Ultrasound Pachymetry Measurements Research Articles

A Comparison Between Ultrasound Pachymetry and CASIA2 (Anterior-Segment Optical Coherence Tomography) in the Measurement of Central Corneal Thickness.

Background and objective Due in part to its effect on intraocular pressure (IOP) measurements, the assessment of central corneal thickness (CCT) is recognized as an essential part of the initial glaucoma assessment. The most widely utilized clinical technique to measure CCT is ultrasound pachymetry (USP). In recent years, many dedicated anterior-segment optical coherence tomography scanners (AS-OCTs) have been developed. Previous studies have compared CCT measurements between USP and various AS-OCTs. This study aimed to assess the degree of agreement between USP and CASIA2 (Tomey Corporation, Nagoya, Japan), a second-generation swept-source AS-OCT developed in Japan. Methodology The data on CCT screening measurements of 156 eyes (88 patients)performed over a period of three months, from January to March 2020, on glaucoma patients attending the Royal Hallamshire Hospital (RHH) in Sheffield, UKwere collected retrospectively and statistically analyzed. Results The average age of the 88 patients included in the study was 66 years (range: 20-86 years). Our findingsshow that when compared to CASIA2 measurements, USP measurement of the CCT resulted in significantly thicker values (paired t-test: t=23.15,p<2.2 x 10-16). The average difference between the two methods was 19.98 ±10.78 μm. It is hypothesized that this difference may be duein partto inaccurate probe placement during ultrasound probemeasurement, resulting in thicker CCT values. Conclusion The observed difference may be clinically significant as it could induce clinical discrepancy in terms of perceived glaucoma risk in patients. Therefore, USP and CASIA2 should not be used interchangeably, and clinicians should take into account the significant difference between these methods.

Evaluation of the Difference between Predicted and Measured Central Corneal Thickness Reduction after SMILE and Femtosecond Laser-assisted LASIK for Myopia

ABSTRACT Purpose To evaluate the agreement between the predicted and measured central corneal thickness (CCT) reduction after the small incision lenticule extraction (SMILE) surgery and femtosecond laser-assisted in situ keratomileusis (FS-LASIK) surgery. Methods A total 165 patients were enrolled in this prospective study. Eighty patients with a mean spherical equivalent (SE) of −4.72 ± 1.80 Diopters (D) were treated with the FS-LASIK procedure and Eighty-five patients with a mean SE of −4.78 ± 1.63 D were treated with SMILE procedure. One eye for each patient was randomly selected and included for statistical analysis. Ultrasound pachymetry measurement and Scheimpflug camera corneal topography were performed preoperatively and 3 months postoperatively. The measured CCT reduction was calculated by comparing the preoperative examinations with postoperative examinations. Comparative statistics and linear regression analyses were performed. Results The mean predicted CCT reduction was 95.02 ± 21.39 μm in FS-LASIK group and 103.49 ± 22.87 μm in SMILE group (P = .015). The prediction of laser platform was found to overestimate the measured CCT reduction for both FS-LASIK group (ultrasound 13.20 ± 9.34 μm) and SMILE group (ultrasound 13.12 ± 8.68 μm). The prediction of laser platform was found to systematically overestimate the measured CCT reduction in FS-LASIK group. In SMILE group, the difference between predicted and measured CCT reduction were found significantly related with the predicted CCT reduction (P < .001 for ultrasound; and P = .004 for Pentacam). Conclusion A systematic overestimation of measured CCT reduction in FS-LASIK group did not influence the refractive precision of FS-LASIK. Due to the different biomechanical distributions in post-SMILE cornea, the measured CCT reduction was influenced as the changes in refractive correction. Nomogram adjustment for high myopic correction needs further research.

Central corneal thickness and intraocular pressure in primary open angle glaucoma suspects in a south Indian population. Is it time for “corneal anthropology”?

