Intraocular pressure and central corneal thickness

Potential for Collider Bias in Studies Examining the Association of Central Corneal Thickness With Glaucoma

Purpose

Central corneal thickness (CCT) may be biologically related to glaucoma or observed as associated with glaucoma simply due to its effect on intraocular pressure (IOP) measurement. We aimed to determine if the previously reported CCT-glaucoma associations, in which the analyses were adjusted for IOP or participants were selected on IOP, could be explained by collider bias.

Methods

We simulated datasets mimicking a longitudinal population-based study (Los Angeles Latino Eye Study) and a trial (Ocular Hypertension Treatment Study) such that: (i) CCT was not truly associated with glaucoma, (ii) CCT and true IOP both contribute to measured IOP, and (iii) true IOP contributes to glaucoma risk. We then tested whether an association between CCT and glaucoma could be spuriously induced simply by adjusting for or selecting on measured IOP.

Results

A thinner CCT was significantly associated with higher glaucoma incidence in the simulated longitudinal population-based study when adjusted for measured IOP, but not crudely (unadjusted). A thinner CCT was crudely associated with glaucoma incidence in the simulated trial in which the participants were selected for high measured IOP. Effect sizes in the simulations were similar to those observed in the original studies.

Conclusions

Our findings question whether CCT is biologically associated with glaucoma and suggest that current evidence may be due to collider bias. This indicates that CCT alone cannot be used as a factor to identify people at high risk of glaucoma in the general population. Using CCT in combination with IOP may be superior to using IOP alone.

Relationship between blood pressure and intraocular pressure in the JPHC-NEXT eye study

Although a positive link between hypertension and intraocular pressure (IOP) has been suggested, the individual effects of systolic and diastolic blood pressure (SBP and DBP, respectively) on IOP remain unclear, particularly among Japanese populations. Here, we conducted a large-scale, cross-sectional study to determine individual and combined effects of SBP/DBP and hypertension on IOP. In total, 6783 Japanese people aged over 40 years underwent systemic and ophthalmological examinations, including measurements of blood pressure and IOP, conducted using non-contact tonometers. After adjusting for a priori known confounding factors, SBP and DBP levels were found to be positively correlated with IOP levels. The multivariable-adjusted odds ratio when comparing the hypertensive and normotensive groups for the prevalence of ocular hypertension was 1.88 (95% confidence interval, 1.14-3.08). When analysing the combined effects of SBP and DBP on ocular hypertension, SBP elevation had a greater effect on ocular hypertension than DBP increase. In conclusion, SBP and DBP levels and the prevalence of systemic hypertension were found to be positively associated with IOP levels and the prevalence of ocular hypertension in an ophthalmologically healthy Japanese population. Our findings suggest that systemic blood pressure control may be key for controlling IOP.

Central corneal thickness, axial length, anterior chamber and optic disc structure in patients with central and branch retinal vein occlusion

PURPOSE

To compare the central corneal thickness (CCT), the structural properties of the anterior chamber and optic disc in patients with central retinal vein occlusion (CRVO), branch retinal vein occlusion (BRVO), and controls.

MATERIAL AND METHODS

In this prospective study, 31 eyes of 31 CRVO patients (group 1) (mean age: 65.7 ± 10.2 male/female:16/15), 42 eyes of 42 BRVO patients (group 2) (mean age: 61.5 ± 9.9, male/female: 21/21), and 41 controls (mean age: 61.2 ± 15.3, male/female:15/26) were enrolled. Intraocular pressure (IOP), corrected IOP (IOPcorr), central corneal thickness (CCT), anterior chamber depth & volume (ACD & ACV), iridocorneal angle (ICA), axial length (AL), retinal nerve fiber layer (RNFL) thickness, ganglion cell layer (GCL) thickness, cup to disc ratio (C/D), cup & rim volume, the scleral canal diameter (SCD), and mean & pattern deviation in visual field of the eyes with CRVO/BRVO, their fellow eyes and control eyes were evaluated.

