Effect of Obstructive Sleep Apnea on Corneal Morphological Characteristics

Sleep deprivation induces corneal endothelial dysfunction by downregulating Bmal1

BACKGROUND

Sleep deprivation (SD) is a common public health problem that contributes to various physiological disorders and increases the risk of ocular diseases. However, whether sleep loss can damage corneal endothelial function remains unclear. This study aimed to determine the effect and possible mechanism of SD on the corneal endothelium.

METHODS

Male C57BL/6J mice were subjected to establish SD models. After 10 days, quantitative RT-PCR (qRT-PCR) and western blot or immunostaining for the expression levels of zonula occludens-1 (ZO-1), ATPase Na+/K + transporting subunit alpha 1 (Atp1a1), and core clock genes in the corneal endothelium were evaluated. Reactive oxygen species staining and mitochondrial abundance characterized the mitochondrial function. The regulatory role of Bmal1 was confirmed by specifically knocking down or overexpressing basic helix-loop-helix ARNT like 1 protein (Bmal1) in vivo. In vitro, a mitochondrial stress test was conducted on cultured human corneal endothelial cells upon Bmal1 knockdown.

RESULTS

SD damaged the barrier and pump functions of mouse corneal endothelium, accompanied by mitochondrial dysfunction. Interestingly, SD dramatically downregulated the core clock gene Bmal1 expression level. Bmal1 knockdown disrupted corneal endothelial function, while overexpression of Bmal1 ameliorated the dysfunction induced by SD. Mitochondrial bioenergetic deficiency mediated by Bmal1 was an underlying mechanism for SD induced corneal endothelial dysfunction.

CONCLUSION

The downregulation of Bmal1 expression caused by SD led to corneal endothelial dysfunction via impairing mitochondrial bioenergetics. Our findings offered insight into how SD impairs the physiological function of the corneal endothelium and expanded the understanding of sleep loss leading to ocular diseases.

The Impact of Donor History of Sleep Apnea on Corneal Tissue Evaluation Parameters

PURPOSE

The goal of this study was to explore whether the donor history of sleep apnea affects corneal tissue evaluation parameters.

METHODS

This was a retrospective study assessing the impact of donor history of sleep apnea in a dataset obtained from the Eversight Eye Bank. Comparative analysis and multivariate regression were used to assess differences in key parameters including endothelial cell density (ECD) and central corneal thickness.

RESULTS

Data analyzed consisted of 50,170 tissues from 25,399 donors with no history of sleep apnea and 5473 tissues from 2774 donors with a history of sleep apnea. Tissue from donors with a history of sleep apnea showed lower ECD than those from donors with no history of sleep apnea (-51 cells/mm2, P < 0.001). Multivariate linear regression demonstrated that history of sleep apnea was a predictor of lower ECD by 13.72 cells/mm2 (P = 0.0264). Secondary analysis demonstrated that underweight and obese body mass indexes were significant predictors of increased ECD in donors with no history of sleep apnea (P < 0.0001, P = 0.025, respectively). Body mass index category was not a significant predictor of ECD in donors with a history of sleep apnea. In a smaller subset of 10,756 tissues, sleep apnea was not a significant predictor of central corneal thickness.

CONCLUSIONS

This is the first study to demonstrate that a donor's history of sleep apnea is associated with a lower ECD in a large eye bank dataset. Future studies are needed to investigate whether history of sleep apnea affects posttransplantation outcomes.

Correlations of Corneal Endothelial Morphology and Corneal Thickness With Anterior Segment Parameters in Healthy Individuals

PURPOSE

The purpose of this study was to investigate the associations between central corneal endothelial cell density (ECD), endothelial morphology, and corneal thickness (central corneal thickness) with the anterior chamber depth, corneal volume (CV), white-to-white (WTW) distance, mean anterior chamber angle (CAmean), and gender in healthy individuals.

METHODS

This observational study included 136 healthy volunteers. The ECD, coefficient of variation of cell area, and hexagonal cell appearance ratio (%Hex) were measured by means of specular microscopy. The central corneal thickness, anterior chamber depth, CV, WTW distance, and the angle width of 12 points were taken by the Pentacam HR Scheimpflug anterior segment imaging. The arithmetical mean of the 12 points was considered as the CAmean. We used mixed effect linear regression model for the statistical analysis of the data.

