All dysteleological arguments make two false assumptions: (1) that the designer must only make things which are pain-free and have no suboptimal features, and (2) that the design is indeed suboptimal. In short, all of these dysteleological arguments about pain or suboptimality are theological arguments which do not make a dent in the scientific theory of design.
Poor design is NOT the absence of design. This theological objection has nothing to do with the scientific theory of intelligent design. This presents a straw-man argument against intelligent design, based upon the view that a designer must design things to withstand a certain type of malicious physical attack.
For example, the inverted retina is a perfect sign. Right external to the retina layer lies a very important tissue of veins that envelop it like a net. There is a reason that the photoreceptors are "inverted." Clearly, there is a strategy here. The inverted arrangement of the retina is not faulty, but is proof that it was designed for a specific purpose.
In his book, An Introduction to the Biology of Vision, Professor James T. McIlwain writes, "Because of the great metabolic needs of the photoreceptors, the eye seems to have adopted the strategy of 'swamping' the choroid with blood to ensure that supply is never a problem."
The eye has been created in a way that permits it to function in the most efficient manner.
1) The cornea assists with the focusing of light.
2) The retina transforms the image into neural signals.
3) Veins in the optical cavity feed the retina.
4) Light enters through the opening of the pupil.
5) The iris muscles control how much light will enter.
6) The sclera is a firm, white layer that covers the eyeball.
7) The lens focuses the image.
8) Optic nerve connects the eye to the brain.
Jonathan Sarfati, Ph.D. (Physical Chemist and Spectroscopist):
Evolutionists claim that the eye has ‘profound optical imperfections,’ so is proof of ‘tinkering’ and ‘blind’ natural selection. However, there is no positive argument for evolution because there's no evidence of a step-by-step way for the retina to have evolved. Ultimatley, this ' arguemnt from poor design' is just an attack on a Designer without any evidence.
No engineer have been able to design something remotely as good as the eye. They would have to design something with all the versatility of the vertebrate eye such as
color perception, resolution, coping with range of light intensity, night vision as well as day vision etc. All this must be done under the constraints of embryonic development.
Source: Refuting Evolution (part 2)
Ophthalmologist Dr George Marshall says: "The idea that the eye is wired backward comes from a lack of knowledge of eye function and anatomy." He explains that the nerves could not go behind the eye, because that space is reserved for the choroid, which provides the rich blood supply needed for the very metabolically active retinal pigment epithelium (RPE). This is necessary to regenerate the photoreceptors, and to absorb excess heat. So it is necessary for the nerves to go in front instead. The claim on the program that they interfere with the image is blatantly false, because the nerves are virtually transparent because of their small size and also having about the same refractive index as the surrounding vitreous humor. In fact, what limits the eye’s resolution is the diffraction of light waves at the pupil (proportional to the wavelength and inversely proportional to the pupil’s size), so alleged improvements of the retina would make no difference.
The more he studies the human eye, the harder it is to believe that it evolved. Most people see the miracle of sight. He sees a miracle of complexity on viewing things at 100,000 times magnification. It is the perfection of this complexity that causes him to baulk at evolutionary theory.
The retina is probably the most complicated tissue in the whole body. Millions of nerve cells interconnect in a fantastic number of ways to form a miniature ‘brain’. Much of what the photoreceptors ‘see’ is interpreted and processed by the retina long before it enters the brain.
Source: An eye for creation
For a more technical account of the retina’s amazing design, see 'Is Our 'Inverted' Retina Really 'Bad Design'? by ophthalmologist Peter Gurney, an article highly commended by Dr Marshall.
We can safely infer that the theoretical risk arising from the blind spot in a one-eyed person, is negligible; and, in keeping with this, it is considered safe for a one-eyed person to drive a private motor car i.e. for non-vocational purposes.
Source: Human Eye
The deterioration in the eye reflect the fact that entropy (the Second Law of Thermodynamics) during aging will increase with time, not decrease. A general picture of vision deterioration can be figured out by understanding the aging mechanisms of the human body and by focusing on 'process' rather than on 'causes' (failures or damages). Visual sharpness declines as the blood vessels convey insufficient quantity of oxygen due to reduced ventilation of lungs as we age. As a consequence, the occipital lobe of the brain is not supplied in correct manner and the view, controlled by the occipital area, is obscured. Also, the eyeball loses flexibility with age and the lens of the eye yellows and makes it harder to detect light at the blue end of the spectrum. Aging eyes also require more light.
Some scientists have recently found an exception to this rule. For one kind of vision, the old see better than the young.
According a Canadian study, subjects 60 years old and over have neurological changes to the areas involved with vision that allow them to better spot small motions in a larger high contrast field.
Source: Science finds vision can improve with age