Optical coherence tomography of the anterior segment

BCLA CLEAR Presbyopia: Evaluation and diagnosis

It is important to be able to measure the range of clear focus in clinical practice to advise on presbyopia correction techniques and to optimise the correction power. Both subjective and objective techniques are necessary: subjective techniques (such as patient reported outcome questionnaires and defocus curves) assess the impact of presbyopia on a patient and how the combination of residual objective accommodation and their natural DoF work for them; objective techniques (such as autorefraction, corneal topography and lens imaging) allow the clinician to understand how well a technique is working optically and whether it is the right choice or how adjustments can be made to optimise performance. Techniques to assess visual performance and adverse effects must be carefully conducted to gain a reliable end-point, considering the target size, contrast and illumination. Objective techniques are generally more reliable, can help to explain unexpected subjective results and imaging can be a powerful communication tool with patients. A clear diagnosis, excluding factors such as binocular vision issues or digital eye strain that can also cause similar symptoms, is critical for the patient to understand and adapt to presbyopia. Some corrective options are more permanent, such as implanted inlays / intraocular lenses or laser refractive surgery, so the optics can be trialled with contact lenses in advance (including differences between the eyes) to better communicate with the patient how the optics will work for them so they can make an informed choice.

Corneal layer thickness in keratoconus using optical coherence tomography

CLINICAL RELEVANCE

Accurate thickness measurement of corneal layers using anterior segment OCT can be used to improve visual outcomes. Understanding its applications is essential for optometric practices to enhance eye care procedures.

BACKGROUND

To evaluate the thicknesses of different corneal layers for identifying keratoconus (KCN) and subclinical keratoconus (SKCN) using spectral-domain optical coherence tomography (SD-OCT).

METHODS

This prospective study analyzed 60 eyes with KCN, 48 eyes with SKCN, and 53 normal eyes. The central corneal thickness (CCT) and thicknesses of the epithelium, Bowman, stroma, and Descemet-endothelium layers were measured using SD-OCT. One way analysis of variance and the area under the curve (AUC) were used to evaluate the parameters. The Delong method was used to compare AUCs.

RESULTS

In KCN, CCT and thicknesses of epithelium, Bowman, stroma, and Descemet-endothelium layers were 495.5 ± 41.7, 52.6 ± 6.4,11.5 ± 1.4, 415.5 ± 38.9, and 12.3 ± 1.7 µm, respectively. These thickness values were respectively 524.5 ± 33.3, 56.8 ± 6.8, 11.5 ± 1.6, 439.8 ± 30.6, and 12.4 ± 1.7 µm in SKCN and 563.8 ± 37.9, 57.7 ± 6.9, 12.2 ± 1.6, 469.5 ± 33.7, and 12.8 ± 2.1µm in normal group. Total cornea and stroma in KCN and SKCN, and epithelium in KCN were significantly thinner compared to the normal group (P < 0.001). The highest AUC values were observed for CCT in KCN (AUC 0.90) and SKCN (AUC 0.782). The diagnostic accuracy was significantly higher for stromal thickness in KCN (sensitivity 81.7%, specificity 73.6%, AUC 0.871) and SKCN (sensitivity 80.0%, specificity 56.6%, AUC 0.751) than other individual corneal layers (Delong, P < 0.001)                                    .

CONCLUSION

CCT can accurately distinguish keratoconus from normal eyes. However, central corneal stromal thinning was the most sensitive diagnostic index for early detection of SKCN. Developing standardized stromal maps may be helpful for detecting SKCN.

How Can We Diagnose Ocular Surface Squamous Neoplasia With Optical Coherence Tomography?

AIM

We aimed to evaluate the effectiveness of optical coherence tomography (OCT) in the differential diagnosis of anterior segment diseases such as ocular surface squamous neoplasia (OSSN) and pterygium.

METHODS

Patients who were pre-diagnosed with either OSSN (21) or pterygium (19) between January 2020 and November 2022 were included in this retrospective study. Anterior segment photographs and anterior segment optical coherence tomography (AS-OCT) measurements were obtained from each patient. Excisional or incisional biopsy materials underwent pathological evaluation.

