Natural history of central islands after laser in situ keratomileusis

Clinical Analysis of Central Islands after Small Incision Lenticule Extraction (SMILE)

PURPOSE

To evaluate the incidence of central islands after 6-month follow-up of Small Incision Lenticule Extraction (SMILE) and to assess their role in safety and accuracy.

METHODS

Analysis of the preoperative and postoperative corneal tomography, best spectacle refraction and corrected distance visual acuity of 82 subjects that underwent SMILE. Incidence of central islands was assessed through total corneal spherical aberration (SA) over 4 mm of central diameter and the SA was compared between two groups with and without safety loss (CDVA difference ≥0.1 logMAR from preoperative). The cut-off value for detecting the risk of postoperative central island development was calculated. The influence in accuracy was calculated through magnitude of error of the spherical equivalent and astigmatism, both for spectacle refraction at corneal plane (SE-Rx and AST-Rx) and for total corneal refractive power at 3 mm (SE-TCRP3 and AST-TCRP3).

RESULTS

Five from 82 eyes resulted in a loss of safety, obtaining significant differences in SA, both preoperatively (p = .01) and postoperatively (p = .007) after stratification by safety loss. A preoperatively cut-off value ≤0.012 μm of SA predicted the appearance of central islands with sensitivity of 100% and specificity of 75%. Despite postoperative SA being related to the preoperative spherical equivalent, for both SE-Rx and SE-TCRP3, this tendency disappeared after readjusting results according to a nomogram.

CONCLUSIONS

Central islands in SMILE, despite being a rare adverse event, can affect the safety of the procedure and are related to preoperative central steepness, not corrected by the spherical lenticule, which is clearly visible postoperatively.

Central island formation after cataract surgery in a laser in situ keratomileusis eye: New etiology

We report a case of central corneal steepness formation after cataract surgery in a post-laser in situ keratomileusis (LASIK) eye. A 51-year-old woman with traumatic cataract and a history of myopic LASIK surgery had uneventful phacoemulsification cataract surgery. Postoperatively, the corneal topography difference map showed a central island formation of 2.1 diopters (D) compared with the preoperative level, which correlated with a clinical myopic shift of 2.00 D from the targeted emmetropia. At 4 months, most of the central island had resolved spontaneously. At 15 months, topography returned to preoperative levels. We speculate that wound hydration in the flap interface during surgery resulted in a pond-like fluid accumulation in the center of the cornea, resulting in a myopic refractive shift. We report this case because of the high probability that this phenomenon could be confounded by an erroneous intraocular lens (IOL) calculation and the potential for a serious iatrogenic complication from a premature IOL exchange or touch-up procedure.

Central islands: rate and effect on visual recovery after phototherapeutic keratectomy

PURPOSE

To retrospectively assess the proportion of patients affected by a central island (CI) and its effect on visual recovery after phototherapeutic keratectomy (PTK).

METHODS

This retrospective study evaluated 30 eyes of 21 consecutive patients (mean age ± standard deviation, 69.6 ± 6.8 years) undergoing PTK for the treatment of band keratopathy or granular corneal dystrophy. We investigated the rate of CI formation, which was defined as a steepening area of 3 D, 1.5 mm in diameter, on each corneal videokeratograph (ATLAS 9000; Carl Zeiss Meditec), and its effect on visual recovery at 3 months and at 1 year postoperatively.

RESULTS

A CI was found in 22 of 30 eyes (73%) 3 months postoperatively and in 14 of 25 eyes (56%) 1 year postoperatively. The degree of CI was significantly correlated with the change in logMAR corrected visual acuity (Spearman correlation coefficient r = 0.445, P = 0.026). The degree of CI in eyes with band keratopathy was significantly larger than that in eyes with granular dystrophy 1 year postoperatively (Mann-Whitney test, P = 0.045). The degree of CI was not significantly correlated with the ablation depth (Spearman correlation coefficient r = 0.116, P = 0.582) or the residual corneal thickness (r = -0.235, P = 0.278).

