Spectral optical coherence tomography: a new imaging technique in contact lens practice

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.

Characterization of Soft Contact Lens Edge Fitting during Daily Wear Using Ultrahigh-Resolution Optical Coherence Tomography

Purpose

To determine conjunctival overlap over the edge of soft contact lens and to visualize the peripheral postlens tear film (PoLTF) underneath soft contact lenses using ultrahigh-resolution optical coherence tomography (UHR-OCT).

Methods

Twenty participants (4 males and 16 females, 23.0 ± 3.7 years) were fitted with two different types of soft contact lenses randomly. The limbus with lens was imaged with the UHR-OCT at the horizontal meridian every two hours up to 6 hours during lens wear. The conjunctival overlap was ranked as the percentage of the edge covered by the conjunctiva. The frequency of occurrence for visualized peripheral PoLTF was determined.

Results

The average conjunctival overlaps at insertion were 49% and 73% for galyfilcon A and balafilcon A lenses and increased significantly to 84% and 90% by 6 hours of lens wear (P < 0.001). Lenses with rounded edges had more conjunctival overlap than the lenses with angled edges (P=0.014). There were significant decreases for PoLTF on the conjunctiva (P=0.014) and peripheral cornea (P=0.004) over the study period compared to insertion. The percentage of subjects with PoLTF on the conjunctiva (32.5%) and peripheral cornea (36%) were greater in subjects wearing balafilcon A lenses (P=0.017).

Conclusions

Increased conjunctival overlap over the lens edges and reduced PoLTF underneath the peripheral region of soft contact lenses were shown during lens daily wear. The lens edge configuration may play a role in conjunctival response and peripheral PoLTF.

Optical coherence tomography to evaluate the interaction of different edge designs of four different silicone hydrogel lenses with the ocular surface

Purpose

To evaluate the lens edge interaction with the ocular surface with different edge designs using optical coherence tomography and to examine the effect of lens power on the lens edge interactions.

Methods

Four types of silicone hydrogel lenses with different edge designs (round-, semi-round-, chisel-, and knife-edged) at six different powers (+5.0, +3.0, +1.0, −1.0, −3.0, and −5.0 diopters) were fitted to both eyes of 20 healthy volunteers. Optical coherence tomography images were taken at the corneal center and at the limbus within 15–30 minutes after insertion. The images were evaluated with respect to two parameters: conjunctival indentation exerted by the lens edge; and the tear film gaps between the posterior surface of the lens and the ocular surface. The amount of conjunctival indentation was measured with the distortion angle of the conjunctiva at the lens edge.

Results

The degree of conjunctival indentation was highest with the chisel-edged design followed by the semi-round design (P<0.0001). Knife- and round-edged lenses exerted similar levels of conjunctival indentation that was significantly lower compared to chisel-edged lens (P<0.001). For each one of the tested lens edge designs, no significant difference was observed in the conjunctival indentation with respect to lens power. The chisel-edged lens produced the highest amount of conjunctival indentation for each one of the six lens powers (P<0.0001). Post-lens tear film gaps at the limbus were observed at most in the round-edge design (P=0.001).

Conclusion

The fitting properties of contact lenses may be influenced by their edge design but not by their lens power.

Spectral optical coherence tomography vs. fluorescein pattern for rigid gas-permeable lens fit

Background

This study aimed to evaluate anterior segment spectral optical coherence tomography (AS SOCT) for assessing the lens-to-cornea fit of rigid gas-permeable (RGP) lenses. The results were verified with the fluorescein pattern method, considered the criterion standard for RGP lens alignment evaluations.

Material/Methods

Twenty-six eyes of 14 patients were enrolled in the study. Initial base curve radius (BCR) of each RGP lens was determined on the basis of keratometry readings. The fluorescein pattern and AS SOCT tomograms were evaluated, starting with an alignment fit, and subsequently, with BCR reductions in increments of 0.1 mm, up to 3 consecutive changes. AS SOCT examination was performed with the use of RTVue (Optovue, California, USA).

Results

The average BCR for alignment fits, defined according to the fluorescein pattern, was 7.8 mm (SD=0.26). Repeatability of the measurements was 18.2%. BCR reductions of 0.1, 0.2, and 0.3 mm resulted in average apical clearances detected with AS SOCT of 12.38 (SD=9.91, p<0.05), 28.79 (SD=15.39, p<0.05), and 33.25 (SD=10.60, p>0.05), respectively.

