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Biomedical subjects

D G Pitts

Publications and source records attributed to D G Pitts.

At least 19 recordsLinked to original sources
PubMed1994

Evaluation of the performance of spectacle lens "transmittance meters".

PURPOSE: Inexpensive transmittance meters have recently been developed for measuring of mean ultraviolet (UV) radiant transmittance and luminous transmittance of spectacle lenses. Our purpose was to determine how accurately these meters measured transmittance. METHODS: The mean UV transmittance and the luminous transmittance of a series of lenses were determined using a spectrophotometer. Transmittance meters were then used to measure the same lenses. RESULTS: In general, the meters overestimated total (mean) UV transmittance. Luminous transmittance was relatively accurately measured by those meters which had this capability. CONCLUSIONS: Although the meters do not measure UV transmittance accurately, they are still useful for determining if a lens transmits any UV radiation. The relatively narrow response range of the meters, centered at 360 to 380 nm, is responsible for the measurement error of mean UV transmittance.

Evaluation Studies as Topic↗
PubMed1991

Residual H2O2 compromises deswelling function of in vivo rabbit cornea.

The purpose of the study was to investigate the effect of H2O2 on corneal swelling, corneal deswelling and to determine the concentration of H2O2 in the aqueous humor. Four types of experiments were performed using the rabbit eye. 1. Central corneal thickness (CCT) measurements after instillation of H2O2 into the cul-de-sac and after wearing H2O2 soaked soft contact lenses (SLC) for 2 h using 60 ppm, 100 ppm and 300 ppm H2O2. 2. Measurement of corneal deswelling induced by wearing SCL and closed eye for 2 h. 3. Determining the H2O2 in the aqueous humor one h after instillation of H2O2 into the cul-de-sac. CCT increases of 7.5% and 10.7% were found after the instillation of 100 ppm and 300 ppm H2O2 into the cul-de-sac. After wearing H2O2 soaked SCLs, CCT increased 4.6% and 5.8%, respectively. The H2O2 in the aqueous humor was 0.087 mM or a 160% increase after using 300 ppm H2O2. The increase in CCT and interference with the deswelling process is interpreted as a toxic effect on the cornea and an interference with the normal dehydration function of the endothelial pump.

Administration, Topical↗
PubMed1990

Sunlight as an ultraviolet source.

An understanding of the spectral composition of sunlight is necessary if the effects of human exposure and protection criteria are to be meaningful. Also provided is a brief review of data for the ultraviolet UV solar spectrum in space and on earth that have been related to ocular damage. In addition, the effects of increases and decreases in the levels of ozone on the amount of ultraviolet radiation (UVR) reaching earth are presented. It is shown that enough UVR is encountered on earth to cause ocular damage and the damage will increase significantly as the levels of ozone decrease.

Eye Diseases↗
PubMed1990

Ultraviolet-absorbing spectacle lenses, contact lenses, and intraocular lenses.

Optical materials that are available to the practitioner for protection of the eye against hazardous exposure to ultraviolet radiation (UVR) are discussed. Principles of protection, procedures for calculating safe ocular exposure duration, and transmittance curves of commonly prescribed spectacle lenses, contact lenses, and intraocular lenses are discussed. Suggestions are made to assist the practitioner in providing adequate protection for the patient.

Animals↗
PubMed1989

Acanthamoeba culbertsoni and contact lens disinfection systems.

Acanthamoeba culbertsoni was used in this study inasmuch as its susceptibility to disinfection has not been examined. Although heat was found to be the most effective means of disinfection some cysts survived this procedure. Chlorhexidine exhibited a dose-response kill curve but the most effective concentrations are also corneo-toxic. Polyaminopropylbiguanide (0.00005%) has good effectiveness against the cyst but was not completely cidal at the dose tested. Thimerosal (0.002%) and hydrogen peroxide (3%) were found to be without effect. These findings should give contact lens practitioners guidelines for selecting a disinfection system for their patients.

Acanthamoeba↗
PubMed1989

The UV problem: have the rules changed?

In summary, the increase in numbers and longevity of the population is clearly demonstrated by the census records. The facts that human behavioral patterns have drastically changed to permit ever-increasing exposure to sunlight is a matter of history. The changes in the environment will have a profound effect on the world in which we live. Our food supply could be severely disrupted, the incidence of skin cancer is likely to increase substantially, and ocular radiation trauma to the cornea, lens and retina will be expected to increase in prevalence. This alarming information has been acknowledged by the national press in the newspapers and magazines, and by the radio and TV networks. The attention has resulted in a striking awareness of the public to the UVR hazard. Likewise, the scientific community has devoted considerable attention to the harmful nature of UVR exposure to the skin and the eye. The brief survey of UV research presented in this paper consistently demonstrates that the cornea, lens and retina are all vulnerable to permanent UVR damage. Our survey of available facts indicates that the "rules have changed dramatically on all counts." Ocular protection against UVR exposure must be provided to our patients in the form of contact, ophthalmic or intraocular lenses. The additional cost of UV protection is insignificant when compared to the cost in visual loss over a lifetime. We are truly talking about trivial costs when UV protection is contrasted to what people spend on getting extra UV exposure at the solarium, spa, ski slopes, beach, mountains, etc.(ABSTRACT TRUNCATED AT 250 WORDS)

Contact Lenses↗
PubMed1988

Protection from harmful UV radiation by contact lenses.

