LEITERS

ure 4 the map's steep area has moved superiorly, al­

though the use of a normalized scale gives the wrong

impression of a central steepness. It is known that the misalignment effect on corneal

topography is not negligible. For computer-assisted videokeratography (CA VK) to fulfill many of the as­sumptions used by the reconstructive algorithms, the cornea must be correctly positioned.2 Small errors in alignment can result in an irregular or asymmetric topo­graphic reconstruction. In one commercially available instrument (£yeSys), poor fixation has been shown to

produce a pattern of pseudokeratoconus; the increase in relative steepness was statistically significant at 5 degrees of deviation. 3

The case described by Singh seems to be an unde­tected case of central keratoconus (Figure 3). Discrep­ancies as large as 6.5 diopters between keratometry and

CA VK measurements of steep meridian power were found in a study of highly irregular corneas,4 while a

systematic bias of the CA VK, i.e., measuring steeper than keratometry for the steep meridian, has been dem­

onstrated in previous studies. 5

References

COSTAS H. KARABATSAS, MD, MRCOPHTH, EBOD H. BING HOH, FRCOPHTH

Bristol, United Kingdom

1. Singh D . Effect of cataract on corneal wpography results. ] Cat­aract Refract Surg 1996; 22:1506-1508

2. Wang], Rice DA, KJyce SD. Analysis of the effects of astigmatism and misalignment on corneal surface reconstruction from pho­rokerawscopic data. Refract Corneal Surg 1991; 7:129-140

3. Hubbe RE, Foulks GN. The effect of poor fixation on computer­assisted topographic corneal analysis: pseudokeratoconus. Oph­thalmology 1994; 101: 1745-1748

4. Karabatsas CH, Cook SD, Powell K, Sparrow]M. Measurement agreement of keratome try and computer assisted videokerarogra­phy on postkeratoplasty corneas. In press, ] Refract Surg

5. Tsilimbaris MK, Vlachonikolis IG, Siganos D, et aI. Comparison of keratometric readings as obtained by ]aval ophthalmometer and corneal analysis system (EyeSys). J Refract Corneal Surg 1991; 7:368-373

Reply: I am happy that my case report has been read very carefully and commented on by experienced col­leagues from the United Kingdom. The possibility of a common problem like a cataract infringing on the accuracy of a technological wonder called corneal topography is a serious matter. It deserves the attention of every ophthal­mologist who depends on this instrument for the accuracy of his or her cataract surgery results.

The patient in the case report was examined not once but many times by me and two other colleagues to be sure that we were not dealing with a case of keratoconus. The

intraocular lens power was determined by readings from small pupil topography and keratometry, which were sim­ilar. The patient ended up as an emmetrope. Furthermore, the phenomenon that I described is not rare. It can be readily verified in any patient who has a dense white cat­aract. If the cataract is not uniformly white, high astigmatic errors will be "detected." I have no doubt that the surface image from the cornea is vitiated by reflections from struc­tures deeper than the surface of the cornea.

To reiterate my point, I present the data of two pa­tients with white cataracts whom I recently saw.

Case 1: 20-year-old man; intumescent (white) cataract Keratometry

K1: 43.75 0; K2: 44.00 0 Topography (TMS-1)

Small pupil: Medium pupil: Large pupil:

K1: 44.30 0; K2: 44.00 0 K1: 46.50 0; K2: 47.10 0 K1: 50.60 0; K2: 51.60 0

Case 2: 50-year-old man; mature (white) cataract Keratoscopy

K1: 42.50 0; K2: 42.25 0 Topography (TMS 1)

Small pupil (well centered): K1: 44.10 0; K2: 43.60 0 Small pupil (purposely misaligned to a similar degree as in the case report): K1: 42.60 0; K2: 41.90 0 Medium pupil: K1: 50.50 0; K2: 49.70 0

In the second patient, the pupil could not be fully dilated. Even so, the topography readings are quite high.

Comeal topography has been around for some time. I was surprised to find that the effect of the reflections from the deeper structures had not been reported in the litera­ture. For a long time, I have been using topography in my photorefractive keratectomy (PRK) cases, preoperatively and especially postoperatively. I, however, did not com­pletely understand the relationship between the appear­ance of the cornea and the topographic pictures. Since discovering the vitiating effect of a cataract on corneal

topography, I have lost most if not all my enthusiasm for this examination. I do not know whether other topography systems show errors similar to those of the TMS-1.

