Comparison of central corneal thickness measurements by PachPen ultrasonic pachymetry and the other two optical measuring instruments / 国际眼科杂志(Guoji Yanke Zazhi)

·AIM:To compare the similarities and differences of central corneal thickness (CCT) measured by different devices, so as to provide a safe, effective, simple and accurate method for measuring corneal thickness. ·METHODS: Totally 95 eyes of 95 cataract patients enrolled continuously for preoperative examination in ophthalmology department of Putuo Hospital Affiliated to Shanghai University of Traditional Chinese Medicine from September 2016 to December 2016. Handheld automatic PachPen ultrasonic pachymetry (USP), anterior segment optical coherence tomography (AS-OCT) and specular microscopy were respectively used to measure the central corneal thickness,and intraocular pressure was measured at the same time. The similarities and differences of these three different devices to measure the central corneal thickness and their correlations with intraocular pressure were observed. Then the data were analyzed statistically. · RESULTS: The CCT value measured by PachPen ultrasonic pachymetry was 544. 43 ± 36. 61μ m, the CCT value measured by AS-OCT was 527.09 ± 35.54μ m, and the CCT value measured by specular microscopy was 533.20 ± 30. 17μ m. There was significant difference between these three groups(F=6.272,P=0.002),and the CCT value measured by PachPen ultrasonic pachymetry was significantly higher than the other two groups. The correlation coefficients between the CCT values of these three groups and intraocular pressure were 0.290, 0.277 and 0.204 (P<0.05) respectively, of which the correlation between the CCT measured by PachPen ultrasonic pachymetry and the intraocular pressure was the highest. There was statistically significant correlation between the CCT values measured by these three measurements (P<0.001). ·CONCLUSION: The CCT value measured by PachPen ultrasonic pachymetry is the highest. The second CCT value is measured by specular microscopy, and the smallest CCT value is measured by AS-OCT. Obvious correlation and good consistency were found in the CCT values measured by three types of devices, and the CCT values were all correlated with intraocular pressure. Therefore,we should take more attention in clinic.

Comparison of ocular anterior segment parameters measured by three kinds of biometric measuring methods in myopic eyes / 中华实验眼科杂志

Background It is essential to measure and assess the parameters of ocular anterior segment for refractive surgery in myopic eyes.Some different imaging devices can be used for biometric measurement of ocular anterior segment,but which is more accurate and convenient is still under investigation.Objective This study was to compare the anterior segment parameters in myopic eyes measured by anterior segment optical coherence tomography (AS-OCT),Orbscan topography and ultrasonic pachymetry (US).Methods One hundred and forty eyes of 70 myopic subjects with the diopter of-0.75 to-10.25 D,who intended to receive corneal refractive surgery in the Second Affiliated Hospital of Zhejiang University School of Medicine from November 2011 to May 2012,were retrospectively analyzed.Central corneal thickness (CCT) was measured using AS-OCT,Orbscan Ⅱ and US,respectively,and anterior chamber depth (ACD) was measured by AS-OCT and Orbscan Ⅱ,and the angle to angle (ATA) distance and corneal white-to-white corneal distance (WTW) were measured by AS-OCT and Orbscan Ⅱ,respectively.The parameters from different apparatuses were statistically compared.Results The mean CCT were (516.57±30.25) μm in AS-OCT,(523.68±31.87) μm in US and (514.69±38.40) μm in Orbscan Ⅱ,without significant difference among them (F =2.775,P =0.063).Then the patients were divided into three groups based on the US measurement of CCT (＜500 μm group,500-569 μm group,and ≥ 570 μm group).In the ＜500 μm group,there was a significant difference in the CCT among the three methods (F =22.236,P =0.000),significant differences were found between AS-OCT and Orbscan Ⅱ,or Orbscan Ⅱ and US(both at P＜0.05).In the 500-569 μm group,there was no significant difference in the CCT among the three methods (F =3.011,P =0.051).In the ≥ 570 μm group,there was a significant difference in the CCT among the three methods (F =4.133,P =0.021),a significant difference was found between AS-OCT and US(P＜0.05),but there was no significant difference between AS-OCT and Orbscan Ⅱ (P＞0.05).The ACD values measured by AS-OCT was (3.83±0.21) mm,which was higher than (3.75 ± 0.21) mm by Orbscan Ⅱ,with a significant difference between them (t =-8.520,P =0.000).In addition,the ATA value by AS-OCT (12.43 mm±0.74 mm) was higher than the WTW value (11.42 mm±0.33 mm) by OrbscanⅡ,with a significant difference between them(t=-18.088,P=0.000).Conclusions AS-OCT,US and Orbscan Ⅱ can offer accurate CCT value,and they can provide references to one another before refractive surgery.However,the ACD,ATA and WTW values by AS-OCT and Orbscan]Ⅱ have large differences.

