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.
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.
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.
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.
Benefits: - no need to wear glasses - no spectacle scotoma - ie "blind-spot" due to frame edge - overcome problems of spectacle magnification, especially when large difference in spectacle prescription between the two eyes.
In general eyedrops shouldnt be used with contact lenses because the lens can absorb the eye drop and result in a concentrated buildup of the solution. There are special, "in-eye" lubricants that many manufacturers/pharmaceutical companies produce for use with contact lenses. Check with your eyecare professional if any doubts about the solution.
Short answer - No !. There are a number of "nasty" micro- organisms, especially acanthomeba (sp) which likes feeding on corneal tissue. Storing lenses in water also defeats the purpose of using a disinfecting solution as there is no disinfection occurring. If anything you are exposing your lenses to more potentially dangerous microorganisms.
he lenses will not automatically self-destruct at the end of the wearing period :-) The lenses should be discarded when the lens wearing time has elapsed, as advised by your eyecare professional. This wearing time/period has been chosen to minimise complications with contact lens wear so it should be adhered to !
Cover the other eye to determine if vision is still clear from the eye where you suspect that youve lost the lens. If vision is blurred then more than likely the lens is either dislodged from the cornea or has fallen from the eye.
Short answer is no. The conjunctiva, the tissue that covers the white part of the eye (the sclera) forms a cul-de-sac between from the edge of the cornea to the eyelid margin. Sometimes a contact lens, especially a soft contact lens may roll up and become difficult to find. An eyecare practitioner will be able to locate the lens and remove it.
The cornea the "clear part of the eye", is avascular or without a blood supply. It is avascular otherwise it wouldnt transmit light without distortion. As a result of this living tissue being avascular it is necessary to obtain oxygen from the atmosphere. The wearing of a contact lens interrupts the flow of oxygen to the cornea and due to changes in the metabolic pump of the corneal cells the tissue thickens, called oedema. Contact lenses, as described in Sections 3.3 and 3.4, are manufactured from material that allows maximum oxygen transmission. But this is still not exactly the same as the 20.4% therefore the lens wearing time must be controlled to reduce oxygen deprivation to the cornea.
SSoft lenses are manufactured from a plastic hydrogel polymer, HydroxyEthylMethacrylate (HEMA) which has a varying water content (38% - ~70%). Lens size is between 13.00 and 14.50mm. Centre thickness from ~30um.
Hard contact lenses are manufactured from a rigid material, PolyMethylMethacrylate (PMMA). This material can be combined with other plastics to increase the oxygen permeability. Lens size is between
8.0mm and 10.00mm. Centre thickness from ~100um.
Visual acuity is the measure of the sensitivity of the visual system. It is expressed in Snellen notation, expressed as a fraction, where the numerator indicates the test distance and the denominator denotes the distance at which the letter read by the patient subtends 5 minutes of arc. Normal vision is expressed as 20/20 or 6/6. An acuity of 20/60 means that the patient was tested at 20feet but could only see letters that a person with normal vision could read at 60feet
Presbyopia describes the condition whereby the amplitude of accommodation, or ability to focus on objects at near, decreases with increasing age. It is corrected by a different prescription for reading, which is additive to the normal spectacle correction used for distance vision. Some recent research indicates that presbyopia may be caused by structural changes in the tendons and elastic fibres of the posterior ciliary body. The age related increase in fibrillar material could cause decreased compliance of the posterior insertion of the ciliary muscle.
An astigmatic eye generally has two different meridians, at 90degrees to each other, which cause images to focus in different planes for each meridian. The meridians can each be either myopic, hyperopic or emmetropic. The correction for astigmatism is a lens power at a particular direction of orientation [ see section 4.1 ] Astigmatism causes images to be out of focus no matter what the distance. It is possible for an astigmatic eye to minimise the blur by accommodating, or focusing to bring the "circle of least confusion" onto the retina.
