Cataracts         

 

 

The lens of the eye is normally clear. If the lens becomes cloudy, the condition is known as a cataract.

Adult cataracts usually develop with advancing age and may run in families. It is estimated that about 50% of the risk for cataract is genetically determined. However, the other 50% of cataract risk might be from environmental factors such as sunlight (ultraviolet) exposure, smoking, oxidative stress from environmental toxins or diet, or use of certain drugs, especially steroids. Metabolic diseases such as diabetes also greatly increase the risk for cataracts.

Adult cataracts are generally associated with the passage of time. About 50% of people aged 65-74, and about 70% of those 75 and older, have cataracts that affect their vision.

Cataracts usually develop slowly and painlessly, and vision in the affected eye may change so gradually that the person is unaware it is happening.  Certain types of cataract, such as plaque-like posterior subcapsular (PSC) cataracts may develop faster, or seem to become suddenly worse; or the person may cover one eye and suddenly “discover” a cataract in the other eye. However, any sudden change in vision requires prompt evaluation for other problems besides a cataract.

Generally, cataracts tend to progress at the same pace in both eyes.  If there is a significant difference in the degree or type of cataract between the two eyes, the reason should be sought. For example, is there a history of trauma, prior surgery, radiation treatment, steroid use, chronic inflammation, congenital problem?

 

Symptoms of cataract

People with cataracts may note:

 

• Difficulty seeing at night

• Seeing halos around lights

• Being sensitive to glare

• Muddling or distortion of colors

• Loss of contrast—for example, difficulty reading when the text is not black and white

 

Although systems have been developed to classify cataracts for documentation and for research, clinically what matters is not what the doctor sees, but what you can see. Your visual function and needs drive the decision to treat a cataract. Cataracts are classified by the patterns of opacity, location of opacity, color, and density, and also whether immature, mature, or hypermature. The doctor can explain or show you what variety of cataract you are developing; but, again, the important thing is how you see and how you are functioning with that cataract.

 

Traumatic cataracts may develop at any time after an eye injury, even years later. When you are evaluated for treatment of a traumatic cataract, it’s important to detect other problems with the eye that might be related to the injury, especially glaucoma. The planning for surgery in a traumatic cataract also has to include any iris scarring or loss (if present), and whether the cataractous lens has been knocked loose. The approach to the surgery and choice of lens implant, including backup implants in case of Plan B, changes in the case of a traumatic cataract.

Congenital cataracts are present at or shortly after birth. Congenital cataracts can be inherited; be caused by infections affecting the mother during pregnancy, such as rubella; or associated with metabolic disorders such as galactosemia. Risk factors include inherited metabolic diseases, a family history of cataracts, and maternal viral infection during pregnancy.

Infantile cataracts develop in the child’s early years, and might represent metabolic diseases, trauma, but, most importantly, might herald the presence of intraocular tumor. Prompt, subspecialty evaluation is often required.

 

Surgery for congenital or infantile cataracts is somewhat different than for adult cataracts, due to the behavior of the tissue and the baby’s special need for visual rehabilitation in a growing eye. Often a team approach is needed to optimize the baby’s chances for best vision, since congenital cataracts are often associated with other problems like amblyopia, glaucoma, retinal dystrophies, congenital anomalies of the nerve, and sometimes systemic diseases.  These children are often medical care intensive, and their families need support, too.[link]

 

 

Intraocular lens (IOL) facts

The clear cornea provides 2/3 of the focusing, or refractive, power of the eye. The lens (that is, the cataract) provides the other 1/3. So, if the cataractous lens is removed, we have to replace about 1/3 of the focusing power of the eye at the time of surgery. This is a great opportunity to fine-tune the focusing power of the eye, replacing the natural lens of the eye with one that incorporates most of your glasses prescription.

 

There is a wide variety of intraocular lens or IOL replacements available on the market today. They are made of several materials, with acrylic plastic, silicone, and collamer being the most widely used. These materials are all foldable, so that they can be placed through the same small incision through which the cataract was removed.  Like glasses, the IOL can eliminate preexisting nearsightedness (myopia) or farsightedness (hyperopia), as appropriate.

 

 

How about correcting astigmatism?

Remember that the cornea provides 2/3 of the eye’s focusing power. It is here that astigmatism lives. Astigmatism is just the cornea being more curved on its surface in one direction than in another direction at a right angle to it.

 

Think of the surface of a rubber ball cut in half. If it’s round, the curved surface is equally curved everywhere. If you stand it on edge and flatten it, it will be more curved vertically than it is curved horizontally.

There are several ways of correcting astigmatism. One is to relax the steeper curve of the cornea with “relaxing” incisions in the peripheral cornea at the time of the cataract surgery. Another is to use an IOL with extra power in one direction that is oriented within the eye so as to neutralize the astigmatism in the cornea above it.

 

This “Toric” IOL costs extra, and is not covered by any insurance. A third way to correct astigmatism is to even out the corneal curvatures after surgery using corneal refractive surgeries using a laser, such as PRK. 

Again, correcting the astigmatism together with an IOL that corrects the nearsightedness (myopia) or farsightedness (hyperopia) makes the vision without glasses clearer at distance OR at near, NOT both.

 

 

Then what about the near vision?

No matter what the material used to manufacture the IOL, a standard monofocal IOL will allow you to see clearly just at one focal point. The outcome can be calculated very accurately for seeing well at distance OR at near. There is just one focal point provided by the monofocal IOL, so your vision will be clearest at that focal point.

A common scenario is when someone wants to avoid wearing glasses as much as possible after cataract surgery. Then we use a trick that people who need bifocals use when they wear monofocal contact lenses, monovision, with one eye corrected for distance and one eye corrected for near. 

In your 40s, when the need for two focusing powers becomes apparent, you start to wear bifocals. Contact lens wearers can only wear one lens power per eye (just as the standard IOL has only one power in it, per eye). So, they wear one contact for distance in one eye, and the appropriate power for near in the fellow eye.

This sounds very confusing, but practically speaking it works out well for at least 60% of people who try it with contact lenses. The brain “chooses” the clearer image, appropriate to the distance of interest, whether reading or driving.

 

 

What if you hate it after your cataract surgery?

 

Fortunately, people are far more accepting of monovision after cataract surgery. There have been less than 5 cases where I have had to reverse it, with refractive surgery (not changing the IOL itself).

With a standard monofocal lens implant, you may need glasses after the surgery if you have much uncorrected astigmatism, and will need glasses for some near vision. With monofocal lens implants chosen so that one eye is a little nearsighted, putting on reading glasses is avoided 80-90% of the time.

 

Monovision (one eye mostly distance, one eye more near) is possibly not a good idea if you have tried it with contacts and didn’t like it.

 

You also have to accept wearing glasses at some times, most commonly night time driving, watching TV in dim light, reading in very dim light, reading very small print such as some medication bottles. Dr Smith can show you what you can expect realistically.

 

 

What about those IOLs advertised that correct distance and near focus?

There are some IOLs that are designed to provide both reading and distance vision in one eye, thus recreating the seamless, all distance vision of the 30 year old. They do this either by splitting the incoming light available into two focal points, or by flexing with the effort to read and shifting the IOL to a different position. They each have their drawbacks, including extra cost, and should be discussed with the surgeon before surgery.

 

 

 

I encourage anyone thinking about having these “premium”, high technology IOLs to check All About Vision’s website, for more information.

 

 

 

 

 

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