Accuracy of clinical estimates of intraocular pressure in Chinese eyes

Comparison between dynamic contour tonometry and Goldmann applanation tonometry correcting equations

In order to investigate the reliability of correcting GAT formulas in comparison with dynamic contour tonometry (DCT), this study included 112 right eyes of 112 healthy subjects aged from 21 to 77 years, whose eyes underwent to a full ophthalmologic exam. IOP was measured in each eye with DCT and then with GAT. IOP values obtained with GAT were corrected with 10 equations and then compared with those provided by DCT. Participants mean age was 42.24 ± 14.08 years; mean IOP measured with DCT was 17.61 ± 2.87 and 15.50 ± 2.47 mmHg, measured with GAT. The mean discordance between DCT and GAT measurements was 2.11 ± 2.24 mmHg. All the correcting formulas, but Srodka one (p ˂ 0.001), tend to increase the difference between GAT and DCT. According to these results Śródka equation provides the best correction, reducing the difference between the two IOP measurement methods of - 0.03 ± 0.85 mmHg. Other equations do not provide a valid improvement of the agreement between the two methods or they provide a worsening of the agreement.

Icare versus Goldmann in a randomised middle-aged population : The influence of central corneal thickness and refractive errors

PURPOSE

The aim of this study was to compare the measurements of intraocular pressure by two tonometers, the Icare rebound tonometer and the Goldmann applanation tonometer, in a randomised screening study. The influence of refraction and central corneal thickness on the measurements was also evaluated.

METHODS

Intraocular pressure was measured with rebound tonometer and Goldmann applanation tonometer in 1266 participants; refraction and central corneal thickness were also determined. One randomised eye of each participant was selected for this report's analysis. A Bland-Altman plot was used to compare the values obtained with the two devices.

RESULTS

The correlation between rebound tonometer and Goldmann applanation tonometer was good: the intraclass correlation coefficient (r) between the two methods was 0.735 (p < 0.001). The mean difference (rebound tonometer-Goldmann applanation tonometer) was 0.11 ± 2.3 mmHg. The difference was not statistically significant (95% confidence interval: 0.11 to 0.13, p = 0.09). With increasing central corneal thickness, not only did intraocular pressure values with both devices increase, but the difference between them also increased. Refraction (spherical equivalent) did not influence intraocular pressure or the rebound tonometer-Goldmann applanation tonometer difference. However, high astigmatism (≥2D) exerted an influence on intraocular pressure values taken with Goldmann applanation tonometer.

CONCLUSION

Measurements with rebound tonometer and Goldmann applanation tonometer are relatively uniform although rebound tonometer slightly overestimated intraocular pressure. Both rebound tonometer and Goldmann applanation tonometer and the difference between these devices were affected by central corneal thickness but not by refraction. Higher astigmatism affected Goldmann applanation tonometer more than rebound tonometer. It is concluded that rebound tonometer is a reliable method for measuring intraocular pressure in a population-based screening study.

Neuroprotection for treatment of glaucoma in adults

BACKGROUND

Glaucoma is a heterogeneous group of conditions involving progressive damage to the optic nerve, deterioration of retinal ganglion cells, and ultimately visual field loss. It is a leading cause of blindness worldwide. Open angle glaucoma (OAG), the most common form of glaucoma, is a chronic condition that may or may not present with increased intraocular pressure (IOP). Neuroprotection for glaucoma refers to any intervention intended to prevent optic nerve damage or cell death.

OBJECTIVES

The objective of this review was to systematically examine the evidence regarding the effectiveness of neuroprotective agents for slowing the progression of OAG in adults compared with no neuroprotective agent, placebo, or other glaucoma treatment.

SEARCH METHODS

We searched CENTRAL (which contains the Cochrane Eyes and Vision Trials Register) (2016, Issue 7), Ovid MEDLINE, Epub Ahead of Print, In-Process & Other Non-Indexed Citations, Ovid MEDLINE Daily (January 1946 to August 2016), Embase (January 1980 to August 2016), Latin American and Caribbean Literature on Health Sciences (LILACS) (January 1982 to August 2016), the ISRCTN registry (www.isrctn.com/editAdvancedSearch), ClinicalTrials.gov (www.clinicaltrials.gov), and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic searches for trials. We last searched the electronic databases on 16 August 2016.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) in which topical or oral treatments were used for neuroprotection in adults with OAG. Minimum follow-up time was four years.

DATA COLLECTION AND ANALYSIS

Two review authors independently reviewed titles and abstracts from the literature searches. We obtained full-text copies of potentially relevant studies and re-evaluated for inclusion. Two review authors independently extracted data related to study characteristics, risk of bias, and outcomes. We identified one trial for this review, thus we performed no meta-analysis. Two studies comparing memantine to placebo are currently awaiting classification until study investigators provide additional study details. We documented reasons for excluding studies from the review.

MAIN RESULTS

We included one multicenter RCT of adults with low-pressure glaucoma (Low-pressure Glaucoma Treatment Study, LoGTS) conducted in the USA. The primary outcome was progression of visual field loss after four years of treatment with either brimonidine or timolol. Of the 190 adults enrolled in the study, the investigators excluded 12 (6.3%) after randomization; 77 participants (40.5%) did not complete four years of follow-up. The rate of attrition was unbalanced between groups with more participants dropping out of the brimonidine group (55%) than the timolol group (29%).Of those remaining in the study at four years, participants assigned to brimonidine showed less progression of visual field loss than participants assigned to timolol (risk ratio (RR) 0.35, 95% confidence interval (CI) 0.14 to 0.86; 101 participants). Because of high risk of attrition bias and potential selective outcome reporting, we graded the certainty of evidence for this outcome as very low. At the four-year follow-up, the mean IOP was similar in both groups among those for whom data were available (mean difference 0.20 mmHg, 95% CI -0.73 to 1.13; 91 participants; very low-certainty evidence). The study authors did not report analyzable data for visual acuity or any data related to vertical cup-disc ratio, quality of life, or economic outcomes. The most frequent adverse event was ocular allergy to the study drug, which affected more participants in the brimonidine group than the timolol group (RR 5.32, 95% CI 1.64 to 17.26; 178 participants; very low-certainty evidence).

AUTHORS' CONCLUSIONS

Although the only trial we included in this review found less visual field loss in the brimonidine-treated group, the evidence was of such low certainty that we can draw no conclusions from this finding. Further clinical research is needed to determine whether neuroprotective agents may be beneficial for individuals with OAG. Such research should focus on outcomes important to patients, such as preservation of vision, and how these outcomes relate to cell death and optic nerve damage. As OAG is a chronic, progressive disease with variability in symptoms, RCTs designed to measure the effectiveness of neuroprotective agents require a long-term follow-up of five years or longer to detect clinically meaningful effects.

Teleglaucoma: ready to go?

