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Background: The aim was to evaluate anterior segment parameters in patients with pseudoexfoliation syndrome (PXS) or pseudoexfoliative glaucoma (PXG) with the Pentacam-Scheimpflug imaging system.
Methods: Eighty eyes of 53 patients with PXS (Group 1), 80 eyes of 57 patients with PXG (Group 2) and 80 eyes of 45 control cases (Group 3) were included in the study. Anterior chamber depth, volume (ACV), angle (ACA) width, central corneal thickness (CCT), central 3.0, 5.0 and 7.0 mm corneal volumes and pupil diameters were compared between groups.
Results: Although anterior chamber depths in the PXG group were significantly lower than the control group (p < 0.05), there was no statistically significant difference between the PXS group and the control group in means of anterior chamber depth values (p > 0.05). There were no statistically significant differences among PXS, PXG and the control group in mean values of ACV, ACA width, CCT, pupil diameters and central 3.0, 5.0 and 7.0 mm corneal volume (p > 0.05).
Conclusions: The anterior chamber depths of PXG patients were lower than those of healthy individuals. Although the difference in anterior chamber depth between PXG patients and normal patients was statistically significant, this finding is unlikely to be of clinical significance. The anterior chamber depths of PXS patients were similar to those of healthy individuals. There were no significant differences in the means of ACV, ACA width, CCT, pupil diameter and corneal volume values on central 3.0, 5.0 and 7.0 mm among patients with PXS, PXG and healthy individuals.
Pseudoexfoliation syndrome (PXS) is characterised by the deposition of a distinctive fibrillar material in the anterior segment of the eye and was first described in 1917 by Lindberg and cited in a later paper.1 Detection of the exfoliation syndrome is clinically important. It has been associated with increased intraocular pressure (IOP), markedly increased intraoperative and post-operative complications such as poorly dilating pupils, zonular instability, zonular rupture and inflammation. PXS is also recognised as an important risk factor for glaucoma.
Pseudoexfoliative glaucoma (PXG) is most often classified as a secondary glaucoma. It occurs in eyes with PXS and usually with an open anterior chamber angle. PXG tends to be more severe than primary open-angle glaucoma and not only responds poorly to medical therapy but also needs surgery for glaucoma more frequently.2,3
Assessment of anterior segment parameters, such as central corneal thickness (CCT), anterior chamber depth (ACD), pupil diameter and anterior chamber angle (ACA) width, is an important part of ophthalmic examination in patients with PXS or PXG. Corneal volume measurements and corneal thickness might be indirect indicators of endothelial function in patients with pseudoexfoliation. In addition, assessment of corneal thickness has become important for IOP evaluation in patients with glaucoma. Anterior segment parameters can give valuable information to the surgeon to be more careful before both cataract and glaucoma surgery in patients with pseudoexfoliation. For example, narrow ACD significantly increases the risk of complications following phacoemulsification surgery.4
In clinical practice, imaging of the anterior segment has traditionally been carried out with slitlamp biomicroscopy but objective quantitative assessment of anterior segment parameters are limited and direct ACA visualisations can only be carried out with the use of diagnostic contact lenses, such as the Goldmann 3-mirror lens. In recent years, different devices for anterior segment evaluation have been used, such as slitlamp optic coherence tomography, ultrasonic biomicroscopy, orbscan scanning slit topography, scanning peripheral ACD analyzer and Pentacam-Scheimpflug imaging.5–10 All of these devices provide quantitative information and qualitative imaging of the anterior segment structure.
Pentacam-Scheimpflug is a fast, non-invasive, easy-to-use, reproducible, user-independent method with high patient comfort. It is also a method that evaluates almost all anterior segment parameters in a short period and does not require topical anaesthesia.11,12
In the present study, we aimed to evaluate PXS or PXG patients' anterior segment parameters such as ACD, anterior chamber volume (ACV), ACA width, CCT, central 3.0, 5.0 and 7.0 mm corneal volume (CV) and pupil size with the Pentacam-Scheimpflug imaging system. To our knowledge, this is the first report that evaluates the anterior segment parameters of patients with PXS and PXG gathered with the Pentacam-Scheimpflug imaging system.
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This cross-sectional study consists of 80 eyes of 53 patients (25 male, 28 female) with PXS (Group 1), 80 eyes of 57 patients (30 male, 27 female) with PXG (Group 2) and 80 eyes of 45 control patients (25 male, 20 female) (Group 3). All of the subjects were evaluated with a Pentacam-Scheimpflug imaging system (rotating Scheimpflug camera; Oculus, Wetzlar, Germany) by the same operator (SD). All measurements were obtained under standard dim-light conditions and with undilated pupils. ACD, ACV, ACA width, CCT, pupil diameters and central 3.0, 5.0 and 7.0 mm CV were compared among the groups. All patients were asked for their consent and an independent ethics committee approved the investigation.
