Comparison of glaucomatous progression between untreated patients with normal-tension glaucoma and patients with therapeutically reduced intraocular pressures. Collaborative Normal-Tension Glaucoma Study Group

PURPOSE

To determine if intraocular pressure plays a part in the pathogenic process of normal-tension glaucoma.

METHODS

One eye of each eligible subject was randomized either to be untreated as a control or to have intraocular pressure lowered by 30% from baseline. Eyes were randomized if they met criteria for diagnosis of normal-tension glaucoma and showed documented progression or high-risk field defects that threatened fixation or the appearance of a new disk hemorrhage. The clinical course (visual field and optic disk) of the group with lowered intraocular pressure was compared with the clinical course when intraocular pressure remained at its spontaneous untreated level.

RESULTS

One hundred-forty eyes of 140 patients were used in this study. Sixty-one were in the treatment group, and 79 were untreated controls. Twenty-eight (35%) of the control eyes and 7 (12%) of the treated eyes reached end points (specifically defined criteria of glaucomatous optic disk progression or visual field loss). An overall survival analysis showed a statistically significant difference between the two groups (P < .0001). The mean survival time +/-SD of the treated group was 2,688 +/- 123 days and for the control group, 1,695 +/- 143 days. Of 34 cataracts developed during the study, 11 (14%) occurred in the control group and 23 (38%) in the treated group (P = .0075), with the highest incidence in those whose treatment included filtration surgery.

CONCLUSIONS

Intraocular pressure is part of the pathogenic process in normal-tension glaucoma. Therapy that is effective in lowering intraocular pressure and free of adverse effects would be expected to be beneficial in patients who are at risk of disease progression.

Human corneal thickness and its impact on intraocular pressure measures: a review and meta-analysis approach

We determined the "normal" central corneal thickness (CCT) value in human corneas based on reported literature values for within-study average CCT values, and used this as a reference to assess the reported impact of physiological variables (especially age and diurnal effects), contact lens wear, pharmaceuticals, ocular disease, and ophthalmic surgery on CCT. With the expected CCT and its variance defined, it should be possible to determine the potential impact of differences in CCT in intraocular pressure (IOP) assessments, especially by applanation tonometry, using a meta-analysis approach. Some 600 sets of CCT data were identified from the worldwide literature over the period of 1968 through mid-1999, of which 134 included IOP measures as well. The within-study average CCT values and reported variance (SD) was noted along with the number of eyes and any special characteristics, including probable ethnic origin of the study subjects. Various sets of data were subjected to statistical analyses. From 300 data sets from eyes designated as normal, the group-averaged CCT was 0.534 mm. From 230 data sets where interindividual variance was reported, the group-averaged CCT was 0.536 mm (median 0.536 mm; average SD of 0. 031 mm, average coefficient of variation = 5.8%). Overall, studies using slit-lamp-based pachometry have reported marginally lower CCT values (average 0.530 mm, average SD 0.029 mm) compared to ultrasound-based studies (average 0.544, average SD 0.034 mm), which perhaps reflects the type of individual studied (non-surgical vs. pre-surgical patients) rather than the technique itself. A slight chronological increase in reported average CCT values (approximately 0.006 mm/decade) was evident, but a substantial chronological increase was evident for ultrasound pachometry studies (approximately 0.015 mm/decade). Within the meta-analysis-generated average and variance, age had no obvious impact on CCT measures for *whites, although an age-related decline in CCT is evident for non-whites. Any diurnal effects are likely concealed within the expected variance in CCT. Contact lens wear and pharmaceuticals generally produced changes in CCT that were well within the expected variance in CCT. Of the ocular diseases, only those associated with collagen disorders (including keratoconus) or endothelial-based corneal dystrophies (e.g., Fuchs) were likely to result in decreases or increases, respectively, of CCT beyond the normal variance. Routine contact lens wear and diseases such as diabetes seem unlikely to produce changes in CCT of a magnitude that would justify pachometry as a monitoring method beyond routine slit-lamp evaluation. Increases in CCT beyond the expected variance were reported after a range of intraocular surgeries (cataract operations, penetrating keratoplasty), whereas photorefractive surgery produces a measurable decrease in CCT. A meta-analysis of possible association between CCT and IOP measures of 133 data sets, regardless of the type of eyes assessed, revealed a statistically significant correlation; a 10% difference in CCT would result in a 3. 4 +/- 0.9 mm Hg difference in IOP (P </= 0.001, r = 0.419). The observed phenomenon was much smaller for eyes designated as healthy (1.1 +/- 0.6 mm Hg for a 10% difference in CCT, P = 0.023, r = 0. 331). For eyes with chronic diseases, the change was 2.5 +/- 1.1 mm Hg for a 10% difference in CCT (P = 0.005, r = 0.450), whereas a substantial but highly variable association was seen for eyes with acute onset disease (approximately 10.0 +/- 3.1 mm Hg for a 10% difference in CCT, P = 0.004, r = 0.623). Based on the meta-analysis, normal CCT in white adults would be expected to be within +/-11.6% (+/-2 SD) of 0.535 mm, i.e., 0.473-0.597 mm (95% CI, 0.474-0.596). The impact of CCT on applanation tonometry of healthy eyes is unlikely to achieve clinical significance, but for corneas of eyes with chronic disease, pachometry should be performed if the tonometry reveals IOP readi

