Non-contact in vivo confocal scanning laser microscopy in exfoliation syndrome, exfoliation syndrome suspect and normal eyes

Pathological Changes of the Anterior Lens Capsule

The anterior lens capsule (ALC), as the thickest basement membrane in the body, is an acellular, soft, smooth, transparent membrane secreted by lens epithelial cells. The ALC has its unique biomechanical properties to serve as a barrier and separate the lens from infectious viruses and bacteria together with the posterior capsule and pericapsular membrane. However, the biomechanical and ultrastructural properties of the ALC can be changed under certain conditions. Here, we provide a brief review of the pathological changes of the ALC in several eye disorders, including cataract, aniridia, climatic droplet keratopathy, exfoliation syndrome, true exfoliation syndrome, Alport syndrome, and silicone oil tamponade.

Analysis of Corneal Densitometry and Endothelial Cell Function in Fuchs Uveitis Syndrome

OBJECTIVES

To evaluate corneal densitometry and endothelial cell properties in patients with unilateral Fuchs uveitis syndrome (FUS), and to compare results with unaffected contralateral eyes and healthy control subjects.

METHODS

A total of 90 participants were included in this prospective cross-sectional study. Forty-five affected eyes of patients with FUS were regarded as group 1 (FUSa), 45 fellow eyes were regarded as group 2 (FUSf), and 45 healthy-control eyes were regarded as group 3. Corneal densitometry was measured with densitometry software of Scheimpflug Corneal Topography (Pentacam HR, Oculus GmbH, Wetzlar, Germany), whereas endothelial cell measurement was evaluated with specular microscopy (Tomey, EM4000, GmbH, Germany).

RESULTS

The mean corneal densitometry values were higher in the midstromal (zones; 2-6, 6-10 mm), posterior (all zones), and total thickness (zones; 2-6, 6-10 mm) layers in the FUSa compared with FUSf and control eyes (P<0.05 for all comparisons). The mean values of average cell area and cell size characteristics (minimum, maximum, SD, and coefficient of variation) were higher; endothelial cell density and percentage of hexagonal cells were lower in the FUSa than in the other two groups (P<0.05 for all comparisons). There was a significantly strong correlation between specular microscopy parameters and posterior corneal densitometry values in the FUSa group.

CONCLUSIONS

Impairment of endothelial cell function in affected eyes of patients with FUS resulted in increased values of corneal densitometry, especially posterior layer.

Corneal Stiffness and Collagen Cross-Linking Proteins in Glaucoma: Potential for Novel Therapeutic Strategy

Biomechanical properties of the cornea have recently emerged as clinically useful in risk assessment of diagnosing glaucoma and predicting disease progression. Corneal hysteresis (CH) is a dynamic tool, which measures viscoelasticity of the cornea. It represents the overall deformability of the cornea, and reduces significantly with age. Low CH has also been associated with optic nerve damage and progression of visual field loss in glaucoma. The extracellular matrix (ECM) constituents of the cornea, trabecular meshwork (TM), sclera, and lamina cribrosa (LC) are similar, as they are predominantly made of fibrillar collagen. This suggests that biomechanical changes in the cornea may also reflect optic nerve compliance in glaucomatous optic neuropathy, and in the known increase of TM tissue stiffness in glaucoma. Increased collagen cross-linking contributes to tissue stiffening throughout the body, which is observed in normal aging and occurs at an accelerated rate in systemic conditions such as fibrotic and cardiovascular diseases, cancer, and glaucoma. We reviewed 3 ECM cross-linking proteins that may have a potential role in the disease process of increased tissue stiffness in glaucoma, including lysyl oxidase (LOX)/lysyl oxidase-like 1 (LOXL1), tissue transglutaminase (TG2), and advanced glycation end products. We also report elevated messenger RNA (mRNA) levels of LOX and TG2 in glaucoma LC cells to support our proposed theory that increased levels of cross-linking proteins in glaucoma play a role in LC tissue stiffness. We highlight areas of research that are needed to better understand the role of cross-linking in glaucoma pathogenesis, leading potentially to a novel therapeutic strategy.

