The shape of a hyperopic eye focuses images behind the retina, resulting in blurred near vision. A ‘plus’ lens increases the focusing power of the eye correctly focusing the image on the retina producing clear vision at all distances.
The shape of a myopic eye focuses the image in front of the retina resulting in blurred distance vision. A ‘minus’ lens decreases the focusing power of the eye correctly focusing the image on the retina producing clear vision at all distances.
Astigmatism is typically present at birth. Over time the condition may slowly increase but generally it remains relatively stable over a lifetime. Forty-five percent of people who require vision correction have some degree of astigmatism. Symptoms include squinting, occasional headaches and eye strain. Astigmatism often accompanies myopia and hyperopia.
The irregular shape of an astigmatic eye produces two focusing points around the retina. The result is blur at all distances. A ‘toric’ lens corrects each toric irregularity so that light is properly focused on the retina producing clear vision at all distances.
To correct this condition lenses of different powers are required. The first lens is a lens to correct the distance vision and the second lens provides the focusing power for reading. This is easily seen in bifocal spectacles. The most common consequence of bifocals is the loss clarity for intermediate distances including computer work. Unfortunately, each lens strength has a very specific distance from the nose in which things will be clear. The same lens needed for reading will NOT work for seeing something a little further away such as the computer. To see the distance needed for the computer, a different strength is needed but that strength will not work for reading. Ultimately, to adequately function in life different lens strengths are needed for every distance. The ideal lens for correcting presbyopia is the progressive lens. This is a molded lens that provides power for all distances including the intermediate distances. Additionally this is a much more natural lens for your brain to accept. Where the bifocal only allows clear vision for two distances, the progressive simulates the eyes natural ability to have clear vision for all distances.
Signs of Dry Eye
Causes of Dry Eye
Long-term contact lens wear is another cause; in fact, dry eye is the most common complaint among contact lens wearers. Recent research indicates that contact lens wear and dry eyes can be a vicious cycle.
Treatment for Dry Eyes
Age Related Macular Degeneration
The macula is the small portion of the retina located at the center of this light sensitive lining at the back of the eye. Light rays from objects that we are looking at come to a focus on the retina and are converted into electrical impulses, which are then sent to the brain. The macula is responsible for sharp straight- ahead vision necessary for functions such as reading, driving a car and recognizing faces. The effect of this disease can range from mild vision loss to central blindness. That is, blindness “straight ahead” but with normal peripheral vision from the non-macular part of the retina remains undamaged by the disease. Ninety percent of cases of AMD are of the atrophic or dry variety. It is characterized by a thinning of the macular tissue, develops slowly and usually only causes mild vision loss. The main symptom is often only a dimming of vision when reading.
The second form of AMD is called exudative or wet because of the abnormal growth of new blood vessels under the macula where they leak and eventually create a large blind spot in the central vision. This form of the disease is of much greater threat to vision than the more common dry type. Macular degeneration is most common in people over the age of 65 but there have been some cases affecting people as young as their 40s and 50s. Symptoms include blurry or fuzzy vision, straight lines like telephone poles and sides of buildings appearing wavy and a dark or empty area appearing in the center of vision.
Currently there is no treatment of macular degeneration. In certain circumstances the progression of retinal damage may be slowed with a steroid injection. Results of a large multi-factorial study found that the ingestion of certain vitamins high in antioxidants and Lutein/zeaxanthin help slow the progression of the dry form of macular degeneration. There are several options of ‘eye vitamins’ such as Preservision but many multivitamins have all the same ingredients such as multivitamin from Biosyntrx. Several new treatments show promise in not only slowing but may also reverse the degeneration for the wet form.
Glaucoma is defined as the gradual deterioration of the optic nerve that is located at the back of the eye and carries visual information to the brain. As the fibers that make up the optic nerve are damaged by glaucoma, the amount and quality of information sent to the brain decreases and a loss of vision occurs. The result is the gradual loss of functional peripheral vision. Thus, while glaucoma sufferers may be able to read the smallest line on the vision test, they may find it difficult to move around without bumping into things or to see moving objects to the side, such as cars. The leading theory as to the cause of glaucoma is that a build-up of pressure inside the eye gradually leading to the destruction of retinal cells. Aqueous fluid, which fills the space at the front of the eye just behind the cornea, is made behind the iris (the colored part of the eye) in the ciliary body. It flows through the pupil (the dark hole in the center of the iris), and drains from the ‘anterior chamber angle,’ which is the junction between the edge of the iris and the cornea. If this outflow of liquid is impaired at all, there is a build-up of pressure inside the eye that damages the optic nerve, which carries visual images to the brain.
Glaucoma is usually treated with prescription eye drops and medications. In some cases, surgery may be required to improve drainage. The goal of the treatment is to slow the loss of vision by lowering the pressure in the eye. Several tests are needed to more accurately form the diagnosis of glaucoma. Measuring the pressure via tonometry in the eye is the first indicator. Later tests include pachymetry that measures the thickness of the cornea. Recent studies have indicated that the thickness of the cornea can alter the tonometry reading. Another test is a visual field test that measures how well the peripheral visual system is working. Small lights or stimuli are presented to the periphery of the eye, by calculating the accuracy of the responses a more accurate determination of the peripheral visual system is made. A third device is the Optical Coherence Tomography that actually measures the thickness or amount of nerve fibers in the retina and compares that to known normals. Deviations from normal could indicate damage from glaucoma. Unfortunately, any vision loss as a result of glaucoma is permanent and cannot be restored. This is why regular eye examinations are important.
Some causes are known, others are not. Causes differ depending on the type of glaucoma. The exact cause of open-angle glaucoma, where the drainage channels for the aqueous appear to be open and clear, is not known. Closed-angle glaucoma can occur when the pupil dilates or gets bigger and bunches the iris up around its edge, blocking the drainage channel. An injury, infection or tumor in or around the eye can also cause a rise in internal eye pressure either by blocking drainage or displacing tissues and liquid within the eye. A mature cataract also can push the iris forward to block the drainage ‘angle’ between the iris and the cornea. Glaucoma can occur secondarily to a number of other conditions, such as diabetes, or as a result of some medications for other conditions.
Glaucoma most frequently occurs after age 40, but can occur at any age. African Americans are more likely to develop open-angle glaucoma and at an earlier age than Caucasians. Asians are more likely to develop narrow-angle glaucoma. You have a higher risk of developing glaucoma if a close family member has it or if you have high blood pressure or high blood sugar (diabetes). There is also a greater tendency for glaucoma to develop in individuals who are nearsighted. Those at heightened risk for glaucoma should have their eyes checked at least once a year. If diagnosed at an early stage, glaucoma can be slowed so that little or no further vision loss should occur. If left untreated however, side awareness (peripheral vision) and central vision will be destroyed and blindness may ultimately occur.