Ординатура / Офтальмология / Английские материалы / Jaypee Gold Standard mini Atlas Series Lasik_Aragawal, Jacob_2009

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the anterior chamber partially obscuring the pupil and the patient’s view of the fixation light (Figure 3.12A). If the bubble(s) is large enough, it may prevent pupil margin tracking by the laser and inhibit the patient’s ability to fixate. The bubbles absorb into the aqueous humor in two to three hours and treatment may be completed. Often the bubble(s) are small and the edge of the pupil is not obscured and the patient is able to fixate around the bubble. In this event then the treatment may proceed without waiting for the bubbles to absorb. The gas bubbles are otherwise innocuous and do not cause any subsequent effect to the eye.

Gas Bubbles in the Cornea

Gas bubbles are routinely formed in the LASIK interface by femtosecond laser photodisruption (“opaque bubble layer, OBL”). These interface bubbles are released when the flap is lifted and therefore they do not interfere with treatment. However, sometimes the bubbles dissect into the superficial layers of the stromal bed during propagation of the laser interface (deep OBL) (Figure 3.12B). These deep bubbles are not released when the flap is lifted. Depending on the location of the deep OBL the pupil or iris landmarks may be obscured preventing either pupil

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lift then it is reasonable to abort the procedure and replace the already lifted edges of the flap to allow for healing over approximately a one month period. The procedure may be reattempted with a blade microkeratome set to cut the flap 50 microns deeper than the original femtosecond flap interface. If the flap were to be recut with the femtosecond laser then the plasma gas bubbles may percolate through to the level of the old unlifted interface preventing passage of the laser light through to the newly programmed interface level.

Non-dissected Islands

If gas bubbles dissect through the stroma anteriorally, the bubbles will come to lie between the applanation plate and the corneal surface. The bubbles will spread ahead of the advancing propagation of the laser raster pattern and block the focused femtosecond laser light. This blocking leaves an undissected zone wherever it occurs. The interface then is not separable in this area. Forceful attempts to delaminate the corneal collagen fibers in this area can result in a tear through to the surface leaving an isolated “island” of undissected tissue similar to the central islands that may occur with blade microkeratome created flaps. This phenomenon of dissection of gas bubbles

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good vision develop photophobia in the absence of any apparent finding on examination.3 Corticosteroid drops are prescribed and symptoms improve within one week of treatment. Invariably symptoms resolve with or without treatment leaving no residual abnormality or symptoms. Its etiology is unknown and speculation has varied among keratocyte activation to laser induced iritis, scleritis or neuritis. The majority of patients feel more comfortable wearing sunglasses during the two to six weeks that it takes to resolve. The incidence of this symptom is approximately 1 percent.

Keratitis

The second complication is intrastromal inflammation localized around the edge of the flap which occurs two to seven days following flap creation. The corneal stromal tissue becomes hazy or white along the side cut and there is associated cellular infiltration in the interface and in the superficial cornea in a narrow band along the edge of the flap. There may be some associated photophobia. Presumably this inflammation results from microscopic cornea tissue damage caused by the laser photo disruption perhaps exaggerated by exogenous inflammatory factors in the tear film. Although this process may share some

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Miscellaneous

Topics

Phakonit

and

MicrophakonitAmar Agarwal

Soosan Jacob

Rahul Tiwari

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In 1983, Professor Stephen Trokel suggested the use of the excimer laser in ophthalmic surgery. Since then, millions of patients have been treated successfully, mostly in the refractive area. The exact edging capability of the excimer laser has been found useful in treating superficial corneal opacities, corneal scars, dystrophies and irregularities. This part of the excimer laser use is commonly referred to as PTK or phototherapeutic keratectomy. PTK aims to change the corneal surface: To correct irregularities of the corneal surface or to change the refraction of the cornea, to make the epithelium adhere better to the basal membrane in recurrent erosions and in some superficial corneal dystrophies. Different techniques have been used to remove the epithelium: Scraping with a knife and later a brush. We prefer to loosen the epithelium by exposure to 30% alcohol for 20 seconds in a ring. After the treatment the epithelium is rolled back and covered by a silicon lens. We have found that this procedure reduces the postoperative pain the patient has to endure. In refractive cases such as anisometropia after previous ocular surgery, LASIK is the preferred technique. Removing the epithelium gives a better situation to accurately measure the degree of the irregularity of the corneal surface, as the epithelium always conceals the minor irregularities.