Zuguo Liu

Evaluation of corneal thickness and topography in normal eyes using the Orbscan corneal topography system

AIMS To map the thickness, elevation (anterior and posterior corneal surface), and axial curvature of the cornea in normal eyes with the Orbscan corneal topography system. METHODS 94 eyes of 51 normal subjects were investigated using the Orbscan corneal topography system. The anterior and posterior corneal elevation maps were classified into regular ridge, irregular ridge, incomplete ridge, island, and unclassified patterns, and the axial power maps were grouped into round, oval, symmetric bow tie, asymmetric bow tie, and irregular patterns. The pachymetry patterns were designated as round, oval, decentred round, and decentred oval. RESULTS The thinnest point on the cornea was located at an average of 0.90 (SD 0.51) mm from visual axis and had an average thickness of 0.55 (0.03) mm. In 69.57% of eyes, this point was located in the inferotemporal quadrant, followed by the superotemporal quadrant in 23.91%, the inferonasal quadrant in 4.35%, and the superonasal quadrant in 2.17%. Among the nine regions of the cornea evaluated (central, superotemporal, temporal, inferotemporal, inferior, inferonasal, nasal, superonasal, and superior) the central cornea had the lowest average thickness (0.56 (0.03) mm) and the superior cornea had the greatest average thickness (0.64 (0.03) mm). The mean simulated keratometry (SimK) was 44.24 (1.61)/43.31 (1.66) dioptres (D) and the mean astigmatism was 0.90 (0.41) D. Island (71.74%) was the most common elevation pattern observed in the anterior corneal surface, followed by incomplete ridge (19.57%), regular ridge (4.34%), irregular ridge (2.17%), and unclassified (2.17%). Island (32.61%) was the most common topographic pattern in the posterior corneal surface, following by regular ridge (30.43%), incomplete ridge (23.91%), and irregular ridge (13.04%) patterns. Symmetric bow tie was the most common axial power pattern in the anterior cornea (39.13%), followed by oval (26.07%), asymmetric bow tie (23.91%), round (6.52%), and irregular (4.53%) patterns. In the pachymetry maps, 47.83% of eyes had an oval pattern, and round, decentred oval, and decentred round were observed in 41.30%, 8.70%, and 2.18% of eyes, respectively. CONCLUSION The information on regional corneal thickness, corneal elevation and axial corneal curvature obtained with the Orbscan corneal topography system from normal eyes provides a reference for comparison with diseased corneas. The Orbscan corneal topography system is a useful tool to evaluate both corneal topography and corneal thickness.

Corneal thickness is reduced in dry eye.

PURPOSE To evaluate and compare corneal thickness in normal and dry eyes. METHODS The Orbscan corneal topography system was used to measure the corneal thickness at nine locations in the central and peripheral (superior, superonasal, nasal, inferonasal, inferior, inferotemporal, temporal, superotemporal) cornea in 38 eyes of 21 patients with aqueous tear deficiency dry eye and 34 eyes of 21 normal subjects. RESULTS The average thickness of nine sites in the central and midperipheral cornea was significantly decreased in dry eyes compared with that of normal eyes. The superior cornea was found to be the thickest area in both groups, measuring 0.629 +/- 0.030 mm in normal eyes and 0.589 +/- 0.031 mm in dry eyes. The center of the cornea was noted to be the thinnest in both groups, measuring 0.571 +/- 0.028 mm and 0.534 +/- 0.034 mm in normal and dry eyes, respectively. In color-coded pachymetry maps, the oval pattern was observed in 67.6% of normal corneas and 39.5% of dry eyes, while the decentered oval pattern was noted in 2.9% and 31.6% of normal and dry eyes, respectively (p < 0.025 for oval pattern and p < 0.005 for decentered oval map). The mean astigmatism was 0.99 +/- 0.43 diopter (D) in normal corneas and 1.42 +/- 0.92 D in dry eyes (p = 0.015). In the anterior elevation maps, the island pattern was the most commonly observed pattern in both groups, 88.3% in normal corneas and 60.5% in dry eyes (p < 0.01). No significant difference in the patterns of posterior corneal elevation maps and axial power maps of the anterior corneal surface was noted between groups. CONCLUSION The corneal thickness of the central and midperipheral cornea was significantly decreased in the dry eyes. It is possible that the chronic state of desiccation and immune activation in dry eye may contribute to the observed corneal thinning. Perhaps the frank corneal ulceration that occurs in some dry eyes is a more severe manifestation of this phenomenon.

