What's the choroid got to do with angle closure?

Impact of Type 2 diabetes mellitus and insulin use on progression to glaucoma surgery in primary open angle glaucoma

PURPOSE

To investigate outcomes of primary open-angle glaucoma (POAG) patients with and without type 2 diabetes mellitus (T2DM).

METHODS

Retrospective observational study using U.S. nationwide healthcare insurance claims database. Patients ≥40 years old with at least one HbA1c within one year of POAG diagnosis were included. Diabetic factors associated with POAG progression requiring glaucoma surgery were evaluated using multivariable Cox proportional hazards regression models adjusted for demographic, diabetic and glaucoma factors. T2DM diagnosis and use of either oral hypoglycaemic agents or insulin therapy were assessed in association with POAG progression requiring glaucoma surgery.

RESULTS

104,515 POAG patients were included, of which 70,315 (67%) had T2DM. The mean age was 68.9 years (Standard deviation 9.2) and 55% were female. Of those with T2DM, 93% were taking medication (65,468); 95% (62,412) taking oral hypoglycaemic agents, and 34% (22,028) were on insulin. In multivariable analyses, patients with T2DM had a higher hazard of requiring glaucoma surgery (Hazard ratio, HR 1.15, 95% CI 1.09-1.21, p < 0.001). Higher mean HbA1c was also a significant predictor of progression requiring glaucoma surgery (HR 1.02, 95% CI 1.01-1.03, p < 0.001). When evaluating only patients who were taking antidiabetic medication, after adjusting for confounders, insulin use was associated with a 1.20 higher hazard of requiring glaucoma surgery compared to oral hypoglycaemic agents (95% CI 1.14-1.27, p < 0.001), but when stratified by HbA1c, this effect was only significant for those with HbA1c > 7.5%.

CONCLUSIONS

Higher baseline HbA1c, particularly in patients taking insulin may be associated with higher rates of glaucoma surgery in POAG.

Impact of improved minimally invasive anterior vitrectomy on the prognosis of patients with malignant glaucoma

BACKGROUND

The importance of communicating the anterior chamber and vitreous cavity for managing malignant glaucoma (MG) is widely recognized. This study investigated the impact of improved minimally invasive anterior vitrectomy (IAV) on the prognosis of MG.

METHODS

This retrospective interventional study included patients with MG who underwent conventional surgery or improved minimally IAV in Nanchang Aier Eye Hospital between January 2011 and April 2021. For the improved step, a small amount of triamcinolone acetonide was injected into the vicinity of the iris. Then, the residual vitreous body adhering to triamcinolone acetonide was excised. Comparisons were made using repeated measures ANOVA, t-test, and chi-squared test.

RESULTS

Thirty-one eyes from 26 patients were included: 15 eyes from 13 patients in the conventional group and 16 eyes from 13 patients in the IAV group. The 1-week, 1-month, and 3-month intraocular pressure (IOP) and the 3-month mean central anterior chamber depth were comparable between the two groups (all P > 0.05). The conventional group showed one eye with intraoperative vitreous hemorrhage and two eyes with postoperative re-shallowing of the anterior chamber; such events did not occur in the IAV group, and none developed corneal endothelial decompensation, IOL deviation, suprachoroidal hemorrhage, or retinal detachment during treatment and follow-up.

CONCLUSION

Patients with MG who undergo improved minimally IAV might have similar postoperative IOP and central anterior chamber depth compared with conventional surgery but with reduced complications such as intraoperative vitreous hemorrhage and postoperative re-shallowing of the anterior chamber. Improved minimally IAV might be an alternative surgery for MG.

Diabetes has no additional impact on retinal ganglion cell loss in a mouse model of spontaneous glaucoma

Purpose

There is no valid medical treatment for diabetic retinopathy mostly because its pathogenesis remains largely unknown. Early stages of diabetic retinopathy, just like glaucoma, are characterized by the loss of retinal ganglion cells. Whether the two diseases may share a similar pathogenic background is unknown.

Methods

To clarify this issue the thickness of retinal nerve fiber layer was studied in vivo by optical coherence tomography in 10 Ins2Akita (diabetic) and 10 C57BL/6J (control) mice. The number of retinal ganglion cells and retina's surface covered by neurofilaments were quantified ex vivo in 12 normoglycemic DBA/2J (glaucoma) and 11 diabetic (alloxan-induced) DBA/2J mice (glaucoma + diabetes).

Results

At 16 weeks of age retinal nerve fiber layer was significantly thinner in Ins2Akita mice confirming the neurodegenerative impact of diabetes. Number of retinal ganglion cells and retina's surface covered by neurofilaments were similar in normoglycemic and diabetic DBA/2J mice with the exception of the superior quadrant where the number of retinal ganglion cells was increased in animals with glaucoma + diabetes.

Conclusions

In presence of glaucoma, diabetes is unable to induce further retinal ganglion cells loss. The hypothesis that the mechanism leading to retinal ganglion cells loss may be shared by the two diseases cannot be ruled out. Whether early diabetes-driven retinal neurodegeneration could be prevented by neuroprotective treatment proven to be effective in case of glaucoma, remains to be clarified.

[Primary anterior chamber angle closure: progression from suspect to glaucoma. Part 2. Predictors of primary angle closure]

To review the literature devoted to the search of predictors of primary angle closure (PAC) progression as an important link in the pathogenesis of primary angle-closure glaucoma. This part presents a cluster analysis, describes the mechanisms of PAC development, and considers the studies aimed at discovering the risk factors for the progression of primary angle closure suspect into true angle closure. The results of the analyzed literature are ambiguous, indicating the need for further research that would involve strict inclusion criteria, and a standard approach to defining the primary angle closure disease and expanding the diagnostic parameters, in which a key role belongs to anterior segment optical coherence tomography (AS-OCT).

Effect of combined water drinking test and dark room provocative testing in Caucasian eyes with narrow angles

PURPOSE

To assess the usefulness of water drinking test and dark room provocative testing (WDT + DRPT) in current clinical practice by evaluating input parameters from Swept-source Optical Coherence Tomography (SS-OCT) images, and to determine if clinical factors like axial length, central endothelial cell count (CECC) and retinal nerve fibre layer thickness (RNFL) thickness are associated with a positive WDT + DRPT.

