Purpose: Details of the posterior eye water dynamics are unclear. Aquaporin-4 (AQP4), a water channel, plays an important role in water dynamics in the central nervous system and is also present in the ocular tissue. The purpose of this study was to reveal the role of AQP4 in the water dynamics of the posterior eye using in vivo JJ vicinal coupling proton exchange (JJVCPE) magnetic resonance imaging (MRI) of AQP4 knockout (KO) mice and their wild-type littermates (controls). Methods: JJVCPE MRI of the eye was performed on five AQP4 KO mice and seven control mice. We assessed the normalized signal intensities of a region of interest (ROI) set in the vitreous body after H₂¹⁷O administration. The results of the two groups were compared using a two-tailed Mann-Whitney U test. Results: A statistical analysis revealed that the normalized ROI signal intensities at the steady state were significantly lower (P = 0.010, <0.05) in the AQP4 KO mice (mean ± SD, 84.5% ± 2.7%) than the controls (mean ± SD, 88.8% ± 1.9%). Conclusions: The present study using JJVCPE MRI of the eye demonstrated that retinal AQP4 has a potential role in the regulation of water inflow into the vitreous body. Absence of AQP4 in the KO mice probably induces lower water outflow from the vitreous body. Our results could help clarify the pathogenesis of various ocular diseases.

Ocular aqueous humor plays an important role in maintaining retinal function. Recent findings indicate that aqueous humor, which flows into the vitreous body, is probably absorbed by Müller cells in the retina, and this process is mediated by aquaporin-4. In this review, we aim to summarize the results of studies on classical aqueous humor circulation and postiridial flow, a pathway proposed in the late 1980s for the inflow of aqueous humor into the vitreous body. In addition, we aim to discuss the retinal glymphatic pathway, inferred by recent findings, with a focus on the anatomical location of aquaporins and barriers that regulate water movement within the tissue. Similarly to the cerebral glymphatic flow, the function of the retinal glymphatic pathway may decline with age, as supported by our findings. In this review, we also discuss age-related ocular diseases that might be associated with the dysfunction of the retinal glymphatic pathway.

Background: Posterior microphthalmos (PM) is a rare condition with poor visual prognosis even after amblyopia treatment. We report a case of PM with achievement of good visual acuity and disappearance of papillomacular retinal folds (PFs) over a period of 7 years. Case presentation: A girl aged 3 years and 5 months was referred to our hospital, after poor visual acuity was identified at a medical checkup for 3-year-olds. She had severe spherical hyperopia: + 17.25 D in the right eye (RE) and + 18 D in the left eye (LE). Her corrected visual acuity was 20/200 in the RE and 20/250 in the LE. PFs were observed in both eyes on optical coherence tomography (OCT), and the diagnosis of PM was made based on the normal corneal diameter and anterior chamber depth. During the course of the disease, a gradual decrease in the height of the PFs was observed on OCT. The corrected visual acuity at age 10 years was 20/20 in the RE and 20/25 in the LE. Conclusions: The visual prognosis of PM is poor, and only one case with good visual acuity has been reported in the literature. The patient in the present case not only developed good visual acuity, but also showed improvement in macular morphology, which was not noted in previous reports. Early diagnosis of PM and early amblyopia treatment is important for the visual development in PM.

Background: To investigate the clinical characteristics of children with congenital ptosis, with particular attention given to the incidence of anisometropia, and the difference in axial length (AL) between the right and left eyes. Methods: The medical charts of 55 patients with congenital ptosis at Niigata University Medical and Dental Hospital were retrospectively analyzed. Clinical characteristics, including age, cycloplegic refraction, AL, and the presence of amblyopia and its causes were analyzed. Results: Age at the initial visit was 16 ± 20 (mean ± standard deviation, the same applies below) months. Of the 49 patients whose cycloplegic refraction was measured, hyperopic anisometropia, defined as ≥ one-diopter difference in spherical equivalent (SE), was observed in 1/11, 9/27 and 5/11 patients with bilateral, right, and left ptosis, respectively. Among 14/38 patients with hyperopic anisometropia involving unilateral ptosis, 13 demonstrated a larger SE in the ptotic eye than in the non-ptotic eye. The inter-eye difference in AL (AL of the ptotic eye minus that of the non-ptotic eye) in six patients with unilateral ptosis and hyperopic anisometropia ipsilateral to the ptotic eye (-0.29 ± 0.40 mm) was significantly smaller than that in three patients with unilateral ptosis and no hyperopic anisometropia (0.38 ± 0.29 mm). Conclusions: At our institute, children with congenital ptosis had a high incidence of hyperopic anisometropia ipsilateral to the ptotic eye. Furthermore, this condition was associated with a shorter axial length. These results indicate that refractive correction for hyperopic anisometropia is important for proper visual development in children with congenital ptosis.