A comparison of two methods for estimating polymegethism in cell areas of the human corneal endothelium.

PURPOSE: To compare the outcome measures from two different methods for estimating the coefficient of variation (COV) in cell area for human corneal endothelia. METHODS: A single non-contact specular micrograph was obtained from the central region of the corneal endothelium of 100 healthy non-contact lens-wearing white European subjects, aged from 32 to 62 years. The captured image file was either assessed using a machine-based algorithm in which 21 cells were marked and their areas reported (designated as the TOPCON 'centre-dot' method), or by an overlay and semi-automated computer-based image analysis system of the entire image of around 200 cells (designated as the AUTO method). The average cell area values were used to calculate the endothelial cell density (ECD), while the COV was calculated from the standard deviation of the cell area measures. RESULTS: The TOPCON and AUTO methods yielded comparable data for average cell area (395 vs 391 microm(2)) and estimated ECD (2566 vs 2575 cells mm(-2)) that were not statistically different (p > or = 0.351), although there was a slight bias between the two methods. However, the mean COV values were very different at 43.5 and 31.4% (p < 0.001). The overestimation of the COV was related to the difference in the largest cell area domain identified by the two methods (p < 0.001, r = > or =0.748). CONCLUSIONS: A centre-dot method using a small number of cells generates useful data on cell area and ECD, but it should be used cautiously for estimates of COV.

A clinical assessment of the anterior eye in arc welders.

BACKGROUND: Corneal irradiation with high doses of ultraviolet-B (UVB) has been shown to damage the corneal endothelium in animals. Human occupational exposure to ultraviolet radiation (UVR) in welding is considered a risk for endothelial damage but the evidence for such an effect is limited. METHODS: External eye photographs and non-contact specular micrographs (Topcon SP2000-P) were obtained from 102 white males aged between 32 and 62 years, 51 being arc welders (with 24 +/- 7 years experience) and 51 office workers. Most welders reported repeated occupational exposure to UVR (that is, welder's 'flashes'). RESULTS: Welders reported a higher level of ocular symptoms and a higher prevalence of pingueculae (47 versus 12 per cent), but only one case with pterygium. The average endothelial cell areas were the same in welders and office workers (398 +/- 55 microm(2) versus 400 +/- 56 microm(2); p = 0.868) as were the endothelial cell density (ECD) values (2,555 +/- 342 cells/mm(2) versus 2,541 +/- 308 cells/mm(2); p = 0.825). ECD decreased with years of welding experience (p < 0.01) but not faster than the decrease in ECD due to age. CONCLUSIONS: Repeated occupational ultraviolet radiation exposure through welding is not associated with any obvious differences in the corneal endothelium. No differences were observed in either ECD or cell polymegethism. Despite the periodic welding flashes, the exposure levels are below those needed to cause damage to the corneal endothelium.

Use of a high molecular weight fluorescein (fluorexon) ophthalmic strip in assessments of tear film break-up time in contact lens wearers and non-contact lens wearers.

PURPOSE: To assess whether fluorexon strips could be used in tear stability [tear film break-up time (TBUT)] measures, as compared with fluorescein strips. METHODS: The pre-ocular tear film stability was assessed in 40 adults (19-29 years of age), half of whom were adapted soft contact lens wearers, using the dye-assisted tear film break-up time (TBUT) method. The measures were carried out between 10.00 and 17.00 hours, with contact lens wearers removing their lenses just before the assessments. For all subjects, fluorescein or fluorexon ophthalmic strips (pre-wetted with preservative-free saline) were used to add dye to the tear film, the TBUT was assessed three times and then the eye lightly irrigated with saline. The measures were repeated 45 min later with the other dye, with half the subjects receiving fluorescein first and the other half receiving fluorexon first. RESULTS: Overall, the mean TBUT times were 12.2 +/- 5.9 s for fluorescein and 12.6 +/- 5.6 s for fluorexon (p = n.s.), but the non-lens wearers had longer TBUT times (14.6 and 14.5 s for the two dyes) compared with contact lens wearers (9.8 and 10.7 s, p < 0.01). While the inter-subject variability (as S.D.) was larger for non-contact lens wearers, the intra-subject variability [as coefficient of variation (COV)] was greater in the contact lens wearers when fluorescein was used (p < 0.001). When analysed as a function of the time of day that the measures were made, there were clear trends for both the fluorescein and fluorexon. TBUT values to increase in non-contact lens wearers and decrease in contact lens wearers. These trends failed to reach statistical significance, but the results with the contact lens wearers showed less variation than the non-contact lens wearers. CONCLUSION: The use of a fluorexon dye-impregnated strip (pre-wetted with preservative-free saline) yielded comparable results with a fluorescein strip for assessments of tear film stability based on TBUT. The studies also indicate that further research is needed on changes in TBUT values during the day.

Central corneal thickness in European (white) individuals, especially children and the elderly, and assessment of its possible importance in clinical measures of intra-ocular pressure.

