Astigmatism

The cornea is dome shaped. It bends light and helps to focus it onto the retina where photo receptors detect light and transmit nerve impulses via the optic nerve to the brain where the image is formed. Where there is any incorrect shaping of the cornea the result is an incorrect focusing of the light that passes through that part of the cornea.

One of the main symptoms of astigmatism is blurred vision but people may also experience headaches and eyestrain. It may be caused by the weight of the upper eyelid resting on the eyeball creating distortion.

 

Treatments:

Laser treatments have been approved but the risk of this surgery is the over or under correction which would result in multiple surgeries. Generally lenses are recommended.

Lenses:

These types of lenses are referred to as cylindrical lenses. The unit of measure in diopter is written in terms of the axis the correction is in (because the correction is in one direction). If the amount of astigmatism low than it may be +1.00 or -1.00.

They are toric contact lenses by name. They come in soft and RGP’s (gas permeable, rigid).  The difference is in the design of the lens. When someone blinks the lens rotates and returns to the same position each time.

Soft lenses are used to mask a small astigmatism correction. They use a higher powered spherical soft lens. They are available is disposable, 30 day and even daily wear.

RGP’s rigidity is often preferred because ones cornea will to some to degree conform to the shape of the lens.

Both should be discussed with your doctor before any selection is made.

 

Hard to Fit Cases:

Sometimes the toric lens rotates too much which causes blurred vision. Other people have a high degree of astigmatism. For those with these conditions it is important to have a professional who has experience in toric lenses. High astigmatism eyes should try to not use the gas permeable lenses. This should provide more clarity of vision.

Presbyopia

Presbyopia symptoms usually occur over time as the lens capsule loses its ability to expand. This happens as a person ages and typically beginning between the ages of 40 and 50.

 

 

 

These symptoms include:

·        Blurry vision of close objects

·        Fine print being difficult to read

·        Eye fatigue

·        Eyestrain

·        Headaches

·        Needing to hold reading material at an arm’s length to read properly

·        Needing extra lighting

 

Treatments:

Surgeries:

Monovision and LASIK

Typically your eyes work together equally when you look at objects. This produces binocular vision. Most people have a dominant eye that your brain tends to favor for "sighting" In monovision, one eye does more work for sight purposes than the other. If one of your eyes is set for distance vision and the other is set for near vision, the distance eye will do most of the work when looking at objects in the distance, and the near vision eye will do most of the work when looking at objects close by.

Some surgeons will produce monovision in patients by leaving the non-dominant eye slightly nearsighted so that one can see up close without glasses  It's better to try monovision with contact lenses first to be sure you can adapt.

 

Monovision and Conductive Keratoplasty (CK)

Conductive keratoplasty uses low-level, controlled radio-frequency energy to shrink collagen found that is in the periphery of the cornea. This steepens the central cornea, and the effect is lengthening a too-short eyeball.

CK is used to help one eye see better up close, while the other eye is not touched. If you are nearsighted that eye would wear a contact lens to see at distance. As mentioned before it is best to try contact lenses first.

Laser Thermal Keratoplasty (LTK)

Laser thermal keratoplasty is when a mild laser heat is used in a three-second procedure to shrink collagen in the periphery of the cornea. This procedure’s results are to steepen the eye's surface for correction of near vision in farsightedness or presbyopia.

 

Surgical Reversal of Presbyopia (SRP) with Scleral Expansion Bands (SEBs)

In this procedure the surgeon inserts four plastic segments made out of polymethyl methacrylate. They are inserted just below the surface of the sclera, which increases the distance between the muscles that focus the lens and the lens itself.

Lenses:

Monovision Lenses-Previously mentioned in the surgeries area was monovision. In contacts one lens it fitted that corrects near vision and the other one for distance. If distance vision is not a problem then only one contact is fitted.

How this process works is by having one eye focus for distant objects while the other eye is used for closer objects such as reading. Ones brain adapts and will then automatically use the eye necessary for the appropriate necessity at hand.

