Transitional Zone of the Corneal Endothelium: Flat Preparation and Ultrastructural Findings

PURPOSE: To evaluate the morphological characteristics of the transitional zone between the corneal endothelium and the trabecular meshwork by flat preparation and electron microscopy. METHODS: The materials comprised 12 eyes examined by the flat preparation and 7 eyes by the electron microscopy. The specimens were derived from the transitional tissue between the corneal endothelium and the trabecular meshwork. The specimens in the flat preparation were stained with hematoxylin-eosin and examined by light microscopy. The specimens for scanning electronic microscopy (SEM) and in transmission electronic microscopy (TEM) were examined through routine processes. RESULTS: In the specimens examined by the flat preparation, unlike peripheral corneal endothelial cells, the endothelial cell nuclei in the transitional zone were overlapped and morphologically oval. On SEM, unlike typical hexagonality and tight interdigitation of corneal endothelial cells, the endothelial cells in the transitional zone were partially successive, spaced intercellularly, and morphologically irregular. On TEM, the endothelial cells in the transitional zone were partially successive. CONCLUSIONS: The loss of cell-cell contact of endothelial cells in the transitional zone may lead to the potential proliferation capacity of endothelial cells in the transitional zone under specific conditions. Therefore, further studies on the proliferation capacity of endothelial cells in the transitional zone are needed together with more research on cell biology.

Intraocular Lens Power Calculation for Cataract Surgery after LASIK in the Absence of Pre-LASIK Data

PURPOSE: To evaluate the correlation between the conventional method and the clinical history method those determine intraocular lens (IOL) power for cataract surgery in eyes with prior laser in situ keratomileusis (LASIK) in the absence of pre-LASIK data. METHODS: The medical records of 200 eyes in 100 patients who had been treated with LASIK for myopia and were followed up for more than 6 months were reviewed. The IOL powers by conventional method using post-LASIK keratometric value and by clinical history method were compared. RESULTS: The mean values of IOL powers by conventional method, and by clinical history method were +20.00+/-1.48D (+13.74~+23.23D) and +20.79+/-1.28D (+17.27~+24.32D), respectively. The following equation describes the regular relationship between the two METHODS: IOL(CHM) (clinical history method)=0.708*IOL(CM) (conventional method) +6.624 (r=0.816, p<.01). CONCLUSIONS: This equation may offer more accurate IOL power for cataract surgery in eyes with prior LASIK surgery in the absence of pre-LASIK data.

Comparison of Refraction-Derived Keratometric Value and Orbscan Corneal Power after Laser in Situ Keratomileusis

PURPOSE: To determine the Orbscan corneal power which gave the best correlation with refraction-derived keratometric value (clinical history method) after LASIK in cataract surgery. METHODS: A total of 38 consecutive eyes of 19 patients who were followed up for at least 1 year after LASIK were included in study. The refraction-derived keratometric values were correlated with Orbscan corneal power within 1, 2, 3, 4, and 5 mm diameter zones of keratometric, anterior and total selections of mean, axial, tangential and optical power maps. RESULTS: The Orbscan corneal power of the 5-mm zone optical power total map gave the best correlation with refraction-derived keratometric value. The following regular relationship in linear regression analysis was derived: RDKV(refraction-derived keratometric value)=0.9 X OPT5(corneal power of Orbscan optical power total map 5-mm zone)+4.941(r=0.883). CONCLUSIONS: These results indicate that the corneal power of the 5-mm zone optical power total map was the most appropriate to calculate IOL power in cataract surgery after LASIK when using Orbscan topography.

Intraocular Lens Power Calculation in the Absence of Pre-PRK Data in Moderate Myopic Eyes

PURPOSE: To evaluate the correlation between the conventional method and the clinical history method for intraocular lens power calculation for cataract surgery in eyes with previous photorefractive keratectomy in the absence of pre-PRK data. METHODS: The medical records of 38 eyes in 23 patients who had been treated with PRK for myopia and were followed up for more than 1 year were reviewed. The IOL powers by conventional method using post-PRK keratometric value and by clinical history method were compared. RESULTS: The mean values of IOL powers by conventional method, and by clinical history method were +20.58 +/- 1.10D (range, +16.37~+22.80D) and +21.06 +/- 0.85D (range, +18.85~+22.8D), respectively. The following equation describes the regular relationship between the two METHODS: IOLCHM (clinical history method)= 0.683*IOLCM (conventional method) +7.005 (r=0.878, p<.01). When the IOL powers by conventional method were applied to this equation, the mean difference of value between the IOL powers calculated from this equation and those of the clinical history method was?0.01 +/- 0.41D (range, -0.99~+0.76D). CONCLUSIONS: This equation will be helpful to calculate the IOL power for cataract surgery in eyes with previous PRK in the absence of pre-PRK data.