Telemedicine technologies and services allow today's ophthalmic clinicians to remotely diagnose, manage and monitor several ophthalmic conditions from a distance. But is this the case for glaucomas? There has been a proliferation of telemedicine friendly devices in recent years that improves the capabilities of the clinician in managing glaucomas. The existing instruments still need to align themselves with accepted industry standards. There are successful programmes running in several areas of the world. The safety and efficacy of these programmes needs further exploration. The inability of a single device or test to diagnose glaucomas satisfactorily has also hampered progress in remotely diagnosing these conditions. There is, however, significant potential for telemedicine-friendly devices to remotely monitor the progress of glaucoma and, thereby, reduce some of the workload on an overstretched health service.

Central corneal thickness in southern Egypt

The study aimed to determine mean central corneal thickness (CCT) in a southern Egyptian population according to gender and age using ultrasonic pachymetry and to compare these CCT measurements to different populations. A prospective, observational, consecutive case series of 4,368 non-glaucomatous subjects (emmetropes and myopes) aged 16-70 years was carried out from August 2010 to March 2013 at the outpatient ophthalmology clinic in Sohag University Hospital and the Laser Vision Center in Sohag City, Egypt. Refraction, keratometry, slit-lamp examination, and intraocular pressure (IOP) measurements were obtained for all subjects. CCT was measured by ultrasonic pachymetry. The average CCT was 530.06 ± 38.03 μm. Average CCT was 532.6 ± 33.3 μm in emmetropes, 531.5 ± 31.3 μm in myopes <6 diopters (D), 531.1 ± 31.4 μm in myopes >6 D and 533 ± 33 μm in hyperopes, with no statistically significant difference between the groups. There was a statistically significant difference in CCT between age groups and gender. There was a strong correlation between CCT and IOP among the non-glaucomatous population. CCT was found to be lower in Egyptians than in Caucasian, Hispanic, and Japanese populations but comparable to African and African American populations.

Corneal biomechanical properties: precision and influence on tonometry

PURPOSE

To assess the precision and reproducibility of the corneal biomechanical parameters, and their relationships with the intraocular pressure (IOP) measured with the Goldmann tonometer and a noncontact tonometer.

METHODS

Readings for biomechanical properties and for IOP measured with the Goldmann and noncontact tonometers, were taken on one randomly selected eye of 106 normal subjects, on each one of two measurement sessions. Measurements with the ocular response analyzer (ORA) and the noncontact tonometer were randomized, followed by the measurement of central corneal thickness and with the Goldmann tonometer.

RESULTS

Repeatability coefficients for CCT, corneal hysteresis (CH) and corneal resistance factor (CRF) in Session 1 were ± 0.01 μm, ± 3.05 mmHg and ± 2.62 mmHg, respectively. The mean CCT, CH, CRF, Goldmann and noncontact tonometry did not vary significantly between sessions. Reproducibility coefficients for CCT, CH and CRF were ± 0.02 μm, ± 2.19 mmHg and ± 1.97 mmHg, respectively. Univariate regression analysis showed that CCT, CH and CRF significantly (P<0.0001) correlated with the IOP measured with the Goldmann and noncontact tonometers (and with the differences between tonometers) in Session 1. There were no significant correlations with the differences between tonometers in Session 2. Multivariate analysis revealed a minimal effect of CCT on Goldmann measurements but a significant effect on those of the noncontact tonometer.

CONCLUSIONS

Measurement of the biomechanical properties of the cornea, using the ORA, are repeatable and reproducible, affect Goldmann tonometry less than noncontact tonometry, and have a minimal influence on the difference in measured intraocular pressure between tonometers.

Correction factors for Goldmann Tonometry

PURPOSE

The purpose of the study was to evaluate the in vitro accuracy of correction factors in decreasing the error in the intraocular pressure (IOP) measurements obtained using the Goldmann Applanation Tonometer (GAT).

METHODS

Nineteen donor corneas, from individuals aged between 57 and 99 years (mean 75.7 years, standard deviation±11.4 years) were subjected to posterior pressure simulating in vivo true IOP (IOPT) using an inflation test rig. Central corneal thickness and corneal curvature were measured. The posterior pressure was set at 25 different pressure levels between 5 and 45 mm Hg and IOP was measured using the GAT. Five different correction equations were applied to the IOP measurements obtained using the GAT to determine corrected IOP. The multiparameter correction equations applied were derived by Elsheikh, Ehlers, Chihara, Shimmyo et al, and Orssengo and Pye. The differences between IOPT and the IOP measured using the GAT were recorded as uncorrected errors, whereas the differences between IOPT and each of the corrected IOP were the tonometry errors after correction.

RESULTS

The mean and standard deviation of error in tonometry before correction was +2.25±0.62 mm Hg. The mean errors in tonometry after correction using the Elsheikh and Chihara equations were +0.78±0.62 and +1.08±0.61 mm Hg, respectively. The mean errors in tonometry for the Ehlers, Shimmyo et al, and Orssengo and Pye equations were negative, indicating an overcorrection; the values were -0.75±2.28, -1.27±1.85, and -0.77±1.83 mm Hg, respectively.

CONCLUSIONS

The Elsheikh and the Chihara et al's equations considerably decreased error in IOP measurements obtained by the GAT when compared with IOPT and were more consistent than other correction equations. The 2 equations may be of clinical utility in obtaining estimates of IOPT.

Clinical evaluation of multiparameter correction equations for Goldmann applanation tonometry

PURPOSE

To evaluate and compare the multiparameter equations in correcting intraocular pressure (IOP) measurements obtained using the Goldmann applanation tonometer (IOPG) for the effects of central corneal thickness (CCT), corneal curvature (R), and age in different ethnic populations.

METHODS

Data of IOPG, CCT, R, and age were collected from three clinical centers. The sample size consisted of 945 eyes of 945 glaucoma patients or suspects (669 Europeans, 127 African Americans, and 149 Indians). The 'corrected IOP' was calculated using five multiparameter equations to decrease the association of CCT, R, and age with measured IOP. Regression analyses were performed to calculate variance (r(2)) and determine the association of CCT, R, and age with IOPG and corrected IOP (residual association).

RESULTS

Overall, CCT accounted for the majority of variance in IOPG, while R and age had a much smaller effect, with the combined effect on IOPG ranging from 4.7 to 7.5% in the three data sets. The residual association of CCT, R, and age with corrected IOP in the three groups ranged from 0.2 to 1.3% and 0.5 to 1.8% with the application of the Elsheikh and the Chihara equations, respectively. The residual association of CCT, R, and age with corrected IOP calculated using the Ehlers, Orssengo and Pye, and Shimmoyo equations were 7-11.5, 1.8-11.7, and 4.6-8.3%, respectively.

CONCLUSION

The Elsheikh and the Chihara equations better decreased the association of CCT, R, and age with measured IOP than the Ehlers, Orssengo and Pye, and Shimmoyo equations.

Neuroprotection for treatment of glaucoma in adults

BACKGROUND

Glaucoma is a heterogeneous group of conditions involving progressive damage to the optic nerve, deterioration of retinal ganglion cells and ultimately visual field loss. It is a leading cause of blindness worldwide. Open angle glaucoma (OAG), the commonest form of glaucoma, is a chronic condition that may or may not present with increased intraocular pressure (IOP). Neuroprotection for glaucoma refers to any intervention intended to prevent optic nerve damage or cell death.