Reliability of RTVue, Visante, and Slit-Lamp Adapted Ultrasonic Pachymetry for Central Corneal Thickness Measurement

PURPOSE: To evaluate reliability of Fourier-domain optical coherence tomography (OCT) (RTVue), time-domain OCT (Visante), and slit-lamp adapted ultrasonic pachymetry (SL-US) in the measurement of central corneal thickness (CCT). MATERIALS AND METHODS: Thirty healthy volunteers visited our clinic 3 times and fifty eyes were measured by one physician. RTVue and Visante were randomly performed, and then SL-US, in which the ultrasound probe was inserted into the Goldmann tonometry mount, was done. During the second visit, each measurement was repeated 3 times. Measurements on the second visit were averaged, and agreement among the instruments was investigated with Bland-Altman plots. RESULTS: RTVue showed smaller repeatability coefficient than Visante and SL-US (4.7, 8.3, and 7.7 microm, respectively). Intersession reproducibility of RTVue and Visante was worse than their repeatability. CCT of RTVue was estimated to be maximally different by 11.8 microm from CCT of Visante and 8.8 microm from CCT of SL-US. The repeatability coefficient of SL-US was 7.7 microm and its reproducibility was similar to the repeatability. CONCLUSION: CCT measured by RTVue showed good reliability and generally agreed with Visante and SL-US. SL-US was as reliable as triple touching conventional US even with a single touch on the cornea.

The Effects of Dry Eye on the Corneal Thickness Measured by Orbscan and Ultrasonic Pachymetry

PURPOSE: To evaluate the effect of dry eye on the corneal thickness measured by Orbscan and ultrasonic pachymetry. METHODS: The central corneal thickness was measured by both ultrasonic and Orbscan pachymetry in 30 eyes with dry eye (dry eye group) and in 30 eyes of normal subjects (control group). Dry eye was diagnosed when a Schirmer test result was less than 10 mm (after topical anesthesia) and the test for tear osmolarity was also performed. RESULTS: Tear osmolarity was 364.4+/-42.9 mOsm/L in dry eye group and 337.8+/-34.5 mOsm/L in control group. It was significantly higher in dry eye group than in the control group (p=0.011). Mean central corneal thickness measured by Orbscan pachymetry was 547.5+/-27.3 microgram in dry eye group and 562.0+/-20.4 microgram in the control group. It was significantly thinner in dry eye group than in the control group (p=0.023). Mean central corneal thickness measured by ultrasonic pachymetry was 535.7+/-27.2 microgram in dry eye group and 547.6+/-20.1 microgram in the control group with out significant difference between the two groups (p=0.059). CONCLUSIONS: The corneal thickness measured by ultrasonic pachymetry is less affected by dry eye compared to that measured by Orbscan pachymetry.

Accuracy of Orbscan Pachymetry Measurements and Ultrasonic Pachymetry before and after LASIK with Orbscan II(R) Topography

PURPOSE: To assess the the accuracy and variability in pachymetry measurements obtained by Orbscan and ultrasonic pachymeter in laser in situ keratomileusis (LASIK). METHODS: Thirty two eyes of 16 patients before LASIK were measured by ultrasonic pachymeter and Orbscan. Thirty eyes of 16 patients that had LASIK were measured by ultrasonic pachymeter and Orbscan postoperatively. The theoretical residual corneal thickness was compared to measurements by both instruments in eyes that had LASIK procedures. RESULTS: The ultrasound pachymeter measurements (543.8+/-24.2 micrometer) were thicker than the Orbscan pachymetry measurements, (541.2+/-24.9 micrometer) by mean of 2.7+/-7.4 micrometer (SD), preoperatively. But this is not statistically significant (p>0.05). Postoperatively, the ultrsound measurements were consistent with theoretical residual corneal thickness, 461.8+/-37.4 micrometer versus 467.9+/-30.71 micrometer (p=0.064), while Orbscan measurements were statistically less than the theoretical residual corneal thickness, 433.2+/-48.75 micrometer versus 464.32+/-33.4 micrometer (p<0.001). CONCLUSIONS: In LASIK eyes, the ultrasonic pachymetry was a more accurate measurement of corneal pachymetry than Orbscan topography system.

Comparison of Corneal Thickness Measurements Between Orbscan Topography System and Ultrasonic Pachymetry before and after LASIK

PURPOSE: To report the difference of the values of the corneal thickness measurement measured by Orbscan topography system and ultrasonic pachymetry is different between pre-LASIK and post-LASIK. METHODS: The corneal thickness measured by these two methods was compared in 32 pre-LASIK eyes of 18 subjects and 31 post-LASIK eyes of 20 subjects passed 3 months after laser in situ keratomileusis (LASIK). RESULTS: In the pre-LASIK eyes, the cornea measured thicker by Orbscan topography system than by ultrasonic pachymeter (16.94+/-13.1 microgram, average +/- standard deviation, p=0.001). In the post-LASIK eyes, there was no statistically significant difference in the values of corneal thickness measurement between two methods (-9.58+/-27.88 microgram, p=0.0653). CONCLUSION: We must give attention to the interpretation of values of corneal thickness measurement measured by Orbscan topography system and ultrasonic pachymetry because the correlations between the two methods in pre and post-LASIK eyes are different. We assume that differences of the values of measurement between the two methods may result from either technical errors of the measurers , interference of corneal interface, or change of tear film.