Inward and outward permeability of the blood-retinal barrier in experimental myopia

To investigate the pathophysiology of the retina in myopia, vitreous fluorophotometry was used to evaluate the permeability of the blood-retinal barrier (BRB) in experimentally induced myopia in cynomolgus monkeys.

Five animals underwent unilateral eyelid suturing. The suture was removed temporarily at 3, 10, 16, 28 and 36 months, and the dioptric power and axial length were measured in both eyes. Vitreous fluorophotometry was performed before and 60 min after intravenous injection of fluorescein-Na. BRB inward permeability (P(in)) was determined by a computer simulation method. At 36 months, fluorescein-Na was injected into the vitreous cavity, and the intraocular fluorescence was measured. BRB outward permeability (P(out)) was determined by the computer simulation method.

Significant myopia developed by 10 months after suturing and progressed thereafter. Starting at 10 months, the P(in) of sutured eyes increased significantly compared with control fellow eyes, and the increase continued throughout the observation period. At 36 months, the BRB P(out) was significantly lower (P < 0.05) in the myopic than in the emmetropic fellow eyes, suggesting decreased active transport mechanisms at the BRB in myopia.

Our study demonstrated, for the first time, abnormal permeability of the BRB in myopic monkey eyes. Such abnormal permeability may play an important role in the development in human myopes of retinal and vitreous changes such as retinal detachment. Thus, simply correcting refractive errors surgically may not represent a cure for myopia. Patients who have had refractive surgery to correct myopia should also be closely followed up by vitreo-retinal specialists to manage vitreo-retinal disorders in originally myopic eyes.