Impact Of Central Corneal Thickness Research Articles

The correlation between the intraocular pressure, central corneal thickness, and signalment of the horse

The impact of central corneal thickness (CCT) on intraocular pressure (IOP) has been demonstrated in humans and various animal species but not yet in horses. The current study investigated the relationship between IOP and CCT in horses of different ages, sex, breed, and body weights using tonometry and pachymetry. Ninety-seven horses without ocular disease were examined at the Equine Clinic of the University of Veterinary Sciences Brno, Czech Republic, between 2019 and 2020. A complete ophthalmological examination was performed, including direct ophthalmoscopy and slit-lamp biomicroscopy, to include only horses with healthy eyes in the study. The central corneal thickness was measured with a pachymeter, and the IOP was measured with a tonometer. The effects of sex, age, breed, and horse weight on IOP and CCT were analysed. Measurements of IOP and CCT were acquired in all 97 horses. There was a significant correlation between CCT and age and weight in both eyes. Older and heavier individuals had high CCT values. Mares had lower IOP mean values compared to geldings and stallions. No correlation was found between IOP and CCT of the same eye. This study confirmed a relationship between individual variables such as age and weight on CCT, and sex on IOP. Based on this report, CCT should be considered a minor indicator when interpreting IOP values in healthy horses. Nevertheless, age and weight are essential constraints when interpreting CCT values and sex on IOP values in horses.

Uticaj centralne debljine rožnjače na vrednosti intraokularno pritiska izmerenog dvema metodama - Goldmanovom aplanacionom i dinamičkom konturnom tonometrijom kod ispitanika sa dijagnozom primarnog glaukoma otvorenog ugla

Uticaj centralne debljine rožnjače na vrednosti intraokularno pritiska izmerenog dvema metodama - Goldmanovom aplanacionom i dinamičkom konturnom tonometrijom kod ispitanika sa dijagnozom primarnog glaukoma otvorenog ugla

Impact of corneal parameters on intraocular pressure measurements in different tonometry methods

To evaluate the impact of central corneal thickness (CCT) and corneal curvature on intraocular pressure (IOP) measurements performed by three different tonometers. IOP in 132 healthy eyes of 66 participants was measured using three different tonometry techniques: Goldmann applanation tonometer (GAT), Pascal dynamic contour tonometer (DCT), and ICare rebound tonometer (RT). CCT and corneal curvature were assessed. In healthy eyes, DCT presents significantly higher values of IOP than GAT (17.34±3.69 and 15.27±4.06 mm Hg, P<0.0001). RT measurements are significantly lower than GAT (13.56±4.33 mm Hg, P<0.0001). Compared with GAT, DCT presented on average 2.51 mm Hg higher values in eyes with CCT<600 µm and 0.99 mm Hg higher results in eyes with CCT≥600 µm. The RT results were lower on average by 1.61 and 1.95 mm Hg than those obtained by GAT, respectively. Positive correlations between CCT in eyes with CCT<600 µm were detected for all IOP measurement techniques, whereas a similar relationship was not observed in eyes with thicker corneas. A correlation between IOP values and keratometry in the group with CCT<600 µm was not detected with any of the tonometry methods. In thicker corneas, a positive correlation was found for GAT and mean keratometry values (R=0.369, P=0.005). The same method should always be chosen for routine IOP control, and measurements obtained by different methods cannot be compared. All analysed tonometry methods are dependent on CCT; thus, CCT should be taken into consideration for both diagnostics and monitoring.

Comparison of the ICare rebound tonometer with goldmann applanation tonometer in refractive errors among patients attending tertiary eye centre in North East India

