retinal phototoxicity… blue light hazards?—what are … · blue light hazards?— what are we...
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RETINAL PHOTOTOXICITYhellip BLUE LIGHT HAZARDSmdashWHAT ARE WE LOOKING AT
David H Sliney PhDConsulting Medical Physicist
Fallston MD USA
andFaculty Associate Bloomberg School of Public Health
Johns Hopkins University Baltimore MD USA
DoE SSL RampD Workshop-Dallas 2019
ldquoBlue-Light Hazardrdquo ndashSurfing the Net hellip
bull ldquorisks associatedhellipLEDsrdquondash Eye fatiguendash Sleep rhythm disordersndash Age-related macular
degeneration (AMD) D Sliney 2018
The conclusion one could arrive at from a ldquoblue-lightrdquo web search
ldquoBlue light is everywhere especially in sunlight Excessive exposure to harmful blue light however is due to the increased use of LED lamps and screens Whether at work or at home we spend a large part of our days in front of a screenrdquo
D Sliney 2018
Message amp Fig from German optometry website on blue light hazard (ergoptometriede)
hellipso what does the science really say
The Puzzle of Light and AMDhellip
bull Despite many in vitro and animal laboratory research studies over the last several decades pointing to the potential role of light mdashparticularly short-wavelength light mdash as a cause of (etiology) or promotion of age-related macular degeneration (AMD) but only limited epidemiological evidence supporting this link
bull Why the lack of agreement in scientific studiesD Sliney 2014
For Retinal-Mediated Effectshellipfor vision for circadian for blue-light
hellipwe need to examine actual retinal exposurebullEr = 027 Lτ de
2
Retinal illumination is directly proportional to luminance and radiance ndash not to illuminance in lux
D Sliney 2006
LIGHT
ROSDisks
LIGHT
ROSLipofuscin
DebrisDrusen
ChoroidalCompromised Transpor
Cell Death
Intra retinal
Courtesy J Marshall
SohellipSome Key Questions
What is the typical retinal exposure from outdoor daylight from lamps and artificial sourcesHow do these levels compare to the retinal
illumination levels used in research studiesHow do outdoor daylight exposures vary with
different action spectraWhat about ultraviolet exposures of retinal
tissues Are they really insignificant
D Sliney 1983
Physiological Levels of Retinal Illuminationbull The retinal illumination in
the ambient outdoors is of the order of 002-01 mWcm2 (lt 1 cdcm2) and these levels are just comfortable to view
bull Retinal illuminance outdoors is ~ 5x105 td
bull The sunrsquos image is more than 10000 times greater ( gt 1 Wcm2) than sunlight from snow
D Sliney 2006
The Macula Lutea - Pigment Lutein
In the inner and outer plexiform layers
Thought to minimize BLH
Photochemically Induced Retinal Injury mdash Exposure Duration
bull At least 2 types of light damage are seen with time
bull Type 1ndash Noell 1966mdash12 hdayndash rhodopsin cone opsins
bull Type 2ndash Ham Mueller Sliney 1976ndash blue-light chromophore 446 nmndash photomaculopathy
Fig from Mellerio Sliney 2010
D Sliney 2009
Two Types of Light Damage for the Mammalian Retina
bullType 1 (Noell) resulting from a full-bleach of retinal pigments resulting in toxic build-up of retinoids in the Retinal Pigment Epithelium (RPE)
bullType 2 (Ham) resulting from phototoxic reaction in RPEmdashthe blue-light hazard -IESNA RP-27bullIs there a third
Two Distinct Action Spectra
Mellerio
TYPE 1
TYPE 2
D Sliney 2006Wavelength (nm)
T
rans
mis
sion
Melanopsin from Berson et al Science 295 2002
00
100
200
300
400
500
600
700
800
900
1000
350 400 450 500 550 600 650 700
V (λ)
-3
-4
-2
-1
0
Blue LightFunction
Log
rel
ativ
e se
nsiti
vity
Lens Transmission
53 years
Melanopsin
Fig Courtesy J Marshall
Changing atmospheric pathlengths- and changing spectral appearance of solar disc
Bluish whiteWhite
Yellow
Orange
Does our brain assess solar SPD through 5 retinal photoreceptors
Staring at the SunhellipWhen is it safe- The risk of acute retinal exposure
D Sliney 2006
UVR and blue light are scattered out of the direct image making the yellow-to-red sun safe to view directly at sunset but staring at the sun at midday produces photomaculopathy
Environmental Agents and Ocular Disease
Epidemiological studies produced surprisingly inconsistent findings relating ocular disease to ambient light as well as estimated UV exposure Can a lack of consistent results be due largely to
incomplete or erroneous estimates of optical dose Of greatest importance are the geometrical
factors that influence retinal exposure as well as UV exposures to different segments of lens cornea and retina (also need local temperature for lens)
Individual Variability
Generally ignored factorsndash Individualrsquos pupil sizendash Individualrsquos sun-avoidance behaviorndash Individual lid opening ndash reallyndash Individualrsquos lenscorneal spectral
transmission ndash varies with age latitudendash Potential photophobia
How big a factor can each of these be
For very small children small amounts of 295-325 nm UV reach the retina
Childhood sunlight exposure frequently overlooked
UVviolet Spectral Transmittance of the Human Lens (Data of Barker amp Brainard)
UV-A absorbing chromophores have fascinated biochemists ndash some lenticular fluorophores
White LEDs do not emit this UV
Pupil Size in Moderate Daylight mostly cloudy (Area gt 3x variation)
1000lt Illuminance lt1500 cdm^2
0
05
1
15
2
25
3
35
0 500 1000 1500 2000
illuminance (cdm^2)
pupi
l dia
met
er
Series1
Series2
Series3
Series4
Series5
Series6
Series7
Series8
II