OBJECTIVES

The objective of this review was to systematically examine the evidence regarding the effectiveness of neuroprotective agents for slowing the progression of OAG in adults.

SEARCH METHODS

We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (The Cochrane Library 2012, Issue 9), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE, (January 1950 to October 2012), EMBASE (January 1980 to October 2012), Latin American and Caribbean Literature on Health Sciences (LILACS) (January 1982 to October 2012), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrials.gov) and the WHO International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic searches for trials. The electronic databases were last searched on 16 October 2012.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) in which topical or oral treatments were used for neuroprotection in adults with OAG. Minimum follow up time was four years.

DATA COLLECTION AND ANALYSIS

Two review authors independently reviewed titles and abstracts from the literature searches. Full-text copies of potentially relevant studies were obtained and re-evaluated for inclusion. Two review authors independently extracted data related study characteristics, risk of bias, and outcome data. One trial was identified for this review, thus we performed no meta-analysis. Two studies comparing memantine to placebo are currently awaiting classification until additional study details are provided. We documented reasons for excluding studies from the review.

MAIN RESULTS

We included one multi-center RCT of adults with low-pressure glaucoma (Low-pressure Glaucoma Treatment Study, LoGTS) conducted in the USA. The primary outcome was visual field progression after four years of treatment with either brimonidine or timolol. Of the 190 adults enrolled in the study, 12 (6.3%) were excluded after randomization and 77 (40.5%) did not complete four years of follow up. The rate of attrition was unbalanced between groups with more participants dropping out of the brimonidine group (55%) than the timolol group (29%). Of those remaining in the study at four years, participants assigned to brimonidine showed less visual field progression than participants assigned to timolol (5/45 participants in the brimonidine group compared with 18/56 participants in the timolol group). Since no information was available for the 12 participants excluded from the study, or the 77 participants who dropped out of the study, we cannot draw any conclusions from these results as the participants for whom data are missing may or may not have progressed. The mean IOP was similar in both groups at the four-year follow up among those for whom data were available: 14.2 mmHg (standard deviation (SD) = 1.9) among the 43 participants in the brimonidine group and 14.0 mmHg (SD = 2.6) among the 48 participants in the timolol group. Among the participants who developed progressive visual field loss, IOP reduction of 20% or greater was not significantly different between groups: 4/9 participants in the brimonidine group and 12/31 participants in the timolol group. The study authors did not report data for visual acuity or vertical cup-disc ratio. The most frequent adverse event was ocular allergy to study drug, which occurred more frequently in the brimonidine group (20/99 participants) than the timolol group (3/79 participants).

AUTHORS' CONCLUSIONS

Although neuroprotective agents are intended to act as pharmacological antagonists to prevent cell death, this trial did not provide evidence that they are effective in preventing retinal ganglion cell death, and thus preserving vision in people with OAG. Further clinical research is needed to determine whether neuroprotective agents may be beneficial for individuals with OAG. Such research should focus outcomes important to patients, such as preservation of vision, and how these outcomes relate to cell death and optic nerve damage. Since OAG is a chronic, progressive disease with variability in symptoms, RCTs designed to measure the effectiveness of neuroprotective agents would require long-term follow up (more than four years) in order to detect clinically meaningful effects.

Effect of instrument orientation on the accuracy of intraocular pressure measurements in human cadaveric eyes: manometric evaluation of the model 30 classic Pneumatonometer and Tono-Pen XL

PURPOSE

To determine the effects of probe orientation on the accuracy of intraocular pressure (IOP) measurements obtained with pneumatonometry (Model 30 Classic Pneumatonometer, Reichert Ophthalmic Instruments, Depew, NY) and with a handheld electronic tonometer (Tono-Pen XL, Reichert Ophthalmic Instruments, Depew, NY).

MATERIALS AND METHODS

Six enucleated human eyes were obtained fewer than 24 hours postmortem. IOP was maintained at 10, 20, and 30 mm Hg, sequentially, via liquid column manometry. At each IOP setpoint, the eyes were positioned to mimic a sitting, supine, and prone patient. Pneumatonometry was performed in the sitting and supine orientations. Tono-Pen measurements were performed in the sitting, supine, and prone orientations. Accuracy was analyzed using multifactor repeated measures analysis of variance, and one-sample t tests.

RESULTS

At all IOP setpoints, for both instruments, probe orientation had no significant effect on the IOP measurement (pneumatonometer P=0.58; Tono-Pen P=0.85). At all 3 setpoints (10, 20, and 30 mm Hg) the pneumatonometer overestimated IOP (P<0.0001; P<0.0001; P=0.005, respectively). The Tono-Pen overestimated IOP at the 10 mm Hg setpoint (P<0.0001), but underestimated IOP at the 20 and 30 mm Hg setpoints (P=0.03; P<0.0001, respectively).

CONCLUSIONS

Under experimental conditions, probe orientation had no significant effect on IOP measurements for either instrument, suggesting that both can be used without correction in the tested orientations. In enucleated human cadaveric eyes, the pneumatonometer overestimated IOP at all setpoints. The handheld electronic tonometer overestimated IOP at 10 mm Hg, but underestimated IOP at the higher setpoints. It is unknown if these findings are generalizable to human eyes in vivo.

Intraocular pressure, central corneal thickness, and glaucoma in chinese adults: the liwan eye study

PURPOSE

To describe the distribution of central corneal thickness (CCT), intraocular pressure (IOP), and their determinants and association with glaucoma in Chinese adults.

DESIGN

Population-based cross-sectional study.

METHODS

Chinese adults aged 50 years and older were identified using cluster random sampling in Liwan District, Guangzhou. CCT (both optical [OCCT] and ultrasound [UCCT]), intraocular pressure (by Tonopen, IOP), refractive error (by autorefractor, RE), radius of corneal curvature (RCC), axial length (AL), and body mass index (BMI) were measured, and history of hypertension and diabetes (DM) was collected by questionnaire. Right eye data were analyzed.

RESULTS

The mean values of OCCT, UCCT, and IOP were 512 ± 29.0 μm, 542 ± 31.4 μm, and 15.2 ± 3.1 mm Hg, respectively. In multiple regression models, CCT declined with age (P < .001) and increased with greater RCC (P < .001) and DM (P = .037). IOP was positively associated with greater CCT (P < .001), BMI (P < .001), and hypertension (P < .001). All 25 persons with open-angle glaucoma had IOP <21 mm Hg. CCT did not differ significantly between persons with and without open- or closed-angle glaucoma. Among 65 persons with ocular hypertension (IOP >97.5th percentile), CCT (555 ± 29 μm) was significantly (P = .01) higher than for normal persons.

CONCLUSIONS

The distributions of CCT and IOP in this study are similar to that for other Chinese populations, though IOP was lower than for European populations, possibly due to lower BMI and blood pressure. Glaucoma with IOP <21 mm Hg is common in this population. We found no association between glaucoma and CCT, though power (0.3) for this analysis was low.

