1. Answer (d). To obtain the correction corresponding to the cycloplegic refraction, a nomogram-adjusted correction is entered into the VISX laser. The larger the myopic correction and the older the patient, the greater the reduction in the myopic power of the sphere. The 250-µm minimum is a rule of thumb only. It has not been proven and some patients may require a thicker residual bed to prevent ectasia. LASIK is not always safer than photorefractive keratectomy (PRK). In the presence of epithelial basement dystrophy, PRK may be the preferred refractive procedure.

2. Answer (b). A central thickness of 635 µm is thicker than normal. However, the endothelium may be normal. A normal cell count, cell shape, and size as measured with specular microscopy would suggest that endothelial dysfunction is not the cause of the thicker-than-normal cornea. If the surgeon felt the thick cornea was due to endothelial dysfunction, the patient would not be a candidate for LASIK surgery. The other tests would not help evaluate the corneal endothelium.

3. Answer (a). It is best to abort the laser surgery at this point, because the full laser treatment cannot fit under the incomplete flap. It would be unwise to attempt to recut a deeper flap during the same surgery. Photorefractive keratectomy (PRK) over a flap is associated with an increased risk of stromal haze.

4. Answer (d). Most microkeratomes have several microkeratome heads or spacer plates to insert to help create thinner or thicker flaps. Studies have also demonstrated that the faster the microkeratome pass, the thinner the flap that will be created. Other studies have shown that the average corneal flap is thinner in the second eye than the first eye, presumably due to the microkeratome blade getting duller after the first pass.

5. Answer (d). There are no published studies that can confirm the absolute safety of maintaining a residual stromal bed (RSB) of 250 µm. There are many published cases of ectasia in patients with an RSB of >250 µm, and cases from the early days of LASIK surgery with <250 µm of RSB that have not developed postoperative ectasia. The RSB is more accurate when calculated using the non-nomogram-adjusted refraction and intraoperative pachymetry. It is believed that several factors might influence the development of ectasia including a subclinical keratoconus, wider ablation diameters, and individual patient healing factors. Please read the following excellent review article on this subject: Binder PS. Ectasia after laser in situ keratomileusis. J Cataract Refract Surg. 2003;29:2419-2429.

6. Answer (c). The Moria microkeratomes must utilize the high-vacuum setting during the actual creation of the LASIK flap. The period of high vacuum is when the optic nerve is most vulnerable to damage, especially if the patient has underlying glaucoma. The low-vacuum setting should not cause optic nerve damage. It is utilized for maintaining control of the globe during laser ablation. The low-vacuum setting does not have any effect on the flap thickness or postoperative dry eye syndrome.

7. Answer (a). The flap thickness varies with each microkeratome head, and even from patient to patient with the same head. Studies have demonstrated that there can be significant variability in flap thickness with each cut. The stromal beds are equally smooth with the manual and automated microkeratomes. Flap complications can occur with any type of microkeratome. One of the main advantages of the manual microkeratome is the ability to vary the translation speed and thereby create thinner or thicker flaps.

8. Answer (b). Thinner corneas result in thinner flaps. Thicker corneas result in thicker flaps. This was verified when six different microkeratomes were studied to determine the depth and size of the flap that was cut. A flatter cornea results in a smaller flap for the same size ring, and a steeper cornea results in a larger flap for the same size ring.

9. Answer (a). The femtosecond laser has many advantages over the blade microkeratome. Because the laser is created using applanation rather than by drawing corneal tissue within a suction ring, it is less dependent on corneal contour. The risks of buttonhole and free-flap that might be seen with a steep cornea or flat cornea, respectively, are not a concern with the laser. The surgeon has more control over the flap diameter with the laser. Remember with the blade microkeratome flap diameter will depend on internal ring diameter and corneal contour. Peripheral neovascularization can lead to problematic bleeding when a blade is used to create a flap. This is less of a problem with the laser. The overall time to create a laser flap when you add in the application of suction is not much different than with the blade.

10. Answer (b). The Bansal-Kay nomogram adjustment is dependent on the age of the patient. It is calculated based on the spherical equivalent. The adjustment, once calculated, is subtracted from the sphere. Nomogram adjustment is not dependent on corneal contour. Always use the non-nomogram adjusted correction to calculate ablation depth

11. Answer (a). A single-piece microkeratome does not require a higher elevation of intraocular pressure (IOP) than a multiple-piece microkeratome. A single-piece microkeratome can offer the advantage of creating either a nasal or superior-hinged flap without causing a prolonged period of elevation of IOP that can result from time necessary to assemble the microkeratome on the eye. With all microkeratomes the assembly must be verified and the IOP must be checked prior to creation of the corneal flap.