Hyperopia is often referred to as "long-sightedness" or "far-sighted". An eye is hyperopic when the far point is at a virtual point behind the eye. Generally the hyperopic eye is too short with respect to the refractive state of the standard eye (ie an emmetropic eye or eye requiring no optical correction) or because the optical power of the eye is too low relative to the length of the standard eye. The focus is correctly adjusted using a "plus" lens power or convex lens.
Myopia is often referred to as "short-sightedness" or "near-sighted". An eye is myopic when the "far point"; a point at which light from an object is focussed on the retina, is located at a finite distance in front of the eye. Myopia can be due to either an eye which is too long relative to the optical power of the eye (axial myopia), or because the optical power of the eye is too high relative to the length of the standard eye (refractive myopia). The focus is correctly adjusted with a "minus" power lens, or concave lens.
Mild twitching of the eyelid is a common phenomenon. Although these involuntary contractions of muscles are annoying, they are almost always temporary and completely harmless. The medical name for this kind of twitching is ocular myokymia. It is quite common and most often associated with fatigue. When your eye is twitching, it is not visible to anyone else. Ophthalmologists often are asked what causes the twitching and what can be done to stop it. Lack of sleep, too much caffeine or increased stress seem to be root causes. Often, gently massaging your eye will relieve the symptoms. Usually, the twitch will disappear after catching up on your sleep.
Some of the newest materials for frames include titanium (virtually indestructible) and polycarbonate materials (recommended for high impact sports). Lenses are also made from polycarbonate materials, other types of light weight plastics and glass. Coatings include UV protection (recommended for all types of lenses), scratch-resistant protection, polarization, anti-glare and others. See the Kellogg Optical Shop for more information about glasses.
There is no predetermined schedule for changing glasses or contacts. It is necessary to change your prescription only when it no longer provide adequate correction. However, it is still a good idea to have regular eye examinations.
There is a benefit to wearing UV protective lenses--wearing them may protect against cataract formation. Clear lenses with UV protection may offer greater protection than dark lenses because they allow the eyes to be exposed to more light. This causes greater constriction of the pupil which lets less light enter the eyes.
No, there is no scientific evidence that TV sets emit rays that are harmful to the eyes.
Why have I gradually found it harder to read without glasses?
The ability to focus on near objects decreases steadily with age and is referred to as presbyopia. Presbyopia is a natural aging of the lens. It is usually near the age of 40, when glasses or bifocals are prescribed to correct this condition.
Yes, viral conjunctivitis (pink-eye/madras eye) is very common and is extremely contagious. Avoid touching eyes with your hands, wash hands frequently, do not share towels, and avoid work, school or daycare activities for a least five days or as long as discharge is present.
No, there is no evidence that working at a computer damages the eyes. However, long hours of work can be fatiguing to the eyes, neck and back. Monitor glare from various light sources can also be a problem. It is often helpful to take periodic breaks, looking off in the distance and adjusting your work station (angle of the monitor, height of the chair, changing the lighting, etc.).
No, because it does not provide the specifications for lens diameter, thickness and base curve. A new prescription must be carefully fitted by an eye care specialist to avoid serious adverse reactions.
Yes, contact lenses provide excellent vision for most sports. However, they do not protect the eyes from injury. Therefore, contact lens wearers should use polycarbonate sports safety goggles or glasses when participating in sports. Also see information about preventing eye injuries.
Low vision is a term describing a level of vision below normal (20/70 or worse) that cannot be corrected with conventional glasses. Low vision is not the same as blindness. People with low vision can use their sight. However, low vision may interfere with the performance of daily activities, such as reading or driving.
If neither of your eyes can see better than 20/60 without improvement from glasses or contacts, you may be defined as visually impaired. In addition, poor night vision, limited side vision, double vision and loss of vision in one eye may also determine visual impairment.
You are legally blind when the best corrected central acuity is less than 20/200 (perfect visual acuity is 20/20) in your better eye, or your side vision is narrowed to 20 degrees or less in your better eye. Even if you are legally blind, you may still have some useful vision. If you are legally blind, you may qualify for certain government benefits.
