When was the last time you met a person who had 20/20 vision with no glasses or contacts? Just think: in 2002 the World Heath Organization estimated that over 161 million people worldwide were visually impaired, of whom 77% had low vision and 23% were blind (1). If humans had superior eagle-like eyes and acute night vision, violent crimes would most likely decline. According to U.S. Bureau of Justice, over half of all violent crimes and nearly two-thirds of sexual assaults occurred at night (2). It is possible that all of this can soon be prevented.
Anatomy and Physiology
The eye is a very special part of the human sensory system. Photoreceptor cells and sight in general have very ancient ancestry, dating back to over 540 million years ago (3). The cornea is the clear convex anterior portion of the eyeball continuous with the sclera, a tough white outer envelope of the eyeball. The cornea plays a crucial role in the eye’s focusing system and covers the iris, a pigmented contractile membrane of the eye that regulates the amount of light that enters the eye through an opening known as the pupil. Behind the iris lies the lens, which is a transparent, biconvex structure made of 90% crystallin proteins, and with the help of the cornea it focuses incoming light rays onto the retina, the light-sensitive tissue lining at the back of the eye that ultimately converts light into electrical impulses that are sent to the brain through the optic nerve. The macula is a small sensitive area of the retina that gives central vision. At the macula’s center is the fovea, which gives the sharpest vision. Three pairs of extraocular muscles move each eyeball in the orbits and allow the image to be focused on the or fovea (4).
Sight is initiated when external photons hit the lens and are focused onto the retina, a mosaic of two basic types of photoreceptive cells called rods and cones. In total, humans have around 125 million rod cells and 6 million cone cells. Cones function best in daylight and are responsible for color detection while rods are more sensitive to light and function in night vision. We have three types of cones that give basic color vision: S-cones (blue), M-cones (green) and L-cones (red). In the fovea of the retina, the maximum concentration of cones is around 180,000 per square millimeter and this density decreases very quickly outside of the fovea to a value of less than 5,000 per square mm. There are no photoreceptors at the optic nerve and hence humans have a blind spot that the brain fills in based on the rest of the visual information provided. Once the incoming photons strike the rods and cones, which are located several layers below the outer layer of the retina (see figure), photoreceptive proteins facilitate phototransduction, the conversion of photons into electrical signals that are sent to the brain. After the electrical impulses travel down the optic fiber, they reach the occipital lobe, where the visual cortex discards extra input and only keeps and translates the useful visual data.
Despite this complex system, the human visual system has many limitations impeding higher performance. The human eye has a visual acuity of around 20/20 vision, and can reach up to a 20/10 maximum, meaning that a person can recognize at 20 feet what the average person with good eyesight can recognize at 20 feet or 10 feet, respectively. To put this into perspective, a hawk’s vision is at least 20/5. Visual acuity is the ability to resolve a spatial pattern separated by a visual angle of one minute of arc where one degree equals sixty minutes, and relates to the minimum size of an object that a person is able to recognize from another object before both are blurred into one image. The resolution limit is determined by the total number of photoreceptor cells in the retina per degree field; in our case, the limit is set for 120 cone cells across one degree of space, which represents 288 µm of the retina as projected by the eye’s lens. Thus, if more than 120 alternating side-by-side white and black lines are together in a single degree of viewing space, they will appear as one gray blur to the human eye. Human visual acuity is also limited by how fast our brain can process all the visual input received (5).
Our night vision is also very limited, due to constraints on our spectral range and intensity range. With regards to spectral range, human vision is restricted to visible light, a small portion of the electromagnetic spectrum. A typical human eye will respond to wavelengths of 380-750 nm. The eye’s cells behave as transducers as they convert light into electrical energy that is transmitted by the optic nerve. A minimal threshold electrical energy must be reached before the visual message is sent to the brain. The first step involves photoconductivity, where electrons with a certain minimum energy are ejected from photoreceptor cells. This minimum threshold frequency required for ejection of electrons is what we perceive as red light. Below this threshold, no electrons will be ejected and no electrical energy will be transmitted. Infrared radiation, for example, cannot be detected by humans although it is key in night vision for many nocturnal animals. Further, our intensity range also limits our vision. The human visual system limits sensitivity to a few tens of photons even under ideal conditions, in contrast to many nocturnal animals that can detect single photons (6, 7). Humans are thus very limited in night vision.
