Entire thickness profiles of the epithelium and contact lens in vivo imaged with high-speed and high-resolution optical coherence tomography

Optical Coherence Tomography Angiography Analysis of Retinal and Choroidal Vascular Networks during Acute, Relapsing, and Quiescent Stages of Macular Toxoplasma Retinochoroiditis

Purpose

To highlight the advantages of optical coherence tomography angiography (OCTA) in delineating the morphological features of the retinal and choroidal vascular network during acute, relapsing, and quiescent stages of macular toxoplasma retinochoroiditis.

Methods

This prospective study included patients presenting with both active and quiescent ocular toxoplasmoses. OCTA was obtained to diagnose and follow the subsequent vascular network changes at diagnosis and six months after acute presentation.

Results

Twenty-three eyes of 23 patients were included. In active lesions, OCTA showed extensive, well-delineated areas of intense hyposignal and perifoveal capillary arcade disruption in the parafoveal superficial capillary plexus (pSCP) and less extensive hyposignal in the parafoveal deep capillary plexus (pDCP). Signals of decreased deep capillary density and disorganization were also seen in the choroid. In nonactive lesions, OCTA demonstrated a homogenous and equally attenuated grayish hyposignal of the pSCP and pDCP and a partial restoration of the nonperfused choroidal areas.

Conclusion

OCTA is a useful technique for vascular network analysis in toxoplasma retinochoroiditis. It allows the visualization of the different network changes and behaviors during the different stages of the infection.

Large Field of View Corneal Epithelium and Bowman's Layer Thickness Maps in Keratoconic and Healthy Eyes

PURPOSE

To assess differences between epithelium thickness (ET) and Bowman's layer thickness (BLT) maps in keratoconic eyes and healthy eyes.

DESIGN

Cross-sectional study.

METHODS

Setting: institutional.

STUDY POPULATION

47 patients (1 eye) with keratoconus (KC) and 20 healthy subjects (1 eye).

OBSERVATION PROCEDURE

epithelium and Bowman's layer measurements were performed by using custom-designed polarization-sensitive optical coherence tomography (PS-OCT) with a conical scanning optics design. En face corneal ET and BLT maps with a diameter of 11 mm were computed. Main outcome measurements were mean ET and BLT of 25 sectors; the thinnest (minET, minBLT) and thickest sectors (maxET, maxBLT) were assessed. Ratios between thinnest/thickest sectors (R1) and between mean ET and BLT of the inferior temporal quadrant/superior nasal quadrant (R2) were calculated (R1ET, R1BLT; R2ET, R2BLT). Receiver operator characteristic (ROC) curve analysis was used to assess the diagnostic power of statistically different parameters.

RESULTS

In healthy eyes, smooth ET maps were observed. KC eyes showed a "doughnut pattern." The BLT maps of healthy eyes had a smooth appearance, but highly irregular "moth"-like damage pattern could be observed in keratoconic eyes. Highest area under the curve values were found for the thinnest sector of the BLT map, the R1ET, and the thinnest sector of the ET map.

CONCLUSIONS

PS-OCT imaging enables the visualization of significant differences of the corneal epithelium and the Bowman's layer in en face maps covering almost the entire cornea. ET and BLT profiles could clearly show their diagnostic importance for the distinguishing of keratoconic eyes and healthy eyes.

Developments in Contact Lens Imaging: New Applications of Optical Coherence Tomography

Optical coherence tomography (OCT) is a high-speed and non-contact optical imaging technology widely used for noninvasive cross-sectional imaging of biological objects. Two main OCT technologies have been developed: time domain and Fourier domain technologies. The latter can be further divided into spectral domain OCT, which uses a broadband light source and a spectrometer as a detector, and swept source OCT, which employs a quickly-rotating laser source. Advances in OCT technology have made it one of the most helpful devices in ophthalmic practice. Fourier OCT has revolutionized imaging of the posterior segment of the eye, as well as of anterior structures and has enhanced the ability to diagnose and manage patients. It provides high-resolution information about the tear film, contact lens (CL), a qualitative and quantitative assessment of the anterior eye that is important in contact lens fitting, and allows possible eye surface changes while wearing contact lenses to be monitored. Potential swept source OCT technology applications include industrial processes of lens design and quality control. In this paper, we describe clinical applications and outline a variety of multifunctional uses of OCT in the field of refractive error correction with contact lenses.