Glaucoma

Glaucoma is a heterogeneous group of diseases characterised by cupping of the optic nerve head and visual-field damage. It is the most frequent cause of irreversible blindness worldwide. Progression usually stops if the intraocular pressure is lowered by 30-50% from baseline. Its worldwide age-standardised prevalence in the population aged 40 years or older is about 3·5%. Chronic forms of glaucoma are painless and symptomatic visual-field defects occur late. Early detection by ophthalmological examination is mandatory. Risk factors for primary open-angle glaucoma-the most common form of glaucoma-include older age, elevated intraocular pressure, sub-Saharan African ethnic origin, positive family history, and high myopia. Older age, hyperopia, and east Asian ethnic origin are the main risk factors for primary angle-closure glaucoma. Glaucoma is diagnosed using ophthalmoscopy, tonometry, and perimetry. Treatment to lower intraocular pressure is based on topical drugs, laser therapy, and surgical intervention if other therapeutic modalities fail to prevent progression.

Determining in vivo biomechanical properties of the cornea with an ocular response analyzer

PURPOSE

To study the results of an ocular response analyzer (ORA) to determine the biomechanical properties of the cornea and their relationship to intraocular pressure (IOP).

SETTING

Reichert Inc., Depew, New York, USA.

METHODS

The ORA (Reichert) makes 2 essentially instantaneous applanation measurements that permit determination of corneal and IOP effects.

RESULTS

Measurements of several populations indicate that corneal hysteresis, a biomechanical measure, varied over a dynamic range of 1.8 to 14.6 mm Hg and was only weakly correlated with corneal thickness (r(2)=0.12); this is related to the observation that some subjects with relatively thick corneas have less-than-average corneal hysteresis. Corneal hysteresis changes diurnally, presumably as a result of hydration changes. Keratoconus, Fuchs' dystrophy, and post-LASIK patients demonstrated low corneal hysteresis.

CONCLUSION

The corneal hysteresis biomechanical measure may prove valuable for qualification and predictions of outcomes of refractive surgery and in other cases in which corneal biomechanics are important.

Interim clinical outcomes in the Collaborative Initial Glaucoma Treatment Study comparing initial treatment randomized to medications or surgery

PURPOSE

To report interim outcome data, using all available follow-up through 5 years after treatment initiation, in the Collaborative Initial Glaucoma Treatment Study (CIGTS).

DESIGN

Randomized clinical trial.

PARTICIPANTS

Six hundred seven newly diagnosed glaucoma patients.

METHODS

In a randomized clinical trial, 607 patients with newly diagnosed open-angle glaucoma were initially treated with either medication or trabeculectomy (with or without 5-fluorouracil). After treatment onset and early follow-up, patients were evaluated clinically at 6-month intervals. In addition, quality of life telephone interviews were conducted at similar frequency to the clinical visits. Patients in both arms of CIGTS were treated aggressively in an effort to reduce intraocular pressure (IOP) to a level at or below a predetermined target pressure specific for each individual eye. Visual field (VF) scores were analyzed by time-specific comparisons and by repeated measures models.

MAIN OUTCOME MEASURES

VF loss was the primary outcome variable in CIGTS. Secondary outcomes of visual acuity (VA), IOP, and cataract were also studied.

RESULTS

On the basis of completed follow-up through 4 years and partially completed through 5 years, VF loss did not differ significantly by initial treatment. Over the entire period of follow-up, surgical patients had a greater risk of substantial VA loss compared with medical patients. However, by 4 years after treatment, the average VA in the two groups was about equal. Over the course of follow-up, IOP in the medicine group has averaged 17 to 18 mmHg, whereas that in the surgery group averaged 14 to 15 mmHg. The rate of cataract requiring removal was greater in the surgically treated group.

CONCLUSIONS

Both initial medical or initial surgical therapy result in about the same VF outcome after up to 5 years of follow-up. VA loss was greater in the surgery group, but the differences between groups seem to be converging as follow-up continues. When aggressive treatment aimed at substantial reduction in IOP from baseline is used, loss of VF can be seen to be minimal in general. Because 4 to 5 years of follow-up in a chronic disease is not adequate to draw treatment conclusions, these interim CIGTS outcomes do not support altering current treatment approaches to open-angle glaucoma.

Treatment outcomes in the Tube Versus Trabeculectomy (TVT) study after five years of follow-up

PURPOSE

To report 5-year treatment outcomes in the Tube Versus Trabeculectomy (TVT) Study.

DESIGN

Multicenter randomized clinical trial.

METHODS

SETTINGS

Seventeen clinical centers.

STUDY POPULATION

Patients 18 to 85 years of age who had previous trabeculectomy and/or cataract extraction with intraocular lens implantation and uncontrolled glaucoma with intraocular pressure (IOP) ≥18 mm Hg and ≤40 mm Hg on maximum tolerated medical therapy.

INTERVENTIONS

Tube shunt (350-mm(2) Baerveldt glaucoma implant) or trabeculectomy with mitomycin C ([MMC]; 0.4 mg/mL for 4 minutes).

