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Subject: sci.med.vision: Frequently Asked Questions (FAQ), Part 3/5

This article was archived around: 19 Feb 1997 08:31:55 +1100

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+============================================================================+ FREQUENTLY ASKED QUESTION: Vision and EyeCare Part 3/5 (Copyright(C), Grant Sayer) (grants@research.canon.oz.au) +============================================================================+ +============================================================================+ + Section 4: Disease of the Eye (Anterior Eye Disease) + +============================================================================+ 4.1 Introduction ------------------ This section, and the subsequent section, are only an overview of some of the typical problems and questions that have appeared in the sci.med news groups. It is not a complete discussion of all the potential ocular diseases, which of course, would occupy a complete medical textbook. At this stage it has been broadly classified into anterior and posterior, for want of a better classification scheme. Also note that the information on eye disease is only provided as an information service and does not replace examination by an eyecare professional. Some attempt has been made to include references to World Wide Web pages which may have more information and/or graphics on the disease. 4.2 Conjunctivitis -------------------- Conjunctivitis is an inflammation of a mucous membrane and therefore in most types there is a red eye, thickening of the conjunctival tissue and some discharge of mucous or mucous and inflammatory cells. The causes of Conjunctivitis include; bacterial infection, viral infection and allergic reactions. Typical bacterial conjunctivitis, is caused by the common staphylococcus and diplococcus pneumoniae to the less common organisms of the haemophilus group. Infection is generally in both eyes with the patient experiencing discomfort in the form of a "smarting" and grittiness, moderate photophobia, but minimal pain. Discharge from the infection causes the well known symptoms of eyelids stuck together on wakening or having a "crusty" appearance. Bacterial conductivities responds well to antibiotic treatment. Viral infections, sometimes caused by adenoviruses which are often involved in upper respiratory tract infections, cause inflammation of the membrane on the back of the eyelid. Allergic conjunctivitis results from hypersensitivity to exogenous antigens. There are many forms, with some examples being, profuse watering due to hay fever, chronic inflammation as a result of a reaction to locally applied drugs. The treatment is to remove the antigen and use of vasoconstrictors 4.3 Dry Eyes ------------- - Causes [Details to be added ] - Treatments, in-eye solutions, tear duct plugs [details to be added ] See URL: http://www.west.net/~eyecare URL:http://www.he.tdl.com/~dakryon/index.html ( pharmaceutical company that manufacturers dry eye products. Also includes pictures of dry eye) URL: http://www.w2.com/ss.html (Sjogrens Sydnrome Foundation) URL: http://www.he.tdl.com/~dakryon/dei.html (Dry Eye Institute) 4.4 Eyelid Problems --------------------- Styes are common eyelid problems and are a type of "boil" involving an eyelash follicle. There is generally a tense swelling with redness and pain, until the abscess escapes. Application of local heat, using a compress can assist in easing the pain and bring the stye more quickly to a "head". Internal stye, tarsal cyst or chalazion is a chronic granuloma of the Meibomain gland of the eyelid. This manifests as a small hard spherical lump within the eyelid, often easily felt but not seen. Treatment varies, depending on the size and/or associated discomfort which may be caused by the swelling of the eyelid. Other common eyelid problems include blepharatis, which is a kind of "dandruff" of the eyelid margin. The eyelid margins are red-rimmed with flakes and scales among the eyelashes. Burning discomfort and itching comes and goes. Treatment involves cleansing of the eyelid margin, using sterile wipes or eye ointments. See also: URL: http://www.west.net/~eyecare 4.5 Keratoconus ----------------- Keratoconus (conical cornea) is an recessive inherited condition usually apparent between the ages of 10-25yrs. Incidence of the condition is approximately 1 in 5,000. The condition manifests as a thinning of the corneal apex, or central area of the cornea. With the weakening of the tissue there is a bulging of the tissue which increases the myopia of the affected eye. Initial correction is via spectacles whereby reasonable vision can be attained. Subsequent treatment is via a rigid contact lens which will provide a new front surface to the optical system of the eye. There is more information about this condition from the CLEK study at http://spectacle.berkeley.edu/CLEK/CLEK.html Other sources of information for readers in the USA are National Keratoconus Foundation (310) 855-6435 National Eye Institute (301) 496-5248 NORD (National Organization for Rare Disorders) 1-800-799-6673 US Public Health Service 1-800-336-4797 4.6 Herpes Zoster ("Shingles") ------------------------------- Affects the eye by encroaching from a skin lesion or starts on the eye. The appearance is white pustules, similar to cold sores in the mouth. This disease is treated by early antiviral treatment. 