The spatial density distribution of macular pigment in primate retinas was described by two-wavelength microdensitometry of retinal sections The macular pigment is most dense along the path of the receptor axons in the center of the fovea Another band of high density is present in the inner plexiform layer in many retinas The density in both fiber layers declines to low, relatively constant levels within 1 mm eccentricity Both the total retinal density of macular pigment and the contributions of subsets of the retinal layers were estimated by integrating along the path of light traversing the retina from the vitreal surface to the outer segments The integrated densities were measured at several eccentricities to establish the profile of macular pigment density along a diameter through the fovea The macular pigment profile was unimodal in some cases and trimodal in others The main central peak always occurred in the center of the fovea The total retinal density of the central peak ranged from 042-10 absorbance Most of the pigment is interposed between the outer segments and the stimulating light and is effective as a visual filter The macular pigment is dichroic, with the major axis of absorption oriented tangential to a circle centered on the fovea This is consistent with commonly accepted explanations of Haidinger's brushes Invest Ophthalmol Vis Sci 25:674-685, 1984 In the companion paper 1 we showed that the macular pigment density is greatest in the fiber layers at the center of the fovea, and it declines rapidly with retinal eccentricity Since the foveal geometry changes drastically within fractions of a millimeter, the resulting spatial pattern of macular pigmentation can be quite complex The functional implications of this spatial distribution are still poorly understood The most widely accepted role of the pigment is to reduce the deleterious effects on visual acuity of the chromatic aberration of the eye 2 " 4 In this regard, the exact location of the pigment within the retina is not critical; the macular pigment can be viewed simply as a filter that lies between the photopigments and the incoming light A second functional role of the macular pigment may be protection of the retina from light damage, since it absorbs wavelengths that are known to be especially damaging to the retina 5 " 8 A protective role is consistent with findings that the pigmented macular

The macular pigment. II. Spatial distribution in primate retinas.

Light-emitting diodes (LEDs) have been used to provide illumination in industrial and commercial environments. LEDs are also used in TVs, computers, smart phones, and tablets. Although the light emitted by most LEDs appears white, LEDs have peak emission in the blue light range (400-490 nm). The accumulating experimental evidence has indicated that exposure to blue light can affect many physiologic functions, and it can be used to treat circadian and sleep dysfunctions. However, blue light can also induce photoreceptor damage. Thus, it is important to consider the spectral output of LED-based light sources to minimize the danger that may be associated with blue light exposure. In this review, we summarize the current knowledge of the effects of blue light on the regulation of physiologic functions and the possible effects of blue light exposure on ocular health.

/pdf/effects-of-blue-light-on-the-circadian-system-and-eye-37qaaosmxg.pdf

Effects of Blue Light on the Circadian System and Eye Physiology

Solar radiation and age-related macular degeneration.

Photochemical damage of the retina.

This paper reviews the biosynthesis and physicochemical properties of the ocular melanin. Age-related changes of melanin granules and the corresponding formation of lipofuscin pigments in the retinal pigment epithelium (RPE) are also described. Adverse photoreactions of the eye and, in particular, light-induced damage to the RPE-retina are reviewed in relation to the ocular pigmentation. A hypothesis on the photoprotective role of the RPE melanin is presented that is based on the ability of the cellular melanin to bind redoxactive metal ions. Since bound-to-melanin metal ions are expected to be less damaging to the pigment cells, it is proposed that sequestration of heavy metal ions by the RPE melanin is an efficient detoxifying mechanism. It is postulated that oxidative degradation of RPE melanin may lower its metal-binding capability and decrease its anti-oxidant efficiency. Cellular and environmental factors that may contribute to possible oxidative damage of the RPE melanin are discussed in connection with the etiology of age-related macular degeneration.

Properties and function of the ocular melanin--a photobiophysical view.

—Exposure of the retina of the rhesus monkey to visible and infrared radiation from CW optical sources like the Sun, xenon lamps, etc. produces small lesions or scotomata which may be classified as thermal or photochemical, depending on the wavelength and duration of exposure. The action spectrum for the production of retinal lesions has been determined for eight monochromatic laser wavelengths extending from 1064 to 441 nm. The corneal power required to produce a lesion decreases by three orders of magnitude in going from 1064 to 441 nm. Exposure to 1064 nm radiation for 1000 s produces a typical thermal lesion at elevated retinal temperatures. whereas a 1000 s exposure to 441 nm light produces a photochemical lesion at power levels too low to raise the retinal temperature by an appreciable amount (<0.1°). The two types of lesion have entirely different characteristics as will be discussed in some detail. The photopathology of thc photochemical lesion has been studied at postexposure times ranging from 1 h to 90 days and will be demonstrated in a number of histological slides. Moreover, this photopathology correlates well with monocular visual acuity tests in the rhesus monkey as defined by the Landolt ring technique.

To further elucidate the differential effects on the retina of short vs long wavelength CW radiation, we have divided a simulated solar spectrum at sea level into two spectral bands. 400–800 nm and 700–1400 nm, and determined the radiant exposures required to produce very mild lcsions on the rhesus retina for exposure times of 1, 10, 100 and 1000 s. To correlate our data with solar retinitis and eclipse blindness the image diameter or spot size on the retina was 159 μm, corresponding to the image size of the Sun on the human retina. Exposure to the 400–800 nm spectrum for durations of 10 s or greater required approximately 400 J/cm2 to produce a mild photochemical lesion. Reciprocity is maintained over the exposure range 10–1000 s. Radiant exposure to the 700–1400 nm spectrum, on the other hand, required roughly 69,100 J/cm2 for a 1000 s exposure. This was a mild thermal lesion. We were unable to produce a lesion for exposure times less than 1000 s. We interpret these data to mean that solar retinitis and eclipse blindness are primarily photochemical events produced by the short wavelength component of the solar spectrum, and that the infrared component of the solar spectrum plays only a minor role in these retinal pathologies.

Sensitivity of the retina to radiation damage as a function of wavelength

The nature of retinal radiation damage: Dependence on wavelength, power level and exposure time

The paper of Verhoeff and Bell (1) in 1916 became a landmark in the history of radiation injury to the retina. These authors demonstrated that high intensities of light on the retina produced burn lesions. In their own words, “our experiments show with the utmost distinctness that the effects known as eclipse blindness are wholly thermic, due to the intense concentrations of the solar energy upon the retina by the refracting system of the eye itself forming an image of destructive energy intensity---”. This emphasis on thermal injury, particularly for solar retinitis and eclipse blindness, tended during the ensuing years to obfuscate other possible effects of light on retinal tissue.

Solar Retinopathy as a Function of Wavelength: Its Significance for Protective Eyewear

Visual performance in the rhesus monkey after exposure to blue light

Recent research has shown that blue light exposure is an important factor in certain types of retinal injury. The mammalian ocular media transmits the spectral band 400-1400 nm to the retina. The short wavelengths (400-550 nm) produce a photochemical or actinic type of damage, while the longer wavelengths (550-1400 nm) produce thermal damage. Distinction between the two types of retinal damage are discussed briefly and the importance of the blue light effect for solar retinitis and eclipse blindness is emphasized. The significance of blue light retinal injury is summarized for various environmental and occupational exposures.

Retinal Effects Of Blue Light Exposure

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