MAIN OUTCOME MEASURES

IOP, visual acuity, use of supplemental medical therapy, and failure (IOP >21 mm Hg or not reduced by 20%, IOP ≤5 mm Hg, reoperation for glaucoma, or loss of light perception vision).

RESULTS

A total of 212 eyes of 212 patients were enrolled, including 107 in the tube group and 105 in the trabeculectomy group. At 5 years, IOP (mean ± SD) was 14.4 ± 6.9 mm Hg in the tube group and 12.6 ± 5.9 mm Hg in the trabeculectomy group (P = .12). The number of glaucoma medications (mean ± SD) was 1.4 ± 1.3 in the tube group and 1.2 ± 1.5 in the trabeculectomy group (P = .23). The cumulative probability of failure during 5 years of follow-up was 29.8% in the tube group and 46.9% in the trabeculectomy group (P = .002; hazard ratio = 2.15; 95% confidence interval = 1.30 to 3.56). The rate of reoperation for glaucoma was 9% in the tube group and 29% in the trabeculectomy group (P = .025).

CONCLUSIONS

Tube shunt surgery had a higher success rate compared to trabeculectomy with MMC during 5 years of follow-up in the TVT Study. Both procedures were associated with similar IOP reduction and use of supplemental medical therapy at 5 years. Additional glaucoma surgery was needed more frequently after trabeculectomy with MMC than tube shunt placement.

Large diurnal fluctuations in intraocular pressure are an independent risk factor in patients with glaucoma

PURPOSE

To study the risk associated with diurnal intraocular pressure (IOP) variations in patients with open-angle glaucoma.

PATIENTS AND METHODS

Sixty-four patients (105 eyes) from the practices of two glaucoma specialists successfully performed home tonometry with a self-tonometer five times a day for 5 days. All patients had open-angle glaucoma and documented IOP below 25 mm Hg over a mean follow-up period of 5 years. Baseline status and time to progression of visual field loss were identified from the clinical charts. The level and variability of diurnal IOP obtained using home tonometry were characterized. Risk of progression was analyzed using a nonparametric time-to-event model, incorporating methods for correlated outcomes.

RESULTS

Although mean home IOP and baseline office IOP were similar (16.4 +/- 3.6 mm Hg and 17.6 +/- 3.2 mm Hg, respectively), the average IOP range over the 5 days of home tonometry was 10.0 +/- 2.9 mm Hg. Baseline office IOP had no predictive value (relative hazard, 0.98). The diurnal IOP range and the IOP range over multiple days were significant risk factors for progression, even after adjusting for office IOP, age, race, gender, and visual field damage at baseline (relative hazards [95% confidence intervals], 5.69 [1.86, 17.35] and 5.76 [2.21, 14.98]). Eighty-eight percent of patients in the upper twenty-fifth percentile of IOP and 57% of patients in the lower twenty-fifth percentile progressed within 8 years.

CONCLUSIONS

In patients with glaucoma with office IOP in the normal range, large fluctuations in diurnal IOP are a significant risk factor, independent of parameters obtained in the office. Fluctuations in IOP may be important in managing patients with glaucoma. Development of methods to control fluctuations in IOP may be warranted.

Postoperative complications in the Tube Versus Trabeculectomy (TVT) study during five years of follow-up

PURPOSE

To describe postoperative complications encountered in the Tube Versus Trabeculectomy (TVT) Study during 5 years of follow-up.

DESIGN

Multicenter randomized clinical trial.

METHODS

SETTINGS

Seventeen clinical centers.

STUDY POPULATION

Patients 18 to 85 years of age who had previous trabeculectomy and/or cataract extraction with intraocular lens implantation and uncontrolled glaucoma with intraocular pressure (IOP) ≥18 mm Hg and ≤40 mm Hg on maximum tolerated medical therapy.

INTERVENTIONS

Tube shunt (350-mm(2) Baerveldt glaucoma implant) or trabeculectomy with mitomycin C (MMC 0.4 mg/mL for 4 minutes).

MAIN OUTCOME MEASURES

Surgical complications, reoperations for complications, visual acuity, and cataract progression.

RESULTS

Early postoperative complications occurred in 22 patients (21%) in the tube group and 39 patients (37%) in the trabeculectomy group (P = .012). Late postoperative complications developed in 36 patients (34%) in the tube group and 38 patients (36%) in the trabeculectomy group during 5 years of follow-up (P = .81). The rate of reoperation for complications was 22% in the tube group and 18% in the trabeculectomy group (P = .29). Cataract extraction was performed in 13 phakic eyes (54%) in the tube group and 9 phakic eyes (43%) in the trabeculectomy group (P = .43).

CONCLUSIONS

A large number of surgical complications were observed in the TVT Study, but most were transient and self-limited. The incidence of early postoperative complications was higher following trabeculectomy with MMC than tube shunt surgery. The rates of late postoperative complications, reoperation for complications, and cataract extraction were similar with both surgical procedures after 5 years of follow-up.

