Relative importance of factors affecting corneal hysteresis measurement

Biomechanical properties of cornea and ocular aberrations in myopic eyes

PURPOSE

To study the correlation of corneal topography, corneal biomechanical properties, and ocular aberrations with the magnitude of refractive error in myopic eyes.

METHODS

All myopic patients attending the clinic for refractive surgery were recruited. Data recorded included visual acuity, axial length (AL), central corneal thickness (CCT), manifest refraction spherical equivalent (MRSE), topography (Pentacam - Oculus), corneal biomechanical factors [ocular response analyzer (ORA)], and optical aberrations (iTrace). They were further categorized into group 1 (suitable for femto-LASIK) and group 2 (unsuitable for femto-LASIK).

RESULTS

Sixty eyes (30 myopes) of mean age 22.78 ± 2.71 years were enrolled. A negative correlation of refractive error was noted with AL (ρ = -0.9; P < 0.001), total aberrations (ρ = 0.53; P < 0.001), and lower-order aberrations (LOA) (ρ = 0.54; P < 0.001). A strongly positive correlation was noted between CCT and corneal hysteresis (CH) (ρ = 0.63; P < 0.001), CCT and CRF (ρ = 0.56; P < 0.001), CH and corneal resistance factor (CRF) (ρ = 0.83; P < 0.001), and Goldmann equivalent intraocular pressure (IOPg) and corneal compensated intraocular pressure (IOPcc) (ρ = 0.78; P < 0.001). An increase in higher-order aberrations (HOAs) as well as lower-order aberrations (LOAs) was noted with increasing sim-K [HOA (r = 0.73, P = 0.001); LOA (r = 0.601, P = 0.014)] and increasing CRF [HOA (r = 0.5, P = 0.006); LOA (r = 0.732, P = 0.001)] in group 2. The amount of refractive error, axial length, central corneal thickness, and sim-K were significantly different in the two groups.

CONCLUSION

Increasing degree of myopia is associated with an increase in axial length, total aberrations, and lower-order aberrations. Corneal biomechanical parameters have a strong correlation with each other. Lower corneal biomechanics are noted in high myopes as they have weaker and thinner corneas. Corneal biomechanics and ocular aberrations do not differ significantly between cases suitable for femto-LASIK and cases unsuitable for femto-LASIK.

Inventory of Ocular Pulse Amplitude Values in Healthy Subjects and Patients With Ophthalmologic Illnesses: Systematic Review and Meta-analysis

PURPOSE

Many studies have examined the ocular pulse amplitude (OPA) to better understand its physiology and clinical relevance, but the papers are scattered, not consistently indexed, and sometimes difficult to locate. We aimed to identify and summarize the relevant published evidence on OPA and, in a meta-analysis, outline specific differences of this parameter between healthy individual, primary open-angle glaucoma, normal-tension glaucoma, ocular hypertension, and cataract patients.

DESIGN

Systematic review and meta-analysis.

METHODS

A thorough literature search and data extraction were conducted by 2 reviewers independently. Reports on OPA measured by the dynamic contour tonometry in conjunction with different ocular and systemic diseases or potential influencing factors were included.

RESULTS

Of the 527 initially found reports, 97 met the inclusion criteria assessing 31 clinical conditions. A meta-analysis based on 6850 eyes and 106 study arms (68.8%) revealed differences in mean OPA values in millimeters of mercury between various entities. Among healthy eyes, the OPA was 2.58 mm Hg (95% CI: 2.45-2.71), whereas OPA values were higher in glaucoma (unspecified glaucoma 2.73 mm Hg, 95% CI: 2.38-3.08; normal-tension glaucoma 2.66 mm Hg, 95% CI: 2.36-2.97; and primary open-angle glaucoma 2.92 mm Hg, 95% CI: 2.75-3.08). Although ocular hypertension showed the highest OPA values (3.53 mm Hg, 95% CI: 3.05-4.01), the lowest values were found in cataract eyes (2.26 mm Hg, 95% CI: 1.57-2.94).

CONCLUSION

We found different OPA values characteristic of different clinical entities, with above-normal values in glaucoma and ocular hypertension and lower values in cataract patients. Our work is intended for clinicians and researchers who want to get a quick overview of the available evidence or who need statistical data on OPA distributions in individual diseases.