RESULTS

Preoperative AS-OCT images of the patients with OSSN showed similarities with histopathological specimens. Both ocular and pathological specimens appeared to have a thicker epithelial layer with a distinct change from healthy to neoplastic epithelium. Preoperative AS-OCT images of individuals with pterygium were also comparable with histopathological samples. Both pathological and AS-OCT images of the pterygium patients showed a normal thickness epithelium and a thickened subepithelial layer under the epithelium. The mean epithelial thickness measured with AS-OCT in OSSN patients was found to be 295.3 ± 111.3 µm, while it was 80.7 ± 43.4 µm in pterygium patients. The difference was statistically significant (P<0.001). The receiver operating characteristic (ROC) curve analysis revealed a cut-off value of 97 µm for the differential diagnosis of OSSN from pterygium, with a sensitivity of 100% and specificity of 94.7%.

CONCLUSIONS

AS-OCT can be used as a noninvasive diagnostic tool for the evaluation of ocular surface lesions. Its ability to distinguish between OSSN and pterygium is demonstrated by the statistically significant difference in epithelial thickness and the significant morphological association with histopathological findings.

Epithelial Remodeling Following Phacoemulsification in Diabetic Patients Using Anterior-Segment Optical Coherence Tomography: A Comparative Study

Purpose

To compare the effect of phacoemulsification on corneal epithelial thickness in diabetic and nondiabetic cataract patients.

Methods

Fifty eyes with cataracts were enrolled in a prospective comparative interventional study. They were divided into two groups: group A (diabetics) and group B (nondiabetics) and underwent uneventful phacoemulsification. Epithelial thickness was assessed in the central, paracentral, and peripheral cornea on the first day and at 1 week, 1 month, and 3 months postoperatively using spectral-domain ocular coherence tomography.

Results

A significant increase in the first-day postoperative central epithelial thickness was noticed in both groups (57.16±3.5 µm and 55.96±2.81 µm in groups A and B, respectively), with increased baseline epithelial thickness of 3.8±2.1 µm and 3.4±2.14 µm in groups A and B, respectively (P<0.001). A significant decrease in epithelial thickness was noticed in both groups after 1 week (−2.40±3.1 µm and −2.76±2.71 µm in group A and B, respectively). No further significant change was noticed in the nondiabetic group at 1 month; however, significant reductions in for central epithelial thickness were found in the diabetic group up to the first month (−0.80±1.9 µm, P=0.05). Central corneal thickness followed the same pattern of change as the epithelium. A nonsignificant delay in visual acuity improvement was noticed in diabetic patients.

Conclusion

Phacoemulsification induces a temporary increase in corneal and epithelial thickness that should resolve by the first week postoperatively. However, diabetic patients had slower epithelial recovery that took up to 1 month, which could be reflected in delayed visual recovery with no effect on the final visual outcome.

New approaches for diagnosis of dry eye disease

We reviewed the literature for different diagnostic approaches for dry eye disease (DED) including the most recent advances, contradictions and promising diagnostic tools and technique. We performed a broad literature search for articles discussing different methods for diagnosis of DED including assessment of tear osmolarity, tear film stability, ocular biomarkers and others. Articles indexed in PubMed and google scholar were included. With the growing cosmetic industry, environmental pollution, and booming of digital screens, DED is becoming more prevalent. Its multifactorial etiology renders the diagnosis challenging and invites the emergence of new diagnostic tools and tests. Diagnostic tools can be classified, based on the parameter they measure, into tear film osmolarity, functional visual acuity, tear volume, tear turnover, tear film stability, tear film composition, ocular biomarkers and others. Although numerous methods exist, the most accurate diagnosis can be reached through combining the results of more than one test. Many reported tests have shown potential as diagnostic/screening tools, however, require more research to prove their diagnostic power, alone or in combination. Future research should focus on identifying and measuring parameters that are the most specific to DED diagnosis.

Use of High-Resolution Optical Coherence Tomography in the Surgical Management of Ocular Surface Squamous Neoplasia: A Pilot Study

PURPOSE

To evaluate whether high-resolution optical coherence tomography (HR-OCT) can detect histologic tumor margins of ocular surface squamous neoplasia (OSSN).

METHODS

Eight eyes of 8 patients with OSSN undergoing excision were studied prospectively. Immediately before surgery, the tumor was imaged using commercially available HR-OCT to identify the conjunctival margins of the neoplastic lesion. The tumor borders of the lesion determined by HR-OCT were mapped in relation to an anatomic reference point and transferred intraoperatively. The tumor was excised with 4-mm margins from the visible edge of the lesion with a "no-touch" technique. The specimens were sent for pathologic analysis and the histologic tumor margin was compared to the HR-OCT predicted tumor border.