Sources of error with use of Goldmann-type tonometers

There are many sources of error in the use of Goldmann-type applanation tonometers. In clinically normal corneas hypofluorescence of the precorneal tear film, accommodation, the Valsalva maneuver and vertical gaze are preventable causes of large tonometric errors. Repeated tonometry may induce a decline in the intraocular pressure (IOP). Variations in the corneal resistance to indentation between eyes cause significant errors. The most significant cause of error in clinically abnormal eyes is corneal epithelial edema, which causes a marked underestimation of IOP. Measurements obtained with Goldmann-type tonometers can be used with confidence to monitor changes in the IOP of an individual, but should not be relied on to determine the absolute manometric pressure within an eye or to compare the IOPs in eyes of different individuals.

Influence of corneal biomechanical properties on intraocular pressure measurement

PURPOSE

To understand and quantify intraocular pressure (IOP) measurement errors introduced by corneal variables during applanation tonometry using a cornea biomechanical model.

SETTING

Department of Ophthalmology, Biomedical Engineering Center, The Ohio State University, Columbus, Ohio, USA.

METHODS

The model assumed an overall resultant pressure that was based on the summation of the applanation pressure, the true IOP, and the surface tension caused by the tear film to determine the final deformation of the corneal apex during IOP measurement. Corneal resistance was varied according to the cornea's biomechanical properties, thickness, and curvature, and the effect of each variable on the accuracy of IOP tonometry readings was examined quantitatively.

RESULTS

The model demonstrated that tonometry readings do not always reflect true IOP values. They deviate when corneal thickness, curvature, or biomechanical properties vary from normal values. Based on the model, predicted IOP readings have a 2.87 mm Hg range resulting from the variation in the corneal thickness in the normal population and a 1.76 mm Hg range from the variation in the corneal radius of curvature. Considering that Young's modulus of the corneal varies from 0.1 to 0.9 MPa in the normal population, the model predicts tonometry IOP readings will have a range of 17.26 mm Hg because of the variation in this corneal biomechanical parameter alone.

CONCLUSIONS

The simulation based on the model demonstrated quantitatively that variations in each corneal variable cause errors in tonometry IOP readings. The simulation results indicate that differences in corneal biomechanics across individuals may have greater impact on IOP measurement errors than corneal thickness or curvature.

Nocturnal arterial hypotension and its role in optic nerve head and ocular ischemic disorders

We measured 24-hour ambulatory blood pressure monitoring and diurnal curve of the intraocular pressure in 166 white patients with anterior ischemic optic neuropathy, normal-tension glaucoma, primary open-angle glaucoma, and other optic nerve head disorders. Hourly average blood pressure data analyses showed a significant (P < .0001) decrease in mean systolic (26%) and diastolic (33%) blood pressure measurements at night. A significantly (P = .0028) lower nighttime mean diastolic blood pressure and a significantly (P = .0044) greater mean percentage decrease in diastolic blood pressure were noted in normal-tension glaucoma than in anterior ischemic optic neuropathy. Patients with arterial hypertension taking oral hypotensive therapy showed a significant association between progressive visual field deterioration and nocturnal hypotension, particularly in anterior ischemic optic neuropathy. Intraocular pressure showed no significant correlation with visual field deterioration in any of these conditions. Our findings suggest that nocturnal hypotension, in the presence of other vascular risk factors, may reduce the optic nerve head blood flow below a critical level, and thereby may play a role in the pathogenesis of anterior ischemic optic neuropathy and glaucomatous optic neuropathy; that is, nocturnal hypotension may be the final insult in a multifactorial situation. The same mechanisms may be true of a number of other ocular ischemic disorders. This finding opens a new dimension in the understanding and management of these visually disabling diseases.

Hypertension, perfusion pressure, and primary open-angle glaucoma. A population-based assessment

OBJECTIVE

To evaluate the association of vascular factors with primary open-angle glaucoma (POAG).

DESIGN

A population-based prevalence survey of ocular disease among black and white residents.

SETTING

Communities of east Baltimore, Md.

PARTICIPANTS

A stratified cluster sample of 5308 residents 40 years of age or older.

MAIN OUTCOME MEASURES

Primary open-angle glaucoma as defined by demonstrable glaucomatous optic nerve damage based on visual fields and/or optic disc findings. Intraocular pressure level was not a criterion for diagnosis.

RESULTS

Systolic and diastolic blood pressure showed modest, positive association with POAG. The effect of blood pressure on POAG was modified by age, with a stronger association among older subjects. Lower perfusion pressure (blood pressure-intraocular pressure) was strongly associated with an increased prevalence of POAG, with a sixfold excess for those in the lowest category of perfusion pressure.

CONCLUSION

These results suggest that POAG is associated with an alteration in factors related to ocular blood flow and a breakdown of autoregulation.

Wearable smart sensor systems integrated on soft contact lenses for wireless ocular diagnostics

Wearable contact lenses which can monitor physiological parameters have attracted substantial interests due to the capability of direct detection of biomarkers contained in body fluids. However, previously reported contact lens sensors can only monitor a single analyte at a time. Furthermore, such ocular contact lenses generally obstruct the field of vision of the subject. Here, we developed a multifunctional contact lens sensor that alleviates some of these limitations since it was developed on an actual ocular contact lens. It was also designed to monitor glucose within tears, as well as intraocular pressure using the resistance and capacitance of the electronic device. Furthermore, in-vivo and in-vitro tests using a live rabbit and bovine eyeball demonstrated its reliable operation. Our developed contact lens sensor can measure the glucose level in tear fluid and intraocular pressure simultaneously but yet independently based on different electrical responses.

