Comparison of corneal thickness in patients with dry eye disease using the Pentacam rotating Scheimpflug camera and anterior segment optical coherence tomography.

The purpose of this study was to compare central corneal thickness, thinnest corneal thickness, and the thinnest point of the cornea between Pentacam and anterior segment optical coherence tomography (ASOCT) in patients with dry eye disease (DED). This cross-sectional study included 195 participants between November 2015-June 2017. DED was diagnosed using the Asia Dry Eye Society criteria and further divided into mild and severe DED based on kerato-conjunctival vital staining. Central corneal thickness, thinnest corneal thickness, and the thinnest point of the cornea measured by Pentacam and ASOCT were compared, and Pearson's correlation coefficients were estimated. The differences in central corneal thickness and the thinnest corneal thickness between Pentacam and ASOCT were analysed using Bland-Altman and multivariate regression analyses adjusted for age and sex. This study included 70 non-DED subjects and 52 patients with mild and 73 with severe DED. The Pentacam and ASOCT measurements of central corneal thickness and thinnest corneal thickness were strongly correlated, but the respective values were higher when measured with Pentacam. The Bland-Altman analysis revealed differences in central corneal thickness (non DED, 11.8; mild DED, 13.2; severe DED, 19.6) and in thinnest corneal thickness (non DED, 13.1; mild DED, 13.4; severe DED, 20.7). After adjusting for age and sex, the differences in central corneal thickness (ß = 7.029 µm, 95%CI 2.528-11.530) and thinnest corneal thickness (ß = 6.958 µm, 95%CI 0.037-13.879) were significantly increased in the severe-DED group. The distribution of the thinnest point of the cornea in the cornea's inferior temporal quadrant between Pentacam and ASOCT deviated in severe DED (Pentacam: 90.4% vs. ASOCT: 83.6%). Clinicians should consider that there were significant differences in corneal-morphology assessment between the measurements with Pentacam and ASOCT in severe DED.

Keratoconus: The ABCD Grading System.

PURPOSE: To propose a new keratoconus classification/staging system that utilises current tomographic data and better reflects the anatomical and functional changes seen in keratoconus. METHOD: A previously published normative database was reanalysed to generate both anterior and posterior average radii of curvature (ARC and PRC) taken from a 3.0 mm optical zone centred on the thinnest point of the cornea. Mean and standard deviations were recorded and anterior data were compared to the existing Amsler-Krumeich (AK) Classification. ARC, PRC, thinnest pachymetry and distance visual acuity were then used to construct a keratoconus classification. RESULTS: 672 eyes of 336 patients were analysed. Anterior and posterior values were 7.65 ± 0.236 mm and 6.26 ± 0.214 mm, respectively, and thinnest pachymetry values were 534.2 ± 30.36 µm. The ARC values were 2.63, 5.47 and 6.44 standard deviations from the mean values of stages 1-3 in the AK classification, respectively. PRC staging uses the same standard deviation gates. The pachymetric values differed by 4.42 and 7.72 standard deviations for stages 2 and 3, respectively. CONCLUSION: A new keratoconus staging incorporates anterior and posterior curvature, thinnest pachymetric values, and distance visual acuity and consists of stages 0-4 (5 stages). The proposed system closely matches the existing AK classification stages 1-4 on anterior curvature. As it incorporates posterior curvature and thickness measurements based on the thinnest point, rather than apical measurements, the new staging system better reflects the anatomical changes seen in keratoconus.

Reliability of Pentacam HR Thickness Maps of the Entire Cornea in Normal, Post-Laser In Situ Keratomileusis, and Keratoconus Eyes.

