Optical Coherence Tomography Reveals Changes to Corneal Reflectivity and Thickness in Individuals with Tear Hyperosmolarity

Impact of Clinician Subjectivity on the Assessment of Dry Eye Disease Prevalence in a UK Public Health Care Patient Population

Purpose

To understand the impact of subjectivity on diagnosis rates of dry eye disease (DED) in an unbiased population.

Patients and Methods

A multicenter study enrolled 818 subjects with complete report forms (465 females, 67.1 ± 16.7 years, 353 males, 65.0 ± 15.9 years). Subjects were evaluated for staining, TBUT, tear osmolarity, meibomian gland disease, and OSDI.

Results

Physicians diagnosed 48.7% of subjects as having DED, ranging from 42.9% to 62.3% between sites. Positivity rates for staining (≥ grade 1) ranged from 41.3% to 84.1% (mean = 0.8 ± 0.9 grade), TBUT (<10s) ranged from 39.1% to 61.6% (mean = 10.4 ± 6.6 seconds), osmolarity (>308 mOsm/L) ranged from 63.7% to 72.4% (mean = 319.7 ± 20.8), MGD grading ranged from 28.9% to 51.3% (mean = 0.5 ± 0.7), and symptoms measured by OSDI ranged from 57.6% to 71.0% (mean = 23.5 ± 20.5) between sites. Tear osmolarity was the most consistent between sites (max/min positivity = 114%), followed by OSDI (123%), TBUT (158%), MGD (178%), and staining (204%). DED markers were uncorrelated (average r2 = 0.05 ± 0.07). A substantial number of subjects (N = 110) exhibited positive symptoms (OSDI = 32.4 ± 15.7) and hyperosmolarity (338.1 ± 20.1 mOsm/L) but no other obvious signs of DED (MGD grade = 0.2 ± 0.4, TBUT = 13.5 ± 7.0 seconds, staining grade = 0.4 ± 0.5).

Conclusion

Subjective signs of DED varied considerably, whereas objective measurements of OSDI and osmolarity were the most consistent between sites. A large proportion of subjects exhibited high symptoms and hyperosmolarity but no other obvious signs of dry eye disease, most of whom were undiagnosed by clinical assessment without access to the osmolarity measurement.

Comparison of Autonomous AS-OCT Deep Learning Algorithm and Clinical Dry Eye Tests in Diagnosis of Dry Eye Disease

Objective

To evaluate a deep learning-based method to autonomously detect dry eye disease (DED) in anterior segment optical coherence tomography (AS-OCT) images compared to common clinical dry eye tests.

Methods

In this study, 27,180 AS-OCT images were prospectively collected from 151 eyes of 91 patients. Images were used to train and test the deep learning model. Masked cornea specialist ophthalmologist diagnoses were used as the gold standard. Clinical dry eye tests were performed on patients in the DED group to compare the results of the model. The dry eye tests performed were tear break-up time (TBUT), Schirmer's test, corneal staining, conjunctival staining, and Ocular Surface Disease Index (OSDI).

Results

Our deep learning model achieved an accuracy of 84.62%, sensitivity of 86.36%, and specificity of 82.35% in the diagnosis of DED. The positive likelihood ratio was 4.89, and the negative likelihood ratio was 0.17. The mean DED probability score was 0.81 ± 0.23 in the DED group and 0.20 ± 0.27 in the healthy group (P < 0.01). The deep learning model accuracy in the diagnosis of DED was significantly better than that of corneal staining, conjunctival staining, and Schirmer's test (P < 0.05). There was no significant difference between the deep learning diagnostic accuracy and that of the OSDI and TBUT.

Conclusion

Based on preliminary results, reliable autonomous diagnosis of DED with our deep learning model was achieved, when compared with standard dry eye clinical tests that correlated significantly more or similarly to diagnoses made by cornea specialist ophthalmologists.

Longitudinal Changes in Corneal Epithelial Thickness and Reflectivity following Simple Limbal Epithelial Transplantation: An Optical Coherence Tomography-Based Study

PURPOSE

To describe the changes in corneal epithelial thickness and reflectivity following simple limbal epithelial transplantation (SLET) using anterior segment optical coherence tomography (ASOCT).

METHODS

This was a prospective imaging study of 31 eyes of 29 patients who had undergone autologous or allogeneic SLET for limbal stem cell deficiency and had stable, avascular surfaces postoperatively. ASOCT scans of all four quadrants were taken preoperatively and at 1-week, 1-month, 3-month, 6-month, and 1-year postoperative time points in the eyes undergoing SLET. Baseline scans were also taken from the normal eye in unilateral cases. The following parameters were obtained from the scans: (i) epithelial thickness (ET), (ii) stromal thickness, (iii) total corneal thickness, (iv) epithelial reflectivity (ER), (v) stromal reflectivity, and (vi) epithelial/stromal (ES) reflectivity ratio.

