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  • Doug Cook

Bifocal Contacts

Around the age of 40, symptoms of presbyopia begin to develop for most people.  Presbyopia is the natural loss of focusing due to physiological changes which occur in the lens of the eye.  The human lens is responsible for focusing and is normally quite elastic in youth.  Beginning in adolescence, the lens gradually becomes more firm.  As a result, the distance which we can focus things clearly lengthens until suddenly you find out that your arms aren’t long enough to read the paper.  A multifocal or reading lens is the treatment of choice for this refractive condtion.

Correction Options for Presbyopia

Eyeglasses have been the most popular and most efficient form of correction.  Contact lens options are also available to help compensate for the natural loss of focusing ability.  A careful evaluation of your vision needs is performed to see what type of challenges you have, what distances do you need to see clearly for, whether you work at a video display terminal for long periods of time and the general environmental conditions of your work such as  lighting and or even the humidity of the workplace.  Your hobbies and leisure activities may be evaluated as well.

Bifocal Contact Lenses Have specialized optics to create a lens which has more than a single power.  The designs include simultaneous vision and alternating vision lenses.  Bifocal lenses are limited in the availability of parameters so not every patient may be a good candidate.

Simultaneous vision lenses provide a focus on the retina for objects at near and for objects at distance at the same time as illustrated below.  Contacts are available in soft and rigid gas permeable materials. Simultaneous vision lenses have areas of the lens with differing powers.  Designs have one power for near and a different power for distance.   This can occur in two distinct areas as shown on the left, alternating zones as in the center, or it may gradually change as shown on the right.

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Simultaneous vision lenses have areas of the lens with differing powers. Designs have one power for near and a different power for distance. This can occur in two distinct areas as shown on the left, alternating zones as in the center, or it may gradually change as shown on the right.



Alternating vision lenses are more like traditional bifocals with the lower portion of the lens providing the near power.  Since we tend to look down as we view things at near, the contact lens must be able to move into proper position in order to work effectively.  Currently, lenses are available in rigid gas permeable materials only. When viewing objects in the distance, the line of sight passes through the top section of the contact.  When viewing near objects the line of sight passes through the bottom section of the lens.  Alternating vision lenses may not work well for people with loose eyelids or irregular corneas.

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When viewing objects in the distance, the line of sight passes through the top section of the contact. When viewing near objects the line of sight passes through the bottom section of the lens. Alternating vision lenses may not work well for people with loose eyelids or irregular corneas.


Visual Phenomena Common to Presbyopic Correction with Contact Lenses…

You may notice an occasional fuzziness surrounding an otherwise clear object.  We call this effect ghosting or halos.  One of the most common side-effects is a perceived blur of a bright object such as a headlight against a dark background.  This glare at night can be eliminated by exchanging the near contact lens for a distance contact lens or through the use of special glasses designed to be worn for specific tasks such as driving.  Bifocal contact lenses may not be optimal for nighttime use and should be worn with caution while driving in the dark.  Monovision may require the use of a supplementary glasses for specific conditions.  Prolonged near activity (computers, needlepoint, form-work), night-time driving, or continued concentrated distance viewing (piloting, truck-driving) are examples.  Eyestrain or headaches which occur at near may indicate a need for a change in the power of the prescription or the need for special eyewear.  Call the doctor at our office to see if any fine-tuning to your specific needs is required.

Monovision


In monovision your doctor designs a contact lens prescription which allows one eye to remain clear for distance viewing while the other eye remains clear for near viewing.  This prescription is determined after a careful evaluation with you in which your visual needs are assessed for the best work, leisure and driving performance with the contact lenses.  Monovision allows the use of traditional contact lens designs. Monovision places your vision under new viewing conditions for combined near and distance viewing.  If you cover one eye you will notice that it will be more clear for the distance but not for near while the opposite will be true for your other eye.  With time, your brain should automatically select which eye is to be used.  This adaptation period lasts 2 to 3 weeks for most patients.  You should be especially careful in all your daily activities (i.e., driving, using curling irons, moving pots and pans on the stove) while you get used to your prescription. Monovision offers a compromise between the best vision possible with bifocal eyeglasses and the freedom from being dependent on some pair of reading prescription.  Some patients may require glasses to work over contacts for extended or critical near or distance tasks.

Modified Bifocal / Monovision Is a fitting technique which utilizes both bifocal contacts and monovision.  Is a method which helps to fine tune a bifocal contact lens prescription to work better at distance or near.  The lens power is modified to enhance near or distance vision according to the needs of the patient. Sometimes only one bifocal on an eye with the other eye set for distance vision may be all the vision correction which is needed.

Contact Lens Tips Wear your contacts when you go to see the doctor for progress checks.  It is important to see the lens after several hours of wear on the eye unless discomfort is severe. Because contact lenses are medical devices, yearly eye exams are required to check the health of the eye when wearing contact lenses.  New contact lenses can not be dispensed if you are past due for a check up.

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