PURPOSE: To measure the repeatability and reproducibility of Pentacam HR system thickness maps for the entire cornea in normal, post-laser in situ keratomileusis (post-LASIK), and keratoconus (KC) eyes. DESIGN: Reliability study. METHODS: Sixty normal subjects (60 eyes), 30 post-LASIK subjects (60 eyes), and 14 KC patients (27 eyes) were imaged with the Pentacam HR system by 2 well-trained operators. For pachymetry the cornea was divided into 4 zones: a central zone (2-mm diameter) and concentric pericentral zone (2-5 mm), transitional zone (5-7 mm), and peripheral zone (7-10 mm). The 3 concentric zones were subdivided into 8 sectors. Intraobserver repeatability and interobserver reproducibility of entire corneal thickness maps were tested by the repeatability and reproducibility coefficients, intraclass correlation coefficients, coefficient of variation, and 95% limits of agreement. RESULTS: From central to peripheral zones, the precision of corneal thickness measurements became gradually smaller. Central zone repeatability and reproducibility were the best in the normal, post-LASIK, and KC groups. The peripheral superior sectors showed poorer repeatability and reproducibility for all subjects. The intraobserver repeatability and interobserver reproducibility for all zones were ≤19.3 µm, ≤22.1 µm, and ≤20.7 µm, in the normal, post-LASIK, and KC groups, respectively. The intraobserver and interobserver coefficients of variation for all zones were ≤1.3%, ≤1.6%, and ≤1.6% for all 3 groups. CONCLUSIONS: Pentacam HR system pachymetry of the entire cornea provided good precision in normal, post-LASIK, and KC corneas. Thickness measurements in the peripheral cornea should be interpreted with caution in abnormal corneas after surgery or with diseases.

Accuracy of optical coherence tomography (OCT) in pachymetry for glaucoma patients.

BACKGROUND: Central corneal thickness (CCT) measurement has become an important test in the diagnosis and management of glaucoma. Currently, ultrasound corneal thickness measurement (pachymetry) is the most frequently used clinical technique and the gold standard to assess CCT. Newer instruments are currently available including the optical coherence tomography (OCT) instrument. The aim of the present study was therefore to evaluate the accuracy of the CCT measurements performed by three different observers, both with the OCT and ultrasound pachymetry (USP), in patients suffering from glaucoma. METHODS: Patients who had been previously diagnosed with glaucoma participated in this cross-sectional study. Glaucoma was defined as patients who had at least two repeatable Humphrey visual fields showing glaucoma damage using the software 24-2, and with the optic nerve showing typical glaucoma damage. The patients CCTs were measured with OCT and USP by three different examiners. RESULTS: Seventy eyes of 35 patients were included. The average age was 74 ± standard deviation (SD) 10.88, the average pachymetry value with OCT was 536 ± 29 µm, and the average pachymetry with USP was 532 ± 32 µm. The differences between OCT and USP were not significant (t-test, p = 0.32). The intraclass correlation coefficients were, for OCT, 0.99 [confidence interval (CI): 0.98-0.996], and for USP, 0.97 (CI: 0.95-0.98). CONCLUSIONS: Agreement among the three observers using OCT or USP for pachymetry measurements was good. OCT might be used as an alternative method for pachymetry in glaucoma patients.

Repeatability of Pentacam peripheral corneal thickness measurements.

PURPOSE: To assess the repeatability of corneal thickness (CT) measurements, along the horizontal meridian up to 5mm from centre, in healthy eyes with the Pentacam instrument. METHODS: CT was measured in 82 right eyes (82 healthy subjects) at 11 corneal locations nominally 1mm apart along the horizontal meridian with Scheimpflug topography Pentacam. Two consecutive scans were performed in quick succession. The repeatability of CT was determined by assessing differences between measurements and calculating the coefficient of variation (CV). The relative repeatability (difference) was calculated as the ratio of the absolute peripheral CT difference to the central thickness. A variant of Bland-Altman analysis was carried out to determine the effect of the overall magnitude of CT on the absolute and relative differences. RESULTS: Mean CT (µm) at the temporal 5mm location was 770 ± 51 and 823 ± 56 µm at the corresponding nasal location; central CT was 554 ± 36 µm. Good repeatability (CV < 1.2%) was found at all corneal locations. Differences (arithmetic; absolute and relative) were 3 ± 17 µm; 13 ± 11 µm; 2 ± 2%; respectively temporally and -1 ± 15 µm; 13 ± 8 µm; 2 ± 1% nasally, both at 5mm from the corneal apex. These values decreased for central CT (0 ± 6 µm; 4 ± 4 µm; 1 ± 1%). Differences between both measurements in all corneal locations were not statistically significant (p = 0.308 ANOVA Games-Howell). CONCLUSIONS: Pentacam shows good repeatability for pachymetry measurements up to 5 mm away from the corneal apex across the horizontal meridian, even though repeatability decreases slightly towards the periphery. A single Pentacam scan will be sufficient for most clinical applications.

