Eye Didn't Know!

What were they thinking?

Did you know? I only watch one television show from network television, but it shall remain nameless here, so as not to spoil the plot of a recent episode. The reason I write, is that the climax of this episode occurs when a character reveals that she has been cured of her retinitis pigmentosa by a corneal transplant! If this were true, it would be a first.

The eye is like a camera. The retina is like film in a camera (okay, like the digital sensor), lining the BACK of the eye. In retinitis pigmentosa, the retina deteriorates. There is no known cure for retinitis pigmentosa at this time.

The cornea is the clear window on the FRONT of the eye. There are many conditions which lead to a damaged cornea (such as getting lye splashed into your eyes, or from keratoconus, which causes the cornea to be misshaped). A cornea transplant will cure these conditions, but it is not related in any way to the retina!

In this same show last season, its title character had a noxious substance thrown into his eyes. A doctor peers into his eyes and declares that his optic nerves had been damaged! This is also ludicrous, as the optic nerve enters the rear of the eye, whereas if a dangerous substance splashes into the eye (as opposed to forceful trauma) one may worry about damage to the cornea.

Did you also know? This same network produces the medical show, House, with its complex and ingenious medical story lines. Surely they can afford to have their medical consultants (or maybe House!) take a few minutes to proofread the other shows in their lineup.

(image from NIH)

Orthokeratology: new and improved?

Did you know? Orthokeratology, or changing the refraction of the eye by overnight use of rigid contact lenses, is making a resurgence under the name of Corneal Refractive Therapy, or CRT.

Recently a friend of mine asked me about its efficacy in children. He was concerned that his daughter’s mild myopia would continue to progress. Since orthokeratology is not used by the vast majority of ophthalmologists, I could not immediately answer his question.

It so happens that the lead article and editorial in the May 2007 issue of Archives of Ophthalmology were about the dangers of orthokeratology! A study from Taiwan, (where myopia is extremely common and the interest in orthokeratology has grown), reported the risk factors for microbial keratitis, or corneal ulcers, which are serious and potentially sight-threatening infections of the cornea, the clear front surface of the eye. A major risk factor was orthokeratology. The authors stated that this risk was:

“...worthy of special attention given the increased popularity of overnight orthokeratology. Eye care practitioners who perform overnight orthokeratology have an obligation to warn their patients of this potential vision-threatening complication...”

The journal’s editors stated:

"The rationale for the ongoing use of overnight orthokeratology in the pediatric and adolescent population is therefore brought into question. Although these techniques can rapidly and effectively reduce myopia, albeit with limited range, accuracy, and precision... complete or near complete regression of effect is the rule, and this technique has not been demonstrated to have any infulence on mypopia progression due to [lengthening of the eye]."

In other words, orthokeratology temporarily reduces myopia, with limited precision, presents a risk of serious infection, and does nothing to reduce progression of near-sightedness.

Parents considering orthokeratology for their children should heed the messages in this article.

Furthermore, it should be pointed out that if you use orthokeratology, every time you stop wearing your overnight lenses, your refraction will be shifting, so that backup glasses will not be useful!

Did you also know? Parents should realize that by the time their children are adults, the science of refractive surgery will be even further refined, safe, predictable, and permanent, which cannot be said of orthokeratology, despite its appeal of being non-surgical.

Corneal thickness and glaucoma

Did you know? The thickness of the cornea (the clear window in the front of the eye) has a direct influence on the measurement of pressure in the eye. With current technology, a thin cornea will lead to a falsely low pressure reading, while a thick cornea will lead to a falsely high reading. This can cause errors in the diagnosis and treatment of glaucoma, which occurs when the eye pressure is too high for the health of the optic nerve. For this reason, I now measure corneal thickness in all patients who are suspects for glaucoma. I often find patients treated unnecessarily for glaucoma, as well as patients with thin corneas who actually need treatment.

Did you also know? A Canadian company is developing a device which uses the reflectance of sound waves off the eye to measure eye pressure. Time will tell if it will replace current methods of measuring eye pressure.

Pterygia

Did you know? A pterygium (plural=pterygia) is a fleshy growth which extends from the conjunctiva (the white part of the eye) onto the cornea (the clear part of the eye). Pterygia are common among those who spend time outdoors, such as farmworkers, surfers, or motorcyclists. It is not clear what causes them to begin, but they grow with continued exposure to the sun and the wind. I see them every time I visit the Flying Samaritans eye clinic in Tecate, Mexico.

Mid-sized pterygium
(the enlarged pupil is after dilating drops from an eye exam.)
(courtesy of ASCRS photo library)

Did you also know? A pterygium which is threatening vision (by approaching the pupil or by distorting the cornea) can be removed surgically. If it is small, then lubricating artificial tears, sunglasses, and a hat for protection from the sun and wind are advised.

Aloe Vera

Did you know? Aloe vera contains an ingredient which may someday prove useful to inhibit scarring in the cornea. Mannose-6-phosphate is a sugar derived from aloe vera. It has been recently shown to inhibit cultured corneal cells from transforming into scar-like tissue. This may reduce haze formation sometimes seen after injury or after refractive surgery. Read more here.

Did you also know? The haze which sometimes occurs after PRK (photorefractive keratectomy) surgery is very rare today with better lasers providing a smoother surface after surgery.

Snow Blindness

Did you know? With ski season upon us, it is worth repeating how important eye protection is while in the mountains. Goggles or quality sunglasses are a necessity before heading to the slopes. Failure to protect your eyes could result in the very uncomfortable ultraviolet keratitis, which is basically a sunburned cornea. While treatable with rest and eyedrops, prevention is the best medicine!

Did you also know? The Inuits used goggles carved from caribou antlers to shield their eyes from the sun.

(image courtesy Cambridge Bay Weather, Wikimedia Commons)