The effects of smoking on corneal endothelial cells: a cross-sectional study on a population from Isfahan, Iran

Effect of smoking on corneal and lens clarity: a densitometric analysis

PURPOSE

To assess the effect of chronic cigarette smoking on corneal and lens densitometry measurements using Pentacam HR and to compare the results obtained with those in non-smokers.

MATERIALS AND METHODS

This cross-sectional comparative study included 40 chronic-smokers and 40 age-matched healthy non-smokers between 18-40 years. After general ophthalmic examination, the Pentacam HR imaging system was used to evaluate corneal and lens densitometry measurements of smokers and non-smokers.

RESULTS

The mean corneal densitometry values were not statistically significantly different in all the concentric zones and layers in the eyes of the smokers and non-smokers (p > 0.05, for all). However, the mean values of zone 1, zone 2, zone 3 and average lens densitometry measurements of the smokers were statistically significantly higher compared to non-smokers (p < 0.05, for all). Additionally, significant positive correlations were detected between the number of pack-years smoked and lens densitometry measurements.

CONCLUSION

Lens densitometry measurements of smokers were significantly increased while corneal densitometry measurements were not significantly altered compared to non-smokers. Smoking may contribute to cataractogenesis and smoking and age-related changes may act synergistically to cataract development among smokers.

Effects of chewing tobacco on corneal endothelium in patients with diabetes mellitus

OBJECTIVE

To determine the impact of tobacco chewing on corneal endothelial structure in patients with diabetes mellitus (DM).

METHODS

Corneal endothelial parameters (endothelial cell count, ECD; coefficient of variation, CV; hexagonality, Hex, and central corneal thickness, CCT) were analysed in 1234 eyes of 1234 patients using non-contact specular microscopy (EM 4000 Tomey Nishi-Ku, Nagoya, Aichi, Japan). The study group (with a present history of tobacco chewing) comprising of 948 subjects, with 473 having DM was compared with age and gender-matched control group comprising of 286 subjects (139 having DM) with no history of tobacco use in any form.

RESULTS

Tobacco chewers had a significantly reduced ECD (P = 0.024) and Hex (P = 0.009) as compared with non-chewers. Similar results were noted in ECD (P = 0.004) and Hex (P = 0.005) in patients with DM. Tobacco chewers had a significantly decreased ECD values among males, HbA1C ≤ 7.5% and duration of DM ≤ 20 years, and significantly decreased Hex among those with >50 years of age, females, and duration of DM > 20 years. The CV and CCT values were comparable between the study and the control groups. Tobacco chewers showed a significant association of ECD with age, HbA1C, and duration of DM; CV with HbA1C; Hex with age and duration of DM; and CCT with gender, age, HbA1C and duration of DM.

CONCLUSIONS

Tobacco chewing may negatively impact corneal health, especially confounded by additional factors like age and DM. These factors must be accounted for in the pre-operative evaluation of such patients prior to any intra-ocular surgery.

Smoking and environmental tobacco smoke exposure: implications in ocular disorders

PURPOSE

This article aims to gather and review the available knowledge on several implications of smoking and environmental tobacco smoke (ETS) exposure in ocular disorders and provides pathomechanistic insights where applicable.

MATERIALS AND METHODS

PubMed and Scopus databases were searched for relevant studies on the association of smoking and ETS exposure with various ocular disorders. Studies with different evidence levels, e.g., in-vivo, case-control, cohort, and meta-analysis, were included.

RESULTS

Smoking is an established, modifiable risk factor in several ocular diseases, including cataract, age-related macular degeneration, and Graves' ophthalmopathy; smokers are subject to more severe disease courses and less favorable treatment outcomes. Uveitis is twice as likely in smokers; smoking may also delay its resolution. Smoking and ETS exposure are major risk factors for diseases of other organs, with associated ocular complications as well, such as diabetes mellitus. ETS exposure is also associated with ocular surface pathologies, including dry eye syndrome. In children, early-life ETS exposure and maternal smoking during pregnancy are strongly associated with refractive errors and strabismus. Currently, available data on potential risks attributable to ETS exposure regarding ocular diseases are scarce and, in some instances, controversial.

CONCLUSION

In addition to smoking, ETS exposure is also a significant public health concern with possible links to several ocular diseases. However, the level of education of at-risk populations in this regard does not match the strength of the evidence.