RESULTS

Chemical injury (24 eyes, 77.4%) was the most common indication for surgery. There was a significant improvement in the ET (184.8 ± 117.1 vs 60.3 ± 10 µm, p < .0001) and ER (144.5 ± 26.4 vs 120.9 ± 28.9, p < .0001) within the initial postoperative period following SLET, which remained stable at the end of 1 year follow-up. There was no difference in the ET of the post-SLET and normal eyes after the 3-month timepoint and this normalization was maintained until the end of the first year. A significant normalization was also noted in the ES reflectivity ratio at the end of 1 year (2.1 ± 0.8 vs 1 ± 0.2, p < .001). A significant correlation was found between the final visual acuity and the total corneal thickness (r = 0.942, p = .005).

CONCLUSION

There is a significant improvement in the epithelial thickness and reflectivity of the cornea in eyes undergoing SLET. ASOCT provides a reliable objective measure of these changes and can be used to monitor the outcomes in these eyes postoperatively.

Conjunctivochalasis and Tear Osmolarity Are Associated With Reduced Conjunctival Epithelial Thickness in Dry Eye

PURPOSE

To investigate the hypothesis that ocular surface epithelial thickness is correlated with tear osmolarity, conjunctivochalasis (CCh), and dry eye clinical tests.

DESIGN

A case-control study.

METHODS

A total of 50 patients with different types of dry eye disease (DED) and 15 age- and sex-matched control subjects were enrolled in this study. We performed a detailed diagnostic assessment of tear film and ocular surface parameters, including Ocular Surface Disease Index questionnaire, visual analog scale questionnaire, topographic surface regularity and surface asymmetry indices, tear film break-up time, corneal and conjunctival dye staining, Schirmer I test, and tear osmolarity. The corneal and bulbar conjunctival epithelial thickness (CET) were obtained using the latest version of spectral domain optical coherence tomography (SDOCT).

RESULTS

Patients with aqueous-deficient DED (ADDED) had lower bulbar CET values, particularly in the temporal region, than those of normal subjects and patients with evaporative-type DED (EDED); however, the difference did not quite reach a statistically significant level. Patients with DED and CCh had lower bulbar CET values in temporal (38.52 ± 9.58 µm) and inferior regions (50.79 ± 9.10 µm) compared to those with DED without CCh (47.39 ± 11.71 µm, 60.38 ± 14.36 µm, respectively, P < .02). In the DED group, tear osmolarity was found to be negatively correlated with CET values in temporal bulbar region (P = .006 and r = -0.403) and central corneal epithelial thickness values (P = .029 and r = -0.325).

CONCLUSIONS

CCh and tear osmolarity are associated with reduced conjunctival epithelial thickness in DED.

The ocular surface immune system through the eyes of aging

Since the last century, advances in healthcare, housing, and education have led to an increase in life expectancy. Longevity is accompanied by a higher prevalence of age-related diseases, such as cancer, autoimmunity, diabetes, and infection, and part of this increase in disease incidence relates to the significant changes that aging brings about in the immune system. The eye is not spared by aging either, presenting with age-related disorders of its own, and interestingly, many of these diseases have immune pathophysiology. Being delicate organs that must be exposed to the environment in order to capture light, the eyes are endowed with a mucosal environment that protects them, the so-called ocular surface. As in other mucosal sites, immune responses at the ocular surface need to be swift and potent to eliminate threats but are at the same time tightly controlled to prevent excessive inflammation and bystander damage. This review will detail how aging affects the mucosal immune response of the ocular surface as a whole and how this process relates to the higher incidence of ocular surface disease in the elderly.

A reliable animal model of corneal stromal opacity: Development and validation using in vivo imaging

PURPOSE

To validate an animal model of corneal stromal opacity by using objective vision-independent in vivo imaging metrics.

METHODS

This was a prospective study, with two arms: (i) observational human arm which included 14 patients with healed unilateral ulcerative keratitis; and (ii) experimental rabbit arm, which included 6 New Zealand white rabbits. A 3-mm central wound was created in the left eye of the rabbits by manually removing 200-250 μm of the superficial stroma, followed by rotating-burr application. Both groups underwent photography, high-resolution anterior segment optical coherence tomography, and Scheimpflug imaging using similar diagnostic platforms and standardized image capturing protocols. Parameters studied were relative change in (i) corneal thickness; (ii) corneal epithelial: stromal (E:S) reflectivity ratio; (iii) corneal stromal light scattering using densitometry; and (iv) central corneal keratometry.

RESULTS

In the experimental arm, there was a significant decrease in corneal thickness (273 ± 51.3 vs. 407.3 ± 10.3 μm, p = 0.0038), E:S reflectivity ratio (0.71 ± 0.09 vs. 0.99 ± 0.06, p = 0.0018), and keratometry (40.4 ± 2.3 vs. 45.8 ± 0.9D, p = 0.0033) and increase in densitometry (54.2 ± 11.65 vs.18.7 ± 3.8 GSU, p = 0.0001) from baseline, which stabilized at 4 to 8-weeks post-wounding (p > 0.3632). At 8-weeks, the relative change from baseline in corneal thickness (28.4 ± 13.5% vs.22.4 ± 13%, p = 0.368), E:S reflectivity ratio (28.1 ± 11.5% vs. 30.6 ± 8.9%, p = 0.603), corneal densitometry (204.17 ± 97.3% vs. 304.9 ± 113.6%, p = 0.1113), and central corneal keratometry (13.6 ± 6.9% vs. 18.9 ± 7.4%, p = 0.1738) in rabbits was similar to human corneal scars.