METHODS

SS-OCT examination was performed in consecutive subjects presenting as new patients in the outpatient clinic aged > 40 years. If at least one eye met the inclusion criteria (anterior chamber angles <20° and anterior chamber depth < 2.5 mm on SS-OCT), subjects were included in this study and WDT + DRPT was carried out. The eye with the smallest angle was analysed. The difference in parameters between eyes with a positive (≥8 mmHg) and negative (<8 mmHg) increase in intraocular pressure (IOP) after WDT + DRPT were statistically analysed. Second, the correlation between IOP increase after WDT + DRPT and anterior chamber angle parameters (RNFL thickness, CECC and axial length) was studied.

RESULTS

A total of 95 subjects with a mean age of 64 years were included. There was an association between IOP increase after WDT + DRPT and anterior chamber angle characteristics, however this was not of clinical significance. No positive results after WDT + DRPT were found in patients with anterior chamber angles ≥ 20°.

CONCLUSIONS

The present findings indicate that this combined provocative test has no definite correlative or predictive value in angle closure disease. Further, the test is not useful in predicting early diagnosis or possible CECC or RNFL loss.

Clinical observation of macular choroidal thickness in primary chronic angle-closure glaucoma

PURPOSE

To comparatively analyze differences in macular choroidal thickness and volume in primary chronic angle-closure glaucoma (PACG) eyes.

METHODS

Thirty-one PACG patients were sequentially selected for this case-control study. Thirty-one eyes with PACG were included in group A, 31 fellow eyes were included in group B, and group C included 67 normal eyes. Enhanced-depth imaging optical coherence tomography (EDI-OCT) was used to measure choroidal thickness and volume.

RESULTS

The choroidal thicknesses and volumes of the central subfield macula (CSM), nasal inner macula (NIM), temporal inner macula (TIM), inferior inner macula (IIM), temporal outer macula (TOM), inferior outer macula (IOM), and mean macula (MM) in group A were all higher than those in group C (P < 0.05). The choroidal thicknesses and volumes of the NIM, superior inner macula (SIM), IIM, nasal outer macula (NOM), and MM in group B were all higher than those in group C (P < 0.05). No statistically significant differences were found between groups A and B (P > 0.05). The choroidal thicknesses of different macular regions in group A were not correlated with the mean defect (MD).

CONCLUSION

Increased macular choroidal thickness may be a common anatomical characteristic of PACD eyes. Macular choroidal thickness is not a good marker for assessing PACG severity.

Deep Learning with Skip Connection Attention for Choroid Layer Segmentation in OCT Images

Since the thickness and shape of the choroid layer are indicators for the diagnosis of several ophthalmic diseases, the choroid layer segmentation is an important task. There exist many challenges in segmentation of the choroid layer. In this paper, in view of the lack of context information due to the ambiguous boundaries, and the subsequent inconsistent predictions of the same category targets ascribed to the lack of context information or the large regions, a novel Skip Connection Attention (SCA) module which is integrated into the U-Shape architecture is proposed to improve the precision of choroid layer segmentation in Optical Coherence Tomography (OCT) images. The main function of the SCA module is to capture the global context in the highest level to provide the decoder with stage-by-stage guidance, to extract more context information and generate more consistent predictions for the same class targets. By integrating the SCA module into the U-Net and CE-Net, we show that the module improves the accuracy of the choroid layer segmentation.

Tissue-Engineered Models for Glaucoma Research

Glaucoma is a group of optic neuropathies characterized by the progressive degeneration of retinal ganglion cells (RGCs). Patients with glaucoma generally experience elevations in intraocular pressure (IOP), followed by RGC death, peripheral vision loss and eventually blindness. However, despite the substantial economic and health-related impact of glaucoma-related morbidity worldwide, the surgical and pharmacological management of glaucoma is still limited to maintaining IOP within a normal range. This is in large part because the underlying molecular and biophysical mechanisms by which glaucomatous changes occur are still unclear. In the present review article, we describe current tissue-engineered models of the intraocular space that aim to advance the state of glaucoma research. Specifically, we critically evaluate and compare both 2D and 3D-culture models of the trabecular meshwork and nerve fiber layer, both of which are key players in glaucoma pathophysiology. Finally, we point out the need for novel organ-on-a-chip models of glaucoma that functionally integrate currently available 3D models of the retina and the trabecular outflow pathway.

[Comparative study of factors associated with the progression of primary open-angle and angle-closure glaucoma]

PURPOSE

To compare the factors associated with the progression of primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG).

MATERIAL AND METHODS

This prospective study analyses clinical data of POAG and PACG patients followed up for 6 years. The progression of glaucomatous optic neuropathy (GON) was determined using perimetry and spectral optical coherence tomography (OCT). The value of each diagnostic indicator (z-value) was calculated using the Wilcoxon-Mann-Whitney test and the area under the ROC-curve (AUC) to identify the parameters reliably associated with the progression in both groups of patients.

RESULTS

According to OCT, 47.3% of PACG patients and 52.46% of POAG patients had GON progressing, while according to perimetry, these figures were 21.8% and 23%, respectively. The common factors associated with progression of these glaucoma forms were age (AUC 0.7, z -1.9 in PACG and AUC 0.7, z -2.9 in POAG) and maximum IOP (0.7; -2.7 in PACG and 0.79; -5.4 in POAG). The progression of PACG is associated with lens size (0.7; -2.4), subfoveal choroidal thickness (AUC 0.8, z -3.3) and peripapillary choroidal thickness (0.79; -3.2), resistive index in the vortex veins (0.81; -3.3) and their end diastolic blood flow velocity (0.83; 3.2). The progression of POAG is associated with a thin peripapillary (0.75; 2.6) and subfoveal choroid (0.74; 2.5), increased resistive index in the posterior short ciliary arteries (0.8; -2.3), and initial retinal nerve fiber layer (RNFL) thickness: 0.69; 2.9.

CONCLUSION

The progression of POAG and PACG has only two common factors - age and maximum IOP. The progression of PACG is mainly related to the lens size, venous dysfunction and the choroid expansion, while the progression of POAG is related to the initial RNFL thickness, reduced arterial blood flow and choroid thinning.

Factors Impacting Outcomes and the Time to Recovery From Malignant Glaucoma

PURPOSE

To identify factors associated with the successful treatment of malignant glaucoma (MG).

DESIGN

Retrospective case series.

METHODS

Setting: single institution; study population: 64 eyes (55 subjects) with MG; observation procedure(s): chart review; main outcome measures: anatomy, intraocular pressure (IOP), best visual acuity (BVA).