Thickness changes in the corneal epithelium and Bowman's layer after overnight wear of silicone hydrogel contact lenses

BACKGROUND

To investigate thickness changes in the corneal epithelium and Bowman's layer after overnight silicone hydrogel contact lens (CL) wear by using ultra-high resolution optical coherence tomography (UHROCT).

METHODS

Eleven subjects without CL wearing history were recruited for this study. An UHROCT was used to measure the thickness of the epithelium (ET), Bowman's layer (BT), stroma (ST), and total cornea (CCT) at the center of both eyes. A silicone hydrogel CL was inserted in the right eye of each subject, and the fellow non-CL wearing left eye served as the control. The lens was inserted at 9:30 pm and removed at 8:00 am the next morning. The subjects were evaluated at 9:00 pm (baseline), 9:30 pm (lens insertion), 10:00 pm (before sleep), 7:00 am (waking), 7:30 am, and 8:00 am (lens removal).

RESULTS

Compared to the lens insertion level, the ET of the lens-wearing eye increased by 5.73% at eye opening (P = 0.001). The ET of the non-CL wearing eye and the BT in both eyes did not change after overnight CL wear. Compared to baseline, the CCT of the lens-wearing eye increased by 2.87% upon waking (P = 0.003) and recovered 30 min later (P = 0.555). In contrast, compared to baseline, the CCT of the non-CL wearing eye did not increase upon waking (P = 0.105).

CONCLUSIONS

By using UHROCT, we found that overnight CL wear induced different swelling responses in the various sublayers of the cornea.

TRIAL REGISTRATION

Retrospectively registered. Registration number: ChiCTR1800015115 . Registered 07 March 2018.

Optical Assessment of Soft Contact Lens Edge-Thickness

PURPOSE

To assess the edge shape of soft contact lenses using Gabor-Domain Optical Coherence Microscopy (GD-OCM) with a 2-μm imaging resolution in three dimensions and to generate edge-thickness profiles at different distances from the edge tip of soft contact lenses.

METHODS

A high-speed custom-designed GD-OCM system was used to produce 3D images of the edge of an experimental soft contact lens (Bausch + Lomb, Rochester, NY) in four different configurations: in air, submerged into water, submerged into saline with contrast agent, and placed onto the cornea of a porcine eyeball. An algorithm to compute the edge-thickness was developed and applied to cross-sectional images. The proposed algorithm includes the accurate detection of the interfaces between the lens and the environment, and the correction of the refraction error.

RESULTS

The sharply defined edge tip of a soft contact lens was visualized in 3D. Results showed precise thickness measurement of the contact lens edge profile. Fifty cross-sectional image frames for each configuration were used to test the robustness of the algorithm in evaluating the edge-thickness at any distance from the edge tip. The precision of the measurements was less than 0.2 μm.

CONCLUSIONS

The results confirmed the ability of GD-OCM to provide high-definition images of soft contact lens edges. As a nondestructive, precise, and fast metrology tool for soft contact lens measurement, the integration of GD-OCM in the design and manufacturing of contact lenses will be beneficial for further improvement in edge design and quality control. In the clinical perspective, the in vivo evaluation of the lens fitted onto the cornea will advance our understanding of how the edge interacts with the ocular surface. The latter will provide insights into the impact of long-term use of contact lenses on the visual performance.

Detailed Distribution of Corneal Epithelial Thickness and Correlated Characteristics Measured with SD-OCT in Myopic Eyes

Purpose

To investigate the detailed distribution of corneal epithelial thickness in single sectors and its correlated characteristics in myopic eyes.

Methods

SD-OCT was used to measure the corneal epithelial thickness distribution profile. Differences of corneal epithelial thickness between different parameters and some correlations of characteristics were calculated.

Results

The thickest and thinnest part of epithelium were found at the nasal-inferior sector (P < 0.05) and at the superior side (P < 0.05). respectively. Subjects in the low and moderate myopia groups have thicker epithelial thickness than those in the high myopia group (P < 0.05). Epithelial thickness was 1.39 μm thicker in male subjects than in female subjects (P < 0.001). There was a slight negative correlation between corneal epithelial thickness and age (r = −0.13, P = 0.042). Weak positive correlations were found between corneal epithelial thickness and corneal thickness (r = 0.148, P = 0.031). No correlations were found between corneal epithelial thickness, astigmatism axis, corneal front curvature, and IOP.