RESULTS

ECD was positively correlated with CV ( P = 0.028), while after adjusting for age, it was negatively correlated with age ( P < 0.001). Coefficient of variation of cell area was positively correlated with CAmean ( P = 0.036), while after adjusting for age, it was positively correlated with age ( P < 0.001) and CAmean ( P = 0.005). Hex was negatively correlated with WTW ( P = 0.023) and CAmean ( P = 0.025), and after adjusting for age, this correlation remained the same ( P = 0.029 when correlated with WTW and P = 0.035 with CAmean).

CONCLUSIONS

There were significant changes in the morphology of the corneal endothelial cells in eyes with wider anterior chamber angle. Greater pleomorphism and polymegethism of the corneal endothelium was observed in healthy patients with wider CAmean. Deepening of the anterior chamber as myopia progresses could render the corneal endothelium more fragile and susceptible to mechanical stress, which is an area worthy of further study.

Aqueous Humor Circulation in the Era of Minimally Invasive Surgery for Glaucoma

Glaucoma surgery with implantation of aqueous humor draining microstents may compromise long-term corneal health by disrupting aqueous humor circulation. The effect of stent numbers on this circulation was interrogated to determine the number of stents associated with minimal circulation disruption. An in vitro anterior eye model perfusion system was constructed with multiple exit ports. A 3-D model of the anterior eye was imported into ABAQUS CFD, analyzes were carried out for unsteady laminar flow and solved using Navier-Stokes equations. DT Vision Foundry was used to analyze velocity contour plot images. The field variable results output for the CFD model were fluid wall shear, fluid pressure and fluid velocity. In vitro, "aqueous" fluid flow is high through a single stent and "aqueous" stagnation is greatest in the quadrants 180° away. Increasing stent port numbers, results in an exponential decrease in the stagnant flow locations. High wall shear stress was seen in the single stent model and is markedly reduced after a second and subsequent stents are introduced. We identify two factors potentially contributing to corneal compromise post glaucoma drainage surgery: aqueous humor stagnation, remote to the stent site and higher exit flows imparting increased stent exit shear stress (particularly with a single stent). With 4 stents, there is minimal disruption of anterior chamber circulation (mimicking physiological conditions). Furthermore we propose that aqueous humor circulation disruption via the usual single-exit port approach disrupts aqueous humor circulation with long-term consequences for corneal health.

Analysis of corneal topographic and endothelial cell properties in newly diagnosed obstructive sleep apnea patients: A case-control study

PURPOSE

To investigate the topographic features and endothelial cell changes in the corneas of patients with newly diagnosed obstructive sleep apnea (OSA).

BACKGROUND

This cross-sectional case-control study included 98 patients with OSA and 90 healthy controls. OSA was diagnosed on the basis of a polysomnographic sleep examination. Patients with OSA were grouped according to their apnea-hypopnea index (AHI) scores. Corneal topographic measurements were obtained using the Scheimpflug-Placido disk topographer, and keratometry values, anterior chamber parameters, thinnest corneal thickness, symmetry index (SI), keratoconus vertex (KV), and the Baiocchi-Calossi-Versaci index, including keratoconus (KC) screening indexes, were recorded. The corneal endothelium was visualizedby specular microscopy, and the endothelial cell density, coefficient of variability (CV), and percentage of hexagonal cells (HEX) were recorded.

RESULTS

In this study, 32 patients had mild, 34 patients had moderate, and 32 patients had severe OSA. The mean back KV (KVb) and back SI values were significantly higher in the OSA group than in the control group (P <0.001, P = 0.035, respectively). As body mass index (BMI) increased, KVb also increased significantly (r = 0.281; P = 0.009). The mean CV and HEX values differed significantly between the OSA and control groups (P = 0.012 and P = 0.002, respectively). In addition, a significant correlation was found between AHI and KVb and CV values (r = 0.315; P <0.001 and r = 0.231; P = 0.011, respectively).

CONCLUSIONS

This study revealed abnormal changes in the corneal endothelial morphology and topographic KC screening indexes in relation to OSA severity in patients and controls. Further research is required to determine the effect of BMI on corneal topographic findings in patients with OSA.