Corneal Alterations Associated with Pseudoexfoliation Syndrome and Glaucoma: A Literature Review

A systematic literature review was performed evaluating articles examining the effects of pseudoexfoliation syndrome (PEX) and glaucoma (PEXG) on the cornea with a focus on the corneal endothelium. We searched for articles relevant to pseudoexfoliation syndrome, pseudoexfoliation glaucoma and corneal endothelial cell counts using Pubmed, Google Scholar Database, Web of Science and Cochrane Library databases published prior to September of 2016. We then screened the references of these retrieved papers and performed a Web of Science cited reference search. Corneal characteristics analyzed included central corneal thickness (CCT), corneal nerve density, endothelial cell density (ECD), polymegathism, and pleomorphism. These parameters were compared in the following populations: control, PEX, PEXG, and primary open angle glaucoma (POAG). Over 30 observational studies were reviewed. Most studies showed a statistically significant lower ECD in PEX and PEXG populations compared to controls. Overall, PEX eyes had a non-statistically significant trend of lower ECDs compared to PEXG eyes. No consistent trends were found when analyzing differences in CCT amongst control, PEX and PEXG groups. For the few studies that looked at corneal nerve characteristics, the control groups were found to have statistically significantly greater nerve densities than PEX eyes, which had significantly greater densities than PEXG eyes. ECD and corneal nerve densities may be potential metrics for risk-stratifying patients with PEX and PEXG. Our literature review provided further evidence of the significant negative influence PEX has on the cornea, worsening as patients convert to PEXG.

Iris ultrastructure in patients with synechiae as revealed by in vivo laser scanning confocal microscopy : In vivo iris ultrastructure in patients with Synechiae by Laser Scanning Confocal Microscopy

BACKGROUND

Iris plays important roles in ocular physiology and disease pathogenesis. Currently it is technically challenging to noninvasively examine the human iris ultrastructure in vivo. The purpose of the current study is to reveal human iris ultrastructure in patients with synechiae by using noninvasive in vivo laser scanning confocal microscopy (LSCM).

METHODS

The ultrastructure of iris in thirty one patients, each with synechiae but transparent cornea, was examined by in vivo LSCM.

RESULTS

Five characteristic iris ultrastructures was revealed in patients with synechiae by in vivo LSCM, which include: 1. tree trunk-like structure; 2. tree branch/bush-like structure; 3. Fruit-like structure; 4. Epithelioid-like structure; 5. deep structure. Pigment granules can be observed as a loose structure on the top of the arborization structure. In iris-associated diseases with Tyndall's Phenomenon and keratic precipitates, the pigment particles are more likely to fall off from the arborization structure.

CONCLUSIONS

The ultrastructure of iris in patients with synechiae has been visualized using in vivo LSCM. Five iris ultrastructures can be clearly observed, with some of the structures maybe disease-associated. The fall-off of the pigment particles may cause the Tyndall's Phenomenon positive. In vivo LSCM provides a non-invasive approach to observe the human iris ultrastructure under certain eye disease conditions, which sets up a foundation to visualize certain iris-associated diseases in the future.

Evaluation of Corneal Microstructure in Pseudoexfoliation Syndrome and Glaucoma: In Vivo Scanning Laser Confocal Microscopic Study

PURPOSE

To quantitatively evaluate corneas of patients with pseudoexfoliation syndrome (PXS) and pseudoexfoliation glaucoma (PXG) using in vivo scanning laser confocal microscopy (IVCM).

MATERIALS AND METHODS

The study population comprised 30 patients with PXS, 30 patients with PXG, and 30 normal control subjects. IVCM of the cornea was performed on all participants using the Rostock Cornea Module of the Heidelberg Retinal Tomograph (HRT). Mean outcome measures included density of basal epithelial cells, endothelial cells, and anterior and posterior keratocytes; and tortuosity and density of subbasal plexus nerves.