The network structure of the corneal endothelium

A generic network model is applied to study the structure of the mammalian corneal endothelium. The model has been shown to reproduce the network properties of a wide range of systems, from low-dimensional inorganic glasses to colloidal nanoparticles deposited on a surface. Available extensive experimental microscopy results are analyzed and combined to highlight the behavior of two key metrics, the fraction of hexagonal rings (p₆) and the coefficient of variation of the area. Their behavior is analyzed as a function of patient age, the onset of diabetes, and contact lens wearing status. Wearing contact lenses for ∼10 years is shown to change the endothelium structure by the equivalent of ∼30 years contact lens-free. Model network configurations are obtained using a Monte Carlo bond-switching algorithm, with the resulting topologies controlled by two potential model parameters (the bond and angular force constants) and the Monte Carlo temperature. The effect of systematically varying these parameters is investigated. In addition, the effect of constraining the ring size distribution is investigated. The networks generated with relatively weak bond force constants are shown to correlate best with the experimental information. The importance of extracting the full ring size distribution (rather than simply the fraction of hexagons) is discussed.

Tobacco effects on ocular surface, meibomian glands, and corneal epithelium and the benefits of treatment with a lipid-based lubricant

PURPOSE

Our aim was to evaluate the ocular surface in chronic smokers and to assess the benefit of sodium hyaluronate (SH) versus semi-fluorinated alkane (SFA) eyedrops on tear film, meibomian glands, and corneal epithelial thickness (CET).

METHODS

This prospective randomized single-blinded study included smokers, who applied one eyedrop of Hyabak® on one eye (SH group) and one eyedrop of EvoTears® on the fellow eye (SFA group) 4 times daily for 2 months, and age-matched non-smokers. Ocular surface parameters, including tear film break-up time (TBUT) test and corneal fluorescein staining (CFS) score, lipid layer thickness (LLT), meibography (LipiView®), and CET measurements (Zeiss Cirrus HD-5000®), were assessed at baseline and after treatment.

RESULTS

Seventy-eight eyes were included in the smokers group (39 in the SH subgroup and 39 in the SFA subgroup) and 42 eyes in the control group. At baseline, the smokers group had a higher prevalence of dry eye (100% vs 0%, p < 0.001) and of meibomian gland dysfunction (MGD) and lower CET measurements than controls (p < 0.05). TBUT, CFS, and LLT (controls vs SFA group: 64.02 ± 1.87 nm vs 49.56 ± 4.33 nm, p = 0.05) improved in the SFA subgroup after treatment, but not in the SH subgroup, and became equivalent to those of controls. Prevalence of dry eye decreased in the smokers group after treatment (controls vs SH group vs SFA group: 0% vs 12.82% vs 16.26%, p > 0.05). Meibomian gland morphological parameters and CET did not improve after treatment (p < 0.05).

CONCLUSIONS

Smoking is associated with dry eye, MGD, and corneal epithelial thinning that seem to be only partially reversible with topical lubricants, preferably SFA.

Effects of Type 2 Diabetes Mellitus and Smoking on Changes in Corneal Endothelial Morphology and Cell Density

PURPOSE

The purpose of this study was to compare the corneal endothelial morphology and cell density of diabetic smokers and nonsmokers with 50 to 70 age-matched healthy subjects and to determine whether smoking increases the effects of type 2 diabetes mellitus (DM) on these corneal parameters.

METHODS

This prospective cohort study included 200 patients who were assigned to 4 groups, including smokers with type 2 DM (group 1), nonsmokers with type 2 DM (group 2), healthy smokers (group 3), and healthy nonsmokers (control group, group 4). Noncontact specular microscopy was used to measure central endothelial cell density (ECD), coefficient of variation of cell area, percentage of hexagonal cells, and central corneal pachymetry (CCT).

RESULTS

According to the ECD and CCT values ( P < 0.001 and P = 0.013, respectively), a significant difference was observed between the groups. The mean ECD was lowest in diabetic smokers (1917 ± 399 cells/mm 2 ). Healthy smokers and diabetic smokers had significantly lower ECD compared with the control group ( P = 0.03 and P < 0.001, respectively). Healthy smokers and diabetic smokers had significantly lower ECD compared with diabetic nonsmokers ( P = 0.012 and P < 0.001, respectively). The cornea was significantly thicker in the diabetic smokers than in the control group ( P = 0.013).