Estudio comparativo en queratoplastia para queratocono entre las técnicas lamelar profunda de Anwar (big bubble) y penetrante procedente de conversión / Comparative study of keratoconus between Anwar's deep anterior lamellar keratoplasty versus converted penetrating keratoplasty

OBJETIVO: El propósito de este grupo de estudio fue comparar los resultados entre los procedimientos de queratoplastia lamelar profunda anterior (deep anterior lamellar keratoplasty [DALK]) y queratoplastia penetrante (penetrating keratoplasty [PK]) en pacientes con queratocono. DISEÑO: Estudio de cohorte retrospectivo. MÉTODO: Se analizaron los resultados de 90 DALK y 49 PK procedentes de reconversión en pacientes con queratocono. Todos los procedimientos fueron realizados por el mismo cirujano (R.D.) desde 2006 hasta 2011. Entre ambos grupos se comparó la agudeza visual a distancia corregida (AVCC), el astigmatismo, el tiempo de la primera refracción, la paquimetría, el recuento de células endoteliales y las complicaciones postoperatorias. RESULTADOS: La media de edad fue de 28,2 años para DALK y de 31,7 años para PK (p = 0,17). El seguimiento medio fue de 14,7 meses para DALK y 19,4 meses para PK (p = 0,13). No hubo diferencia significativa alguna entre los grupos de PK y DALK en la media postoperatoria de AVCC (LogMAR) (0,17 frente a 0,17; p = 0,59), astigmatismo refractivo (-3,19 frente a -3,01 dioptrías; p = 0,65) ni en el tiempo de la primera refracción subjetiva (60,5 frente a 68 días; p = 0,50). Las principales complicaciones postoperatorias fueron 8% de rechazo endotelial en el grupo PK y 10% de vascularización de la interfaz en el grupo DALK. CONCLUSIONES: La única diferencia entre ambos grupos fue la neovascularización estromal profunda en DALK y el rechazo endotelial en PK, por lo que el procedimiento DALK debe ser considerado como primera opción en el tratamiento de pacientes con queratocono

OBJECTIVE: To compare outcomes between penetrating keratoplasty (PK) and deep anterior lamellar keratoplasty (DALK) in patients with keratoconus. DESIGN: Retrospective cohort study. METHODS: Data of 90 DALK and 49 procedures from conversion to PK, performed by a single surgeon (R.D.) from 2006 to 2011 were analysed. Outcomes on corrected distance visual acuity (BCVA), astigmatism, time to first refraction, pachymetry, endothelial count cell, and postoperative complications were compared between these groups. RESULTS: The mean age of the patients who underwent DALK and PK was 28.2 and 31.7 years, respectively (P=.17). The mean follow up for DALK and for the PK group was 14.7 and 19.4 months, respectively (P=.13). There was no significant difference between PK and DALK groups in the mean postoperative for: BCVA (LogMAR) (0.17 vs. 0.17; P=.59); refractive astigmatism (-3.19 vs.-3.01 diopters; P=.65), and time for the first subjective refraction (60.5 versus 68 days; P=.50). Main postoperative complications were 8% of endothelial rejection in PK group and 10% of deep stromal vascularization in DALK group. CONCLUSIONS: The only differences in postoperative results between groups were stromal neovascularization in DALK group and endothelial rejection in PK group. DALK should be considered as the first option when keratoplasty is indicated in keratoconus

Age-related changes in central corneal thickness in normal eyes among the adult Lithuanian population.