Poor utility of intraocular pressure correction formulae in individual glaucoma and glaucoma suspect patients

BACKGROUND

To compare Pascal dynamic contour tonometry (DCT) measurements with Goldmann applanation tonometry (GAT) readings after adjustment with correction formulae in a population of Caucasian glaucoma and glaucoma suspect patients.

DESIGN

Retrospective cross-sectional case series in a specialist glaucoma practice.

PARTICIPANTS

Consecutive glaucoma and glaucoma suspect Caucasian patients.

METHODS

Case notes review of the GAT and DCT intraocular pressure (IOP) measurements from patients who presented on a non-acute basis over a 30-month period. The GAT measurement was adjusted with six different correction formulae. Agreement between GAT IOP, adjusted GAT IOP and DCT IOP was evaluated with the Bland-Altman analysis.

MAIN OUTCOME MEASURES

Agreement between GAT IOP (both unadjusted and adjusted) and DCT IOP.

RESULTS

Data from 200 patients with a mean age of 58.4 (±12.7) years were analysed. The mean central corneal thickness was 554.8 (±36.9) µm and the mean corneal hysteresis was 9.8 (±1.9) mm Hg. Sixty five (32.5%) had confirmed glaucomatous optic neuropathy. GAT IOP demonstrated poor agreement with DCT IOP. GAT IOP was on average 2.1 mm Hg less than DCT IOP. None of the six correction formulae resulted in improved agreement with DCT IOP. General linear model analysis found no statistically significant measurement differences between the glaucoma and glaucoma suspect groups.

CONCLUSIONS

GAT demonstrated poor agreement with DCT, and agreement did not improve after adjustment with correction formulae. Our results suggest that correction formulae for GAT IOP are unsuitable to clinically approximate 'true' IOP in Caucasian glaucoma and glaucoma suspect patients.

Changes of corneal central thickness of aphakia following congenital cataract surgery under the first six months of life

AIM

To observe the central corneal thickness (CCT) changes in infants and young children who had been undergone bilateral congenital cataract surgery, and to compare the changes with normal control group which was selected from healthy population.

METHODS

A cross section case-control study contained 28 cases (56 eyes) of bilateral aphakia (aphakic group) due to congenital cataract surgery combining with posterior continuous curvilinear capsulorhexis and with anterior vitrectomy during 2-6 months after birth. Fourteen children (28 eyes) of age-sex matched with the aphalic group were selected as normal control group. CCT and intraocular pressure (IOP) were measured postoperatively and the results were compared between groups.

RESULTS

The mean CCT was 653.5±82.4μm in the aphakic group and 579.6±39.2μm in the control group, with a significant difference (P=0.000). The mean value of IOP in aphakic group (22.0±1.6mmHg) was greater than that of control group (16.9±2.1mmHg), P=0.023. There was a negative correlation between age and CCT in normal control group (r=-0.531, P=0.026), and there was no correlation in bilateral aphakia group (r=-0.324, P=0.165)

CONCLUSION

Aphakic children due to congenital cataract surgery have a greater CCT than normal children. It is necessary to consider CCT in evaluating IOP for children after congenital cataract surgery.

Central corneal thickness and intraocular pressure in the Cameroonian nonglaucomatous population

Aim:

We performed a prospective, analytical study from 01 January to 31 March 2009 in the Ophthalmology Unit of the Gyneco-Obstetric and Pediatric Hospital of Yaounde, aiming to determine the profile of central corneal thickness (CCT) in the Cameroonian nonglaucomatous black population and its relationship with intraocular pressure (IOP).

Results and discussion:

Four hundred and eighty-five patients (970 eyes) meeting our inclusion criteria were selected for this study. The average CCT was 529.29 ± 35.9 μm in the right eye (95% confidence interval [CI]: 526.09–532.49), 528.19 ± 35.9 μm in the left eye (95% CI: 524.99–531.40) and 528.74 ± 35.89 μm in both eyes (95% CI: 526.48–531.00), range 440 to 670 μm. The average IOP was 13.01 ± 2.97 mmHg in both eyes (95% CI: 12.82–13.19). A rise in CCT by 100 μm was followed by an increase in IOP of about 2.8 mmHg (95% CI: 2.3–3.6) for both eyes taken together. Linear regression analysis showed that corneal thickness was negatively correlated with age and IOP was positively related with age.

Conclusion:

CCT in the Cameroonian nonglaucomatous black population was found to be lower compared with CCT values in Caucasian and Asian populations. On the basis of reference values ranging between 527 and 560 μm, an adjustment of IOP values by a correction factor is required for many Cameroonian patients. This will improve the diagnosis and follow-up of glaucoma by helping to detect true ocular hypertension.

Clinical evaluation of the Canon TX-10 noncontact tonometer in healthy eyes

PURPOSE

To assess the accuracy and repeatability of intraocular pressure (IOP) measurements obtained with the Canon TX-10 noncontact tonometer (NCT), using the Goldmann applanation tonometer (GAT) as the gold standard.

METHODS

Seventy-three young healthy subjects were enrolled in the study. Central corneal thickness (CCT) was obtained with Orbscan Topography System and then repeated IOP measurements were obtained with both tonometers. Canon TX-10 NCT was performed first, followed by GAT. Another study sample of 32 young healthy subjects was used to test the repeatability with both tonometers. Two sets of data were acquired separated by 1 week. Plotting the difference between the methods against the mean was done to compare the tonometers and the intersession variability. The hypothesis of zero bias was examined by a paired t test. The 95% limits of agreement (LoA) were also calculated.

RESULTS

No statistically significant differences were found when comparing the Canon TX-10 NCT with GAT, displaying close level of agreement with GAT as seen by the 95% LoA (-4.78 mmHg to +4.00 mmHg). CCT ranged from 419 microm to 585 microm and no relationship was found between CCT and IOP measurements. The coefficients of repeatability were 3.70 mmHg and 3.41 mmHg for GAT and TX-10 tonometers, respectively.

CONCLUSIONS

There was a good agreement between Canon TX-10 and GAT in healthy subjects. From the results obtained here, CCT appears to not affect IOP measurements when CCT is thinner than 570 microm.

Neuroprotection for treatment of glaucoma in adults

BACKGROUND

Glaucoma is a heterogeneous group of conditions involving progressive damage to the optic nerve, deterioration of retinal ganglion cells and ultimately visual field loss. It is a leading cause of blindness worldwide. Open angle glaucoma (OAG), the commonest form of glaucoma, is a chronic condition that may or may not present with increased intraocular pressure (IOP). Neuroprotection for glaucoma refers to any intervention intended to prevent optic nerve damage or cell death. The treatment can target extracellular factors such as reducing IOP, or cellular factors derived from the optic nerve itself such as blocking intracellular death signals.

OBJECTIVES

The objective of this review was to systematically examine the evidence regarding the effectiveness of neuroprotective agents, either topical or oral, for slowing the progression of OAG in adults.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (which contains the Cochrane Eyes and Vision Group Trials Register) (The Cochrane Library, Issue 4, 2009), MEDLINE (January 1960 to January 2010), EMBASE (January 1980 to January 2010), Latin American and Caribbean Literature on Health Sciences (LILACS) (January 1982 to January 2010) and ClinicalTrials.gov (http://clinicaltrials.gov). (5 January 2010). There were no language or date restrictions in the search for trials. The electronic databases were last searched on 5 January 2010.