RESULTS

87.5% (n=56/64) of eyes with MG required surgical intervention. Vitrectomy was more likely to be successful in eyes with a history of <3 incisional surgeries, <3 glaucoma drops, or IOP ≤30 mm Hg (P < .05). If vitrectomy was performed within 30 days, recovery of anatomy, BVA, and IOP occurred sooner (P < .05). IOP reduction was greater in subjects treated with oral carbonic anhydrase inhibitors (P = .016) or Nd:YAG laser hyaloidotomy (P = .007), and without a history of MG (P = .007). Time to maximal improvement was significantly longer for IOP and BVA than anatomy (P < .001). Treatment of MG with an oral carbonic anhydrase inhibitor hastened anatomic recovery (P = .01). Time to improvement in BVA was significantly faster in men and African Americans (P < .05). Time to maximal reduction in IOP occurred sooner in eyes that underwent anterior chamber reformation in clinic (P < .002). Trabeculectomy surgery prior to MG was associated with prolonged recovery of anatomy, BVA, and IOP (P < .05).

CONCLUSIONS

Earlier vitrectomy may shorten recovery times for MG. Nd:YAG laser hyaloidotomy and oral carbonic anhydrase inhibitors may lead to greater IOP reduction. The time to maximal improvement in IOP and BVA may be longer than the time to anatomic resolution. Although trabeculectomy may impede time to recovery from MG, oral carbonic anhydrase inhibitors may shorten the time to anatomic recovery and anterior chamber reformation may hasten IOP recovery.

Upside-down position leads to choroidal expansion and anterior chamber shallowing: OCT study

Background

To determine whether dynamic changes in choroidal thickness (CT) cause shallowing of the anterior chamber.

Methods

34 healthy volunteers were enrolled. The participants in our study adopted the upside-down position for 1.5 min, which was the model we used to study the dynamic changes in CT. Intraocular pressure (IOP) elevation, optical coherence tomography images of the choroid and anterior chamber were obtained at baseline, after being in an upside-down position in an inversion machine and after 15 min of rest. The changes in IOP, anterior chamber and choroidal blood flow between the baseline and the upside-down position were compared.

Results

Sixty-eight eyes from 34 subjects were analysed. After being in upside-down position for 1.5 min, there was a significant increase in CT from 226.39±52.44 µm to 238.34±54.84 µm (p<0.001). Choroidal flow index decreased from 0.3357±0.0251 to 0.3004±0.0190 in upside-down position, and there was a decrease in anterior chamber depth (3.21±0.22 mm to 3.13±0.21 mm, p<0.001) and angle opening distance at 500 µm from the scleral spur (0.65±0.24 mm to 0.58±0.20 mm, p=0.007). Pearson correlation analysis showed that the increase in CT was positively related with CT at baseline CT (p=0.001).

Conclusion

When the body position changed from sitting to upside-down position, there was choroidal thickening, anterior chamber shallowing and IOP elevation with reduced choroidal blood flow. The data provide evidence about the relationship between choroid expansion and shallowing of the anterior chamber, which may be of relevance for the pathogenesis of angle closure.

Water-drinking Test and Pharmacologic Mydriasis as Provocative Tests in Primary Angle Closure Suspects

Purpose

To compare the water-drinking test (WDT) and pharmacologic mydriasis as provocative tests in patients with primary angle closure suspect (PACS).

Methods

This observational non-randomized comparative study evaluated changes in intraocular pressure (IOP) in 21 patients with PACS who underwent pharmacologic mydriasis and compared it with IOP changes in 26 patients given the WDT. Ocular biometric and anterior chamber parameters were also assessed. Tests were repeated on the same patient two weeks after performing laser peripheral iridotomy (LPI).

Results

The mean age ± standard deviation was 60 ± 7 and 57 ± 9 years in the mydriasis and WDT groups, respectively (P = 0.201). Before LPI, both provocative tests were associated with a significant increase in IOP (mydriasis: 15.1 ± 3.1 to 16.6 ± 3.5 mmHg, P = 0.025; WDT: 16.2 ± 2.8 to 18.5 ± 3.3 mmHg, P < 0.001). However, the IOP changes were not statistically different between groups (P = 0.102). After LPI, only the WDT group showed a continued significant IOP elevation after the test (mydriasis: 16.4 ± 3.3 to 16.7 ± 3.5 mmHg, P = 0.569; WDT: 14.9 ± 3.0 to 17.8 ± 4.1 mmHg, P < 0.001). The post-test IOP change was significantly greater in the WDT than in the mydriasis group (3.0 versus 0.3 mmHg, respectively; P = 0.002). Step-wise multiple regression analysis verified the type of provocative test as the only independent factor affecting the post-test IOP change after LPI (regression coefficient: 2.664; P = 0.002).

Conclusion

Pharmacologic mydriasis and the WDT had similar IOP elevation before LPI, but after LPI, IOP elevation was much greater in the WDT group.

Visual Assessment of Aqueous Humor Outflow

In the past decade, many new pharmacological and surgical treatments have become available to lower intraocular pressure (IOP) for glaucoma. The majority of these options have targeted improving aqueous humor outflow (AHO). At the same time, in addition to new treatments, research advances in AHO assessment have led to the development of new tools to structurally assess AHO pathways and to visualize where aqueous is flowing in the eye. These new imaging modalities have uncovered novel AHO observations that challenge traditional AHO concepts. New behaviors including segmental, pulsatile, and dynamic AHO may have relevance to the disease and the level of therapeutic response for IOP-lowering treatments. By better understanding the regulation of segmental, pulsatile, and dynamic AHO, it may be possible to find new and innovative treatments for glaucoma aiming at these new AHO behaviors.

Effects of Choroidal Thickness on Refractive Outcome Following Cataract Surgery in Primary Angle Closure

Purpose

To identify the preoperative biometric factors, including subfoveal choroidal thickness (CT), associated with refractive outcome after cataract surgery in eyes with primary angle closure (PAC).

Methods

This study included 50 eyes of 50 PAC patients who underwent uneventful cataract surgery. Preoperatively, anterior segment parameters including anterior chamber depth (ACD) and lens vault were determined by anterior segment optical coherence tomography. Subfoveal CT was measured by spectral domain optical coherence tomography enhanced depth imaging before and at one month after surgery. Mean refractive error (MRE) was calculated as the difference in spherical equivalent between actual postoperative refraction determined one month postoperatively and that predicted using each of three IOL calculation formulas (SRK/II, SRK/T, and Haigis). Regression analyses were performed to investigate potential associations between MRE and putative factors.

