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- From: grants@research.canon.com.au (Grant Sayer)
- Newsgroups: sci.med.vision,sci.med,sci.answers,news.answers
- Subject: sci.med.vision: Frequently Asked Questions (FAQ), Part 3/5
- Supersedes: <faq-part3_843777040@research.canon.com.au>
- Followup-To: sci.med.vision
- Date: 19 Feb 1997 08:31:55 +1100
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- Summary: This posting contains a list of Frequently Asked Questions concerning
- vision and eyecare.
- Xref: senator-bedfellow.mit.edu sci.med.vision:22076 sci.med:202856 sci.answers:5926 news.answers:95065
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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: http://128.173.80.71/lensnet.html
- (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
-