A clinical assessment of the anterior eye in arc welders

BACKGROUND

Corneal irradiation with high doses of ultraviolet-B (UVB) has been shown to damage the corneal endothelium in animals. Human occupational exposure to ultraviolet radiation (UVR) in welding is considered a risk for endothelial damage but the evidence for such an effect is limited.

METHODS

External eye photographs and non-contact specular micrographs (Topcon SP2000-P) were obtained from 102 white males aged between 32 and 62 years, 51 being arc welders (with 24 +/- 7 years experience) and 51 office workers. Most welders reported repeated occupational exposure to UVR (that is, welder's 'flashes').

RESULTS

Welders reported a higher level of ocular symptoms and a higher prevalence of pingueculae (47 versus 12 per cent), but only one case with pterygium. The average endothelial cell areas were the same in welders and office workers (398 +/- 55 microm(2) versus 400 +/- 56 microm(2); p = 0.868) as were the endothelial cell density (ECD) values (2,555 +/- 342 cells/mm(2) versus 2,541 +/- 308 cells/mm(2); p = 0.825). ECD decreased with years of welding experience (p < 0.01) but not faster than the decrease in ECD due to age.

CONCLUSIONS

Repeated occupational ultraviolet radiation exposure through welding is not associated with any obvious differences in the corneal endothelium. No differences were observed in either ECD or cell polymegethism. Despite the periodic welding flashes, the exposure levels are below those needed to cause damage to the corneal endothelium.

Evaluation of treatment by pulsed electromagnetic fields in a rabbit hyphema model

PURPOSE

Previous clinical studies have suggested a positive effect of low-frequency pulsed electromagnetic fields (PEMF) on wound healing and inflammation in the eye. We tried to test the value of PEMF treatment in a hyphema animal model with well-defined conditions.

METHODS

After injection of citrated autologous blood for the production of hyphema, 16 rabbit eyes were treated with 10 or 20 mT for 60 min on 4 days within the postoperative week. Two control groups with hyphema alone (n = 8) and PEMF irradiation without hyphema (n = 4) were also included. The rate of resorption was recorded daily. Histopathologic evaluation was performed.

RESULTS

The incidence of endothelial cell damage and fibrotic clots was markedly reduced in the 10-mT group while the resorption time of 8 days was identical with the control group. In the 20-mT group, the complication rate and the resorption time was increased versus the control group.

CONCLUSIONS

The use of PEMF treatment is of some, however, limited value as it did not reduce the resorption time of hyphema but displayed a dose-dependent, beneficial influence on some serious side effects. Future clinical studies with low-dose PEMF irradiation are justified and should determine the optimal dosage and suitable indications of PEMFs as an adjunctive treatment in ocular inflammation or trauma.

Flicker parameters are different for suppression of myopia and hyperopia

Axial eye growth rates in the chicken are controlled by local retinal image-processing circuits. These circuits quantify the loss of contrast for different spatial frequencies and promote axial eye growth rates in correlation with the amount of retinal image degradation ("deprivation myopia"). They also distinguish whether the plane of focus lies in front of or behind the retina. How the sign of defocus is detected still remains unclear. Cues from chromatic aberration are not important. In an attempt to isolate retinal circuits controlling the development of myopia or hyperopia, young chickens were raised in flickering light of different frequencies (12 and 6 Hz) and duty cycles (4-75%) produced by rotating chopper disks. The effects of flickering light on refractive errors and change in axial growth rates induced by translucent occluders or defocusing lenses were measured by infrared retinoscopy and A-scan ultrasound, respectively. Retinal electrical activity was evaluated by flicker ERG after matching flicker parameters and stimulation brightness at retinal surface. Changes in retinal and vitreal dopamine content caused by flicker in occluded and normal eyes were determined by HPLC-ECD. Strikingly, suppression of myopia occurred for similar flicker parameters, whether induced by translucent occluders ("deprivation") or negative lenses ("defocus"). The degree to which myopia was suppressed was correlated with the duration of flicker dark phase and with the ERG amplitude. In contrast, suppression of hyperopia did not correlate with these parameters. We conclude that two different retinal circuits with different temporal characteristics are involved in the processing of hyperopic defocus/deprivation and of myopic defocus, the first one dependent on flicker ERG amplitude. However, we did not find any correlation between the rate of dopamine release and the degree of inhibition of deprivation myopia in flickering light.