Effect of corneal stiffness decrease on axial length elongation in myopia determined based on a mathematical estimation model

Purpose: To investigate the relationship between the corneal material stiffness parameter stress-strain index (SSI) and axial length (AL) elongation with varying severities of myopia, based on a mathematical estimation model. Methods: This single-center, cross-sectional study included data from healthy subjects and patients preparing for refractive surgery in the Qingdao Eye Hospital of Shandong First Medical University. Data were collected from July 2021 to April 2022. First, we performed and tested an estimated AL model ( A L M o r g a n ) based on the mathematical equation proposed by Morgan. Second, we proposed an axial increment model ( Δ A L ) corresponding to spherical equivalent error (SER) based on A L e m m e t r o p i a ( A L M o r g a n at SER = 0) and subject's real AL. Finally, we evaluated the variations of Δ A L with SSI changes based on the mathematical estimation model. Results: We found that AL was closely associated with A L M o r g a n (r = 0.91, t = 33.8, p < 0.001) with good consistency and SER was negatively associated with Δ A L (r = -0.89, t = -30.7, p < 0.001). The association of SSI with AL, A L e m m e t r o p i a , and Δ A L can be summarized using the following equations: A L = 27.7 - 2.04 × S S I , A L e m m e t r o p i a = 23.2 + 0.561 × S S I , and Δ A L = 4.52 - 2.6 × S S I . In adjusted models, SSI was negatively associated with AL (Model 1: β = -2.01, p < 0.001) and Δ A L (Model 3: β = -2.49, p < 0.001) but positively associated with A L e m m e t r o p i a (Model 2: β = 0.48, p < 0.05). In addition, SSI was negatively associated with Δ A L among subjects with AL ≥ 26 mm (β = -1.36, p = 0.02). Conclusion: AL increased with decreasing SSI in myopia.

Corneal Refractive Surgery Considerations in Patients with Cystic Fibrosis and Cystic Fibrosis Transmembrane Conductance Regulator-Related Disorders

This article discusses common ocular manifestations of cystic fibrosis (CF) and cystic fibrosis transmembrane conductance regulator-related disorders (CFTR-RD). A structured approach for assessing and treating patients with CF/CFTR-RD seeking corneal refractive surgery is proposed, as well as a novel surgical risk scoring system. We also report two patients with various manifestations of CFTR dysfunction who presented for refractive surgery and the outcomes of the procedures. Surgeons seeking to perform refractive surgery on patients with CF/CFTR-RD should be aware of mild to severe clinical manifestations of CFTR dysfunction. Specific systemic and ocular manifestations of CF include chronic obstructive pulmonary disease (COPD), bronchiectasis, recurrent pulmonary infections, CF-related diabetes and liver disease, pancreatic insufficiency, conjunctival xerosis, night blindness, meibomian gland dysfunction (MGD), and blepharitis. Corneal manifestations include dry eye disease (DED), punctate keratitis (PK), filamentary keratitis (FK), xerophthalmia, and decreased endothelial cell density and central corneal thickness. Utilization of the appropriate review of systems (ROS) and screening tests will assist in determining if the patient is a suitable candidate for refractive surgery, as CF/CFTR-RD can impact the health of the cornea. Collaboration with other medical professionals who care for these patients is encouraged to ensure that their CF/CFTR-RD symptoms are best controlled via systemic and other treatment options. This will assist in reducing the severity of their ocular manifestations before and after surgery.

Evaluation of corneal, ocular surface, and meibomian gland changes in obstructive sleep apnea syndrome

PURPOSE

To evaluate the ocular surface, eyelid changes, meibomian gland morphology, corneal endothelial morphology, and corneal topographic measurements in patients with obstructive sleep apnea syndrome (OSAS).

METHODS

There were 47 patients diagnosed with OSAS and 47 healthy volunteers included in the study. Non-invasive tear break-up time (NITBUT), corneal topography, meibography, and specular microscopy were performed.

RESULTS

The mean ages of the study and control groups were 45.77±9.65 years and 44.26±8.54 years, respectively (P=0.229). The presence of floppy eye lid (17% vs. 0%; P=0.006) and lid margin abnormality score (1.09±0.8 vs. 0.21±0.51; P<0.001) were significantly different between the study and the control groups. There were insignificant differences between the groups in NITBUT and corneal topographic measurements, except for the ACT (556.96±42.4μm vs. 569±103μm, P=0.037). The mean endothelial cell density (CD) in the OSAS and control groups were 2609±259.96 and 2756±179 cells/mm², respectively (P=0.002). Meibomian gland loss in the lower and upper eyelids was significantly higher in the OSAS group (P<0.001 for both).

CONCLUSION

OSAS patients develop eyelid margin abnormalities, loss of meibomian glands, and morphological changes in the meibomian glands. A significant reduction in corneal endothelial CD indicates that systemic hypoxia in OSAS has an effect on the cornea.

