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Myopia (Nearsightedness)

Near­sight­ed­ness, or myopia, is the most com­mon refrac­tive error of the eye, and it has become more preva­lent in recent years.

In fact, a recent study by the Nation­al Eye Insti­tute (NEI) shows the preva­lence of myopia grew from 25 per­cent of the U.S. pop­u­la­tion (ages 12 to 54) in 1971–1972 to a whop­ping 41.6 per­cent in 1999–2004.

Though the exact cause for this increase in near­sight­ed­ness among Amer­i­cans is unknown, many eye doc­tors feel it has some­thing to do with eye fatigue from com­put­er use and oth­er extend­ed near vision tasks, cou­pled with a genet­ic pre­dis­po­si­tion for myopia.

Myopia Symptoms And Signs

If you are near­sight­ed, you typ­i­cal­ly will have dif­fi­cul­ty read­ing road signs and see­ing dis­tant objects clear­ly, but will be able to see well for close-up tasks such as read­ing and com­put­er use.

Oth­er signs and symp­toms of myopia include squint­ing, eye strain and headaches. Feel­ing fatigued when dri­ving or play­ing sports also can be a symp­tom of uncor­rect­ed near­sight­ed­ness.

If you expe­ri­ence these signs or symp­toms while wear­ing your glass­es or con­tact lens­es, sched­ule a com­pre­hen­sive eye exam­i­na­tion with your optometrist or oph­thal­mol­o­gist to see if you need a stronger pre­scrip­tion.

What Causes Myopia?

Myopia occurs when the eye­ball is too long, rel­a­tive to the focus­ing pow­er of the cornea and lens of the eye. This caus­es light rays to focus at a point in front of the reti­na, rather than direct­ly on its sur­face.

Near­sight­ed­ness also can be caused by the cornea and/or lens being too curved for the length of the eye­ball. In some cas­es, myopia is due to a com­bi­na­tion of these fac­tors.

Myopia typ­i­cal­ly begins in child­hood and you may have a high­er risk if your par­ents are near­sight­ed. In most cas­es, near­sight­ed­ness sta­bi­lizes in ear­ly adult­hood but some­times it con­tin­ues to progress with age.

Myopia Treatment

Near­sight­ed­ness can be cor­rect­ed with glass­es, con­tact lens­es or refrac­tive surgery. Depend­ing on the degree of your myopia, you may need to wear your glass­es or con­tact lens­es all the time or only when you need very clear dis­tance vision, like when dri­ving, see­ing a chalk­board or watch­ing a movie.

If you’re near­sight­ed, the first num­ber (“sphere”) on your eye­glass­es pre­scrip­tion or con­tact lens pre­scrip­tion will be pre­ced­ed by a minus sign (–). The high­er the num­ber, the more near­sight­ed you are.

Refrac­tive surgery can reduce or even elim­i­nate your need for glass­es or con­tacts. The most com­mon pro­ce­dures are per­formed with an excimer laser.

In PRK the laser removes a lay­er of corneal tis­sue, which flat­tens the cornea and allows light rays to focus more accu­rate­ly on the reti­na.
In LASIK — the most com­mon refrac­tive pro­ce­dure — a thin flap is cre­at­ed on the sur­face of the cornea, a laser removes some corneal tis­sue, and then the flap is returned to its orig­i­nal posi­tion.

Then there’s ortho­ker­a­tol­ogy, a non-sur­gi­cal pro­ce­dure where you wear spe­cial rigid gas per­me­able (RGP or GP) con­tact lens­es at night that reshape your cornea while you sleep. When you remove the lens­es in the morn­ing, your cornea tem­porar­i­ly retains the new shape, so you can see clear­ly dur­ing the day with­out glass­es or con­tact lens­es.

Ortho­ker­a­tol­ogy and a relat­ed GP con­tact lens pro­ce­dure called corneal refrac­tive ther­a­py (CRT) have been proven effec­tive at tem­porar­i­ly cor­rect­ing mild to mod­er­ate amounts of myopia. Both pro­ce­dures are good alter­na­tives to surgery for indi­vid­u­als who are too young for LASIK or are not good can­di­dates for refrac­tive surgery for oth­er rea­sons.

Implantable lens­es known as pha­kic IOLs are anoth­er sur­gi­cal option for cor­rect­ing near­sight­ed­ness, par­tic­u­lar­ly for indi­vid­u­als with high amounts of myopia or thin­ner-than-nor­mal corneas that could increase their risk of com­pli­ca­tions from LASIK or oth­er laser vision cor­rec­tion pro­ce­dures.