Corneal Biomechanical Measures for Glaucoma: A Clinical Approach

Over the last two decades, there has been growing interest in assessing corneal biomechanics in different diseases, such as keratoconus, glaucoma, and corneal disorders. Given the interaction and structural continuity between the cornea and sclera, evaluating corneal biomechanics may give us further insights into the pathogenesis, diagnosis, progression, and management of glaucoma. Therefore, some authorities have recommended baseline evaluations of corneal biomechanics in all glaucoma and glaucoma suspects patients. Currently, two devices (Ocular Response Analyzer and Corneal Visualization Schiempflug Technology) are commercially available for evaluating corneal biomechanics; however, each device reports different parameters, and there is a weak to moderate agreement between the reported parameters. Studies are further limited by the inclusion of glaucoma subjects taking topical prostaglandin analogues, which may alter corneal biomechanics and contribute to contradicting results, lack of proper stratification of patients, and misinterpretation of the results based on factors that are confounded by intraocular pressure changes. This review aims to summarize the recent evidence on corneal biomechanics in glaucoma patients and insights for future studies to address the current limitations of the literature studying corneal biomechanics.

Ocular Biomechanics and Glaucoma

Biomechanics is a branch of biophysics that deals with mechanics applied to biology. Corneal biomechanics have an important role in managing patients with glaucoma. While evidence suggests that patients with thin and stiffer corneas have a higher risk of developing glaucoma, it also influences the accurate measurement of intraocular pressure. We reviewed the pertinent literature to help increase our understanding of the biomechanics of the cornea and other ocular structures and how they can help optimize clinical and surgical treatments, taking into consideration individual variabilities, improve the diagnosis of suspected patients, and help monitor the response to treatment.

Corneal Biomechanics in Primary Open Angle Glaucoma and Ocular Hypertension: A Systematic Review and Meta-analysis

PRCIS

Normal tension glaucoma patients had softer corneas than normal controls, whereas high-tension glaucoma and ocular hypertension patients had stiffer corneas.

PURPOSE

To comprehensively identify the corneal biomechanical differences of patients with primary open angle glaucoma (POAG) and ocular hypertension (OHT) using the Ocular Response Analyzer or the Corvis ST.

METHODS

The electronic databases PubMed, Embase, and Web of Science were comprehensively searched for studies comparing corneal biomechanical differences between POAG and OHT patients with normal controls by Ocular Response Analyzer or Corvis ST. The weighted mean differences and 95% confidence intervals (CIs) were calculated. Subgroup analyses were performed according to the subtypes of POAG, including high-tension glaucoma (HTG) and normal tension glaucoma (NTG).

RESULTS

Thirty-one case-control studies were ultimately included, with 2462 POAG patients, 345 OHT patients, and 3281 normal controls. The corneal hysteresis (CH), corneal resistance factor (CRF), and highest concavity time (HC-t) were all lower in POAG patients than in normal controls. The CH, time at the second applanation (A2t), HC-t, highest concavity radius (HC-R), and deformation amplitude at the highest concavity (HC-DA) were lower in OHT patients, while the CRF, time at the first applanation (A1t), and stiffness parameter at the first applanation (SP-A1) were greater in OHT patients than in normal controls. The subgroup analyses showed that the CH, A2t, length at the second applanation (A2L), and HC-DA were lower in HTG, and the CH, CRF, A1t, and HC-t were lower in NTG patients than in normal controls.

CONCLUSION

The corneas of NTG patients are more deformable than normal controls, whereas the corneas of HTG and OHT patients are stiffer.

Clinical Ocular Biomechanics: Where Are We after 20 Years of Progress?

Purpose: Ocular biomechanics is an assessment of the response of the structures of the eye to forces that may lead to disease development and progression, or influence the response to surgical intervention. The goals of this review are (1) to introduce basic biomechanical principles and terminology, (2) to provide perspective on the progress made in the clinical study and assessment of ocular biomechanics, and (3) to highlight critical studies conducted in keratoconus, laser refractive surgery, and glaucoma in order to aid interpretation of biomechanical parameters in the laboratory and in the clinic.Methods: A literature review was first conducted of basic biomechanical studies related to ocular tissue. The subsequent review of ocular biomechanical studies was limited to those focusing on keratoconus, laser refractive surgery, or glaucoma using the only two commercially available devices that allow rapid assessment of biomechanical response in the clinic.Results: Foundational studies on ocular biomechanics used a combination of computer modeling and destructive forces on ex-vivo tissues. The knowledge gained from these studies could not be directly translated to clinical research and practice until the introduction of non-contact tonometers that quantified the deformation response of the cornea to an air puff, which represents a non-destructive, clinically appropriate load. The corneal response includes a contribution from the sclera which may limit corneal deformation. Two commercial devices are available, the Ocular Response Analyzer which produces viscoelastic parameters with a customized load for each eye, and the Corvis ST which produces elastic parameters with a consistent load for every eye. Neither device produces the classic biomechanical properties reported in basic studies, but rather biomechanical deformation response parameters which require careful interpretation.Conclusions: Research using clinical tools has enriched our understanding of how ocular disease alters ocular biomechanics, as well as how ocular biomechanics may influence the pathophysiology of ocular disease and response to surgical intervention.