Transscleral ciliary body photodynamic therapy using phthalocyanine and a diode laser: functional and morphologic implications in albino rabbits

BACKGROUND AND OBJECTIVES

To evaluate the morphologic and functional effects of ciliary body photodynamic therapy (PDT) using phthalocyanine and a diode laser.

MATERIALS AND METHODS

The upper half of the left eye ciliary body of 16 albino rabbits was irradiated transsclerally using a 670-nm diode laser (400 mW/cm2) after intravenous injection of phthalocyanine (6 mg/kg). The animals were observed for a maximum of 2 months by means of tonometry, biomicroscopy, and fundus examination. At the end of the follow-up period, they were killed and their eyes were prepared for light and electron microscopy.

RESULTS

Transscleral PDT resulted in intraocular pressure (IOP) reduction in the treated eye, which lasted about 2 weeks. During this time, the treated eye had IOP values that were significantly lower than its baseline IOP values and the IOP values of the untreated eye (P < .05). One month after the procedure, the IOP had returned to baseline values. Histologic examination revealed vascular endothelial cell damage causing vascular thrombosis in the treated areas. The architecture of the two ciliary epithelium layers showed a significant abnormality. Disappearance of epithelial apical junction complexes and loss of the normal b-cytomembrane enfolding were observed in the course of electron microscopic examination. Large intercellular spaces between epithelial cells were noticed. All of these changes had subsided by the end of the second postoperative month.

CONCLUSION

Transscleral phthalocyanine-mediated PDT with the parameters used in this experiment results in significant but temporary functional and morphologic alterations in the ciliary bodies of albino rabbits.

Irritation of the anterior segment of the eye by ultraviolet radiation: influence of nerve blockade and calcium antagonists

The aim of this investigation was to determine the influence on anterior segment inflammation elicited by UV radiation, of ocular denervation and pharmacological blockade of sensory nerve fibers with capsaicin, tetrodotoxin and calcium antagonists. Both eyes of pigmented rabbits were exposed for 5 min to UV radiation (254 nm); 24 h later, inflammatory signs were evaluated by biomicroscopy of the corneal epithelium, the stroma and the endothelium and scored from 0 to 4. Conjunctival vasodilation and miosis were also assessed. Two weeks before UV exposure, a group of rabbits received a retrobulbar injection of ethanol or of 1% capsaicin. Intact, capsaicin-treated and alcohol-denervated animals were treated topically, prior to UV exposure, with tetrodotoxin (0.78 mM) and the calcium antagonists diltiazem (1-28 mM) and nifedipine (10 mM). UV radiation produced at 24 h signs of corneal irritation, conjunctival hyperemia, miosis and elevated protein content of the aqueous humor. Retrobulbar injection of 99% alcohol or 1% capsaicin did not diminish significantly the inflammation of tissues directly exposed to UV radiation, although extension of inflammatory signs to unaffected areas was prevented. Pre-treatment of normal and denervated eyes with diltiazem attenuated UV-induced eye irritation signs at concentrations of 10 mM or over. The effect was less pronounced with tetrodotoxin and was not obtained with nifedipine. These findings suggest that the contribution of a neurogenic mechanism to anterior segment inflammation induced by UV exposure is modest. They also show that high concentrations of diltiazem, but not of nifedipine, effectively reduced inflammation of the anterior segment of the eye evoked by UV radiation.(ABSTRACT TRUNCATED AT 250 WORDS)

The appearance of active plasminogen activator of urokinase type (u-PA) in the rabbit anterior eye segment irradiated by UVB rays. A histochemical and biochemical study

Repeated irradiation of the rabbit eye with UV rays of 312 nm wavelength (UVB) evoked the appearance of active plasminogen activator of urokinase type (u-PA) in the anterior eye segment. Using histochemistry, active u-PA appeared first in the corneal epithelium followed by the corneal endothelium, inflammatory cells in the corneal stroma and the lens epithelium. With a semiquantitative fluorescent method active u-PA was also found in the tear fluid and aqueous humour. UV rays of 365 nm wavelength (UVA) under the same conditions did not cause the appearance of active u-PA in the anterior eye segment.