Results

Mean ACD was 1.9 ± 0.4 mm, and preoperative subfoveal CT was 250.8 ± 56.9 µm. The SRK/T (MRE, 0.199 ± 0.567 diopters [D]) and Haigis (MRE, 0.190 ± 0.727 D) formulas showed slight hyperopic shift, while the SRK/II formula demonstrated a myopic shift (MRE, −0.077 ± 0.623 D) compared with that expected after cataract surgery. Mean absolute refractive error was not significantly different between formulas. Higher preoperative lens vault and shallower ACD were associated with a hyperopic shift in all formulas, but not in a statistically significant manner. Thicker preoperative subfoveal choroid was associated with a myopic shift after cataract surgery in all formulas (SRK/II: β = −0.511, p < 0.001; SRK/T: β = −0.652, p < 0.001; Haigis: β = −0.671, p < 0.001). Greater postoperative reduction of subfoveal CT was associated with a myopic shift after cataract surgery in all formulas (SRK/II: β = −0.511, p < 0.001; SRK/T: β = −0.652, p < 0.001; Haigis: β = −0.671, p < 0.001).

Conclusions

Our results indicate that preoperative subfoveal CT and the difference between pre- and postoperative subfoveal CT are significant factors for predicting refractive error after cataract surgery in PAC patients. These findings should be considered when performing cataract surgery to optimize visual outcomes.

Evaluation of the lamina cribrosa in patients with diabetes mellitus using enhanced depth imaging spectral-domain optical coherence tomography

PURPOSE

To compare the lamina cribrosa thickness and anterior lamina cribrosa depth between patients with and without diabetes mellitus and to investigate the effect of metabolic control and duration of diabetes mellitus on lamina cribrosa thickness and anterior lamina cribrosa depth using enhanced depth imaging spectral-domain optical coherence tomography.

METHODS

A total of 70 patients were enrolled in this cross-sectional study and were divided into the diabetes and control groups. Intraocular pressure, circumpapillary retinal nerve fibre layer thickness, anterior lamina cribrosa depth and lamina cribrosa thickness were compared between the groups.

RESULTS

In the control group, the mean intraocular pressure was 14.6 ± 3.1 (mean ± standard deviation) mmHg, mean circumpapillary retinal nerve fibre layer thickness was 105.41 ± 5.86 μm, mean anterior lamina cribrosa depth was 420.3 ± 90.2 μm and mean lamina cribrosa thickness was 248.5 ± 5.4 μm. In the diabetes group, the mean intraocular pressure was 13.9 ± 2.2 mmHg, mean circumpapillary retinal nerve fibre layer thickness was 101.37 ± 10.97 μm, mean anterior lamina cribrosa depth was 351.4 ± 58.6 μm and mean lamina cribrosa thickness was 271.6 ± 33.9 μm. Lamina cribrosa thickness was significantly higher ( p < 0.001) and anterior lamina cribrosa depth was significantly lower ( p = 0.003) in the diabetes group. There was no statistical difference between the groups with regard to age, spherical equivalent, axial length, circumpapillary retinal nerve fibre layer thickness and intraocular pressure ( p  = 0.69, 0.26, 0.47, 0.06 and 0.46, respectively). Lamina cribrosa thickness and anterior lamina cribrosa depth were not significantly correlated with duration of diabetes mellitus (lamina cribrosa thickness: r = -0.078, p = 0.643; anterior lamina cribrosa depth: r = -0.062, p = 0.710) or HbA1c levels (lamina cribrosa thickness: r = -0.078, p = 0.596; anterior lamina cribrosa depth: r = -0.228, p = 0.169).

CONCLUSION

The results of this study showed that the optical coherence tomography measurement of lamina cribrosa revealed thicker and more anteriorly positioned lamina cribrosa for patients with diabetes mellitus compared with those for healthy controls.

Difference of uveal parameters between the acute primary angle closure eyes and the fellow eyes

Purpose

To measure the anterior and posterior ocular biometric characteristics concurrently and to explore the relationship between iris, ciliary body and choroid in acute primary angle closure eyes (APAC) and fellow eyes.

Methods

It is a prospective, cross-sectional study. Thirty patients with recent APAC were finally enroled in it. Anterior and posterior uveal parameters were measured simultaneously by anterior segment optical coherence tomography (AS-OCT), swept-source optical coherence tomography (SS-OCT) and ultrasound biomicroscopy (UBM). The parameters were measured including: pupil diameter (PD); iris thickness, curvature (ICURV), area (IAREA); anterior chamber depth (ACD), width (ACW), area (ACA), volume (ACV); lens vault (LV); choroidal thickness and retinal thickness; maximum ciliary body thickness (CBTmax); ciliary body thickness at the point of the scleral spur (CBT0) and 1000 mm away (CBT1000); anterior placement of the ciliary body (APCB); and trabecular-ciliary angle (TCA).

Results

Compared with fellow eyes, APAC eyes had narrower anterior biometric parameters and presented with smaller anterior segment parameters (including ACD and ACW); (p < 0.01)), smaller IAREA and ICURV (p < 0.001), larger LV (p = 0.035), thinner ciliary body and less anterior ciliary process (p < 0.01). After adjustment for potential confounders (axial length, spherical equivalent and PD), APCB was positive correlated with choroidal thickness and CBT, and CBT was positive correlated with choroidal thickness.

Conclusions

Compared with fellow eyes, APAC eyes had narrower anterior biometric parameters, thinner ciliary body and smaller iris area and curvature. APCB, CBT and choroidal thickness were positively correlated. However, further studies are required before these conclusions are generalised.

Results for Water-drinking Test, before and after Laser Iridotomy, in Primary Angle-closure Suspects

SIGNIFICANCE

Intraocular pressure and ocular biometric changes were similar before and after laser iridotomy in response to the water-drinking test in a cohort of patients at risk of angle closure. The water-drinking test does not seem to be a good provocative test to determine which eyes would benefit from a laser iridotomy. Our data call into question the preoperative predictive value of this test.

PURPOSE

The aim of this study was to evaluate the effect of water-drinking test on intraocular pressure and ocular biometric parameters, before and after laser peripheral iridotomy, in patients with an occludable angle.