The inclusion criteria of group 1 were normal IOP (under 21 mmHg), visible pseudoexfoliation material on the anterior segment structures with a dilated pupil, normal optic nerve head and normal visual field examination (Humprey 30-2, SITA-FAST). The inclusion criteria of group 2 were high IOP (over 21 mmHg), visible pseudoexfoliation material on the anterior segment structures with a dilated pupil, glaucomatous optic nerve head changes and glaucomatous visual field defects with computerised visual field examination. The inclusion criteria of group 3 were normal IOP (under 21 mmHg), absence of pseudoexfoliation material on the anterior segment structures, normal optic nerve head and normal visual field examination.
Patients with corneal pathology, uveitis, previous ocular surgery (including laser surgery), ocular trauma, posterior segment pathology, diabetes, topical or systemic medication usage that might influence anterior segment parameters, evident cataract and over one dioptre of cylindrical and/or three dioptres of spherical refractive errors were excluded from the study.
The Pentacam-Scheimpflug imaging system is based on a 180-degree rotating Scheimpflug camera, which can take 12 to 50 single captures to reconstruct the anterior chamber. In the present study, anterior segment reconstructions were produced with 25 single captures. After completing a scan, the Pentacam-Scheimpflug imaging system software constructs a three-dimensional image of the anterior segment and calculates the anterior chamber parameters. This imaging provides measures of ACD, ACV, ACA width, CCT, CV and pupil size.
Statistical analysis was performed with SPSS for Windows version 13.0 (SPSS Inc, Chicago, IL, USA). All data were reported as means and standard deviation. Normality for continued variables in a group was determined by the Shapiro-Wilk test. Unpaired t-test, one-way analysis of variance and post-hoc least significant difference test were used. A value of p < 0.05 was considered statistically significant.
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The average ages of the three groups were 65.71 ± 7.38, 66.22 ± 5.47 and 66.90 ± 3.58 years, respectively. There was no statistically significant difference with respect to gender and age between groups (p > 0.05).
Group 1, group 2 and group 3 means for ACD, ACV, ACA width, CCT, central 3.0, 5.0 and 7.0 mm CV and pupil size measurements are given in Figure 1 and Table 1. The mean ACD in group 2 was significantly lower than in group 3 (p < 0.05). There was no statistically significant difference between groups 1 and 3 in ACD (p > 0.05). There was no statistically significant difference (p > 0.05) among the groups for ACV, ACA width and CCT. Statistical analysis did not reveal any significant alteration between groups for 3.0, 5.0 and 7.0 mm central CV (Figure 1 and Table 2). There were no statistically significant differences among the groups for pupil size (p > 0.05).
Figure 1. Group 1, group 2 and group 3 anterior segment parameters. ACA: anterior chamber angle, ACD: anterior chamber depth, ACV: anterior chamber volume, CCT: central corneal thickness, CV: corneal volume, Group 1: pseudoexfoliation syndrome, Group 2: pseudoexfoliative glaucoma, Group 3: normal control group. *Differences are statistically significant (p < 0.05).
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Table 1. Group 1, group 2 and group 3 anterior segment parameter values (mean ± SD)
| ||ACD (mm)||ACV (mm3)||ACA (degrees)||CCT (µm)||Pupil size (mm)|
|Group 1||2.50 ± 0.29||123.02 ± 24.28||29.20 ± 5.19||539.72 ± 32.29||2.54 ± 0.41|
|Group 2||2.49 ± 0.39*||124.00 ± 27.88||29.57 ± 5.08||538.78 ± 29.85||2.58 ± 0.37|
|Group 3||2.60 ± 0.31*||129.75 ± 26.57||30.36 ± 4.98||547.30 ± 27.35||2.63 ± 0.28|
Table 2. Group 1, group 2 and group 3 corneal volume (CV) values (mean ± SD)
| ||Central 3 mm CV (mm3)||Central 5 mm CV (mm3)||Central 7 mm CV (mm3)|
|Group 1||3.91 ± 0.30||11.52 ± 0.73||24.20 ± 1.54|
|Group 2||3.89 ± 0.24||11.46 ± 0.65||24.06 ± 1.31|
|Group 3||3.92 ± 0.22||11.59 ± 0.61||24.47 ± 1.30|
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PXS is an age-related disease characterised by the production and progressive accumulation of a fibrillar extracellular material in many ocular and non-ocular tissues. The pathogenesis and exact composition of pseudoexfoliation material is unknown; however, there are two competing theories on its pathogenesis. The first theory links exfoliation fibres with the microfibrillar component of the elastic system of connective tissue or oxytalan fibres.13 The second considers PXS to be a generalised disorder of the basement membranes and this theory is supported by immunohistochemical studies.14,15
PXS is the most common identifiable cause of secondary open-angle glaucoma, while PXG is believed to be difficult to manage clinically. The worse prognosis might be related to the clinical characteristics of PXG, which are typically associated with higher mean IOP levels, greater diurnal fluctuation in IOP and marked IOP pressure spikes.16,17
Anterior chamber parameters such as ACD and ACA width have a role in diagnosis and evaluation of every kind of glaucoma.18 Evaluation of the ACA is indispensable in glaucoma patients and it is very important in routine ophthalmological practice. Gonioscopy with contact lenses is the general method for evaluation of the ACA. This is a subjective method and totally related to visibility of tissues specific to the iridocorneal angle. ACA width, which is very important especially in angle-closure glaucoma, can be evaluated quantitatively by optical coherence tomography, ultrasonic biomicroscopy, Orbscan and Pentacam.