4.7 Effects of Radiation on the Eye ----------------------------------- 4.7.1 General Effects of Radiation on the eye ----------------------------------------- UV radiation is classified as UV-A UV-B (280-315nm) UV-C (200-280nm) Potential hazards from UV radiation are photokeratitis, conjunctivitis and lenticular cataracts (Elliot et.al - see reference below). Parrish JA, Anderson RR, Urbach F, Pitts D. "UV-A Biological effects of ultraviolet radiation with emphasis on human responses to longwave ultraviolet", New York, Plenum, 1978 - UV radiation less than 320nm causes photokeratitis and conjunctivitis - large doses of wavelengths greater than 350nm are required to induce cataract formation, perhaps of the order of 0.5 to 1.0 MJ/m^2 4.7.2 Visual Displays and Radiation ----------------------------------- From the Journal of Theoretical Biology 1986, 122, 491-492 as a letter to the editor from Liden, Bergqvist and Wennersten they comment that the CRT worker has less exposure to UV-A than other office workers. The details of the radiation levels are given below UV-A Detector's Direction UV-A (W/m^2, mean) Towards the screen at 60cm distance 0.03 Towards the ceiling (VDT operators) 0.04 Towards the ceiling (other office workers) 0.13 The author's conclusions were that UV-A emmission from VDT's is very low and can not be of biological relevance in comparison to normal UV-A exposure. Also that VDT work and health is a multi-factorial problem and that a common single-factor explaination of ill health during VDT use is not viable In another paper - Elliot G., Gies P., Joyner K.H, and Roy C.R. "Electromagnetic radiation emmissions from video display terminals (VDTS)", Clinical and Experimental Optometry 69.2: MArch 1986, pp53-61. - report that there is no ocular hazard from the RF emmissions from VDTs. Also that VDTs emit no UV radiation below 350nm. 4.8 Iridology ------------- This is postulated as a means of determining general health by variations in the iris pigment and structure Some papers and references (contributed by Roberty Sekuler from Sekuler R. and Blake R., "Instructors Manual to accompany Perception", McGraw-Hill, Third Edition, 1994, pp4-5) which tested and debunked iridology include: A Simon, DM Worthen and JA Mitas, An evaluation of iridology, Journal of the American Medican Association, 1979, 242, 1385-1389. P Knipschild, Looking for gall bladder disease in the patient's iris. British Medical Journal 1988, 297, 1578-1581. In this paper five iridologists were asked to judge stereo color slides of the right eyes of various people for signs of gall bladder disease. According to iridology texts, gall bladder is projected in the lower lateral part of the right eye's iris. Further, gall stones are supposed to induce small, dark spots in that part of the right iris, while inflammation of the gall bladder is said to induce white line there. Among the slides that were to be judged for telltale signs of gall bladder disease were slides of the right eyes of patients who were to have their gall bladders removed the next day. The slide set also contained slides of the right eye of age- and gender-matched controls, presumably free of gall bladder disease. Now the results: the five trained iridologists did really well in spotting gall bladder disease in the eyes of patients who actually had g.b. disease. They judged 56% of the patients' slides as showing evidence of gall bladder disease. Unfortunately, they gave just about the same percentage of FALSE positive --identifying people as having g.b. disease who actually did not. Too bad that the experiment included those pesky control measurements!!! But those interested in pursuing it further there are locations of Iridologists on the WWW - http://www.itlnet.com/natural http://www.sasknet.com/~bulmj/ +============================================================================+ + Section 5: Disease of the Eye (Posterior Eye Disease) + +============================================================================+ 5.1 Floaters and Spots in the Field of View --------------------------------------------- Floaters (muscae volitantes - "flying flies") are spots before the eyes of different shapes, sizes and number. They appear often when looking at a plain coloured field of view, eg blue sky, a wall. Typically when the patient tries to look at them they report that the spots "run- away". The spots are due to corpuscles circulating in the retinal vessels and specks within the vitreous. These opacities cause shadows to be cast onto the retinal sensory apparatus; the rods and cones; and thereby appear as dark spots in the field of vision. Slight cases or observations require no treatment. There are other retinal and vitreous conditions that may cause increased presence of floaters indicative of more serious complications, for example, vitreous or retinal detachment. It is therefore advisable in the presence of an increased occurrence of floaters that you get a check-up by a eyecare professional. 