Altered Corneal Nerves in Aqueous Tear Deficiency Viewed by In Vivo Confocal Microscopy

Purpose: To define the alterations of corneal nerves in aqueous tear deficiency dry eye patients with or without Sjögren syndrome and to identify the relationship between the morphologic changes of corneal nerves and the extent of dry eye. Methods: Confocal microscopy was used to examine 38 consecutive aqueous tear deficiency patients (8 Sjögren syndrome and 30 non-Sjögren syndrome) and 30 age- and gender-matched normal controls. Images taken by Confocal2 slit-scanning microscope at subbasal epithelial cell layer of central cornea were analyzed. The number and density of corneal nerves and their size, beads, tortuosity, and branching pattern were compared. These data were correlated with age and the degree of dry eye. Results: Sjögren syndrome patients showed a significant increase in average nerve number and tortuosity as compared with normal controls (P = 0.031 and 0.021, respectively). Severe nerve tortuosity (grade 4) and nerve branching appeared more frequently in aqueous tear deficiency than in normal subjects (P = 0.024 and 0.042, respectively). A decreased nerve number was observed with age in the normal controls (P = 0.002). However, such a correlation did not exist in aqueous tear deficiency. In aqueous tear deficiency, rose bengal staining score correlated positively with nerve density (P = 0.048) and nerve number (P = 0.001). Corneal fluorescein staining score was also positively correlated with nerve number (P = 0.027). Conclusions: Abnormal morphologic changes are observed in aqueous tear deficiency that are more severe in Sjögren syndrome. The distinct changes of corneal nerves include increased nerve number, tortuosity, and chances of branching, suggesting an attempted nerve regeneration. A strong correlation exists between the changes of nerve morphology and the degree of dry eye. These results provide some possible evidence for the abnormal corneal sensation in dry eye.

TFOS DEWS II Definition and Classification Report

The goals of the TFOS DEWS II Definition and Classification Subcommittee were to create an evidence-based definition and a contemporary classification system for dry eye disease (DED). The new definition recognizes the multifactorial nature of dry eye as a disease where loss of homeostasis of the tear film is the central pathophysiological concept. Ocular symptoms, as a broader term that encompasses reports of discomfort or visual disturbance, feature in the definition and the key etiologies of tear film instability, hyperosmolarity, and ocular surface inflammation and damage were determined to be important for inclusion in the definition. In the light of new data, neurosensory abnormalities were also included in the definition for the first time. In the classification of DED, recent evidence supports a scheme based on the pathophysiology where aqueous deficient and evaporative dry eye exist as a continuum, such that elements of each are considered in diagnosis and management. Central to the scheme is a positive diagnosis of DED with signs and symptoms, and this is directed towards management to restore homeostasis. The scheme also allows consideration of various related manifestations, such as non-obvious disease involving ocular surface signs without related symptoms, including neurotrophic conditions where dysfunctional sensation exists, and cases where symptoms exist without demonstrable ocular surface signs, including neuropathic pain. This approach is not intended to override clinical assessment and judgment but should prove helpful in guiding clinical management and research.

Changes in corneal epithelial layer inflammatory cells in aqueous tear-deficient dry eye.

PURPOSE To investigate the morphology, distribution, and density of inflammatory cells in the corneal epithelium of aqueous tear-deficient dry eye. METHODS Thirty-two patients with non-Sjögrens syndrome (NSS) dry eye, 14 patients with Sjögrens syndrome (SS) dry eye, and 33 healthy volunteers were studied. In vivo laser scanning confocal microscopy was used to investigate both Langerhans cell (LCs) and leukocyte distribution and density in the peripheral and central corneal epithelium. LC morphology was also evaluated. Multifactor regression analysis assessed whether there is a correlation between clinical manifestations and inflammatory cell densities. RESULTS LCs were present in both central (34.9 +/- 5.7 cells/mm(2)) and peripheral (90.7 +/- 8.2 cells/mm(2)) parts of the normal corneal epithelium. Moreover, LC density increased dramatically in the central corneal epithelium in patients with NSS (89.8 +/- 10.8 cells/mm(2)) and SS (127.9 +/- 23.7 cells/mm(2)). The ratio of LCs with obvious processes was much higher in patients with dry eye than in healthy volunteers. LC density also increased in peripheral corneal epithelium in patients with SS, but not in those with NSS. Leukocyte density in normal corneal epithelium was very low, whereas it increased in the central corneal epithelium (4.6 +/- 1.0 cells/mm(2)) in NSS and in both central (49.0 +/- 12.9 cells/mm(2)) and peripheral (84.2 +/- 36.8 cells/mm(2)) corneal epithelium in SS. Densities of LCs and leukocytes showed significant correlation with the severity found in clinical evaluation. CONCLUSIONS The LC and leukocyte changes in the corneal epithelium suggest their involvement in aqueous tear-deficient dry eye pathophysiology. In vivo dynamic assessment of central corneal inflammatory cell density may serve as an indicator of dry eye severity and provide new insight for dry eye treatment.