The incidence of narrow angle and closed-angle glaucoma is high and should not be underestimated in patients with pseudoexfoliation. Some factors, such as increased iris thickness, posterior synechiae and zonular weakness might cause angle closure in patients with pseudoexfoliation.
The ACD was measured in 34 eyes of patients with PXS and in 334 normal controls by Bartholomew.19 No significant difference was found in ACD in eyes with or without pseudoexfoliation.19 In another study, Lanzl, Merté and Graham20 investigated the changes in ACD and whether the increased mobility of the lens influences ACD in patients with pseudoexfoliation, while assuming a prone position. That study showed that in patients with clinically apparent unilateral pseudoexfoliation, the lens seems to be more mobile in the affected eye. In addition, results suggest that a shallower anterior chamber occurs when the head is placed in a prone position.
PXG is generally regarded as an open-angle type and angle-closure glaucoma is considered much less common. Layden and Shaffer21 reported a 23 per cent incidence of occludable angles in PXS cases compared with a five per cent incidence in the normal population. Although the mechanism of angle-closure glaucoma in association with PXS is unknown, investigators postulate a variety of mechanisms, such as posterior synechiae, zonular weakness, enlargement of the lens due to cataract formation, a thick or a rigid iris with predisposition to relative pupillary block and the use of parasympathomimetic drugs.22–27 A prospective clinical study of the ACA was performed in 263 eyes (152 patients) with PXS.28 No significant difference was found in width and depth of the anterior chamber in comparison with the normal population.28
To our knowledge, there is no prospective clinical study that quantitatively evaluates ACA width and ACV in PXS and PXG patients by using Pentacam-Scheimpflug imaging. It is rational to expect an increase of ACV in parallel with the increase of ACD and ACA width. We found a statistically significant difference in ACD measurements in patients with PXG as compared with normal controls; however, there was no significant difference with respect to ACV and ACA width among all groups.
Corneal thickness is a clinically important factor when evaluating IOP. There are conflicting studies about CCT in patients with PXS or PXG. Most reports have found similar CCT in PXS and normal eyes and we have found similar CCT in PXS, PXG and healthy individuals.29–31 Some authors have reported a lower or higher CCT in PXS than in normal eyes.32,33
Pseudoexfoliation material and pigment deposits might be seen using slitlamp examination on the endothelial surface of the cornea. There is some evidence for corneal endothelial cell loss together with morphological changes in size and shape of endothelial cell in PXS.34–37
In clinical practice, corneal endothelial changes are assessed using specular microscopy. This assessment gives cell density and morphology in an area smaller than one square millimetre. Therefore, it is difficult to evaluate the entire cornea. Unlike specular microscopy, Pentacam-Scheimpflug calculates CV.38 Thus, it can be used in the statistical assessment of the entire cornea and can indicate the degree of endothelial damage. No study has evaluated CV in patients with PXS or PXG. Hence, this is the first study that compares central 3.0, 5.0 and 7.0 mm CV in the PXS and PXG groups. No significant differences were found among the groups in the present study.
The iris expands or contracts to control the amount of light entering the eye. The pupil can range in diameter from 8.0 mm in very dim light down to approximately 1.5 mm in very bright conditions. In addition to preventing glare, the pupil has important roles in visual functions affecting depth of focus, binocular function and visual acuity. Clinically, the iris of patients with PXS is characteristically rigid with reduced dilating properties. Hahnenberger39 reported that the pupil in patients with PXG might be smaller; however, no statistically significant difference was found with respect to pupil diameters among the PXG, PXS and normal groups in the present study.
In conclusion, all anterior segment parameters were evaluated in patients with PXG or PXS using Pentacam-Scheimpflug imaging in the present study. Measurements of anterior segment parameters, such as ACV, ACA width and central 3.0, 5.0 and 7.0 mm CV were found to be similar in patients with PXG, PXS and normal cases. The mean ACD measurement in patients with PXG was found to be shallower than normal cases; however, there was no statistically difference in ACD between PXG and PXS. Unlike the other groups, the ACD in patients with PXG was statistically shallower but this might not be clinically significant. Further large clinical trials with different devices are necessary to more clearly understand these changes.