CONCLUSIONS

The coexistence of DM and smoking causes a significant decrease in ECD and an increase in CCT. Cigarette smoking is more harmful to corneal endothelial cells than DM alone.

Risk Factors for Repeat Keratoplasty after Endothelial Keratoplasty - an IRIS® Registry Analysis

PURPOSE

To assess risk factors for repeat keratoplasty after endothelial keratoplasty (EK).

DESIGN

Retrospective cohort study METHODS: : EK procedures performed between 2013-2018 in the IRIS® Registry (Intelligent Research in Sight) were identified.

STUDY POPULATION

Patients aged 18 years and older who underwent EK.

MAIN OUTCOME MEASURES

1) Risk factors for repeat keratoplasty, and 2) complication rates after EK. A Kaplan-Meier survival analysis was used to determine the probability of repeat keratoplasty. A multivariable shared frailty survival model was used to assess risk factors.

RESULTS

59,344 procedures were identified in the registry, of which 30,600 EK procedures met the inclusion criteria for the analysis. The probability of repeat keratoplasty was 17.4% (95% CI:16.7-18.0%) at five years. Risk factors for repeat keratoplasty include post-operative re-bubbling procedure (HR 2.24, 95% CI:2.05-2.45); prior failed graft (HR 2.07, 95% CI:1.84-2.32) or bullous keratopathy (HR 1.47, 95% CI:1.33-1.61) versus Fuchs dystrophy as surgical indication; subsequent routine cataract surgery (HR 1.61, 95% CI:1.45-1.79); as well as subsequent (HR 1.53, 95% CI:1.39-1.69) and prior/concurrent (HR 1.23, 95% CI:1.11-1.36) glaucoma surgery or history of glaucoma (HR 1.24, 95% CI:1.14-1.35). Medicaid (HR 1.47, 95% CI:1.13-1.92), military/government (HR 1.29, 95% CI:1.03-1.60), Medicare Fee-for-Service (HR 1.17, 95% CI:1.05-1.31) or Medicare Managed (HR 1.17, 95% CI:1.01-1.36) insurances versus private insurance, as well as Black versus White race (HR 1.25, 95% CI:1.11-1.40) and smoking (HR 1.16, 95% CI:1.05-1.27) were also associated with an increased risk of undergoing repeat keratoplasty.

CONCLUSIONS

Black race, government-based insurance plans, and smoking were identified as independent factors associated with repeat keratoplasty in addition to history of glaucoma, glaucoma surgery, and prior graft failure or bullous keratopathy as surgical indication.

Analysis of risk factors of rapid attenuation of graft endothelium in the early stage after penetrating keratoplasty

This study aimed to analyze the factors of rapid attenuation of graft endothelium in the early stage after penetrating keratoplasty (PKP), with a view to guiding patients with PKP to better long-term outcomes. This study included 226 patients who underwent PKP with follow-up time >1 year at the Qingdao Eye Hospital of Shandong First Medical University from January 2018 to June 2020. Medical records were retrospectively studied, and donor factors, patient factors, and surgical factors were comparatively analyzed to clarify those affecting the rapid decay of graft endothelium after PKP. The median time between excision and death >60 min and patient age >60 years were risk factors for endothelial cell loss (ECL) rate >30% at 1 month postoperatively. However, a higher percentage of patients with donor age ≤60 years and Optisol preservation solution had endothelial cell density (ECD) >2000 cells/mm² in the graft at postoperative 1 year. A year after the surgery, patients with corneal endothelial decompensation and immune rejection were at risk for ECD < 1000 cells/mm². The combined operations had a significant effect on the ECL in the early postoperative period. Patients who underwent combined extracapsular cataract extraction or intraocular lens implantation had a significantly higher rate of ECL at postoperative 1 month than other patients, and no significant effect at postoperative 1 year. However, patients without combined operations have a higher probability of maintaining a high level of graft ECD. The graft diameter also affected postoperative ECL. In patients with a larger graft diameter, attenuation of ECD was slower. The ultimate goal of PKP is to maintain graft transparency for extended periods. The use of younger donors, minimizing unnecessary operation in the anterior chamber, and minimizing immune rejection may maintain a greater donor corneal endothelium in the long term.

Impact of tobacco use on corneal thickness and endothelial health: a systematic review with meta-analyses

PURPOSE

To investigate the impact of tobacco use on corneal thickness and corneal endothelial health.

