The role of fluorescein angiography in the detection of laser-induced damage to the retina: A threshold study for Q-switched, neodymium and ruby lasers

doi:10.1016/0014-4835(78)90025-8

Experimental Eye Research

Volume 27, Issue 4, October 1978, Pages 471-493

https://doi.org/10.1016/0014-4835(78)90025-8 Get rights and content

Abstract

Present codes of practice for laser workers contain maximum permissible exposure levels for eye safety. These figures are derived by combining some safety factor with empirically determined figures for threshold damage detected by ophthalmoscopic examination. The present paper re-examines such safety factors by determining the energy correlates for threshold damage using three different techniques. In order of increasing sensitivity these are ophthalmoscopy, fluorescein angiography, and electron microscopy. The sensitivity and statistical reliability of fluorescein angiography are discussed and related both to the mechanisms of laser induced retinal damage, and to the role of angiography in the detection of laser accidents.

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FA is typically used to demarcate neovascular areas, but also regions where the blood-retina barrier is not intact, e.g. for pathologic changes or in regions of damaged the RPE, like after laser irradiations. In the latter case the fluorescein molecules can pass through the broken tight junctions between the RPE cells and becomes visible as bright spots after excitation by the FA system [16–19]. Even though FA became a standard procedure, costs, time, and adverse effects like allergic reactions [20,21] make it unattractive to apply in the clinical daily use.
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Fifteen patients suffering from central serous chorioretinopathy and diabetic macula edema were treated with a SRT laser using a wavelength of 527 nm, a pulse duration of 1.7 µs and a pulse energy ramp (15 pulses, 100 Hz repetition rate). An ultrasonic transducer for MBF detection was embedded in a contact lens. RPE damage was verified with fluorescence angiography.
An algorithm to detect MBF as an indicator for RPE cell damage was evaluated. Overall, 4646 irradiations were used for algorithm optimization and testing. The tested algorithms were superior to a baseline model. A sensitivity/specificity pair of 0.96/1 was achieved. The few false algorithmic decisions were caused by unevaluable signals.
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Ultrashort laser pulses have been adapted for use in a variety of applications from micromachining of dielectrics to atmospheric spectrochemistry and multiphoton microscopy. These lasers emit almost exclusively in the retinal hazard wavelength regime, making them potential sources for accidental vision loss, but also candidates for biomedical applications where precise alteration of tissues is an objective. The present article reviews the mechanisms for damaging the retina at the threshold for the lowest energy, where any change in tissue is barely perceptible. For laser pulses between several picoseconds and 10 μs, the threshold retinal damage is caused by microbubble formation around melanosomes in the retinal pigment epithelium (RPE). Below 1 ns, both stress confinement in melanosomes and self-focusing reduce the threshold for damage as measured in corneal radiant exposure, although the mechanism for damage is the same. Below several picoseconds, laser-induced breakdown produces intra-retinal damage, sparing the RPE at threshold levels. These mechanisms have been determined in the past decade and provide an understanding of trends in retinal damage with variation in laser parameters, but also elucidate potential techniques for producing precise alteration to tissues.
Ultrakurz gepulste Laser werden in einer Vielzahl von Anwendungen eingesetzt, von der Mikrobearbeitung dielektrischer Materialien, über die Atmosphärenspektroskopie bis zur Multiphotonen-Mikroskopie. Diese Laser strahlen fast ausschließlich im netzhautgefährdenden Wellenlängenbereich, wodurch sie zu potentiellen Quellen eines unfallbedingten Verlusts der Sehfähigkeit werden, aber auch zu Kandidaten für biomedizinische Anwendungen, bei denen es auf präzise Gewebemodifikationen ankommt. Dieser Artikel gibt einen Überblick über die Schädigungsmechanismen der Netzhaut an den niedrigsten Energieschwellen, an denen eine gerade wahrnehmbare Veränderung des Gewebes eintritt. Für Laserpulsdauern zwischen einigen Pikosekunden und zehn Mikrosekunden wird die Schädigungsschwelle durch die Bildung von Mikrobläschen um die Melanosomen im retinalen Pigmentepithel (RPE) bestimmt. Unterhalb von einer Nanosekunde reduzieren sowohl das „stress confinement” in den Melanosomen als auch die Selbstfokussierung die (als Bestrahlung der Hornhaut gemessene) Schädigungsschwelle, obwohl der Schädigungsmechanismus derselbe ist. Unterhalb einiger Pikosekunden erzeugen laserinduzierte optische Durchbrüche Schäden innerhalb der Netzhaut, wobei an der Schädigungsschwelle das RPE unbeeinflusst bleibt. Diese im Laufe des letzten Jahrzehnts entdeckten Mechanismen machen die Abhängigkeiten der Netzhautschäden von den Laserparametern verständlich, werfen aber auch ein Licht auf mögliche Techniken zur Erzeugung präziser Gewebeveränderungen.
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Laser instruments are used in many spheres of human activity, including medicine, industry, laboratory research, entertainment, and, notably, the military. This widespread use of lasers has resulted in many accidental injuries. Injuries are almost always retinal, because of the concentration of visible and near-infrared radiation on the retina. The retina is therefore the body tissue most vulnerable to laser radiation. The nature and severity of this type of retinal injury is determined by multiple laser-related and eye-related factors, the most important being the duration and amount of energy delivered and the retinal location of the lesion. The clinical course of significant retinal laser injuries is characterized by sudden loss of vision, often followed by marked improvement over a few weeks, and occasionally severe late complications. Medical and surgical treatment is limited. Laser devices hazardous to the human eye are currently in widespread use by armed forces. Furthermore, lasers may be employed specifically for visual incapacitation on future battlefields. Adherence to safety practices effectively prevents accidental laser-induced ocular injuries. However, there is no practical way to prevent injuries that are maliciously inflicted, as expected from laser weapons.
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The role of fluorescein angiography in the detection of laser-induced damage to the retina: A threshold study for Q-switched, neodymium and ruby lasers

Abstract

Exp. Eye Res.

Exp. Eye Res.

Retina: Ultrastructural alterations produced by extremely low levels of coherent radiations

Science

Fluorescein angiographic and electronmicroscopic findings of the retinas of pigmented rabbits immediately after ruby laser photocoagulation

Folia Ophthal. Jap.

Investigations on laser coagulated rat eyes by fluorescence angiography and microscopy

Albrecht v. Graefes Arch. Ophthal.

Retinal laser damage thresholds as a function of image diameter

Arch. Environ. Health

Q-switched Neodymium Laser Retinal Damage in Rhesus Monkey

Ocular examination of laser workers and investigation of accidents

Ocular complications of industrial lasers

Early breakdown of the blood retinal barrier with diabetes

Br. J. Ophthalmol.

Ocular spectral characteristics as related to hazards from lasers and other light sources

Am. J. Ophthalmol.

Retinal sensitivity to damage from short wavelength light

Effects of laser radiation on the mammalian eye

Trans. N.Y. Acad. Sci.

Laser induced acoustic breakage of tobacco mosaic virus

Nature London

Prolonged colour blindness induced by intense spectral lights in Rhesus monkeys

Science

Ophthalmoscopic and fluorescein angiographic and histological study of chorioretinal lesion produced by ruby laser on rabbit

Acta. Soc. Ophthal. Jap.