Objective: To measure intraocular pressure (IOP) in patients with refractive errors and compare variations by means of ICare Rebound Tonometer (RT) and Goldmann Applanation Tonometer (GAT) and to also study the impact of central corneal thickness (CCT) on IOP measurements by these techniques. Materials and Methods: A total of 182 eyes from 182 subjects were included in this prospective cross sectional study. They were grouped as emmetropia (n=101), hypermetropia (n=11), low myopia (n=43) and high myopia (n=27). Each group underwent IOP measurements first by RT followed by GAT. CCT was assessed by ultrasound pachymetry. Subject preference for the method of IOP measurement was also assessed. Results: In all four groups, RT detected higher IOP readings than the GAT, significantly more in high myopia (RT-GAT=1.612.88mmHg, p=0.002) and low myopia (RT-GAT=1.162.72mmHg, p=0.004) as compared to emmetropia (RT-GAT =0.963.27mmHg, p=9.450) and hypermetropia (RT-GAT= 0.233.38 mmHg, p=0.398). CCT also showed positive relationship with RT especially in hypermetropia and emmetropia, the overestimation of IOP by 4.63mmHg (p=0.225) and 4.28mmHg (p=0.001) respectively. On the other hand the GAT underestimates IOP in thicker cornea. 52.75% patients preferred GAT as a measuring tool to RT (43.96%). Conclusions: IOP measurements by RT are overestimated as compared to GAT in both low and high myopia. CCT also has a positive relationship on the IOP measurements by RT. The GAT is therefore still the gold standard for IOP measurement but we cannot rule out the RT as a useful screening tool especially when we want to consider screening patients in peripheral care centres. Keywords: Goldmann applanation Tonometer, ICare rebound tonometer, Intraocular pressure, Refractive errors.

Impact of diurnal IOP variations on the dynamic corneal hysteresis measured with air-puff swept-source OCT

The deformation amplitudes measured with air-puff OCT are sensitive to both (intraocular pressure) IOP and biomechanical properties of the cornea. Analysis of the amplitudes of corneal deformation is challenging due to interrelation of IOP and corneal biomechanics. In this study, we used natural diurnal IOP fluctuations to investigate corneal deformations in a number of subjects whose eyes were measured multiple times during a day. The results of analysis, based on corneal hysteresis, revealed a corneal hysteresis parameter, which remains constant during a day for each individual eye. We hypothesize that above-mentioned metric might correlate with biomechanical properties of the cornea without influence of IOP. Full Text: PDF ReferencesMeek KM, Tuft SJ, Huang Y, Gill PS, Hayes S, Newton RH, Bron AJ, "Changes in Collagen Orientation and Distribution in Keratoconus Corneas", Invest Ophthalmol Vis Sci, 2005. 46(6): p. 1948-56. CrossRef Zimmermann DR, Fisher RW, Winterhalter KH, Witmer R, Vaughan L, "Comparative studies of collagens in normal and keratoconus corneas", Exp Eye Res, 1988. 46(3): p. 431-42. CrossRef Andreassen TT, Simonsen AH, and Oxlund H, "Biomechanical properties of keratoconus and normal corneas", Experimental Eye Research, 1980. 31(4): p. 435-441. CrossRef Heijl A, Leske MC, Bengtsson B, Hyman L, Bengtsson B, Hussein M, "Reduction of Intraocular Pressure and Glaucoma Progression", Arch Ophthalmol, 2002. 120(10): p. 1268-79. CrossRef Chauhan BC and Drance SM, "The influence of intraocular pressure on visual field damage in patients with normal-tension and high-tension glaucoma", Investigative Ophthalmology &amp; Visual Science, 1990. 31(11): p. 2367-2372. DirectLink Gelaw Y, "The impact of central corneal thickness on intraocular pressure among Ethiopian glaucoma patients: a cross-sectional study", BMC Ophthalmology, 2012. 12(1): p. 58. CrossRef Doughty MJ and Zaman ML, "Human Corneal Thickness and Its Impact on Intraocular Pressure Measures: A Review and Meta-analysis Approach", Surv Ophthalmol, 2000. 44(5): p. 367-408. CrossRef Liu J, and Roberts CJ, "Influence of corneal biomechanical properties on intraocular pressure measurement: Quantitative analysis", J Cataract Refract Surg, 2005. 31(1): p. 146-55. CrossRef Ehlers N, Hansen FK, and Aasved H, "Biometric Correlations of Corneal Thickness", Acta Ophthalmol (Copenh), 1975. 53(4): p. 652-9. CrossRef Harada Y, Hirose N, Tawara A, "The Influence of Central Corneal Thickness and Corneal Curvature Radius on The Intraocular Pressure as Measured By Different Tonometers: Noncontact and Goldmann Applanation Tonometers", J Glaucoma, 2008. 17(8): p. 619-25. CrossRef Alonso-Caneiro D, Karnowski K, Kaluzny BJ, Kowalczyk A, Wojtkowski M, "Assessment of corneal dynamics with high-speed swept source Optical Coherence Tomography combined with an air puff system", Optics Express, 2011. 19(15): p. 14188-14199. CrossRef Dorronsoro C, Pascual D, Perez-Merino P, Kling S and Marcos S, "Dynamic OCT measurement of corneal deformation by an air puff in normal and cross-linked corneas", Biomedical Optics Express, 2012. 3(3): p. 473-487. CrossRef Karnowski K, Kaluzny BJ, Szkulmowski M, Gora M, Wojtkowski M, "Corneal topography with high-speed swept source OCT in clinical examination", Biomedical Optics Express, 2011. 2(9): p. 2709-2720. CrossRef A. N. S. Institute, "American National Standard for Safe use of Lasers," (American National Standards Institute, Orlando, FL, 2000) DirectLink David R, Zangwill L, Briscoe D, Dagan M, Yagev R, Yassur Y, "Diurnal intraocular pressure variations: an analysis of 690 diurnal curves", Br J Ophthamlom, 1992, 76(5): p. 280-282 CrossRef Maczynska E, Karnowski K, Szulzycki K, Malinowska M, Dolezyczek H, Cichanski A, Wojtkowski M, Kaluzny BJ, Grulkowski I, Journal of Biophotonics (to be published).