The predictability of graft thickness for Descemet's stripping automated endothelial keratoplasty using a mechanical microkeratome system

Descemet's stripping automated endothelial keratoplasty (DSAEK) is used for treating corneal endothelial dysfunction, and the postoperative visual acuity outcome depends on the thickness of the graft. We created a simple nomogram using factors affecting the cutting thickness during graft preparation via a mechanical microkeratome system for DSAEK. This retrospective study was conducted from May 2018 through October 2022 and included donor eyes cut by automatic methods. We measured the graft thickness, cutting accuracy, and assessed ten variables with donor/cornea-related factors potentially affecting the cutting thickness. Subsequently, we created a simple nomogram. We analyzed 81 donor tissues, and the donor median age was 76 years. The mean central graft thickness was 122.2 μm, with 62% of the grafts that could be cut within the target central graft thickness range. Comparatively, donor corneas from those with cardiac diseases were cut deeper (P = 0.007). The developed nomogram provided a 83% probability of estimating the post-cutting graft thickness within 25 µm. Our nomogram, which considers cause of death, enables reproducible production of graft of a desired thickness. A detailed analysis of donor tissues, including the cause of donor death and the characteristics from pressurization to cutting, will enable more precise DSAEK graft preparation.

Corneal Biomechanical Changes Caused by Acute Elevation of IOP in Eyes with and without Glaucoma

SIGNIFICANCE

Although corneal biomechanical parameters are well linked with glaucoma, their clinical utility has not yet been fully elucidated. This study was designed to provide unique evidence about the dynamic nature of corneal biomechanical parameters and their potential prognostic ability for glaucoma.

PURPOSE

This study aimed to evaluate the effect of acute intraocular pressure (IOP) elevation on corneal hysteresis (CH) and corneal resistance factor (CRF) and the associations of these biomechanical parameters with glaucomatous disease.

METHODS

Subjects participating in a prospective, longitudinal glaucoma research study had CH and CRF measured before and during ophthalmodynamometry during visits in the years 2011 to 2012. All participants were diagnosed with primary open-angle glaucoma, ocular hypertension, glaucoma suspect, or normal eyes and had a minimum of 3 years of study participation with at least five reliable visual field (VF) tests. Changes in CH, CRF, and IOP induced by ophthalmodynamometry were compared between diagnostic groups and evaluated for relationships with existing and future glaucomatous VF loss.

RESULTS

In 248 eyes of 248 subjects followed up for 7.7 ± 2.3 years, ophthalmodynamometry induced a mean IOP increase from 15.1 to 29.9 mmHg, causing a mean 34 ± 28% increase in CRF and 21 ± 25% decrease in CH. Magnitude of CH change did not differ between diagnostic groups or between eyes that did (n = 20) and did not (n = 95) develop new VF loss during the study period, nor was it related to rate of future VF progression.

CONCLUSIONS

Ophthalmodynamometry-induced IOP elevation resulted in significant acute changes in CH and CRF in this study; this suggests accounting for IOP may be important in clinical interpretation of these parameters. However, because the degree of CH change was not related to glaucoma or its progression, acute changes in CH and CRF do not seem to have a prognostic value for glaucoma.