RESULTS

Mean age of the 8 patients was 67 ± 9.9 years. Seven were male, 7 were white, and, ethnically, 3 were Hispanic. All 8 tumors were bulbar and in the exposure zone. Seven tumors were limbal. Corneal extension was present in 5. Mean tumor area was 17.5 ± 11.1 mm². Clinically, 2 of the tumors were leukoplakic, 1 papillomatous, and 3 gelatinous. A conjunctival tumor margin identified with the HR-OCT coincided with the pathologically confirmed margin mark in all eyes.

CONCLUSIONS

HR-OCT has the potential to predict histologic tumor margins in OSSN. Optical identification of tumor margins could potentially decrease the incidence of residual positive margins and minimize healthy tissue removal. Advances in HR-OCT technology and integration into a microscope for "real-time" imaging are needed to further improve this technique. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Imaging Techniques in the Diagnosis and Management of Ocular Tumors: Prospects and Challenges

Different types of imaging modalities are used in the diagnosis of ocular cancer. Selection of an imaging modality is based on the features of a tumor as well as the inherent characteristics of the imaging technique. It is vital to select an appropriate imaging modality in diagnosis of ocular tumor with confidence. This review focuses on five most commonly used imaging modalities, i.e., positron emission tomography-computed tomography (PET/CT), single photon emission computed tomography (SPECT), optical coherence tomography (OCT), ultrasound (US), and magnetic resonance imaging (MRI). The principal of imaging modalities is briefly explained, along with their role in the diagnosis and management of the most common ocular tumors such as retinoblastoma and uveal melanoma. Further, the diagnostic features of ocular tumors corresponding to each imaging modality and possibilities of utilizing imaging techniques in the process of ocular drug development are included in this review.

Evaluation of anterior chamber parameters with spectral-domain optical coherence tomography

PURPOSE

To evaluate several anterior chamber parameters in healthy young adults using spectral-domain optical coherence tomography and to describe the repeatability and reproducibility of this method.

STUDY DESIGN

Prospective clinical study.

METHODS

Fifty-two eyes of 52 healthy volunteers were enrolled. Manual measurements of the anterior chamber angle (ACA₅₀₀ and ACA₇₅₀), angle opening distance (AOD₅₀₀ and AOD₇₅₀), angle-to-angle distance (ATA), anterior chamber width (ACW), and lens vault (LV) were obtained.

RESULTS

The mean nasal ACA₅₀₀ was 44.87 ± 12.92°; ACA₇₅₀, 43.94 ± 10.41°; AOD₅₀₀, 672.54 ± 270.19 µm; AOD_750, 881.87 ± 290.55 µm. The mean temporal ACA₅₀₀ was 41.46 ± 11.20°; ACA₇₅₀, 41.27 ± 11.31°; AOD₅₀₀, 603.15 ± 232.28 µm; AOD_750, 823.46 ± 308.76 µm. The differences between the corresponding nasal and temporal parameters were statistically significant. The ACW was 11.97 ± 0.42 mm, the ATA was 12.10 ± 0.43 mm, and the LV was 3.71 ± 232.93 µm. The ACA was highly associated with the LV. The intraclass correlation coefficients ranged from 0.984 to 0.999 for the intraobserver repeatability and from 0.966 to 0.998 for the interobserver reproducibility.

CONCLUSIONS

This study assessed anterior chamber parameters in healthy young adults using spectral-domain optical coherence tomography. This technique reveals the spatial relationships of the ocular structures, provides high-resolution images, and results in high degrees of intraobserver and interobserver repeatabilities.

Role of high resolution optical coherence tomography in diagnosing ocular surface squamous neoplasia with coexisting ocular surface diseases

PURPOSE

Coexistence of an ocular surface disease can mask the typical features of ocular surface squamous neoplasia (OSSN). The purpose of this study was to evaluate high resolution optical coherence tomography (HR-OCT) as an adjunct in the detection and differentiation of OSSN within coexisting ocular surface pathologies.

METHODS

Retrospective study of 16 patients with ocular surface disease and lesions suspicious for OSSN that were evaluated with HR-OCT. HR-OCT images of the lesions were taken to look for evidence of OSSN. Biopsies were performed in all cases, and the HR-OCT findings were compared to the histological results.

