Combined simultaneous photorefractive keratectomy and collagen cross-linking in keratoconus suspect patients.

PURPOSE: To evaluate the safety and efficacy of combined simultaneous photorefractive keratectomy (PRK) with collagen cross-linking (CXL) in keratoconus suspects (KCS). METHODS: This was a retrospective, non-randomized study of KCS patients who underwent combined simultaneous PRK with CXL. The efficacy, safety, refractive outcomes, and corneal wavefront aberration changes were assessed after the surgery and compared with existing preoperative data. RESULTS: Fifty-six eyes of 28 patients, including 20 females (71.4%), with a mean age of 30.92±4.09 years, were enrolled. The mean follow-up was 19.46±8.48 months (range: 7-35). At the conclusion of the study, mean uncorrected distance visual acuity LogMAR improved from 0.89±0.44 preoperatively to 0.04±0.09 postoperatively (P<0.001). In addition, a statistically significant corneal flattening was observed postoperatively, with a decrease in manifest refraction. A statistically significant increase was found in higher-order aberrations (P<0.001), horizontal coma (P<0.001), and spherical aberration (P<0.001) compared with preoperatively. Postoperatively, 41% exhibited refractive astigmatism of 0.50 diopter (D) or less; 83.8% showed 1.00 D or less. CONCLUSION: The results of our study indicate that combined simultaneous PRK with CXL can be a safe and effective method for treating refractive instability in KCS patients.

Understanding Corneal Epithelial Thickness Mapping.

Corneal epithelial thickness (CET) and the regional variations in response to changes in corneal architecture and biomechanics have recently drawn the interest of corneal surgeons. Corneal epithelium possesses the tremendous capability of remodeling and changing its thickness. This remodeling of corneal epithelium takes place in response to underlying stromal irregularities which can result from a variety of corneal disorders including corneal ectasia. Measurement of CET can reveal the underlying stromal abnormalities and supplement in early diagnosis of corneal disorders especially corneal ectasia which has been one of the leading challenges in planning corneal refractive surgery. A significant number of patients ends up in ectasia after refractive surgery and the most common cause of this complication is the presence of preoperative subclinical keratoconus. Furthermore, postoperative complications of corneal refractive surgery are partly masked by epithelial remodeling and make the diagnosis and management difficult and extremely challenging. This leads not only to unpredictable visual and refractive outcome but also the need of multiple interventions to treat these complications. Although corneal tomography is considered as gold standard in the detection and diagnosis of corneal ectasia, a small number of subclinical cases may still go undetected. In this review, we have highlighted the underlying mechanism of epithelial remodeling, the devices and imaging modalities used to measure CET, and application of epithelial mapping in the diagnosis and management of various corneal disorders.

Corneal Haze after Excimer Laser Photorefractive Keratectomy for Myopia

To evaluate croneal haze related to amount of correction, age and sex following excimer laser photorefractive keratectomy(PRK) in myopic eyes, 39months follow-up study on 358 eyes was performed prospectively. The preoperative spherical equivalent refraction ranged from -1.0D to 11.25D(mean -6.18D). The subjective corneal haze grading showed a maximum with mean grading of 0.92 at 2 months and a gradual decrease to 0.14 at 24 months after PRK. The degree of haze was statistically greater with higher amount of correction(p0.05). Clinically significant corneal haze and scarring was frequent in higher myopia group(p<0.05). Individual variation in corneal haze after PRK was found. However, high myopia is a risk factor of the corneal haze following PRK, and further study to decrease the corneal haze after PRK is necessary.

Prevalence of Central Islands in Corneal Topographic Analysis after Excimer Laser Photo refractive Keratectomy for Myopia

We analyzed the central islands in corneal topography after excimer laser photo refractive keratectomy(VISX Twenty/Twenty B(R) with VisionKey(TM) VISX, Inc. Santa Clara, CA, USA) to evaluate the prevalence of central island and the factors associated with their occurrence, prospectively. Corneal topographic analysis using Corneal Analysis System(EyeSys Technologies, Inc. Houston, TX, USA) was performed in 94 eyes of 77 patients at the postoperative 1-, 3- and 6-months after excimer laser PRK. Central islands were seen in 27%(25/92), 10%(8/79) and 8%(5/64) of patients at postoperative 1-, 3- and 6-months, respectively. There was statistically significant decrease in the occurrence of central island between postoperative 1 and 3 months follow-up groups(p0.05). We found that there was no demonstrable effect of central islands on the decrease of best spectacle corrected visual acuity at postoperative 1 month(p>0.05). Occurrence was statistically significantly decreased in the patients treated with the version 4.01 of central island removal software(1 month: p<0.01, 3 months: p<0.05). We suggest that the version 4.01 software of VISX 20/20B(R) was very effective to reduce the prevalence of central island after excimer laser PRK. In conclusion, if the software would be adjusted to increase the number of pulses centrally, this might reduce the prevalence of central island. New strategies and algorithms might be developed to reduce the prevalence of central islands.