On left, the patient’s left eye has no cataract and all structures are visible. On right, retinal image from fundus camera confirms the presence of a cataract. (From Choi, Hjelmstad, Taibl, and Sayegh, SPIE Proc. 85671Y, 2013)
Article by guest blogger Roger S. Reiss, SPIE Fellow and recipient of the 2000 SPIE President's Award. Reiss was the original Ad Hoc Chair of SPIE Optomechanical Working Group. He manages the LinkedIn Group “Photonic Engineering and Photonic Instruments.”
The human eye and its interface with the human brain fit the definition of an "instrument system." The human eye by itself is also an instrument by definition.
After the invention of the microscope and the telescope, the human eye was the first and only detector for hundreds of years, only to be supplemented and in most cases supplanted by an electro-optical detector of various configurations.
The evolution of the eye has been and still is a mystery. In National Geographic (February 2016) an excellent article titled "Seeing the Light" has a very good explanation of the eye's development.
Having recently had cataract surgery, my interest in the eye was stimulated. First, I wondered why "cataract surgery" is called "cataract surgery."
In cataract surgery, no surgery is performed on the cataracts (cataract material). A very small incision is made in the lens pocket and the cataract material is flushed out by using the opening to introduce the flushing substance, and the flushing substance carries out the cataract material through that opening. The cataract material may require ultrasonic fracturing to reduce particle size. A man- and machine-made lens is inserted into the opening. The opening may or may not require suturing. This procedure should more accurately be known as "lens replacement surgery."
Why are a large number of measurements made on the eye before the eye surgery?
Without invasion of the eyeball, a great many measurements from outside it must be made to determine the required focal length of the replacement lens. (Some people do need corrective glasses to achieve the correct value.) When I asked about all these measurements (made by high-precision lasers) other important factors were brought up, including knowledge of the instruments by the operator, guesswork, and finally…some luck. Luckily, without glasses distance vision is infinite after surgery, but reading glasses are a necessity. Today, there are many options available to cataract patients, including multifocal lenses, which may enable complete independence from glasses.
After having lens replacement surgery myself, two haunting questions remain unanswered in my mind.
A. Where did the optical-quality fluid (vitreous) in the original eye lens and the eyeball come from, and how did it know where it belonged? Optical-quality liquid or gel occurs in the human eye but nowhere else in the human body.
B. How did the Creator (or whoever or whatever, a religious question) -- without Physics 101 or Optics 101 or Warren Smith's book on basic optics -- determine the focal length of the eye lens (the distance from the eye lens to the retina; some people do need corrective glasses to achieve the correct value). The focal length of the human eye lens is a mathematical value based on measurements and calculations or both and could not have just evolved without some knowledge and information about basic optics.
I wish I could answer either of these two questions but I will have to wait for someone smarter than me. Until then let’s at least change the name of the operational procedure to reflect what is actually being performed, so that people will understand that their cataracts are not being operated on but that their eye lens is being replaced.
Meanwhile, beyond these everyday procedures for improving vision, exciting advances are emerging from labs around the world, enabled by photonics. These include smart contact lenses for monitoring and even treating disease. Artificial retinas under development at Stanford, USC, and elsewhere offer the promise of vision to the blind. The results might not be as clear as what we are used to (yet), but imaging technologies and/or nanomaterials that send visual signals to the brain are helping counter the effects of age-related macular degeneration and other vision problems. New devices and treatments may offer a bright future to those with previously intractable vision problems.