Expression of the receptor tyrosine kinases, epidermal growth factor receptor, ErbB2, and ErbB3, in human ocular surface epithelia.

Purpose. To investigate the distribution and relative level of expression of the receptor tyrosine kinases, epidermal growth factor receptor (EGFR), ErbB2 and ErbB3, in human ocular surface epithelia. Methods. Immunofluorescent staining was performed to identify expression of the EGFR, ErbB2 and ErbB3 in the corneal, limbal and conjunctival epithelium in tissue sections and impression cytologies taken from normal human eyes. Western blotting was undertaken to confirm the results of immunofluorescent staining. Results. The three receptor tyrosine kinases, EGFR, ErbB2 and ErbB3, were detected in human corneal, limbal and conjunctival epithelia by immunofluorescent staining. Strong staining for the EGFR was observed in the basal epithelial cells at all 3 sites and throughout the corneal epithelium. Minimal or no staining for the EGFR was observed in the superficial conjunctival and limbal epithelia. The strongest staining for ErbB2 and ErbB3 was observed in the superficial ocular surface epithelium. All three receptors were detected in the corneal, limbal and conjunctival epithelium by western blot. Conclusion. EGFR, ErbB2 and ErbB3 are expressed by the ocular surface epithelia. EGFR is preferentially expressed by the basal epithelial cells that have the greatest proliferative potential. In contrast, ErbB2 and ErbB3 are preferentially expressed by the superficial differentiated ocular surface epithelia.

Corneal Alternations Induced by Topical Application of Benzalkonium Chloride in Rabbit

Benzalkonium chloride (BAC) is the most common preservative in ophthalmic preparations. Here, we investigated the corneal alternations in rabbits following exposure to BAC. Twenty-four adult male New Zealand albino rabbits were randomly divided into three groups. BAC at 0.01%, 0.05%, or 0.1% was applied twice daily to one eye each of rabbits for 4 days. The contralateral untreated eyes were used as control. Aqueous tear production and fluorescein staining scores of BAC-treated eyes were compared with those of controls. The structure of the central cornea was examined by in vivo confocal microscopy. Expression of mucin-5 subtype AC (MUC5AC) in conjunctiva was detected by immunostainig on cryosections. Corneal barrier function was assessed in terms of permeability to carboxy fluorescein (CF). The distribution and expression of ZO-1, a known marker of tight junction, and reorganization of the perijunctional actomyosin ring (PAMR) were examined by immunofluorescence analysis. Although there were no significant differences between control and BAC-treated eyes in Schirmer scores, corneal fluorescein scores and the number of conjunctival MUC5AC staining cells, in vivo confocal microscopy revealed significant epithelial and stromal defects in all BAC-treated corneas. Moreover, BAC at 0.1% resulted in significant increases in central corneal thickness and endothelial CF permeability, compared with those in control eyes, and endothelial cell damage with dislocation of ZO-1 and disruption of PAMR. Topical application of BAC can quickly impair the whole cornea without occurrence of dry eye. A high concentration of BAC breaks down the barrier integrity of corneal endothelium, concomitant with the disruption of PAMR and remodeling of apical junctional complex in vivo.