CONCLUSION

The animal model of corneal opacification was objectively comparable to human post-keratitis scars and can be valuable for in vivo evaluation of emerging therapies for corneal opacities.

Impact of Attrition, Intercellular Shear in Dry Eye Disease: When Cells are Challenged and Neurons are Triggered

The mechanical component in the pathophysiology of dry eye disease (DED) deserves attention as an important factor. The lubrication deficit induced impaired mechano-transduction of lid pressure to the ocular surfaces may lead to the dysregulation of homeostasis in the epithelium, with sensations of pain and secondary inflammation. Ocular pain is possibly the first sign of attrition and may occur in the absence of visible epithelial damage. Attrition is a process which involves the constant or repeated challenge of ocular surface tissues by mechanical shear forces; it is enhanced by the thinning of corneal epithelium in severe DED. As a highly dynamic process leading to pain and neurogenic inflammation, the identification of the impact of attrition and its potential pathogenic role could add a new perspective to the current more tear film-oriented models of ocular surface disease. Treatment of DED addressing lubrication deficiencies and inflammation should also consider the decrease of attrition in order to stimulate epithelial recovery and neural regeneration. The importance of hyaluronic acid, its molecular characteristics, the extracellular matrix and autoregulative mechanisms in this process is outlined. The identification of the attrition and recognition of its impact in dry eye pathophysiology could contribute to a better understanding of the disease and optimized treatment regimens.

The frequency of non-pathologically thin corneas in young healthy adults

Purpose: Measurement of normal corneal thickness and corneal epithelial thickness is important in keratorefractive surgery, glaucoma, following extended contact lens wear, and in patients with corneal disease. Clinically, a central corneal thickness less than 500 µm is considered to be moderately-to-extremely thin. The purpose of this study was to compare biological differences in patients with clinically thin compared to normal corneal thickness values in healthy young adults using Fourier domain optical coherence tomography. Patients and methods: In total, 168 eyes from 84 patients aged 19-38 years were scanned using an Avanti optical coherence tomographer. To eliminate circadian effects on corneal thickness, all patients were scanned within a 4-hour window. Corneal thickness was measured across the central 6 mm of the cornea. Total central corneal thickness, corneal epithelial thickness, and corneal stromal thickness were compared between males and females and tested for correlations with age, use of systemic hormones, degree of myopia, and corneal curvature. Results: The average central corneal thickness for males and females was 540.5±32.0 μm and 525.2±33.0 μm, respectively (P=0.020). Thirty-eight eyes had corneal thickness measurements below 500 µm; 12% (6 eyes) from males and 28% (16 eyes) from females (P=0.008). All women with corneas below 500 μm were bilaterally thin. This finding differed for men. Corneal thinning was not associated with age, use of systemic hormones, or degree of myopia. Females had steeper keratometry (K) readings (P=0.01 for flat K, P=0.002 for steep K) than males. No differences in layer offset values between normal thickness corneas and thin corneas were evident, suggesting that the reduced thickness was not pathological. Conclusion: The results of this study indicate that a subpopulation of healthy young adults have non-pathologically thin corneas, well below 500 μm; and that these thinner corneas are more frequent in females. This underscores the importance of accurate corneal thickness measurements prior to keratorefractive surgery and when evaluating intraocular pressure in glaucoma.

Anterior segment optical coherence tomography: its application in clinical practice and experimental models of disease

Optical coherence tomography (OCT) provides non-invasive, high-resolution in vivo imaging of the ocular surface and anterior segment. Over the years, it has become an essential tool for evaluating the anterior segment of the eye to monitor ocular development and ocular pathologies in both the clinical and research fields of ophthalmology and optometry. In this review, the clinical applications relating to the use of anterior segment OCT for imaging and quantifying normal and pathological features of the ocular surface, cornea, anterior chamber, and aqueous outflow system are summarised in a range of human ocular diseases. Applications of anterior segment OCT technology that have improved imaging and quantitation of ocular inflammation in experimental animal models of ocular diseases, such as anterior uveitis, microbial keratitis and glaucoma, are also described. The capacity to longitudinally evaluate anterior segment anatomical changes during development, and inflammation facilitates the understanding of the dynamics of tissue responses, and further enhances the intra-operative in vivo imaging during procedures, such as corneal transplantation and drug delivery. Future developments including in vivo ultrahigh-resolution anterior segment OCT, automated analyses of anterior segment OCT images and functional extensions of the technique, may revolutionise the clinical evaluation of anterior segment, corneal and ocular surface diseases.