12. Answer (b). When a small epithelial defect is noted after the LASIK flap has been created on the first eye, it is not necessary to abort the LASIK procedure. The flap should be replaced after the laser treatment is performed and carefully repositioned. After an adequate period of time has transpired and the flap is in position, a bandage contact lens should be placed on the eye and topical prednisolone acetate should be started.

An intraoperative epithelial defect can result in diffuse lamellar keratitis (DLK) during the early postoperative period. It is important for the surgeon to recognize this potential complication and initiate topical prednisolone acetate early. Because the presence of a bandage contact lens and an epithelial defect put the patient at risk for possible bacterial keratitis, it is necessary to concomitantly treat the patient with a broad-spectrum antibiotic also.

For the second eye, care should be taken to avoid an epithelial defect. A methylcellulose-based lidocaine jelly can be placed on the cornea prior to placement of the microkeratome, and the microkeratome should be lubricated with a glycerin-based sterile artificial tear solution while it is advancing forward. After the microkeratome has advanced forward completely, suction can be released and the microkeratome can be gently removed, allowing the flap to slide out of the microkeratome without the epithelial trauma induced by reversal of the microkeratome head.

13. Answer (b). Extreme caution is advised in communicating the proper concentration and in accurate compounding of the MMC. The two concentrations of 0.02% and 0.2 mg/mL are equivalent.

14. Answer (b). Steep corneas, particularly with keratometry readings >47.00 D, are more likely to buckle centrally during the microkeratome pass, creating a buttonhole. Buttonholes can occur in corneas with keratometry readings <47.00 D, but are less likely. Do not proceed with the laser ablation if a buttonhole is detected in the ablation zone.

15. Answer (d). The Orbscan can provide a pachymetric map of the cornea. The values should not be used in calculating ablation depth. It provides elevation data and is useful in identifying early keratoconus. The Pentacam topography system uses Scheimpflug photography.

16. Answer (d). The Zyoptix (Bausch & Lomb) system for custom LASIK is not currently approved for treatment of hyperopia, mixed astigmatism, or myopic treatment above —7.00 D. It is approved for myopia with astigmatism where the astigmatic component is not > -3.00 D and the spherical equivalent does not exceed -7.50 D.

17. Answer (a). The Technolas 217 laser utilizes an active tracking system, but does not track cyclotorsional movements. While it has a customizable optical zone size, the blend zone size cannot be customized. The system is FDA-approved for hyperopia with or without astigmatism.

18. Answer (c). Mitomycin-C (MMC) inhibits scar formation because of its effect on DNA synthesis. It is derived from Streptomyces caespitosus, a fungus, and is not an antifungal or anti-inflammatory agent.

19. Answer (c). Haze associated with photorefractive keratectomy (PRK) is more common in deeper ablations. It is less likely to occur with modern lasers, but it is unpredictable. In general, it is less common in low myopic ablations, but the incidence is probably more closely related to ablation depth than to the degree of myopia. PRK haze can occur with LASEK.

20. Answer (c). Most cases of clinically significant diffuse lamellar keratitis (DLK) have been a result of laser settings that were too powerful, resulting in interface inflammation. While pretreatment with topical steroids is important to some, it is less important than making sure the raster energy and side cut energy are properly set. Nonsteroidal agents and doxycycline have not been shown to be important components in prevention of DLK.

21. Answer (a). Although it has been suggested that IntraLase causes fewer dry eye problems postoperatively, a patient with severe dry eye should not undergo LASIK. In those patients with moderate dryness, Restasis and punctal plugs may control the condition and allow for LASIK to be performed safely. Despite the ability of an IntraLase flap to create consistently thinner flaps than a blade microkeratome, the —12.00 D myope would not be a good candidate for LASIK with either technique—the cornea is too flat and the correction needed is too great. A young healthy male has an excellent chance to have a good flap with a standard microkeratome. However, in a postmenopausal woman, the incidence of epithelial sliding with blade LASIK is much higher than with the IntraLase, and as such would be the preferred method of flap creation.

22. Answer (c). A small palpebral fissure can make it difficult to obtain proper suction. At times suction can be better acquired by not using a speculum. Multiple attempts at achieving suction may result in the conjunctiva becoming chemotic with adequate suction becoming impossible to obtain. An occasional faulty suction ring may need to be replaced. Brimonidine (e.g., Alphagan) drops may actually help obtain better suction because it can quiet the conjunctiva, but should be avoided nonetheless because of the increased risk of flap displacement postoperatively.

23. Answer (d). The IntraLase creates a lamellar flap via the process of photodisruption.

24. Answer (a). Photorefractive keratectomy (PRK) cannot be performed with an IntraLase. Stromal channels can be made with the laser for insertion of intrastromal ring segments. The laser has also been used experimentally for corneal trephination in penetrating keratoplasty and deep lamellar dissections for the deep lamellar endothelial keratoplasty (DLEK) procedure.