RESULTS

Of the 16 patients with OSSN and a coexisting ocular surface disease, 12 were found to have OSSN by HR-OCT and all were subsequently confirmed by biopsy. Two patients had OSSN with rosacea, one with pingueculum, two within pterygia, one with Salzmann' nodular degeneration, six with limbal stem cell deficiency (LSCD)/scarring. In all 12 cases HR-OCT images revealed classical findings of hyper-reflective, thickened epithelium and an abrupt transition from normal to abnormal epithelium. OSSN was ruled out by HR-OCT in four cases (2 Salzmann's, 1 mucous membrane pemphigoid, and 1 LSCD). Negative findings were confirmed by biopsy. HR-OCT was used to follow resolution of the OSSN in positive cases, and it detected recurrence in 1 case.

CONCLUSIONS

While histopathology is the gold standard in the diagnosis of OSSN, HR-OCT can be used to noninvasively detect the presence of OSSN in patients with coexisting ocular conditions.

The role of anterior segment optical coherence tomography in the management of an intra-corneal foreign body

Introduction

Corneal foreign bodies are reported to be the second most common type of ocular injury. Anterior segment optical coherence tomography (AS-OCT) is a valuable tool for the early diagnosis and monitoring the progress of treatment in cases of ocular trauma. Herein we aimed to report on a patient with an intra-corneal foreign body and the role of AS-OCT in management.

Case presentation

A 34-year-old male presented with foreign body sensation in his left eye. Slit-lamp biomicroscopic examination revealed a peripherally located intrastromally embedded foreign body with a free anterior edge extending outwards from the cornea. It was not possible to visualize the foreign body’s entire route through the cornea because of localized corneal edema. AS-OCT showed shadowing of the corneal layers corresponding to the location of the corneal foreign body. A hyper-reflective lesion was observed close to the inside edge of the foreign body in the cornea, indicating that the foreign body had not completely penetrated the cornea. The foreign body was removed via the external route, as it had not completely penetrated the cornea. During the postoperative period the patient was asymptomatic, although the left eye’s cornea healed with scar tissue.

Discussion and Evaluation

AS-OCT facilitates non-invasive rapid imaging of ocular tissue at va rious depths, thereby providing accurate assessment of foreign body characteristics.The location of an intracorneal foreign body and the status of the surrounding ocular structure dictate the optimal surgical technique to be employed.

Conclusions

AS-OCT in the present case facilitated localization and determination of the size of a corneal foreign body. In addition, AS-OCT findings assisted in selection of the appropriate surgical intervention.

Using optical coherence tomography to assess the role of age and region in corneal epithelium and palisades of vogt

Using spectral-domain optical coherence tomography (OCT) to observe the morphology and epithelial thickness (ET) of the palisades of Vogt (POV), and to evaluate the role of age and region on these structures.One hundred twelve eyes of 112 healthy subjects were enrolled and divided into 4 groups: A (0-19), B (20-39), C (40-59), and D (≥60 years old). RTvue-100 OCT was applied on the cornea and the limbus. The morphology of the subepithelial stroma underneath the epithelium of POV was classified into typical and atypical types. Maximum ET of POV was measured manually from OCT images.The positive rate of typical POV in superior, nasal, temporal, and inferior limbus was: Group A: 100%, 69.2%, 65.4%, 100%; Group B: 100%, 73.5%, 61.8%, 94.1%; Group C: 95.8%, 41.7%, 37.5%, 83.3%; Group D: 67.9%, 0%, 3.6%, 25%, showing a significant decreasing tendency with age. The maximum ET of POV in superior, nasal, temporal, and inferior limbus was: Group A: 103.5 ± 10.1 um, 89.2 ± 9.7 um, 87.9 ± 13.6 um, 104.7 ± 14.1 um; Group B: 111.4 ± 15.8 um, 85.3 ± 9.9 um, 88.2 ± 8.6 um, 112.6 ± 19.7 um; Group C: 116.4 ± 16.4 um, 82.8 ± 11.6 um, 87.0 ± 11.6 um, 120.0 ± 25.6 um; Group D: 96.3 ± 17.9 um, 73.8 ± 15.9 um, 79.2 ± 16.7 um, 87.4 ± 18.5 um. Age-dependent change was observed. In general, the maximum ET of POV in superior/inferior quadrants was thicker than the other 2 quadrants.Spectral-domain OCT is a useful tool to observe the limbal microstructure and provide invaluable information. Aging and anatomic regions had significant effects on the microstructure of these areas.

