Investigation of corneal biomechanics at moderate to high refractive errors

Purpose

Corneal hysteresis (CH) and corneal resistance factor (CRF) are corneal biomechanical parameters which were measured by ocular response analyzer (ORA). Aim of this study was to define the CH and CRF in high myopic and hyperopic patients and compare the results with emmetropic control group.

Methods

A total of 193 eyes of 100 healthy volunteers were included. Study groups were high myopic patients (n = 27) with spherical refractive errors (SRE) of greater than ?5.00D, high hyperopic patients (n = 20) with SRE of greater than +3.00D and controls (n = 53) with SRE between ± 1.00D. All subjects underwent IOP and corneal biomechanical evaluation with the ORA. Also Goldmann applanation tonometry (GAT), central corneal thickness (CCT), corneal curvature and axial length measurements were taken.

Results

Mean age of groups was 30.7 ± 6.9, 29.1 ± 7.7, 28.9 ± 5.6 years (p > 0.05). Among study groups except CRF and CCT, all parameters were significantly different between study groups. CH was lowest in the high myopic group and highest in the high hyperopia. In all groups, there were significant correlations between CH and CRF, CCT, SRE, SE (spherical equivalent), AL (axial length) and between CRF and CCT. GAT and IOPg (Goldmann-correlated intraocular pressure) measurements were significantly correlated with CCT (p < 0.05). One of the major findings was as the CH approaches 11.2 mmHg, IOPcc (corneal-compensated intraocular pressure) and IOPg get close to each other.

Conclusions

The results revealed that CRF is not affected by refractive errors and IOPcc is not affected by any other ocular parameter. The difference between IOPcc and IOPg was greatest in myopic group, and IOP (intraocular pressure) measurement in these patients deserves high suspicion.

     

Impact of dehydration and fasting on intraocular pressure and corneal biomechanics measured by the Ocular Response Analyzer

Purpose

To investigate the effects of dehydration and fasting on the intraocular pressure (IOP) and corneal biomechanics during Ramadan in healthy subjects.

Methods

A total of 36 healthy fasting male volunteers with a mean age of 32.7 ± 5.1 years (range 28–38 years) were enrolled in the study. A Reichert Ocular Response Analyzer (ORA) was used to measure the corneal resistance factor (CRF), corneal hysteresis (CH), Goldman-correlated IOP (IOPg), and corneal-compensated IOP (IOPcc), additionally IOP with Goldmann applanation tonometer (IOP-GAT) was taken. All measurements were recorded at 8:00 am and 4:00 p.m. during Ramadan and during a 1-month follow-up after Ramadan was over.

Results

Statistical analysis demonstrated no difference in the ORA measurements including CH, CRF, IOPcc, and IOPg; CCT and CV values between fasting and non-fasting periods or within a single day (diurnal changes). Nine volunteers (25% of total subjects) were excluded because eyedrops were believed to disrupt the Ramadan fast consequently IOP-GAT could not be measured from these subjects. No statistically significant difference was noted between IOP-GAT and IOPg measurements of twenty-seven subjects at the different periods and time points.

Conclusions

Our results reveal that fasting during Ramadan does not profoundly affect corneal biomechanics and IOP values in healthy volunteers without ocular diseases such as glaucoma. When planning corneal refractive surgery and determining IOP, the ORA measurements can be done safely during a Ramadan fast. Moreover, ORA may be a better alternative for patients that refuse IOP measurement via GAT for examining the accuracy of IOP during fasting. Further studies are needed to better understand the role of these parameters on corneal disease and glaucoma during fasting.

     

Hornhautdickenunabhängige Methoden der Messung des Augeninnendrucks

Introduction

Goldmann applanation tonometry (GAT) has been the gold standard for measuring intraocular pressure (IOP) for about 50 years. However, it depends on central corneal thickness (CCT) and is, therefore, prone to being incorrect. Dynamic contour tonometry (DCT) has recently been introduced to measure IOP independently of CCT; however, DCT is costly and difficult. IOP measurement using the ocular response analyzer (ORA) offers noncontact tonometry with declaration of the corneal-compensated IOP (IOPcc), which takes corneal hysteresis (CH) into account and is supposed to be independent of CCT.