PURPOSE: To ascertain the impact of central corneal thickness (CCT, as assessed by pachometry) and central corneal curvature (as assessed by keratometry) on clinical measures of intra-ocular pressure (IOP, as assessed by tonometry), especially in the young and elderly. METHODS: Pachometry, keratometry and tonometry were carried out on three groups, namely children aged 5-15 years, adults aged 32-60 years, and elderly individuals aged between 61 and 82 years. For children, ultrasound pachometry was combined with non-contact tonometry (NCT), specular microscopy was used with Perkins tonometry in the adults, and ultrasound pachometry was used with Perkins tonometry for the elderly. Central corneal curvature was assessed by keratometry. RESULTS: The average CCT in children was 0.529+/-0.034 mm (n = 104, +/-S.D.), averaged 0.533+/-0.033 in adults (n=75) and 0.527+/-0.034 mm (n=91) in the elderly. Tonometry values averaged 16.7+/-2.9 mm in children, 13.0+/-3.5 mmHg in adults and 13.6+/-2.5 mm in the elderly group. Central corneal thickness values were not predictably different in relation to central corneal curvature values. Regression analyses indicated that the tonometry values were higher in both children and the elderly who had thicker corneas (and vice versa) (p < 0.003), with the measures increasing by 1.3+/-0.4 and 2.6+/-0.4 mmHg for a 10% difference in CCT in children and the elderly, respectively. For adults, no statistically significant difference in tonometry values could be demonstrated with respect to CCT (<1 mmHg for a 10% difference in CCT), and for no group were the CCT or tonometry values predictably different in relation to central comeal curvature values. CONCLUSIONS: The results of these studies, albeit relatively small scale, indicate that in young or elderly individuals with essentially normal IOP and CCT measures, the tonometry values show only small differences with respect to CCT. The slope in the observed relationship was not that different from an average of 1.5 mmHg for a 10% different in CCT, as obtained from a literature analysis over a 30-year period. The magnitude of the effect does not provide evidence that pachometry needs to be routinely performed in glaucoma screening protocols based on tonometry. Notwithstanding, the finding of higher than expected tonometry values should be further investigated, by pachometry, especially in very young children and in the elderly.

The tear (lacrimal) meniscus height in human eyes: a useful clinical measure or an unusable variable sign?

PURPOSE: To review notes and reports in the literature on assessments of human tear meniscus height (TMH) with the view to defining what the current state of knowledge is, and allow comparisons with data obtained on elderly individuals. METHODS: TMH data was obtained from 97 elderly individuals without significant eye disease. Photo-slit-lamp views, perpendicular to the lower marginal tear strip, were used to obtain close-up images by videography over approximately 30s. Repeated measures at the same location separated by a few seconds (time-dependent TMH measures, tTMH), or repeated measures along the length of the middle portion of the lower eyelid (position-dependent TMH measures, pTMH) were made. The results were compared to those from published reports of TMH. RESULTS: For elderly individuals, tTMH averaged 0.185+/-0.088 mm, while pTMH averaged 0.189+/-0.093 mm. The distribution of TMH measures however included a number of data sets with a much higher average, and which could be separated from the main group of data using cluster analyses approach (> 0.23 mm, P < 0.001). Literature-reported values for TMH, assessed by a perpendicular view, average 0.215 mm (range of average values from 0.163 to 0.350 mm), whereas those made from a tangential view average 0.343 mm (range 0.215-0.460 mm). CONCLUSIONS: The average TMH value of close to 0.2mm in the elderly, as compared to the small number of individuals with rather greater TMH values of up to 0.7 mm, might therefore be considered as indicative of their having normal tear volume, with a few individuals having reflex tearing. Based on the data and literature values, a lower cut-off limit for normal would be /=0.25 mm would indicate reflex tearing and/or sub-optimal tear drainage. An alternative interpretation is that elderly individuals have a subnormal tear film volume, with just a few individuals having adequate tear volume. Further work is clearly needed to resolve this issue.

Chronic exposure to the ultraviolet radiation levels from arc welding does not result in obvious damage to the human corneal endothelium.

Occupational exposure of the cornea to ultraviolet radiation (UVR, e.g. in welding) is a well-known cause of 'arc eye' (photo-keratoconjunctivitis), but has also been considered to be a risk for the development of alterations in the size (polymegethism) and shape (pleomorphism) of the deeper-lying human corneal endothelial cells. Human data are however limited and so a further study was undertaken, with a control group. Non-contact specular micrographs of the central region of the corneal endothelium were obtained from 40 white males aged between 32 and 63 years; 20 were arc welders with an average of 25 +/- 7 years job experience, while the others were office workers (n = 20). All the welders reported occupational exposure to UVR (i.e. welders 'flashes') and up to 3 times per year. None of the subjects had a history of contact lens wear, major eye disease or surgery. The endothelial image was scanned, projected onto an overlay and cell border marking carried out in a masked fashion. The overlay was independently analysed, by a customised semi-automated method, providing cell-border-adjusted data on cell areas and cell shape (sides) on 124 to 260 cells per image. The endothelial cell density (ECD) values were also calculated from individual cell area values. All corneas appeared to be healthy, and showed no fluorescein staining indicating damage to the surface epithelium. Central corneal thickness values were normal at 0.531 +/- 0.031 (mean +/- SD) and 0.527 +/- 0.036 mm in the welders and non-welders respectively. All endothelia appeared healthy, with no evidence of cell oedema. The group-mean endothelial cell area was 393 +/- 35 and 392 +/- 21 microm2, ECD values were 2855 +/- 224 cells mm(-2) and 2852 +/- 210 cells mm(-2), while the percentages of 6-sided cells were 60 +/- 5.2 and 59 +/- 4.1% respectively. Cell area distributions were statistically identical (p > or = 0.8), and cell area-side relationships were marginally, but not statistically different. This study does not indicate that chronic ultraviolet radiation exposure, through occupational welding (mainly electrical arc), results in or is associated with endothelial cell polymegethism and pleomorphism. This may indicate that, despite the periodic flash welding exposures, the exposure levels are still below those needed to cause damage to the corneal endothelium. This study outcome can be taken to indicate that despite the occurrence of welders flash episodes, the eye protection habitually used by these workers was adequate to protect their corneal endothelium.