretinal Injury as Function of Exposure Time.
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From page 55... ...
and King, R G., Jr., In Vitro Exposure of Retinal Pigment Cells to 0_-swi tched Ruby Laser Radiation as a Function of Pigment Density.
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From page 56... ...
J., Q-switched Ruby Laser Radiation on Retinal Pigment Epithelium in Vitro: Cellular Reaction as a Means of Irradiated Spot Size. In press.
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