Ординатура / Офтальмология / Английские материалы / Jaypee Gold Standard mini Atlas Series Lasik_Aragawal, Jacob_2009
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BASICS AND PREOPERATIVE ASSESSMENT / 47
collagenopathies, rheumatoid arthritis, systemic lupus erythematosous, dermatomyositis, psoriasis, Behçet’s disease, Crohn’s disease, histocytosis or multiple sclerosis). Most autoimmune diseases are listed in the US Food and Drug Administration (FDA) as contraindications for LASIK due to concerns about potentially damaging effect of wound healing. The American Academy of Ophthalmology (AAO), lists in its guidelines relative and absolute contraindications to laser assisted in situ keratomileusis (LASIK) and considers connective tissue or autoimmune diseases and systemic immunosuppression as relative contraindications and only uncontrolled diseases and uncontrolled ocular allergy as absolute contraindications.
Some diseases, like Ehlers-Danlos syndrome (cutis laxa with laxity of joints) still remain absolute contraindications for corneal refractive procedures. While the molecular basis of this syndrome is heterogeneous, there are three fundamental mechanisms of disease known to produce Ehlers-Danlos syndrome: Deficiency of collagen processing enzymes, dominant-negative effects of mutant collagen α-chains, and haploinsufficiency. These mechanisms compromise the strength of the connective tissue complex, and often the collagen fibril itself. This
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abnormal collagen strength contraindicates laser refractive surgery, as the risk of post-surgical ectasia is presumed higher and the risk of devastating intra operative complication like globe rupture is possible. Apart from angioid streaks, strabismus or retinal detachment EhlersDanlos patients may present limbus to limbus thin corneas, keratoglobus, keratoconus, cornea plana, and corneal opacities: The cornea is very fragile (fragilitas oculi in Ehlers-Danlos syndrome type VI, or kyphoscoliosis) and the risk of keloid formation is extremely high. Indeed, abnormal bleeding may cause extreme difficulty with any surgical procedure.
Nevertheless, every case has to be considered and evaluated specifically: Careful preoperative evaluation holds the key to identifying appropriate candidates. When cornea is intact, LASIK is the safest refractive technique in risky patients. Avoid PRK and other superficial techniques that suppose a higher degree of inflammation.
There are special considerations for autoimmune disorders or collagen disease patients who undergo cataract, clear lens exchange or refractive surgery (Figure 1.15).
1. Write a proper informed consent.
BASICS AND PREOPERATIVE ASSESSMENT / 49
2.Consider LASIK as your first refractive option: PRK creates a large epithelial defect that may predispose the cornea to ulceration.
3.Profit from periods of calm of the disease, especially in treatment pauses or when the disease is stable.
4.Make sure that biologic constants are stable when you perform surgery.
5.Carefully check for infectious concomitant diseases.
6.Give antiherpetic oral prophylaxis prior to surgery and a few days after surgery (ocular herpes can be devastating in such cases).
7.Corneal melting tends to occur mainly in elderly autoimmune patients, and almost exclusively in those with extraarticular disease. LASIK is relatively safe in rheumatoid arthritis patients that only manifest in the joints. Modern immune response modulators such as etanercept (a class of medications called tumor necrosis factor –TNF-inhibitors) may help to stabilize rheumatoid arthritis, thus making viable the practice of a refractive procedure. Etanercept is used alone or in combination with other medications to reduce the pain and swelling associated with rheumatoid arthritis, juvenile rheumatoid arthritis, and psoriatic arthritis.