RESULTS

There was no significant difference in IOP among groups (p:0.239), while IOPcorr was significantly higher in eyes with CRVO compared with eyes with BRVO (p:0.003). Central corneal thickness was significantly thinner in CRVO than both BRVO and controls (p:0.005, p:0.002 respectively). The difference in the RNFL thickness was significant among groups (p:0.019), and it was detected significant between CRVO eyes and controls (p:0.05). Anterior chamber volume was lower in eyes with BRVO than in normal eyes (p:0.009). There was no significant difference in AL, ACD, rim volume, cup volume, GCL thickness, C/D ratio, ICA, and PSD among groups.

CONCLUSION

The patients with CRVO tend to have thinner corneas, and the evaluation of IOP and CCT can be overlooked during retinal follow-up. Intraocular pressure values corrected with CCT should always be take into account to prevent possible optic nerve damage.

Factors Associated With Differences in the Initial Location of Structural Progression in Normal-Tension Glaucoma

PRCIS

Different clinical factors are associated with the location of the first structural progression in glaucoma.

PURPOSE

The aim was to investigate the underlying clinical parameters affecting the location of the initial structural progression of glaucoma in patients with normal-tension glaucoma (NTG).

METHODS

This retrospective study included 228 eyes of 228 patients with NTG. In total, 130 eyes of 130 patients demonstrated structural progression (as determined by event-based guided progression analysis using Cirrus HD-optical coherence tomography) in the peripapillary retinal nerve fiber layer (ppRNFL) or macular ganglion cell inner plexiform layer (mGCIPL). Depending on where the progression occurred first, it was defined as either ppRNFL first progression or mGCIPL first progression. Clinical parameters associated with each first progression were identified using logistic regression.

RESULTS

In total, 50 eyes showed ppRNFL first progression and 64 eyes showed mGCIPL first progression. ppRNFL first progression was significantly associated with female sex [odds ratio (OR)=5.705, P=0.015], lack of systemic hypertension (OR=0.199, P=0.014), disc hemorrhage (OR=4.188, P=0.029), higher mean intraocular pressure (OR=1.300, P=0.03), and lower pattern SD (OR=0.784, P=0.028). In contrast, male sex (OR=0.450, P=0.043), lower central corneal thickness (OR=0.987, P=0.032), higher intraocular pressure fluctuation (OR=1.753, P=0.047), lower systolic blood pressure fluctuation (OR=0.839, P=0.002), and higher diastolic blood pressure fluctuation (OR=1.208, P=0.015) were significantly associated with mGCIPL first progression.

CONCLUSIONS

Different clinical factors were associated with the initial site of structural glaucoma progression in patients with NTG depending on its peripapillary or macular location, and these findings suggest possible differences in underlying mechanisms of glaucoma damage.

Changes in corneal thickness after vitrectomy-Implications for glaucoma practice

Purpose

To evaluate changes in central corneal thickness (CCT) following vitrectomy.

Methods

All consecutive old and new patients referred to glaucoma services for possible secondary glaucoma after vitrectomy and who had undergone corneal pachymetry between July 2013 to June 2020, were included. The eye that developed elevated intraocular pressure (IOP) and was diagnosed clinically as glaucoma after vitrectomy, was labelled as the “affected” eye. The contralateral eye of the patient with normal IOP and no history of vitrectomy was labelled as the “control” eye. The difference in CCT in the affected eye and the contralateral control eye (ΔCCT) and CCT were compared between different age groups. Correlation of CCT in the affected eye with age, diagnosis, type of surgery done, lens status and pre-existing glaucoma was done using multivariate regression analysis.

Results

Of 127 eyes of 120 patients (M:F = 85:35), the average CCT in the affected eye was significantly higher than the unaffected contralateral control eye (p<0.0001). The ΔCCT in eyes presenting at an age <25 years was higher (median 582, 497–840) than those that presented later (median 518, 384–755), p <0.0001, with maximum ΔCCT seen in eyes that had undergone vitrectomy at age<12 years. The CCT in the affected eye was significantly higher in aphakic eyes (588±81.6 microns) than in pseudophakic eyes (552±79.03 microns), p = 0.03. On multivariate analysis, age<25 years remained as a significant influencer of CCT in the affected eye (β = -1.7, p<0.001, R2 = 28.3%).

Conclusions

Young age group<25 years are more prone to corneal remodelling and CCT changes after vitrectomy.