Evaluation of Total Corneal Thickness and Corneal Layers With Spectral-Domain Optical Coherence Tomography

PURPOSE:

To evaluate total corneal thickness and corneal layers in healthy young adults using spectral-domain optical coherence tomography and to describe its repeatability and reproducibility.

METHODS:

Eighty-six eyes from 86 healthy volunteers were prospectively and consecutively enrolled. Manual measurements of central corneal thickness (CCT) and central thickness of epithelium, Bowman's layer, stroma, and the Descemet–endothelium complex were performed using Spectralis OCT (Heidelberg Engineering, Heidelberg, Germany). To assess the reliability of the repeated measurements, intraclass correlation coefficients and coefficients of variation were used.

RESULTS:

Mean CCT, epithelium, Bowman's layer, stroma, and Descemet–endothelium values were 555.50 ± 29.64, 54.60 ± 4.25, 16.70 ± 1.73, 467.51 ± 28.91, and 16.74 ± 1.66 µ m, respectively. The intraclass correlation coefficients ranged from 0.746 (Bowman's layer) to 0.999 (CCT and stroma) and from 0.483 (Bowman's layer) to 0.995 (CCT) and 0.998 (stroma) for intraobserver repeatability and interobserver reproducibility, respectively. The measurements showed coefficients of variation lower than 11% in all cases.

CONCLUSIONS:

This study establishes a normal database for corneal thickness and all its layers in healthy young adults with spectral-domain optical coherence tomography. This device exhibited a high degree of intraobserver repeatability and interobserver reproducibility for all regions except Bowman's layer.

[ J Refract Surg. 2016;32(1):27–32.]

Evaluation of the anterior chamber angle in keratoconus and normal subjects

PURPOSE

To evaluate the anterior chamber angle in keratoconus eyes by use of the Visante™ OCT and Orbscan™ II.

METHODS

Anterior chamber angle was measured with the Visante™ OCT and Orbscan™ II in 52 subjects, 26 KC subjects and 26 age and control subjects.

RESULTS

When comparing the nasal and temporal angles obtained with the two techniques no correlation was found (R(2) always below 0.01) in either the control subjects or in the KC subjects. Despite this, there was an overall statistically significant difference in mean anterior chamber angles (p<0.001) between Visante™ OCT and Orbscan™ II. There was no statistical difference (p>0.05) between nasal and temporal anterior chamber angles when comparing controls and KC subjects with either of the two instruments. In general, the Visante™ OCT gave a smaller estimate of the anterior chamber angle.

CONCLUSION

The values from the Visante™ OCT and Orbscan™ II cannot be interchanged since the difference in measurement of the anterior chamber angle was significantly different between the two instruments.

En-face optical coherence tomography as a novel tool for exploring the ocular surface: a pilot comparative study to conventional B-scans and in vivo confocal microscopy

PURPOSE

To explore the potential of spectral-domain optical coherence tomography (SD-OCT) using the en-face technology for the imaging of ocular surface diseases and to correlate the findings with in vivo confocal microscopy (IVCM) images.

PATIENTS AND METHODS

113 eyes of 75 subjects with various ocular surface diseases were investigated with the RTVue(®) anterior-segment en face OCT. En face OCT images were compared to B-scan OCT and IVCM images.

RESULTS

Patients with corneal dystrophies, corneal deposits, keratitis, pterygium, conjunctivochalasis, or ocular surface squamous neoplasia and patients who underwent lamellar corneal surgeries were included. En-face OCT images showed ocular surface tissue changes that were not discernible using conventional B-scan OCT. Nevertheless, there was a good correlation with IVCM analysis. Compared with IVCM, the major advantages of en-face OCT included easy operation and rapid image acquisition, with minimal operator experience required. In addition, the non-contact method avoided patient discomfort and external pressure on the globe, which was especially useful in patients with corneal dystrophies, ulcers, or corneal abscesses. Although the resolution of en-face OCT was lower than that of IVCM, it allowed useful overall visualization of corneal lesions due to the larger areas analyzed.

CONCLUSION

En-face SD-OCT is a novel, valuable tool to assess a wide variety of ocular surface diseases. It can provide additional information and new insight into different ocular surface conditions with no corneal contact.