To study correlation between central corneal thickness (CCT) and intraocular pressure (IOP) in the primary open angle glaucoma (POAG) suspects and to assess the importance of the local population reference CCT in pachymetry adjusted IOP.Prospective, cross sectional study.A total of 100 patients aged 40-70 years of age diagnosed as POAG suspects were included. CCT measurements using ultrasound pachymetry and IOP measurement with Goldmann applanation tonometer (GAT) was done. IOP was corrected to the local south-Indian baseline CCT and also to the International CCT and comparison was done.The study included 100 patients (58 male and 42 female) with mean age of 51.7 ± 6.1 years. The mean CCT was 518.91 ± 24.26 μm, 522.19 ± 21.56 μm among females, males respectively. The mean uncorrected IOP (GAT) was 19.50 mmHg, 20.14 mmHg (right, left sides). Significant, moderate positive correlation between CCT and IOP was observed. The two groups i.e mean IOP corrected for South-Indian CCT (Mean_CX_IOP) versus IOP corrected for CCT international (Mean_CX_INT_IOP) showed significant difference. The mean IOP in Indian CCT corrected group was 19.76 ± 2.81 mmHg and in international CCT group was 21.51 ± 2.83 mmHg. Levene's test indicated significant difference in mean IOP of 2 groups (p=0.000).CCT is an important parameter in glaucoma management and known to vary in different ethnic groups. Local ethnicity specific CCT should be used in IOP correction with the help of anthropologists.

Investigation of predictability and influence factors of the achieved lenticule thickness in small incision lenticule extraction

BackgroundTo evaluate the differences between the predicted and achieved lenticule thickness (ΔLT) after small incision lenticule extraction (SMILE) surgery and investigate relationships between ΔLT and predicted lenticule thickness in SMILE.MethodsA total of 184 eyes from 184 consecutive patients who underwent SMILE were included in this prospective study. One eye for each patient was randomly selected and included for statistical analysis. To achieve emmetropia, nomogram adds 10% correction of spherical refractive. An ultrasound pachymetry measurement and Scheimpflug camera corneal topography were obtained before and at 3 months after SMILE. The achieved lenticule thickness was calculated by comparing the preoperative examinations with postoperative examinations using ultrasound pachymetry and Pentacam software measurements. The pupil center and corneal vertex were selected as the 2 locations for measurement calculation on Pentacam. Analysis of variance (ANOVA) was performed to compare mean pachymetry values using different instruments. Linear regression analyses were performed between the VisuMax readout lenticule thicknesses and the measured maximum corneal change, between ΔLT and predicted lenticule thickness.ResultsOn average, the achieved lenticule thickness measured with ultrasound pachymetry was 13.02 ± 8.87 μm thinner than the predicted lenticule thickness. The proportion of ΔLT in predicted values is 11.9% (ultrasound) and about 15% (Pentacam). Linear regression analysis showed significant relationships between the predicted and each achieved lenticule thickness. Each ΔLT was significantly related to predicted lenticule thickness (ultrasound: R2 = 0.242; pupil center from Pentacam: R2 = 0.230).ConclusionsAn overestimation of achieved lenticule thickness was evident in this study which may exclude eligible SMILE patient. Also, our results showed that 10% increase of spherical refractive correction in the nomogram is appropriate. Furthermore, clinicians should subtract 10% of the predicted lenticule thickness to calculate the residual corneal stroma bed thickness.

Difference in Central Corneal Thickness between Applanation Ultrasound and Oculus Wave � 152 Light Occulyzer II

Purpose: To determine the mean difference of central corneal thickness measurements by using ultrasound Pachymetry and oculus Wave light Occulyzer II. Study Design: Cross-sectional comparative study using non-probability consecutive sampling. Place and Duration of Study: This study was conducted at Department of Ophthalmology, Liaquat National Hospital Karachi from November 2018 to June 2019. Material &amp; Methods: After approval from ethical committee, patients were included in our study on the basis of inclusion &amp; exclusion criteria. Central corneal thickness measurements were taken by using ultrasound Pachymetry &amp; oculus Wave light Occulyzer II. All the data was collected by single researcher. The results were plotted, compared &amp; analyzed. Paired t-test was used for the comparison of quantitative variables. Results: There were 130 patients included in the study out of which 73 (56.2%) were males and 57 (43.8%) were females. Mean age of these patients was 33.9 � 8.9 years. The mean � SD thinnest oculus Wave light Occulyzer II measurement was 538.61 � 23.46 ?m and ranged between 476.0 and 619.0 ?m whereas the mean thinnest ultrasound Pachymetry measurement was 535.1 � 21.816 ?m and ranged between 482 and 601 ?m. There was highly significant correlation of central corneal thickness between both the instruments. (r = 0.96, p &lt; 0.001). Conclusion: There is a high correlation of central corneal thickness between the readings obtained from ultrasound and optical pachymetry machines therefore oculus Wave light Occulyzer II can be used as an alternative technique to ultrasound pachymetry while assessing CCT in clinical settings. Key Words: Central corneal thickness, Ultrasound Pachymetry, Optical Pachymetry.