Patients and methods

Using the ORA instrument, IOPcc was determined in 192 glaucoma eyes and 59 nonglaucoma eyes. Subsequently, measurement by DCT and GAT was performed. IOP measurements were compared and analyzed with respect to CCT and CH.

Results

Average values were as follows: IOPcc, 18.38±6.3 mmHg; GAT, 14.69±4.5 mmHg; DCT, 15.17±3.9 mmHg; CH, 9.96±2.5 mmHg; CCT, 552±57 μm. Neither CCT nor CH differed between the two groups. There was a positive correlation between GAT and CCT that did not exist for IOPcc and DCT values. However, IOPcc and DCT differed significantly in Bland–Altman analysis (p<0.01). Furthermore, these two IOP values differed significantly with respect to CH and the level of IOP.

Conclusion

Because IOPcc is not a primarily measured variable but also takes CH into account, a direct comparison of DCT and IOPcc values is not acceptable, and a simple correction factor may not be valid.     

Vergleich des iCare-Tonometers mit dem Goldmann-Tonometer in Malawi

Background

The risk for glaucoma is 4?C5 times higher in patients from sub-Saharan Africa. Thus, especially in developing countries an easy and effective method for assessing the intraocular pressure (IOP) is needed.

Methodology

In this hospital-based survey 150 eyes were divided into 3 groups concerning the IOP (group I <?16?mmHg, group II 16?C23?mmHg and group III >?23?mmHg) and underwent examination with ultrasound pachymetry followed by iCare tonometry (ICT) and Goldmann applanation tonometry (GAT). Agreement of the measurements by two tonometers was assessed with the Bland-Altman method and the influence of the central corneal thickness (CCT) on the ICT measurements was determined.

Results

The mean difference between the IOD measured with GAT and ICT was 0.84?±?2.63?mmHg. The differences were similar in all three groups (0.77?C0.97?mmHg), however, the standard deviation in group III (4.04?mmHg) was greater than in groups I (1.98?mmHg) and II (1.79?mmHg). The mean CCT was 513.51?±?36.22???m.

Conclusions

The agreement of measurements by GAT and ICT was good for lower IOP values but less accurate in patients with higher IOP values (group III). A dependency of the CCT on the ICT measurements was observed. In comparison to other countries the lowest CCTs were found in Malawian patients.     

Evaluierung der dynamischen Konturtonometrie bei Keratokonus

Purpose

The gold standard for measuring intraocular pressure (IOP) until now has been Goldmann applanation tonometry (GAT), which depends on the central corneal thickness (CCT) and curvature. In patients with keratoconus who have an abnormal corneal geometry and thickness, measurement of pressure with GAT is often difficult and not very reproducible. We compared the impact of the central corneal thickness (CCT) on the IOP measured with dynamic contour tonometry (DCT), a digital method which is adapted to the corneal geometry, and GAT in patients with keratoconus.

Methods

IOP was measured in 54 patients (38 men and 16 women, mean age of 36±9.9 years) with GAT and DCT in randomized order. All patients had a keratoconus which was assured by topography. In addition central corneal thickness (CCT) was measured with the Pentacam. For statistical analysis the Pearson correlation was calculated and a Bland-Altman diagram plotted.

Results

Mean corneal thickness was 486.2±45.5 μm. DCT measured the IOP at a mean value of 14.9±2.6 mmHg and GAT at 13.3±2.9 mmHg. With a mean difference of 1.6±2.4 mmHg DCT measured significantly higher than GAT (p≤0.05) Neither IOP measurements with GAT (r=?0.03; p>0.05) nor those with DCT (r=0.08; p>0.05) showed a significant correlation to central corneal thickness.

Conclusion

The example of keratoconus confirms that IOP measured by GAT is lower than if measured by DCT. Because both methods are independent of the CCT they are equally acceptable for IOP follow-up in eyes with keratoconus, which may result in progressive corneal thinning in the long term.     