METHODS

We searched the PubMed/MEDLINE, EMBASE, the Cochrane Central and all affiliated databases of the Web of Science on 20 July 2020. Two authors reviewed the studies and extracted the data in an independent fashion. Studies were reviewed qualitatively in the text, and central corneal thickness (CCT) and corneal endothelial characteristics (endothelial cell density, endothelial cell variability, average of endothelial cell size and endothelial cell hexagonality) were introduced for quantitative analyses.

RESULTS

Eighteen studies (2077 were smokers and 6429 non-smokers) were identified, of which 17 studies provided data eligible for one or more of the quantitative analyses. When compared to non-smokers, smokers had a higher CCT (+3.3 μm, 95% CI: +0.9 to +5.7 μm, p = 0.007) and a lower endothelial cell density (-140 cells/mm² , 95% CI: -30 to -250 cells/mm² , p = 0.01). Other corneal endothelial measures did not differ significantly.

CONCLUSION

Tobacco use is associated with a higher CCT and lower corneal endothelium cell density, but the clinical impact of these findings is small. Further studies are warranted on patients with a priori poor corneal health, where smoking may constitute an important risk of further progression, for example upon anterior segment surgery.

The effect of smoking on corneal densitometry and endothelial cell morphology

PURPOSE

We investigated corneal endothelial morphology and corneal densitometry in smokers and compared our results with findings observed in non-smokers.

MATERIALS AND METHODS

This cross-sectional observational study included 100 participants (50 smokers, 50 non-smokers) aged 18-80 years in whom corneal endothelial morphology was analysed using a non-contact Tomey EM-4000 specular microscope (Tomey Corporation, Japan). The Pentacam HR system was used to measure corneal densitometry spatially in three concentric zones (from the centre to the periphery) and at three different corneal depths (from the anterior to the posterior aspects). Endothelial morphology findings and corneal densitometry values were recorded in all participants, and these results were compared between smokers and non-smokers.

RESULTS

Endothelial morphology and corneal densitometry analysis showed significantly lower endothelial cell counts (Num) in smokers (228 cells/mm² vs. 246 cells/mm², p = 0.02) in addition to increased maximum cell area (Max) values (986.5 µm² vs. 935 µm², p = 0.04). We observed no statistically significant intergroup difference in corneal densitometry values (p > 0.05 for each zone); however, we observed a moderately positive correlation between densitometry values in the 6-10 mm concentric zone and between the all total corneal zones and number of pack-years in smokers.

CONCLUSIONS

Our study highlights that among the morphometric corneal endothelial variables analysed in this study, only the Num value was significantly correlated with smoking. We observed no statistically significant intergroup difference in corneal densitometry values in this study; however, a positive correlation was observed between the number of pack-years and corneal densitometry findings. Therefore, as the pack-years increase, the increase in corneal densitometry values may indicate a decrease in corneal clarity, considering the possible contribution of secondary factors such as age.

Cigarette Smoke Triggers Loss of Corneal Endothelial Cells and Disruption of Descemet's Membrane Proteins in Mice

Purpose

To investigate changes at a molecular level in the mouse corneal endothelium (CE) exposed to chronic cigarette smoke (CS).

Methods

Pregnant mice (gestation days 18–20) were placed in a whole-body exposure smoking chamber, and a few days later pups were born. After 3.5 months of CS exposure, a ConfoScan4 scanning microscope was used to examine the corneal endothelial cells (CECs) of CS-exposed and control (Ct) mice. The CE was peeled under a microscope and maintained as four biological replicates (two male and two female) for CS-exposed and Ct mice; each replicate consisted of 16 CEs. The proteome of the CE was investigated through mass spectrometry.

Results

The CE images of CS-exposed and Ct mice revealed a difference in the shape of CECs accompanied by a nearly 10% decrease in CEC density (P < 0.00003) following CS exposure. Proteome profiling identified a total of 524 proteins exhibiting statistically significant changes in CE from CS-exposed mice. Importantly, proteins associated with Descemet's membrane (DM), including COL4α1, COL4α2, COL4α3, COL4α4, COL4α5, COL4α6, COL8α1, COL8α2, and FN1, among others, exhibited diminished protein levels in the CE of CS-exposed mice.

Conclusions

Our data confirm that exposure to CS results in reduced CEC density accompanied by diminished levels of multiple collagen and extracellular matrix proteins associated with DM.