The wavelength region where the retina is most vulnerable to damage from light is the region from 435 to 440 nm. This wavelength region has caused much concern among specialists in Occupational Safety for adult industrial workers.

The 1974 Symposium on Illumination, sponsored by the U.S. National Institute of Occupational Safety and Health, NIOSH, warned that high lighting levels in that region of the spectrum could cause much damage to the eye, particularly retinal and macular degeneration (the macula is the most light-sensitive part of the retina).

Included in the Public Health Service's "Guide to the Recognition of Occupational Diseases" is this statement in the section on laser light:

"even a diffuse reflection from a high power laser can present an ocular hazard. An action spectrum has been recently developed to account for the variation in retinal sensitivity with wavelength for exposure times greater than ten seconds. The minimum threshold dose for retinal lesions occurs at 440 nm and is thought to be due to a photochemical process rather than to a thermal mechanism as in wavelengths greater than 500 nm" (47).

NIOSH's action spectrum or "blue-light hazard function" was published in 1980. It shows this maximum vulnerability range from 435 to 440 nm (48), as reproduced below in the second column of Table 1 for each of the wavelengths in column 1.

The third column gives the reciprocal of this hazard value, or the "retinal protection barrier" against that hazard. The last column indicates how much of the irradiance from the lamp in column 4 penetrates this barrier as the damage- weighted irradiance that harms the retina.
 

Table 1. Damage weighted irradiance from "Deluxe Cool White" fluorescent lamp

Transcriber's Note: This table has 5 columns: Wavelength in nanometers; Blue-light hazard function value; Reciprocal: blue light protection factor; Irradiance Watts per 10 nm as scaled; and Blue-light damage weighted irradiance. The point of this table is that the last column represents how much damage that frequency of light is causing. Look at the entry for 435 nanometers, you will see that the last column for that line is much larger than any other entry in the last column. This represents how dangerous this one spike of energy is in the fluorescent light.

The NIOSH data for this table and graph derive mostly from experiments which destroyed the retinae of monkeys, pigs, rats, and a variety of other mammals. The retinal structure of all mammals is virtually the same (49). Clinical experience with victims of welding accidents and accidental exposures to excess laser light confirms that humans are just as vulnerable in the same wavelength region as test animals. There is, thus, no basis for assuming that the developing preemie retina during its period of greatest vulnerability is immune to irradiation in a wavelength which quickly burns the retinae of other mammals. Much of the nursery lamps' energy is concentrated in precisely the wavelength that is known to cause the most damage to the retina.

Yet, the American Academy of Pediatrics prescribes for unprotected preemies weeks and months of continuous irradiation with lamps of extra high output in that most damaging wavelength, and at an intensity which is far in excess of adult tolerance levels. Its Committee on Fetus and Newborn specified in its 1977 Standards and Recommendations for Hospital Care of Newborn Infants that all infant care areas should have 100 foot-candles (ftc) of illumination from "Deluxe Cool White" fluorescent tubes (44). In October 1988 it reduced this intensity to 60 ftc (50).
 
As I will show in the next section, 60 ftc intensive care nursery lightning will expose a preemie's retinae in 15 min or less to the dose of retinal irradiance which NIOSH has established as the occupational danger limit for healthy adult industrial workers.
 

Continue reading