Effect of Riboflavin Solution With Hydroxypropyl Methylcellulose and Eyelid Speculum on Pachymetry Changes During Accelerated Collagen Crosslinking.

To assess corneal thickness changes with isotonic riboflavin (RF) solution with hydroxylpropyl methylcellulose in patients undergoing accelerated corneal collagen crosslinking (CXL) with and without an eyelid speculum. Fifty-two eyes of 48 patients with progressive keratoconus were enrolled in this study. The patients in this study were divided into 2 groups: in group 1 an eyelid speculum was removed during 20-minute RF (0.1%) + hydroxylpropyl methylcellulose (Mediocross M; Avedro Inc, Waltham, MA) instillation, and in group 2 the eyelid speculum was retained in place during the entire CXL procedure. All patients underwent accelerated CXL using continuous ultraviolet-A (UVA) light exposure at 9 mW/cm for 10 minutes; total energy dose was 5.4 J/cm. Intraoperative ultrasound pachymetry measurements were obtained before and after epithelial removal, after RF loading, and after UVA light exposure at 5 and 10 minutes. The preoperative pachymetric measurements decreased in both groups after the removal of epithelium [group 1 (n = 26): -25 μm, group 2 (n = 26): -31 μm, P = 0.234]. Although the thinnest pachymetry significantly increased after soaking in both group 1 (52.26 μm) and group 2 (27.88 μm, P < 0.001), closure of the eyelids during RF instillation further increased the pachymetry readings (P < 0.0001). The corneal thickness remained stable in both groups during UVA irradiation at 5 and 10 minutes (P > 0.05). Closure of the eyelids further induces corneal swelling that may offer an advantage to improve safety of the procedure particularly in thin corneas.

Cornea and anterior eye assessment with placido-disc keratoscopy, slit scanning evaluation topography and scheimpflug imaging tomography.

Current corneal assessment technologies make the process of corneal evaluation extremely fast and simple and several devices and technologies allow to explore and to manage patients. The purpose of this special issue is to present and also to update in the evaluation of cornea and ocular surface and this second part, reviews a description of the corneal topography and tomography techniques, providing updated information of the clinical recommendations of these techniques in eye care practice. Placido-based topographers started an exciting anterior corneal surface analysis that allows the development of current corneal tomographers that provide a full three-dimensional reconstruction of the cornea including elevation, curvature, and pachymetry data of anterior and posterior corneal surfaces. Although, there is not an accepted reference standard technology for corneal topography description and it is not possible to determine which device produces the most accurate topographic measurements, placido-based topographers are a valuable technology to be used in primary eye care and corneal tomograhers expanding the possibilities to explore cornea and anterior eye facilitating diagnosis and follow-up in several situations, raising patient follow-up, and improving the knowledge regarding to the corneal anatomy. Main disadvantages of placido-based topographers include the absence of information about the posterior corneal surface and limited corneal surface coverage without data from the para-central and/or peripheral corneal surface. However, corneal tomographers show repeatable anterior and posterior corneal surfaces measurements, providing full corneal thickness data improving cornea, and anterior surface assessment. However, differences between devices suggest that they are not interchangeable in clinical practice.

Measurements of donor endothelial keratoplasty lenticules prepared from fresh donated whole eyes by using ultrasound and optical coherence tomography.