METHODS

Twenty-seven patients, who met the inclusion criteria and had at least 180 degrees of iridotrabecular apposition, underwent a complete eye examination followed by the measurement of ocular biometric (using LenStar LS-900; Haag-Streit AG, Koeniz, Switzerland) and anterior chamber parameters (using Pentacam HR; Oculus Optikgerate GmbH, Wetzlar, Germany). All the measurements were repeated 30 minutes after the water-drinking test. Two weeks after laser peripheral iridotomy, all the measurements were repeated both before and after the water-drinking test.

RESULTS

The mean ± SD of the age of the participants was 57 ± 9 years, and 23 (85.2%) were male. Intraocular pressure increased after the water-drinking test in both pre-laser peripheral iridotomy (17.0 vs. 19.3 mmHg, P < .001) and post-laser peripheral iridotomy (15.6 vs. 18.6 mmHg, P < .001) conditions. The thickness values of central cornea increased slightly after the water-drinking test in pre-laser peripheral iridotomy (535 vs. 538 μm, P = .001) compared with post-laser peripheral iridotomy (532 vs. 536 μm, P = .003). The water-drinking test had no significant effect on other biometric or anterior chamber parameters, before or after laser peripheral iridotomy.

CONCLUSIONS

The water-drinking test increased intraocular pressure, both before and after laser peripheral iridotomy. Laser peripheral iridotomy had no significant effect on the amount of intraocular pressure change after the water-drinking test. The water-drinking test has no effect on other biometric or anterior chamber parameters.

An automated method for choroidal thickness measurement from Enhanced Depth Imaging Optical Coherence Tomography images

The choroid is vascular tissue located underneath the retina and supplies oxygen to the outer retina; any damage to this tissue can be a precursor to retinal diseases. This paper presents an automated method of choroidal segmentation from Enhanced Depth Imaging Optical Coherence Tomography (EDI-OCT) images. The Dijkstra shortest path algorithm is used to segment the choroid-sclera interface (CSI), the outermost border of the choroid. A novel intensity-normalisation technique that is based on the depth of the choroid is used to equalise the intensity of all non-vessel pixels in the choroid region. The outer boundary of choroidal vessel and CSI are determined approximately and incorporated to the edge weight of the CSI segmentation to choose optimal edge weights. This method is tested on 190 B-scans of 10 subjects against choroid thickness (CTh) results produced manually by two graders. For comparison, results obtained by two state-of-the-art automated methods and our proposed method are compared against the manual grading, and our proposed method performed the best. The mean root-mean-square error (RMSE) for finding the CSI boundary by our method is 7.71±6.29 pixels, which is significantly lower than the RMSE for the two other state-of-the-art methods (36.17±11.97 pixels and 44.19±19.51 pixels). The correlation coefficient for our method is 0.76, and 0.51 and 0.66 for the other two state-of-the-art methods. The interclass correlation coefficients are 0.72, 0.43 and 0.56 respectively. Our method is highly accurate, robust, reliable and consistent. This identification can enable to quantify the biomarkers of the choroidin large scale study for assessing, monitoring disease progression as well as early detection of retinal diseases. Identification of the boundary can help to determine the loss or change of choroid, which can be used as features for the automatic determination of the stages of retinal diseases.

Flat Anterior Chamber after Trabeculectomy in Secondary Angle-Closure Glaucoma with BEST1 Gene Mutation: Case Series

Purpose

Trabeculectomy has been regarded as a mainstay of initial treatment in eyes of angle closure glaucoma (ACG) with peripheral anterior synechia > 180° in the Chinese population while its efficacy in secondary ACG with BEST1 gene mutation remains unclear. We set out to investigate the treatment outcome of trabeculectomy for secondary ACG in a group of patients with autosomal recessive bestrophinopathy (ARB).

Methods

In this retrospective case series study, 8 secondary ACG patients with ARB and their 4 recruited family members underwent a thorough ophthalmic examination including best-corrected visual acuity, Goldmann applanation tonometry, gonioscopy, and fundus examinations. Ultrasound biomicroscopy, optical coherence tomography (OCT), ultrasound A-scan, B-scan, electro-oculography (EOG), Humphrey perimetry, fundus photography, fundus fluorescein angiography (FFA) and indocyanine green angiography (ICGA) were also performed. Blood samples were obtained in the patients and their available family members to analyze the variants of the BEST1 gene. Trabeculectomy was performed in the 8 patients (15 eyes).

Results

The age of onset varied from 13 to 38 years. The average axial length (AL) of the affected eyes was 21.82 ± 0.92 mm and the average anterior chamber depth (ACD) was 2.19 ± 0.29 mm. There was marked axial shallowing of the anterior chamber in all 15 eyes after trabeculectomy, and was not improved with potent mydriatics. The IOP was elevated in 3 eyes. Variable degree of yellowish subretinal deposits was observed in the posterior retina. The FFA showed punctuate or patched hyperfluorescence suggesting retinal pigment epithelium impairment. The ICGA demonstrated dilatation of choroidal vessels. The OCT revealed diffused neuroretinal detachment in the posterior and midperipheral retina, with intraretinal fluid collections, and hyperreflective subretinal accumulations. The average subfoveal choroidal thickness of the patients was 382.36 ± 80.09 μm. All the patients and enrolled family members carried mutation in BEST1 gene.

Conclusions

ARB is a rare condition with fundus manifestations mimicking various diseases. Careful discrimination should be taken to exclude any secondary causes for ACG before treatment. Concerning the high incidence of postoperative shallow anterior chamber, selection of filtering surgery should be very careful in these patients.

Topographic profile of choroid in eyes after acute primary angle-closure

OBJECTIVE

To characterize and compare the topographic profile of choroid in eyes after acute primary angle-closure (APAC) and in normal controls.

DESIGN, SETTING, AND PARTICIPANTS

A prospective observational study was conducted. Forty-four consecutive patients who had experienced unilateral APAC that was resolved by treatment were recruited. Seventy age- and sex-matched normal individuals were recruited as controls.

METHODS

Enhanced depth imaging-optical coherence tomography was used to measure choroidal thickness (CT) in 9 diffuse locations of macular region. The average CT was compared among each location in the APAC and control groups and between the same locations in the 2 groups.