 

Bifocal Lenses-These lenses are similar to bifocal glasses as the top portion is for distance and the lower portion is for close up. Bifocal contact lenses come in both soft materials and rigid gas permeable materials. There are some disposable ones as well. It is important to have moist eyes and have occupations that do not involve a great deal of visual demand. Another note is that they may limit binocular vision.

 

Multifocal Contact Lenses- This simultaneous vision lens requires your eye to be looking through both distance and near powers at the same time. Your visual system learns to select the correct power choice depending on how close or far you're trying to see. Simultaneous vision lenses come in two types:

·        Concentric ring designs

·        Aspheric designs

 

Concentric Ring Designs Lenses- These bifocal contact lens feature a prescription in the center and one or more rings of power surrounding it. If there are multiple rings, they alternate between the near and distance prescription.

Typically at least two rings are within your pupil area, but this can vary as your pupil expands and contracts due to varying light.

Concentric ring bifocal contact lenses can be made of either soft or rigid (GP) material. The locations of the powers will vary:

• GP bifocals usually have the distance power in the center. They are called center-distance.
• Soft bifocal contact lenses usually have the near power in the center and are referred to as center-near.
• Some soft multifocal designs are center-near on your dominant eye but center-distance on your non-dominant eye.

Aspheric Multifocal Contact Lenses-These are multifocal contact lens that work more like progressive eyeglasses. The different prescriptive powers are blended across the lens. The difference is that aspheric contact lenses are simultaneous vision lenses, so your visual system must learn to select the proper prescription for the moment. It is described as progressive. It is also concentric. It has become the most popular type of multifocal contact lens.

 

 

Kerataconos:

The clear front window of the eye (the cornea) becomes thin and protrudes. In the above picture one can see how it is cone shaped.

Kerataconos generally appears in ones late teens to the twenties. And slowly progresses for 10 to 20 years. As it progresses the cornea steepens and scars. This may affect both eyes but normally one is more pronounced than the other.

Treatments:

Surgeries:

Cornea transplants

When having a cornea transplant, a surgeon replaces a portion of your cornea with another one from a donor. Donor corneas (grafts) become available from a donor. Compared to other organ and tissue donations, there usually isn't a long waiting list for people who need cornea transplants.

The most common type of cornea transplant is called penetrating keratoplasty. The surgeon cuts through your entire cornea to remove a small button-sized disc. An instrument, called a trephine, makes a precise circular cut. The donor cornea, cut to fit, is placed in the opening. The surgeon then uses a fine thread to stitch the new cornea into place. The stitches are removed at a later visit to your eye doctor. The entire surgery takes about an hour, depending on your individual condition.

Sometimes a full-thickness transplant isn't always the best treatment. Partial-thickness (lamellar) transplants may be used in certain situations. Those types are:

Deep lamellar transplant- This transplant replaces only the innermost of your cornea's five layers. A small incision is made in the side of the eyeball to allow for removal of the cornea's inner layer without injuring the outer layers. A donor graft replaces the removed portion. This procedure is still being studied and should be discussed with your doctor.

Surface lamellar transplant- Although this is very uncommon, eye damage may only involve the outer layers of the cornea. These layers, too, can be removed and replaced with a donor graft.

Afterwards:

The healing process following transplant is long. The time from surgery to the removal of the stitches is commonly 6 to 17 months and one may be on steroids for months.

Graft rejection reactions occur in 11% to 18% of the patients (Kirkness et al 1990; Troutman and Lawless 1987). Signs of graft rejection are reported to occur from 1 month to 5 years following surgery (Kirkness et al 1990). The rejection rate for bilateral grafts is higher than if only one eye is grafted. In the bilateral cases, when a rejection reaction occurs it is commonly in both eyes. If the second eye is to be grafted, there is usually a period of at least a year between grafts. If signs of rejection occur, aggressive treatment with steroids is begun. Usually the reaction is overcome and the graft remains clear. Over 90% of the corneal grafts are successful with some studies reporting 97% to 99% success rates at 5 and 10 years (Kirkness et al 1990, Troutman and Lawless 1987, Epstein).