Corneal hysteresis as a risk factor for optic nerve head surface depression and retinal nerve fiber layer thinning in glaucoma patients

To evaluate the role of corneal hysteresis (CH) as a risk factor for progressive ONH surface depression and RNFL thinning measured by confocal scanning laser ophthalmoscopy (CSLO) and spectral-domain optical coherence tomography (SD-OCT), respectively in glaucoma patients. Prospective study. A total of 146 eyes of 90 patients with glaucoma were recruited consecutively. The CH measurements were acquired at baseline and 4-months interval using the Ocular Response Analyzer (Reichert Instruments, Depew, NY). Eyes were imaged by CSLO (Heidelberg Retinal Tomograph [HRT]; Heidelberg Engineering, GmbH, Dossenheim, Germany) and SD-OCT (Cirrus HD-OCT; Carl Zeiss Meditec AG, Dublin, CA) at approximately 4-month intervals for measurement of ONH surface topography and RNFL thickness, respectively. Significant ONH surface depression and RNFL thinning were defined with reference to Topographic Change Analysis (TCA) with HRT and Guided Progression Analysis (GPA) with Cirrus HD-OCT, respectively. Multivariate cox proportional hazards models were used to investigate whether CH is a risk factor for ONH surface depression and RNFL progression after adjusting potential confounding factors. All patients with glaucoma were followed for an average of 6.76 years (range, 4.56–7.61 years). Sixty-five glaucomatous eyes (44.5%) of 49 patients showed ONH surface depression, 55 eyes (37.7%) of 43 patients had progressive RNFL thinning and 20 eyes (13.7%) of 17 patients had visual field progression. In the cox proportional hazards model, after adjusting baseline diastolic IOP, CCT, age, baseline disc area and baseline MD, baseline CH was significantly associated with ONH surface depression and visual field progression (HR = 0.71, P = 0.014 and HR = 0.54, P = 0.018, respectively), but not with RNFL thinning (HR = 1.03, P = 0.836). For each 1-mmHg decrease in baseline CH, the hazards for ONH surface depression increase by 29%, and the hazards for visual field progression increase by 46%. The CH measurements were significantly associated with risk of glaucoma progression. Eyes with a lower CH were significantly associated with an increased risk of ONH surface depression and visual field progression in glaucoma patients.

The Association Between Ocular Rigidity and Neuroretinal Damage in Glaucoma

Purpose

Ocular rigidity (OR) is an important biomechanical property, thought to be relevant in the pathophysiology of open-angle glaucoma (OAG). This study aims to evaluate the relationship between OR and neuroretinal damage caused by glaucoma.

Methods

One hundred eight subjects (22 with healthy eyes, 23 with suspect discs, and 63 with OAG) were included in this study. OR was measured using a noninvasive optical coherence tomography (OCT)-based method developed by our group. We also measured central corneal thickness (CCT), corneal hysteresis (CH), and corneal resistance factor (CRF). Pearson and partial correlations were performed to evaluate the relationship between OR and glaucomatous damage represented by ganglion cell complex (GCC), retinal nerve fiber layer (RNFL) thicknesses, and neuroretinal rim area.

Results

Significant positive correlations were found between OR and minimum GCC thickness (r = 0.325, P = 0.001), average GCC thickness (r = 0.320, P = 0.002), rim area (r = 0.344, P < 0.001), and RNFL thickness in the superior (r = 0.225, P = 0.023), and inferior (r = 0.281, P = 0.004) quadrants. These correlations were generally greater than those found for CCT, CH, and CRF. Furthermore, no correlation was found between OR and corneal biomechanical parameters. After adjusting for age, sex, and ethnicity, significant correlations were found between OR and minimum and average GCC thickness (r = 0.357, P = 0.001 and r = 0.344, P = 0.001, respectively), rim area (r = 0.327, P = 0.001), average RNFL thickness (r = 0.331, P = 0.001), and RNFL thickness in the superior (r = 0.296, P = 0.003) and inferior (r = 0.317, P = 0.001) quadrants.

Conclusions

In this study, we found a positive correlation between structural OCT-based parameters and OR, indicating more neuroretinal damage in eyes with lower OR. These findings could provide insight into the pathophysiology of OAG.

Intraocular pressure measurements and corneal biomechanical properties using a dynamic Scheimpflug analyzer, after several keratoplasty techniques, versus normal eyes

PURPOSE

To evaluate the biomechanical properties of the cornea and their impact on intraocular pressure (IOP) measurement after lamellar keratoplasty, compared to healthy eyes, using a non-contact tonometer with a Scheimpflug camera.

METHODS

This study, from 2014 to 2015, included 22 primary DSAEK, 5 DALK, 6 DSAEK after PK, and 50 control eyes. Using a non-contact tonometer with a high-speed Scheimpflug camera (CORVIS ST, Oculus Optikgeräte GmbH, Wetzlar, Germany), several biomechanical parameters were recorded, including radius at highest concavity (R_hc) and defomation amplitude (DA). Central corneal thickness (CCT) and uncorrected IOP, were also recorded. For the control eyes only, a corrected IOP was calculated, based on age, central corneal thickness, and biomechanical parameters.