Conclusions

The epithelial thickness is not evenly distributed across the cornea. The thickest location of the corneal epithelium is at the nasal-inferior sector. People with high myopia tend to have thinner corneal epithelium than low–moderate myopic patients. The corneal epithelial thickness is likely to be affected by some parameters, such as age, gender, and corneal thickness.

SINGLE ACQUISITION OF THE VITREOUS, RETINA AND CHOROID WITH SWEPT-SOURCE OPTICAL COHERENCE TOMOGRAPHY IN ACUTE TOXOPLASMOSIS

BACKGROUND/PURPOSE

To report the swept-source optical coherence tomography (SS-OCT) findings in a case of acute toxoplasmosis chorioretinitis.

METHODS

A 35-year-old male presented with acute blurry vision and floaters in his left eye. Ophthalmic examination, color photographs, spectral-domain OCT (SD-OCT), enhanced depth imaging OCT (EDI-OCT), SS-OCT and wide-field fluorescein angiography images were obtained to diagnose and follow the subsequent changes of toxoplasmosis chorioretinitis over a 2-month period.

RESULTS

Initial imaging with different modalities of SD- and EDI-OCT including radial vitreous scans and horizontal high-speed B-scan raster lines demonstrated thickening of the posterior hyaloid and acute vitreous cells emanating from the retinal blood vessels, thickening and disorganization of the retinal layers within the chorioretinal lesion, and increased sub-lesional choroidal thickness, respectively. SS-OCT demonstrated all of these same findings in a single 12-mm B-scan. Topical steroids were initiated and imaging over the next 2 months showed separation of the posterior hyaloid, decrease in vitreous cell, and atrophy of the chorioretinal lesion.

CONCLUSION

We report the first SS-OCT images of an acute case of toxoplasmosis chorioretinitis. SS-OCT can visualize the choroidal, retinal, and vitreous changes in a single scan, compared with the different imaging algorithms required with SD-OCT.

In pursuit of objective dry eye screening clinical techniques

Dry eye is a multifactorial, progressive, and chronic disease of the tears and ocular surface. The disease is multi-factorial and has intermittent symptoms. Discomfort, visual disturbance, tear film instability with potential damage to the ocular surface, and increased tear film osmolarity are known associates.

Dry eye is a common clinical problem for eye-care providers worldwide and there is a large number of clinical investigative techniques for the evaluation of dry eye. Despite this, however, there is no globally accepted guideline for dry eye diagnosis and none of the available tests may hold the title of the ‘gold standard’. The majority of the techniques involved in the diagnosis of the disease, particularly for its early stages, has a large degree of subjectivity.

The purpose of this article is to review existing dry eye investigative techniques and to present a new objective dry eye screening technique based on optical coherence tomography.

Corneal epithelial thickness map in long-term soft contact lenses wearers

PURPOSE

To map the corneal epithelial thickness in vivo with Fourier-domain optical coherence tomography in long-term soft contact lens (SCL) wearers.

METHODS

This is a cross-sectional observational study. Forty eyes from 40 normal subjects who had never worn SCL and 40 eyes from 40 SCL wearers who had worn lenses for more than 2 years were enrolled. Corneal epithelium over the entire cornea was topographically imaged using a novel optical coherence tomography system. An epithelial thickness map was automatically generated. Epithelial thicknesses of the central 2-mm, paracentral 2- to 5-mm (P1), and midperipheral 5- to 6-mm (P2) zones were obtained. In addition, the epithelial map variability in P1 and P2 zones, including maximum - minimum (MAX - MIN), map SD, and coefficient of variation (CV), was measured and analyzed.

RESULTS

The average epithelial thickness of the central, P1, and P2 zones was 54.4 ± 1.1 μm, 53.2 ± 2.2 μm, and 52.3 ± 2.0 μm, respectively, in normal eyes and 49.2 ± 1.9 μm, 48.8 ± 2.2 μm, and 48.7 ± 2.8 μm, respectively, in eyes wearing SCL. Compared with normal control subjects, eyes with long-term SCL had significantly thinner epithelial thickness in all three zones (p < 0.05). However, there was no difference in MAX - MIN, SD, and CV of P1 and P2 zones between two groups. In both groups, there was significant difference in the epithelial thickness among different sectors in the paracentral and midperipheral zones.