This study was conducted to analyze the profile and thickness of endothelial keratoplasty lenticules prepared from fresh donated whole eyes with Visante optical coherence tomography (V-OCT) compared to measurements obtained from ultrasound pachymetry (USP) at the Central Eye Bank of Iran. Microkeratome-assisted precut corneas were prepared for Descemet stripping automated endothelial keratoplasty by using standard eye bank protocol. Central posterior lenticule thickness (CPLT) on fresh whole eye, before excising corneoscleral disc and transferring to Optisol-GS, was measured by USP. V-OCT was used to measure central, paracentral, and midperipheral thicknesses of lenticules after transferring the tissue to Optisol-GS. Chi Square and Bonferroni tests were respectively used to uncover the differences between the USP and V-OCT measurements and also the thickness profile of lenticules. Postoperative reports for the entire transplanted lenticules were recorded. Accordingly, on evaluation of 312 enrolled precut corneas, CPLT measurements by V-OCT versus USP were statistically different (mean: 136µm vs 165µm, respectively; P=0.008). Thickness profile of the posterior lenticules revealed increased thickness from the central to the peripheral parts of the cornea (mean increase of 16µm at the pericentral and 64.2µm at the peripheral locations, respectively); however, the increase in the thickness was relatively symmetrical. Postoperative reports of transplanted lenticules were unremarkable, since there were no posterior flap detachments. In essence, V-OCT measurements of microkeratome-assisted precut lenticules prepared from fresh donated whole eyes averaged 29μm thinner than USP measurements and revealed a significant but symmetric increase of thickness towards the peripheral parts of the corneas. However, the variation in the thickness profile did not affect the attachment or the clarity of transplanted precut lenticlues.

Comment on: Intraocular pressure and anetrior segment anatomy after phacoemulsification surgery

Sir, We read the article, “The effect of phacoemulsification surgery on intraocular pressure and anterior segment anatomy of the patients with cataract and ocular hypertension.” by Cetinkaya et al. with a great interest.[1] The authors aimed to evaluate the effect of phacoemulsification surgery on intraocular pressure (IOP), anterior chamber depth (ACD), iridocorneal angle (ICA), and central corneal thickness (CCT) of the patients with cataract and ocular hypertension. They concluded that phacoemulsification surgery decreases IOP and increases ACD and ICA in the short-term, but in the long-term, it does not cause any significant changes. We congratulate the authors for their lightening study and would like to make some contributions and criticism about IOP, ICA, and CCT measurement methods and times of the measurements in the study. We know that CCT value is very important for the exact evaluation of many ophthalmologic diseases such as glaucoma, keratoconus, corneal dystrophy, and kerato-refractive surgery.[2,3,4] Ultrasound pachymetry (USP) is the most frequently used clinical technique and the gold standard of measuring CCT. However, placement of the probe on the corneal center is important and the perpendicularity of the probe in relation to the cornea is often difficult to ascertain. This is subjective and may cause operator-dependent errors due to off-center placement.[3] Usually, topical anesthesia is instilled before USP examination, and this could also induce bias. It is reported that topical anesthesia needed for USP may cause the cornea to swell and may give variations in CCT from −10 μm to +30 μm.[4] The results of the iridocorneal angle evaluation using Goldmann 3-mirror lens is also affected by examiner. We think that if measurements were performed by different examiners, this might be affected the results. The authors did not inform if all measurements were performed by the same examiner or not during 2 years study period. In addition, using the mean value of multiple USP measurements in a period for one person could reduce the risk of error. Another important factor which might be affected the results is a diurnal variation of the CCT and IOP. It is reported that there cornea swells during sleep upon eye opening and deswells about 2 h after eye opening. It is known that the mean circadian fluctuations of CCT are about 15 µm, and the circadian fluctuations may affect the IOP up to about 11 mmhg.[5] The authors also did not give any information about the time of the day during measurements. We think that if measurement were performed in different times of the day, this might be affected the results. We congratulate the authors and thanks for their understanding. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

Comparison of Gebauer SLc and Moria CBm Carriazo-Barraquer ALK Microkeratomes for Descemet’s Stripping Automated Endothelial Keratoplasty Preparation