Hypoxia adaptation in the cornea: Current animal models and underlying mechanisms

The cornea is an avascular, transparent tissue that is essential for visual function. Any disturbance to the corneal transparency will result in a severe vision loss. Due to the avascular nature, the cornea acquires most of the oxygen supply directly or indirectly from the atmosphere. Corneal tissue hypoxia has been noticed to influence the structure and function of the cornea for decades. The etiology of hypoxia of the cornea is distinct from the rest of the body, mainly due to the separation of cornea from the atmosphere, such as prolonged contact lens wearing or closed eyes. Corneal hypoxia can also be found in corneal inflammation and injury when a higher oxygen requirement exceeds the oxygen supply. Systemic hypoxic state during lung diseases or high altitude also leads to corneal hypoxia when a second oxygen consumption route from aqueous humor gets blocked. Hypoxia affects the cornea in multiple aspects, including disturbance of the epithelium barrier function, corneal edema due to endothelial dysfunction and metabolism changes in the stroma, and thinning of corneal stroma. Cornea has also evolved mechanisms to adapt to the hypoxic state initiated by the activation of hypoxia inducible factor (HIF). The aim of this review is to introduce the pathology of cornea under hypoxia and the mechanism of hypoxia adaptation, to discuss the current animal models used in this field, and future research directions.

Comparison of obstructive sleep apnea syndrome and keratoconus patients on elevation maps

PURPOSE

This study aimed to compare the tomographic features of the cornea on elevation maps between obstructive sleep apnea syndrome (OSAS) and keratoconus (KC) patients and to investigate the presence of susceptibility to ectatic corneal diseases in OSAS patients.

DESIGN

This is a comparative cross-sectional case-control study.

METHODS

This study included 84 eyes of 42 patients diagnosed with severe OSAS using polysomnography (apnea/hypopnea index > 30), 84 eyes of 56 patients diagnosed with keratoconus, and 84 eyes of 42 healthy subjects as control group and evaluated in three groups. Elevation maps of all the groups were performed using Pentacam, and topometric, pachymetric, and deviation indices were recorded.

RESULTS

The study included 252 eyes of 130 participants divided in three groups. Comparing all the tomographic keratometric values, a significant difference was found among the three groups. All keratometric values were found to be higher in the OSAS patients group compared to those in the control group. Also topometric indices and Belin-Ambrosio enhanced ectasia display (BAD) were observed to be higher as in subclinical keratoconus and statistically significant when compared to those in the control group.

CONCLUSION

The study reveals the tomographic corneal characteristics and topometric and pachymetric indices of patients with severe OSAS at the time of diagnosis; these findings statistically significantly differ from the control group. In addition to the known association of floppy eyelid in OSAS patients, the suspicion of keratoconus should be kept in mind.

Corneal Endothelial Morphology and Thickness Alterations in Patients With Severe Obstructive Sleep Apnea-Hypopnea Syndrome

PURPOSE

To investigate central endothelial cell density (ECD), morphology, and central corneal thickness (CCT) in patients newly diagnosed with severe obstructive sleep apnea-hypopnea syndrome (OSAHS) and to determine the correlation between these parameters and OSAHS severity.

METHODS

This prospective, comparative case series was conducted in a university ophthalmology clinic. In total, 51 patients recently diagnosed with severe OSAHS (apnea-hypopnea index above 30) and a paired, age and sex-matched control group of 44 healthy individuals were enrolled. After detailed ophthalmologic examination, specular microscopy measurement was performed for all participants. Central ECD, average cell area, coefficient of variation (CV) of cell area, hexagonal cell appearance ratio (% Hex), and CCT were compared between the groups. The Pearson correlation test was also used to assess the influence of the polysomnographic findings, that is, the proportion of each stage of sleep, apnea-hypopnea index, SpO2, mean and maximum duration of apneas, oxygen desaturation index, and arousal index on corneal endothelial morphometric parameters and CCT.

RESULTS

A total of 190 eyes were examined: 102 eyes of patients with severe OSAHS and 88 eyes of the control group. The mean ECD, CV, % Hex, and CCT values in the OSAHS group were 2439.25 ± 344.36 cells/mm, 41.41 ± 11.62, 45.22 ± 7.06%, and 533.88 ± 40.53 μm, respectively. ECD and CCT did not significantly differ between the groups (P = 0.46, P = 0.55, respectively). CV value was significantly higher (P = 0.009), whereas the %Hex was significantly lower (P = 0.01) in the OSAHS group. We observed a significant negative correlation between CCT and REM sleep percentage (P = 0.005).