The Impact of Central Corneal Thickness on the Risk for Glaucoma in a Large Multiethnic Population

To investigate the relationship between central corneal thickness (CCT) and demographics, and determine whether CCT may be a substantial mediator of the relationships between glaucoma and its demographic risk factors. This cross-sectional study included patients in the Kaiser Permanente Northern California health plan from January 1, 2007 to December 31, 2011 who were 40 years and older and had a documented CCT measurement (N=81,082). Those with any cornea-related diagnoses or a history of corneal refractive surgery were excluded. Demographic characteristics, including age, sex, and race/ethnicity, as well as clinical information including glaucoma-related diagnosis, diabetic status, CCT, and intraocular pressure were gathered from the electronic medical record. Multivariate linear regression analysis indicated that female sex, increased age, and black race were significantly associated with thinner corneas. A subgroup analysis among Asians revealed that Chinese, Japanese, and Koreans had corneas 6 to 13 µm thicker than South and Southeast Asians, Filipinos, and Pacific Islanders for each diagnosis (P<0.001). In our population, 24.5% (N=19878) had some form of open-angle glaucoma; 21.9% (N=17,779) did not have any glaucoma-related diagnosis. Variation in CCT accounted for only 6.68% [95% confidence interval (CI), 6.14%-7.24%] of the increased risk of open-angle glaucoma seen with increasing age, but explained as much as 29.4% (95% CI, 27.0%-32.6%) of the increased risk of glaucoma seen among blacks, and 29.5% (95% CI, 23.5%-37.0%) of the increased risk of glaucoma seen among Hispanics. CCT seems to explain a substantial portion of the increased risk of glaucoma seen among blacks and Hispanics.

The impact of central corneal thickness on intraocular pressure among Ethiopian glaucoma patients: a cross-sectional study