ABSTRACTPurpose: We compared the hand-guided Moria Carriazo-Barraquer (CBm) microkeratome with the fully automatic SLc microkeratome for Descemet’s stripping automated endothelial keratoplasty (DSAEK)-lamella preparation and storage, vis-à-vis accuracy, endothelial cell loss (ECL), and lamellar surface roughness (LSR).Methods: A total of 18 human corneas were dissected with both the 300 μm CBm multi-use (n = 9) and the 300 µm SLc (n = 9) single-use heads, after which they were incubated for 6 d in a 5% dextran medium. Before preparation (0 h) and 1, 24, and 144 h after dissection, ECL and corneal thickness (CT) were measured by ultrasound pachymetry (USP) and optical coherence tomography (OCT). LSR was assessed by scanning electron microscopy (SEM) and evaluated by three masked observers.Results: Prior to cutting, CTs did not differ significantly between OCT or USP measurements, with a high correlation between the two modalities (r2 = 0.94, p < 0.0001). One hour after preparation the anterior lamella showed a significantly higher dissection depth with the CBm (429.4 ± 21.8 µm) than the SLc (311.7 ± 54.8 µm, p = 0.0006), with the variance of the SLc system showing a trend towards higher values (p = 0.07). Anterior and posterior lamellae swelled significantly in the subsequent culture period. Both groups showed a significant ECL 1 h after preparation (p < 0.0001) with no significant difference between the systems (1 h: p = 0.44; CBm: − 9.4%, SLc: −11.7%), which stabilized over 144 h (144 h CBm: −13.9%, 144 h SLc: −10.3%).LSR did not differ significantly between both systems (p = 0.60).Conclusions: The SLc system agrees more with the designated cutting depth than the CBm. The dissection produced a comparable LSR and a ∼10% ECL independently of the system. Further incubation of the prepared lamellae led to a swelling, but no further ECL.

Precision of corneal thickness measurements obtained using the scheimpflug-placido imaging and agreement with ultrasound pachymetry.

Purpose. To assess the reliability and comparability of measuring central corneal thickness (CCT) and thinnest corneal thickness (TCT) using a new Scheimpflug-Placido analyzer (TMS-5, Japan) and ultrasound (US) pachymetry. Methods. Seventy-six healthy subjects were prospectively measured 3 times by 1 operator using the TMS-5, 3 additional consecutive scans were performed by a second operator, and ultrasound (US) pachymetry measurements were taken. The test-retest repeatability (TRT), coefficient of variation (CoV), and intraclass correlation coefficient (ICC) were calculated to evaluate intraoperator repeatability and interoperator reproducibility. Agreement among the devices was assessed using Bland-Altman plots and 95% limits of agreement (LoA). Results. The intraoperators TRT and CoV were <19 μm and 2.0%, respectively. The interoperators TRT and CoV were <12 μm and 1.0%, respectively, and ICC was >0.90. The mean CCT and TCT measurements using the TMS-5 were 15.97 μm (95% LoA from −26.42 to −5.52 μm) and 20.32 μm (95% LoA from −30.67 to −9.97 μm) smaller, respectively, than those using US pachymetry. Conclusions. The TMS-5 shows good repeatability and reproducibility for measuring CCT and TCT in normal subjects but only moderate agreement with US pachymetry results. Caution is warranted before using these techniques interchangeably.

Comparison of Central Corneal Thickness Measurements Obtained by RTVue OCT, Lenstar, Sirius Topography, and Ultrasound Pachymetry in Healthy Subjects

ABSTRACTPurpose: To compare central corneal thickness (CCT) measurement results obtained by RTVue OCT, Lenstar, Sirius topography, and ultrasound pachymetry (UP) (OcuScan RxP Ophthalmic Ultrasound System, Alcon Laboratories) in healthy subjects. Materials and Methods: 256 eyes of 128 healthy subjects were included in the study. CCT measurements were obtained from the eyes for each subject using the UP, Lenstar, Sirius topography, and RTVue OCT instruments. Ultrasound pachymetry measurements were performed after the eyes were anesthetized with one drop of 0.5% proparacaine hydrochloride and were performed at the same day after 15 minutes after previous measurements. Results: Of 128 participants, 84 were male and 44 were female with a mean age of 33.15 ± 12.95 years (ranging from 18 to 75 years). The mean CCTs for UP, Lenstar, Sirius topography, and RTVue OCT were 535.60 ± 35.15 (440,00–668,00); 532.63 ± 34.44 (449,00–650,00); 526.05 ± 36.45 (314,00–640,00); 525.89 ± 33.21 (437,00–646,00) µm, respectively. The mean CCT measurements were statistically different among the three groups (p = 0.002). CCT measurements obtained using RTVue-OCT were significantly thinner than those obtained using UP (p = 0.009). Sirius CCT measurements were also thinner than UP (p = 0.011). Mean CCT measurements between UP and Lenstar were similar (p = 0.769). Measurements with Lenstar (r = 0.849), Sirius topography (r = 0.883), and RTVue OCT (0.949) were highly correlated with UP measurements. Conclusion: RTVue OCT and Sirius topography significantly underestimated the CCT compared with UP. Although highly correlated, the measurement values with these devices are not directly interchangeable in clinical practice.