5.2 Macular Degeneration -------------------------- The macular is the innermost part of the central retina; an area where the retina has the highest concentration of cones (sensory apparatus of vision). The degeneration which occurs within this area of the retina can be due to a breakdown of the retinal receptor cells, leakage of exudate between the retinal layers and occasionally destructive bleeding. As a result of the changes to the retina there is a decrease in central vision, often with little to no involvement in the peripheral retina. Hand magnifiers, spectacle magnifiers and low vision aids can be used by the patient to assist with reading. More information can be obtained from the National Eye Institute located in Bethesda, MD on (301)496-4000. Internet Resources include: URL: http://ops.ophth.uiowa.edu (contains 2 pages including photographs of macular degeneration conditions) URL: http://pharminfo.com/pubs/msb/amd.html (information on preventing macular degeneration with dietary carotenoids a medical sciences bulletin) URL: http://www.pharmatech.com/ind.html ( medical research and development with information on Ophthalmic research) 5.3 Retinal Detachments ------------------------- The retina is one of the three layers of the human eye. The innermost layer is a complex and delicate layer (0.4mm in thickness) which lines the innerside of 2/3rds of eyeball. There are a number of sub-layers to this tissue which comprise the neural layers and photoreceptors necessary for vision. Detachment of the retina is a separation of the neural retina from the pigment epithelium; a layer of pigment cells providing nutrients to the photreceptors and attaching the retina to the next outermost layer - the choroid. As a result of the separation there is a loss of function in the photoreceptors, vision is affected. The accompanying symptoms of a retinal detachment include; blurring of vision, sensation of "flashing lights", loss of vision like a shade or curtain moving across the field of vision. The presence of a retinal detachment is a serious visual problem and should be thoroughly investigated by an eyecare professional. Retinal detachment occurs in some hereditary conditions, e.g Stickler Syndrome. More information is available on the Web at URL: http://ops.ophth.uiowa.edu/MOL_WWW/RD.html (contains fundus photograph) 5.4 Diabetes and The Retina ----------------------------- Diabetes causes a number of retinal changes which can include haemorrhages, micro-anueryisms of the capillaries, exudates, abnormalities of arteries and veins and retinal detachment. The combination of these changes can result in reduced vision to severe complications. The examination of the status of the diabetes and it's impact on the retina is assessed with a technique called fluorescein angiography. Other information is available at URL: http://www.niddk.nih.gov/DiabetesDocs.html (contains detailed information on diabetes and particular section on diabetic eye disease which includes questions and answers) 5.5 Retinitis Pigmentosa ------------------------- Retinitis Pigmentosa is a degeneration of the retinal pigment epithelium. This is a single celled layer of pigment cells that is between the retina and the choroid, the second "coat" of the eye. In this condition pigment granules are lost from the epithelium layer and deposited in clumps in the retina. See section [11.1] for details of a listserv group that discusses the condition RP. This listserv (RPLIST@sjuvm.stjohns.edu) contains the following information files: GET RPLIST VITAMIN -> two letters regarding E. Berson's vitamin A study GET RPLIST TRANSPL -> an article on retinal cell transplants GET RPLIST REFSUM -> an article on Refsum's disease Internet Resources include: URL: http://ops.ophth.uiowa.edu/MOL_WWW/RP.html (contains 2 pages including photographs of macular degeneration conditions) URL: http://dux.dundee.ac.uk/~glewis/rp.htm ( 5.6 Glaucoma -------------- Glaucoma is a symptomatic condition and not a disease "sui generis". It is a collection of physicals signs: raised intra-ocular pressure, visual field loss, enlargement of the blind spot and changes in the appearance of the optic nerve head. There are a variety of clinical classifications of glaucoma. Treatment details - eyedrops to reduce aqueous fluid production, increase fluid drainage. - laser trabeculotomy to increase outflow of the aqueous humor. Glaucoma may be defined as "those situations were IOP is too high for normal functioning of the optic nerve head (Shields, 1992.) IOP is closely linked to aqeous humor (clear, watery, fluid in the eye) dynamics. IOP is a function of aqeous humor outflow (AHO) and production (AHP) (IOP = AHO - AHP). Therefore