Use of non-subjective analysis of lens transparency in experimental radiation cataract research

Historically the major impediment to radiation cataract follow-up has been the necessarily subjective nature of assessing the degree of lens transparency. This has spurred the development of instruments which produce video images amenable to digital analysis. One such system, the Zeiss Scheimpflug slit lamp measuring system (SLC), was incorporated into our ongoing studies of radiation cataractogenesis. It was found that the Zeiss SLC measuring system has high resolution and permits the acquisition of reproducible images of the anterior segment of the eye. Our results, based on about 650 images of lenses followed over a period of 91 weeks of radiation cataract development, showed that the changes in the light scatter of the lens correlated well with conventional assessment of radiation cataracts with the added advantages of objectivity, permanent and transportable records and linearity as cataracts become more severe. This continuous data acquisition, commencing with cataract onset, can proceed through more advanced stages. The SLC exhibits much greater sensitivity reflected in a continuously progressive severity thereby avoiding the artifactual plateaus in staging which occur using conventional scoring methods.

The damaging effect of UV rays (with the wavelength shorter than 320 nm) on the rabbit anterior eye segment. I. Early changes and their prevention by catalase-aprotinin application

In experiments carried out in rabbit eyes, UV rays of 254 or 312 nm wavelength damaged the anterior eye segment, whereas those of 365 nm wavelength did not. Two min irradiation with 254 nm UV rays led to a decrease of catalase activity in the corneal epithelium. After 5 min irradiation the catalase activity in the epithelium was not detectable at all. Catalase activity was also diminished in the corneal endothelium and lens epithelium. In this stage the changes were accompanied by decreased activities of Na(+)--K(+)-dependent adenosine triphosphatase, gamma-glutamyl transpeptidase and increased activities of lysosomal enzymes in the corneal and lens epithelium as well as in the corneal endothelium. The transparency of the cornea and lens was decreased. Plasmin activity appeared in the tear fluid. The irradiation with UV rays of 312 nm caused similar disturbances, however, a longer exposure was necessary. In contrast, irradiation with UV rays of 365 nm did not produce any changes. The described corneal disturbances were prevented by dropping of catalase solution on the eye surface during the irradiation or shortly after it. However, after a protracted irradiation aprotinin had to be added to catalase to achieve the healing. The decrease of catalase activity and its prevention by a local application of catalase suggests a key role of oxyradicals in the damage of the eye by UV rays.

Histopathologic findings in large uveal melanomas after brachytherapy with iodine 125 ophthalmic plaques

Eyes of 25 patients among a series of 100 consecutive patients who underwent iodine 125 brachytherapy for extremely large uveal melanomas measuring more than 7-8 mm in height had to be enucleated after an average interval of 1.4 years. The dose delivered to the tumor apex was 120-150 Gy. Indications for enucleation were most frequently radiation-induced alterations in the anterior segment with loss of fundus visibility. Eight cases showed insufficient tumor regression, and two cases were suspicious for growth. Microscopically complete tumor necrosis was found in ten eyes. Six cases were classified as "uncertain tumor regression." Apparently "viable" tumor cells were seen in nine eyes. This group of eyes showed a significantly shorter interval between therapy and enucleation. One specimen showed extraocular tumor extension. Brachytherapy with iodine 125 may result in complete tumor necrosis, even in large uveal melanomas. The morphologic extent of tumor necrosis seems to be positively correlated with the interval after therapy.

Cephalic radiation and retinal vasculopathy

The retinal vascular complications in patients receiving cephalic radiation for various lesions over a ten year period were reviewed. The incidence of retinopathy was 17% overall, but increased with proximity of the treatment site to the eye, being highest in irradiation of the eye/orbit (85.7%), paranasal sinuses (45.4%) and nasopharynx (36.4%). The risk of retinopathy increased significantly when the total dose of radiation exceeded 3000 cGy. The occlusive vasculopathy and capillary incompetence which were the most clinically important features of radiation retinopathy may be exacerbated by pre-existing diabetes. Radiation retinopathy has a long latency and may not be clinically detectable for eight years or more. Long follow-up times with sequential fundoscopy should increase early detection and optimise treatment with laser photocoagulation.

