Enhancements (Retreatments)

CHAPTER 10

The Role of Enhancements

A retreatment or enhancement may be needed with all refractive surgical procedures. The fact that one, or both eyes, may need retreatment in no way implies a failure. It is the surgeon’s responsibility, however, to inform the patient about this possibility preoperatively. It is wise in telling the patient to use phrases such as “sometimes the surgery is done in two or more stages”, may need “enhancement” or “touchup”, etc. As a matter of fact, the need for enhancements may be interpreted as a prudent and responsible way to manage a refractive error, particularly in cases of high ametropias.

The end result of the first operation may also be selected to meet the patient’s visual goal and needs. Some patients prefer to see more sharply at far and others at near. Of course, everyone desires to see very well far and near but in some cases, this may not be possible.

Causes of Residual Ametropias

Unless the residual ametropia was done on purpose, such as ending up with small myopia to allow reading without spectacles, it is important to determine its cause.

The main causes are: 1) postoperative unstable refraction with changes in the spherical and cylindrical correction; 2) a poorly calculated or misdiagnosed ametropia preoperatively; 3) inexact calibration of the different parameters in the excimer laser computer; 4) a slightly humid stromal bed at the time of ablation with the excimer laser; 5) insufficient depth of the cuts with diamond knife or the use of non-optimal optical zone in cases operated with RK or astigmatic keratotomy; and 6) each patient has his or her own biological variables and responses independent of the refractive procedure performed.

ENHANCEMENTS WITH LASIK

When a patient has undergone a LASIK primary procedure and there is residual ametropia that the surgeon wishes to retreat or enhance, it is important to delay the second LASIK procedure until 2-3 months after the primary operation to allow for accurate corneal stability.

Preoperative Evaluation Before Enhancement

The post-op refraction and corneal topography must be stable before proceeding with the LASIK enhancement (Figs. 172, 173). It is also fundamental that adequate corneal thickness remains to allow performing another LASIK procedure. 250 microns residual tissue below the LASIK flap is essential, after either the primary or the enhancement procedure; or a total of 410 microns, minimal.

In some cases, corneal topography (Chapter 3) may help us in determining if the patient’s remaining ametropia is due to a significant amount of residual ametropia or to an anomaly or deficiency in the primary operation as in the case of a decentration.

Indications for LASIK Enhancements

The main indications are:

1) Residual myopia or hyperopia larger than 1

D.

2)Residual astigmatism larger than 1 D.

3)Visual acuity less than 20/40.

If the primary LASIK procedure is unsuccessful because of a decentration, or a patient unhappy with glare or with the correction obtained, the remaining options are limited.

SurgicalTechnique for LASIK Enhancements

This depends on each surgeon’s preferences. The standard procedure is to lift the inferior or temporal border of the flap with a fine spatula and BSS irrigation. This is done very delicately to prevent migration of epithelial cells under the flap toward the center of the stromal bed (Figs. 172, 69, 70, 71, 72).

The stromal bed is dried with a sponge and additional pulses with the excimer are applied to obtain the ablation previously calculated, that will accomplish

Figure 172: Enhancement with LASIK - Step 1

The inferior or the temporal border of the previously performed LASIK corneal flap (F) is lifted (yellow arrow) using a fine spatula (S), accompanied by irrigation with BSS.

Hyperopic LASIK After RK in Overcorrections (click over videoclip)

Figure 173: Enhancement with LASIK -

Step 2

After lifting the flap (F), the stromal bed is irrigated with BSS to eliminate any epithelial cells that may have moved in when lifting the flap. The stromal bed is then dried with a sponge. After adequate centration and calibration of the laser, the excimer laser beam

(L) is applied to obtain the desired ablation.

the correction the patient desires.

During and after the ablation it is important to maintain the corneal interface clean by means of a flat cannula with BSS irrigation (Fig. 173). With large undercorrections, the flap may be lifted earlier than 2-3 months and the stroma ablated. In most cases after 4 months, re-cutting the flap is preferable because a smoother surface is created and the risk of epithelial ingrowth is less (Figs. 69 - 72).

LASIK Enhancement Following an

Unsatisfactory RK

Undercorrections following radial keratotomy (RK) may be due in some cases to insufficient depth of the incisions, or when incisions were made too short to correct the myopia. Hypercorrections, on the other hand, may be related to very deep incisions or more incisions than necessary, particularly in cases of low myopia.

The modern approach to these cases is to perform either a myopic LASIK or hyperopic LASIK as shown in Fig. 174 in which a standard LASIK flap and stromal ablation with excimer is done.

Figure 174: Enhancement with LASIK Following Unsatisfactory RK

The LASIK corneal flap (F) is elevated on its hinge. The scars from the previous RK incision are clearly seen both in the flap as well as the stromal bed.