Evaluation of corneal biomechanical properties on ocular response analyzer and their correlation with the clinical profile of the patients with thyroid-associated ophthalmopathy

Purpose: The study evaluates the corneal biomechanical properties on Ocular Response Analyzer (ORA) and aims to establish their correlation with the clinical profile of patients with TAO.Methods: A tertiary care centre-based cross-sectional observational study was conducted. Eighty patients with stage I and II TAO (EUGOGO classification), categorized as group A, were age and sex matched with 85 controls constituting group B. The disease activity was assessed using clinical activity score (CAS). The thyroid hormonal profile of within one-week duration was recorded for each patient of group A. Mean IOP-GAT (IOP using Goldmann applanation tonometer), IOPg (Goldmann-correlated IOP value), IOPcc (cornea-compensated IOP value), CRF (corneal resistance factor), and mean corneal hysteresis (CH) of group A and B were compared. The variation of CH with disease severity, activity, and thyroid status in group A was evaluated.Results: Mean GAT, IOPg, and IOPcc of group A were significantly higher than that of group B (p < .001). Mean CH of group A i.e the visco-elastic dampening ability of cornea was significantly lower than that of group B (p < .001). In group A, mean CH of patients with stage 1 disease severity and CAS<3 was significantly higher than that of patients with stage 2 severity and CAS≥3 (p < .001). CH of hyperthyroid patients was significantly lower than CH of hypothyroid patients (p < .01).Conclusion: TAO affects the biomechanical properties of the globe as reflected by the corneal biomechanics on ORA. The disease severity, activity, and hyperthyroid status are negatively correlated with the CH.

Risk Factors for Rapid Glaucoma Disease Progression

PURPOSE

To determine the intraocular and systemic risk factor differences between a cohort of rapid glaucoma disease progressors and nonrapid disease progressors.

DESIGN

Retrospective case-control study.

METHODS

Setting: Five private ophthalmology clinics.

STUDY POPULATION

Forty-eight rapidly progressing eyes (progression ≥1 dB mean deviation [MD]/year) and 486 non-rapidly progressing eyes (progression <1 dB MD/year). Patients were eligible if they had a diagnosis of glaucoma from their ophthalmologist and if they had greater than or equal to 5 Humphrey visual fields (24-2) conducted. Patients were excluded if their sequential visual fields showed an improvement in MD or if they had greater than 5 dB MD variation in between visits. Patients with obvious neurologic fields were excluded.

OBSERVATION PROCEDURE

Clinical and demographic data (age, sex, central corneal thickness [CCT], intraocular pressure [IOP], refraction, medications), as well as medical, surgical, and ocular histories, were collected.

MAIN OUTCOME MEASURES

Risk factor differences between the cohorts were measured using the independent t test, Wald χ², and binomial regression analysis.

RESULTS

Rapid progressors were older, had significantly lower CCT and baseline IOPs, and were more likely to have pseudoexfoliation, disc haemorrhages, ocular medication changes, and IOP-lowering surgery. They also had significantly higher rates of cardiovascular disease and hypotension. Subjects with cardiovascular disease were 2.33 times more likely to develop rapidly progressive glaucoma disease despite significantly lower mean and baseline IOPs.

CONCLUSION

Cardiovascular disease is an important risk factor for rapid glaucoma disease progression irrespective of IOP control.

Evaluation of Corneal Biomechanical Properties in Patients With Thyroid Eye Disease Using Ocular Response Analyzer

PURPOSE

To assess variations in the corneal biomechanical properties in thyroid eye disease (TED) patients using ocular response analyzer (ORA).

PATIENTS AND METHODS

In this observational cross-sectional study, 75 patients with TED and 57 healthy subjects were enrolled. The mean age of the patients and healthy subjects were 47.50±1.55 and 43.6±1.23 years, respectively (P=0.06). All study participants underwent comprehensive ophthalmologic examination, Goldmann applanation tonometry (GAT), corneal pachymetry, and corneal biomechanical analysis using ORA. Corneal hysteresis (CH), corneal resistance factor (CRF), cornea-compensated IOP value (IOPcc), and Goldmann-corrected IOP value (IOPg) were measured with ORA.