RESULTS

Variants of CT at different macular locations were found in both groups; it was greatest at subfoveal locations and spread thinner around them, to reach a significant decrease (all p ≤ 0.05) 3 mm away in all directions from the fovea except for the superior direction in normal controls (p = 0.472). Among the 4 directions, the superior had the thickest CT in both groups, followed by the temporal, inferior, and nasal directions in both groups, whereas the APAC had a thicker choroid profile at each location (all p < 0.05). Univariate analysis showed that age, sex, anterior chamber depth, axial length, and spherical equivalent were all associated with the subfoveal choroidal thickness (SFCT) (all p < 0.1). Multivariable linear regression analysis showed that the SFCT was significantly thicker in association with an APAC diagnosis, shorter axial length, greater spherical equivalent refractive error, and younger female subjects (all p ≤ 0.05).

CONCLUSIONS

APAC eyes have a thicker choroid than normal eyes in the macular region, and the increase in CT in APAC eyes follows topographic distribution as in normal control eyes.

Association between choroidal thickness and anterior chamber segment in eyes with narrow or open-angle

AIM

To investigate the relationship between choroidal thickness and anterior chamber segment in subjects with eyes with narrow or open-angle.

METHODS

The subfoveal choroidal thickness was measured with enhanced depth-imaging optical coherence tomography and anterior chamber parameters were measured with ultrasound biomicroscopy in one eye of 23 subjects with open-angle eyes and 38 subjects with narrow-angle eyes. The mean age was 59.52±7.04y for narrow-angle subjects and 60.76±7.23y for open-angle subjects (P=0.514). Multivariate linear regression analysis was performed to assess the association between choroidal thickness and narrow-angle parameters.

RESULTS

There were no differences in subfoveal choroidal thickness between open- and narrow-angle subjects (P=0.231). Anterior chamber parameters, including central anterior chamber depth, trabecular iris angle, iris thickness 500 µm from the scleral spur (IT500), and ciliary body thickness at 1 mm and 2 mm from the scleral spur (CBT1, CBT2) showed significant differences between the two groups (P<0.05). Subfoveal choroidal thickness showed negative correlation (β=-0.496, P=0.016) only with anterior chamber depth in the open-angle group and with age (β=-0.442, P=0.003) and IT500 (β=-0.399, P=0.008) in the narrow-angle group. However, subfoveal choroidal thickness was not correlated with trabecular iris angle, anterior chamber depth, ciliary body thickness, or central corneal thickness in the narrow-angle group.

CONCLUSION

Choroidal thickness does not differ in the two groups and has not correlated with anterior chamber parameters in narrow-angle subjects, suggesting a lack of relationship between choroidal thickness and primary angle-closure glaucoma.

Distal retinal ganglion cell axon transport loss and activation of p38 MAPK stress pathway following VEGF-A antagonism

There is increasing evidence that VEGF-A antagonists may be detrimental to neuronal health following ocular administration. Here we investigated firstly the effects of VEGF-A neutralization on retinal neuronal survival in the Ins2^Akita diabetic and JR5558 spontaneous choroidal neovascularization (CNV) mice, and then looked at potential mechanisms contributing to cell death. We detected elevated apoptosis in the ganglion cell layer in both these models following VEGF-A antagonism, indicating that even when vascular pathologies respond to treatment, neurons are still vulnerable to reduced VEGF-A levels. We observed that retinal ganglion cells (RGCs) seemed to be the cells most susceptible to VEGF-A antagonism, so we looked at anterograde transport in these cells, due to their long axons requiring optimal protein and organelle trafficking. Using cholera toxin B-subunit tracer studies, we found a distal reduction in transport in the superior colliculus following VEGF-A neutralization, which occurred prior to net RGC loss. This phenomenon of distal transport loss has been described as a feature of early pathological changes in glaucoma, Alzheimer's and Parkinson's disease models. Furthermore, we observed increased phosphorylation of p38 MAPK and downstream Hsp27 stress pathway signaling in the retinas from these experiments, potentially providing a mechanistic explanation for our findings. These experiments further highlight the possible risks of using VEGF-A antagonists to treat ocular neovascular disease, and suggest that VEGF-A may contribute to the maintenance and function of axonal transport in neurons of the retina.

Enhanced depth imaging-optical coherence tomography of the choroid in moderate and severe primary angle-closure glaucoma

PURPOSE

To compare the choroidal thickness (CT) in eyes with moderate and severe primary angle-closure glaucoma (PACG) with the eyes of healthy controls.

METHODS

Fifty-nine patients (59 eyes) with PACG and 56 age-matched normal subjects underwent macular CT scanning using enhanced depth imaging-optical coherence tomography. The subjects with PACG were further classified as having moderate [-12 dB ≤ visual field mean deviation (VF-MD) ≤ -6 dB] or severe (VF-MD < -12 dB) glaucoma. The average CT of the PACG eyes at each location was compared to that of normal eyes.

RESULTS

The CT was significantly increased in moderate and severe PACG eyes compared with the normal eyes at all nine macular locations, with the exception of 1 and 3 mm superior to the fovea. The mean CT under the fovea was 292.0 ± 48.2 μm in the moderate PACG eyes, 277.1 ± 58.3 μm in the severe PACG eyes and 249.9 ± 72.1 μm in the normal eyes, respectively. There were no significant differences between the macular CTs in the eyes with moderate PACG and those in severe PACG eyes (all p > 0.05). Factors associated with a thinner choroid were ageing (p < 0.001), female (p = 0.036) and increasing axial length (p = 0.021). Neither the VF-MD nor pattern standard deviation was found to be associated with CT.

CONCLUSIONS

The CT is greater in patients with PACG, but it does not differ between moderate and severe PACG, suggesting a lack of relationship between CT and the progression of glaucoma based on EDI-OCT measurements.

Phacoemulsification combined with posterior capsulorhexis and anterior vitrectomy in the management of malignant glaucoma in phakic eyes

PURPOSE

  To describe sequential phacoemulsification-intraocular lens (IOL) implantation-posterior capsulorhexis-anterior vitrectomy in the management of phakic malignant glaucoma.

METHODS

  Twenty consecutive patients (25 eyes) with phakic malignant glaucoma were enrolled at the Zhongshan Ophthalmic Center, Sun Yat-sen University. All patients underwent phacoemulsification, IOL implantation and posterior capsulorhexis together with anterior vitrectomy via a clear corneal paracentesis. Visual acuity, intraocular pressure (IOP), anterior chamber depth (ACD), surgical complications and medications required after the surgery were recorded.