Netrin-1 Simultaneously Suppresses Corneal Inflammation and Neovascularization

PURPOSE To investigate the effect of netrin-1 on alkali burn-induced corneal inflammation and neovascularization. METHODS The expression of netrin-1 and its receptors UNC5A, UNC5B, UNC5C, UNC5D, adenosine 2b receptor (A2BAR), deleted in colorectal cancer (DCC), and neogenin in normal and alkali-burned rat cornea were determined by RT-PCR and/or Western blot analysis, or immunostaining. Topical netrin-1 protein was applied to treat rat corneal alkali-burn injury for 14 consecutive days, started right after the injury or 10 days postinjury. Corneal inflammation and neovascularization were observed under slit lamp microscope. The apoptosis of corneal cells was determined by terminal deoxynucleotidyl transferase-mediated nick end labeling assay. Corneal inflammatory cell infiltration was evaluated by immunostaining of anti-PMN and anti-ED1 antibodies. The expression of epidermal growth factor (EGF), vascular epidermal growth factor (VEGF), and pigment epithelium-derived factor (PEDF) in rat cornea was determined by Western blot analysis. RESULTS Netrin-1 and its receptor UNC5B were expressed in normal rat corneal epithelium and stromal cells, and their expression decreased after corneal alkali burn. Exogenous netrin-1 administered on rat ocular surfaces resolved alkali burn-induced corneal inflammation, and also suppressed corneal neovascularization. Furthermore, netrin-1 could reverse neovascularization in alkali-burned cornea. The authors found that netrin-1 executed the functions through various mechanisms, including upregulating EGF expression, accelerating epithelial wound healing, inhibiting neutrophil and macrophage infiltration, reducing corneal cell apoptosis, and restoring the equilibrium of VEGF and PEDF in the wounded cornea. CONCLUSIONS Netrin-1 could dampen inflammation, inhibit, and reverse neovascularization in alkali-burned cornea.

In vivo and in vitro inhibitory effect of amniotic extraction on neovascularization

Purpose: To prepare amniotic extraction (AE) and to test its antiangiogenic effect in vivo and in vitro. Methods: AE was prepared and diluted to 50, 100, and 200 μg/mL concentrations. Alkali burn-induced corneal neovascularization (NV) was produced and topically treated with different concentrations of AE or 0.1% dexamethasone for 7 days. Normal saline was used as a control. Corneal NV was visualized by heart perfusion of Chinese ink and quantified as the percentage of corneal NV area to the whole corneal area. Human umbilical vein endothelial cells (HUVECs) were primarily cultured. The effects of AE on proliferation and tube formation of HUVECs were tested by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method and in vitro angiogenesis assay. Pigment epithelium-derived factor (PEDF) in AE was detected by Western blot. Results: Relative corneal NV area in the control group was 56.6% ± 9.9%, which was significantly reduced by 50 μg/mL AE (47.6% ± 6.9%; P = 0.043) and 200 μg/mL AE (34.3% ± 7.8%; P < 0.001) and by 0.1% dexamethasone (21.1% ± 1.8%; P < 0.001). HUVEC cell proliferation was significantly decreased after treatment with AE at concentrations of 50 and 100 μg/mL compared with control (P = 0.036 and 0.001, respectively). The tube formation was significantly suppressed by 100 μg/mL AE (70.03% ± 4.35%) compared with control (100% ± 4.84%; P = 0.002). No expression of PEDF was detected in AE. Conclusion: AE inhibits NV induced by alkali burn. This effect may be elicited at least in part through the inhibiting activity of blood vessel endothelial cells and is not associated with PEDF.

Anti-Angiogenic and Anti-Inflammatory Effects of SERPINA3K on Corneal Injury

SERPINA3K is a member of the serine proteinase inhibitor (SERPIN) family. Here we evaluated the therapeutic effects of SERPINA3K on neovascularization and inflammation in a rat cornea alkali burn model that is commonly employed to study corneal wounding. Topical treatment of the injured rat cornea with SERPINA3K (20 µg/eye/day) for 7 days significantly decreased the neovascular area, compared with the groups treated with BSA or PBS. The SERPINA3K treatment also ameliorated the corneal inflammation as evaluated by the inflammatory index. Furthermore, SERPINA3K enhanced the recovery of corneal epithelium after the alkali injury. Toward the mechanism of action, SERPINA3K down-regulated the expression of the pro-angiogenic and pro-inflammatory factors, vascular endothelial growth factor and tumor necrosis factor-α and up-regulated the expression of the anti-angiogenic factor, pigment epithelium-derived factor. SERPINA3K specifically inhibited growth of vascular endothelial cells. Meanwhile, SERPINA3K significantly up-regulated the expression of EGFR in the corneal epithelium. These findings suggest that SERPINA3K has therapeutic potential for corneal inflammation and NV.