Reis-Bücklers corneal dystrophy: a reappraisal using in vivo and ex vivo imaging techniques

PURPOSE

To characterize the phenotype of Reis-Bücklers corneal dystrophy (RBCD) using in vivo and ex vivo imaging techniques.

METHODS

Five RBCD patients with penetrating keratoplasty (PK) were enrolled. Before surgery, all patients underwent a complete ophthalmological examination including slitlamp biomicroscopy, in vivo confocal microscopy (IVCM) and anterior segment (AS) optical coherence tomography (OCT). After PK, corneal buttons were examined by light and transmission electron microscopy (TEM). Correlations between in vivo and ex vivo images were analyzed.

RESULTS

In all cases, irregular geographic-like subepithelial gray-white opacities were observed in the central and mid-peripheral cornea. AS-OCT images of the cornea of all patients revealed hyperreflective homogeneous and continuous deposits concentrated at the level of Bowman's layer and anterior stroma. Using IVCM, a highly reflective irregular amorphous material was observed from intermediate epithelial cells to the anterior stroma. Sparse deposits of highly reflective material were also detected in the posterior stroma. TEM showed in all specimens basal epithelial cells containing small vesicles with rod-shaped dense material.

CONCLUSIONS

IVCM and AS-OCT may be a useful adjunct to biomicroscopy for the diagnosis and management of RBCD. The correlations between the different in vivo and ex vivo imaging techniques emphasize the hypothesis of an epithelial origin for RBCD.

Ultra high-resolution anterior segment optical coherence tomography in the diagnosis and management of ocular surface squamous neoplasia

The development of optical coherence tomography (OCT) technology has helped to usher in a new era of in vivo diagnostic imaging of the eye. The utilization of OCT for imaging of the anterior segment and ocular surface has evolved from time-domain devices to spectral-domain devices with greater penetrance and resolution, providing novel images of anterior segment pathology to assist in diagnosis and management of disease. Ocular surface squamous neoplasia (OSSN) is one such pathology that has proven demonstrable by certain anterior segment OCT machines, specifically the newer devices capable of performing ultra high-resolution OCT (UHR-OCT). Distinctive features of OSSN on high resolution OCT allow for diagnosis and differentiation from other ocular surface pathologies. Subtle findings on these images help to characterize the OSSN lesions beyond what is apparent with the clinical examination, providing guidance for clinical management. The purpose of this review is to examine the published literature on the utilization of UHR-OCT for the diagnosis and management of OSSN, as well as to report novel uses of this technology and potential directions for its future development.

Use of fourier-domain optical coherence tomography to evaluate anterior stromal opacities in donor corneas

Purpose. To evaluate Fourier-domain optical coherence tomography (FD-OCT) as an adjunct to traditional slit lamp examination of donor corneas with suspected Anterior Stromal Opacities. Methods. Seven corneas suspected of having anterior stromal opacities by slit lamp examination were evaluated with FD-OCT. Each cornea was evaluated to confirm the presence of opacity and, if present, the depth of opacity was measured. Results. The opacity depth ranged from 82  μ m to 624  μ m. The initial slit lamp impressions of five of the seven corneas were confirmed by OCT. In two corneas, the OCT findings were different from the initial slit lamp impressions. Slit lamp examination of the first cornea gave the impression of anterior stromal scarring, but OCT showed that the opacity was limited to the epithelium. Slit lamp examination of the second cornea suggested opacity limited to the epithelium, but OCT identified significant sub-Bowman's scarring. In all cases, the Eye Bank Technicians reported that the location and depth of corneal opacity were more sharply defined by OCT than by slit lamp. Conclusion. The high resolution of OCT makes it easier to determine the location of corneal opacities compared to slit lamp examinations. This enhanced visualization can improve decisions regarding transplant suitability of donor corneas.

Ultra-high resolution optical coherence tomography for imaging the anterior segment of the eye

Developments in optical coherence tomography (OCT) have expanded its clinical applications for ultra-high resolution imaging of the anterior segment of the human eye. This review presents the latest advances for imaging the anterior segment of the eye using ultra-high resolution OCT (UHR-OCT). Unique applications of UHR-OCT technology in clinical and basic scientific laboratory research are discussed and a summary of the results is provided. The authors focused on the use of UHR-OCT for imaging of tear dynamics, contact lens interactions with the corneal surface, and in vivo histological diagnosis of disorders of the cornea, as well as the future direction in this field.