RESULTS

  After surgery, the mean LogMAR visual acuity and ACD increased significantly (visual acuity from -1.56 ± 1.17 to -0.54 ± 0.81, p < 0.001; ACD from 0.367 ± 0.397 mm to 2.390 ± 0.575 mm, p < 0.001), and mean IOP decreased significantly (from 39.6 ± 10.6 mm Hg to 14.5 ± 4.1 mmHg, p < 0.001). No serious perioperative complications occurred, and only five eyes required topical glaucoma medications after surgery.

CONCLUSION

  Combined phacoemulsification-IOL implantation-posterior capsulorhexis-anterior vitrectomy surgery is a safe and effective method for treating patients with phakic malignant glaucoma.

Myopia and diabetes mellitus as modificatory factors of glaucomatous optic neuropathy

Myopic deformation of the eye and metabolic alterations of the nerve tissue of patients with diabetes may modify glaucomatous optic neuropathy (GON). Blockage of axonal transport of neurotrophic factors (NTFs) is the event crucial to understanding the factors that affect GON. The primary, but not sole, blockage site is at the lamina cribrosa (LC). Other than this primary site of damage at the LC, 7 other factors may explain atypical nerve fiber layer (NFL) defects and the vulnerability of the nerve fibers in eyes with high myopia and glaucoma: a second point of blockage at the edge of the posterior scleral foramen; ectatic strain on the NFL; ectasia and distortion of the LC; association of a hypoplastic optic disc; thin and weak collagen fibers; peripapillary chorioretinal atrophy; and myopic neuropathy. Among diabetic patients, diabetic neuropathy in the retinal NFL is present initially, and increased resistance to aqueous outflow leads to ocular hypertension. Superimposition of GON on diabetic neuropathy and ocular hypertension in patients with diabetes may enhance their susceptibility to nerve damage. Results of a meta-analysis study suggested a positive association between diabetes mellitus and glaucoma whereas other reports suggested that leakage of vascular endothelial growth factor, a survival mechanism of ischemic neural tissue, and enhanced stiffness of the LC as a result of diabetic glycation may protect neurons from apoptosis. Thus, modification of GON as a result of diabetes remains controversial.

Automatic measurements of choroidal thickness in EDI-OCT images

Enhanced Depth Imaging (EDI) optical coherence tomography (OCT) provides high-definition cross-sectional images of the choroid in vivo, and hence is used in many clinical studies. However, measurement of choroidal thickness depends on the manual labeling, which is tedious and subjective of inter-observer differences. In this paper, we propose a fast and accurate algorithm that could measure the choroidal thickness automatically. The lower boundary of the choroid is detected by searching the biggest gradient value above the retinal pigment epithelium (RPE) and the upper boundary is formed by finding the shortest path of the graph formed by valley pixels using dynamic programming. The average of Dice's Coefficient on 10 EDI-OCT images is 94.3%, which shows good consistency of the algorithm with the manual labeling. The processing time for each image is about 2 seconds.

Increased urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG)/creatinine level is associated with the progression of normal-tension glaucoma

PURPOSE

The objective of this study was to investigate the association between systemic oxidative stress and visual field defect progression in normal-tension glaucoma (NTG).

PATIENTS AND METHODS

The subjects were 40 consecutive patients with NTG who were admitted to Keio University Hospital for 24-h intraocular pressure (IOP) evaluation; all subjects underwent six or more visual field tests in either eye and were followed up for >5 years. Spot samples of morning urine were collected during admission from all participants to determine the levels of urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) by ELISA kit. A linear regression line was calculated with the least squares method. Those subjects whose regression lines were negative and the p value <0.05 were classified as progressive, while all others were defined as non-progressive. Urinary 8-OHdG/creatinine level was compared between the two groups. Adjusted odds ratio and 95% confidence intervals for the progression were estimated with logistic regression models.

RESULTS

Seventeen subjects showed visual field defect progression (age: 59.9 ± 9.5 years, untreated IOP in the right eye: 15.8 ± 2.1 mmHg), and 23 subjects showed no progression (age: 57.4 ± 10.4 years, untreated IOP in the right eye: 16.0 ± 2.6 mmHg). Urinary 8-OHdG/creatinine level was significantly higher in the progressive group than in the non-progressive group (progressive group: 9.0 ± 2.4 ng/mg creatinine, non-progressive group: 7.3 ± 1.8 ng/mg creatinine, p = 0.02). Multivariable analysis revealed that higher urinary 8-OHdG/creatinine level was a significant risk factor for the progression (odds ratio 1.54, 95% confidence interval 1.03-2.29).

CONCLUSIONS

Increased urinary 8-OHdG/creatinine was associated with glaucomatous visual field progression in subjects with NTG.

Automatic segmentation of the choroid in enhanced depth imaging optical coherence tomography images

Enhanced Depth Imaging (EDI) optical coherence tomography (OCT) provides high-definition cross-sectional images of the choroid in vivo, and hence is used in many clinical studies. However, the quantification of the choroid depends on the manual labelings of two boundaries, Bruch's membrane and the choroidal-scleral interface. This labeling process is tedious and subjective of inter-observer differences, hence, automatic segmentation of the choroid layer is highly desirable. In this paper, we present a fast and accurate algorithm that could segment the choroid automatically. Bruch's membrane is detected by searching the pixel with the biggest gradient value above the retinal pigment epithelium (RPE) and the choroidal-scleral interface is delineated by finding the shortest path of the graph formed by valley pixels using Dijkstra's algorithm. The experiments comparing automatic segmentation results with the manual labelings are conducted on 45 EDI-OCT images and the average of Dice's Coefficient is 90.5%, which shows good consistency of the algorithm with the manual labelings. The processing time for each image is about 1.25 seconds.

The choroid is thicker in angle closure than in open angle and control eyes

PURPOSE

To study factors associated with choroidal thickness (CT) and to compare CT in angle closure (AC), open angle (OA), and normal eyes.

METHODS

Forty controls, 106 OA, and 79 AC subjects underwent measurements of posterior CT by spectral domain-optical coherence tomography, and of intraocular pressure (IOP), blood pressure, axial length (AL), and central corneal thickness (CCT).