CONCLUSIONS

Greater pleomorphism and polymegathism of corneal endothelium was found in patients with severe OSAHS when compared with healthy subjects. Low percentage of REM sleep, usually found in patients with OSAHS, may cause an increase in corneal thickness.

Effects of Continuous Positive Airway Pressure Treatment for Obstructive Sleep Apnea-Hypopnea Syndrome on Corneal Morphological Characteristics

PURPOSE

To evaluate the effects of continuous positive airway pressure (CPAP) therapy on corneal endothelial morphometry and pachymetry in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS).

METHODS

This prospective, observational study included patients with OSAHS who were evaluated right before and after the commencement of CPAP treatment. Each patient underwent a detailed ophthalmologic examination and assessment of their corneal endothelium with a noncontact specular microscope (Tomey EM-3000; Tomey Corp). Endothelial cell density, coefficient of variation of cell area (CV), hexagonal cell appearance ratio (%Hex), and central corneal thickness were measured. The post-CPAP results were compared with the results of a control group. The differences in the corneal parameters between pre- and post-CPAP therapy of the OSAHS group were correlated with the pretreatment polysomnography results.

RESULTS

Twenty-seven distinct eyes of 27 patients recently diagnosed with OSAHS and 30 eyes of 30 healthy individuals were used for the statistical analysis. The mean age of patients with OSAHS was 54.2 ± 11.8 years, and after 9.6 months (range 3-18 mo) of good adherence to CPAP treatment, their CV values, indicating polymegathism, decreased from 41.7 ± 8.7 to 38.3 ± 5.8 (P = 0.04), whereas %Hex, indicating pleomorphism, increased from 45.8% ± 8.2% to 48.4% ± 6.6% (P = 0.008). Their post-CPAP corneal parameters did not differ significantly from those of the control group (P > 0.05). A significant positive correlation was observed between the decrease in CV and the duration of the treatment (Rs = 0.566, P = 0.002), as well as the pre-CPAP nonrapid eye movement (NREM) sleep percentage (Rs = 0.459, P = 0.02). A negative correlation was noted between the decrease in CV and the percentage of rapid eye movement (REM) sleep (Rs = -0.459, P = 0.02).

CONCLUSIONS

Better oxygenation during sleep, resulting from increased CPAP adherence, had a significant influence on corneal endothelium, providing an improvement in corneal polymegathism and pleomorphism, with a potential return of CV and %Hex to their normal values. Greater improvement in polymegathism was observed in patients with greater proportion of NREM sleep.

Lack of association between obstructive sleep apnea syndrome and specular microscopic features of the corneal endothelium

BACKGROUND

Obstructive sleep apnea syndrome (OSAS) is characterized by recurrent episodes of hypoxemia and hypercapnia during sleep. The aim of this study was to determine whether OSAS causes significant changes in corneal endothelium detectable by specular microscopy.

METHODS

This prospective, cross-sectional study compared the specular microscopic features of the corneal endothelium of patients with OSAS and age-and gender-matched controls. Patients diagnosed with OSAS by polysomnography in the sleep unit were classified using apnea-hypopnea indexes into two groups as mild-moderate OSAS group and severe OSAS group. All participants were divided into three age groups: 30-45, 46-60, and > 60 years. Corneal endothelial cell density (ECD), percentage of hexagonal cells (Hex), and coefficient of variation of cell area (CV) were obtained using a non-contact specular microscope. The measurements of each group were compared statistically.

RESULTS

A total of 66 patients (51.1 ± 9.4 years) and 88 controls (49.2 ± 10.5 years) were examined. The mild-moderate OSAS group and the severe OSAS group had no significant differences in measures of specular microscopy compared with the controls (ECD, p = 0.84; Hex, p = 0.18; CV, p = 0.41). The mean values of ECD, Hex, and CV were 2552.56 ± 302.49 cells/mm², 54.13 ± 8.13%, and 36.41 ± 5.92, respectively, in the mild-moderate OSAS group; 2510.52 ± 377.12 cells/mm², 54.85 ± 8.68%, and 34.77 ± 5.02, respectively, in the severe OSAS group; 2543.37 ± 286.94 cells/mm², 51.89 ± 9.09%, and 36.03 ± 5.32, respectively, in the control group.

CONCLUSIONS

There were no significant differences in corneal endothelial features between patients and controls. Although OSAS causes systemic hypoxia, its effects do not appear to result in corneal endothelial alterations detectable by specular microscopy.