A comparison between Goldmann applanation tonometry and dynamic contour tonometry after photorefractive keratectomy

Background

The intraocular pressure (IOP) could be measured by both Goldmann applanation tonometry (GAT) and dynamic contour tonometry (DCT). Although these two methods have been discussed widely after laser-assisted sub-epithelial keratectomy (LASIK), there is little data in the cases undergoing photorefractive keratectomy (PRK). We aimed to compare the changes of IOP measurements obtained by GAT and DCT after PRK for myopia/myopic astigmatism.

Methods

This prospective study enrolled 77 candidates (154 eyes) for PRK to correct myopia or myopic astigmatism and 30 matched patients (30 eyes) with myopia or myopic astigmatism who served as controls. Changes of the IOP measurements (ΔIOP) obtained by GAT and DCT before and at 6 months after PRK in the operated eyes, and at baseline and 6 months later in the controls, were documented. Changes of the central corneal thickness (ΔCCT) were determined in the same fashion.

Results

The mean IOP readings obtained by DCT were comparable before and at 6 months after procedure (18.34 ± 3.03 mmHg and 17.87 ± 2.61 mmHg respectively, p?=?0.41); whereas the mean IOP reading obtained by GAT decreased significantly 6 months postoperatively (17.92 ± 3.63 mmHg and 16.25 ± 2.66 mmHg, p?<?0.001). A significant correlation was present between the ΔIOP obtained by GAT and ΔCCT (r?=?0.61, p?<?0.001). Similar correlation was not significant between the DCT-obtained ΔIOP and the ΔCCT (r?=?0.07, p?=?0.44). The mean ΔIOP obtained by GAT was significantly higher in the operated eyes than in the controls (?1.54?±?1.45 vs 0.07?±?0.44 mmHg, p?=?0.02). The mean DCT-obtained ΔIOP was just marginally insignificant between the operated and nonoperated eyes (?0.63?±?0.59 vs 0.02?±?0.38 mmHg respectively; p?=?0.09).

Conclusions

The authors recommend DCT after PRK in the cases with myopia or myopic astigmatism     

Evaluating internal and ocular residual astigmatism in Chinese myopic children

Purpose

To investigate the nature of internal astigmatism (IA) and ocular residual astigmatism (ORA) in Chinese myopic children and to identify factors that may influence IA and ORA.

Methods

A total of 206 eyes of 206 myopic children (97 boys and 109 girls; 10.95 ± 2.2 years) were enrolled in this cross sectional study. Total ocular astigmatism (TOA), anterior corneal astigmatism (ACA), posterior corneal astigmatism (PCA) and total corneal astigmatism (TCA) were measured directly using either a Hartmann–Shack wavefront sensor or a Pentacam. IA and ORA were calculated by Fourier vector analyses (the definitions of IA and ORA are: IA = TOA ? ACA ? PCA, ORA = TOA ? ACA). Spearman or Pearson correlation was adopted to detect multiple factors that may influence IA and ORA, which were then predicted by linear regressions. Modified compensation factors were applied to evaluate the inter-relationship between corneal astigmatism and ORA.

Results

While the mean values of IA and ORA were ?0.52 DC × 94.8° and ?0.63 DC × 93.0°, respectively, the percentage of ORA power over 1.00 D was as high as 28.64%. Full or under-compensation of ACA by ORA predominated in the enrolled subjects. The mean ORA J₀ and J₄₅ were ?0.311 ± 0.236 and ?0.032 ± 0.156 D, respectively, negatively correlated with the corresponding ACA components (J₀: r = ?0.276, J₄₅: r = ?0.616, p < 0.001). While age was not correlated with either IA or ORA (p > 0.1), the power of IA or ORA was correlated inversely with the axial length (IA: r = ?0.193, p = 0.005; ORA: r = ?0.169, p = 0.015) and positively with the spherical equivalent refraction (IA r = 0.195, p = 0.005; ORA r = 0.213, p = 0.002) and power of corneal astigmatism (IA-ACA: r = 0.302, IA-TCA: r = 0.368, ORA-ACA: r = 0.334, ORA-TCA: r = 0.293). Girls had larger IA powers than boys (0.741 ± 0.345 D vs 0.651 ± 0.340, p = 0.036).