Argon versus krypton panretinal photocoagulation side effects on the anterior segment

The modification of corneal sensitivity, accommodation, pupillary diameter and endothelial cell density after argon versus krypton panretinal photocoagulation were studied prospectively in 88 eyes of 64 diabetic patients with proliferative diabetic retinopathy, randomized for one of the two laser treatments. In both groups a marked internal ophthalmoplegia and reduction of corneal sensitivity occurred after laser photocoagulation. At no time, 2, 90 and 180 days after PRP, were these parameters significantly different. Endothelial cell loss was non significantly greater in the krypton group. The results indicated that the side effects commonly observed on the anterior segment after PRP are comparable using argon or krypton lasers.

Albedo concentration in the anterior eye: a phenomenon that locates some solar diseases

I describe concentrations of reflected solar radiation (albedo) found at the usual sites of various conditions associated with exposure to the sun--pterygium, pinguecula, climatic droplet keratopathy and cataract and eyelid malignancy. Since the degree of limbal albedo concentration appears to be related to corneal curvature, patients at risk can be identified by a simple test and preventative measures taken.

Effects of microwave-induced hyperthermia on the anterior segment of healthy rabbit eyes

Hyperthermia was induced in nine healthy rabbit eyes by means of a microwave 2450 MHz stripline applicator. The anterior segment of each eye was heated to a fixed temperature of between 42 degrees C and 46 degrees C for 30 min. The temperature distribution in the eye was calculated using a thermal model and the actual boundary temperatures and microwave intensity were measured. The effects of treatment were evaluated by daily macroscopic examination, fluorescein angiography and fluorophotometry, as well as by histology. Histological examination of changes induced by this hyperthermic delivery system revealed a sharp transition at 44 degrees-45 degrees C from no permanent damage to the anterior chamber at lower temperatures to serious damage such as local necrosis, pigment disruption and local cataract at high temperatures. A sharp transition in the same temperature range was observed in vivo in the fluorescein leakage of the iris vessels by comparative fluorescein angiography and by anterior segment fluorophotometry.

Experimental models of anterior segment dysgenesis

Normal anterior segment embryogenesis is summarized followed by a review of syndromes of spontaneous and inherited conditions of abnormal development in humans and animals. The study of teratogen-induced malformations in animal models has provided valuable information about critical periods during gestation for the initiation of anterior segment dysgenesis. Although the major developmental events leading to iridocorneal angle formation occur during the third trimester, it appears that embryonic insult much earlier in human gestation (during the first three to five weeks post fertilization) can induce an abnormal sequence of events leading to anterior segment dysgenesis.

The potential damaging effects of light on the eye (Part I)

The electromagnetic spectrum consists of radiant energy that is classified according to specific wavelengths. Man is constantly exposed to a portion of the electromagnetic spectrum, particularly to radiation in the ultraviolet, visible and infrared regions. The tissues of the eye and skin are particularly sensitive to the non-ionizing wavelengths of radiant energy. Although both tissues possess endogenous protective mechanisms to minimize the effects of such exposure, problems still occur due to the absorption of radiation. The cornea, lens and retina have been shown to be susceptible to damage from light in the ultraviolet, visible and infrared range. Part I of this two-part article examines the structures of the eye that are most susceptible to light damage; part II, which will be published in the next issue of the Journal, focuses on eye protection.

Effects of XeCl excimer laser on the eyelid and anterior segment structures

We evaluated the in vitro and in vivo effects of an XeCl excimer laser on the eyelid and anterior segments of the eye. The wavelength of this laser was successfully transmitted through a quartz fiberoptic system. The action of the XeCl excimer laser through our system was more photocoagulative than photoablative.

Shock-wave effect on anterior segment structures following experimental neodymium:YAG laser iridectomy

The short-pulse laser may prove superior to the argon laser in producing noninvasive iridectomies. Little is known of the effects of the laser shock-wave on anterior segment structures adjacent to the iris. To investigate this question, iridectomies were produced in two owl monkeys using a neodymium (Nd):YAG laser and tissues were evaluated by light microscopy and scanning and transmission electron microscopy. For purposes of comparison, one eye received an iridectomy produced by an argon laser. Results indicate that while clean iris colobomas can be produced with a well-focused Nd:YAG laser, its shock-wave affects tissues in both the trabecular meshwork and corneal endothelium if the iridectomy is located within 0.8 mm of the limbus. No damage to the trabecular meshwork or corneal endothelium was evident after the argon laser iridectomy.