Surgical Correction of Hyperopia

Surgical modalities to correct hyperopia include photorefractive keratectomy (PRK), laser in situ keratomileusis (LASIK), Ho:YAG laser thermal keratoplasty (LTK), conductive keratoplasty (CK), phakic IOL, and refractive lens exchange. Excimer laser-based techniques, which include LASIK, LASEK, and PRK, are currently the most popular forms of surgery to correct not only myopia and astigmatism but also hyperopia. These techniques have been reported to be safe and effective for both primary surgeries and enhancements. However, various complications related to the flap and loss of best corrected visual acuity associated with a smaller optic zone, decentration, and irregular ablation caused by longer treatment time in high hyperopia over +5 diopter can have adverse effects on visual outcomes. The development of non-excimer laser-based techniques offers viable alternatives for laser vision correction techniques. More recent non-excimer-based thermal refractive techniques include LTK and CK. Earlier forms of thermal techniques showed a lack of predictability and stability, resulting in no further development of them. Recently, CK, a laserless, radiofrequency-based technique, has been approved by the FDA for the correction of low to moderate hyperopia even though the refractive instability has not been solved yet. In high hyperopia, lens approach like phakic IOL or refractive lens exchange instead of corneal surgery is preferred. ICL (Implantable contact lens) and Artisan is the most popular lens model that has well proven clinical results concerning its safety and effectiveness. Accommodative IOL or multifocal IOL could be the solution for pseudophakic presbyopia in refractive lens exchange in the future.

Superficial Punctate Keratopathy after LASIK

PURPOSE: To evaluate the clinical characteristics of superficial punctate keratopathy following LASIK and to estabilish the management and prevention of superficial punctate keratopathy. METHODS: We retrospectively analyzed the medical records of 476 eyes followed up for more than 6 months after LASIK. RESULTS: Of the 476 eyes, the SPK has deveolped in 118 eyes (24.8%). The incidence was higher when there was a history of dry eye symptoms or contact lens intolerance (p<0.05%). In 68 eyes (57.6%), SPK has developed within 1 month after LASIK and the inferior cornea (85.6%) was the most frequently involved site. Most cases were asymptomatic and treated with preservative-free artificial tear solution. There were no visually significant complications. CONCLUSIONS: Corneal sensitivity decreases after LASIK by cutoff of the sensory innervation. As LASIK-induced neurotrophic epitheliopathy has an influence on tear film dynamics, it may be a possible cause of dry eye syndrome or epithelial keratopathy after LASIK. Careful attention should be taken into the contributing factors such as pre-existing dry eye syndrome, contact lens intolerance, previous history of blepharoplasty, lagopthalmos and so on. Adequate hydration of cornea preoperatively, careful manipulation during procedure, conservative treatment with artificial tears may be helpful in reducing symptoms and preventing further complications.

A Case of Herpes Zoster Sine Herpete following Pediatric Penetrating Keratoplasty

Herpes zoster ophthalmicus sine herpete(HZSH), which means herpes zoster ophthalmicus(HZO)without skin eruption, is one of the atypical manifestations of varicella-oster virus(VZV)infection. Idiopathic iridocyclitis or acute retinal necrosis without skin lesion secondary to varicella-oster virus are good examples. Diagnosing zoster iridocyclitis without skin eruption is difficult because in the absence of typical skin eruption it is difficult to suspect varicella-zoster virus as the cause of inflammation in the absence of typical skin eruption. We describe here a rare case of a pediatric patient with severe iridocyclitis in a pediatric patient after penetration of keratoplasty in whom VZV DNA was detected using the DNA amplification and polymerase chain reaction(PCR)method. To our best knowledge, this is the first case report of varicella-zoster virus iridocyclitis in a pediatric patient after penetrating keratoplasty.