BACKGROUND: The purpose of this study was to estimate mean central corneal thickness (CCT) and determine whether there are any correlations between CCT, age, and sex in the adult Lithuanian population. METHODS: A total of 1,650 Caucasians of Lithuanian origin (aged 18-89 years) comprising 688 (41.7%) men and 962 (58.3%) women were examined. Subjects were stratified by age into seven groups. CCT was measured using ultrasonic pachymetry. Correlations between CCT, age, and sex were sought. RESULTS: Mean (± standard deviation) CCT for both eyes was 544.6±30.5 µm. Mean CCT was 545.2±30.5 µm in the left eye and 544.6±30.5 µm in the right eye, and was 545.0±25.6 µm in men and 544.4±33.5 µm in women. Mean CCT was 550.8±35.7 µm in subjects aged 18-29 years, 557.5±27.6 µm in those aged 30-39 years, 551.3±31.4 µm in those aged 50-59 years, 544.0±31.4 µm in those aged 50-59 years, 544.2±31.6 µm in those aged 60-79 years, 535.1±27.8 µm in those aged 70-79 years, and 530.1±16.8 µm in those aged 80-89 years. No statistically significant difference in CCT was found between the sexes (P>0.05). However, there was a significant difference in subjects aged 18-29 years; men had higher CCT than women (P<0.05). A statistically significant negative correlation was found between CCT and age (r=-0.263, P<0.05) that was stronger in men (r=-0.406, P<0.05) than in women (r=-0.118, P<0.05). CONCLUSION: The mean CCT in adult Lithuanians was 544.6±30.5 µm, of the left eye 545.2±30.5 µm and of the right - 544.6±30.5 µm. CCT of the right eye was equal to the CCT of both eyes. Mean CCT was 545.0±25.6 µm in men and 544.4±33.5 µm in women. Young men tended to have higher CCT than women. CCT decreases over the lifetime, meaning that older people have thinner corneas. CCT's dependence on age is stronger in men.

A spectral-domain optical coherence tomography device provides reliable corneal pachymetry measurements in canine eyes.

The objective of this study was to determine central corneal thickness (CCT) and the intra- and interuser reliability using a portable spectral-domain optical coherence tomography (SD-OCT) device in canine eyes. Twenty clinically normal dogs were examined. CCT measurements were obtained from both eyes of each animal three times by two operators in succession. The CCT was automatically calculated using the pachymetry software generated from eight radial scans, 6 mm in length. Mean canine CCT was 606.83±39.45 µm for all eyes examined. There was no significant difference in CCT based on the eye examined (OD vs OS), age or gender of the animal. There was no significant difference in CCT between replicates performed by the same operator; however, a small but significant difference was noted in CCT between operators. The mean difference in CCT between operators was 1.9 µm (P=0.03). The coefficient of variation for each user and between users was very low (range 0.64-1.7 per cent). The intraclass correlation coefficient comparing operators was 0.975. Based on these results, the SD-OCT device evaluated is capable of obtaining precise CCT measurements with excellent intra- and interoperator reliability in canine eyes.

Intraobserver reliability of contact pachymetry in children.

BACKGROUND: Central corneal thickness (CCT) is an important measurement in the treatment and management of pediatric glaucoma and potentially of refractive error, but data regarding reliability of CCT measurement in children are limited. The purpose of this study was to evaluate the reliability of CCT measurement with the use of handheld contact pachymetry in children. METHODS: We conducted a multicenter intraobserver test-retest reliability study of more than 3,400 healthy eyes in children aged from newborn to 17 years by using a handheld contact pachymeter (Pachmate DGH55; DGH Technology Inc, Exton, PA) in 2 clinical settings--with the use of topical anesthesia in the office and with the patient under general anesthesia in a surgical facility. RESULTS: The overall standard error of measurement, including only measurements with standard deviation ≤5 µm, was 8 µm; the corresponding coefficient of repeatability, or limits within which 95% of test-retest differences fell, was ±22.3 µm. However, standard error of measurement increased as CCT increased, from 6.8 µm for CCT less than 525 µm, to 12.9 µm for CCT 625 µm and greater. The standard error of measurement including measurements with standard deviation >5 µm was 10.5 µm. Age, sex, race/ethnicity group, and examination setting did not influence the magnitude of test-retest differences. CONCLUSIONS: CCT measurement reliability in children via the Pachmate DGH55 handheld contact pachymeter is similar to that reported for adults. Because thicker CCT measurements are less reliable than thinner measurements, a second measure may be helpful when the first exceeds 575 µm. Reliability is also improved by disregarding measurements with instrument-reported standard deviations >5 µm.