Ultraviolet radiation (UVR) has been demonstrated to be harmful to the cornea, the lens and the retina. Recent research has indicated that, in addition to the epithelial trauma found in UVR-induced keratitis, the deeper corneal layers are also involved. Since trauma to keratocytes and endothelial cells can result in permanent damage or cell loss, it is imperative to protect eyes against excessive dosages of UVR. Standard hydrogel contact lenses (Vistamarc normal) and newly developed UV-filtering hydrogel lenses (Vistakon UV-BLOC) were fitted on five rabbits and compared in protection from harmful UVR (300 nm). The eyes that wore the UV-filtering lens maintained normal corneas; however, the eyes that wore the standard hydrogel lens showed pronounced epithelial, stromal and endothelial changes. We concluded that the UV-filtering lens effectively absorbed the hazardous UV radiation while the standard soft lens provided little protection.

Animals↗
PubMed1987

Ultrastructural analysis of corneal exposure to UV radiation.

The primate cornea was exposed to 300 nm UVR with five levels of radiant exposure from 0.08 to 0.6 Jcm-2. All cellular layers of the cornea were damaged at the 0.08 Jcm-2 exposure, and damage became more severe as the exposure level was increased. The corneal cells showed variable response in that essentially normal cells were found among damaged cells. Eight days post-exposure using the 0.6 Jcm-2 level, the epithelium had regained its normal thickness and was populated largely by normal appearing cells; however, the stroma showed damaged keratocytes and the loss of keratocytes. The corneal basement membranes (the epithelial basement membrane and the posterior limiting lamina) and the anterior limiting lamina were not damaged at any exposure level except for an isolated area along the epithelial basement membrane in one cornea. Therefore, one is lead to conclude that basement membranes are unaffected by UVR. The endothelium continued to demonstrate the loss of mitochondria, endoplasmic reticulum and some vacuoles at 8 days after exposure. However, the endothelium appeared to have resumed its physiological function as demonstrated by the reduced stromal oedema. This research gives the first complete description of UV-B induced corneal damage and repair of the full, in-depth cornea of the primate using the EM.

Animals↗
PubMed1987

The efficacy of a UV-blocking soft contact lens in protecting cornea against UV radiation.

Recently, it has been shown that UV keratitis is more serious than previously thought because it is not limited to the corneal epithelium but also involves the stroma and the endothelium. It is, therefore, very important to avoid ultraviolet radiation (UVR) damage, and the purpose of the present study was to examine the ability of a UV absorbing hydrogel lens to filter such wavelengths. Ultrastructural observations of rabbit corneas showed that a regular soft (Vistamarc normal) contact lens offered no protection, and since wearing one adds stress to the cornea it seems possible that the cornea may be more vulnerable to UVR trauma. A UV absorbing soft contact lens (Vistakon UV-BLOC) provided complete protection to all corneal layers. Subepithelial nerve fibres in the traumatized corneas were mostly of normal morphology and may explain why UV keratitis is a very painful experience. It was concluded that a UV absorbing soft contact lenses with acceptable clinical performance may be prescribed on a routine basis.

Animals↗
PubMed1986

An evaluation of lenses designed to block light emitted by light-curing units.

A number of protective lenses are available to prevent ocular injury from wavelength spectrum generated by visible light. Four of the five lenses tested absorbed virtually all of the radiation transmitted in the 200 to 800 nm level. Protective eyewear should be used when blue and ultraviolet light-curing units are involved.

Composite Resins↗
PubMed1985

Wavelength dependency of cataracts in albino mice following chronic exposure.

Albino mice exposed to 1 X 10(-4) W cm-2 of UV radiation in the range 290-400 nm for 12 hr per day developed anterior lens opacities within 1-2 months after onset of the exposure. Histological changes demonstrated marked derangement of the lens epithelium. When the radiation was filtered with glass, eliminating radiation shorter than 320 nm, these opacities did not develop and the histology of the lenses was normal. We conclude that following chronic exposure, UV-B (290-320 nm) radiation is cataractogenic and acts via a mechanism involving the lens epithelium. UV-A (320-400 nm) does not appear to be cataractogenic, even with chronic exposure.

Animals↗
PubMed1985

DNA repair synthesis in the rat retina following in vivo exposure to 300-nm radiation.

Quantitative autoradiography was used to study the incorporation of 3H-thymidine into the retina of albino rats following in vivo exposure to 300-nm radiation. Relative to background labeling in unexposed eyes, there was 8-20 times as much label per unit area in the outer nuclear layer, inner nuclear layer, and ganglion cells of 300-nm exposed retinas. The photoreceptor inner segments also showed thymidine labeling in both control and exposed retinas.