RESULTS

Mean densities of basal epithelial cells, endothelial cells, anterior and posterior keratocytes, and subbasal nerves differed significantly among the three groups. Subbasal nerve densities were significantly diminished in PXS and PXG patients (12.36 ± 2.89 and 6.8 ± 3.42 mm/mm(2), respectively) compared with that of control subjects (16.13 ± 3.42 mm/mm(2)) (p < 0.05). Mean densities of anterior and posterior stromal keratocytes were significantly lower in PXS and PXG patients compared with control subjects (p < 0.05). Endothelial cell densities were 3073.63 ± 654.49, 2592.60 ± 276.36, and 2110.20 ± 620.53 cells/mm(2) for control, PXS, and PXG groups, respectively (p < 0.05). The percentages of endothelial cell polymegathism and pleomorphism were higher in PXS and PXG patients compared with control subjects. Endothelial cell polymegathism and pleomorphism were more frequently associated with PXG.

CONCLUSIONS

Results of this study demonstrate the existence of alterations in the (i) density of cells in the various layers of the cornea, (ii) cellular configuration of corneal endothelial cells, and (iii) density/diameter of the subbasal nerve plexus in patients with PXS, and that such alterations are common in patients with PXG. It would be beneficial to employ IVCM to assess the severity of pseudoexfoliation keratopathy (PXK).

Corneal biomechanical comparison of pseudoexfoliation syndrome, pseudoexfoliative glaucoma and healthy subjects

PURPOSE

To evaluate the differences in corneal biomechanical properties between healthy subjects and patients with pseudoexfoliation syndrome (PEX) and pseudoexfoliative glaucoma (PEXG) using the ocular response analyzer (ORA).

MATERIALS AND METHODS

One hundred eighteen eyes of 45 healthy, 43 PEX and 30 PEXG eyes were included in to the study. Corneal biomechanical parameters measurements were obtained using ORA. The main parameters assessed were corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-correlated pressure measurement (IOPg) and corneal compensated intraocular pressure (IOPcc). Ultrasound pachymetry was used for measurement of central corneal thickness (CCT).

RESULTS

In healthy subjects, PEX and PEXG eyes' mean CH values were 10.3 ± 1.4, 8.2 ± 1.4 and 6.8 ± 1.7 mmHg, respectively. The difference in mean CH between the PEXG and other two groups were statistically significant (p < 0.001). Mean CRF values were 10.3 ± 0.7, 7.9 ± 1.6 and 7.9 ± 1.9 mmHg, in healthy subjects PEX and PEXG, respectively. The difference in mean CRF between the PEX and PEXG was not statistically significant (p = 0.630), however the mean CRF was significantly higher in healthy subjects, compared to other two groups. Mean CCT were 546.3 ± 28, 525.5 ± 35 and 509 ± 36 μ, in healthy subjects, PEX and PEXG, respectively. The differences on CCT were also significant among the three groups (p < 0.001).

CONCLUSION

In this study, the corneal biomechanical features of subjects with PEX were found to be changed as compared to healthy controls. In these patients; CH, CRF and CCT were decreased which was more obvious in patients with PEXG in comparison to PEX patients.

In vivo laser scanning confocal microscopy of the ocular surface in glaucoma

Over the past decade, knowledge about the ocular surface in glaucoma has significantly increased through the use of in vivo laser scanning confocal microscopy (LSCM). This in vivo imaging method can show modifications at the cellular level induced by anti-glaucoma drugs on ocular surface structures and adnexa in the eye. High-quality images of the conjunctiva, cornea, limbus, meibomian glands, and lymphoid structures during therapy can be obtained. In addition, LSCM opened new fields of research on the patho-physiology of aqueous humor (AH) hydrodynamics in untreated, and in medically or surgically treated glaucomatous patients. In these conditions, an enhancement of the trans-scleral AH outflow contributed to clarification of the mechanism of action of different anti-glaucoma medications and surgical approaches. Finally, the use of LSCM represented a huge advance in evaluation of bleb functionality after filtration surgery, defining the hallmarks of AH filtration through the bleb-wall and distinguishing functional from nonfunctional blebs. Thus, signs seen with LSCM may anticipate clinical failure, guiding the clinician in planning the appropriate timing of the various steps in bleb management. In this review we summarize the current knowledge about in vivo LSCM of the ocular surface in glaucoma.