RESULTS

R_hc was significantly lower after DALK (R_hc=5.54±0.71, P=0.007) and DSAEK (R_hc=6.26±0.77, P=0.042) compared to control eyes (R_hc=6.82±0.76). DA was higher after DALK and DSAEK, but not significantly (respectively 1.24±0.09 P=0.41 and 1.22±0.15, P=0.923) compared to normal eyes (1.18±0.15). Uncorrected IOP was not significantly different between post-keratoplasty and control eyes. In control eyes, the corrected IOP (15.23±1.88) was lower than the uncorrected IOP (16.10±2.34); a statistically significant positive correlation between R_hc and CCT (R²=0.6020, P<0001), and a significant negative correlation between DA and CCT (R²=-0.641, P<0.0001) were found.

CONCLUSION

Our study showed that, after lamellar keratoplasty, corneal biomechanics are altered. Corneas with higher ocular rigidity will show a lower DA and a higher R_hc.

In vivo measurement of regional corneal tangent modulus

Currently available clinical devices are unable to measure corneal biomechanics other than at the central region. Corneal stiffness (S), thickness, and radius of curvature was measured at the central cornea (primary fixation) and 3 mm from the temporal limbus (primary and nasal fixations). The corneal tangent modulus (E) of 25 healthy subjects was calculated from these data. After confirming normality, repeated measures analysis of variance (RMANOVA) revealed significant difference in S (F(2, 48) = 21.36, p < 0.001) at different corneal regions and direction of fixations. E also varied significantly at different corneal regions and direction of fixations (RMANOVA: F(2, 48) = 23.06, p < 0.001). A higher S and a lower E were observed at the temporal region compared with the corneal centre. Nasal fixation further increased S and E values compared with primary fixation. Due to the specific arrangement of corneal collagen fibrils, heterogeneity of corneal biomechanical properties is expected. In future clinical practice, localized corneal biomechanical alternation and measurement might assist corneal disease detection and post-surgery management. In addition, practitioners should be aware of the fixation effect on corneal biomechanical measurement.

Corneal Biomechanics Determination in Healthy Myopic Subjects

Purpose. To determine the corneal biomechanical properties by using the Ocular Response Analyzer™ and to investigate potential factors associated with the corneal biomechanics in healthy myopic subjects. Methods. 135 eyes from 135 healthy myopic subjects were included in this cross-sectional observational study. Cornea hysteresis (CH), corneal resistance factor (CRF), cornea-compensated intraocular pressure (IOPcc), and Goldmann-correlated intraocular pressure (IOPg) were determined with the Reichert Ocular Response Analyzer (ORA). Univariate and multivariate regression analyses were performed to investigate factors associated with corneal biomechanics. Results. The mean CH and CRF were 9.82 ± 1.34 mmHg and 9.64 ± 1.57 mmHg, respectively. In univariate regression analysis, CH was significantly correlated with axial length, refraction, central corneal thickness (CCT), and IOPg (r = −0.27, 0.23, 0.45, and 0.21, resp.; all with p ≤ 0.015), but not with corneal curvature or age; CRF was significantly correlated with CCT and IOPg (r = 0.52 and 0.70, resp.; all with p < 0.001), but not with axial length/refraction, corneal curvature, or age. In multivariate regression analysis, axial length, IOPcc, and CCT were found to be independently associated with CH, while CCT and IOPg were associated with CRF. Conclusions. Both CH and CRF were positively correlated with CCT. Lower CH but not CRF was associated with increasing degree of myopia. Evaluation of corneal biomechanical properties should take CCT and myopic status into consideration.

Changes in Corneal Biomechanical Properties After Descemet Stripping Automated Endothelial Keratoplasty for Pseudophakic Bullous Keratopathy

PURPOSE

To compare corneal biomechanical properties and intraocular pressure (IOP) in eyes with pseudophakic bullous keratopathy (PBK) before and after Descemet stripping automated endothelial keratoplasty (DSAEK).