Extracellular matrix in the trabecular meshwork

The extracellular matrix (ECM) of the trabecular meshwork (TM) is thought to be important in regulating intraocular pressure (IOP) in both normal and glaucomatous eyes. IOP is regulated primarily by a fluid resistance to aqueous humor outflow. However, neither the exact site nor the identity of the normal resistance to aqueous humor outflow has been established. Whether the site and nature of the increased outflow resistance, which is associated with open-angle glaucoma, is the same or different from the normal resistance is also unclear. The ECMs of the TM beams, juxtacanalicular region (JCT) and Schlemm's canal (SC) inner wall are comprised of fibrillar and non-fibrillar collagens, elastin-containing microfibrils, matricellular and structural organizing proteins, glycosaminoglycans (GAGs) and proteoglycans. Both basement membranes and stromal ECM are present in the TM beams and JCT region. Cell adhesion proteins, cell surface ECM receptors and associated binding proteins are also present in the beams, JCT and SC inner wall region. The outflow pathway ECM is relatively dynamic, undergoing constant turnover and remodeling. Regulated changes in enzymes responsible for ECM degradation and biosynthetic replacement are observed. IOP homeostasis, triggered by pressure changes or mechanical stretching of the TM, appears to involve ECM turnover. Several cytokines, growth factors and drugs, which affect the outflow resistance, change ECM component expression, mRNA alternative splicing, cellular cytoskeletal organization or all of these. Changes in ECM associated with open-angle glaucoma have been identified.

Factors influencing optic nerve head biomechanics

PURPOSE

The biomechanical environment within the optic nerve head (ONH) may play a role in retinal ganglion cell loss in glaucomatous optic neuropathy. This was a systematic analysis in which finite element methods were used to determine which anatomic and biomechanical factors most influenced the biomechanical response of the ONH to acute changes in IOP.

METHODS

Based on a previously described computational model of the eye, each of 21 input factors, representing the biomechanical properties of relevant ocular tissues, the IOP, and 14 geometric factors were independently varied. The biomechanical response of the ONH tissues was quantified through a set of 29 outcome measures, including peak and mean stress and strain within each tissue, and measures of geometric changes in ONH tissues. Input factors were ranked according to their aggregated influence on groups of outcome measures.

RESULTS

The five input factors that had the largest influence across all outcome measures were, in ranked order: stiffness of the sclera, radius of the eye, stiffness of the lamina cribrosa, IOP, and thickness of the scleral shell. The five least influential factors were, in reverse ranked order: retinal thickness, peripapillary rim height, cup depth, cup-to-disc ratio, and pial thickness. Factor ranks were similar for various outcome measure groups and factor ranges.

CONCLUSIONS

The model predicts that ONH biomechanics are strongly dependent on scleral biomechanical properties. Acute deformations of ONH tissues, and the consequent high levels of neural tissue strain, were less strongly dependent on the action of IOP directly on the internal surface of the ONH than on the indirect effects of IOP on the sclera. This suggests that interindividual variations in scleral properties could be a risk factor for the development of glaucoma. Eye size and lamina cribrosa biomechanical properties also have a strong influence on ONH biomechanics.

Detection of Keratoconus With a New Biomechanical Index

PURPOSE

To evaluate the ability of a new combined biomechanical index called the Corvis Biomechanical Index (CBI) based on corneal thickness profile and deformation parameters to separate normal from keratoconic patients.

METHODS

Six hundred fifty-eight patients (329 eyes in each database) were included in this multicenter retrospective study. Patients from two clinics located on different continents were selected to test the capability of the CBI to separate healthy and keratoconic eyes in more than one ethnic group using the Corvis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany). Logistic regression was employed to determine, based on Database 1 as the development dataset, the optimal combination of parameters to accurately separate normal from keratoconic eyes. The CBI was subsequently independently validated on Database 2.

RESULTS

The CBI included several dynamic corneal response parameters: deformation amplitude ratio at 1 and 2 mm, applanation 1 velocity, standard deviation of deformation amplitude at highest concavity, Ambrósio's Relational Thickness to the horizontal profile, and a novel stiffness parameter. The receiver operating characteristic curve analysis of the training database showed an area under the curve of 0.983. With a cut-off value of 0.5, 98.2% of the cases were correctly classified with 100% specificity and 94.1% sensitivity. In the validation dataset, the same cut-off point correctly classified 98.8% of the cases with 98.4% specificity and 100% sensitivity.

CONCLUSIONS

The CBI was shown to be highly sensitive and specific to separate healthy from keratoconic eyes. The presence of an external validation dataset confirms this finding and suggests the possible use of the CBI in everyday clinical practice to aid in the diagnosis of keratoconus. [J Refract Surg. 2016;32(12):803-810.].

Visual field progression in the Collaborative Initial Glaucoma Treatment Study the impact of treatment and other baseline factors

PURPOSE

To evaluate factors associated with visual field (VF) progression, using all available follow-up through 9 years after treatment initiation, in the Collaborative Initial Glaucoma Treatment Study (CIGTS).