SELECTION CRITERIA

This review was limited to randomized controlled trials (RCTs) in which topical or oral treatments were used to prevent retinal ganglion cell death. Our population of interest was adults with OAG. As the primary outcome for this review was the proportion of participants who developed any progression of visual field loss at five years post intervention, only trials with at least five years of follow-up were included.

DATA COLLECTION AND ANALYSIS

Two review authors independently reviewed titles and abstracts from the literature searches. Full text copies of relevant or potentially relevant studies were obtained and re-evaluated for inclusion. There were no trials identified for this review, thus we performed no data extraction or meta-analysis. Two studies comparing memantine to placebo are currently awaiting classification until additional study details are provided. Reasons for excluding studies from the review were documented.

MAIN RESULTS

In accordance with the selection criteria for inclusion, we identified no studies relevant for this review. The results of short-term trials and other studies are discussed in this review.

AUTHORS' CONCLUSIONS

Although neuroprotective agents are intended to act as pharmacological antagonists to prevent cell death, the evidence that they are effective in preventing retinal ganglion cell death, and thus preserving vision in patients with OAG, has not been demonstrated. Long-term RCTs are needed to determine whether or not neuroprotective agents may be beneficial for individuals with OAG.

Corneal hysteresis measured with the Ocular Response Analyzer in normal and glaucomatous eyes

PURPOSE

To identify differences in corneal hysteresis (CH) and central corneal thickness (CCT) between healthy and glaucomatous patients.

METHODS

Retrospective observational study. One hundred and thirty-three eyes of 75 healthy and 58 glaucomatous patients were included. CH was measured in each patient using Ocular Response Analyzer. CCT was determined by ultrasonic pachymetry. For each patient, one eye was randomly selected. We used a Student t-test to search for significant differences between the different groups (p<0.05).

RESULTS

In healthy and glaucomatous eyes, mean CH values were 10.46 +/- 1.6 and 8.77 +/- 1.4 mm Hg, respectively. Mean CCT values were 560.2 +/- 36.3 and 535.3 +/- 42.7 microm, respectively. CH and CCT were significantly lower in glaucomatous eyes than in normal eyes, (p<0.05).

DISCUSSION

In our series, CH was lower in glaucomatous than in normal eyes. The relationship between glaucoma, IOP, and ocular structures may not be confined to the consideration of CCT. A low CH value could be responsible for under-estimation of IOP. CH could also be a risk factor for glaucoma, independent of IOP. Further studies are needed to support these hypotheses.

CONCLUSION

In our investigation, CCT and CH were significantly lower in glaucomatous eyes than in healthy eyes.

Comparison of Pentacam Scheimpflug Camera with Ultrasound Pachymetry and Noncontact Specular Microscopy in Measuring Central Corneal Thickness

PURPOSE

Although central corneal thickness (CCT) can be measured by several methods, interchangeability of different modalities has not been fully investigated. CCT is known to correlate with intraocular pressure (IOP). The aim of this study was to evaluate the agreement of Pentacam Scheimpflug system with noncontact specular microscopy (NCSM) and ultrasound (US) pachymetry in measuring CCT and the relation between IOP taken with Goldmann applanation tonometer (GAT) and the CCT measured with these three methods.

METHODS

The right eyes of 135 enrolled persons without antiglaucoma drug use (100 females and 35 males), who comprised 32 patients with primary open-angle glaucoma, 14 with ocular hypertension, 45 with primary angle-closure glaucoma, and 44 controls, were studied. Intermethod comparison of CCT was made by the 95% limits of agreement analysis according to Bland and Altman. Linear regression analysis was used to assess the relationship between IOP and CCT taken with each modality.

RESULTS

The mean CCT (+/-SD) taken with Scheimpflug, US, and NCSM was 559.49 +/- 38.44 microm, 553.01 +/- 39.33 microm, and 552.04 +/- 42.95 microm, respectively. The average values of CCT taken with the three instruments were not significantly different (one-factor ANOVA; p = 0.26), although the marginal mean difference between Scheimpflug and US or NCSM was statistically significant (paired t test; p = 0.0009 and 0.005, respectively). The 95% limits of agreement were 6.47 +/- 43.21 microm between Scheimpflug and US, 7.45 +/- 58.86 microm between Scheimpflug and NCSM, and 0.98 +/- 51.69 microm between US and NCSM. There was a positive association between IOP and CCT measured with US or NCSM, whereas there was no correlation between IOP and CCT measured with Scheimpflug.

CONCLUSIONS

Although CCT values measured with Scheimpflug, US, and NCSM are closely similar, clinicians should keep in mind that these methods are not simply interchangeable.

A methodology based on the "anterior chamber of rabbit eyes" model for noninvasively determining the biocompatibility of biomaterials in an immune privileged site

In this study, a novel methodology based on the anterior chamber of rabbit eyes model was developed to evaluate the in vivo biocompatibility of biomaterials in an immune privileged site. The 7-mm-diameter membrane implants made from either a biological tissue material (amniotic membrane, AM group) or a biomedical polymeric material (gelatin, GM group) were inserted in rabbit anterior chamber for 36 months and characterized by biomicroscopic examinations, intraocular pressure measurements, and corneal thickness measurements. The noninvasive ophthalmic parameters were scored to provide a quantitative grading system. In this animal model, both AM and GM implants were visible in an ocular immune privileged site during clinical observations. The implants of the AM group appeared as soft tissue patches and have undergone a slow dissolution process resulting in a partial reduction of their size. Additionally, the AM implants did not induce any foreign body reaction or change in ocular tissue response for the studied period. By contrast, in the GM groups, significant corneal edema, elevated intraocular pressure, and increased corneal thickness were noted in the early postoperative phase (within 3 days), but resolved rapidly with in vivo dissolution of the gelatin. The results from the ocular grading system showed that both implants had good long-term biocompatibility in an ocular immune privileged site for up to 3 years. It is concluded that the anterior chamber of rabbit eyes model is an efficient method for noninvasively determining the immune privileged tissue/biomaterial interactions.

Corneal hysteresis and axial length among Chinese secondary school children: the Xichang Pediatric Refractive Error Study (X-PRES) report no. 4

PURPOSE

To evaluate the association between corneal hysteresis and axial length/refractive error among rural Chinese secondary school children.

DESIGN

Cross-sectional cohort study.

METHODS

Refractive error (cycloplegic auto-refraction with subjective refinement), central corneal thickness (CCT) and axial length (ultrasonic measurement), intraocular pressure (IOP), and corneal hysteresis (Reichert Ocular Response Analyzer) were measured on a rural school-based cohort of children.