CONCLUSIONS

There is a decrease in epithelial thickness in subjects who wear SCL long term. Clinicians should take note of the nonuniformity of the paracentral and midperipheral corneal epithelium thicknesses. This method may be useful for detecting early changes in corneal epithelial thickness caused by long-term SCL wear.

Assessment of corneal epithelial thickness in dry eye patients

PURPOSE

To investigate the features of corneal epithelial thickness topography with Fourier-domain optical coherence tomography (OCT) in dry eye patients.

METHODS

In this cross-sectional study, 100 symptomatic dry eye patients and 35 normal subjects were enrolled. All participants answered the ocular surface disease index questionnaire and were subjected to OCT, corneal fluorescein staining, tear breakup time, Schirmer 1 test without anesthetic (S1t), and meibomian morphology. Several epithelium statistics for each eye, including central, superior, inferior, minimum, maximum, minimum - maximum, and map standard deviation, were averaged. Correlations of epithelial thickness with the symptoms of dry eye were calculated.

RESULTS

The mean (±SD) central, superior, and inferior corneal epithelial thickness was 53.57 (±3.31) μm, 52.00 (±3.39) μm, and 53.03 (±3.67) μm in normal eyes and 52.71 (±2.83) μm, 50.58 (±3.44) μm, and 52.53 (±3.36) μm in dry eyes, respectively. The superior corneal epithelium was thinner in dry eye patients compared with normal subjects (p = 0.037), whereas central and inferior epithelium were not statistically different. In the dry eye group, patients with higher severity grades had thinner superior (p = 0.017) and minimum (p < 0.001) epithelial thickness, more wide range (p = 0.032), and greater deviation (p = 0.003). The average central epithelial thickness had no correlation with tear breakup time, S1t, or the severity of meibomian glands, whereas average superior epithelial thickness positively correlated with S1t (r = 0.238, p = 0.017).

CONCLUSIONS

Fourier-domain OCT demonstrated that the thickness map of the dry eye corneal epithelium was thinner than normal eyes in the superior region. In more severe dry eye disease patients, the superior and minimum epithelium was much thinner, with a greater range of map standard deviation.

Vertical and horizontal corneal epithelial thickness profile using ultra-high resolution and long scan depth optical coherence tomography

Purpose

To determine the vertical and horizontal thickness profiles of the corneal epithelium in vivo using ultra-long scan depth and ultra-high resolution spectral domain optical coherence tomography (SD-OCT).

Methods

A SD-OCT was developed with an axial resolution of ∼3.3 µm in tissue and an extended scan depth. Forty-two eyes of 21 subjects were imaged twice. The entire horizontal and vertical corneal epithelial thickness profiles were evaluated. The coefficient of repeatability (CoR) and intraclass correlation (ICC) of the tests and interobserver variability were analyzed.

Results

The full width of the horizontal epithelium was detected, whereas part of the superior epithelium was not shown for the covered super eyelid. The mean central epithelial corneal thickness was 52.0±3.2 µm for the first measurement and 52.3±3.4 µm for the second measurement (P>.05). In the central zone (0–3.0 mm), the paracentral zones (3.0–6.0 mm) and the peripheral zones (6.0–10.0 mm), the mean epithelial thickness ranged from 51 to 53 µm, 52 to 57 µm, and 58 to 72 µm, respectively. There was no difference between the two tests at both meridians and in the right and left eyes (P>.05). The ICCs of the two tests ranged from 0.70 to 0.97 and the CoRs ranged from 2.5 µm to 7.8 µm from the center to the periphery, corresponding to 5.6% to 10.6% (CoR%). The ICCs of the two observers ranged from 0.72 to 0.93 and the CoRs ranged from 4.5 µm to 10.4 µm from the center to the periphery, corresponding to 8.7% to 15.2% (CoR%).

Conclusions

This study demonstrated good repeatability of ultra-high resolution and long scan depth SD-OCT to evaluate the entire thickness profiles of the corneal epithelium. The epithelial thickness increases from the center toward the limbus.