[PEX syndrome. Clinical diagnosis and systemic manifestations]

As a result of demographic changes pseudoexfoliation (PEX) syndrome, an age-related systemic disorder of the extracellular matrix, will become an increasingly important issue in clinical practice. Apart from its well-known association with cataract and glaucoma, PEX syndrome predisposes to a broad spectrum of spontaneous and surgical ocular complications due to characteristic alterations of all anterior segment tissues. In view of the high risk of glaucoma development and potential complications during cataract surgery, an accurate and early diagnosis of PEX syndrome is of considerable clinical relevance. Since the characteristic central PEX deposits are lacking in up to 50 % of patients, a reliable diagnosis requires pupillary dilation. Early stages of the disease may be recognized on the basis of subtle alterations of the lens surface in addition to poor pupillary dilation and pigment-related signs including pigment dispersion and peripupillary atrophy. Any asymmetric clinical signs, e.g., regarding pupil width, pigmentation, cataract and intraocular pressure, should alert the ophthalmologist to the potential presence of PEX syndrome. Although the description of PEX syndrome as a systemic disorder of the extracellular matrix associated with the deposition of PEX material in the skin, blood vessel walls and various organ systems dates back to the early 1990s, a causal relationship between the abnormal material deposits and systemic diseases has not yet been clearly established. A growing number of smaller studies have found suggestive evidence for associations between PEX syndrome and cardiovascular/cerebrovascular diseases. The current evidence, however, is ambiguous and requires further investigation through multicenter or population-based, prospective, randomized clinical studies.

In vivo confocal microscopy of the ocular surface: from bench to bedside

In vivo confocal microscopy (IVCM) is an emerging technology that provides minimally invasive, high resolution, steady-state assessment of the ocular surface at the cellular level. Several challenges still remain but, at present, IVCM may be considered a promising technique for clinical diagnosis and management. This mini-review summarizes some key findings in IVCM of the ocular surface, focusing on recent and promising attempts to move "from bench to bedside". IVCM allows prompt diagnosis, disease course follow-up, and management of potentially blinding atypical forms of infectious processes, such as acanthamoeba and fungal keratitis. This technology has improved our knowledge of corneal alterations and some of the processes that affect the visual outcome after lamellar keratoplasty and excimer keratorefractive surgery. In dry eye disease, IVCM has provided new information on the whole-ocular surface morphofunctional unit. It has also improved understanding of pathophysiologic mechanisms and helped in the assessment of prognosis and treatment. IVCM is particularly useful in the study of corneal nerves, enabling description of the morphology, density, and disease- or surgically induced alterations of nerves, particularly the subbasal nerve plexus. In glaucoma, IVCM constitutes an important aid to evaluate filtering blebs, to better understand the conjunctival wound healing process, and to assess corneal changes induced by topical antiglaucoma medications and their preservatives. IVCM has significantly enhanced our understanding of the ocular response to contact lens wear. It has provided new perspectives at a cellular level on a wide range of contact lens complications, revealing findings that were not previously possible to image in the living human eye. The final section of this mini-review provides a focus on advances in confocal microscopy imaging. These include 2D wide-field mapping, 3D reconstruction of the cornea and automated image analysis.

Biomechanical profile of the cornea in primary congenital glaucoma

PURPOSE

The aim of our study was to investigate the biomechanical properties of the cornea in primary congenital glaucoma (PCG) and to identify the potential ocular determinants, which affect the corneal biomechanical metrics.