Our eyes are further limited by coupled vision, as opposed to eyes that can move independently and synchronously. There are six incredibly strong and efficient extraocular muscles that act to turn or rotate an eye, but must always move both eyes together.
Superhuman Vision in Animals
Many animal species have surpassed human capabilities of vision, including sharper visual acuity, night vision and independent eye movement. In addition, some animals have adapted ways to protect the vulnerable features of the eyes.
An eagle has one of the highest visual acuities in the animal kingdom. In a human, the fovea has 200,000 cones per millimeter while in the central fovea of an eagle there are about a 1,000,000 cones per millimeter. Along with having five times our visual resolution, eagles also have two foveae regions, regions where the photoreceptor cells are densest and where vision is sharpest. There is a central fovea that looks forward in tandem with the other eye, and a lateral fovea for looking monocularly outward. Two foveae further allow an eagle a greater field of vision (200°) than ours (140°). Further, eagles have a nictitating membrane that lies between the eyelids and cornea with a lubricating duct used in cleaning and protecting the eye (8).
Having a greater density of photoreceptor cells, particularly rods, helps explain the greatly enhanced night vision of some diurnal animals and nocturnal animals like owls, cats, geckos, and snakes. Many bats, snakes, and lizards have rods but no cones at all, while others have only a few cones. These rods have become highly specialized, including a pigment molecule called rhodopsin that is specifically sensitive to red light. They are also very sensitive to infrared radiation, and thus have a greater spectral range than humans. Further, many nocturnal animals such as cats have a feature called the tapetum that amplifies the amount of light reaching the retina, thereby increasing their intensity range. The tapetum is a mirror-like membrane that reflects light that has already passed through the retina back through the retina a second time, giving the light another chance to strike the light-sensitive rods. Whatever is not absorbed passes out of the eye through the pupil, explaining the glowing eyes of nocturnal animals (9). Just recently it was discovered that nocturnal animals also have an inverted structure nuclei of rods, which act as collecting lenses that help focus light and prevent scattering (10).
Certain animal species including reptile, herbivore and fish are capable of controlling each eye independently. For instance, chameleons are able to switch from independent saccadic eye movements to strictly synchronized eye and head movements during prey tracking. Like humans, they also have a central fovea and perform saccadic fixation movements. In addition, chameleons have a specialized organization between extraocular muscles and motoneurons that control eye movements. This dexterity allows them to move their eyes over a range of more than ±90°, resulting in one of the greatest viewing fields of all creatures, 180° (11).
In humans we also see examples of diseases like mydriasis (excessive dilation of pupil) and strabismus (lazy eye) that give us a hint as to how to surpass our limitations, just as other animals have done throughout their evolution.
Augmenting Technologies
Scientists have already developed several laser surgery techniques to correct non-severe vision impairments like myopia or hyperopia and are currently looking into cyborg implants for the blind. Cyborg implants are implants that aid a person’s physiological processes by mechanical or electronic devices and are physically connected to the body they modify. The technology of laser refractive surgery includes PRK (Photorefractive Keratectomy), LASIK (Laser-Assisted in-Situ Keratomileusis) and LASEK (Laser-Assisted Sub-Epithelial Keratectomy). PRK carefully reshapes the cornea by removing small amounts of tissue from the outer surface using an automated ultraviolet beam of light. According to FDA, clinical studies showed that about 5 percent of patients still needed glasses following PRK and up to 15 percent needed glasses only occasionally. LASIK is a more complex procedure than PRK and is used for all degrees of myopia. The surgeon uses a knife called a microkeratome to cut a flap of corneal tissue, removes the targeted tissue beneath it with the laser, and then replaces the flap. Another technique is the LASEK procedure, which involves preserving the extremely thin epithelial layer by lifting it from the eye’s surface before laser energy is applied for reshaping. After the procedure the epithelium is replaced on the eye’s surface. Side effects from any of the three refractive surgeries include corneal haze, glare and halos around lights. All three laser refractive surgeries are invasive and involve manipulating eye tissue, but are generally effective in improving vision (12, 13).
