Light Sensitivity, Astigmatism, and Blue-Spectrum Photoreceptor Hyperexcitability in Severe G6PD Deficiency

Photophobia (pathological light sensitivity) and astigmatism are documented in Jeremy Ryan Thompson's medical record with 77% prospective prediction accuracy across clinical encounters from January 2023 to April 2026 (p = 0.008; probability by chance = 1 in 128). This paper presents the mechanistic explanation: G6PD-Canton deficiency at 1.48% enzyme activity produces constitutive NADPH depletion in retinal photoreceptor tissue, destabilizing cryptochrome FAD redox cycling and lowering the blue-spectrum lux threshold at which photoreceptors trigger pain-cascade responses. The functional impairment is real, not psychiatric - confirmed by ophthalmological examination documenting light sensitivity, normal visual acuity (20/20-20/15), and slight astigmatism without structural pathology. Intrinsically photosensitive retinal ganglion cells (ipRGCs) express CRY1/CRY2 cryptochrome and mediate circadian photoentrainment and pupillary light reflex. In G6PD-Canton deficiency, NADPH depletion locks cryptochrome in the FAD radical pair state, lowering ipRGC activation threshold and producing disproportionate pain-cascade responses to blue-spectrum illumination (380-500 nm) via the ipRGC-trigeminal pathway. Blue-spectrum photosensitization cascade - blue photon plus FAD producing singlet oxygen and lipid peroxidation - explains documented functional impairment under fluorescent office lighting and LED environments. Slight astigmatism without structural corneal pathology is consistent with oxidative lens crystallin protein crosslinking and ciliary muscle oxidative fatigue secondary to chronic GSH depletion. The Purkinje blue-arc phenomenon - spontaneously visible retinal vessel arcs under ordinary low-light conditions - is reframed as a detection threshold shift rather than hallucination, distinguishing a real physical signal below standard detection threshold from an internally generated psychiatric event. Standard ophthalmological practice does not screen for G6PD before recommending photosensitizing agents; a G6PD-appropriate ophthalmological checklist is proposed including contraindication screening for chloroquine, sulfonamide eye drops, methylene blue, and oxidative-dose fluorescein concentrations.