It is not the purpose of this website to review specific ocular pathologies (such as cataract, glaucoma, macular degeneration, diabetic retinopathy) which are beautifully described in other websites. We intend here to answer general vision questions and will provide pointers to other websites that discuss specific ocular conditions.
As described in The Eye & Vision, there is a lens that is suspended in the eye behind the pupil and is focused by a muscle that pulls on the ligaments that suspend it, changing the shape of the lens that changes its focus. This allows the eye, like a camera, to be focused for objects on the horizon as well as for reading material up close. As we get older, the lens gel becomes hardened and cannot be focused so easily by the muscle resulting in slower as well as reduced ability to focus. Therefore as we grow older (chronologically gifted!) we need either longer arms or glasses to focus on objects up close (except for near-sighted persons who in the relaxed state can focus without glasses up close but can't see well at a distance).
Glare is most often caused by a crystallization of the gel protein within the lens of the eye. Such crystallization occurs generally with aging, but may be hastened with diabetes, or with inﬂammation or bleeding, or with injury of the eye. The glare washes out the contrast and usually can be reduced with ﬁltering lenses (pale yellow lenses indoors while reading or at night to reduce oncoming headlight glare, yellow-amber lenses, orange "blue blockers," gray lenses that reduce the light level overall, or polarizing lenses that reduce the glare from reﬂective surfaces). When the glare is not reduced adequately by such lenses, then surgery, most commonly cataract surgery is done that removes the cloudy lens in the eye and replaces it with a clear plastic lens that is implanted.
Rarely, glare can be caused by an iris that cannot adequately close down the size of the pupil (the opening in the center) or by a cloudiness of the cornea.
These symptoms are caused by a lack of tears. Normally tears are continuously produced by glands under the upper lids and are spread over the surface of the cornea with each blink. However during periods with less abundant tears or with intensive periods of concentrated viewing of an object (such as while reading, driving, or looking at the screen of a monitor or television) the blinking rate is reduced significantly. The cornea under these conditions may become dry and irritated, producing a sandy or burning sensation sometimes with blurred vision and sometimes with enough irritation that excessive tearing is stimulated (by the same mechanism as when peeling onions). The condition most often is normal and aggravated in the winter with dry heat or on a dry, windy day. Remedies include periodically:
The macula is the center portion of the retina that is responsible for vision quality at the center of our field of vision — it is responsible for our vision when reading, driving, or for face recognition, etc. Macular degeneration most often occurs with aging (affecting approximately 30% of persons in North America and Europe), but appears to be genetic, with many different inheritance patterns, There are most commonly two types, a "dry" form in which the blood vessels behind the retina atrophy or dry out in regions and cannot support the overlying retina, or a "wet" form in which abnormal blood vessels develop behind the retina. These vessels leak producing fluid but may also bleed and and form a scar behind the retina in the center. The scarring process leads to smudges in the center of vision with blurring, loss of contrast and color, and often producing distortions or crookedness in the central vision. The key to improving vision is to increase the lighting on the object with focal, off axis lighting that doesn't reﬂect into the face and with ﬁlter lenses that reduce glare and improve contrast. Magniﬁcation devices that magnify the image and also increase light are of significant help, if the visual ﬁeld defect is not large. If the smudge or blur in the center is large or severe, then devices which assist the person in using the remainder "peripheral" vision may be of help but this requires rehabilitative teaching and learning by practice.
Nearly all diabetics, after 5 to 10 years of diabetes, will develop leakages and blockages of the retinal vessels which cause smudges in the central ﬁeld of vision with blurring, loss of contrast, often distortions, and sometimes ﬂoaters from abnormal blood vessels that bleed into the vitreous gel. Frequently diabetics may develop signiﬁcant retinopathy before it causes problems with vision and therefore all diabetics should be examined by an eye-care professional at least once a year even if they do not notice problems with their vision.
A few studies suggest a role for antioxidants, particularly vitamin E, zinc, and ascorbic acid, or the carotenoids, lutein and zeaxanthin, in the prevention of cataracts and possibly in the prevention of macular degeneration, but the research is often contradictive and inconclusive.
Furthermore we don't know which forms of the supplement are most effective. We don't even know whether vitamin supplements are as effective as eating nutritious foods. Unfortunately there is a multi-billion dollar industry that advertises without control but won't conduct the research to prove their efﬁcacy. The National Eye Institute has sponsored a large study of these supplements (AREDS which studied vitamins A,C, and E with lutein, zexanthin and the minerals zinc and coper that did show some effectiveness at reducing the rate of vision loss. The best advice is to eat foods high in antioxidants or carotenoids such as spinach, egg yolks, corn, kiwi fruit, red seedless grapes and zucchini, take the AREDS formula vitamins but most of all stop smoking!
Floaters are produced by the clear gel, the vitreous, in the center of the eye. When we are born, the gel is solid and clear, but as we grow older, the gel develops ﬁbers and debris which cast shadows as the light passes through the eye focused on the retina. The shadows produce spots and lines that ﬂoat in our vision. A few ﬂoaters are very common, but the sudden appearance of new ﬂoaters or myriads of ﬂoaters with cobwebs may signal a detachment of the gel from the surface of the retina (a normal aging change caused by contraction of the gel away from the retina in the back) and it is recommended that the eye be examined to determine if the retina may have been torn when the gel detached. Floaters usually fade with time (over months to years).
Double vision is most often observed only when both eyes are open (and disappears when one eye is covered) and occurs either because the eyes are not lined up to look at the same object, or because one of the images is distorted or of a different size than that in the other eye.
In these cases the brain has difﬁculty when it attempts to combine the different images from each eye to make one image. These problems often require neurologic or retinal evaluation and sometimes require surgery to correct (or if impossible to correct, then permanent patching of one eye may be required to remove the distracting second image).
A doubling or even tripling of the image or ghosting of the image) may be present in one eye and is caused by crystalline changes in the lens (a cataract).
Kinks or crookedness of the image is caused by distortions or kinks of the retina which normally lies ﬂat against the back wall of the eye. Most often the distortions are caused by scar tissue that lies on the surface or under the retina, and like scar tissue elsewhere in the body, it contracts pulling on and distorting the retina. Sometimes distortions of the retina are caused by leakage of the blood vessels that nourish the retina. Such conditions need to be evaluated by an eye care professional without delay.
No, it does not harm your eyes to read in dim light. But in dim light the contrast of the light reaching the retina is reduced making it more difﬁcult to see the print. Therefore we will commonly concentrate harder on what it is we are reading which means staring at the print. This results, obviously, in less blinking, and causes corneal drying which makes the eyes irritated, red, and tired, and often produces periodic over-tearing from the irritation.
Severe eye injuries occur very commonly while playing sports. From the most amateur and inexperienced to the most competent and professional, all athletes are at signiﬁcant risk. The only method to prevent serious eye injury (often with total loss of sight) is to wear adequate eye protection. Over the past decade standards for protective eye wear have been established for those sports where eye injuries occur most commonly -- racket sports, women's lacrosse, ﬁeld hockey, basketball, paintball, ice hockey, baseball, and alpine skiing. Look for and demand that athletes use eyewear clearly marked with the "Protective Eyewear Certiﬁcation Council" symbol.
No, but it can certainly fry your brain!
No — How did this idea ever get started? However, unprotected sex with partners that carry the AIDS virus can result in infections that may result in severe eye blinding retinal infections. We recommend that you be careful.