BackgroundRaised intraocular pressure (IOP) is the only causal risk factor for glaucoma that can be therapeutically manipulated to change the course of the disease process. Though Goldman applanation tonometry (GAT) is the “gold standard” for IOP measurement, readings of IOP with GAT are affected by central corneal thickness (CCT). The aim of this study is to determine the impact of CCT on IOP among Ethiopian glaucoma patients.MethodsIt was a multicenter cross-sectional study and all glaucoma patients visiting their respective eye clinic during the study period were included. A total of 199 randomly selected glaucomatous eyes from 199 patients aged 18 years and above were employed. The CCT was measured by OcuScan™ RxP Ophthalmic Ultrasound and IOP was measured with Goldmann applanation tonometer. Linear regression and bivariate correlation analysis were carried out and level of significance was taken at 5%.ResultsThe mean IOP was 19.46(±7.05) mmHg and mean CCT was 508.07(±33.26) μm. The mean IOP for primary open angle glaucoma (POAG), ocular hypertension (OHT), normal tension glaucoma (NTG), pseudoexfoliative glaucoma (PXG) and primary chronic angle closure glaucoma (PCAG) patients was 19.22 mmHg, 21.39 mmHg, 14.33 mmHg, 33.25 mmHg and 14.75 mmHg respectively. The mean CCT values were 502.24 μm (POAG), 524.32 μm (OHT), 500.75 μm (NTG), 579.00 μm (PXG) and 530.25 μm (PCAG). Age of the patient and glaucoma surgery had an influence on corneal thickness. A positive relationship was found between CCT and IOP (p < 0.001).ConclusionsThe mean CCT of Ethiopian glaucoma patients is thin in comparison to other ethnic groups and patients with OHT have thicker corneas than POAG patients. Hence determination of CCT for each patient is necessary in the up-to-date glaucoma management.

Biomechanical concepts in Glaucoma

AbstractPurpose Title: Corneal biomechanics and glaucoma risk‐ where are we now?Methods The impact of central corneal thickness (CCT) on intraocular pressure (IOP) measurement accuracy has been well documented, and CCT has become part of the routine work up of a glaucoma suspect patient. What is relatively unclear is whether corneal properties, such as CCT and in vivo measures of corneal biomechanics, give an indication of the risk of glaucoma susceptibility. This talk will consider whether there is a role for the cornea that lies beyond the limits of IOP measurement accuracy, discussing the evidence as to whether current measures of corneal biomechanics may be used as a surrogate marker of optic nerve compliance.

Intraocular Pressure, Central Corneal Thickness, and Prevalence of Open-Angle Glaucoma: The Los Angeles Latino Eye Study

To examine the relationship between the prevalence of open-angle glaucoma (OAG) and intraocular pressure (IOP) and the impact of central corneal thickness (CCT) on this relationship. Population-based cross-sectional study. The study cohort consisted of 5,970 participants from the Los Angeles Latino Eye Study (LALES) with no history of glaucoma treatment and with complete ophthalmic examination data. The relationship between the prevalence of OAG and IOP was contrasted across persons with CCT designated as thin, normal, or thick. Prevalence of OAG was exponentially related to IOP. When stratified by CCT, persons with thin CCT had a significantly higher prevalence of OAG than did those with normal or thick CCTs at all levels of IOP. Adjusting each IOP individually for CCT did not impact significantly the relationship between the prevalence of OAG and IOP. These findings suggest that adjusting for the impact of CCT on IOP by correction algorithms is not necessary in a population based assessment of glaucoma prevalence; CCT, however, is an important independent risk factor for the prevalence of OAG.

Effect of central corneal thickness on Goldmann applanation tonometry measures—a different result with different pachymeters

To assess whether the use of Orbscan pachymetry, as an alternative to ultrasound pachymetry, had an effect on the IOP-CCT relationship for Goldmann tonometry in normal human eyes. The right eye of 50 healthy subjects, aged 19 to 82 years, were assessed by Orbscan (three scans), and then central corneal thickness (CCT) measured by ultrasound pachymetry (three readings) and Goldmann tonometry performed (three readings). Goldmann tonometry indicated average IOP values from 9.7 to 20 mm Hg (group mean 14.3 +/- 2.5 mm Hg) that were highly highly correlated with ultrasound pachymetry (r = 0.608, p < 0.001). Orbscan central zone pachymetry (2-mm sample zone) yielded higher values than ultrasound, averaging 0.591 +/- 0.044 mm compared to 0.523 +/- 0.037 mm (p < 0.001), with the differences between the instruments being proportional to the average thickness (p < 0.001; r = 0.461). Notwithstanding, the Goldmann tonometry values were still highly correlated with the Orbscan central zone thickness data (r = 0.595, p < 0.001); but, due to the difference in the thickness data generated by the two pachymeters, the absolute slope of the IOP-CCT relationship was slightly less if Orbscan measures were used, with or without use of the acoustic factor. Orbscan measures of the thickness of a central corneal zone can be used to assess the impact of central corneal thickness on Goldmann tonometry data.

