AbstractBackgroundLight
exposure entrains the circadian clock through the intrinsically
photosensitive retinal ganglion cells, which sense light in addition to
the cones and rods. In congenital achromatopsia (ACHM; prevalence
1:30-50,000), the cone system is non-functional, resulting in severe
light avoidance and photophobia at daytime light levels. How this
condition affects circadian and neuroendocrine responses to light is not
known.MethodsIn
genetically confirmed ACHM patients (n=7; age 30-72 years; 6 women, 1
male), we examined survey-assessed sleep/circadian phenotype (PSQI, ESS,
MEQ, MCTQ), self-reported visual function (NEI-VFQ-25), sensitivity to
light (VLSQ-8) and use of spectral filters that modify chronic light
exposure. In all but one patient, we measured rest-activity cycles using
actigraphy over 3 weeks and measured the melatonin phase angle of
entrainment using the dim-light melatonin onset
(DLMO).ResultsACHM
patients experience a severely attenuated light-dark cycle due to severe
light sensitivity and habitual use of filters to reduce retinal
illumination. In aggregate, both MEQ and MCTQ indicated a tendency to
late chronotype. We found regular rest-activity patterns in all patients
and normal phase angles of entrainment in participants with a measurable
DLMO.ConclusionsOur
results reveal that a functional cone system and exposure to daytime
light intensities are not necessary for regular behavioural and hormonal
entrainment, even when survey-assessed sleep and circadian phenotype
indicated a tendency for a late chronotype and sleep problems in our
ACHM cohort. Our results can be explained by an adaptation mechanism in
circadian photoreception which adjusts to the range of habitual light
exposures.
