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Two views are better than one
If you are over 45, you probably know all about bifocal lenses. If you are under 45, your time is coming. (Well, maybe not, as bifocals are rapidly being replaced by graded lenses.) With bifocals, flicking your eyes up and down enables you to get a sharp image of, alternately, distant objects and close-up objects. Since the two parts of the lens are physically separated from each other, you are forced to actually move your head up if, say, the closer object you want to focus on is above your line of sight - for instance, a spider dangling on a thread close to your head at forehead level.
Even with perfectly healthy and youthful eyes, the structure of your eye's lens makes it impossible to focus on both the dangling spider and a distant tree at the same time; the lens can focus on objects at only one distance at a time. When you switch from observing the near spider to the distant tree, or vice versa, muscles distort your lens to change the degree of refraction of incoming light rays so that they are focused on the retina at the back of your eye. (The retina is like a screen towards the rear of your eye onto which the image is focused. It contains light-sensitive cells that send information from the light striking it to the brain.)
Stop and imagine. What if you had an inbuilt bifocal lens consisting of two distinct parts, each with a different focal length, so that each one focused on objects at a different distance? Pretty clever idea. But on its own, such an arrangement wouldn't do you any good, would it? Why not? Because the two separate images would have different focal points inside the eye, and you have only one retina. O.K. Keep imagining. What if, now, you had two retinas, one behind the other, so that each bifocal could focus its image on a different retina? Now you're talking business. This would mean that you had the potential to do one or both of two pretty neat tricks: focus on a near and a far object at the same time or get two distinct views of the same object at the same moment. Of course, such an arrangement would be useless unless your brain was capable of processing and making sense of two different images simultaneously.
So it can't be done, you might say. Well, believe it or not, eye scientists are convinced they have discovered a creature with just such a bifocal system. Being so sophisticated in concept and design, of course, you would imagine that such an evolutionary development could only be found in a most advanced creature - at least a bird or, more likely, a primate. Well, as readers of this column know well, this site is going hoarse with repetition; evolution theory is bunkum. But when it comes to the Creator of heaven and earth, nothing that is logically possible is impossible (Jer. 32:27, Matt. 19:26). As of this writing, such an optical arrangement is known from just one creature — the larva of Thermonectus marmoratus (top left), a water beetle (top right) found in the southwest of the United States. The
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August, 24th, issue of Science Daily reports,
University of Cincinnati researchers are reporting on the discovery of a bug with bifocals - such an amazing finding that it initially had the researchers questioning whether they could believe their own eyes.
Thermonectus is a member of the Dytiscidae, a family of water beetles with over 400 species worldwide, most of which are approximately an inch long. If you have ever spent time looking for water bugs you have almost certainly seen both adults and larvae. Swimming pools that have been allowed to "return to nature" are the perfect place to find them. The adults are generally shiny black and are very conspicuous as they race around underwater, coming often to the surface to breathe and to recharge the air reservoir trapped between their abdomen and wing case. The sinister-looking larvae, sometimes known as water tigers, are armed with a pair of ferocious, sickle-shaped mandibles which they use to seize their prey - mostly mosquito larvae but including, occasionally, tadpoles or small fish - and inject them with digestive juices.
Investigators published their findings on the remarkable eyes of Thermonectus in a recent issue of Current Biology. They found that the eye has two distinct retinas, one lying immediately behind the other and that the lenses of the main eyes have two separate focal planes "separated by about 100 µm,1 which roughly matches the anatomical separation of these two retinas".2 They report,
Almost all animal eyes follow a few, relatively well-understood functional plans. Only rarely do researchers discover an eye that diverges fundamentally from known types. The principal eye. of sunburst diving beetle larvae clearly falls into the rarer category. On the basis of two different tests, we here report that it has truly bifocal lenses, something that has been previously suggested only for certain trilobites. T. marmoratus larvae have two retinas at different depths behind the lens, and these are situated so that each can receive its own focused image. It is plausible that T. marmoratus larvae. benefit from being able to simultaneously focus far and near objects on individual retinas. In addition, we think that within the principal eyes, separate images of the same object could be focused on each of two retinas, allowing each eye to function as ''two eyes in one.''
Reading the report, one picks up a distinct sense of wonderment felt by the authors. If only they could cast off the shackles of evolutionary thinking and realize that they are getting a glimpse into the infinitely creative mind of God.
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