We are looking into the possibility of topographically controlled PRK systems. I therefore think it is time to take a hard look at the possible pitfalls that can afflict topogra­phy systems rather than take their accuracy for granted.­Da/jit Singh, MD

Incidence and Treatment of Wrinkled Corneal Flap Following LASIK

I read with great interest the guest editorial about laser in situ keratomileusis (LASIK).l I agree with Dr.

Giiell's experience and conclusions about the procedure. Laser in situ keratomileusis definitely has a steep and

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LETTERS

difficult learning curve. However, once the surgeon be­comes comfortable, the procedure is extremely reward­ing for the patient as well as the surgeon.

Once the procedure is learned, few serious compli­cations occur. I would like to report one complication that I encountered in 350 LASIK surgeries. All proce­dures except one of the flaps were performed by me. The one flap repositioning was done by my associate.

All patients had simultaneous bilateral LASIK. The right eye was done first, followed by the left eye. A 160 /-Lm hinged flap was made. After laser ablation, the flap was floated back on a drop of saline. A Murocell sponge was used to dry excess fluid. After about 5 min­utes, the adhesions were checked, and in some cases a bandage contact lens was placed. The bandage lens was placed to see whether it would prevent corneal wrinkles and slippage. The patients were sent home without a dressing with instructions to use a shield at bedtime. Postoperatively, the patients were seen 1 day, 1 week, and 1 and 3 months or as often as necessary.

The wrinkles were treated by reflecting the hinged flap using a Sinskey hook and laying it down on the nasal side of the globe with the stromal side facing up. The wrinkles were smoothed using a Caro iron, and the flap was floated back in its bed on a drop of saline. The flap was dried and checked for adhesions. No sutures were used. In all but two cases the corneal wrinkles were still there. No further treatment was done to remove the wrinkles except in one case. In this case, the wrinkles

radiated from one edge of the hinge. This part of the hinge was cut to relieve the tension on the flap. A ban­dage lens was placed on the eyes. The eyes were not patched. The next morning the bandage lens was re­moved. All corneas including the ones with residual wrinkles were smooth and wrinkle free. The patients made a routine recovery.

The wrinkles were seen in seven right eyes and three left eyes. Seven eyes had no gross slippage of the flap. Three eyes had gross slippage of the flap; in two of the three, the bandage lens had been placed at the time of surgery.

One of these patients complained of foreign-body sensation, pain, and blurry vision shortly after going home. Her symptoms became worse and she was seen as an emergency that night. The examination showed the patient had lost the contact lens. The flap was folded and hanging by the hinge. Fortunately, the patient did not

try to remove the flap thinking it was the lost contact lens. The flap was repositioned and the patient made a routine recovery.

The second patient was doing well on the day after surgery. However, at the time of contact lens removal the patient squeezed and rubbed her eyes causing a dis­location of the flap. Again the flap was repositioned with routine recovery.

The third patient had minimal displacement. Her main complaint was blurry vision and some discomfort. She was also treated successfully.

The following is a summary of the postoperative observation and treatment of these patients: 1 day in seven cases; 12 days in one case; 26 days in one case; 6 weeks in one case. In the last case, the wrinkles did not disappear after the first repositioning 8 days postopera­tively. This may be because the first time the flap was not ironed before repositioning. Six weeks later the flap was retreated using the Caro iron, with routine recovery. In the other patients, the ironing was done at the initial treatment.

The complication I have described is not seen very often and is not sight threatening. However, in an elec­tive procedure like refractive surgery, it can be signifi­cant. If not handled properly, it may be a source of vision distortion, requiring a far more invasive treatment. What we need is a tissue adhesive that will enhance the healing process, thus making this complication less likely. As laser technology improves, the stromal beds

will become even more smooth, increasing the chance of slippage.

My presumption is enhanced by the fact that in 349 automated lamellar keratoplasty (ALK) procedures I did not have one corneal flap wrinkle. This may be because the ALK bed is not as smooth and slippery as the LASIK bed.

Reference

]ASWANT SINGH PANNU, MD Lauderdale Lakes, Florida, USA

1. Gliell]L. Experience with laser in situ keratomileusis (guest edi­torial).] Cataract Refract Surg 1996; 22:1391

General or Topical Anesthesia?

The letter "Surgical Repair of Multiple Ruptures of Rapid and Transverse Incisions Under Topical An­

esthesia"] was in error in several points and does not reflect current thinking in the field of anesthesia. The

696 J CATARACT REFRACT SURG-VOL 23, JUNE 1997