DESIGN

Longitudinal follow-up of participants enrolled in a randomized clinical trial.

PARTICIPANTS

Six hundred seven newly diagnosed glaucoma patients.

METHODS

In a randomized clinical trial, 607 subjects with newly diagnosed open-angle glaucoma initially were treated with either medication or trabeculectomy. After treatment initiation and early follow-up, subjects were evaluated clinically at 6-month intervals. Study participants in both arms of the CIGTS were treated aggressively in an effort to reduce intraocular pressure (IOP) to a level at or below a predetermined, eye-specific target pressure. Visual field progression was analyzed using repeated measures models.

MAIN OUTCOME MEASURES

Visual field progression, measured by Humphrey 24-2 full-threshold testing and assessed by the change in the mean deviation (MD), and an indicator of substantial worsening of the VF (MD decrease of > or =3 dB from baseline), assessed at each follow-up visit.

RESULTS

Follow-up indicated minimal change from baseline in each initial treatment group's average MD. However, at the 8-year follow-up examination, substantial worsening (> or =3 dB) of MD from baseline was found in 21.3% and 25.5% of the initial surgery and initial medicine groups, respectively. The effect of initial treatment on subsequent VF loss was modified by time (P<0.0001), baseline MD (P = 0.03), and diabetes (P = 0.01). Initial surgery led to less VF progression than initial medicine in subjects with advanced VF loss at baseline, whereas subjects with diabetes had more VF loss over time if treated initially with surgery.

CONCLUSIONS

The CIGTS intervention protocol led to a lowering of IOP that persisted over time in both treatment groups. Progression in VF loss was seen in a subset, increasing to more than 20% of the subjects. The findings regarding initial surgery being beneficial for subjects with more advanced VF loss at presentation, but detrimental for patients with diabetes, are noteworthy and warrant independent confirmation.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Inherited glaucoma in DBA/2J mice: pertinent disease features for studying the neurodegeneration

The glaucomas are neurodegenerative diseases involving death of retinal ganglion cells and optic nerve head excavation. A major risk factor for this neurodegeneration is a harmfully elevated intraocular pressure (IOP). Human glaucomas are typically complex, progressive diseases that are prevalent in the elderly. Family history and genetic factors are clearly important in human glaucoma. Mouse studies have proven helpful for investigating the genetic and mechanistic basis of complex diseases. We previously reported inherited, age-related progressive glaucoma in DBA/2J mice. Here, we report our updated findings from studying the disease in a large number of DBA/2J mice. The period when mice have elevated IOP extends from 6 months to 16 months, with 8-9 months representing an important transition to high IOP for many mice. Optic nerve degeneration follows IOP elevation, with the majority of optic nerves being severely damaged by 12 months of age. This information should help with the design of experiments, and we present the data in a manner that will be useful for future studies of retinal ganglion cell degeneration and optic neuropathy.

Twenty-four-hour intraocular pressure pattern associated with early glaucomatous changes

PURPOSE

To characterize the 24-hour pattern of intraocular pressure (IOP) in untreated patients with newly diagnosed early glaucomatous changes.

METHODS

Measurements of IOP, blood pressure, and heart rate were taken every 2 hours during a 24-hour period from a group of 24 untreated patients (ages 40-78 years) with newly diagnosed abnormal optic discs and/or abnormal visual fields. In the 16-hour diurnal awake period, IOP was measured sitting and supine, and blood pressure and heart rate were measured supine. In the 8-hour nocturnal sleep period, all measurements were taken in the supine position. Mean diurnal and nocturnal IOP, blood pressure, and heart rate in the glaucoma group were compared with data obtained from an age-matched control group of 24 individuals with healthy eyes.

RESULTS

Mean diurnal IOP, either sitting or supine, was significantly higher in the glaucoma group than in the control group. For both subject groups, nocturnal supine IOP was higher than diurnal sitting IOP. However, this diurnal-to-nocturnal increase in IOP was significantly smaller in the glaucoma group. When compared with the diurnal supine IOP, the nocturnal supine IOP was lower in the glaucoma group but higher in the control group. Around normal awakening time, the supine IOP increased in the glaucoma group and did not change in the control group. There was a diurnal-to-nocturnal decrease in mean blood pressure only in the glaucoma group.

CONCLUSIONS

Compared with healthy eyes, the diurnal IOP is higher, the diurnal-to-nocturnal change of habitual IOP is less, and the posture-independent IOP pattern around normal awakening time is different in eyes with early glaucomatous changes.

Corneal biomechanical properties in normal, post-laser in situ keratomileusis, and keratoconic eyes

PURPOSE

To compare the biomechanical properties of normal, post-laser in situ keratomileusis (LASIK), and keratoconic corneas evaluated by corneal hysteresis and the corneal resistance factor measured with the Reichert Ocular Response Analyzer (ORA).

SETTINGS

Instituto Oftalmológico de Alicante, Vissum, Alicante, Spain.