Conclusions

Full or under-compensation of ACA by ORA is common in Chinese myopic children, and the compensation efficiency may decrease with age. Among Chinese children with myopia, a larger ORA is more prevalent with less myopia and greater corneal astigmatism.

     

Comparison of dynamic contour tonometry and Goldmann applanation tonometry in relation to central corneal thickness in primary congenital glaucoma

Background

To compare intraocular pressure (IOP) measurements obtained with dynamic contour tonometer (DCT) and Goldmann applanation tonometer (GAT), and to investigate their relationship to central corneal thickness (CCT) in primary congenital glaucoma (PCG) eyes.

Methods

Thirty-one eyes of 31 PCG patients (25.7?±?7.2 years old) were examined. PCG was defined as elevated IOP, enlarged corneal diameter (buphthalmos), Haab’s striae and abnormal findings at gonioscopy. The mean of three measurements of GAT, DCT (quality scores 1 and 2), and CCT were obtained and assessed for agreement by means of Bland–Altman plot and for Spearman correlation test.

Results

Mean CCT was 534?±?72.3 μm (range: 430 to 610 μm). Mean IOP measurements were 15.1?±?4.2 mmHg (range: 5.5 to 22.7 mmHg) for DCT and 14.5?±?5.6 mmHg (range: 7.0 to 34.0 mmHg) for GAT (P?=?0.244). Spearman correlation tests showed that IOP difference (DCT ? GAT) was not correlated with CCT (r ²?=?0.023, P?=?0.417). IOP measurements by DCT were weakly but statistically correlated with those obtained with GAT (r²?=?0.213, P?=?0.0089). Bland–Altman analysis revealed poor agreement between DCT and GAT readings, considering the 95 % confidence intervals of ±10.45 mmHg.

Conclusions

The differences between DCT and GAT readings were not influenced by CCT in this series of patients. Considering the weak correlation and the poor agreement observed between GAT and DCT measurements and that they both may be affected by corneal biomechanical changes, these methods should not be used interchangeably, and may possibly give no meaningful IOP values in PCG patients.     

Evaluation of the Icare-ONE rebound tonometer as a self-measuring intraocular pressure device in normal subjects

Purpose

To compare Icare ONE rebound self-tonometer (ICRBT) measurements with Goldman applanation tonometry (GAT).

Methods

A trained examiner instructed each of 60 normal subjects on use of the ICRBT. Each subject then took two measurements of his/her own pressure using the ICRBT. Finally, a different examiner, who was masked to the earlier readings, measured IOP by GAT. Bland–Altman limits of agreement (LOA), intraclass correlation coefficients (ICCs), Kappa values, and paired t-test were used to assess the agreement between the two methods. Pearson’s correlation coefficient was used for correlation analysis.

Results

All of the subjects were able to obtain correct measurements with ICRBT after three attempts. The mean intraocular pressure with ICRBT and GAT measurements were 16.0?±?3.3?mmHg and 13.7?±?2.5?mmHg respectively. The mean difference between patient’s ICRBT and technician’s GAT measurements was 2.3?mmHg (p?p?r?=?0.48, p?r?=?0.31, p?=?0.015), indicating that greater thickness is associated with greater differences between the two methods.

Conclusion

The ICRBT was reliable in the hands of normal subjects, and may be used for self-monitoring of IOP. ICRBT measurements generally overestimated GAT measurements.     

Comparison of iCare tonometer and Goldmann applanation tonometry in normal corneas and in eyes with automated lamellar and penetrating keratoplasty

Purpose

To compare intraocular pressure (IOP) measurements with Goldmann applanation tonometry (GAT) and iCare tonometry in normal and post-keratoplasty corneas and to assess the influence of central corneal thickness (CCT), corneal curvature (CC), and corneal astigmatism (CA) on IOP.

Methods

This prospective cross-sectional study included one eye of 101 subjects with normal corneas (58 healthy subjects, 43 glaucoma); and 90 post-keratoplasty patients: 34 penetrating keratoplasties (PK); 20 automated-lamellar-therapeutic keratoplasties (ALTK); 19 Descemet-stripping-automated-endothelial keratoplasties (DSAEK); 17 edematous grafts. All subjects underwent GAT and iCare IOP measurements in random order, and CCT, CC, and CA evaluation. The Bland–Altman method and multivariate regression analysis were used to assess inter-tonometer agreement and the influence of CCT, CC, and CA on IOP.