25. Answer (d). It is imperative that a patient refrain from contact lens use long enough for the cornea to return to its original shape. Although 1 to 2 weeks for a soft lens and 1 month for a gas-permeable contact lens is usually sufficient time for the cornea to resume its normal shape, this reversal of the contact lens effect can be quite variable. Therefore, the surgeon should wait until refractive and topographic stability can be documented before attempting refractive surgery.

26. Answer (b). It is not uncommon for the cycloplegic refraction (CR) to differ from the manifest refraction by 0.75 D in a 26-year-old myope. Although there is always a risk of ectasia in every LASIK patient, having an adequate corneal thickness and normal topography and Orbscans probably portends a low risk of ectasia despite the high myopic correction needed. Astigmatism measured by keratometry is usually slightly greater in magnitude than astigmatism measured in a manifest refraction. The 0.50 D difference in this case is within the expected range. To fully correct this patient’s myopia, approximately 9 D of refractive correction is needed. Each diopter of correction will flatten the cornea approximately 0.8 D. Therefore, this patient’s cornea will be flattened approximately 7.25 D. Her average preoperative keratometry was 41.00 D; thus her preoperative keratometry will be 33.75 D, which is too flat. Corneas with an average corneal power <35 D have a degradation of vision due to the loss of the normal prolate corneal shape, and this makes this patient a poor candidate for LASIK.

27. Answer (c). Loose epithelium after the microkeratome pass may mean that the patient has an occult corneal epithelial basement membrane dystrophy. This can lead to a number of postoperative problems, including diffuse lamellar keratitis (DLK), epithelial ingrowth, delayed epithelialization of the cornea, and irregular astigmatism secondary to an irregular epithelial surface. Although the surgeon must anticipate these problems, continuing with the planned LASIK procedure and then applying a bandage contact lens is still the best treatment option. The chance for DLK and epithelial ingrowth exists once the flap is created whether the laser treatment is applied or not. Performing photorefractive keratectomy (PRK) over a freshly cut laser flap can lead to both DLK and intense corneal haze. Amputation of the flap is excessive and not necessary. Therefore, continuing with the planned ablation under the LASIK flap is the best option in this difficult situation. The ideal scenario would be to recognize the epithelial basement membrane abnormality preoperatively and treat the patient with PRK instead of LASIK.

28. Answer (b). Blanching of conjunctival vessels is not a sign of increased intraocular pressure (IOP). The surgeon should use all of the other clues to be certain adequate suction exists prior to creating the flap with the microkeratome. Some surgeons use finger tension instead of a tonometer; however, finger tension may not be as accurate. Surgeons should listen for a hissing sound, which indicates lack of proper suction. If the machine does not indicate adequate suction is achieved, it isn’t. However, the converse is not true. Just because the machine indicates adequate suction, it may not actually exist. The suction port may be blocked by conjunctiva, causing the machine to indicate adequate suction without necessary intraocular pressure (IOP) elevation. This scenario is termed pseudosuction.

29. Answer (d). Free caps need to be recognized immediately, prior to removing the microkeratome from the surgical field, to have the best chance of locating the free cap. In the event of a free cap, the cap needs to be found and stored in a safe place until it is needed. It can be placed epithelial side down on a moist 4 × 4 gauze pad or on the conjunctiva, ideally not hydrating the stroma. If the epithelial marks are fading, they can be augmented at this time. These marks are critical to correct orientation of the cap when it is replaced on the stromal bed. Once the cap is located, remarked if necessary, and safely stored, the surgeon needs to decide whether the laser ablation can proceed. Generally, if the stromal bed is uniform, well centered on the pupil, and large enough to accommodate the intended ablation, the laser treatment can proceed. The cap is then placed back on the stromal bed, being very careful to line up the epithelial marks. If the marks were placed asymmetrically, then the cap cannot be placed upside down. The interface is gently irrigated and the cap allowed to adhere. Some surgeons will place one to four interrupted sutures to secure the cap. Most will simply place a bandage soft contact lens on the eye. Corneas with keratometry readings flatter than approximately 40 D are thought to be at greater risk of a free cap. Larger suction rings should be used in eyes with lower keratometry readings. The femtosecond laser is advantageous in patients with flat corneas to reduce the risk of free cap.

30. Answer (c). Older patients, patients whose fellow eye has had an epithelial adherence issue, those with anterior basement membrane dystrophy, and those with a history of recurrent erosions are at greater risk for epithelial loosening or defects during LASIK. The type of refractive error probably plays no role.

31. Answer (c).

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