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Nerve impulses convey humans’ special senses. Without nerve impulses, humans are unable to feel, taste, smell, hear or see. These impulses depend on special proteins known as ion channels, that allow electrolytes like sodium, potassium, and chloride to pass across cell membranes. In single cell organisms, like algae, some of these ion channels are light-sensitive (light-gated ion channels); meaning, light can activate the ion channel, and subsequently affect a downstream cellular process (like cellular motility). These light-gated ion channels have been utilized extensively in the past two decades to study neural circuits. This technique is referred to as optogenetics. Earlier this week, researchers in Pittsburgh, Switzerland and France reported results of using optogenetics for the first time in humans. A microbial protein conferring light sensitivity onto retinal ganglion cells was expressed using viral-based gene therapy delivered with an intravitreal injection (an injection into the vitreous cavity of the eye). The protein expressed was a modified channelrhodopsin. Channelrhodopsins are what permit single cell organisms like algae to display phototaxis (i.e., their ability to move in response to light). This molecular trick bypassed degenerated light-sensing photoreceptor cells in a patient with retinitis pigmentosa, and allowed a patient to recover some limited sight with image-enhancing goggles.
A patient who was initially doing well after a recent cataract surgery, experienced a sudden worsening of vision. Their eye became red, and they developed severe pain. The vision had worsened from 20/30 (two lines from 20/20) to counting fingers (only able to count fingers of the examiner presented one foot away from their face). I examined the patient, who had severe inflammation in the eye, and I performed an ultrasound of the eye, which showed dense inflammation in the vitreous cavity.
Much like a cast immobilizes a limb and helps it heal, during retinal surgery, your surgeon may use an analogous immobilization/healing aid. Surgery on the retina that requires removal of the vitreous gel (called a vitrectomy) sometimes requires placing a vitreous substitute that exerts a force on the retina to flatten the retina. While the vitreous can be replaced with saline in cases where no such force is necessary, many retinal conditions such as retinal detachments and macular holes, require placing a gas mixture or oil in the eye.