Pha­kic IOLs work like con­tact lens­es, except they are sur­gi­cal­ly placed with­in the eye and typ­i­cal­ly are per­ma­nent, which means no main­te­nance is need­ed. Unlike IOLs used in cataract surgery, pha­kic IOLs do not replace the eye’s nat­ur­al lens, which is left intact.

Controlling Myopia

With more and more peo­ple get­ting near­sight­ed these days, there is a lot of inter­est in find­ing ways to con­trol the pro­gres­sion of myopia in child­hood.

A num­ber of dif­fer­ent tech­niques have been tried — includ­ing fit­ting chil­dren with bifo­cals, pro­gres­sive lens­es and gas per­me­able con­tact lens­es — with mixed results.

Recent­ly, researchers in New Zealand have report­ed encour­ag­ing out­comes from spe­cial­ly designed “dual focus” soft con­tact lens­es for myopia con­trol in near­sight­ed chil­dren. The exper­i­men­tal lens­es have sig­nif­i­cant­ly less pow­er in the periph­ery of the lens com­pared to the cen­ter, and it is thought that this “periph­er­al defo­cus” may reduce the ten­den­cy for greater length­en­ing of the eye that leads to pro­gres­sive myopia.

In a study pub­lished in 2011, the researchers found that in 70 per­cent of near­sight­ed chil­dren (ages 11 to 14) who wore the exper­i­men­tal lens­es in one eye and a stan­dard soft con­tact lens in the oth­er, myopia pro­gres­sion was reduced by 30 per­cent or more in the eye wear­ing the dual focus con­tact lens.

Though dual focus con­tact lens­es for myopia con­trol are not yet avail­able in the Unit­ed States, research is ongo­ing to eval­u­ate the effec­tive­ness of the lens­es on a larg­er pop­u­la­tion of chil­dren.

Degenerative Myopia

In most cas­es, near­sight­ed­ness is sim­ply a minor incon­ve­nience and pos­es lit­tle or no risk to the health of the eye. But some­times myopia can be so pro­gres­sive and severe it is con­sid­ered a degen­er­a­tive con­di­tion.

Degen­er­a­tive myopia (also called malig­nant or patho­log­i­cal myopia) is a rel­a­tive­ly rare con­di­tion that is believed to be hered­i­tary and usu­al­ly begins in ear­ly child­hood. About 2 per­cent of Amer­i­cans are afflict­ed, and degen­er­a­tive myopia is a lead­ing cause of legal blind­ness.

In malig­nant myopia, the elon­ga­tion of the eye­ball can occur rapid­ly, lead­ing to a quick and severe pro­gres­sion of myopia and loss of vision. Peo­ple with the con­di­tion have a sig­nif­i­cant­ly increased risk of reti­nal detach­ment and oth­er degen­er­a­tive changes in the back of the eye, includ­ing bleed­ing in the eye from abnor­mal blood ves­sel growth (neo­vas­cu­lar­iza­tion).

Degen­er­a­tive myopia also may increase the risk of cataracts.

Sur­gi­cal treat­ment for com­pli­ca­tions of degen­er­a­tive myopia includes a com­bi­na­tion drug and laser pro­ce­dure called pho­to­dy­nam­ic ther­a­py that also is used for the treat­ment of mac­u­lar degen­er­a­tion.

Also, a recent pilot study found that an oral med­i­cine called 7-methylx­an­thine (7-mx) was effec­tive in slow­ing the elon­ga­tion of the eye in near­sight­ed chil­dren ages 8 to 13. Stud­ies of this type might even­tu­al­ly lead to an effec­tive med­ical treat­ment for degen­er­a­tive myopia.

SOURCE

July 15th, 2017|Comments Off on Myopia (Nearsightedness)

About the Author:

Born in Connecticut and raised in Upstate New York , Dr. Stetson graduated Cum Laude from Colgate University in New York, and then earned an MD degree with honors at the University of Vermont College of Medicine. He distinguished himself again in residency at the Albany Medical Center, where he obtained the highest percentile in the Ophthalmology Knowledge Assessment Examinations. Dr. Stetson has performed more than 50,000 refractive surgeries and has been on staff at Diamond Vision since 2004, before becoming Medical Director in 2006.

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