A less invasive method is a contact lens that contains an electric circuit and red light-emitting diodes for a display. These smart circuit contact lenses may soon prove beneficial in enhancing human vision. The lenses have been tested in rabbits with no adverse effects, and the lenses would also be convenient to wear (14).
Currently, the retinal implant is principally an ongoing project to aid the blind. Scientists view sight as an electrochemical signal in the brain, so in the blind something is preventing the incoming light from becoming a proper signal. Often, the problem lies in the retina’s cones and rods. Some solutions proposed would circumvent the damaged parts of the eye and send signals to cells that still function. Some hope to place miniature light-sensitive photo arrays (“retinal implant”) in the retina itself, effectively replacing the damaged rods and cones. In this case, the retinal implant will act like normal rods and cones, transforming light into an electrical pulse that stimulates the optic nerve. Great challenges lie in how many electrodes acting as photoreceptors can be implanted. Presently the upper limit is no more than 1,000 photoreceptors, one hundredth of the amount in our fovea, suggesting that the resulting images would be blurry at best, if achieved at all with this method (15).
Improving Ocular Design
To increase human visual acuity, I propose an increase in the foveal area as well as in the density of photoreceptor cells through low level laser irradiation and complementary usage of modified smart circuit contact lenses for eye empowerment and night vision. This method can be applied both to the blind, who often have some functional sensor cells, and to the general population with normal or impaired vision.
Modern eye surgery has enabled people to have their vision restored or sharpened.
Laser technology in treating eyes is not a new or foreign phenomenon. Refractory surgery is well tested and is able to correct the vision of 95% of patients without inducing significant side-effects. My approach differs here from the conventional one. I propose using low laser irradiation, specifically Helium-Neon irradiation, which has been shown to be successful in promoting skeletal muscle regeneration and growth in vivo (16). The first step is to shine a low level laser He-Ne irradiation at the photoreceptor cells located at the back of the retina for three seconds, the amount of time that caused peak induction of cell-cycle regulatory proteins in the mouse muscle cells. The goal is to stimulate growth of photoreceptor cells at the retina and fovea region in order to have a dense mat of photoreceptor cells and a greater fovea area. This would imitate the greater visual acuity of eagles, which have two foveal regions with one million photoreceptor cells in each fovea. Achieving greater area and thickness of the retina and fovea will also allow a higher percentage error if light focuses slightly in front or in back of the retina. In these cases there would be no need for eye correctors since light will still shine on the increased retina area.
To monitor the growth of the photoreceptor cells and to prevent uncontrolled growth, the patient should wear a pair of smart circuit contact lenses. These can send electrical signals along the inner cell lining of the eye to the sensor cells to cause a start or stop in cell growth, in order to maintain an ideal number of photoreceptors for the particular patient. This number, as well as the time needed for irradiation, may vary among patients. So before each procedure we will map each patient’s eye, just as is currently done for refractory surgery, and this information will be entered into a computer algorithm that will determine the ideal numbers for the patient. Hence, this technique is patient-specific and avoids making errors that could result from making generalizations for all patients. These smart contact lenses are easy to use and comfortable to wear.
Further, the smart circuit contact lenses can resolve more severe myopia or hyperopia not covered by the region of sensor cell growth if the image is either focused too far front or in back of the retina. Like a computer processor, the smart contact lenses can directly monitor the prescription of the eye to produce the clearest vision possible with the patient’s given number of photoreceptor cells. This may not only surpass normal vision but may also be a solution to the imprecise common prescriptions given at the ophthalmologist’s office, since eyesight is not static and may change depending on the time and place. Further, electron flow across the diodes in the smart contact lenses can project a display of the visual image as big and as small as needed; that is, the patient can zoom in and zoom out like a camera does. This feature can help improve public health if people are aware of all the microorganisms around them, and can help prevent road accidents and traffic if people are able to see a greater distance ahead of them. In addition, the smart circuit lenses can send separate signals to the extraocular muscles so that the eyes can move independently.