RESULTS

Central corneal thickness (CCT) in patients group (536.18±36.20 μm) and control group (539.22±28.83 μm) were not significantly different (P=0.1). In TED group, the IOPcc (20.23±0.54 mm Hg) was significantly higher than both IOP-GAT (17.54±0.49 mm Hg, P<0.001) and IOPg (18.35±0.52, P<0.001). CH in TED patients (9.01±0.20) was significantly lower compared with CH in healthy subjects (10.45±0.21) (P<0.001). Although CRF was lower in TED patients (10.06±0.16) in comparison with normal subjects (10.42±0.29), this difference was not statistically significant (P=0.25). Both CH and CRF were positively correlated with CCT (r=0.52, P<0.001 and r=0.62, P<0.001, respectively) in TED group.

CONCLUSIONS

In TED patients, CH seems to be lower than in normal subjects. GAT might underestimate the IOP due to differences in corneal properties of cornea in TED patients.

Mice Homozygous for a Deletion in the Glaucoma Susceptibility Locus INK4 Show Increased Vulnerability of Retinal Ganglion Cells to Elevated Intraocular Pressure

A genomic region located on chromosome 9p21 is associated with primary open-angle glaucoma and normal tension glaucoma in genome-wide association studies. The genomic region contains the gene for a long noncoding RNA called CDKN2B-AS, two genes that code for cyclin-dependent kinase inhibitors 2A and 2B (CDKN2A/p16(INK4A) and CDKN2B/p15(INK4B)) and an additional protein (p14(ARF)). We used a transgenic mouse model in which 70 kb of murine chromosome 4, syntenic to human chromosome 9p21, are deleted to study whether this deletion leads to a discernible phenotype in ocular structures implicated in glaucoma. Homozygous mice of this strain were previously reported to show persistent hyperplastic primary vitreous. Fundus photography and optical coherence tomography confirmed that finding but showed no abnormalities for heterozygous mice. Optokinetic response, eletroretinogram, and histology indicated that the heterozygous and mutant retinas were normal functionally and morphologically, whereas glial cells were activated in the retina and optic nerve head of mutant eyes. In quantitative PCR, CDKN2B expression was reduced by approximately 50% in the heterozygous mice and by 90% in the homozygous mice, which suggested that the CDKN2B knock down had no deleterious consequences for the retina under normal conditions. However, compared with wild-type and heterozygous animals, the homozygous mice are more vulnerable to retinal ganglion cell loss in response to elevated intraocular pressure.

Emerging risk factors for glaucoma onset and progression

Glaucoma is a complex, multifactorial neurodegenerative disease process that leads to progressive damage to the optic nerve and irreversible visual impairment. Identification of ocular and systemic risk factors for disease onset and progression is critical for disease detection and surveillance. Although a great deal is known about risk factors for glaucoma, our expanding knowledge of glaucoma genotypes and phenotypes combined with advancements in technology and understanding of disease progression is rapidly enhancing our understanding of who is at greatest risk for glaucomatous visual impairment.

Corneal biomechanical properties and glaucoma-related quantitative traits in the EPIC-Norfolk Eye Study

PURPOSE

We examined the association of corneal hysteresis (CH) with Heidelberg retina tomograph (HRT)- and Glaucoma Detection with Variable Corneal Compensation scanning laser polarimeter (GDxVCC)-derived measures in a British population.

METHODS

The EPIC-Norfolk Eye Study is nested within a multicenter cohort study--the European Prospective Investigation of Cancer. Ocular response analyzer (ORA), HRT3, and GDxVCC measurements were taken at the research clinic. Three ORA measurements were taken per eye, and the single best value used. Participants meeting predefined criteria were referred for a second examination, including Goldmann applanation tonometry (GAT) and central corneal thickness (CCT) measurement. Generalized estimating equation models were used to examine the associations of CH with HRT and GDxVCC parameters, adjusted for disc area. The GDxVCC analyses were adjusted further for typical scan score to handle atypical retardation.