Results

iCare significantly underestimated IOP in all groups compared with GAT (GAT minus iCare of 3.5±3.5 mm Hg, P<0.001), but overestimated IOP in the edematous grafts (GAT minus iCare of −6.5±1.9 mm Hg, P<0.001). In normal corneas, both tonometer measurements were directly related to CCT values; iCare readings appeared inversely related to CC. There was no significant relationship between IOP and CCT, CC and CA in post-keratoplasty eyes, except between CC and iCare measurements for PK eyes.

Conclusions

The agreement between GAT and iCare was clinically acceptable in control, ALTK and DSAEK groups, and poor in PK and edematous grafts eyes. In normal corneas, GAT was significantly affected by CCT; iCare was influenced by CCT and CC. The iCare appeared less influenced by corneal edema when compared with GAT. High IOP readings taken with both tonometers in grafts should raise suspicion of true elevated IOP.     

Quantitative evaluation of corneal epithelial edema after cataract surgery using corneal densitometry: a prospective study

Purpose

The optical density of the cornea can be evaluated quantitatively by “densitometry” using a rotating Scheimpflug camera. Densitometry allows evaluation of corneal opacity in the anterior segment of the eye by quantitative measurement of scattering light. In the present investigation, we evaluate quantitatively minimal subclinical corneal edema after cataract surgery using densitometry.

Methods

Fifty four eyes of 34 patients who underwent cataract surgery were enrolled. Measurement of corneal density was performed using Pentacam® before and on days 1, 3 and 7 after surgery.

Results

Densitometry scores increased from 18.12?±?1.76 before cataract surgery to 21.03?±?3.84 on day 1 (P?<?0.001) and 19.90?±?2.46 on day 3 (P?=?0.018), but recovered to 19.44?±?1.58 on day 7 (P?=?0.131). Total corneal thickness was 549.1?±?32.7?μm before surgery and increased to 582.7?±?46.3?μm on day 1 (P?=?0.001), but recovered to 566.4?±?29.7?μm on day 3 (P?=?0.097). Densitometry reading correlated positively with corneal thickness (correlation coefficient?=?0.13, P?=?0.003).

Conclusions

Densitometry is useful to detect corneal edema that is not detectable by slit-lamp examination.

     

Hornhautdickenabhängige Korrekturfaktoren bei der Goldmann-Applanationstonometrie

Background

For many years researchers have discussed which corneal parameters can influence the measurement of intraocular pressure (IOP). As a substantial parameter, the central corneal thickness (CCT) is assumed; however, different measuring methods – including Goldmann applanation tonometry (GAT), dynamic contour tonometry (DCT), and corneal compensated pressure measured with the ocular response analyzer (IOPcc) – may lead to a completely different dependence on corneal thickness.

Method

In a study approved by the ethics commission, the anterior chamber of 92 eyes of cataract patients and 85 eyes of glaucoma patients with very different CCT measurements was cannulized before surgery (cataract operation or trabeculectomy), and the IOP values were measured simultaneously with a pressure absorber and with GAT (Perkins tonometer) at different pressure values.

Results

The individual measurements exhibited an extraordinarily wide dispersion. In both groups, weak correlations of the difference between GAT and IOP values with the CCT were found (correction factors of 0.95 mmHg/100 µm CCT at pressure level 20 mmHg, 1.2 mmHg/100 µm CCT at pressure level 30 mmHg, and 1.7 mmHg/100 µm CCT at pressure level 40 mmHg).

Conclusions

Measurement of CCT is valuable for prognostic assessment of glaucoma, but not for correction factors for corneal thickness.     

Evaluation of corneal biomechanics in patients with keratectasia following LASIK using dynamic Scheimpflug analyzer

Purpose

To investigate the corneal biomechanics in eyes with keratectasia following LASIK using a dynamic Scheimpflug analyzer.