pharmaocological treatment is aimed at either increasing outflow or decreasing production of aqeous humor. IOP is measured by many different types of machines by your health care proffesionals. These exams are important because as with hypertension, when symptoms are noticed by the patient the damage has already been done. For patients who are refractory to medical treatment a surgical operation is performed. This operation makes an external drainage system for the AH and thus increased outflow. This proceedure called a trabeculectomy, is done in the operating room with local anesthesia. Sucess rates for normal risk patients is very high. OTher information located on the Web includes: URL:http://ops.ophth.uiowa.edu/MOL_WWW/Glau.html (information on the condition including cross section of the eye and optic nerve head fundus photography) URL:http://www.dorsai.org/~glaucoma/index.html (extensinve information on glaucoma including FAQ's on the disease, medication research and drug information) URL:http://eyesite.ucsd.edu/text/Glaucoma.html (maintains a listserver for ophthalmic specialists, and FAQ's - under construcion) URL:http;//catalog.com/dicon (manufacturer of visual field equipment which is used for testing of effects of glaucoma.) 5.7 Cataracts -------------- Cataracts are opacifications of the crystalline lens of the eye, causing a loss of transparency. The crystalline lens is the "focussing" mechanism of the human eye. The change in light transmission is due to accumulation of water and/or denaturation of the lens protein. A variety of factors cause cataracts, eg diabetes, eye trauma, age related changes. The predominant symptoms of cataract are an increasing loss in vision. There can be associated fluctuations in the vision depending on water changes in the lens. The rate at which the cataract changes varies depending on physiological factors. The surgical procedure is described below (contribued by Dr W.Wan M.D): There are two standard techniques for modern cataract surgery: phacoemulsification (PE) and nucleus expression or planned extracapsular cataract extraction (ECCE). There are numerous variants on these, especially PE, which may get advertised as no-stitch, one-stitch, clear cornea, topical, etc. In general: 1) PE is technically more difficult to learn, however, once you learn it, most surgeons feel it is a better technique in their hands; 2) the incidence of complications is dependent on the surgeon and the patient population, not the particular technique used (PE was previously thought to have a greater incidence of complications, but this was primarly due to a learning curve; for a given surgeon, the complication rate will be lowest with the technique that he is best with); and 3) PE is generally quicker than ECCE, but again this is very surgeon-dependent. My personal preference is for PE 95% of the time; ECCE is reserved for cases where it may be better than PE based on the type of cataract, the patient, the surgical goals, and occasionally the type of equipment available. (If you want to know how I decide which are in that 5%, you need to go to ophthalmology residency!) PE generally offers quicker visual recovery, and arguably quicker healing and overall rehabilitation, better wound stability, and less risk of disastrous complications such as an expulsive hemorrhage during surgery. However, the bottom line is, good surgeons get good results with either technique, pick a surgeon who gets good results and let him decide what technique is best for you in his hands. (Even then, of course, keep in mind that although it is 95% successful, cataract surgery IS surgery, and complications can occur.) The indication for removing the cataract in a second eye is the same as the first: If the decreased vision in that eye is bothering the patient. (Unless there is some other eye disease, e.g. glaucoma or inflammation being caused by the cataract, or it is preventing management and treatment of some other eye problem in the interior of the eye, which would be unlikely if it is mild.) Other internet resources that provide information on cataracts URL: http://cpmcnet.columbia.edu/dept/eye/rad/intro.html (Eye Radiation and Environmental Research Laboratory) URL: http://www.west.net/~eyecare (EyeCare Connection homepage with information on cataracts) URL: (Lens and Cataract Researcher Internet Directory) URL: http://www.ascrs.org/ ( American Society of Cataract & Refractive Surgery - patient FAQ on cataract) 5.8 Uveitis: ------------ [ TBD - details to be added ] Internet resources: URL: http://www.wilmer.jhu.edu/services.htm (The Wilmer Eye Institute - has a page on ocular immunology ) URL: http://www-sci.lib.uci.edu/~martindal/Medical.html (The Virtual Medical Centre) URL: http://wings.buffalo.edu/medicine/oph (SUNY at Buffalo Ophthalmology Dept - Case presentation on ocular pathology and uveitis) 5.9 Ocular Migraines: --------------------- Internet Resources: http://umt.umt.edu:700/0h/general/migraine.html Migraine Headaches gopher://gopher.uiuc.edu:70/11/UI/CSF/health/heainfo/diseases/head