Contact Lenses

Contact Lenses is 2% of the COA exam. The assistant takes the lens history, teaches insertion, removal, and care, checks lenses against the order, and recognizes the complications that cannot wait.

Lens families — soft (hydrogel and silicone hydrogel: comfort, easy adaptation) vs rigid gas-permeable (crisper optics, corrects corneal astigmatism through the tear lens, masks irregular corneas). Torics correct astigmatism; multifocals address presbyopia.

Wearing schedule and replacement — daily wear means the lens comes out every night; extended wear means it is approved for overnight use. Soft lens replacement runs from daily disposable to every two weeks or monthly. Daily disposables carry the lowest infection risk: a fresh sterile lens each day, with no case and no solutions.

Oxygen — with the eyes open, the cornea takes most of its oxygen from the air. A lens material's oxygen permeability is its Dk. A cornea kept short of oxygen over a long period grows new blood vessels into the clear cornea, a finding to document and flag for the physician.

What the package says — base curve (BC), diameter (DIA), and power, plus cylinder and axis for torics and an add for multifocals. Check every package against the prescription before it is dispensed.

Fit vocabulary — base curve (larger radius number = flatter = looser fit), diameter (larger = tighter), and power (converted from the spectacle Rx for vertex distance above ±4.00 D).

Not a glasses prescription — a contact lens prescription names the lens itself as well as its power, and the power often differs from the glasses because the lens sits on the eye.

Before fluorescein or applanation — soft lenses come out. Standard fluorescein stains a soft lens, and applanation is done on the bare cornea.

Start clean — wash hands with soap, rinse, and dry them with a lint-free towel. Work over a clean surface with the sink drain plugged, and handle the same eye first every time so the lenses never get swapped.

Check the lens — a soft lens the right way out is a smooth bowl with its edges curving inward. An inside-out lens flares outward at the rim. Some lenses carry markings that read correctly only when the lens is the right way out.

Insertion (soft lens) — balance the lens on the dry tip of the index finger. With the middle finger of the same hand pull the lower lid down; with the other hand hold the upper lid at the lashes. Look straight ahead or up, set the lens on the eye, release the lids slowly, and blink gently.

Removal (soft lens) — look up, pull the lower lid down, slide the lens down onto the white of the eye, and pinch it off gently with the pads of the thumb and index finger, never the nails.

Removal (rigid lens) — with a hand cupped below the eye, open the eyes wide, pull the outer corner of the lids toward the ear, and blink; the lens pops out into the hand. A small suction remover also works, but it is placed only on the lens, never on a bare eye.

The lost lens — a lens that seems to vanish has usually slid under the upper lid. It cannot get behind the eye, because the conjunctiva forms a closed pocket.

Care rules that prevent disasters — fresh disinfecting solution every night, never top off, never tap water (Acanthamoeba), no sleeping in lenses unless the physician has prescribed overnight wear, no swimming or showering in them, and replace cases quarterly.

Multipurpose solution — rub and rinse the lens with fresh solution as the product directs, then store it in fresh solution in a clean case.

Hydrogen peroxide systems — peroxide disinfects powerfully, then must be neutralized in the special case that comes with it, by a disc built into the case or a tablet, typically over six hours or more. Peroxide that has not been neutralized burns the eye, so peroxide never goes into an ordinary lens case.

The case — rinse it with solution, never water, and let it air-dry upside down with the caps off. Replace it at least every three months.

Never — tap water, well water, lake or pool water, homemade saline, or saliva on a lens or in a case. Water carries Acanthamoeba.

Sleeping in lenses — raises the risk of microbial keratitis several-fold, even in lenses approved for overnight wear.

Red flags — pain, redness, light sensitivity, or discharge in a lens wearer is a keratitis until proven otherwise: lenses out, same-day exam, bring the lenses and case for culture.

Do not mask the sign — redness-relief drops hide a red eye without treating its cause. A wearer with a red eye needs the lens out and an exam, not whitening drops.

The lens history — lens type, wearing schedule, overnight wear, care system, and replacement schedule each change the infection risk.

Be ready to compare soft and rigid lenses, explain how a rigid lens corrects corneal astigmatism, read a lens package, relate base curve and diameter to fit, describe insertion and removal, teach a care system, explain why tap water and sleeping in lenses are dangerous, and recognize the complications that need a same-day visit.