Conclusions

BCR steepening of 0.1 mm or more led to measurable changes in lens-to-cornea fits. Although AS SOCT represents a new method of assessing lens-to-cornea fit, apical clearance detection with current commercial technology showed lower sensitivity than the fluorescein pattern assessment.

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.

Retinal, anterior segment and full eye imaging using ultrahigh speed swept source OCT with vertical-cavity surface emitting lasers

We demonstrate swept source OCT utilizing vertical-cavity surface emitting laser (VCSEL) technology for in vivo high speed retinal, anterior segment and full eye imaging. The MEMS tunable VCSEL enables long coherence length, adjustable spectral sweep range and adjustable high sweeping rate (50-580 kHz axial scan rate). These features enable integration of multiple ophthalmic applications into one instrument. The operating modes of the device include: ultrahigh speed, high resolution retinal imaging (up to 580 kHz); high speed, long depth range anterior segment imaging (100 kHz) and ultralong range full eye imaging (50 kHz). High speed imaging enables wide-field retinal scanning, while increased light penetration at 1060 nm enables visualization of choroidal vasculature. Comprehensive volumetric data sets of the anterior segment from the cornea to posterior crystalline lens surface are also shown. The adjustable VCSEL sweep range and rate make it possible to achieve an extremely long imaging depth range of ~50 mm, and to demonstrate the first in vivo 3D OCT imaging spanning the entire eye for non-contact measurement of intraocular distances including axial eye length. Swept source OCT with VCSEL technology may be attractive for next generation integrated ophthalmic OCT instruments.

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.

"In situ" corneal and contact lens thickness changes with high-resolution optical coherence tomography

PURPOSE

To show the use of high-resolution spectral-domain optical coherence tomography (HR-SOCT) for the in situ evaluation of epithelial, stromal, and contact lens (CL) thickness changes under closed-eye conditions without lens removal.

METHODS

Eight young healthy patients wore a thick soft CL for 90 minutes under closed-eye conditions, and measures of epithelial and stromal corneal thickness were obtained at regular intervals using a HR-SOCT (Copernicus HR; Optopol Tech. SA, Zawiercie, Poland).

RESULTS

Minimal changes in epithelial thickness were detected with a transient statistically significant increase in epithelial thickness in the fellow control eye 30 minutes after insertion (P = 0.028). A significant and progressive increase in stromal thickness up to 8% after 90 minutes of lens wear was observed at a constant rate of 2.5% every 30 minutes, being statistically significant in all observations (P < 0.001). Fellow control eyes also showed a significant increase in stromal thickness at a much lower rate of 0.5% every 30 minutes. Lens thickness decreased significantly by 2% after 90 minutes of lens wear under closed-eye conditions (P < 0.001). Individual analysis showed that all eyes displayed stromal swelling, whereas only half of them showed epithelial swelling.

CONCLUSIONS

Increase in stromal thickness and a slight decrease in lens thickness were observed in response to a hypoxic stimulus under closed-eye conditions. HR-SOCT is a powerful tool to investigate in vivo the physiological interactions between cornea and CLs.

Assessment of corneal dynamics with high-speed swept source optical coherence tomography combined with an air puff system

We present a novel method and instrument for in vivo imaging and measurement of the human corneal dynamics during an air puff. The instrument is based on high-speed swept source optical coherence tomography (ssOCT) combined with a custom adapted air puff chamber from a non-contact tonometer, which uses an air stream to deform the cornea in a non-invasive manner. During the short period of time that the deformation takes place, the ssOCT acquires multiple A-scans in time (M-scan) at the center of the air puff, allowing observation of the dynamics of the anterior and posterior corneal surfaces as well as the anterior lens surface. The dynamics of the measurement are driven by the biomechanical properties of the human eye as well as its intraocular pressure. Thus, the analysis of the M-scan may provide useful information about the biomechanical behavior of the anterior segment during the applanation caused by the air puff. An initial set of controlled clinical experiments are shown to comprehend the performance of the instrument and its potential applicability to further understand the eye biomechanics and intraocular pressure measurements. Limitations and possibilities of the new apparatus are discussed.

In situ visualization of tears on contact lens using ultra high resolution optical coherence tomography

OBJECTIVE

To demonstrate the capability of directly visualizing the tear film on contact lenses using optical coherence tomography (OCT).

