Corneal iron lines have been reported in normal and pathological corneas, as well as after corneal surgical procedures. In 1906, Fleischer1 was the first to report the iron ring deposition associated with keratoconus. Hudson2 and Stähli3 also reported the presence of a discrete iron line along the lower third of the cornea in otherwise normal eyes. Iron lines have been associated with other corneal conditions including elevated corneal scars, Salzmann's nodular degeneration, and Coats' white ring and have been observed central to the head of pterygium and along the anterior edge of trabeculectomy blebs.4,5
Corneal iron lines have also been associated with several therapeutic and refractive corneal procedures. An arcuate iron ring can occur along the anterior suture border after penetrating keratoplasty.6 A corneal iron ring has been identified adjacent to the margin of the donor lenticule after epikeratophakia.7 A central stellate iron deposition pattern has been reported in approximately 80% of eyes after radial keratotomy,5 and an inferior corneal iron line has been identified after insertion of the intrastromal corneal ring.8
Recently, central corneal iron deposition has been associated with photorefractive keratectomy (PRK). A central corneal iron line can occur after uneventful PRK,9 while a small central iron ring can be associated with steep central islands after PRK.10 To date, there have been no reports of corneal iron deposition after laser in situ keratomileusis (LASIK).
We report the occurrence of a corneal iron ring 6 months after hyperopic LASIK.
A 37-year-old white woman was evaluated for hyperopic LASIK. The preoperative refractive error was +7.00 −1.50 × 153 in the right eye and +7.50 −1.50 × 165 in the left. Best corrected visual acuity (BCVA) was 20/20 in both eyes. A complete ocular examination was normal with no contraindications to LASIK. Corneal topography indicated regular astigmatism. Simulated K-values were 43.37/45.75 × 74 in the right eye and 42.87/45.37 × 82 in the left. Central pachymetry values measured on the Humphrey Ultrasonic Pachymeter were 512 μm in the right eye and 511 μm in the left. Before the procedure, the patient was thoroughly counseled about the risks and benefits of hyperopic LASIK and signed a detailed consent form.
Topical proparacaine 0.5% was instilled in the eye 5 minutes before the procedure, and the lids were cleaned. The corneal flaps were created with the Chiron Automated Corneal Shaper since at that time the Chiron Hansatome was not available for hyperopic LASIK at our center. A 200 μm depth plate was selected to maximize the flap size to approximately 8.5 mm. The Chiron Technolas 217 excimer laser with a 2.0 mm scanning spot and pupil tracking was used. The full hyperopic refractive error was programmed into the laser using a 6.0 mm optical zone with a 9.5 mm blend zone. The procedure was completed without complication. Postoperatively, the patient was instructed to use tobramycin and dexamethasone (TobraDex®) and ofloxacin 0.3% drops 4 times a day for 4 days. Sunglasses and eyeshields were given to the patient for eye protection for the first week.
At the 6 month follow-up visit, induced astigmatism of approximately 3.0 diopters was noted and an enhancement procedure was scheduled. On examination, the uncorrected visual acuity was 20/30 in the right eye and 20/40 in the left. The manifest refraction was +1.00 −2.75 × 15 in the right eye and +2.00 −2.75 × 170 in the left, which resulted in a BCVA of 20/20− and 20/25, respectively.
Slitlamp examination revealed a moderately dense yellow-brown ring on both corneas. The intensity of the pigmentation faded on either side of the central aspect of the ring; the complete ring width measured less than 0.5 mm. The diameter of the pigmentation ring measured approximately 5.0 mm at the slitlamp. This iron deposition was similar in appearance to the Fleischer ring of keratoconus (Figure 1). The iron ring was located at the base of the hyperopic laser ablation on the corneal topography (Figure 2).
Corneal iron lines result from iron deposition in the basal epithelial cells. They tend to form in areas in which the eyelids do not smoothly sweep the tears from the corneal surface.5 Iron deposition can occur as the Hudson-Stähli line at the junction of the middle and inferior third of the cornea,11 where the tears pool between the eyelid margins when the eye is at rest.12 It can also occur adjacent to elevations of the cornea and limbus, which prevent even contact between the lid and cornea.5
Various theories attempt to explain the origin of the iron lines. Gass13 has proposed the tear-pool hypothesis, in which sequestered iron in the tear film is preferentially deposited in areas of the cornea with pooling of the tear film. While this theory could explain the location of the Hudson-Stähli line corresponding to the position of the lids at rest, several clinical and laboratory investigations have questioned the tear-pool theory because of the low concentration of iron in the tears,14 the protective effect of mucus,15 and the occurrence of the iron lines in eyes without tears.16
Rose and Lavin17 have proposed the basal-cell-migration theory, in which the abrasive lid action on the cornea surface induces enhanced mitotic activity. The dividing, nonmigrating, basal cells become mature and accumulate iron. Assil and coauthors8 have proposed 2 additional theories to explain the iron lines: the tear desiccation hypothesis, in which iron deposits occur in areas of the initial tear breakup; the senescent basal cell hypothesis, in which iron accumulates in the epithelial cells where there are diminished rates of cell turnover.
Hyperopic LASIK achieves the refractive correction with an excimer photoablation in a circular pattern around the visual axis. This flattening of the peripheral cornea results in an overall steepening of the central cornea, which produces an increased refractive power and corrects the hyperopic refractive error. With the Chiron Technolas 117c and 217 excimer lasers, optical zones of at least 5.0 mm have been used to achieve adequate corrections with hyperopic LASIK.18 Our results with hyperopic LASIK have been optimal when a 5.5 or 6.0 mm optical zone is used,19 because the effects of small decentrations and night-vision distortions are minimized.
The identification of the iron ring after hyperopic LASIK has some clinical value. Our case used an optical zone size of 6.0 mm, which is slightly larger than the diameter of the iron ring identified on the cornea. This suggests that an approximation of the optical zone size used for hyperopic LASIK can be made from the diameter of the corneal iron ring. The location of the iron ring also provides useful information about the centration of the correction. When the iron ring does not align with the position of the pupil, it suggests a decentered ablation.
In summary, we have identified a corneal ring after hyperopic LASIK, which we have termed the pseudo-Fleischer ring because of the similarities between this pigmentation pattern and the Fleischer ring associated with keratoconus. The characteristics of this ring provide information about the size and location of the excimer laser ablation used in hyperopic LASIK.
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