How does the eye work?

When you take a picture, the lens in 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.

 

When should my child's eyes be examined?

Most physicians test vision as part of a child's 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 baby's 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 serious eye disease, an ophthalmologist can begin checking your child's vision at a very early age.

 

When should an adult's eyes be examined?

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.

• Adults ages (ages 40 - 64) should have their eyes examined every two-four years.

• Seniors (over 65 years of age) should have their eyes examined every one-two years.

High-risk adults include:

• People with diabetes

• People with glaucoma or strong family history of glaucoma

• People with AIDS/HIV

 

What are the medical terms for nearsightedness and farsightedness?

* The medical term for nearsightedness is myopia, correctable with glasses, contact lenses or, in some cases, refractive surgery (LASIK or Corneal Ring Implants).
* The medical term for farsightedness is hyperopia, correctable with glasses, contact lenses, or, in some cases, refractive surgery.
* Related conditions (also correctable with glasses or contact lenses) include astigmatism and presbyopia.

 

What is visual acuity?

Acuity is the measure of the eye's 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.

 

What is legal blindness?

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.

 

What is visual impairment?

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.

 

What is low vision?

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.

 

Can eyes be transplanted?

No. Currently, there is no way to transplant a whole eye. However, corneas have been successfully transplanted for many years.

Can my child wear contact lenses during sports activities?

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 the information about preventing eye injuries.

 

Do contact lenses prevent nearsightedness (myopia) from getting worse?

No, there is no evidence that wearing contact lenses improves vision or prevents myopia from getting worse. Also, see the information about contact lenses

 

Is it safe for me to clean my contact lenses with a homemade solution?

Using commercial saline solutions is the safest method of cleaning lenses. Some studies have shown that homemade solutions may lead to corneal infections. Also, see the information about contact lenses.

 

Will working at a computer screen hurt my eyes?

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, look off in the distance and adjust your workstation (angle of the monitor, height of the chair, changing the lighting, etc.).

 

Is pink-eye / Madras eye contagious?

Yes, viral conjunctivitis (pink-eye/madras eye) is very common and is extremely contagious. Avoid touching your eyes with your hands, wash your hands frequently, do not share towels, and avoid work, school or daycare activities for a least five days or as long as the discharge is present.

 

Will sitting too close to the television set hurt my child's 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.

 

Are sunglasses good for my eyes?

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.

 

Is my child likely to inherit my need for glasses?

Possibly. If both biological parents wear glasses, your children are likely to need them as well.

 

Will reading in dim light hurt my eyes?

No, but most people are more comfortable reading with proper lighting which is bright enough to provide good illumination but not so bright as to cause glare.

 

How often do I need to get my prescription changed?

There is no predetermined schedule for changing glasses or contacts. It is necessary to change your prescription only when it no longer provides adequate correction. However, it is still a good idea to have regular eye examinations

 

What materials are available for glasses?

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 lightweight 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.

 

Why Does My Eye Twitch?

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.

 

What is Myopia?

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.

 

What is Hyperopia?

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.

 

What is Emmetropia?

Emmetropia is just another name for an eye that has no optical defects and a precise image is formed on the retina.

 

What is Astigmatism?

An astigmatic eye generally has two different meridians, at 90 degrees to each other, which causes 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. Astigmatism causes images to be out of focus no matter what the distance. It is possible for an astigmatic eye to minimize the blur by accommodating or focusing to bring the "circle of least confusion" onto the retina.

 

What is Presbyopia?

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 fibers of the posterior ciliary body. The age-related increase in fibrillar material could cause decreased compliance of the posterior insertion of the ciliary muscle.

 

How is Visual Acuity Measured?

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 20 feet but could only see letters that a person with normal vision could read at 60feet

 

Difference between soft and hard contact lenses

Soft 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 oxygen permeability. Lens size is between 8.0mm and 10.00mm. Centre thickness from ~100um.

 

Why do I have to clean my Contact Lenses?

Cleaning removes surface debris and bacteria that may adhere to contact lenses.

 

Why is there a limit to the length of wearing time?

The cornea the "clear part of the eye", is avascular or without a blood supply. It is avascular otherwise it wouldn't 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 edema. Contact lenses, as described in Sections 3.3 and 3.4, are manufactured from a 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.

 

Why is there a limit to the length of wearing time?

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 edema. Contact lenses are manufactured from a 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.

 

Can I lose the lens behind my eye?

The short answer is no. The conjunctiva, the tissue that covers the white part of the eye (the sclera) forms a cul-de-sac between 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.

 

How do I tell if I've lost the lens from my eye?

Cover the other eye to determine if vision is still clear from the eye where you suspect that you've 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.

 

How can I tell if I've put them in the wrong eye?

Check the vision of each eye by covering alternate eyes with your hand. If the vision is unclear then try swapping the lenses and then recheck the vision.

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How to tell if the lenses are inside out?

Soft lenses will appear as a smooth dish shape when placed on the end of a finger and when the lens is the right way around.

How do I know when to dispose of my disposable lenses?

The 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 minimize

complications with contact lens wear so it should be adhered to!

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Can I store my lenses in tap water?

Short answer - No !. There are a number of "nasty" micro-organisms, especially acanthamoeba (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.

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Can I use eyedrops with my contact lenses?

In general, eyedrops shouldn't 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.

 

How do I get around dryness with contact lenses?

Try using lubricant eye drops. There can be some dryness if you work in an air-conditioned environment. If the problem persist consult a professional.

Risks and Benefits of Contact Lenses

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. Risks: - corneal odema - corneal ulcers - contact lens-induced conjunctivitis Permanent Solution: Lasik treatment to get rid of contact lens / spectacles.

 

What is 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.

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What are common 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". An 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 blepharitis, 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.

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What is Keratoconus?

Keratoconus (conical cornea) is a recessively inherited condition usually appears 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.

 

What is 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.