METHODS

Six eyes of three healthy subjects wearing PureVision and ACUVUE Advance soft and Boston RGP hard contact lenses were imaged with a custom built, high speed, ultra-high resolution spectral domain optical coherence tomograph. Refresh Liquigel was used to demonstrate the effect of artificial tears on the tear film.

RESULTS

Ultra high resolution images of the pre- and post-lens films were directly visualized when each lens was inserted onto the eye. After the instillation of artificial tears during lens wear, the tear film was thicker. The post-lens tear film underneath the lens edge was clearly shown. Interactions between the lens edges and the ocular surface were obtained for each of the lens types and base curves. With a contrast enhancement agent, tear menisci on the contact lenses around the upper and lower eyelids were highlighted. With hard contact lenses, the tear film was visualized clearly and changed after a blink when the lens was pulled up by the lid.

CONCLUSIONS

Ultra-high resolution OCT is a potentially promising technique for imaging tears around contact lenses. This successful demonstration of in situ post-lens tear film imaging suggests that OCT could open a new era in studying tear dynamics during contact lens wear. The novel method may lead to new ways of evaluating contact lens fitting.

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.

Full-range imaging of eye accommodation by high-speed long-depth range optical frequency domain imaging

We describe a high-speed long-depth range optical frequency domain imaging (OFDI) system employing a long-coherence length tunable source and demonstrate dynamic full-range imaging of the anterior segment of the eye including from the cornea surface to the posterior capsule of the crystalline lens with a depth range of 12 mm without removing complex conjugate image ambiguity. The tunable source spanned from 1260 to 1360 nm with an average output power of 15.8 mW. The fast A-scan rate of 20,000 per second provided dynamic OFDI and dependence of the whole anterior segment change on time following abrupt relaxation from the accommodated to the relaxed status, which was measured for a healthy eye and that with an intraocular lens.

Entire contact lens imaged in vivo and in vitro with spectral domain optical coherence tomography

OBJECTIVES

To demonstrate the capability of directly visualizing the entire ocular surface and the entire contact lens on the eye using spectral domain optical coherence tomography (SD-OCT).

METHODS

A custom-built, high-speed, and high-resolution SD-OCT was developed with extended scan depth and width. The eye was imaged before and after wearing a toric soft contact lens (PureVision; Bausch & Lomb). A lubricant eye drop (Soothe; Bausch & Lomb) was instilled in the eye to enhance the image contrast on the lens. The same toric soft contact lens immersed in the contact lens solution was also imaged with a contrast enhancement medium (0.5% Intralipid).

RESULTS

Cross-sectional OCT images of the entire ocular surface were acquired with high-resolution 2,048 x 2,048 pixels. Quantitative surface height map of the ocular surface was obtained from a radial scan data set containing 32 B-scans. With the contrast enhancement agent, the entire toric soft contact lens was clearly visualized, both in vitro and on the eye. The surfaces of the lens were detected and used to generate the thickness maps of the soft contact lens.

CONCLUSIONS

Spectral domain optical coherence tomography with extended scan depth and width is a promising tool for imaging the entire ocular surface shape and soft contact lenses. This successful demonstration suggests that the extended depth SD-OCT is effective in studying ocular surface shape and its interaction with a soft contact lens. The novel method is helpful for the evaluation of contact lens fitting and lens design.

Ultrahigh-resolution measurement by optical coherence tomography of dynamic tear film changes on contact lenses

Purpose. To determine the dynamic pre- and postlens tear film (PLTF and PoLTF) thicknesses by using optical coherence tomography (OCT). Methods. Ultrahigh-resolution OCT was used to image the tear film of 22 subjects before and after contact lens wear. A soft lens with 1 drop of artificial tears on its concave surface was inserted onto one randomly selected eye. OCT images were taken before insertion, immediately afterward, and every 2 minutes for 10 minutes. For the contralateral eye, the lens inserted was not prewetted on the concave surface. OCT images were taken before insertion, immediately afterward, and at 3 minutes. Then another drop was instilled, and images were taken immediately afterward and every 2 minutes for 10 minutes. Images were processed by custom software to yield tear film thickness. Results. The thickness of precorneal tear film (PCTF) was 1.9 +/- 0.9 mum. The PoLTF was visualized clearly in all cases immediately after lens insertion, with 1 drop on the lens concave surface. Through the first 6 minutes after insertion, the PoLTF was greater than the PCTF. The PLTF (n = 12) and PoLTF (n = 9) were visualized immediately after lens insertion. After 3 minutes, the PLTF in most subjects and PoLTF in all subjects were invisible. The thickness of the PLTF increased after the instillation of artificial tears, whereas the PoLTF did not at any checkpoint for 10 minutes. Conclusions. Ultrahigh-resolution OCT is a promising tool for measuring the tear film. The PoLTF did not increase after instillation of artificial tears.

