Myopia

Myopia is fundamentally a symptom of hypothyroidism and a chronic deficiency of glucose supply to the eye, a connection Ray Peat began drawing from his own childhood observations. 2 Peat noted that the onset of nearsightedness often begins in puberty, particularly in girls, as a result of low thyroid function, and he witnessed cases where timely thyroid supplementation corrected vision to normal. 2 He argued that the eyeball elongates because the smooth muscle cells in its wall, responsible for maintaining its roundness against the near-focus apparatus, are chronically starved of glucose. 7 This starvation is exacerbated by estrogen, which lowers blood sugar, explaining why many young women rapidly become myopic within weeks of starting the oral contraceptive pill, and why their vision can return to normal upon stopping the pill or beginning thyroid therapy. 2

The biochemical environment of the eye's connective tissues is central to the pathology. Peat explained that the sclera and cornea are rich in mucopolysaccharides, and that hypothyroidism leads to a condition of "myxedema," where tissues become overloaded with these glycoproteins, causing swelling and softening. 2 He identified high prolactin, associated with high estrogen or low thyroid, as a likely factor in this process, since several pituitary hormones stimulate mucin overproduction. 2 In experimental models, keeping animals in darkness or covering their eyes causes the eyeball to grow larger than normal, producing a soft and weak sclera. 2 Peat theorized that darkness mimics hypothyroidism by reducing nerve stimulation, which normally consumes oxygen and emits carbon dioxide, thereby allowing the connective tissues to swell. 6

Peat placed carbon dioxide at the center of both the problem and the solution, linking it directly to the anti-swelling and structural integrity of the eye. He reasoned that carbon dioxide maintains the fluidity of the aqueous humor and prevents edematous swelling in the cornea and lens, whereas in hypothyroidism, lactic acid is substituted for carbon dioxide, increasing viscosity and potentially contributing to glaucoma. 2 The therapeutic effect of high altitude on myopia—where Peat himself experienced a 3-diopter improvement—is explained by the Haldane-Bohr effect: reduced oxygen pressure causes hemoglobin to retain more carbon dioxide, creating the same tissue condition that optimal thyroid function does. 2 He also suggested that carbon dioxide saturates amino groups on structural proteins, inhibiting the chemical cross-linking that hardens connective tissue in aging. 6

The role of serotonin provides another mechanistic layer. Peat cited research showing that animals kept in darkness or with blurring lenses become nearsighted as the eyeball grows longer under the influence of increased serotonin, and that serotonin antagonists protect against this experimental myopia. 3 He connected this to the higher incidence of myopia and migraines in females, noting that estrogen inhibits the monoamine oxidase-A enzyme that detoxifies serotonin, while progesterone activates it. 3 An antithyroid effect from substances like excess dietary iodine can also manifest as nearsightedness. 9 Peat's recommended interventions included anti-estrogen and anti-stress nutrients, adequate light exposure, and thyroid supplementation to restore the anabolic, carbon dioxide-rich metabolic state that maintains the eye's normal shape. 2