Central Corneal Thickness and Corneal Hysteresis Associated With Glaucoma Damage

We sought to measure the impact of central corneal thickness (CCT), a possible risk factor for glaucoma damage, and corneal hysteresis, a proposed measure of corneal resistance to deformation, on various indicators of glaucoma damage. Observational study. Adult patients of the Wilmer Glaucoma Service underwent measurement of hysteresis on the Reichert Ocular Response Analyzer and measurement of CCT by ultrasonic pachymetry. Two glaucoma specialists (H.A.Q., N.G.C.) reviewed the chart to determine highest known intraocular pressure (IOP), target IOP, diagnosis, years with glaucoma, cup-to-disk ratio (CDR), mean defect (MD), pattern standard deviation (PSD), glaucoma hemifield test (GHT), and presence or absence of visual field progression. Among 230 subjects, the mean age was 65 +/- 14 years, 127 (55%) were female, 161 (70%) were white, and 194 (85%) had a diagnosis of primary open-angle glaucoma (POAG) or suspected POAG. In multivariate generalized estimating equation models, lower corneal hysteresis value (P = .03), but not CCT, was associated with visual field progression. When axial length was included in the model, hysteresis was not a significant risk factor (P = .09). A thinner CCT (P = .02), but not hysteresis, was associated with a higher CDR at the most recent examination. Neither CCT nor hysteresis was associated with MD, PSD, or GHT "outside normal limits." Thinner CCT was associated with the state of glaucoma damage as indicated by CDR. Axial length and corneal hysteresis were associated with progressive field worsening.

Central corneal thickness in European (white) individuals, especially children and the elderly, and assessment of its possible importance in clinical measures of intra-ocular pressure.

To ascertain the impact of central corneal thickness (CCT, as assessed by pachometry) and central corneal curvature (as assessed by keratometry) on clinical measures of intra-ocular pressure (IOP, as assessed by tonometry), especially in the young and elderly. Pachometry, keratometry and tonometry were carried out on three groups, namely children aged 5-15 years, adults aged 32-60 years, and elderly individuals aged between 61 and 82 years. For children, ultrasound pachometry was combined with non-contact tonometry (NCT), specular microscopy was used with Perkins tonometry in the adults, and ultrasound pachometry was used with Perkins tonometry for the elderly. Central corneal curvature was assessed by keratometry. The average CCT in children was 0.529+/-0.034 mm (n = 104, +/-S.D.), averaged 0.533+/-0.033 in adults (n=75) and 0.527+/-0.034 mm (n=91) in the elderly. Tonometry values averaged 16.7+/-2.9 mm in children, 13.0+/-3.5 mmHg in adults and 13.6+/-2.5 mm in the elderly group. Central corneal thickness values were not predictably different in relation to central corneal curvature values. Regression analyses indicated that the tonometry values were higher in both children and the elderly who had thicker corneas (and vice versa) (p < 0.003), with the measures increasing by 1.3+/-0.4 and 2.6+/-0.4 mmHg for a 10% difference in CCT in children and the elderly, respectively. For adults, no statistically significant difference in tonometry values could be demonstrated with respect to CCT (<1 mmHg for a 10% difference in CCT), and for no group were the CCT or tonometry values predictably different in relation to central comeal curvature values. The results of these studies, albeit relatively small scale, indicate that in young or elderly individuals with essentially normal IOP and CCT measures, the tonometry values show only small differences with respect to CCT. The slope in the observed relationship was not that different from an average of 1.5 mmHg for a 10% different in CCT, as obtained from a literature analysis over a 30-year period. The magnitude of the effect does not provide evidence that pachometry needs to be routinely performed in glaucoma screening protocols based on tonometry. Notwithstanding, the finding of higher than expected tonometry values should be further investigated, by pachometry, especially in very young children and in the elderly.