Headaches http://synapse.uah.ualberta.ca/aan/000o0000.htm AAN migraine information [ The following information was contributed by D.Nelson M.D (eyedoc@mindlink.bc.ca - ] 5.9.1 Introduction: ------------------- The following is an attempt to give an_introduction_only to this vast subject with protean manifestations. Migraine affects about 10% of the population. It affects all ages from babies to adults although age does seem to have a protective quality. The general mechanism seems to be a constriction of blood vessel(s) followed by a dilation the the vessel. The aura (when present) accompanies the vasoconstriction and the headache (when present), the vasodilation. There are identifiable "trigger factors" notably: 1. certain foods. Caffiene (coffee, colas, chocolate), citrus fruits, alcohol, nitritate and nitrites, aged cheese, and others. 2. hormonal changes esp. puberty, pregnancy, menopause and "the pill". 3. fatigue/stress. This can be physical (heat/cold) or emotional 4. bright lights 5. loud noises 6. trauma 7. refractive error As well, there are cerain associations with migraine. Cyclic vomiting as a child, car or motion sickness, a family history of migraine, drusen of the optic nerve. 5.9.2 Classification of migraine: --------------------------------- I. Common migraine. The comprises about 80% of those with migraines. It is the typical "sick headache" possibly with mood changes. The headache can be localized or generalized. It may last for hours to days. II.Classical migraine. The triad of aura, headache, nausea+/-vomiting, and a feeling of "being out of sorts". It is typically of shorter duration than the common migraine. The aura may be any sort of neurologic deficit but of course the ones we see are usaully visual. The visual aura usually starts near fixation and expands to the periphery then dissappears to be followed by the headache. The aura may be jagged, coloured lines, "grey blotches" or "missing patches" or many other type of visual disturbance. Classical migraine account for about 10% of migraines. III. Complicated migaine (expanded below) 1.Cerebral 2.Ophthalmoplegic 3.Retinal (or ocular, see below) 4.basilar 5.other IV. Cluster headaches SEVERE episodic unilateral head or facial pain, nasal stuffiness, +/-ipsilateral Horners, lacrimation. Complicated migraine expanded: 1. Cerebral This is a headache which may be severe and focal neurologic signs which last longer than the headache. This is the hallmark of the complicated migraine in which the neurologic deficit may even be permanent. For example, there can be permanent visual field defects. 2. Ophthalmoplegic migraine The patient is usually young (less than 30, usually less than 20). There is a severe unilateral headache. As_the_headache_clears, one or more ocular muscles on the side of the headache become paretic and may take days or weeks to recover their function. As you can appreciate, the first time this happens, the patient is subjected to a lot of investigations including angiograms as this is mimicing such things as aneurysm, tumour and other very bad things. If the ophthalmoplegia recurs, the sequence of events and the previously negative tests are reassuring. 3. Retinal migraine (ocular migraine) The patient is typically under 40 and suddenly loses a portion (retinal) or all (ocular) of the visual field in one eye. There is rarely headache. Never, according to some experts. The differentiation between retinal and ocular migraine is how much of the visual field is affected. In other words, what vessel has been affected. If it is distal to the bifurcation at the optic nerve head, it is retinal. If it involves the central retinal artery, all of the vision is lost and it can be called ocular migraine. Note too, that there are seldom if ever flashing lights with this form of migrain. Again, the vision recovers (ususally, sometimes permanent) in 20 to 45 minutes. With ocular migraine there can be retinal hemorrhages, vitreous hemorrhages. macular edema, ischemic swelling of the optic nerve. 4. Basilar migraine Mimics vertebrobasilar attacks. Bilateral blurred vision, vertigo, ataxia, nausea, incoordination, loss of balance, speech difficulties. 5. Other There is a host of symptom-complexes which fit the criteria for migraine. Sudden, episodic, self-limited, lasting 30-45 minutes. These can be chest pains, vomiting, neurologic symptoms and many others. These are sometimes called migraine equivalents. The most common migraine type problem that I see in my practice is that of a person who may or may not have previously had migraine diagnosed who has a 15-30 minute episode of visual disturbance, often quite classically starting off small near fixation and expanding to fill a hemifield. When the probable diagnosis is explained to the patient, the response is almost invariably "Oh, but it can't be migraine, I don't have a headache!" Remember, if it walks like a duck and quacks like a duck, it's probably migraine. 