Design

Case–Control study.

Method

The subjects in the study included 12 eyes with keratectasia after LASIK (KE), 24 eyes with keratoconus (KC), 17 eyes without keratectasia after LASIK (LASIK), and 34 eyes with normal corneas (Normal). Corneal biomechanics of the four groups were evaluated using a dynamic Scheimpflug analyzer.

Results

Compared with Normal (7.06?±?0.54), the radius at the highest concavity (radius, mm) of LASIK (5.96?±?0.76), KE (4.93?±?0.61) and KC (5.39?±?1.02) were significantly small. The Deflection Amplitude (HCDLA, mm) of Normal (0.94?±?0.07) was significantly lower than those of KE (1.11?±?0.10) and KC (1.06?±?0.16), and was not significantly different from that of LASIK (0.98?±?0.07). There were significant differences between LASIK and KE in radius and HCDLA (P?<?0.05), whereas KE and KC had no differences in these parameters.

Conclusions

Corneal biomechanical features evaluated using the dynamic Scheimpflug analyzer suggest that biomechanical properties in eyes with keratectasia, keratoconus, and LASIK are different from those of normal eyes. Although the biomechanics in eyes with keratectasia differs from that in eyes with LASIK, it is similar to that in eyes with keratoconus.

     

Measurement repeatability of the dynamic Scheimpflug analyzer

Purpose

To evaluate the repeatability of corneal deformation parameters measured using a dynamic Scheimpflug analyzer and the impact of baseline clinical factors on the repeatability of each parameter.

Study design

Retrospective, cross-sectional study.

Methods

Forty-eight eyes (48 healthy subjects; mean age, 49.0 ± 19.5 years) underwent repeated examinations with the Scheimpflug analyzer to evaluate the test–retest variability. The intraclass correlation coefficient (ICC) and repeatability coefficient as indicators of variability were computed for 35 parameters measured with the Scheimpflug analyzer. The associations between the magnitude of the test–retest variability and baseline factors, such as age, axial length (AL), intraocular pressure (IOP), and central corneal thickness (CCT), were analyzed.

Results

The test–retest repeatability was excellent for 22 (62.9%) of 35 parameters (ICC ≥ 0.75), good for seven (20%), (ICC ≥ 0.6), fair for four (11.4%), (ICC ≥ 0.4), and poor for two (5.7%) parameters (ICC < 0.4). Age was associated positively with the magnitude of variability in 13 (37.1%) parameters; measurement variability was affected significantly by AL (5 parameters, 14.3%) and CCT (7 parameters, 20%) but, except for one parameter not by IOP.

Conclusion

Most parameters of the dynamic Scheimpflug analyzer showed favorable measurement reliability in healthy subjects. However, six parameters showed poor-to-fair repeatability. Age, AL, and CCT significantly affected the repeatability of several parameters. These results should be considered when clinicians use this device in clinical practice.

     

Ab interno gel implant in patients with primary open angle glaucoma and pseudoexfoliation glaucoma

Purpose

To compare efficacy and safety results of an ab interno gel implant in patients with pseudoexfoliation glaucoma (PXG) and primary open angle glaucoma (POAG).

Methods

Retrospective analysis of the medical records of 110 consecutive eyes with open angle glaucoma who had received a XEN45 gel implant between March 2014 and June 2015. Intraocular pressure course, number of glaucoma medications, the need for additional intervention (including needling) and complications were evaluated until 12?months postoperatively.

Results

Data of 67 eyes with POAG and 43 eyes with PXG were analyzed. At 12?months postoperatively, the mean IOP had significantly decreased by 54.0% from preoperatively 31.85?±?8.5?mmHg to 13.99?±?2.6?mmHg in the POAG group, (p?=?0.000; Wilcoxon test), and by 55.2% from 31.63?±?9.0?mmHg to 13.28?±?3.1?mmHg in the PXG group (p?=?0.000; Wilcoxon test). The mean number of anti-glaucoma medications had significantly decreased from 3.25?±?0.8 at baseline to 0.3?±?0.7 medications at 12?months postoperatively in POAG eyes (p?=?0.000; Wilcoxon test), and from 3.05?±?1.0 to 0.3?±?0.6 medications in PXG eyes (p?=?0.000; Wilcoxon test). Hypotony (IOP?≤?6?mmHg) was observed in 2 POAG eyes (3.0%) and in 5 PXG eyes (11.7%) at 1?month but normalized in all eyes at 12?months postoperatively. Severe complications were not observed. No statistically significant differences were found between PXG eyes and POAG eyes.