METHODS

This prospective nonrandomized intrasubject comparative study was conducted on 44 eyes of 22 patients with the diagnosis of PBK who underwent DSAEK in one eye. IOP was measured by Goldmann applanation tonometer, and central corneal thickness was measured by ultrasound pachymetry. The ocular response analyzer was used to measure corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-related IOP, and cornea-compensated IOP. The same measurements were performed in the normal fellow eyes which served as controls. All measurements were performed preoperatively and 6 months postoperatively.

RESULTS

The mean patient age was 67 ± 14 years. Mean preoperative CH and CRF values in the DSAEK group were 5.77 ± 2.94 and 6.39 ± 2.72 mm Hg, respectively, which were significantly lower than those measured in the control group (8.2 ± 2.47 and 8.43 ± 2.49 mm Hg, respectively, P = 0.001 for both comparisons). Postoperatively, CH and CRF demonstrated a significant increase (7.09 ± 3.68 mm Hg, P = 0.05 and 8.21 ± 3.84 mm Hg, P = 0.03, respectively) in operated eyes approaching the normal values measured in the control eyes.

CONCLUSIONS

Corneal biomechanical parameters were significantly lower in PBK eyes than in the normal fellow eyes. These metrics significantly increased after DSAEK and reached values measured in the normal fellow eyes.

Graft Biomechanics Following Three Corneal Transplantation Techniques

Purpose:

To compare corneal biomechanical properties following three different transplantation techniques, including Descemet stripping automated endothelial keratoplasty (DSAEK), deep anterior lamellar keratoplasty (DALK) and penetrating keratoplasty (PK) in comparison to normal eyes.

Methods:

This cross-sectional comparative study included 118 eyes: 17 eyes of 17 patients received DSAEK, 23 eyes of 21 patients underwent DALK using Anwar's big bubble technique, and 45 eyes of 36 patients had PK; 33 right eyes of 33 normal subjects served as the control group. Using the ocular response analyzer (ORA, Reichert Ophthalmic Instruments, Buffalo, New York, USA), corneal hysteresis (CH) and corneal resistance factor (CRF) were measured and compared among the study groups at least 3 months after all sutures were removed.

Results:

Mean patient age was 26.9 ± 5.0 years in the control group, 28.8 ± 4.2 in the PK group, 27.2 ± 6.5 in the DALK group, and 62.5 ± 16.8 in the DSAEK group (P < 0.001). Central corneal thickness (CCT) was 539.0 ± 24.8, 567.5 ± 38.8, 547.0 ± 42.6 and 631.1 ± 84.8 μm, respectively (P < 0.001). CH and CRF were significantly lower in the DSAEK group (7.79 ± 2.0 and 7.88 ± 1.74 mmHg, respectively) as compared to the PK (10.23 ± 2.07 and 10.13 ± 2.22 mmHg, respectively) and DALK (9.64 ± 2.07 and 9.36 ± 2.09 mmHg, respectively) groups. The two latter groups demonstrated biomechanical parameters comparable to normal subjects (9.84 ± 1.59 and 9.89 ± 1.73 mmHg, respectively).

Conclusion:

Graft biomechanical parameters after DSAEK are lower than those following PK and DALK. After PK and DALK in keratoconic eyes, these metrics are increased to normal values. These differences may have implications for interpreting intraocular pressure or planning graft refractive surgery after keratoplasty.

Optic Disc Change during Childhood Myopic Shift: Comparison between Eyes with an Enlarged Cup-To-Disc Ratio and Childhood Glaucoma Compared to Normal Myopic Eyes

BACKGROUND

Progressive disc tilting and the development or enlargement of peripapillary atrophy (PPA) are observed during a myopic shift in children. This could be related to the changes around the optic nerve head during eyeball elongation. If the biomechanical properties at or around the optic nerve head are changed after exposure to elevated intraocular pressure (IOP) in glaucoma eyes, different response of the disc tilting and PPA changes could take place during eyeball elongation by myopic shift. On the basis of this background, the aim of this study was to compare the morphological changes in the optic disc induced by a myopic shift during childhood between normal control eyes, eyes from disc suspects with an enlarged cup-to-disc ratio (CDR), and eyes with childhood glaucoma.

METHODS

Total of 82 eyes from 82 subjects younger than 14 years of age were included in the study. Serial disc photographs were classified into one of two groups: eyes with an optic nerve head (ONH) or peripapillary atrophy (PPA) change or without an ONH/PPA change. Using ImageJ software, the outlines of the optic disc and PPA were plotted, and the vertical disc diameter (VDD), horizontal disc diameter (HDD), and maximum PPA width (PPW) were measured. The changes in the ratios of these parameters and the relationships between the degree of myopic shift or the ONH/PPA change were analyzed.