5.10 Chorioditis: ---------------- Choroiditis is an inflammation of the choroid, the second "coat" of the eye. This tissue layer is a vascular rich layer located between the sclera (outer white coat) and the retina (sensory layer). +============================================================================+ + Section 6: Binocular Vision Problems + +============================================================================+ 6.1 Strabismus (Turned Eye) ------------------------------ A squint or strabismus is a failure of the two eyes to look at the same object thereby preventing binocular vision. Human binocular vision develops during the first few years of life. Interruption to the motor, sensory or central components, for example nerve or muscle defect, can lead to sensory or central defect. Causes of many squints are not fully understood although the majority are either a hereditary factor or a responsible defect. Such factors causing squints include; + ocular abnormalities that prevent good central vision, eg congenital cataract. + paresis of one of the eye's muscle + brain damage, eg cerebral palsy + large refractive errors, eg accommodative esotropia Refractive errors are an important causative factor to strabismus since it can prevent clear vision - impeding development of the sensory mechanism, and affecting the normal relationship between accommodation and convergence. When the eye's require vision at a near distance there both a movement of the two eyes (convergence) and change in focus (accommodation). A child that is hypermetropic (long sighted) has to accommodate more than is normally required for distance and near vision. Because of the linkage between accommodation and convergence the excess accommodation causes an excess convergence of the two eyes. The result, in a young child whose visual system is still developing is what is called a convergent squint. When binocular vision is disturbed double vision results. Young infants are able to suppress one of the images to one eye to remove the double vision that occurs at the onset of strabismus. The effect of the suppression of the image causes the vision in the "squinting" eye to fail to develop normally. This is called AMBLYOPIA. There are other visual abnormalities that can develop as a result of squint. The treatment for squint depends on the cause. Some essential treatments include: + search for ocular defects + refraction and glasses to remove any refractive errors + patching or occlusion of the eyes to prevent amblyopia + surgical adjustments to the muscles of the eye. These treatments aim to remove amblyopia, restore binocular vision and if necessary cosmetic corrections to the appearance of the turned eye. 6.2 Amblyopia ("Lazy Eye") ----------------------------- Amblyopia is defined by Schapero et al. as the condition of reduced visual acuity which cannot be corrected by refractive means and is not attributed to structural or pathological ocular anomalies. Acuities of worse than 20/30 (6/9) are considered to meet the criteria of amblyopia according to Griffins reference on Binocular Anomalies. There are a variety of classifications of amblyopia, in general the categories are organic or functional. Examples of organic amblyopia include; + nutritional, e.g poor diet in the case of alcoholism + toxic, e.g methyl alcohol poisoning or salicylate poisoning + congenital, e.g bilateral or unilateral central scotoma at birth. Functional amblyopia also has three classifications; + hysterical, e.g psychogenic causes giving central visual field defect + refractive, e.g uncorrected isometropia resulting in poor visual acuity development + strabismic, e.g long standing suppression in cases of strabismus Commonly used therapy for amblyopia is occlusion or lens therapy in the case of refractive. The patching is associated with general to increasing eye-hand coordinated tasks to stimulate development of the amblyopic eye. 6.3 Problem(s) When Wearing Glasses ------------------------------------- - Reflections. - Misaligned centres affecting binocular vision. [ TBD ] 6.4 Vision Therapy ------------------ 6.4.1 Introduction ------------------ Common problems that require vision therapy include + accommodation insufficiency + accommodation excess + convergence insufficiency + convergence excess Treatment is often by a combination of either lenses or prisms with or without convergence training. The next level of 'therapy' is the tracking exercises, eye-hand coordination and similar coordination tasks. Details of the training is beyond the scope of this FAQ and the interested reader/patient is recommended to seek professional examination 6.4.2 Bates Method ------------------ Vision therapy, especially people claiming improvement of vision through 'holistic' medicine can often lead into a *very* heated debate. The techniques generally describe some form of eye excerise associated with relaxation technique to improve the 'perception' of letters/images. There is limited to virtually no statistical studies/results indicating the success or failure of these methods. Often the central theme is to "to getting the eyes