The effect of the design and fitting ofsoft lenses on corneal physiology

We determined the “normal” central corneal thickness (CCT) value in human corneas based on reported literature values for within-study average CCT values, and used this as a reference to assess the reported impact of physiological variables (especially age and diurnal effects), contact lens wear, pharmaceuticals, ocular disease, and ophthalmic surgery on CCT. With the expected CCT and its variance defined, it should be possible to determine the potential impact of differences in CCT in intraocular pressure (IOP) assessments, especially by applanation tonometry, using a meta-analysis approach. Some 600 sets of CCT data were identified from the worldwide literature over the period of 1968 through mid-1999, of which 134 included IOP measures as well. The within-study average CCT values and reported variance (SD) was noted along with the number of eyes and any special characteristics, including probable ethnic origin of the study subjects. Various sets of data were subjected to statistical analyses. From 300 data sets from eyes designated as normal, the group-averaged CCT was 0.534 mm. From 230 data sets where interindividual variance was reported, the group-averaged CCT was 0.536 mm (median 0.536 mm; average SD of 0.031 mm, average coefficient of variation = 5.8%). Overall, studies using slit-lamp-based pachometry have reported marginally lower CCT values (average 0.530 mm, average SD 0.029 mm) compared to ultrasound-based studies (average 0.544, average SD 0.034 mm), which perhaps reflects the type of individual studied (non-surgical vs. pre-surgical patients) rather than the technique itself. A slight chronological increase in reported average CCT values (approximately 0.006 mm/decade) was evident, but a substantial chronological increase was evident for ultrasound pachometry studies (approximately 0.015 mm/decade). Within the meta-analysis-generated average and variance, age had no obvious impact on CCT measures for *whites, although an age-related decline in CCT is evident for non-whites. Any diurnal effects are likely concealed within the expected variance in CCT. Contact lens wear and pharmaceuticals generally produced changes in CCT that were well within the expected variance in CCT. Of the ocular diseases, only those associated with collagen disorders (including keratoconus) or endothelial-based corneal dystrophies (e.g., Fuchs) were likely to result in decreases or increases, respectively, of CCT beyond the normal variance. Routine contact lens wear and diseases such as diabetes seem unlikely to produce changes in CCT of a magnitude that would justify pachometry as a monitoring method beyond routine slit-lamp evaluation. Increases in CCT beyond the expected variance were reported after a range of intraocular surgeries (cataract operations, penetrating keratoplasty), whereas photorefractive surgery produces a measurable decrease in CCT. A meta-analysis of possible association between CCT and IOP measures of 133 data sets, regardless of the type of eyes assessed, revealed a statistically significant correlation; a 10% difference in CCT would result in a 3.4 ± 0.9 mm Hg difference in IOP (P ≤ 0.001, r = 0.419). The observed phenomenon was much smaller for eyes designated as healthy (1.1 ± 0.6 mm Hg for a 10% difference in CCT, P = 0.023, r = 0.331). For eyes with chronic diseases, the change was 2.5 ± 1.1 mm Hg for a 10% difference in CCT (P = 0.005, r = 0.450), whereas a substantial but highly variable association was seen for eyes with acute onset disease (approximately 10.0 ± 3.1 mm Hg for a 10% difference in CCT, P = 0.004, r = 0.623). Based on the meta-analysis, normal CCT in white adults would be expected to be within ±11.6% (±2 SD) of 0.535 mm, i.e., 0.473–0.597 mm (95% CI, 0.474–0.596). The impact of CCT on applanation tonometry of healthy eyes is unlikely to achieve clinical significance, but for corneas of eyes with chronic disease, pachometry should be performed if the tonometry reveals IOP readings that are borderline or unusual. The meta-analysis confirms that, for these eyes, low CCT values can result in low tonometry readings and high CCT values can result in elevated tonometry readings. The correction for eyes with chronic disease should be 2 or 3 mm Hg for a 0.05-mm difference in CCT from 0.535 mm. It is unknown whether this same correction should be specifically applied to the elderly, especially in non-whites.