Effect of the eyelid speculum on pachymetry during corneal collagen crosslinking in keratoconus patients

To compare central corneal thickness (CCT) with and without using an eyelid speculum during corneal collagen crosslinking (CXL). University Medical Center Utrecht, Utrecht, the Netherlands. Prospective nonrandomized comparative study. Eyes with progressive keratoconus were treated by CXL and consecutively divided into 2 groups. In Group A, an eyelid speculum remained in place throughout the entire CXL procedure. In Group B, the eyelids remained closed during the 30-minute riboflavin instillation. Intraoperative ultrasound pachymetry measurements were performed at different timepoints. The visual acuity, refraction, keratometry, pachymetry, and endothelium were evaluated 6 months after CXL. The main outcome measures were intraoperative CCT measurements and the clinical CXL effect after 6 months. Fifty-two eyes (50 patients) were treated. After riboflavin instillation, a statistically significant difference in CCT reduction was found between the 2 groups (P<.001), with a mean CCT decrease of 62 μm±53 (SD) (13%±11%) in Group A and 11±35 μm (2%±8%) in Group B. No statistically significant between-group differences were found after epithelial removal or ultraviolet-A (UVA) irradiation. Six months after CXL, no statistically significant between-group difference was found in the visual acuity, refraction, keratometry, pachymetry, or endothelium. Avoidance of an eyelid speculum during riboflavin instillation resulted in less CCT reduction during CXL. This finding could increase the chance of attaining the required pachymetry safety margin for applying UVA and thus decrease the chance of premature CXL treatment termination. No author has a financial or proprietary interest in any material or method mentioned.

Ocular findings in children with thalassemia major in Eastern Mediterranean.

To investigate ophthalmologic findings in children with thalassemia major (TM) and compare the findings with healthy controls. In a cross-sectional study, 43 children with thalassemia major from pediatric hematology outpatient clinics from two university hospitals and age/sex matched 47 healthy children were included in the study. After a complete ophthalmic examination, tear function tests including the Schirmer test, fluorescein tear break-up time (BUT), ultrasound pachymetry, and axial length measurement were performed. Obtained data was recorded for statistical analysis and the values of right eyes were compared between groups. The mean best corrected visual acuity was 1.34±0.75 in TM and 1.08±0.28 in controls. It was found lower than 0.1 logMAR unit in 10 (23.2%) children with TM and 2 (4.2%) in controls, and the difference was statistically significant (P<0.05). The mean central corneal thickness was 540±26.95 in children with TM and 536.98±20.45µm in controls (P>0.05). The mean axial length was 22.53±0.50 in TM and 22.57±0.43mm in the control group. The mean Schirmer test score was 19.94±6.91 in TM and 24.22±3.95mm in the control group (P<0.01). The mean BUT score was 9.62±1.28 in TM and 9.73±0.6s in the control group (P>0.05). In TM, while corneal thickness, axial length, and BUT are close to controls, the Schirmer scores are less than normal. The study revealed that TM may be affected by the tear function and visual acuity.

Evaluation of corneal thickness using a Scheimpflug–Placido disk corneal analyzer and comparison with ultrasound pachymetry in eyes after laser in situ keratomileusis

To evaluate the repeatability and reproducibility of corneal thickness measurements in post-laser in situ keratomileusis (LASIK) eyes using a rotating Scheimpflug camera combined with a Placido disk corneal topographer (Sirius) and compare the results with those of ultrasound (US) pachymetry. Eye Hospital of Wenzhou Medical College, Wenzhou, China. Comparative evaluation of a diagnostic test or technology. Patients were examined 3 times with the Scheimpflug-Placido topographer by 2 examiners. The central pupil corneal thickness (CTpupil), apical corneal thickness (CTapex), and thinnest corneal thickness (CTthinnest) were recorded. After noncontact examinations, US pachymetry was used to obtain the central corneal thickness (CCT). The Scheimpflug-Placido topographer showed high intraoperator repeatability as indicated by a test-retest repeatability of less than 8.5 μm for CTpupil, CTapex, and CTthinnest, The coefficients of variation (CoV) were less than 0.7%, and the intraclass correlation coefficient was higher than 0.99. Excellent results were also obtained for interoperator reproducibility. All CoVs were less than 0.5%. The 95% limits of agreement between the Scheimpflug-Placido measurement and the US pachymetry measurements were narrow (-16.62 to 12.44 μm for CTpupil versus US pachymetry CCT; -17.49 to 12.16 μm for CTapex versus US pachymetry CCT; -18.59 to 10.90 μm for CTthinnest versus US pachymetry CCT). The Scheimpflug-Placido topographer showed excellent intraoperator repeatability and interoperator reproducibility of CTpupil, CTapex, and CTthinnest measurements in post-LASIK eyes. The CCT measurements obtained using the device were in high agreement with those obtained by US pachymetry, suggesting that the 2 devices are interchangeable. No author has a financial or proprietary interest in any material or method mentioned.