Anterior segment tomography with the cirrus optical coherence tomography

Optical coherence tomography (OCT) is an optical acquisition method to examine biological tissues. In recent years, OCT has become an important imaging technology used in diagnosing and following macular pathologies. Further development enabled application of optical coherence tomography in evaluation of the integrity of the nerve fiber layer, optic nerve cupping, anterior chamber angle, or corneal topography. In this manuscript we overview the use of OCT in the clinical practice to enable corneal, iris, ciliary body, and angle evaluation and diagnostics.

Corneal topography from spectral optical coherence tomography (sOCT)

We present a method to obtain accurate corneal topography from a spectral optical coherence tomography (sOCT) system. The method includes calibration of the device, compensation of the fan (or field) distortion introduced by the scanning architecture, and image processing analysis for volumetric data extraction, segmentation and fitting. We present examples of three-dimensional (3-D) surface topography measurements on spherical and aspheric lenses, as well as on 10 human corneas in vivo. Results of sOCT surface topography (with and without fan-distortion correction) were compared with non-contact profilometry (taken as reference) on a spherical lens, and with non-contact profilometry and state-of-the art commercial corneal topography instruments on aspheric lenses and on subjects. Corneal elevation maps from all instruments were fitted by quadric surfaces (as well as by tenth-order Zernike polynomials) using custom routines. We found that the discrepancy in the estimated radius of curvature from nominal values in artificial corneas decreased from 4.6% (without fan distortion correction) to 1.6% (after fan distortion correction), and the difference in the asphericity decreased from 130% to 5%. In human corneas, the estimated corneal radius of curvature was not statistically significantly different across instruments. However, a Bland-Altman analysis showed consistent differences in the estimated asphericity and corneal shape between sOCT topographies without fan distortion correction and the rest of the measurements.

Evaluation of Corneal Epithelial Healing Under Contact Lens with Spectral-Domain Anterior Segment Optical Coherence Tomography (SD-OCT)

Purpose:

To describe a novel technique of using Spectral-domain (SD) anterior segment optical coherence tomography (SD-OCT) in the evaluation of corneal epithelial healing under a therapeutic contact lens (TCL) after lamellar keratoplasty and Epi-LASIK procedures.

Design:

Prospective, non-comparative, observational case series.

Methods:

Ten eyes of eight patients undergoing lamellar corneal transplantation and Epi-LASIK procedures at the Singapore National Eye Centre were included in the study. Ultra-high resolution SD-OCT scans of the cornea with a TCL in-situ were performed sequentially on the first, third and fifth day after procedure, with the RTVue (Optovue, Inc, Fremont, CA, USA), and the image findings were correlated with the clinical picture. Complete epithelial healing was verified with removal of TCL and fluorescein staining.

Results:

5 eyes underwent Descemet’s stripping automated endothelial keratoplasty (DSAEK), 1 eye underwent deep anterior lamellar keratoplasty (DALK) and 4 eyes underwent Epi-LASIK. All eyes had complete epithelial healing with TCL in-situ by the third post-operative day. SD-OCT images were able to demonstrate the epithelial layer distinctly under the TCL in all cases.

Conclusions:

SD-OCT is a valuable imaging tool for monitoring the progression of epithelial healing with TCL in situ in patients following corneal surgical procedures.

In vivo imaging of corneal inflammation: new tools for clinical practice and research

PURPOSE

Infectious and inflammatory corneal diseases are a major cause of blindness. To date, assessment of corneal inflammation, has only been possible by slit-lamp biomicroscopy. The purpose of this study is to review the current state of imaging technologies enabling in vivo imaging of inflammation in the cornea.

METHODS

Literature review of peer-reviewed articles on in vivo imaging modalities.

RESULTS

Current means of diagnosis and treatment follow-up for immune and infectious keratitis are limited to slit-lamp biomicroscopy. Several modalities are currently emerging, allowing for in vivo imaging of corneal inflammation, including in vivo confocal microscopy, anterior segment optical coherence tomography, and intravital multiphoton microscopy.

CONCLUSION

Several in vivo imaging technologies are currently evolving, allowing for objective assessment of corneal inflammation and treatment response.

High-resolution spectral domain optical coherence tomography technology for the visualization of contact lens to cornea relationships

PURPOSE

To study the utility of high-resolution spectral domain optical coherence tomography (HR SOCT) in imaging the contact lens (CL) to cornea relationships with advanced CL designs for ecstatic corneas and corneal refractive therapy.