METHODS

Two hundred fifty eyes were divided into 3 groups: normal (control group), post-LASIK, and keratoconus. The corneal biomechanical properties were measured with the ORA, which uses a dynamic bidirectional applanation process. The main outcome measures were intraocular pressure, corneal hysteresis, and the corneal resistance factor.

RESULTS

The control group had 165 eyes; the LASIK group, 65 eyes; and the keratoconus group, 21 eyes. In the control group, the mean corneal hysteresis value was 10.8 mm Hg +/- 1.5 (SD) and the mean corneal resistance factor, 11.0 +/- 1.6 mm Hg. The corneal hysteresis value was lower in older eyes, and the difference between the youngest age group (9 to 14 years) and oldest age group (60 to 80 years) was statistically significant (P = .01, t test). One month after LASIK, corneal hysteresis and the corneal resistance factor decreased significantly, from 10.44 to 9.3 mm Hg and from 10.07 to 8.13 mm Hg, respectively. In the keratoconus group, the mean corneal hysteresis was 7.5 +/- 1.2 mm Hg and the mean corneal resistance factor, 6.2 +/- 1.9 mm Hg. There were statistically significant differences in both biomechanical parameters between keratoconic eyes and post-LASIK eyes (P<.001, t test).

CONCLUSIONS

The corneal hysteresis and corneal resistance factor values were significantly lower in keratoconic eyes than in post-LASIK eyes. Future work is needed to determine whether these differences are useful in detecting keratoconus when other diagnostic tests are equivocal.

Changes in corneal biomechanics and intraocular pressure following LASIK using static, dynamic, and noncontact tonometry

PURPOSE

To compare the preoperative and postoperative measurement of corneal biomechanical properties and intraocular pressure (IOP) using Goldmann applanation tonometry (GAT), the ocular response analyzer (ORA), and the Pascal dynamic contour tonometer (PDCT) in eyes undergoing myopic laser in situ keratomileusis (LASIK).

DESIGN

Prospective, nonrandomized clinical trial.

METHODS

IOP was measured in 66 myopic eyes before and after LASIK by GAT, ORA, and PDCT in a randomized sequence. Metrics of corneal biomechanical properties (corneal hysteresis [CH], corneal resistance factor [CRF], and ocular pulse amplitude [OPA]) were recorded.

RESULTS

After LASIK, there was a reduction in mean corneal pachymetry of 90.2 mum and in IOP measurements with GAT (Delta = -1.8 +/- 2.8 mm Hg; P < .01), ORA-Goldmann (Delta = -4.6 +/- 2.8 mm Hg, P < .01), and ORA-corneal compensated (Delta - 2.1 +/- 2.6 mm Hg; P < .05). However, there was no statistically significant difference between preoperative and postoperative IOP measurements taken by PDCT (Delta = -0.5 +/- 2.6 mm Hg). Postoperatively, CRF decreased by 28.6% (P < .01), CH by 16.2% (P < .01), and OPA by 1.8% (P = .32).

CONCLUSIONS

Measurement of IOP with PDCT appears to be relatively immune to changes in corneal biomechanics and pachymetry after LASIK, in comparison to GAT and ORA measures of IOP. PDCT and ORA both showed statistically lower variation in measurement than GAT. LASIK produced a marked decline in CH and CRF, which may reflect respective changes in the viscous and elastic qualities of the post-LASIK cornea. In contrast, there was no statistical change in OPA.

Intracranial pressure in primary open angle glaucoma, normal tension glaucoma, and ocular hypertension: a case-control study

PURPOSE

To compare intracranial pressure (ICP) in subjects with primary open-angle glaucoma (POAG), normal-tension glaucoma (NTG; subset of POAG), and ocular hypertension (OHT) with that in subjects with no glaucoma.

METHODS

The study was a retrospective review of medical records of 62,468 subjects who had lumbar puncture between 1985 and 2007 at the Mayo Clinic. Of these, 57 POAG subjects, 11 NTG subjects (subset of POAG), 27 OHT subjects, and 105 control subjects met the criteria and were analyzed. A masked comparison of the relationship between ICP and other ocular and nonocular variables was performed by using univariate and multivariate analyses.

RESULTS

ICP was significantly lower in POAG compared with age-matched control subjects with no glaucoma (9.1 +/- 0.77 mm Hg vs. 11.8 +/- 0.71 mm Hg; P < 0.0001). Subjects with NTG also had reduced ICP compared with the control subjects (8.7 +/- 1.16 mm Hg vs. 11.8 +/- 0.71 mm Hg; P < 0.01). ICP was higher in OHT than in age-matched control subjects (12.6 +/- 0.85 mm Hg vs. 10.6 +/- 0.81 mm Hg; P < 0.05).

CONCLUSIONS

ICP is lower in POAG and NTG and elevated in OHT. ICP may play an important role in the development of POAG and NTG and in preventing the progression of OHT to POAG. Further prospective and experimental studies are warranted to determine whether ICP has a fundamental role in the pathogenesis of glaucoma.

Effect of Central Corneal Thickness, Corneal Curvature, and Axial Length on Applanation Tonometry

OBJECTIVE

To evaluate the effect of central corneal thickness (CCT), corneal curvature, and axial length on applanation tonometry in an in vivo study.