For night vision, the electrons on the smart circuit contact lenses can be made hypersensitive to infrared radiation. When excited, electrons will travel down the inner lining of cells in the eye until they reach the optical nerve, where the electrical signal can be directly sent to the brain. In effect, they will act as a substitute photoreceptor, now sensitive to shorter wavelengths.
The advantage to this proposal is the noninvasive nature of the low irradiation, and that the circuit contact lenses do not cut or tear delicate eye tissue. The goal is to build upon our eyes’ natural design instead of starting from scratch. Further, this proposal erases the worry about lens prescription since smart circuit eye contacts can adjust to a changing prescription. Additionally, the blind will have a greater potential to regain vision and thus may no longer be dependent on others. Of course, as with all new technology, there are a few caveats. Since the circuit contact lenses are a relatively new phenomenon, there is no guarantee that the circuit lenses or electron flow within the eye will not have adverse effects on human health. There is also a small chance that the low level laser irradiation may stimulate sensor cells to divide uncontrollably, but this will be carefully monitored.
Furthermore, ethical issues consistently arise as we attempt to change human capabilities. First, should we all be allowed to have hyper-vision if the technology exists? If yes, can we make hyper-vision mandatory? If not, who will decide who can get superhuman vision? Additionally there is a concern of new technology and capabilities being used for terrorist purposes. How do we protect society? Is it morally permissible to manipulate human body, interfering with natural selection by, in John Harris’ words, “enhancing evolution”? (17) Could we be leading to our own rise or fall if a new enhanced human species is created?
There is certainly no clear answer to any of these questions. In any case, there seems to be a great potential here to better the human species. Perhaps in the future we will be able to very readily splice genes for high vision acuity, night vision and independent eye movement from other animals into our own genome (18). The benefits of hyper-vision both during the day and night may lead to unfathomable human strides.
References
1. World Health Organization’s Magnitudes and Causes of Visual Impairment (2004). Available at http://www.who.int/mediacentre/factsheets/fs282/en/ (April 10, 2009).
2. Bureau of Justice Statistics’ Crime Characteristics (2005). Available at http://www.ojp.usdoj.gov/bjs/cvict_c.htm (April 9, 2009).
3. S. Ings, A Natural History of Seeing: The Art and Science of Vision (W.W. Norton & Co., United States, 2008).
4. T. Montgomery, Anatomy, Physiology & Pathology of the Human Eye (2009). Available at http://www.tedmontgomery.com/the_eye/ (April 10, 2009).
5. De Valois, Russell, and K. De Valois, Spatial Vision. (Oxford University Press , 1988).
6. Visual Acuity (2008). Available at http://www.ndt-d.org/EducationResources/CommunityCollege/PenetrantTest/Introduction/visualacuity.htm (April 10, 2009).
7. S. Hecht, S. Schlaer, and M. H. Pirenne, Journal of the Optical Society of America, 196-208 (1942).
8. Vision: An In-Depth Look at Eagle Eyes (2009). Available at http://www.learner.org/jnorth/tm/eagle/VisionA.html (April 10, 2009).
9. J. Kremers, The Primate Visual System: A Comparative Approach (Wiley, United States, 2005)
10. I. Soloveil, et al., Cell, 356-368 (2009).
11. M. Ott, Environmental Brain Research, 173-179 (2001).
12. U.S. Food and Drug Administration, Laser Eye Surgery: Is it Worth Looking into? (1999). Available at http://www.fda.gov/fdac/features/1998/498_eye.html (April 10, 2009 ).
13. Laser Eye Surgery (2009). Available at http://www.nlm.nih.gov/medlineplus/lasereyesurgery.html (April 10, 2009)
14. Contact lenses with circuits, lights a possible platform for superhuman vision (2009). Available at http://uwnews.washington.edu/ni/article.asp?articleID=39094 (April 10, 2009).
15. MIT Technology Review’s Next Generation Retina Implant (2007). Available at http://www.technologyreview.com/Biotech/18193/ (April 11, 2009).
16. F. Schwartz, et al., Journal of Photochemistry and Photobiology B: Biology, 66(3), 195-200 (2001)..
17. J. Harris., Enhancing Evolution (Princeton University Press, United States, 2007).
18. H.C. Hughes, Sensory Exotica: A World beyond Human Experience (Bradford Press, United States, 2001).