Acuity is the measure of the eyes ability to distinguish the smallest identifiable letter or symbol, its details and shape, usually at a distance of 20 feet. This measurement is usually given in a fraction. The top number refers to the testing distance measured in feet and the bottom number is the distance from which a normal eye should see the letter or shape. So, perfect vision is 20/20. If your vision is 20/60, that means what you can see at a distance of 20 feet, someone with perfect vision can see at a distance of 60 feet.
Adult examinations of the eyes should be performed on a regular basis.
o Young adults (ages 20 - 39) should have their eyes examined every three-five years.
o Adults ages (ages 40 - 64) should have their eyes examined every two-four years.
o Seniors (over 65 years of age) should have their eyes examined every one-two years.
High risk adults include:
o People with diabetes
o People with glaucoma or strong family history of glaucoma
o People with AIDS/HIV
Most physicians test vision as part of a childs medical examination. They may refer a child to an ophthalmologist (a medical eye doctor) if there is any sign of an eye condition. The American Academy of Ophthalmology and the American Academy of Pediatrics recommend the first vision screening occur in the hospital as part of a newborn babys discharge examination. Visual function (including ocular alignment, etc.) also should be checked by the pediatrician or family physician during routine well-child exams (typically at two, four and six months of age). Later amblyopia and alignment screenings should take place at three years of age and then yearly after school age.
If you suspect your child suffers from decreased vision - amblyopia (poor vision in an otherwise normal appearing eye), refractive error (nearsightedness or farsightedness) or strabismus (misalignment of the eye in any direction) - or if there are hereditary factors that might predispose your child to eye disease, please make an appointment with an ophthalmologist as soon as possible. New techniques make it possible to test vision in infants and young children. If there is a family history of misaligned eyes, childhood cataracts or a serious eye disease, an ophthalmologist can begin checking your childs vision at a very early age.
When you take a picture, the lens in the front of the camera allows light through and focuses that light on the film that covers the back inside wall of the camera. When the light hits the film, a picture is taken. The eye works in much the same way. The front parts of the eye (the cornea, pupil and lens) are clear and allow light to pass through. The light also passes through the large space in the center of the eye called the vitreous cavity. The vitreous cavity is filled with a clear, jelly-like substance called the vitreous or vitreous gel. The light is focused by the cornea and the lens onto a thin layer of tissue called the retina, which covers the back inside wall of the eye. The retina is like the film in a camera. It is the seeing tissue of the eye. When the focused light hits the retina, a picture is taken. Messages about this picture are sent to the brain through the optic nerve. This is how we see.
* An Ophthalmologist (MD) has a medical degree and is licensed to practice medicine and perform eye surgery.
* An ophthalmologist has had at least 12 years of education and training beyond high school and is qualified to diagnose and treat all eye diseases; perform surgery; prescribe and fit glasses and contact lenses.
* An Optometrist (OD) has a degree in optometry and is licensed to practice optometry. An optometrist has had at least six years of education and training beyond high school and is qualified to determine the need for glasses and contact lenses; prescribe optical correction; and screen for some eye conditions.
* An Optician usually has a combination of college (or two years of opticianry school) and on-the-job training. An optician is trained to fit and dispense eyeglasses or contact lenses based upon a prescription from a licensed ophthalmologist or optometrist.
Newborn infants are able to see, but as they use their eyes during the first months of life, vision improves. During early childhood years, the visual system changes quickly and vision continues to develop. If a child cannot use his or her eyes normally, vision does not develop properly and may even decrease. After the first nine years of life, the visual system is usually fully developed and usually cannot be changed.
The development of equal vision in both eyes is necessary for normal vision. Many occupations are not open to people who have good vision in one eye only. If the vision in one eye should be lost later in life from an accident or illness, it is essential that the other eye have normal vision. Without normal vision in at least one eye, a person is visually impaired.