Risks Following LASIK Enhancements

As in all operations, there may be risks. The following need to be taken into consideration:

1)Overcorrections

2)Epithelial ingrowth (Figs. 69-72)

3)Flap striae

4)Infection

Postoperative Care

In the specific case of LASIK, we must always be observant for a possible epithelial ingrowth. And, of course, determine the refractive outcome.

ENHANCEMENTS WITH PRK

The technique for corneal epithelial debridement (Fig. 75) in patients undergoing a second operation with PRK has given rise to some controversies. Some surgeons prefer to perform epithelial debridement directly with the excimer laser to prevent somewhat the reappearance of haze (Fig. 77). Whether this really works remains controversial. Other surgeons prefer to perform the conventional mechanical epithelial debridement with a spatula (Fig. 75) and proceed with the stromal ablation with excimer (Fig. 76).

It is highly recommended to wait from 3-6 months post PRK before doing an enhancement with the excimer laser. This will allow you to perform the PRK enhancement on a stable cornea.

ENHANCEMENTSWITH INTACS (ISCRS)

Daniel Durrie, M.D., who has extensive experience with INTACS, emphasizes that if a myopic or hyperopic enhancement after LASIK is indicated, and if the cornea’s thickness remaining is too thin to perform a second LASIK, INTACS can be implanted to treat low, residual myopia or hyperopia. This is another important, new and safe procedure highly useful for enhancements.

Patient Selection

Whenever an enhancement with INTACS is contemplated following LASIK or PRK, the selection of patients is the same as if a primary operation with INTACS were to be done, as follows: myopia between 1 D and 3 D and astigmatism of less than 0.75, maximum 1 D.

Surgical Procedure for Enhancements with INTACS

The surgical technique for residual myopia with INTACS following LASIK or PRK is the same as if the primary INTACS operation were being performed (Figs. 83-86).

Enhancements Following an Insufficient

INTACS Operation

If a patient previously had an INTACS operation and the myopic correction remains insufficient and the patient is unhappy, the following procedure is advisable:

1)Remove the INTACS segments and replace them either by: a) thicker ring segments to correct more myopia, or b) thinner ring segments to correct less myopia.

The INTACS segments are available in three thicknesses: 0.25 mm (corrects -1 D to -1.75 D); 0.3 mm (corrects from -1.75 D to 2.25 D); 0.35 mm, (corrects from -2.25 D to 3.00 D).

Of course, if the patient, or the surgeon, decide not to use INTACS for enhancements, the following options remain:

2)Remove the INTACS segments and perform another refractive procedure such as LASIK or PRK. In order to do LASIK or PRK, the INTACS first need to be removed.

3)Remove the INTACS segments, perform no other refractive procedure, and leave the patient with the preoperative refractive error, if he/she so prefers.

Enhancements Following Incisional

Keratotomy

Undercorrections

Buzard emphasizes that the three possible causes of an undercorrection with RK are: 1) a poorly planned operation; 2) shallow incisions; 3) a patient who under responds.

Errors in the preoperative plan can be easily checked. Shallow incisions are observed on slit lamp evaluation as incisions which do not appear to extend completely through the cornea on a thin slit beam directly adjacent to the clear central zone.

Patients who respond poorly to appropriately planned incisional refractive surgery are relatively rare and seem to be more common in the younger age group. Pregnant women have a remarkable ability to heal refractive incisions. Impending or coexisting pregnancy should be a contraindication to incisional refractive surgery.

Figure 176: Enhancement for Undercorrected

RK

The 4 (four) incisions from a previous RK are opened with a blunt hook (H) and the diamond knife, set to the depth of the primary operation, is inserted into the incision and moved centripetally and centrifugally in the incision until no resistance is felt. The procedure can be repeated several times with increasing effect, if necessary. Watch for any sign of perforation: the appearance of fluid in the incision.

Shallow corneal incisions are the most common cause of undercorrections and are easily corrected either in the operating room or at the slit lamp with Buzard’s procedure (Fig. 176). Briefly, the incision is opened with a blunt hook and the diamond knife, set to the depth of the primary operation, is inserted into the incision and moved both centripetally and centrifugally in the incision until no resistance is felt. The knife is “bumped” against the paracentral end of the incision to eliminate any beveling of the incision.

The incisions are re-examined and if an undercorrection persists and shallow incisions are still present, the procedure can be repeated with a slight (0.02 to 0.03) extension of the diamond knife. If care is taken to remain within the incision(s), the procedure can be repeated several times with increasing effect. This procedure can be performed even several years after the primary procedure with good results and no corneal instability. Beware of perforation: watch for and stop if there is any appearance of fluid in the incision.