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By: Sam Melki
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There comes a time in every laser eye surgical procedure when leaving

the battlefield is the best of two (or more) evils. When is it best to

reposition the flap, abandon the procedure and possibly attempt the LASIK

procedure at a later time…?

Obtaining adequate suction to certain globes is occasionally an elusive

target. This includes small hyperopic eyes, flat or small diameter

corneas, narrow palpebral fissures… If the level of myopia permits, one

has to remember that PRK is always an available option and patients

must be made aware of this alternative and be consented for it prior to

the procedure. A surgeon might be tempted to extend an incomplete flap

with a crescent blade or similar instrument . This might lead to an

uneven bed and scarring. The closer the hinge to the visual axis the

riskier this maneuver will be. If the bed is large enough (not more

than 0.5 mm of unexposed stroma at the hinge) laser treatment may be

applied (with adequate protection to the underside of the flap).

A thin flap with an underlying shiny bed probably indicated an uncut

underlying Bowman’s layer. It is not clear if performing laser in this

situation has similar or higher risk of haze formation as PRK. Until

more is known about this issue, it is probably safest to reposition the

flap and abort the procedure especially in high levels of correction.

An irregular flap indicates an irregular stromal bed and is best

allowed to heal back in position rather than risk inducing irregular

astigmatism.

If a buttonhole occurs, immediate laser ablation of a central

epithelial island by scraping or by the laser was reported to lead to

uneven ablation and loss of BCVA.

The Free Cap

    A free cap results from unintended complete

dissection of the corneal flap by the microkeratome head. If the cap is

trapped in the keratome head, it should be gently retrieved, stretched

and kept in a dessication chamber if the diameter of the exposed stroma

allows laser ablation.  A small cap (i.e smaller than the optical

zone) should prompt the surgeon to replace it in position and avoid the

laser ablation. If the cap cannot be recovered, the epithelium will

grow centrally as after other “superficial” keratectomy procedures and

may result in a significant hyperopic shift.

 Intraoperative factors leading to a free cap are the same as

those leading to a thin or perforated flap, a poor blade to cornea

coupling. This is especially true for flatter corneas which are more

prone to a smaller cap. Other maneuvers such as malpositioning and/or

misadjusting of the flap thickness foot-plate during assembly of

certain microkeratomes can lead to a free cap.

In certain instances, the microkeratome can jam preventing head

reversal. This might prompt the surgeon to release the suction thus

lifting the instrument with an incarcerated flap resulting in a free

cap. 

Placing corneal marks with gentian violet is time well spent prior to

cutting a corneal flap. When recovered, a cap can be repositioned using

the preplaced marks to allow proper orientation. A bandage contact lens

is usually helpful to tamponade the cap and prevent slippage upon lid

contact. Suturing is rarely necessary.

 If the cap is lost, the corneal epithelium is allowed to heal as

in PRK with a more profound central applanation effect. Laser treatment

is deferred until refractive stability is achieved.

<b>Author Bio:</b><br>

Adapted from: “101 Pearls in Refractive, Cataract and Corneal Surgery”

Samir Melki MD PhD and Dimitri T. Azar MD editors, Slack inc.

www.slackinc.com Dr. Melki is a experienced <a href="http://bostonlaser.com/lasik-boston-vision-correction-lasik-affordable.php">Boston affordable LASIK surgeon, Laser Eye Surgery</a>,

Vision Correction and <a href="http://bostonlaser.com/lasik-boston-cosmetic-procedures.php">Cosmetic Surgery</a>

http://bostonlaser.com/

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