RESULTS

Among 1,233 examined children, the mean age was 14.7 +/- 0.8 years and 699 (56.7%) were girls. The mean spherical equivalent (n = 1,232) was -2.2 +/- 1.6 diopters (D), axial length (n = 643) was 23.7 +/- 1.1 mm, corneal hysteresis (n = 1,153) was 10.7 +/- 1.6 mm Hg, IOP (n = 1,153) was 17.0 +/- 3.4 mm Hg, and CCT (n = 1,226) was 553 +/- 33 microns. In linear regression models, longer axial length was significantly (P < .001 for both) associated with lower corneal hysteresis and higher IOP. Hysteresis in this population was significantly (P < .001) lower than has previously been reported for normal White children (n = 42, 12.3 +/- 1.3 mm Hg), when adjusting for age and gender. This difference did not appear to depend on differences in axial length between the populations, as it persists when only Chinese children with normal uncorrected vision are included.

CONCLUSIONS

Prospective studies will be needed to determine if low hysteresis places eyes at risk for axial elongation secondary or if primary elongation results in lower hysteresis.

Corneal Thickness Measurement in the Management of Primary Open-angle Glaucoma

OBJECTIVE

To evaluate published literature to assess whether central corneal thickness (CCT) is a risk factor for the presence, development, or progression of glaucomatous optic nerve damage related to primary open-angle glaucoma (POAG).

METHODS

A PubMed literature search limited to English language articles conducted on November 15, 2004 retrieved 195 articles. The authors reviewed these abstracts and selected 57 to review in full text to determine relevance to the assessment questions. A further 24 studies of interest were identified from periodic updates to the literature search, surveillance of the literature, and reference lists of reviewed articles. From the 81 published reports identified, the first author applied specified selection criteria that yielded 37 articles for methodological review because of relevance to the assessment questions. The articles were rated according to the strength of evidence by the panel methodologist. A level I rating was assigned to well-designed properly conducted randomized clinical trials or similar quality-validated cohort studies with appropriate reference standards. A level II rating was assigned to well-designed case-control studies, exploratory cohort studies, and other nonrandomized clinical studies lacking consistently applied reference standards. A level III rating was reserved for poorly designed case-control studies, case series, and papers consisting only of expert opinion without supporting evidence. In addition, each study was graded as positive if it supported a statistical association of CCT with the risk of having or developing glaucomatous optic nerve damage or as negative if no such association was found.

RESULTS

There is strong and consistent level I and level II evidence that CCT is a risk factor for progression from ocular hypertension to POAG. Studies that were rated as providing the highest quality of evidence revealed mixed results with respect to glaucoma prevalence. One population-based study (level II) showed a positive association, another larger study (level I) revealed an association of marginal significance, and 3 studies (all level I) found no association of CCT with POAG prevalence.

CONCLUSIONS

There is strong evidence that measuring CCT is an important component of a complete ocular examination, particularly for patients being evaluated for the risk of developing POAG. Therefore, CCT measurement should be included in the examination of all patients with ocular hypertension. Although the evidence supporting the necessity of measuring CCT as part of screening for POAG or as a risk factor for glaucoma progression is not as strong, intraocular pressure (IOP) is the only modifiable risk factor in the treatment of glaucoma, and CCT has the potential to significantly impact IOP measurement by applanation tonometry in all patients.

Laser peripheral iridotomy in primary angle-closure suspects: biometric and gonioscopic outcomes: the Liwan Eye Study

PURPOSE

To assess the immediate effect of laser peripheral iridotomy (LPI) and mechanisms of angle closure in a population-based study of primary angle closure (PAC) suspects.

DESIGN

Prospective interventional study.

PARTICIPANTS

People identified as PAC suspects aged 50 to 79 years from a population-based survey in Guangzhou, China.

INTERVENTION

Laser peripheral iridotomy was performed in 1 randomly selected eye. Examinations were carried out before and 2 weeks after the intervention.

MAIN OUTCOME MEASURES

Intraocular pressure (IOP), ultrasound biometry, optical pachymetry, and gonioscopy.

RESULTS

A total of 72 people with bilateral suspected PAC participated in the study. Mean IOP decreased by 3 mmHg (P<0.001), but axial anterior chamber depth did not change significantly (P = 0.784) after LPI. Median limbal anterior chamber depth increased from 15% to 25% of peripheral corneal thickness (P<0.001, Wilcoxon signed-rank test). Median iridotrabecular angle width increased from 0 degrees to 10 degrees in the superior quadrant and from 10 degrees to 30 degrees in the inferior quadrant (P<0.001). Nevertheless, 14 eyes (19.4%) still had 3 or more quadrants in which the posterior (usually pigmented) trabecular meshwork could not be seen after laser iridotomy.

CONCLUSIONS

This study confirms that LPI results in a significant increase in the angle width in Chinese people with narrow angles. However, one fifth of eyes had residual angle closure after LPI. Although this report confirms that iridotomy widens the anterior chamber angle in most PAC suspects, long-term prospective studies with a larger sample size are required to determine if the risks of PAC glaucoma and other related pathologic sequelae are reduced after prophylactic LPI and to investigate the risk-to-benefit ratio before recommending widespread use of prophylactic LPI in this population.

Central corneal thickness and corneal hysteresis associated with glaucoma damage

PURPOSE

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.

DESIGN

Observational study.

METHODS

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.

RESULTS

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."

CONCLUSIONS

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.

Intermediate-term comparison of trabeculectomy with intraoperative mitomycin-C between Asian American and Caucasian glaucoma patients: a case-controlled comparison

PURPOSE

Compare the efficacy and survival of trabeculectomy with intraoperative mitomycin-C (MMC) between Asian American and Caucasian patients in the same clinical setting.

METHODS

In total, 29 Asian American patients (29 eyes) with trabeculectomies were matched case to case with 29 Caucasian patients (29 eyes) retrospectively. Matching criteria included age, glaucoma subtype, and preoperative intraocular pressure (IOP), gender, surgeon, ocular history, and glaucoma medications. Criteria of success included: (1) Final IOP>5 and <22 mmHg, (2) IOP reduction>or=20%, or final IOP<or=10 mmHg, and (3) without additional glaucoma surgery, loss of light perception, or complication.

RESULTS

Mean follow-up durations of Asian American and Caucasian group were 40.11+/-22.5 months and 38.8+/-17.7 months, respectively (P=0.81). At the final visits, IOP decreased from 18.7+/-6.1 to 10.9+/-4.0 mmHg (P<0.0001) in the Asian American group, and from 19.0+/-5.5 to 11.0+/-3.8 mmHg (P<0.0001) in the Caucasian group. There were no significant differences between the two groups in IOP levels at 6 months, 1 year, and final visits. The probabilities of trabeculectomy survival (continuing to meet definition of success criteria) at 12 and 48 months were 75.9 and 56.6% in the Asian American group and 82.8 and 66.6% in the Caucasian group, respectively. (P=0.46) There were no significant differences for rates of surgical success, failure, complication, vision decrease, hypotony, and cataract development. Patients who had episodes of hypotony had a higher rate of diagnosis of low-tension glaucoma subtype (P=0.02).