Precision of a new Scheimpflug and Placido-disk analyzer in measuring corneal thickness and agreement with ultrasound pachymetry

To assess the precision of corneal thickness measurements obtained by a new Scheimpflug camera combined with Placido-disk corneal topography (Sirius) and compare the measured values with those obtained by ultrasound (US) pachymetry. Eye Hospital of Wenzhou Medical College, Wenzhou, China. Comparative evaluation of a diagnostic test or technology. Eyes of healthy subjects were examined with the Scheimpflug-Placido topographer. Central (CCT) and thinnest (TCT) corneal thickness were recorded after 3 consecutive measurements. For US pachymetry, only CCT was measured. Measurements were repeated within 1 week. The within-subject standard deviation (S(w)), test-retest repeatability, coefficient of variation (CoV), and intraclass correlation coefficient (ICC) were calculated to evaluate intrasession repeatability and intersession reproducibility. Interdevice comparison was analyzed with paired t tests and Bland-Altman plots. The intrasession repeatability of Scheimpflug-Placido measurements was high, with test-retest and CoV close to 9 μm and 0.6% for CCT and TCT, respectively. The intersession test-retest and CoV were close to 10 μm and 0.7%, respectively. The ICC was higher than 0.98 for repeatability and reproducibility. High agreement was found between Scheimpflug-Placido and US pachymetry measurements, with narrow 95% limits of agreement. The Scheimpflug-Placido instrument showed excellent intrasession repeatability and intersession reproducibility of CCT and TCT measurements in healthy eyes. High agreement and lack of statistically significant difference suggest that the instrument's TCT and the US pachymetry-CCT measurements can be used interchangeably in subjects with normal corneal thickness. No author has a financial or proprietary interest in any material or method mentioned.

Corneal Thickness Measurement Using Orbscan, Pentacam, Galilei, and Ultrasound in Normal and Post-Femtosecond Laser In Situ Keratomileusis Eyes

To compare corneal pachymetry assessment using slit scanning imaging (Orbscan), rotating Scheimpflug imaging (Pentacam), dual Scheimpflug system (Galilei), and ultrasound pachymetry in normal and post-femtosecond (FS) laser in situ keratomileusis (LASIK) eyes. Sixty eyes of 60 patients were enrolled for this study, which consisted of 30 unoperated eyes (normal corneas) and 30 eyes after FS-LASIK (post-LASIK corneas). Central corneal thickness was measured sequentially using Orbscan II, Pentacam, Galilei, and ultrasound pachymetry, and the average value of measurements obtained by the 4 different methods were compared in each group. In normal corneas, corneal thickness measurements were not different by all 4 methods [P = 0.202, 1-way analysis of variance (ANOVA)]. In post-LASIK corneas, the measurement was significantly different among those achieved by 4 methods (P < 0.001, 1-way ANOVA). Orbscan measurement was thinner than those yielded by Galilei, Pentacam, or ultrasound pachymetry with average of 47.7, 38.5, and 34.4 μm, respectively (all P values < 0.001, 1-way ANOVA and the Tukey multiple comparisons test) in post-LASIK corneas. Orbscan, Pentacam, and Galilei measurements showed good agreement with ultrasound pachymetry data in both groups, except Orbscan data in post-LASIK corneas showed a statistically significant difference from ultrasound pachymetry measurements (P value = 0.001, 1-way ANOVA and the Tukey multiple comparisons test). Any of central corneal thicknesses obtained by all 4 measurement modalities might be acceptable before refractive surgery. However, in post-FS-LASIK eyes, measurements using Orbscan were thinner than those obtained with other modalities; in contrast, those with Pentacam or Galilei were comparable with ultrasound pachymetry.