Comparison of Refractive Errors Measured by Several Different Methods

PURPOSE: Preoperative measurement of refractive error before LASIK or PRK is very important for good postoperative result because the measured refractive error is the basis of correction amount of operation. We analyzed the difference in spherical equivalent values of manifest refraction by operator (OMR), manifest and cycloplegic refraction by resident (RMR and RCR), noncycloplegic automated refraction (AMR). METHODS: The randomized charts of 50 patients (100 eyes) who had undergone LASIK or PRK for myopia at the Department of Ophthalmology at Samsung Medical Center between May 2000 and November 2000 were reviewed retrospectively and spherical equivalent values of preoperative OMR, RMR, RCR, and AMR by Nikon NRK-8000 autorefractor were analyzed by paired T-test. RESULTS: The mean spherical equivalent values of OMR, RMR, RCR, AMR were -5.40+/-2.10 D, -5.47+/-2.23 D, -5.36+/-2.18 D, -6.25+/-2.24 D, respectively. The spherical equivalent value of AMR was more myopic than the values of others and the bias was statistically significant. The absolute difference of spherical equivalent diopter between OMR and RMR was 0.27+/-0.27 D and that between OMR and RCR was 0.30+/-0.33 D. These two absolute difference did not show statistical significance. CONCLUSIONS: This study revealed that there was statistically significant difference in spherical equivalent diopter measured by AMR compared to those measured by OMR, RMR, or RCR. So we recommend the method of manifest and cycloplegic refraction by two ophthalmologists before LASIK or PRK for accurate measurement of refractive error.

Clinical, Physical Stability and Histological Biocompatibility of Experimental Seoul Type Keratoprosthesis

In cases that penetrating keratoplasty do not help to improve vision, keratoprosthesis implantation is necessary. This study was performed to assess clinical and mechanical stability of Seoul type-keratoprosthesis[SKPro], bio-compatibility and effect of amniotic membrane transplantation on clinical and mechanical stability of SKPro. SKPro consists of an optic portion made of PMMA, a skirt of Gore-tex or polyurethane and a haptic of prolene. The skirt of SKPro was covered with recipient conjunctiva completely at postoperative 1 month and melting of covered conjunctiva and exposure of skirt developed at postoperative 2 months and progressed slowly to postoperative 6 months. But retroprosthetic membrane formation, extrusion of SKPro, posterior segment complication such as retinal detachment did not develop and transplanted SKPro showed relatively good clinical stability during 6 months. Pressure loading test showed relatively good mechanical stability under high pressure at postoperative 2 months. Histologic study showed moderate inflammatory reaction and abnormal pattern of collagen and extracellular matrix in lamellar pocket and anterior flap. There was no deposit of collagen in Gore-tex skirt. But histology of posterior flap of lamellar pocket was nearly normal. Group that was transplanted with amniotic membrane twice showed more better stability than once and without amniotic membrane transplantation on clinical and mechanical stability.

Clinical, Physical Stability and Histological Biocompatibility of Experimental Seoul Type Keratoprosthesis

In cases that penetrating keratoplasty do not help to improve vision, keratoprosthesis implantation is necessary. This study was performed to assess clinical and mechanical stability of Seoul type-keratoprosthesis[SKPro], bio-compatibility and effect of amniotic membrane transplantation on clinical and mechanical stability of SKPro. SKPro consists of an optic portion made of PMMA, a skirt of Gore-tex or polyurethane and a haptic of prolene. The skirt of SKPro was covered with recipient conjunctiva completely at postoperative 1 month and melting of covered conjunctiva and exposure of skirt developed at postoperative 2 months and progressed slowly to postoperative 6 months. But retroprosthetic membrane formation, extrusion of SKPro, posterior segment complication such as retinal detachment did not develop and transplanted SKPro showed relatively good clinical stability during 6 months. Pressure loading test showed relatively good mechanical stability under high pressure at postoperative 2 months. Histologic study showed moderate inflammatory reaction and abnormal pattern of collagen and extracellular matrix in lamellar pocket and anterior flap. There was no deposit of collagen in Gore-tex skirt. But histology of posterior flap of lamellar pocket was nearly normal. Group that was transplanted with amniotic membrane twice showed more better stability than once and without amniotic membrane transplantation on clinical and mechanical stability.