RESULTS

CT was significantly greater in AC than in OA and normal eyes (HSD test, P ≤ 0.05), but there was no significant difference between OA and normal CT; mean CT was 234, 235, and 318 μm in the normal, OA, and AC groups, respectively. With multivariable analysis among all participants, thinner CT was associated with older age, longer AL, higher IOP, and thicker CCT (all P ≤ 0.03, R(2) = 0.45). Adjusting for other relevant variables, the AC group had a significantly greater CT than either the normal or the OA group (P = 0.003 and 0.03, respectively). In multivariable analysis including only OA and AC patients, neither cup-to-disc ratio nor visual field mean deviation were significantly associated with CT. Multivariable analysis for CT among normal eyes found longer AL to be associated with thinner CT (P = 0.04).

CONCLUSIONS

AC eyes had significantly thicker CT than OA and normal eyes, even after adjusting for the shorter AL in AC eyes, supporting hypotheses that choroidal expansion contributes to the development of AC disease. Age, AL, CCT, and IOP were also significantly associated with CT, while severity of glaucoma damage was not.

Choroidal thickness change after water drinking is greater in angle closure than in open angle eyes

PURPOSE

To study change in choroidal thickness (CT) after water drinking test (WDT), comparing angle closure (AC) to open angle (OA) eyes.

METHODS

Before and 30 minutes after drinking 1 L of water, 88 glaucoma subjects underwent measurements of CT by spectral domain-optical coherence tomography, IOP, blood pressure (BP), axial length (AL), and anterior chamber depth (ACD).

RESULTS

Baseline CT was significantly greater in AC than in OA eyes (P = 0.002). After WDT, BP, IOP, and AL increased significantly (all P ≤ 0.0001). Mean CT increased significantly in the AC group (5.6 μm, P = 0.04, n = 40) and among 80 subjects whose IOP rose > 2 mm Hg (responders; 3.2 μm, P = 0.048), but not in the OA group or among all subjects (2.5 μm increase overall, <1% of baseline CT, P = 0.10). ACD decreased in AC (-18 μm, P = 0.07), but not in OA eyes (+3 μm, P = 0.74). AC eyes had a significantly greater IOP increase after WDT than OA eyes (P = 0.002, multivariate regression). Among responders, CT increased more in those with larger diastolic perfusion pressure increase and in AC compared to OA eyes (P = 0.04 and P = 0.053, respectively, multivariate regression).

CONCLUSIONS

A significant increase in CT and a decrease in ACD after WDT were observed in AC but not in OA eyes, and IOP increased significantly more in AC than in OA eyes, suggesting that the dynamic behavior of the choroid may play a role in the AC process. IOP increase after the WDT was not fully explained by CT increase.

Topiramate-induced acute bilateral angle closure and myopia: pathophysiology and treatment controversies

PURPOSE

To discuss the unusual features of topiramate-induced acute angle closure glaucoma, its pathophysiologic mechanisms, and treatment controversies, and to report the first anterior segment optical coherence tomography (OCT) of this condition.

METHODS

Literature review and case report with OCT findings.

RESULTS

Topiramate-induced angle closure is usually bilateral and associated with acute myopia; the ocular pressure is often not very highly elevated. Ciliochoroidal detachment with ciliary body anterior rotation is typically present and was demonstrated easily in our case with anterior segment OCT. Pilocarpine exacerbates this condition and peripheral iridotomy is not indicated, nor is iridoplasty. Treatment consists of replacing topiramate with appropriate medication, strong cycloplegia, and topical steroids.

CONCLUSIONS

It is important to recognize this form of acute secondary angle closure in order to treat it properly, avoiding harmful medication and unnecessary surgery.

Alteration of the serine protease PRSS56 causes angle-closure glaucoma in mice and posterior microphthalmia in humans and mice

Angle-closure glaucoma (ACG) is a subset of glaucoma affecting 16 million people. Although 4 million people are bilaterally blind from ACG, the causative molecular mechanisms of ACG remain to be defined. High intraocular pressure induces glaucoma in ACG. High intraocular pressure traditionally was suggested to result from the iris blocking or closing the angle of the eye, thereby limiting aqueous humor drainage. Eyes from individuals with ACG often have a modestly decreased axial length, shallow anterior chamber and relatively large lens, features that predispose to angle closure. Here we show that genetic alteration of a previously unidentified serine protease (PRSS56) alters axial length and causes a mouse phenotype resembling ACG. Mutations affecting this protease also cause a severe decrease of axial length in individuals with posterior microphthalmia. Together, these data suggest that alterations of this serine protease may contribute to a spectrum of human ocular conditions including reduced ocular size and ACG.

Factors associated with topographic changes of the optic nerve head induced by acute intraocular pressure reduction in glaucoma patients

PURPOSE

To investigate factors associated with changes in optic nerve head (ONH) topography after acute intraocular pressure (IOP) reduction in patients with primary open-angle glaucoma (POAG).

METHODS

Untreated POAG patients (IOP >21 mm Hg) were prospectively enrolled. Systemic and ocular information were collected, including central corneal thickness (CCT) and corneal hysteresis (CH). All patients underwent confocal scanning laser ophthalmoscopy and tonometry (Goldmann) before and 1 h after pharmacological IOP reduction. The mean of three measurements was considered for analysis. Changes in each ONH topographic parameter were assessed (one eye was randomly selected), and those that changed significantly were correlated with patient's systemic and ocular characteristics.

RESULTS

A total of 42 patients were included (mean age, 66.7 ± 11.8 years). After a mean IOP reduction of 47.3 ± 11.9%, significant changes were observed in cup area and volume, and in rim area and volume (P < 0.01), but not in mean cup depth (P = 0.80). Multiple regression analysis (controlling for baseline IOP and magnitude of IOP reduction) showed that CH (r(2) = 0.17, P < 0.01) and diabetes diagnosis (r(2) ≥ 0.21, P < 0.01) were negatively correlated with the magnitude of changes in ONH parameters, whereas the cup-to-disc ratio was positively correlated (r(2) = 0.30, P < 0.01). Age, race, disc area, and CCT were not significant (P ≥ 0.12). Including all significant factors in a multivariable model, only the presence of diabetes remained significantly associated with all ONH parameters evaluated (P < 0.01).

CONCLUSIONS

Different systemic and ocular factors, such as diabetes, CH, and the relative size of the cup, seem to be associated with the magnitude of changes in ONH topography after acute IOP reduction in POAG patients. These associations partially explain the ONH changes observed in these patients and suggest that other factors are possibly implicated in an individual susceptibility to IOP.