気ままなリライト６０

「大人になって近視」増加　スマホやパソコン凝視影響か

Whether a growing number of the younger generation are living with agnogenic disease with a symptom called myopia or a neurological tendency toward nearsightedness is chosen by the brain unconsciously as the optimal way in competition for survival in the modern age, the eyesight crisis is spreading across the globe. Japan is no exception. Before nearsighted people are aware of the blurred image of far-off objects created in their brains, the source of the image comes to the brain from the eye as a visual sensor system arranged especially for close-up things. The brain, the visual cortex seems to stop being flexible enough to correct or reconstruct the sensor data with reflective errors in the signals from the retina, the sheet of photoreceptors at the back of the eye as the brain cherishes what a nearsighted brain owner is unwittingly inclined to adjust to.

Myopia is more likely to be linked to a decline in the performance of the human camera eye. Having vision means being aware of the 3-D image adjusted or reconstructed in the brain, based on the visual data about the light rays entering the eye through the cornea, pupil and crystalline lens. In nearsighted eyes where the distance between the cornea and the retina is too long for the light rays to focus on the retina, the data sent to the brain has reflective errors because the vision focused in front of the retina, instead of being on it becomes blurry when objects at distance are seen by nearsighted eyes. A lack of elasticity of ciliary muscle to stretch the crystalline lens is likely to be to blame for the elongated eyeball with too long a distance between the cornea and the retina as the ciliary muscle serving as a self-focusing function by stretching the lens fails to work to keep pace with the eye growth, thus restricting the eye expansion like a balloon pinched on one end. The eyeball with the stiffened ciliary muscle tends to get oblong in the process of the eye growth in childhood and adolescence.

The brain cared about dealing with certain types of tasks the brain owner devoted much time to when the eye’s function was adjusted to the lifestyle of self-quarantine during the pandemic. The incoming data from the retina played an important role in determining whether the perception of the visual world should be tilted toward nearsightedness or farsightedness. The home-confined lifestyle dealt a blow to young people’s eye health as quarantine myopia due to the increased time spent watching the screens of TVs, computers and smartphones as a habit of being exposed to the light rays being focused in front of the retina. According to an ophthalmologic survey by the Ministry of Health in fiscal 2021, the myopia rate measured among children shot up. Below the baseline vision of 20/20 in visual acuity were 23 % of children aged six and nearly 50 % of children aged eleven. A teleworking female in her thirties in Tokyo fell prey to quarantine myopia as her overstained ciliary muscle brought a decline in her eyesight to 20/200 vision for the right eye and 20/75 vision for the left eye in January 2023, compared with 20/20 vision with both naked eyes five years ago.

Once myopia has begun to develop in childhood, it seems that the resilient response from the brain hasn’t worked without a drastic change in the lifestyle with risk factors associated with myopia. As an effective and safe way of slowing its progression, many parents of nearsighted children are relying on ophthalmologic treatment and therapy. For nearsighted children enthusiastic about doing sports without the help of glasses, orthokeratology lenses and bifocal contact lenses are available as vision correction surgeries like LASIK are not recommended until adulthood when vision is stable. Ortho-k is designed to temporarily reshape the cornea to improve the blurry vision with the contact lenses wearing overnight, then removing during the day. The national insurance doesn’t cover the cost of ortho-k lenses including follow-up care. Atropine eye drops in small doses are being prescribed by many pediatric ophthalmologists across the globe to stop or slow the progression of nearsightedness in children and teenagers. Like the sunshine stimulating dopamine release in the eye, the drops boost dopamine to slow the eye growth, keeping nearsightedness from worsening and developing glaucoma, retinal detachment, cataracts and maculopathy.