Conclusion

Our data indicate that the XEN45 gel implant provides significant and comparable reduction in IOP and anti-glaucoma medication during the one-year follow-up period in POAG as well as PXG eyes. This suggests that it may be a noteworthy alternative to traditional filtering procedures in patients with POAG and PXG respectively.

     

Corneal biomechanics predict the outcome of selective laser trabeculoplasty in medically uncontrolled glaucoma

Purpose

To evaluate the predictive value of clinical parameters, including biomechanical properties on the outcome of selective laser trabeculoplasty (SLT) in medically uncontrolled open angle glaucoma (OAG).

Methods

Sixty-eight eyes from 68 patients with OAG and IOP insufficiently regulated by topical medications were enrolled. Patients’ follow-up occurred 6 and 12 months after the procedure. The recorded parameters intraocular pressure (IOP), angle characteristics, central corneal thickness (CCT) and biomechanical properties of the eyes, including corneal hysteresis CH and corneal resistance factor CRF measured with the Ocular Responses Analyzer (ORA, Reichert Ophthalmic Instruments) were tested on their predictive value of SLT-induced IOP lowering effect using correlation analyses and regression models.

Results

Mean IOP reduction 12 months after SLT was 4.2?±?5.7 mmHg (23.2 %, from baseline 18.1?±?5.2 mmHg). The preoperative IOP correlated significantly with IOP reduction (maximum Spearman’s correlation r?=?0.75, p?<?0.001). In linear regression analysis, the corneal biomechanical properties (CH and CRF) together with the baseline IOP revealed good modelling for the IOP lowering effect of SLT (R²?=?0.64, respectively).

Conclusions

In addition to the baseline IOP biomechanical properties (CH and CRF) are significant predictors of SLT induced IOP lowering effect in medically uncontrolled OAG.     

Transplantation of PEDF-transfected pigment epithelial cells inhibits corneal neovascularization in a rabbit model

Background

The purpose of this study was to investigate the effect of recombinant pigment epithelium-derived factor (rPEDF), secreted by ARPE-19 cells transfected with the human PEDF gene and transplanted subconjunctivally in normal and in rabbits in which corneal neovascularization was elicited by a chemical burn.

Methods

Twenty grey Chinchilla Bastard rabbits were randomly assigned to four groups; neovascularization was induced in groups A, B, and C by alkali cauterization. Seven days later, group A received no cell implantation, non-transfected ARPE-19 cells were implanted subconjunctivally in group B, and PEDF-transfected ARPE-19 cells were implanted subconjunctivally in groups C and D (non-cauterized). In-vivo rPEDF secretion was analyzed by immunoblotting, and ELISA of extracts of conjunctival tissue samples taken at different time points. Digital photographs acquired on days 7, 14, and 21 after cauterization were evaluated for lead vessel length, vascular invasion area, and overall neovascularization rate.

Results

At days 14 and 21 after cauterization, significant differences were observed between groups A, B, and C in lead vessel length (day 21: 5.91?±?0.45, 5.11?±?1.22, 3.79?±?0.59 mm, repectively), vascular invasion area (day 21: 35.5?±?8.65, 34.86?±?4.92, 19.2?±?5.03 mm² respectively), and rate of corneal neovascularization. Compared to controls, neovascularization was reduced by 37.5 % on day 14 and 47 % on day 21. Analysis of conjunctival tissue extracts showed that rPEDF was secreted by the transplanted PEDF-transfected cells.

Conclusion

Subconjunctivally transplanted, PEDF-transfected ARPE-19 cells secrete rPEDF, which inhibits the corneal neovascularization elicited by alkali cauterization.