to shift more rapidly, to get you centre of focus to hit directly on the fovea, and to reduce tension in the eyes so that the above can be accomplished". As described by one internet reader (aeulenbe@silver.ucs.indiana.edu) the method for improved sight involves : 1) KEEP YOUR EYES MOVING. Your eyes have to be fast to catch all the 2) GET LOTS OF SUNLIGHT. Don't be afraid of the sun. If it's too bright 3) WEAR A PATCH. If you do this even for as little as fifteen minutes, 4) STRETCH YOUR NECK. If your neck is cramped, then so are your eyes. Some references are Bates, William Horatio. The Bates method forbetter eyesight without glasses. New York : Holt, Rinehart, and Winston, 1981, c1943. Corbett, Margaret Darst. Help yourself to better sight. New York, Prentice-Hall, 1949. Corbett, Margaret Darst. A quick guide to better vision; how to have good eyesight without glasses, 1957. Huxley, Aldous. The art of seeing. Seattle : Montana Books, 1975. Goodrich, Janet. Natural vision improvement. Berkeley, Calif. Celestial Arts, 1986. Kaplan, Robert-Michael. Seeing beyond 20/20. Hillsboro, OR: Beyond Words Pub., 1987. Seiderman, Arthur. 20/20 is not enough : the new world of vision. New York : Knopf : Distributed by Random House, 1989. Kavner, Richard S. Total Vision. New York : A & W Publishers, 1978. Windolph, Michael. Easy eye exercises for better vision : self-helps to sight improvement. Hicksville, N.Y. : Exposition Press, 1974. Chaney, Earlyne. The eyes have it : a self-help manual for better vision. New York : Instant Improvement, 1991. Revien, Leon. Sportsvision : Dr. Revien's eye exercises Program for athletes. New York : Workman Pub., 1981. Scholl, Lisette. Visionetics : the holistic way to better eyesight. Garden City, N.Y. : Double day, 1978. Hughes, Barbara. 12 weeks to better vision : a remarkable technique to restore your eyesight. New York : Pinnacle Books, c1981. +============================================================================+ + Section 7: Colour Vision Problems + +============================================================================+ 7.1 Defective Colour Vision: ----------------------------- Defects in colour vision, often incorrectly referred to as colour "blindness" fall into two main categories: (a) Congenital Colour Vision Defects (b) Acquired Colour Vision Defects The distinction between the two varieties are that acquired defects are often the result of some disease process which affects the colour vision receptors or higher neural pathways. Congenital colour vision defects are genetically related. 7.2 Classification of Congenital Colour Vision Defects --------------------------------------------------------- Colour vision defects are classified via the number of primary spectral colours which an individual requires to match any other spectral colour. The normal individual usually requires 3 primaries and is classified as a trichromat. (a) Achromatic (Monochromatic) Colour Vision + no colour vision + only light - dark discrimination + lack of retinal function (typical case) + higher centre defects (generally atypical) (b) Dichromatic Colour Vision + colour distinctions of 2 kinds (achromatic or R-G/Y-B) + 4 types - protanopia and deutranopia (confusion of colours from green through yellow to red) - tritanopia and tetartanopia (confusion of colours from blue through green to yellow. (c) Trichromatic Colour Vision + anomalous type requires 3 stimulus primaries to match stimuli but matches are outside the normal range + 3 types - protan, deutran, tritan The colour defective person has difficult in distinguising colours that are on "confusion lines". For example, protanopes confuse blue-greens (and greys) with red (and browns). The deutranopes make mistakes with blue-greens and purple. While tritanopes confuse yellow with violet. The last dichromat group; tetartanopes, confuse yellow with blue. The anomalous types have difficulty with light tints and dark shades. Colour defective vision is inherited as a sex-linked recessive characteristic. It is more common in men than women. The most common defect is deutranomoly with an incidence of 5% or males, protanomaly affects 1.5% and protanopia and deutranopia about 1% each. 7.3 Classification of Acquired Colour Vision Defects ------------------------------------------------------- Acquired colour vision problems can be the result of lesions of the macula, optic nerve, or visual cortex. Also changes in the optical media, eg cataract changes, or toxic effects of chemicals can alter colour perception. Acquired colour vision defects are generally asymmetrical in the two eyes, eg affecting red-green as well as yellow-blue, while also there may be other defects of visual function ( visual field defects). 7.4 WWW Resources on Colour --------------------------- Information on Gamma and Colour are contained in Charles A Poynton's FAQs URL: http: -- Grant Sayer EMAIL: grants@research.canon.oz.au PHONE: +61-2-805-2937 SNAIL: Canon Information Systems Research Australia 1 Thomas Holt Drive, North Ryde, Australia 2113