RESULTS

There were complete research clinic data from 5134 participants. Corneal hysteresis was associated positively with HRT rim area (P < 0.001), and GDxVCC retinal nerve fiber layer (RNFL) average thickness (P = 0.006) and modulation (P = 0.003), and associated negatively with HRT linear cup-to-disc ratio (LCDR, P < 0.001), after adjustment for Goldmann-correlated IOP and other possible confounders. In the 602 participants undergoing the second examination, CH was associated negatively with LCDR (P = 0.008) after adjustment for GAT, CCT, and other possible confounders.

CONCLUSIONS

Lower CH was associated with HRT and GDxVCC parameters in a direction that is seen in glaucoma and with ageing. Further research is required to establish if this is a causal relationship, or due to residual confounding by age, IOP, or CCT.

Acute changes in central corneal thickness according to experimental adjustment of intraocular pressure in normal canine eyes

Central corneal thickness (CCT) can be a promising source of glaucoma monitoring and diagnosis. This study evaluated changes in CCT according to experimental adjustment of intraocular pressure (IOP) in canine eyes. To adjust and measure IOP, each eye was cannulated with two 26-gauge needles under inhalant anesthesia. One needle was connected to a pressure transducer, and the other was connected to an adjustable bag of physiologic saline. IOP was stepwise increased from 10 mmHg to 70 mmHg in 10 mmHg increments (Group T). IOP was maintained at 15 mmHg (Group C15), 30 mmHg (Group C30), 45 mmHg (Group C45), 60 mmHg (Group C60) and 75 mmHg (Group C75) during the experiment. CCT was measured with an ultrasonic pachymeter every 10 min after cannulation. There was a significant difference in the effect of time on CCT (P<0.001) and difference in CCT (dCCT; P<0.001) between groups. The CCT of group C15 remained constant during the experiment. However, group T showed an initial decrease and then an increase after passing the lowest point. Group C30 showed decreasing values for 30 min, after which the values remained constant. The values in Group C45 showed no changes for 40 min and then increased. The values in group C60 showed no change for 20 min and then increased. Group C75 showed a steady increase. In conclusion, the CCT showed two core changes according to increased IOP. This study provides essential basic data to enable further investigation into the association of IOP and CCT in dogs.

Clinical characteristics of glaucomatous subjects treated with refractive corneal ablation surgery

Purpose

To evaluate the clinical characteristics of newly diagnosed glaucomatous subjects who had a history of refractive corneal ablation surgery (RCAS).

Methods

Sixty-eight glaucomatous subjects who had a history of RCAS and 68 age- and visual field (VF) mean deviation-matched glaucomatous subjects with no history of RCAS were included. Intraocular pressure (IOP), central corneal thickness (CCT), VF, and retinal nerve fiber layer thickness determined by optical coherence tomography were assessed. Parameters were compared between patients with and without a history of RCAS. Between-eye comparisons in the same participant (more advanced vs. less-advanced eye, in terms of glaucoma severity) were performed in the RCAS group.

Results

With similar levels of glaucoma severity, those with a history of RCAS showed significantly lower baseline IOP and a thinner CCT than the eyes of individuals without a RCAS history (13.6 vs. 18.7 mmHg, 490.5 vs. 551.7 µm, all p < 0.001). However, the extent of IOP reduction after anti-glaucoma medication did not significantly differ between the two groups (17% vs. 24.3%, p = 0.144). In the between-eye comparisons of individual participants in the RCAS group, the more advanced eyes were more myopic than the less-advanced eyes (-1.84 vs. -0.58 diopter, p = 0.003).

Conclusions

Eyes with a history of RCAS showed a similar level of IOP reduction as eyes without such a history after anti-glaucoma medication. Our finding that the more advanced eyes were more myopic than the less-advanced eyes in the same participant may suggest an association between glaucoma severity and myopic regression.