Corneal thickness and volume measurements by swept source anterior segment optical coherence tomography in normal subjects.

PURPOSE: To evaluate central corneal thickness (CCT) and corneal volume (CV) in healthy eyes using swept source anterior segment optical coherence tomography (SS-AS-OCT) and other devices. METHODS: Thirty-three healthy right eyes of 33 subjects were investigated. CCT was measured with SS-AS-OCT, rotating Scheimpflug camera, ultrasonic pachymetry and specular microscopy. CV was determined within a diameter of 10 mm at the center using SS-AS-OCT and Scheimpflug camera. RESULTS: Mean CCT was 523.5 ± 25.2 µm by SS-AS-OCT, 523.9 ± 26.1 µm by Scheimpflug camera, 532.1 ± 26.6 µm by ultrasonic pachymetry, and 525.5 ± 33.5 µm by specular microscopy. The CCTs measured with SS-AS-OCT, Scheimpflug camera and specular microscopy were significantly thinner than those measured with ultrasonic pachymeter (p < 0.001). The mean CV within a diameter of 10 mm at the center was 57.2 ± 3.0 mm(3) by SS-AS-OCT and 59.4 ± 2.9 mm(3) by Scheimpflug camera. Scheimpflug measurements of CV were statistically larger than SS-AS-OCT measurements (p = 0.0008). Statistically significant correlation was found between the CCT and CV measurements of each imaging devices (p < 0.0001, r = 0.527, and p < 0.0001, r = 0.749, respectively). CONCLUSION: SS-AS-OCT enables the measurements of CCT and CV, demonstrating agreement with other devices. CV in addition to CCT measurement may serve as a practical parameter of the corneal endothelial pump function.

Improving interobserver variation in corneal sublayer pachymetry using ConfoScan4 with z ring.

OBJECTIVES: To observe and improve the interobserver variation of corneal sublayer pachymetry using ConfoScan4 (CS4) z ring. METHODS: Right corneas of 34 normal subjects were scanned using CS4 (z ring) (Nidek Technologies, Padova, Italy). Corneal sublayer pachymetry was performed by two masked observers based on the written frame selection criteria from literature. The full stromal thickness (FST), epithelial and Bowman layer thickness (Epi+BT), endothelial thickness (EndoT), and total corneal thickness (CT) were obtained. Upon completion of the measurements (measurement 1), the frame selection criteria were reviewed between the observers by going through some corneal frames together. Eight subjects were excluded and corneal sublayer pachymetry was re-evaluated by the two observers using the revised criteria (measurement 2). RESULTS: Corneal thickness showed significant interobserver difference in measurement 1 (n=34), but no significant difference in measurement 2 (n=26). Endothelial thickness remained significant difference between observers throughout the study. Interobserver difference significantly reduced using the revised criteria in CT (1.93 ± 3.23 µm to 0.28 ± 1.75 µm) and EndoT (4.01 ± 4.82 µm to 0.86 ± 1.81µm). There was no significant difference between observers in Epi+BT and FST for the two measurements. Interobserver variation and the 95% confidence limits between observers for CT and corneal sublayers were reduced at least by half in measurement 2. CONCLUSIONS: The interobserver variation in corneal sublayer pachymetry could be improved by having the observers going through some corneal frames together rather than just following the written criteria. The use of CS4 (z ring) to measure CT, FST, and Epi+BT is suitable for monitoring corneal changes clinically.