CONCLUSIONS

In a case-controlled comparison of an intermediate-term follow-up of trabeculectomy with intraoperative MMC, Asian American patients have a similar efficacy and survival probability as Caucasian patients.

A comparison of four methods of tonometry: method agreement and interobserver variability

AIM

To compare the inter-method agreement in intraocular pressure (IOP) measurements made with four different tonometric methods.

METHODS

IOP was measured with the Goldmann applanation tonometer (GAT), Tono-Pen XL, ocular blood flow tonograph (OBF), and Canon TX-10 non-contact tonometer (NCT) in a randomised order in one eye of each of 105 patients with ocular hypertension or glaucoma. Three measurements were made with each method, and by each of two independent GAT observers. GAT interobserver and tonometer inter-method agreement was assessed by the Bland-Altman method. The outcome measures were 95% limits of agreement for IOP measurements between GAT observers and between tonometric methods, and 95% confidence intervals for intra-session repeated measurements.

RESULTS

The mean differences (bias) in IOP measurements were 0.4 mm Hg between GAT observers, and 0.6 mm Hg, 0.1 mm Hg, and 0.7 mm Hg between GAT and Tono-Pen, OBF, and NCT, respectively. The 95% limits of agreement were smallest (bias +/-2.6 mm Hg) between GAT observers, and larger for agreement between the GAT and the Tono-Pen, OBF, and NCT (bias +/-6.7, +/-5.5, and +/-4.8 mm Hg, respectively). The OBF and NCT significantly underestimated GAT measurements at lower IOP and overestimated these at higher IOP. The repeatability coefficients for intra-session repeated measurement for each method were +/-2.2 mm Hg and +/-2.5 mm Hg for the GAT, +/-4.3 mm Hg for the Tono-Pen, +/-3.7 mm Hg for the OBF, and +/-3.2 mm Hg for the NCT.

CONCLUSIONS

There was good interobserver agreement with the GAT and moderate agreement between the NCT and GAT. The differences between the GAT and OBF and between the GAT and Tono-Pen probably preclude the OBF and Tono-Pen from routine clinical use as objective methods to measure IOP in normal adult eyes.

The influence of central corneal thickness and age on intraocular pressure measured by pneumotonometry, non-contact tonometry, the Tono-Pen XL, and Goldmann applanation tonometry

AIMS

To evaluate the influence of central corneal thickness (CCT) on intraocular pressure (IOP) measurements made with the Goldmann applanation tonometer (GAT), Tono-Pen XL, ocular blood flow tonograph (OBF), and Canon TX-10 non-contact tonometer (NCT).

METHODS

CCT was recorded for either eye (randomly selected) of each of 105 untreated patients with ocular hypertension and glaucoma attending the glaucoma research unit at Moorfields Eye Hospital. For each of the selected eyes, IOP was measured with the GAT (two observers), Tono-Pen, OBF, and NCT in a randomised order. The relation of measured IOP and of inter-tonometer differences with CCT and subject age was explored by linear regression analysis.

RESULTS

A significant association between measured IOP and CCT was found with each instrument. The change in measured IOP for a 10 mum increase in CCT was 0.28, 0.31, 0.38, and 0.46 for the GAT, Tono-Pen, OBF, and NCT, respectively (all p< or = 0.05). There was a significant association between the NCT/GAT differences and CCT, with a tendency of NCT to overestimate GAT in eyes with thicker corneas. There was a significant association between GAT/Tono-Pen and OBF/Tono-Pen differences and age, with a tendency of GAT and OBF to overestimate the Tono-Pen in eyes of older subjects.

CONCLUSION

IOP measurement by all four methods is affected by CCT. The NCT is affected by CCT significantly more than the GAT. Subject age has a differential effect on the IOP measurements made by the GAT and OBF compared to the Tono-Pen.

Glaukomdiagnostik und Hornhautdicke

In recent years the role of pachymetry in the correction of applanation tonometry values was controversially disputed. At the present time it is undoubtedly proven that central corneal thickness affects the accuracy of applanation tonometry. The dimension of this influence is 1 mmHg of pressure per 25 microm of change in corneal thickness. It is important to remember that Goldmann and Schmidt calibrated the applanation tonometer according to the central corneal thickness of their population by using the optical method. Therefore, it is first necessary to determine the corneal thickness for each examiner and his methods. The linear correction formula should be used only in the range of corneal thickness in which the formula was determined. The correction according to Orssengo and Pye and further developments in tonometry may offer alternatives for better estimation of intraocular pressure.

Central corneal thickness and its relationship to the patient's origin

OBJECTIVES

To report central corneal thickness (CCT) measurements on patients requesting refractive surgery and to search for possible associations between CCT and patient's origin, age, sex, and preoperative data.

SETTING

Department of Ophthalmology, Soroka University Medical Center, and Enaim Refractive Center, Beer-Sheva, Israel.

METHODS

Subjects were patients undergoing preoperative examination at our refractive centre during 2003. Patient's age, sex, preoperative CCT, refractive status, keratometry, and intraocular pressure (IOP) were obtained together with country of origin of the patients and their parents. Main outcome measures were CCT measurements and relationship between CCT and patient's origin and preoperative data.

RESULTS

A total of 204 patients were included in the study. Patients of North African origin had statistically significantly thinner corneas than patients of other origins (518.9+/-31.5 vs. 545.4+/-30.4 microm in the right eye and 518.4+/-32.1 vs. 546.3+/-29.7 microm in the left eye; P<0.00001). Patients of North African origin were significantly older than patients of other origins (P=0.028). No differences were found when comparing for sex, intraocular pressure, refractive status, and keratometry. When multivariate analysis was performed patient's origin was the only independently associated factor associated with CCT.

CONCLUSIONS

This is the first work in reporting lower CCT in people of North African origin examined in a refractive surgery centre. Studies from similar populations are needed to confirm our results.

Comparison of intraocular pressure measured by Pascal dynamic contour tonometry and Goldmann applanation tonometry

AIMS

To compare the intraocular pressure (IOP) measurements obtained using the Pascal dynamic contour tonometer (PDCT) with the standard Goldmann applanation tonometer (GAT) and to correlate these with central corneal thickness (CCT) in patients with normal corneas.

METHODS

A prospective, masked, comparative case series of 116 eyes from patients attending a glaucoma clinic. IOP was measured with PDCT by one examiner and with GAT by a masked, independent examiner. A mean of six CCT readings was used for analysis.

RESULTS

IOP measured by the two instruments correlated significantly (r=0.77; P<0.0001). IOP measured by GAT correlated strongly with CCT (r=0.37, P=0.0001) whereas the relationship between IOP measured by PDCT and CCT approached significance (r=0.17, P=0.073). The differences between GAT and PDCT measured IOP also correlated strongly with CCT (r=0.37, P<0.0001). The 95% limits of agreement between GAT and PDCT were +/-4.2 mmHg. Dividing the eyes into three groups on the basis of CCT, demonstrated those in the thickest tertile showed a poorer agreement between instruments and the GAT measured significantly higher IOP in this group (P=0.003) while the PDCT showed no significant differences with different CCTs (P=0.37).