METHODS

Copernicus HR SOCT (Optopol Technology SA, Zawiercie, Poland) was used to evaluate different lens materials and designs in situ and for the preliminary assessment of the materials and corneal response to hypoxic situations.

RESULTS

SOCT is capable of highlighting very subtle and interesting features of the CL-cornea relationships in a wide range of applications such as in rigid gas-permeable corneal and semiscleral lenses, in corneal refractive therapy and application of CLs in ocular pathology, and in the evaluation of the physiological response of the cornea.

CONCLUSIONS

HR SOCT is a powerful tool capable of providing sharp images of the anterior ocular surface highlighting the relationship between lens and cornea with great detail. This methodology has several applications to enhance fitting modeling with modern designs for advanced CL treatments.

Optical coherence tomography for corneal diseases

Anterior segment optical coherence tomography (OCT) is currently used for investigating the distribution of the corneal thickness, shape of the stromal interface after lamellar corneal surgery, association between host and corneal graft in keratoplasty, dimension of the anterior chamber, and lesions of the corneal diseases. In addition, the advances of OCT technology has enabled three-dimensional imaging, tissue imaging, cell imaging, and topographic analysis. In this review, examples of tissue imaging with 840-nm spectral-domain OCT, cell imaging with full-field OCT, and corneal topographic analysis with 1,310-nm swept-source OCT were introduced.

Optical distortion correction in optical coherence tomography for quantitative ocular anterior segment by three-dimensional imaging

A method for three-dimensional 3-D optical distortion (refraction) correction on anterior segment Optical Coherence Tomography (OCT) images has been developed. The method consists of 3-D ray tracing through the different surfaces, following denoising, segmentation of the surfaces, Delaunay representation of the surfaces, and application of fan distortion correction. The correction has been applied theoretically to realistic computer eye models, and experimentally to OCT images of: an artificial eye with a Polymethyl Methacrylate (PMMA) cornea and an intraocular lens (IOL), an enucleated porcine eye, and a human eye in vivo obtained from two OCT laboratory set-ups (time domain and spectral). Data are analyzed in terms of surface radii of curvature and asphericity. Comparisons are established between the reference values for the surfaces (nominal values in the computer model; non-contact profilometric measurements for the artificial eye; Scheimpflug imaging for the real eyes in vivo and vitro). The results from the OCT data were analyzed following the conventional approach of dividing the optical path by the refractive index, after application of 2-D optical correction, and 3-D optical correction (in all cases after fan distortion correction). The application of 3-D optical distortion correction increased significantly both the accuracy of the radius of curvature estimates and particularly asphericity of the surfaces, with respect to conventional methods of OCT image analysis. We found that the discrepancies of the radii of curvature estimates from 3-D optical distortion corrected OCT images are less than 1% with respect to nominal values. Optical distortion correction in 3-D is critical for quantitative analysis of OCT anterior segment imaging, and allows accurate topography of the internal surfaces of the eye.

Confocal microscopy and optical coherence tomography imaging of hereditary granular dystrophy

OBJECTIVES

This case report examines the clinical characteristics of hereditary granular dystrophy through the use of slit lamp digital photography, confocal microscopy (CM) and optical coherence tomography (OCT). A review of the literature describing the histopathological and genetic associations of stromal dystrophies, suggest it may be possible to differentiate dystrophies based on their clinical manifestations, and appearances of CM and OCT images, with or without the use of genetic testing.

CASE REPORT

Two sisters, previously diagnosed with Granular (Groenouw I) Dystrophy, were examined. Examination included the use of digital slit lamp photography, CM and OCT imaging.

RESULTS

"Breadcrumb" opacities were visualized in the anterior two-thirds of the stroma with all three imaging techniques. Opacities were demonstrated in the posterior third of the stroma with the digital photography and OCT techniques.

CONCLUSIONS

The digital photography, CM and OCT images support the sister's diagnosis of Granular (Groenouw I) Dystrophy. Currently, genetic and histopathological testing are the only techniques available to determine exactly which corneal dystrophy and gene mutation are present. The results of this case report demonstrate that slit lamp digital photography, combined with CM and OCT may be capable of providing sufficient diagnostic information to diagnose corneal granular dystrophies in a clinical setting.