METHODS

Corneal hysteresis (CH), corneal resistance factor (CRF) and central corneal thickness (CCT) were measured in 26 patients with PCG (40 eyes) with the aid of ocular response analyser. In vivo laser-scanning confocal microscopy was used for the estimation of stromal keratocyte density (KD) and the evaluation of corneal endothelium. Twenty normal subjects (40 eyes) served as controls. Student's t-test and Pearson's correlation coefficients were used for statistical analysis. p Values <0.05 were considered statistically significant.

RESULTS

Corneal hysteresis, CRF and CCT were significantly reduced in patients with PCG (all p < 0.05). Corneal hysteresis and CRF negatively correlated with the corneal diameter in both groups (r(1) = -0.53, r(2) = -0.66, p < 0.001 for CH and r(1) = -0.61, r(2) = -0.69, p < 0.001 for CRF). Moreover, we identified a significant correlation between CH and CRF with CCT in both groups (r(1) = 0.51, r(2) = 0.48, p < 0.001 for CH and r(1)  = 0.45, r(2) = 0.44, p < 0.001 for CRF). Mean KD was significantly reduced both in the anterior and posterior corneal stroma in patients with PCG (764 ± 162 and 362 ± 112 cells/mm(2) , respectively) compared with controls (979 ± 208 and 581 ± 131 cells/mm(2) , respectively) (p < 0.001). There was no significant correlation between the keratocyte density in anterior and/or posterior stroma and CH or CRF in any group (r(1) = 0.29, r(2) = 0.31, p < 0.06). Mean endothelial cell density was also significantly reduced in PCG group (2920 ± 443 cells/mm(2) ) compared with control group (3421 ± 360 cells/mm(2) ) (p < 0.001). Pleomorphism and polymegalism were significantly increased in corneal endothelium of patients with PCG.

CONCLUSIONS

  Our results showed a significant reduction in CH and CRF in PCG. Both CH and CRF were negatively correlated with corneal diameter. A significant correlation of CH and CRF with CCT was identified in both groups. Keratocyte density was decreased in PCG, but did not have a significant impact on CH and CRF. Mean endothelial density was also decreased in PCG. Our results suggest that reduced CCT and increased corneal diameter are major ocular determinants for the modified corneal biomechanical profile in PCG, while cellular alterations in corneal stroma and endothelium have no significant biomechanical impact.

Corneal biomechanical properties of patients with pseudoexfoliation syndrome

PURPOSE

To assess the corneal biomechanical properties of patients with pseudoexfoliation syndrome (PEX syndrome).

METHODS

Fifty-two eyes of 52 patients (27 unilateral and 25 bilateral) and 42 eyes of 42 age-matched control subjects were enrolled in the study. Metrics of corneal biomechanical properties, including corneal hysteresis (CH) and corneal resistance factor (CRF), were measured with the ocular response analyzer (ORA). The ORA also determined the values of Goldmann-correlated intraocular pressure and corneal-compensated intraocular pressure. Central corneal thickness (CCT) was measured by the ORA integrated handheld ultrasonic pachymeter. The values recorded by the ORA were compared between eyes with PEX syndrome and those without PEX syndrome. Eyes with unilateral PEX syndrome and fellow eyes without PEX syndrome were also compared.

RESULTS

The mean CH and CRF of all eyes with PEX syndrome were significantly lower than those of control eyes (P < 0.05). Neither corneal-compensated intraocular pressure nor Goldmann-correlated intraocular pressure showed a statistically significant difference in both the groups. Mean CCT values also did not show significant difference. Comparison of the unilateral eyes with PEX syndrome with the apparently normal fellow eyes revealed no significant difference between the mean CCT, mean CH, and mean CRF values (P > 0.05). However, the mean corneal-compensated intraocular pressure and Goldmann-correlated intraocular pressure were relatively higher in the PEX syndrome eye (P < 0.05). There was no significant difference between the mean CCT values of these groups (P > 0.05).

CONCLUSIONS

The CH and CRF decrease in both unilateral and bilateral PEX syndrome suggested that PEX syndrome has a weakening effect on corneal biomechanical properties. Moreover, in subjects with clinically unilateral PEX syndrome, these properties were closer to eyes with PEX syndrome than to normal control eyes.