Association study of multiple gene polymorphisms with the risk of adult-onset primary open-angle glaucoma in a Mexican population

The aim of this study was to investigate the association of multiple primary open-angle glaucoma (POAG)-risk alleles in a Mexican population for the first time. Genotyping was performed for a total of 26 previously associated alleles located in 11 different genes, including MYOC, CYP1B1, OPTN, IL1A, TNF, OPA1, EDNRA, AGTR2, MTHFR, GSTM1, and GSTT1. The frequencies of these variants were compared in a group of 218 individuals (118 with POAG and 100 adult controls without the disease). Genomic DNA was extracted from blood leukocytes, and genotyping was performed using PCR followed by direct sequencing. GSTM1 and GSTT1 deletion variants were screened by agarose gel analysis. Individual SNP analysis showed that no specific variants conferred an elevated risk for developing POAG. However, the CG genotype for rs5335 polymorphism in EDNRA showed a protective effect against the development of POAG, as it provides an estimated odds ratio of 0.5 (95% CI, 0.3-0.9; p = 0.03). Moreover, one haplotype consisting of rs1056827 and rs100012 in CYP1B1 gene was significantly associated with a protective effect against POAG (p = 0.0045; OR = 0.3; 95% CI, 0.1-0.7). This is the first case-control investigation of POAG-risk alleles in multiple genes in a Latino population. Although our results support that the analyzed variants are not major risk factors for POAG in this ethnic group, they also point toward a protective effect conferred by EDNRA rs5335, as well as by a CYP1B1 haplotype consisting of rs1056827 and rs100012. Our study emphasizes the importance of genotyping ethnic groups with a complex admixture of ancestral populations for contributing to dissecting the genetics of POAG.

Baseline risk factors that predict the development of open-angle glaucoma in a population: the Los Angeles Latino Eye Study

OBJECTIVE

To determine which baseline sociodemographic, lifestyle, anthropometric, clinical, and ocular risk factors predict the development of open-angle glaucoma (OAG) in an adult population.

DESIGN

A population-based, prospective cohort study.

PARTICIPANTS

A total of 3772 self-identified Latinos aged ≥40 years from Los Angeles, California, who were free of OAG at baseline.

METHODS

Participants from the Los Angeles Latino Eye Study had standardized study visits at baseline and 4-year follow-up with structured interviews and a comprehensive ophthalmologic examination. We defined OAG as the presence of an open angle and a glaucomatous visual field abnormality and/or evidence of glaucomatous optic nerve damage in ≥1 eye. Multivariate logistic regression with stepwise selection was performed to determine which potential baseline risk factors independently predict the development of OAG.

MAIN OUTCOME MEASURES

Odds ratios for various risk factors.

RESULTS

Over the 4-year follow-up, 87 participants developed OAG. The baseline risk factors that predict the development of OAG include older age (odds ratio [OR] per decade, 2.19; 95% confidence interval [CI], 1.74-2.75; P<0.001), higher intraocular pressure (IOP; OR per mmHg, 1.18; 95% CI, 1.10-1.26; P<0.001), longer axial length (OR per mm, 1.48; 95% CI, 1.22-1.80; P<0.001), thinner central cornea (OR per 40 μm thinner, 1.30; 95% CI, 1.00-1.70; P = 0.050), higher waist-to-hip ratio (OR per 0.05 higher, 1.21; 95% CI, 1.05-1.39; P = 0.007) and lack of vision insurance (OR, 2.08; 95% CI, 1.26-3.41; P = 0.004).

CONCLUSIONS

Despite a mean baseline IOP of 14 mmHg in Latinos, higher IOP is an important risk factor for developing OAG. Biometric measures suggestive of less structural support such as longer axial length and thin central corneal thickness were identified as important risk factors. Lack of health insurance reduces access to eye care and increases the burden of OAG by reducing the likelihood of early detection and treatment of OAG.

FINANCIAL DISCLOSURE(S)

The authors have no proprietary or commercial interest in any of the materials discussed in this article.

Comparison of central corneal thickness measurements using ultrasound pachymetry, ultrasound biomicroscopy, and the Artemis-2 VHF scanner in normal eyes

Purpose

To compare the precision of central corneal thickness (CCT) measurements taken with the handheld ultrasound pachymeter (USP), ultrasound biomicroscopy (UBM), and the Artemis-2 very high frequency ultrasound scanner (VHFUS) on normal subjects.

Design

Prospective study.

Methods

One eye from each of 61 normal subjects was randomly selected for this study. The measurements of the CCT were taken with the USP, VHFUS, and UBM. Results were compared statistically using repeated-measures analysis of variance (ANOVA), Pearson’s correlation coefficient, and limits of agreement.