Animals↗
PubMed1983

Rabbit eye exposure to broad-spectrum fluorescent light.

Two F40CW fluorescent lamps mounted in an EYS-2404 fixture and 300 nm, 5 nm waveband UV radiation were used to expose pigmented rabbit eyes. The results of the exposures to the eye were evaluated with the biomicroscope, ophthalmoscope, light microscope and electron microscope. The following conclusions were reached: The adverse ocular responses to fluorescent radiation exposure were due to long-duration, broadband radiation. These reactions were more generalized for fluorescent exposures when the cornea and lens are compared to UV exposures. The differences between the levels of threshold exposure needed to cause damage for the fluorescent source and UV radiation were attributed to exposure duration and the rate of delivery of the radiation. Corneal and lenticular damage was mild when compared with UV 300 nm exposures, and the threshold occurred after 8 h to 12 h of exposure. The effect of the radiation was to interfere with the normal functions of the cell while changes to the inert materials in the tissues was secondary to injury to the cell. The damage was mild in the corneal epithelium, somewhat more severe in the corneal endothelium, but minimal in the corneal stroma. Early retinal changes were found after 8 h of exposure to the fluorescent source. These induced changes were evident in the neural retina as spaces and were assumed to represent oedema. The retinal oedema was initially found only in the receptor cell, outer nuclear and nerve fibre layers. Many vacuoles or spaces were located in the junctional area between the ganglion cell and nerve fibre layers while smaller spacing occurred also within the nerve fibre layer. Twelve h of exposure to the fluorescent source produced a further increase in the oedema in the retina. The outer segments of the receptor cells appear to disintegrate and significant open spaces are evident among the inner and outer segments of the receptors. The inner plexiform layer shows an increased number of spaces within and among the neural elements, and the mitochondria appeared to be undergoing changes. The 20-h and longer exposure induced severe changes affecting all layers of the retina. These changes include massive retinal oedema with degenerative signs in all retinal neurons. A sympathetic reaction of the unexposed, contralateral eye occurred as the result of the damage to the exposed eye. Minimal sympathetic responses to the cornea and the lens began at exposure durations at or above 12 h, while the retina showed the sympathetic reaction beginning at 8 h.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1982

Space shuttle suit alert system visual acuity problem.

The National Aeronautics and Space Administration (NASA) requested solution of a visual acuity problem that presbyopic astronauts had when viewing an alert system visual display attached to their Space Shuttle suits. Solutions wee analyzed in the context of constraints which prohibited major modifications of the suits. The solution to the problem was to mount Fresnel lens strips on the helmet so that presbyopic astronauts could view the visual display clearly.

Adult↗
PubMed1982

Dark adaptation and aging.

The literature relating aging and dark adaptation is discussed. The final threshold shows a significant rise in the increase in age which is more marked above the age of 60. The effects of stimulus hue (color), miosis, and the changes in the transmittance of the ocular media are explored as causes of the threshold rise. When the data are corrected for all of these effects, a threshold rise of about 0.5 log units remains which may be due to the interference in metabolism and to changes in the neural system.

Adolescent↗
PubMed1982

Visual acuity as a function of age.

The literature relating visual acuity and the aging process is reviewed. The Snellen fraction, parameters affecting visual acuity and difficulties in comparing different studies in visual acuity are discussed. Visual acuity was found to be a poor 20/1,000 to 20/800 at birth but improved to an almost normal acuity of 20/20 during the first year of life and remained relatively constant from 40 to 50 years of age. There was a moderate but steady decline in acuity as a person ages above 60 and on to the age of 80. The disease and physiological etiologies for this loss in acuity are provided. Methods which may be used to maintain or improve visual performance with age are suggested.

Adolescent↗
PubMed1981

Determination of infrared radiation levels for acute ocular cataractogenesis.

One hundred pigmented rabbit eyes and ten primate eyes were exposed to infrared (IR) radiation in the 715 to 1,400 nm wavelength range and to the full spectrum output from a 5,000 W Xenon high-pressure source. The ocular exposures were evaluated independently with a slitlamp by two researchers and classified for ocular damage. The primary ocular lesions resulting from exposure to IR radiation were corneal, iritic, and lenticular. Corneal damage varied from epithelial haze to epithelial erosion but no endothelial damage was found. The iris showed stromal haze and swelling. Lenticular changes showed small white dots that, occur at the level of the anterior cortex. All lens damage depended on iris involvement. Ocular damage was related to the rate of delivery of the IR radiation since the data show that as the irradiance level increases, the radiant exposure threshold decreases. Exposures for the full spectrum were found to be additive for irradiance levels at 4 W.cm-2 and above. The threshold radiant exposures for the full spectrum of 750 J.cm-2 for the cornea, 1,000 J.cm-2 for the iris, and 2,000 J.cm-2 for the lens were essentially identical to the IR exposure thresholds for the same irradiance levels. The primate threshold radiant exposure was a factor of six above the respective rabbit thresholds.

Animals↗