# *Questions for creationist

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Posted by Retina -Phero [Phero] on November 28, 1999 at 12:26:12 {hcnmikA.FkdmhhsMJ.h2KYT0XYayR.}:

In Reply to: Questions for creationist posted by J.H. on November 28, 1999 at 09:25:18:

The question of the inverted retina:

Although it would appear at first sight that the inverted arrangement of the retina has disadvantages and is inefficient, in reality these objections amount to little. Even evolutionists concede that the inverted retina serves those creatures that possess it, very well; it affords them superb visual acuity. We have reviewed the necessity for this arrangement which turns on the nature of the photoreceptors.
The eyes are further shielded from excessive exposure to light and UVR by anatomical features: the normal horizontal orientation of the eyes when in the upright posture, the eyebrows (particularly for those with deep-set eyes), the nose and the cheeks. But any natural defence system can be overwhelmed and so it is sensible when necessary (just as it is to wear extra clothing in cold weather) to wear or use extra protection against UVR and blue light; all the more is this so with the depletion of our ozone layer.
Light at various wavelengths is capable of very damaging effects on biological machinery. The retina, besides being an extremely sophisticated transducer and image processor, is clearly designed to withstand the toxic and heating effects of light. The eye is well equipped to protect the retina against radiation we normally encounter in everyday life. Besides the almost complete exclusion of ultraviolet radiation by the cornea and the lens together, the retina itself is endowed with a number of additional mechanisms to protect against such damage:

- The retinal pigment epithelium produces substances which combat the damaging chemical by-products of light radiation.
- The retinal pigment epithelium plays an essential part sustaining the photoreceptors. This includes recycling and metabolising their products, thereby renewing them in the face of continual wear from light bombardment.
- The central retina is permeated with xanthophyll pigment which filters and absorbs short-wavelength visible light.

The photoreceptors thus need to be in intimate contact with the retinal pigment epithelium, which is opaque. The retinal pigment epithelium, in turn, needs to be in intimate contact with the choroid (also opaque) both to satisfy its nutritional requirements and to prevent (by means of the heat sink effect of its massive blood flow) overheating of the retina from focused light.
If the human retina were 'wired' the other way around (the verted configuration), as evolutionists such as Dawkins propose in The Blind Watchmaker, these two opaque layers would have to be interposed in the path of light to the photoreceptors which would leave them in darkness!
Thus it would seem that the need for protection against light-induced damage, which a verted retina in our natural environment could not provide to the same degree, is a major, if not the major reason for the existence of the inverted configuration of the retina.

Phero

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