METHODS

In a masked, prospective clinical trial, we examined 125 eyes of 125 patients scheduled for cataract surgery. Corneal curvature was measured by means of keratometry and axial length by A-scan ultrasonography. By cannulating the anterior chamber before surgery, intraocular pressure (IOP) was set to 20, 35, and 50 mm Hg in a closed system by means of a water column. After measuring thickness, the IOP was measured with an applanation tonometer. Pearson product moment correlations and multiple linear regression analyses were performed, and significance levels were evaluated by the paired, 2-tailed t test.

RESULTS

The difference between measured and real IOP was significantly dependent (P < .001) on CCT. The associations between IOP and corneal curvature or IOP and axial length were not statistically significant (P = .31). The association between IOP reading and CCT is shown in the "Dresdner correction table," which illustrates an approximately 1-mm Hg correction for every 25-microm deviation from a CCT of 550 microm. The correction values were positive as thickness decreased and negative as thickness increased.

CONCLUSIONS

Central corneal thickness significantly affects IOP readings obtained by applanation tonometry according to the Goldmann principle. A correction of IOP readings by considering CCT according to the Dresdner correction table might be helpful for determining an accurate IOP value.

Intraocular pressure, Goldmann applanation tension, corneal thickness, and corneal curvature in Caucasians, Asians, Hispanics, and African Americans

PURPOSE

This is to investigate whether there are differences in Goldmann applanation tonometry (GAT), central corneal thickness, and corneal curvature among four racial groups. If differences are present, they may alter GAT reading, diagnosis, and management of glaucoma in the population.

DESIGN

Observational retrospective cross-sectional study.

METHODS

Charts of patients who have had keratorefractive surgery were examined. Central corneal thickness, corneal curvature, refractive power, and GAT were measured in 1482 Caucasian, 172 Asian, 204 Hispanic, and 118 African-American eyes (total 1976 eyes). Refractive components and GAT were compared. We compared intraocular pressure (IOP) adjusted by GAT, central corneal thickness, and corneal curvature among the four groups.

RESULTS

There was a statistically significant difference between the mean (+/- standard deviation) central corneal thickness of African American (535.46 +/- 33.39) and Caucasian (552.59 +/- 34.48) eyes. Mean central corneal thickness was near 550 microm in Caucasians, Asians, and Hispanics. No significant difference was noted in corneal curvature in the four groups. There was a significant correlation between central corneal thickness and corneal curvature, and GAT was similar among the four groups. When IOP was adjusted for central corneal thickness, it was significantly greater in African Americans (16.12 +/- 3.27) than in Caucasians (14.32 +/- 2.93). Corneas of women were significantly thinner than corneas of men.

CONCLUSIONS

African Americans had significantly thinner central corneal thickness than Caucasians, Asians, or Hispanics, causing the underreading of true IOP. Significant correlation between central corneal thickness and corneal curvature was demonstrated. Uncorrected GAT underreading of African Americans may lead to delay in diagnosis, inadequate treatment target setting, and higher morbidity. Goldmann applanation tonometry needs to be corrected by central corneal thickness and corneal curvature for proper diagnosis and management of glaucoma.

Ability of cirrus HD-OCT optic nerve head parameters to discriminate normal from glaucomatous eyes

PURPOSE

To determine the ability of optic nerve head (ONH) parameters measured with spectral domain Cirrus HD-OCT (Carl Zeiss Meditec, Inc., Dublin, CA) to discriminate between normal and glaucomatous eyes and to compare them with the discriminating ability of peripapillary retinal nerve fiber layer (RNFL) thickness measurements performed with Cirrus HD-OCT.

DESIGN

Evaluation of diagnostic test or technology.

PARTICIPANTS

Seventy-three subjects with glaucoma and 146 age-matched normal subjects.

METHODS

Peripapillary ONH parameters and RNFL thickness were measured in 1 randomly selected eye of each participant within a 200 × 200 pixel A-scan acquired with Cirrus HD-OCT centered on the ONH.

MAIN OUTCOME MEASURES

Optic nerve head topographic parameters, peripapillary RNFL thickness, and area under receiver operating characteristic curves (AUCs).

RESULTS

To distinguish normal from glaucomatous eyes, regardless of disease stage, the 6 best parameters (expressed as AUC) were vertical rim thickness (VRT, 0.963), rim area (0.962), RNFL thickness at clock-hour 7 (0.957), RNFL thickness of the inferior quadrant (0.953), vertical cup-to-disc ratio (VCDR, 0.951), and average RNFL thickness (0.950). The AUC for distinguishing between normal eyes and eyes with mild glaucoma was greatest for RNFL thickness of clock-hour 7 (0.918), VRT (0.914), rim area (0.912), RNFL thickness of inferior quadrant (0.895), average RNFL thickness (0.893), and VCDR (0.890). There were no statistically significant differences between AUCs for the best ONH parameters and RNFL thickness measurements (P > 0.05).

CONCLUSIONS

Cirrus HD-OCT ONH parameters are able to discriminate between normal eyes and eyes with glaucoma or even mild glaucoma. There is no difference in the ability of ONH parameters and RNFL thickness measurement, as measured with Cirrus OCT, to distinguish between normal and glaucomatous eyes.