CONCLUSIONS

CI formation was found in as many as 73 and 56% of patients 3 months and 1 year after PTK, respectively, using the VISX Star S4 excimer laser system, and significantly affected the improvement of visual acuity. The anti-CI program should be applied by the manufacturer, not only for corneal refractive surgery but also for PTK in a clinical setting.

Proper Positioning of the Plume Evacuator in the VISX Star3 Excimer Laser Minimizes Central Island Formation in Patients Undergoing Laser in situ Keratomileusis

PURPOSE

To identify risk factors in a series of patients who developed steep central islands after laser in situ keratomileusis (LASIK).

METHODS

We analyzed and compared the refractive and topographic outcome of a study group composed of 83 eyes of 44 patients who underwent LASIK using the VISX Star3 excimer laser with a refraction-matched control group of 83 eyes treated later. The vacuum aspirator of the excimer laser was abnormally positioned during the surgeries performed in the study group.

RESULTS

Mean preoperative spherical equivalent refraction in the study group was -6.75 +/- 2.50 D. Four eyes with a mean preoperative spherical equivalent refraction of -9.27 +/- 2.29 D developed steep central islands. Thirty-three (38%) of 83 eyes treated needed retreatment for residual myopia or myopic astigmatism. In the control group, mean preoperative spherical equivalent refraction was -6.76 +/- 2.50 D. Ninety-three percent of eyes were within +/- 1.00 D of target refraction. Five (6.02%) of 83 eyes required retreatment and no eyes developed central islands.

CONCLUSION

The abnormally positioned vacuum aspirator coupled with the higher preoperative refractive correction were the likely causative factors for central island formation and the increased incidence of undercorrection in these patients.

Astigmatism and LASIK

Although laser in situ keratomileusis (LASIK) enjoys a high success rate, postoperative residual or induced astigmatism may limit uncorrected visual acuity and cause starbursts and glare at night. Irregular astigmatism can also cause loss of best-corrected visual acuity, monocular diplopia, and ghosting of images. Astigmatism may be measured by keratometry and refraction, while corneal topographic techniques help to define irregular astigmatism, in particular. Further information may be obtained regarding induced higher-order aberrations with aberrometry. Because astigmatism has both direction and magnitude, its analysis is more complex than that of the spherical component of the treatment. There are multiple approaches to the analysis of surgically induced astigmatism, including vector analysis, conversion to a Cartesian coordinate system, matrix formalism, and linear optics. Both excimer laser and incisional techniques may be used to correct astigmatism after LASIK, but the treatment of irregular astigmatism requires selective zonal ablation techniques or customized corneal ablations, using topographic or wavefront derived data.

LASIK complications: etiology, management, and prevention

Laser in situ keratomileusis (LASIK) is a rapidly evolving ophthalmic surgical procedure. Several anatomic and refractive complications have been identified. Anatomic complications include corneal flap abnormalities, epithelial ingrowth, and corneal ectasia. Refractive complications include unexpected refractive outcomes, irregular astigmatism, decentration, visual aberrations, and loss of vision. Infectious keratitis, dry eyes, and diffuse lamellar keratitis may also occur following LASIK. By examining the etiology, management, and prevention of these complications, the refractive surgeon may be able to improve visual outcomes and prevent vision-threatening problems. Reporting outcomes and mishaps of LASIK surgery will help refine our approach to the management of emerging complications.

Surgically induced topographical abnormalities after LASIK: management of central islands, corneal ectasia, decentration, and irregular astigmatism

Proper preoperative evaluation is critical for avoiding many postoperative complications associated with laser in-situ keratomileusis (LASIK). Proper nonsurgical management includes careful monitoring of patients during the recovery period using various testing procedures, including corneal topography. When surgical intervention is required, a stepwise approach often is used as a conservative treatment, allowing further treatment if necessary. Many complications after LASIK are amenable to further treatment. However, it often is advisable to monitor patients until improved instrumentation is developed. The authors review the etiology and management of several complications after LASIK by reviewing the literature and relaying their own clinical experiences.