1. Three-Year Follow-up after LASIK in Eye with Extremely Thin Corneal Bed
Hidemasa Torii, MD, Kazuno Negishi, MD, Murat Dogru, MD, Takefumi Yamaguchi, MD, Nanae Kawaguchi, MD,
Megumi Saiki, CO, and Kazuo Tsubota, MD
Authors have no financial interest
Department of Ophthalmology
Keio University School of Medicine, Tokyo, Japan
ASCRS Symposium & Congress, San Francisco, 2009

2. Purpose
To report the three-year observation of a patient who underwent laser in situ keratomileusis (LASIK) with an extremely thin residual stromal bed (below 100 μm).
Case report
Case: 35-year-old male
Chief complaint: Visual disturbance in the right eye
Onset and course: He was referred to our clinic for a second opinion. He had undergone bilateral LASIK using a 15-KHz IntraLase femtosecond laser microkeratome (Advanced Medical Optics, Irvine, CA) 1 week previously.

3. Onset and course (continued)
The patient stated that his preoperative corrected vision was 20/20 or above in each eye, and he had blurry vision in his right eye immediately after LASIK, while the uncorrected visual acuity (VA) in his left eye increased. Our repeated requests to retrieve the patient’s surgical data from the referral clinic were unsuccessful.
The surgeon who performed LASIK prescribed 0.1% betamethasone sodium phosphate and 0.1% sodium hyaluronate eye drops. We continued the medication.
Past history: unremarkable
Family history: unremarkable

4. 1st visit: 7 days after LASIK
BCVA (best corrected visual acuity) Right eye 20/160 ( X100) Left eye 20/12.5 Intraocular pressure 10 mmHg both eyes Biomicroscopic examination There was a severe diffuse inflammatory reaction at the flap interface in his right eye and no abnormal findings in the left eye. The right eye was diagnosed with severe DLK. The anterior chamber, lens, vitreous, and fundus appeared normal in both eyes. The corneal endothelial cell density Right eye 3,144 cells/mm2 Left eye 3,067 cells/mm2

5. 1st visit: 7 days after LASIK (continued)
Pentacam examination (Oculus Optikgerate GmbH, Wetzlar, Germany)
Pentacam measurements showed a total central corneal thickness of 535 μm in the right eye and 537 μm in the left eye, and there was a diffuse high pixel intensity layer (arrow) in the deep stroma of the right eye which we assumed to be the flap interface. The distance of the high pixel intensity layer from the central corneal surface was 470 μm as measured by Pentacam . There were no remarkable findings in the left eye.
right eye

6. 14 months after LASIK
BCVA (best corrected visual acuity) Right eye 20/66 Left eye 20/10 Intra ocular pressure 13 mmHg both eyes Biomicroscopic examination The examination of the right eye showed a scar (arrow) in the deep stroma. Pentacam examination The high pixel intensity layer in the deep stroma (assumed to be the flap interface) persisted.
right eye

7. 3 years after LASIK
BCVA (best corrected visual acuity) Right eye 20/66 Left eye 20/10 Intraocular pressure Right eye 12 mmHg Left eye 11 mmHg Biomicroscopic examination The examination of the right eye still showed the deep stromal scar (arrow).
right eye

8. Pachymetry map and corneal topography of the right eye
A: 14 months postoperatively
The　pachymetry map and the corneal topography of the right eye were almost stable during the observation period.
B: 3 years postoperatively

9. Discussion
The reported case was followed for 3 years after LASIK with an extremely thin residual bed.
There were two noteworthy points in this case as follows:
DLK in the early postoperative period which caused formation of a stromal scar.
The presence of an extremely thin residual bed that might have led to iatrogenic keratectasia.
In this case, we could not obtain information on the amount of laser energy used during LASIK; however, severe DLK might develop even when the energy level is within the standard range (Javaloy et al. 2007). Further studies on association between the depth of the interface and inflammation after LASIK should be carried out.

10. Discussion (continued)
A thin residual bed is a major risk factor for the development of post-LASIK ectasia.
In this case, an extremely thick flap was created for unknown reasons despite using a laser keratome, which is able to create predictably thin corneal flaps, and the estimated central residual bed thickness in this eye was 65 μm.
Randleman et al. reported that the mean time to the development of ectasia is 16.3 months (range, 1–45 months) and most cases of ectasia develop within the first 6 months after surgery; although some eyes develop delayed-onset ectasia (Ophthalmology 2003).

11. Discussion (continued)
In this case, the right eye remained stable topographically and the visual acuity remained stable for more than 3 years despite a very thin residual bed.
We speculate that the corneal stromal scar after DLK might have stiffened the cornea and contributed to the stability of the corneal shape; a hypothesis which needs to be verified in future studies.
We believe that longer follow-up is necessary in our case and such cases to identify late-onset keratectasia.