Contact lenses may be needed afterwards due to significant astigmatism and often some distortion. The types of lenses recommended are rigid gas permeable corneal lenses. Those being scleral (haptic) lenses, and the SoftPerm lens.

 

Lenses:

SoftPerm lenses are for those with early stage keratoconus, post corneal graft or those who require the visual acuity of an RGP (rigid) and the comfort of a soft lens.

 

Scleral lenses are different than other contact lenses in many ways. Unlike other contacts, a scleral contact lens does not rest on your eye's cornea. The hard lens doesn't touch the cornea at all, but rests on the sclera which is the white part of your eye outside the iris. This forms a dome over the cornea. Because it reaches over your entire cornea, a scleral lens is much larger than a standard contact lens. The space between the lens and the cornea must contain fluid for the lens to work properly. This means that when you insert a scleral contact lens into your eye, the lens needs to be filled with a sterile saline solution to ensure clear vision. Those who cannot tolerate smaller rigid lenses, may find they can get the vision and comfort they need with these lenses as well as people who have persistent dry-eye symptoms, or who have damage to the surface of their eyes due to an inadequate or poor quality tear film.

Hard to Fit Cases:

For those with kerataconos there are instances when the cornea is so irregular that it needs cushioning. In this case a piggyback technique would be used. This technique is where two lenses are worn on each eye. A soft lens drapes over a gas permeable one (RPG). There is another option available for some being a lens that is rigid in the middle with a soft skirt around it.

 

Dry Eyes:

Many contact users experience dry eyes. Some of the symptoms are:

·        Tearing for no reason

·        Having watery eyes

·        Red or burning eyes

·        The feeling as if something is in your eyes

Factors involved with lenses may be from a very thin lens that is drying up fast. In this case a thinker, soft one may be prescribed. Many times soft lenses are prescribed with low water content. Other times they may use gas permeable ones because they do not absorb the water from your eyes.

Other treatments:

·        Artificial tears, which are lubricating eyedrops

·        Restasis eyedrops (cyclosporine in a castor oil base).Keep in mind that many eye drops, especially artificial tears, cannot be used while your contacts are in your eyes.

·        Drinking more water

·        Punctal plugs

 

Small collagen or silicone devices are inserted into the tear ducts. This blocks the tears from leaving the eyes and creates a moisture environment for the lens. The entire procedure takes a few minutes to do.

Giant Papillary Conjunctivitis:

 

Giant papillary conjunctivitis is primarily found in those that wear soft lenses. It is an allergic reaction that is caused by proteins that are secreted in your eyes.

Symptoms:

·        Red, irritated, and itchy eyes

·        Blurry vision even though you are wearing your contact lenses

·        Increased lens movement with each blink

·        Stringy mucous secretions in your tears

·        Being very uncomfortable while wearing lenses

 

Options to correct:

Disposable Contacts so the accumulation does not occur

Gas permeable lenses- These lenses do not allow proteins to reside upon them if cleaned properly.

Contacts for After Corrective Surgery:

After LASIK surgery it may be necessary to use contact lenses. The reasons for this are in the cases of:

·        High astigmatism

·        Irregular astigmatism

·        After you have had LASIK for monovision

·        Excessive glare after LASIK surgery

·        LASIK surgery which results in off center ablation (This is the optical status of the eye resembles that of irregular astigmatism.)

 

Many time gas permeable lenses will be prescribed especially in the cases of irregular astigmatism, excessive glare, and off center ablation.

 

Toric lenses are usually prescribed for those with high astigmatism but soft lenses, or RPG’s may work as well.

 

Monovision will usually require only one lens and that is mainly for distance.

 

 

 

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