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Medical Forum / General / Vision / November 2005Conditions that affect vision.
Dear colleagues: This is my first post to the group and I hope it will be in line with the issues that are normally discussed here. I am an Oral and Maxillofacial Surgeon currently working on a project that involves, among other things, the ability of humans to discriminate and communicate color accurately. I decided to post my questions here in hope to obtain answers and guidance as well as suggestions on additional reading material. The questions are: 1. What conditions affect ones vision as well as color discrimination ? These conditions can be acquired, congenital, genetic and age-related. 2. Presbyopia has been discussed here (I have seen the title but haven't actually followed the thread). How does it develop, what is the incidence in the overall population, at what age does it usually begin and how does it affect vision and color discrimination ? 3. What are the major conditions that affect ones ability to discriminate color properly and accurately ? 4. It is my understanding that men and women don't see color the same way. Perhaps I should rephrase the question. I have read that men and women are not affected equally by color blindness and other conditions that affect color discrimination and vision. What can you share with me on these differences between vision in male and female patients ? 5. What is the dynamic range of human vision, how many colors is the eye human eye able to discriminate (comparing to a computer, would the human eye be able to discriminate 16-bit color depth, 24-bit color depth, 32-bit color depth, ...), how does the human eye respond in terms of gamma curve compared to conventional film (negative or slide) and digital cameras ? 6. Where can I find detailed but succinct material (preferably texts) describing the physiology of human vision as far as the initial receptors responding to RGB wavelengths and how it is then converted to a Lab system where there are opposites as in red-green axis and blue-yellow axis ? Any suggestions on good texts (title and/or author) describing the phenomena above will be extremely helpful and appreciated. I am also looking for a good atlas where images can be found and scanned for a presentation. Thank you in advance for your help. Best regards, Joseph --- Joseph Chamberlain, D.D.S. Oral and Maxillofacial Surgery You have asked such sweeping and multifaceted questions that I'm not sure what kind of response you are going to get. I would recommend reading some basic texts on physiological optics and physiology of the eye. Perhaps a little googling will turn up some Scientific American articles or something. I will give you a few remarks-- its late and I'm going to hit the sack soon. > The questions are: > > 1. What conditions affect ones vision as well as color discrimination ? > These conditions can be acquired, congenital, genetic and age-related. Color discrimination is usually genetic. The color visual pigment genes (red, green, blue, rhodopsin) seem to be where the defects occur. They are located on the X chromosome so men are affected much more than women. You'll have to sort out the exact proportions of affected individuals but clinically speaking color defects in men are quite common-- I encounter them almost on a weekly to monthly basis. On the other hand, in my clinical experience I have only encountered two affected women (but I don't test them very often). There are some acquired color defects as well. Optic nerve damage, and certain drugs (e.g. digitalis) can affect color vision. > 2. Presbyopia has been discussed here (I have seen the title but haven't > actually followed the thread). How does it develop, what is the incidence > in > the overall population, at what age does it usually begin and how does it > affect vision and color discrimination ? Presbyopia occurs in virtually 100% of the population. It is age-related manifesting in the 40-45 year old age group. It does not affect color vision. It relates to the ability of the eye to adjust focus for near tasks. Actually there is still some debate over the exact cause. The original Helmholtz theory is that the lens becomes less pliable with age but there is data to suggest that is not true. A more recent theory that seems more probable is that the lens continues to grow with age (embryologically derived from the same ectodermal cells that differentiate into hair, fingernails, etc.) so that eventually the tension on the zonule fibers becomes slack. Thereafter ciliary muscle contraction produces little effect on the lens. > 3. What are the major conditions that affect ones ability to discriminate > color properly and accurately ? Certainly having genetically intact pigment genes is the biggest factor. Color is most accurately discriminated under high illumination levels. Here are a couple of web references for you: 1. http://webvision.med.utah.edu/Color.html (Peter Gouras' site) 2. http://mbb.harvard.edu/evolution_of_mind_and_brain/Livingstone.pdf (Jeremy Nathans is the guy who first defined the molecular genetics of human color vision) good luck RM > 1. What conditions affect ones vision as well as color discrimination ? > These conditions can be acquired, congenital, genetic and age-related. Cataracts tends to yellow the lens, so that people add blue to make "white." Optic nerve disease (demyelinating, space-occ lesions) can affect color perception, often asymmetrically. Toxicity can affect color perception, as in Van Gogh's color distortions ascribed to absinthe. Otherwise it's usually genetic, bilateral, and very static. > 2. Presbyopia has been discussed here (I have seen the title but haven't > actually followed the thread). How does it develop, what is the incidence > in > the overall population, at what age does it usually begin and how does it > affect vision and color discrimination ? P is universal and occurs in many species. In humans it occurs on a remarkably consistent schedule. Around age 25 we start detecting changes in the near point of accommodation, and it's around 40-42 that the nearpoint usually extends past the individual's habitual reading distance. Some maintain usable accommodation into their 50's, but very few 60-year-olds have measurable accommodation. > 3. What are the major conditions that affect ones ability to discriminate > color properly and accurately ? Genetic defects. Otherwise, cataract is probably the most common cause. Cataracts are universal too, though not all of them turn yellow. Multiple sclerosis and toxic neuropathy generally have a desaturating effect, but it may only affect certain colors and it may not be obvious. These conditions are usually accompanied by a significant decrease in acuity. > 4. It is my understanding that men and women don't see color the same way. > Perhaps I should rephrase the question. I have read that men and women are > not affected equally by color blindness and other conditions that affect > color discrimination and vision. What can you share with me on these > differences between vision in male and female patients ? Most genetic color problems are x-linked recessive. So the incidence is about 8% in males, 0.5% in females. > 5. What is the dynamic range of human vision, how many colors is the eye > human eye able to discriminate (comparing to a computer, would the human > eye > be able to discriminate 16-bit color depth, 24-bit color depth, 32-bit > color > depth, ...), I think I remember a couple hundred "just-noticeable-differences"... 8-bit? :) > how does the human eye respond in terms of gamma curve compared > to conventional film (negative or slide) and digital cameras ? It switches between high-ISO black-and-white film and daylight color film on demand. Autoexposure is accomplished by the pupil, two different sets of photoreceptors, and a neural net that can adjust intensity over a couple of f-stops. The neural net uses lateral inhibition to enhance intensity and contrast prn. See http://www.michaelbach.de/ot/lum_contrast-adapt/index.html -MT Thank you very much RM and Mike for your detailed and thorough answers. I appreciate the time you both took to give such detailed answers to my original post and your replies will save me literally days of research. Are there any particular texts on ophthalmology, optometry or human vision that you could recommended me ? I am looking for something that will discuss the questions I have as well as the points you discussed in your posts. It doesn't have to be a 2000 page treatise on the fundamentals of human vision, but it would be nice to find texts that explain in an objective and succinct manner these issues. Thank you again for your help and responses. Best regards, Joseph --- Joseph Chamberlain, D.D.S. Oral and Maxillofacial Surgery ---------------------------------------------------------------------------- On 10/31/05 9:33 PM, in article L6D9f.3406$m81.917@newsread1.news.atl.earthlink.net, "Mike Tyner" <mtyner@mindspring.com> wrote: >> 1. What conditions affect ones vision as well as color discrimination ? >> These conditions can be acquired, congenital, genetic and age-related. [quoted text clipped - 67 lines] > > -MT |
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