The Accuracy of the Orbscan-derived Total Refractive Power after Laser in Situ Keratomileusis

PURPOSE: This study was performed to evaluate the correlation between the change of the manifest refraction and change of the Orbscan-derived total refractive and axial power after laser in situ keratomileusis (LASIK). METHODS: A total of 34 consecutive eyes of 19 patients who were followed up for at least6 months after LASIK were included in study. The manifest refraction and Orbscan topography analysis of the 2, 3, 4, and 5 mm diameter zones of total refractive power and axial power maps were measured preoperatively and at least 6 month postoperatively. RESULTS: There were statistically significant correlations between all Orbscan-derived corneal power changes and changes of manifest refraction. Especially the total refractive power map in the central 4.0 mm zone gave the best statistically significant correlation with manifest refractive change (r2=0.790, p<0.01). CONCLUSIONS: These results indicate that the change of the manifest refraction in LASIK is best correlated with the change of the total refractive power map in the central 4.0 mm zone.

Correlation between Corneal Diameter and Corneal Flap in LASIK using the Innovatome Microkeratome

No abstract available.

Comparison of IOL Powers by Different Formulae Used in Corrected Method at Cataract Surgery in Eyes after PRK

PURPOSE: By statistical analysis, to evaluate the comparison of the intraocular lens (IOL) powers by different formulae in patients who have been treated with excimer laser photorefractive keratectomy (PRK) for mild to moderate myopia. METHODS: A total of 38 consecutive eyes of 23 patients who were treated with PRK for mild to moderate myopia have been followed up for more than 6 months. IOL powers by SRK-II, SRK/T, Binkhorst-II, HofferQ, Holladay formula using autorefractokeratometer measured keratometric (K) values by autorefractokeratometer (RK-2, Canon, Japan) and refraction derived K values were compared . RESULTS: The mean IOL powers using autorefractokeratometer measured K values and refraction derived K values were 20.46+/-0.92 and 20.57+/-0.86 diopter (D) by SRK-II, 20.69+/-0.93 and 20.81+/-0.88 D by SRK/T, 21.27+/-0.94 and 21.40+/-0.95 D by Binkhorst-II, 20.93+/-0.09 and 21.05+/-0.06 D by Hoffer Q, and 20.65+/-0.90 and 20.76+/-0.87 D by Holliday respectively. The mean IOL powers using autorefractokeratometer measured K values and refraction derived K values were high in oder of Binkhorst-II, HofferQ, SRK/T, Holladay, and SRK-II, but there was no significant statistical difference between the IOL powers by SRK/T and those by Holladay (p>0.05). In all formulae, the mean IOL powers using refraction derived K values were higher than the mean IOL powers using autorefractokeratometer measured K values, but there was no statistically significant difference (p>0.05). CONCLUSIONS: In patients with excimer laser PRK treatment for mild to moderate myopia, refractive error after cataract surgery is caused by IOL calculation formula as well as its method for IOL power. IOL powers by Binkhorst-II using refration derived keratometric values of all formulae were statistically highest.

Comparison of IOL powers by corrected method in eyes after PRK and LASIK

The purpose of this study is to compare, by statistical analysis, intraocular lens (IOL) powers by SRK/T formula using autorefractokeratometer-measured keratometric (K) values (SRK/T-ARK-mK), by SRK/T formula using refraction-derived K values (SRK/T-R-dK), and by refraction corrected method (RCM), in eyes treated with photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) for myopia. Thirty-eight consecutive eyes of 23 patients with PRK for mild to moderate myopia and 35 consecutive eyes of 25 patients with LASIK for high myopia were followed up for more than 1 year. In the two groups, IOL powers by SRK/T-ARK-mK, by SRK/T-R-dK, and by RCM were compared by statistical analysis. In PRK group, the mean value of IOL powers by RCM was statistically higher than that obtained by the other two methods (p 0.05). However, in LASIK group, the mean values of IOL powers by RCM and by SRK/T-R-dK, which did not differ statistically (p > 0.05), were both statistically higher than that by SRK/T-ARK-mK (p < 0.05). In conclusion, there is a statistical difference in IOL powers by the methods used for IOL calculation, as there is according to the level of myopia in patients with PRK and LASIK treatment. We suggest that, in IOL power calculation in eyes with previous corneal refractive surgery, correction methods such as RCM and SRK/T-R-dK are more effective at higher levels of myopia.