2
LASIK,Wavefront
GuidedLASIKand
Phakonit
Femtosecond
Lasersand
MicrophakonitAmar Agarwal, Soosan Jacob
Dhivya Ashok Kumar
Gaurav Prakash
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A B
C D
Figures 2.1A to D: LASEK (Courtesy: Massimo Camellin)
(A)Shows Shahinian well containing 20% alcohol solution in distilled water for 20 seconds before applying the epi-keratome;
(B)Shows the Nordwood instrument applied slightly de-centered nasally to avoid creating the hinge in the photoablation area where it can be damaged by the laser; (C) Shows that the epithelial flap is rolled back after moistening the stromal surface with BSS and; (D) Shows that the applanator is used to squeeze all fluid from under the flap, helping to fix the flap position
Due to its main characteristics, the LASEK technique (Figure 2.1) has shown very few complications some of which are also common in PRK. For this reason, it is
LWGLF LASERS/ 53
important to emphasize that some LASEK surgeries may became PRK if the flap is lost during the first few postoperative hours. If the surgeon is not very skilled, he will believe that he has accomplished a LASEK and will be unable to understand why his results are like those of a PRK.
Epithelium management is the first step towards a good LASEK but, despite its relative feasibility, requires some tricks that must be taken into account in order to avoid postoperative pain and flap loss during the early hours. Thus, use of a toothed trephine means that every epithelium can be pre-cut, independently of its thickness; however, when the instrument is rotated, be careful not to rotate the globe, otherwise the effect is to create a circular series of notches that do not lead to the same result of increasing the alcohol flow under the epithelium itself. It is true, however, that in some cases the solution can nevertheless pass the epithelium barrier but the problem is to allow its flow, as much as possible, to detach even stubbornly attached epithelium. When one starts to rotate the trephine aid with a fixation ring it is important to pay attention and make sure that the instrument moves at least 10° in comparison to the globe. Do not exceed
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this safety value, as it risks the creation of a hinge that is too small, thereby increasing the risk of flap loss.
The well contains an alcohol solution and leakage onto the conjunctiva must be avoided. An adapted well has been designed with a double edge that works better both in keeping the eye firm and at the same time containing the solution. When the correct amount of time (20 sec) has elapsed, do not take the well away before having dried the contents and rinsed it with diclofenac. Having followed this rule, make sure that no contamination of the conjunctiva has occurred. Unfortunately, despite best efforts, some patients move their eye during alcohol exposure and there may be some leakage onto the conjunctiva, which will immediately feel painful. At this point, abundantly rinse with diclofenac and, if exposure has been too short, apply alcohol into the well again.
Starting detachment of the flap edge is the best way to begin flap making and also serves to understand how well the flap is attached. If strong resistance is perceived, stop and re-use alcohol for 5-10 seconds more. This maneuver increases the alcohol flow because now there will be a real groove on the periphery of the flap and 5-10 seconds is enough to enormously increase the detachment. The more adherent the epithelium, the higher the pressure
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on the spatula must be, which must be used vertically at its shortest side. Sometimes, tears may occur but the worst complication is a hinge tear because of the drawback of making it difficult to recognize the right side of the flap when it has been rolled back. It is always better to manage the flap with two rounded spatulas; and in this unfortunate case the surgery can be saved by operating calmly.
Having lost the hinge, one must try to increase flap stability and this can be achieved by drying the flap for two minutes at the end of the procedure before fitting the contact lens.
In these cases, it is a good idea to brush the surface with MMC 0.01% before rolling the flap back.It is usually more difficult to detach epithelium at the periphery, particularly in the upper area close to the hinge. Wide flaps are therefore more difficult to manage (i.e. hyperopic treatments). When the corneal diameter is small we must separate the epithelium close to the limbus, where it is strongly attached.
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Figure 2.2: Epi-LASIK (Courtesy: Ioannis Pallikaris and
Massimo Camellin)
Epipolis laser in situ keratomileusis (Epi-LASIK) refers to an alternative surgical approach for epithelial separation by mechanical means. With this technique, the epithelial separation is performed using an instrument (Figure 2.2) that was initially designed at the University of Crete and operates in a manner similar to that of a microkeratome. The epithelial flap after stromal ablation is placed on the corneal surface reducing patient discomfort postoperatively and modulating the wound healing response of the cornea.
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