CONCLUSION

Demonstration of the relative independence of PDCT IOP measurements from CCT supports a potential clinical role for this instrument, particularly for subjects with CCT outside the normal range.

Causes of low vision and blindness in rural Indonesia

AIM

To determine the prevalence rates and major contributing causes of low vision and blindness in adults in a rural setting in Indonesia

METHODS

A population based prevalence survey of adults 21 years or older (n=989) was conducted in five rural villages and one provincial town in Sumatra, Indonesia. One stage household cluster sampling procedure was employed where 100 households were randomly selected from each village or town. Bilateral low vision was defined as habitual VA (measured using tumbling "E" logMAR charts) in the better eye worse than 6/18 and 3/60 or better, based on the WHO criteria. Bilateral blindness was defined as habitual VA worse than 3/60 in the better eye. The anterior segment and lens of subjects with low vision or blindness (both unilateral and bilateral) (n=66) were examined using a portable slit lamp and fundus examination was performed using indirect ophthalmoscopy.

RESULTS

The overall age adjusted (adjusted to the 1990 Indonesia census population) prevalence rate of bilateral low vision was 5.8% (95% confidence interval (CI) 4.2 to 7.4) and bilateral blindness was 2.2% (95% CI 1.1 to 3.2). The rates of low vision and blindness increased with age. The major contributing causes for bilateral low vision were cataract (61.3%), uncorrected refractive error (12.9%), and amblyopia (12.9%), and the major cause of bilateral blindness was cataract (62.5%). The major causes of unilateral low vision were cataract (48.0%) and uncorrected refractive error (12.0%), and major causes of unilateral blindness were amblyopia (50.0%) and trauma (50.0%).

CONCLUSIONS

The rates of habitual low vision and blindness in provincial Sumatra, Indonesia, are similar to other developing rural countries in Asia. Blindness is largely preventable, as the major contributing causes (cataract and uncorrected refractive error) are amenable to treatment.

Hypertension, diabetes, and longitudinal changes in intraocular pressure

PURPOSE

Diabetes and hypertension are recognized risk factors for raised intraocular pressure (IOP). This report examines the longitudinal relationship of hypertension and diabetes to a 4-year IOP change in a black population with high prevalence of these conditions.

DESIGN

Population-based cohort study of a simple random sample of residents of Barbados, West Indies, aged >/=40 years.

PARTICIPANTS

A total of 2996 persons without open-angle glaucoma or receiving IOP-lowering medication at baseline.

METHODS

Participants underwent standardized examinations including applanation tonometry, measurement of blood pressure, and anthropometric indices; a detailed interview; various ocular measurements; and venipuncture for glycosylated hemoglobin (GHb). Diabetes was defined by self-reported physician diagnosis and hypertension by blood pressure >/=140/90 mmHg and/or treatment history.

MAIN OUTCOME MEASURES

The 4-year person-based IOP change between baseline and follow-up was defined as the more positive IOP difference in either eye.

RESULTS

An IOP >21 mmHg at baseline was more likely in black and in mixed (black and white) participants (age-gender adjusted odds ratio [OR], 3.9 and 3.8, respectively) than in whites. Similarly, these groups had more hypertension (age-gender adjusted OR, 2.4 and 2.1, respectively) and diabetes (age-gender adjusted OR, 3.9 and 1.7, respectively) than did whites. Mean IOP in black participants increased by 2.5 (standard deviation, 3.9) mmHg over 4 years. Multiple regression analyses showed that baseline diabetes history and hypertension, as well as older age, elevated GHb, higher blood pressures, and lower baseline IOP were associated with a 4-year increase of IOP. The association between diabetes history/GHb and IOP increase became borderline/nonsignificant when persons who underwent cataract surgery during follow-up were excluded.

CONCLUSIONS

This report provides new data on the relationship of systemic factors to longitudinal increases in IOP in an African-origin population. Results highlight the increased risk of elevated IOP in populations with high prevalences of diabetes and hypertension.

Correlational study of central corneal thickness measurements on Hong Kong Chinese using optical coherence tomography, Orbscan and ultrasound pachymetry

BACKGROUND

Central corneal thickness (CCT) of 74 eyes from 39 normal Hong Kong Chinese subjects with ages ranging from 39 to 86 years were studied.

AIM & PURPOSE

To compare the measurements of different devices and to compare the results of ethnic groups in other studies.

METHODS

Non-contact measurements by Orbscan and Optical Coherence Tomography (OCT) were first carried out, followed by contact measurement using Ultrasound Pachymetry. The results of five measurements of Ultrasound Pachymetry and three measurements of OCT and Orbscan were each averaged and compared using correlation, linear regression and one-way analysis of variance methods.

RESULTS

The measurements of three devices were significantly correlated (P < 0.01). The mean CCT in our study group measured by Orbscan (with an acoustic factor set at 0.92), Ultrasound Pachymetry and OCT were 555.96 +/- 32.41, 555.11 +/- 35.30 and 523.2 +/- 33.54 microm respectively. A linear regression model (using ultrasound measurements as standard) was presented.

CONCLUSIONS

When a correction factor of 32 microm was applied to OCT measurements, the means of three devices became significantly equal. The adjusted OCT measurements were less precise within subjects but more accurate than Orbscan when compared with ultrasound pachymetry as a reference standard. The mean CCT measurement of our sample was comparable to some studies on Hong Kong Chinese, Caucasians and Japanese but higher than those on some Europeans, Asian and North Americans of African origin.

The corneal thickness and intraocular pressure story: where are we now?

A review of the current literature was conducted regarding the effect of corneal thickness on the diagnosis of glaucoma, and the influence of excimer laser refractive surgery on intraocular pressure (IOP) measurement with Goldmann applanation tonometry. In general, normals and primary open angle glaucoma patients have a similar distribution of corneal thickness; however, there is a wide variation, ranging from 427 to 716 micro m. Normal tension glaucoma patients have a tendency towards thinner corneas than normals; however, there is an overlap of thickness measurements of more than two-thirds in 95% of patients. There is a trend for ocular hypertensives to have thicker corneas than normals, but again there is an overlap of about one-third in 95% of patients. The general trend after excimer laser refractive surgery is for a decrease in IOP, with a mean fall in IOP measured of 0.63 mmHg per dioptre correction. There is, however, a large scatter of values with some patients having the same or lower IOP post-laser, but with other patients measuring higher pressures. Corneal thickness can influence IOP measurement by Goldmann applanation tonometry; however, the magnitude of the effect is subject to much individual variation.

The reliability of clinical methods in ophthalmology

The reliability of clinical methods is often taken for granted. There is considerable evidence, however, that variability of clinical measurements, interpretations, and judgements are greater than commonly thought. Inconsistency of clinical methods has profound and widespread implications in clinical practice. The inferential capacity of measurements depends on accuracy and reproducibility. Appropriate medical decisions cannot be reached without accurate and reliable data. This review will examine the conceptual relationship of reliability, accuracy, and validity. The role of observer reliability in ophthalmic test measurements and interpretations will be addressed in the context of three case reports.