RESULTS

Twenty-five eyes with normal optic disc appearance, 36 eyes with enlarged cup-to-disc ratio, and 21 eyes of glaucoma patients were analyzed. The initial intraocular pressure (IOP) at diagnosis was significantly different among the groups (P<0.001). The degree of myopic shift during follow-up period was not significantly different among the groups (P=0.612). However, the changes in the HDD/VDD and PPW/VDD ratios were significantly greater in the disc suspect group and significantly smaller in the glaucoma group. Among the 42 eyes with an ONH/PPA change, 16 (38.1%) were from the normal control group, 24 (57.1%) were from the disc suspect group, and 2 (4.8%) were from the glaucoma group (P < 0.001).

CONCLUSIONS AND RELEVANCE

The optic disc change during childhood myopic shift was different in eyes with various conditions. Eyes of childhood glaucoma showed less change in the disc morphology during myopic shift compared to eyes with normal disc or enlarged cup-to-disc ratio.

Relationship between corneal hysteresis and optic nerve parameters measured with spectral domain optical coherence tomography

BACKGROUND

Corneal hysteresis (CH) has been associated with visual field damage in glaucoma and is related to the velocity of perimetric glaucoma progression. We undertook this investigation to determine whether CH is associated with structural markers of glaucoma damage on spectral domain optical coherence tomography (SD-OCT).

METHODS

In this retrospective study, 131 patients under glaucoma evaluation were evaluated with SD-OCT (Cirrus; Carl Zeiss Meditec, Dublin, CA) and had CH measurements with the ocular response analyzer (Reichert, Inc., Buffalo, NY). Pearson and partial correlation adjusting for age were preformed to examine the association between CH and variables of interest. Generalized estimating equations were used to construct simple and multiple linear models.

RESULTS

While Pearson correlations were modest overall, CH best correlated with mean deviation (MD; r = 0.19) followed by average retinal nerve fiber layer (RNFL) thickness (r = 0.18) and vertical cup to disc ratio (r = -0.11) in the open angle glaucoma group. In univariable models, CH varied as a function of MD (ß = 0.1, 95 % CI 0.03, 0.1; p < 0.001) and of average RNFL thickness (ß = 0.2, 95 % CI 0.1, 0.4; p = 0.001). In a multivariable analysis including MD, age, average RNFL thickness, and glaucoma status, MD (p = 0.001) and age (p < 0.001) retained significant associations with CH.

CONCLUSIONS

In patients under evaluation and treatment for glaucoma, CH was more closely related to visual field MD than to structural markers of glaucoma damage as measured by SD-OCT.

Combining corneal hysteresis with central corneal thickness and intraocular pressure for glaucoma risk assessment

PURPOSE

To determine whether adjusting corneal hysteresis (CH) values for central corneal thickness (CCT) and intraocular pressure (IOP) improves its capability to differentiate primary open-angle glaucoma (POAG) from ocular hypertension (OH).

METHODS

This prospective, observational, cross-sectional study included 169 eyes of 169 subjects with a diagnosis of POAG (n=81) or OH (n=88). We utilized the Ocular Response Analyzer (ORA), Pascal Dynamic Contour Tonometer (DCT), Goldmann applanation tonometer (GAT), and ORA ultrasound pachymeter to obtain CH, IOP, and CCT values. Correlational, regression, and t-test analyses were conducted before and after the sample was divided into low, intermediate, and thick CCT subgroups.

RESULTS

In the full sample, CH and CCT were moderately correlated (r=0.44, P<0.001). Although both were related to diagnosis in univariate regression analysis, only CH was independently related to glaucoma diagnosis in multivariate analysis. After the sample was divided into CCT tertiles, CH was significantly lower in POAG vs OH eyes within all three CCT subgroups, and CH was the only multivariate variable that differentiated POAG from OH in each CCT subgroup. Moreover, the relationship between CH and diagnosis was more robust within the CCT subgroups compared with the full sample, suggesting that integrating CCT into CH interpretation is beneficial. Adjusting CH for IOP did not aid diagnostic precision in this study.

CONCLUSION

Our findings suggest that combining CH and CCT for glaucoma risk assessment improves diagnostic capability compared to using either factor alone. Conversely, adjusting CH for IOP provided no clear clinical benefit in this study.