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

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1.RGP lenses can be worn to slow down or halt the process of ectasia and they may delay the need for any surgical intervention.

2.Topical ocular antihypertensives have been used and act by relieving the biomechanical strain on the cornea.

3.Intacs or intrastromal corneal ring segments are clear micro-thin PMMA intracorneal inserts, hexagonal in cross-section. Intacs act by distending the peripheral cornea and hence flattening the central cornea, thicker segments producing a greater effect. For central ectasia, two segments can be inserted and in cases of inferior keratectasia, the irregular astigmatism can be corrected with a single Intacs segment placed at the site where corneal flattening is needed, that is, inferiorly or inferotemporally. The placement of a single Intacs segment prevents overcorrection of the myopia. The exact role of Intacs in slowing or halting the progression of ectasia is still not known. A unique characteristic of the Intacs refractive surgical procedure is its potential reversibility.

4.New bonds between adjacent collagen molecules are created by the C3-R treatment or collagen cross linking with riboflavin (Figure 3.3). This increases the stiffness of the cornea one and a half times, making it less

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Figure 3.4A

Figure 3.4B

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Figure 3.4C

Figure 3.4D

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Figure 3.4E

Figures 3.4A to E: Deep anterior lamellar keratoplasty (DALK) (Courtesy: Vladimir Pfeifer). (A) Injection of air bubble starting so that one can dissect till the Descemet’s membrane; (B) Air bubble injected; (C) Dissection started; (D) Anterior cornea removed. Only Descemt’s membrane and endothelium left behind and

(E) Donor cornea placed on the reciepent bed and sutured

Deep anterior lamellar keratoplasty (Figure 3.4) is a new technique based on adding tissue to strengthen the cornea. Here, a host bed consisting of Descemet’s membrane and endothelium is created into which a full-thickness corneal stroma and epithelial button is placed. The recovery time is faster and visual recovery quicker than a penetrating keratoplasty. The risk of endothelial rejection is not there.

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Figure 3.5A

Figure 3.5B

Figures 3.5A and B: (A) Buttonholing of the flap and

(B) Corneal scarring after buttonholing of a flap

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Flap related problems after LASIK have always been a bugbear for any refractive surgeon. Common causative factors are inadequate suction, microkeratome malfunction and corneal curvature anomalies. Buttonholing of the flap is one of the dreaded complications of LASIK (Figure 3.5A) as they are often in the visual axis and may heal with scarring (Figure 3.5B) and loss of best corrected visual acuity. Poor quality blades, inadequate IOP, keratome malfunction and steep corneas are predisposing factors. The procedure should be aborted and the flap realigned. The patient may require a deeper recut with customized ablation or a PRK/PTK/ mitomycin C with transepithelial approach.

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Figure 3.6: Free cap (Courtesy: Jairo Hoyos)

A free cap is a disastrous complication. The cap is carefully placed epithelial side down in a drop of BSS to avoid stromal hydration. Alignment marks on the flap help in identifying the side as well as in realignment. Sufficient time is given for good flap adhesion (Figure 3.6). One may secure it either with sutures or a bandage contact lens.

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Figure 3.7: Incomplete or partial flap

Partial flaps can occur due to a loss of suction mid way, any mechanical obstruction to the microkeratome or premature diskontinuation of the pass (Figure 3.7). The surgeon generally has to abort the procedure and make a new flap with a deeper cut 3-6 months later. Never attempt to manually dissect as it can lead to loss of BCVA and topographical abnormalities and necessitate procedures such as phototherapeutic keratectomy.