     

Comparation of the new rebound tonometer IOPen and the Goldmann tonometer, and their relationship to corneal properties

Purpose

To compare the intraocular pressures (IOPs) obtained with the IOPen rebound tonometer, Goldmann applanation tonometer (GAT) and the ocular response analyzer (ORA) and investigate the effects of corneal biomechanical properties on IOPen measurements.

Methods

A total of 198 normal eyes were included in this cross-sectional and randomized study. Three measurements were taken using IOPen. Agreement between tonometers was calculated using the Bland and Altman limits of agreement (LoA) analysis.

Results

The median IOPen IOP was 3 mm Hg below the GAT (P<0.001), 3 mm Hg below the ORA IOP similar to Goldmann (IOPg), and 3 mm Hg below the ORA IOP corrected using corneal parameters (IOPcc)(P<0.01). The LoA width between the IOPen and GAT IOPs varied between 13.92 (mean IOPen IOP) and 15.99 mm Hg (third IOPen measurement). The central corneal thickness (CCT) was unrelated to IOPen measurements (P>0.05). Corneal hysteresis (CH) and corneal rigidity factor (CRF) were correlated with IOPen and GAT.

Conclusions

IOPen underestimated the IOP compared with GAT and ORA. The effect of measurement quality or measurement order on IOPen was low. CCT did not affect the IOPen, but the CH and CRF did. The LoA width between the IOPen and GAT IOPs was higher than between the ORA IOPg or ORA IOPcc and GAT IOPs.     

Can we trust intraocular pressure measurements in eyes with intracameral air?

Purpose

To evaluate the effect of intracameral air on intraocular pressure (IOP) measurements using Goldmann applanation tonometry (GAT) and applanation resonance tonometry (ART) in an in-vitro porcine eye model.

Methods

IOP was measured on thirteen freshly enucleated eyes at three reference pressures: 20, 30, and 40 mmHg. Six measurements/method were performed in a standardized order with GAT and ART respectively. Air was injected intracamerally in the same manner as during Descemet’s stripping endothelial keratoplasty (DSEK) and Descemet’s membrane endothelial keratoplasty (DMEK), and the measurements were repeated.

Results

Measured IOP increased significantly for both tonometry methods after air injection: 0.7?±?2.1 mmHg for GAT and 10.6?±?4.9 mmHg for ART. This difference was significant at each reference pressure for ART but not for GAT.

Conclusions

Although slightly affected, this study suggests that we can trust GAT IOP-measurements in eyes with intracameral air, such as after DSEK/DMEK operations. Ultrasound-based methods such as ART should not be used.     

Repeatability and agreement of central corneal thickness measurement with non-contact methods: a comparative study

Purpose

To compare the central corneal thickness (CCT) measurements and reliability of RTVue XR-100 anterior segment optical coherence tomography (AS-OCT), AL-scan optical biometer and Schwind Sirius anterior segment analysis system.

Methods

The CCT was measured in one hundred and twenty-seven eyes of 127 healthy subjects with AS-OCT, AL-scan and Sirius system. Mean CCT was compared among the instruments, and the level of agreement was assessed using Bland–Altman plots. One eye each of 30 subjects was randomly assigned for intrasession intraoperator and interoperator repeatability which was assessed using coefficient of variation and intraclass correlation coefficient.

Results

Mean CCT with AS-OCT, AL-scan and Sirius system was 496.72 ± 32.75, 507.43 ± 33.54 and 512.08 ± 33.1 µm, respectively. There was no statistically significant difference between AL-scan and Sirius system (p = 0.26). Significant difference was found between AS-OCT/AL-scan (p = 0.01) and AS-OCT/Sirius system (p < 0.0001). Bland–Altman analysis showed a high level of agreement between AL-Scan/Sirius system (Mean difference ?4.6 µm) and a low level of agreement between AS-OCT/AL-scan (Mean difference ?10.7 µm) and OCT/Sirius system (Mean difference ?15.4 µm).

Conclusions

AS-OCT underestimated CCT measurements when compared to other two devices in healthy subjects. Hence, one must be cautious when analyzing the results from different machines and should be aware that the measurement values are not interchangeable.