Results

The average CCT (± standard deviation) was 530.1 ± 30.5 μm, 554.9 ± 31.7 μm, and 559.5 ± 30.7 μm for UBM, VHFUS, and USP respectively. The intraobserver repeatability analyses of variance are not significant for USP, UBM, and VHFUS. P-values were 0.17, 0.19, and 0.37 respectively. Repeated-measures ANOVA showed a significant difference between the three different methods of measuring CCT (P = 0.0001). The ANOVA test revealed no statistically significant difference between USP and VHFUS (P > 0.05), yet statistical significant differences with UBM versus USP and UBM versus VHFUS (P < 0.001). There were high correlations between the three instruments (P < 0.0001). The mean differences (and upper/lower limits of agreement) for CCT measurements were 29.4 ± 14.3 (2.7/56), 4.6 ± 8.6 (−14.7/23.8), and −24.8 ± 13.1 (−50.4/0.8) for USP versus UBM, USP versus VHFUS, and UBM versus VHFUS, respectively.

Conclusion

The UBM produces CCT measurements that vary significantly from those returned by the USP and the VHFUS, suggesting that the UBM may not be used interchangeably with either equipment for monitoring the CCT in the clinical setting.

The influence of central corneal thickness on response to topical prostaglandin analogue therapy

OBJECTIVE

Central corneal thickness (CCT) affects intraocular pressure (IOP) readings; however, CCT influence on topical medication efficacy is unknown. We evaluated the IOP-lowering effect of topical prostaglandin analogues (PGAs) in relation to CCT.

DESIGN

Post hoc analysis of a randomized prospective trial.

METHOD

Subjects randomized to a PGA were followed for 24 weeks and were analyzed for relationship between CCT and IOP lowering.

PARTICIPANTS

Patients with either newly diagnosed ocular hypertension or open-angle glaucoma.

RESULTS

75 subjects were enrolled. The mean age was 62.7 ± 10.5 years; 48 were Caucasian. The mean CCT was 562.4 ± 41.4 μ. At repeated measures, ANCOVA analysis showed a significant effect of both baseline IOP (p < 0.0001) and CCT (p = 0.003) on IOP. At week 12, a regression analysis of the effect of CCT on baseline IOP showed that for every 10 μ increase in CCT there was 0.3 mm Hg less IOP decrease from baseline.

CONCLUSIONS

We found a statistically significantly association between a lower mean IOP and a thinner cornea when baseline IOP is controlled for. The magnitude of the relationship is small but may be clinically significant in patients with either very thin or very thick corneas.

GALC deletions increase the risk of primary open-angle glaucoma: the role of Mendelian variants in complex disease

DNA copy number variants (CNVs) have been reported in many human diseases including autism and schizophrenia. Primary Open Angle Glaucoma (POAG) is a complex adult-onset disorder characterized by progressive optic neuropathy and vision loss. Previous studies have identified rare CNVs in POAG; however, their low frequencies prevented formal association testing. We present here the association between POAG risk and a heterozygous deletion in the galactosylceramidase gene (GALC). This CNV was initially identified in a dataset containing 71 Caucasian POAG cases and 478 ethnically matched controls obtained from dbGAP (study accession phs000126.v1.p1.) (p = 0.017, fisher's exact test). It was validated with array comparative genomic hybridization (arrayCGH) and realtime PCR, and replicated in an independent POAG dataset containing 959 cases and 1852 controls (p = 0.021, OR (odds ratio) = 3.5, 95% CI -1.1-12.0). Evidence for association was strengthened when the discovery and replication datasets were combined (p = 0.002; OR = 5.0, 95% CI 1.6-16.4). Several deletions with different endpoints were identified by array CGH of POAG patients. Homozygous deletions that eliminate GALC enzymatic activity cause Krabbe disease, a recessive Mendelian disorder of childhood displaying bilateral optic neuropathy and vision loss. Our findings suggest that heterozygous deletions that reduce GALC activity are a novel mechanism increasing risk of POAG. This is the first report of a statistically-significant association of a CNV with POAG risk, contributing to a growing body of evidence that CNVs play an important role in complex, inherited disorders. Our findings suggest an attractive biomarker and potential therapeutic target for patients with this form of POAG.