Analysis of Microkeratome Thin Flap Architecture Using Fourier-domain Optical Coherence Tomography

To assess the corneal architecture and reproducibility of LASIK flap thickness created by the Amadeus II mechanical microkeratome (Ziemer Ophthalmic Systems AG) using Fourier-domain optical coherence tomography (OCT; Optovue Inc). Anterior segment Fourier-domain OCT was used to analyze the morphology of 58 LASIK flaps from 30 patients created with the Amadeus II microkeratome 140-μm head and ML7090CLB blades (Med-Logics Inc) at 2 weeks postoperatively. Flap thickness was assessed at 10 points across the central 6 mm of the cornea (horizontal and vertical meridians). Postoperative central corneal flap thickness measured by Fourier-domain OCT was compared with intraoperative ultrasound pachymetry measurements. No significant difference was noted between central flap thickness measured by intraoperative pachymetry (107.2 ± 14 μm) and postoperative OCT (111.7 ± 11 μm; P=.07, correlation coefficient=0.86). Fourier-domain OCT measurements demonstrated functionally planar flap architecture (standard deviation [SD] of thickness across the flap=4.9 μm, SD range across the flap=2 to 9 μm) for the microkeratome flaps. The Amadeus II microkeratome with Med-Logics blades created thin, reproducible, functionally planar flaps as measured by Fourier-domain OCT. Central flap thickness measured by intraoperative ultrasound pachymetry was equivalent to that measured 2 weeks postoperatively by OCT.

A Comprehensive Comparison of Central Corneal Thickness Measurement

To assess the repeatability and reproducibility of central corneal thickness (CCT) measurements by high-resolution rotating Scheimpflug imaging (Pentacam, Oculus) and Fourier-domain optical coherence tomography (RTvue-100, Optovue) after laser in situ keratomileusis (LASIK) and to compare the agreement with ultrasound pachymetry (USP). Forty-seven eyes of 47 patients after LASIK were included in the study. The first examiner took two successive Pentacam and RTvue CCT measurements, and this was repeated once again by the second examiner to assess intraobserver and interobserver repeatability and reproducibility. After performing non-contact examinations, the corneas were measured by USP to compare the level of agreement among the three devices. All Pentacamcenter, Pentacamapex, Pentacamthinnest, and RTvue CCT measurements demonstrated high intraobserver repeatability, with respective precision (1.96 within-subject standard deviation) and intraclass correlation coefficients of 7.52, 7.43, 7.55, and 3.81 μm and 0.985, 0.986, 0.986, and 0.997; interobserver repeatability results were similar. All coefficients of variation were low: <1% for all measures. Compared with Pentacam and USP measurements, the RTvue measurement significantly underestimated CCT by a mean of 10.52 to 15.28 μm (p < 0.001) and 9.17 μm (p < 0.001), respectively. The agreement of USP with Pentacam and RTvue by Bland-Altman analysis spanned over 30 μm. The agreement of Pentacam with RTvue spanned approximate 20 μm. Both Pentacam imaging and RTvue Fourier-domain optical coherence tomography provide reliable and interchangeable measurement of CCT in post-LASIK corneas. However, they cannot be considered to be clinically interchangeable with USP.

Visante™ OCT Measurement of Central Corneal Thickness Following Descemet’s Stripping Endothelial Keratoplasty

A 63-year-old man with Fuchs’ dystrophy and cataract underwent successful phacoemulsification, insertion of a posterior chamber intraocular lens, and Descemet’s stripping endothelial keratoplasty (DSEK) of the right eye. At 1-month follow-up, measurement of central corneal thickness (CCT) obtained by ultrasound pachymetry was 549 μm. The ultrasound pachymetry measurement was thought to be an artifact, so anterior segment optical coherence tomography analysis of the right eye was performed. Both host and graft tissue were imaged in cross-section; optical coherence tomography measurement of CCT was 769 μm. Reliable measurements of CCT are clinically important following DSEK. This case demonstrates that anterior segment optical coherence tomography imaging and analysis software may provide a more appropriate measurement of CCT in patients who have undergone DSEK.