Ultra high-speed swept source OCT imaging of the anterior segment of human eye at 200 kHz with adjustable imaging range

We present an application of in vivo anterior segment imaging of the human eye with an ultrahigh speed swept source OCT instrument. For this purpose, a dedicated OCT system was designed and constructed. This instrument enables axial zooming by automatic reconfiguration of spectral sweep range; an enhanced imaging range mode enables imaging of the entire anterior segment while a high axial resolution mode provides detailed morphological information of the chamber angle and the cornea. The speed of 200,000 lines/s enables high sampling density in three-dimensional imaging of the entire cornea in 250 ms promising future applications of OCT for optical corneal topography, pachymetry and elevation maps. The results of a preliminary quantitative corneal analysis based on OCT data free form motion artifacts are presented. Additionally, a volumetric and real time reconstruction of dynamic processes, like pupillary reaction to light stimulus or blink-induced contact lens movements are demonstrated.

Anterior segment imaging with Spectral OCT system using a high-speed CMOS camera

We describe a new ultrahigh speed Spectral OCT instrument making use of a CMOS camera and demonstrate high quality in vivo imaging of the anterior segment of the human eye. The high flexibility of the designed imaging system allows a wide range of imaging protocols. Two- and three-dimensional high quality OCT images of the cornea, the anterior chamber and the crystalline lens are presented. A high acquisition rate, up to 135,000 A-scans/second enables three-dimensional reconstruction of the anterior segment during lenticular accommodation, blinking and pupillary reaction to light stimulus. We demonstrate OCT tomographic real time imaging of the lens dynamics during accommodation and high quality OCT cross-sectional images of the entire anterior segment of the eye from the cornea up to posterior part of the crystalline lens.

Optical coherence tomography of the anterior segment

Perhaps no diagnostic technology has emerged as rapidly in ophthalmology as optical coherence tomography (OCT). A single clinical device for this noninvasive imaging technique was first released in 1996, and now at least ten clinical devices are available. Although the first clinical anterior segment OCT was marketed only 2 years ago, a substantial amount of work has been done using modified retinal imagers or prototype laboratory-based imagers. In this review, we discuss OCT imaging primarily of the cornea. We also highlight previous and current publications on nonclinical and clinical uses of the device to illustrate how anterior segment OCT can be used to understand corneal structure and function in health and disease.

In vivo corneal high-speed, ultra high-resolution optical coherence tomography

OBJECTIVE

To introduce new corneal high-speed, ultra-high-resolution optical coherence tomography (hsUHR-OCT) technology that improves the evaluation of complicated and uncomplicated cataract, corneal, and refractive surgical procedures.

DESIGN

This case series included a control subject and 9 eyes of 8 patients who had undergone phacoemulsification, Descemet membrane stripping endokeratoplasty, corneal implantation for keratoconus, and complicated and uncomplicated laser in situ keratomileusis. These eyes underwent imaging using a prototype ophthalmic hsUHR-OCT system. All the scans were compared with conventional slitlamp biomicroscopy.

RESULTS

Cross-sectional hsUHR-OCT imaging allowed in vivo differentiation of corneal layers and existing pathologic abnormalities at ultrahigh axial image resolution. These images illustrate the various incisional and refractive interfaces created with corneal procedures.

CONCLUSIONS

The magnified view of the cornea using hsUHR-OCT is helpful in conceptualizing and understanding basic and complicated clinical pathologic features; hsUHR-OCT has the potential to become a powerful, noninvasive clinical corneal imaging modality that can enhance surgical management.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00343473.

Analysis of posterior retinal layers in spectral optical coherence tomography images of the normal retina and retinal pathologies

We present a computationally efficient, semiautomated method for analysis of posterior retinal layers in three-dimensional (3-D) images obtained by spectral optical coherence tomography (SOCT). The method consists of two steps: segmentation of posterior retinal layers and analysis of their thickness and distance from an outer retinal contour (ORC), which is introduced to approximate the normal position of external interface of the healthy retinal pigment epithelium (RPE). The algorithm is shown to effectively segment posterior retina by classifying every pixel in the SOCT tomogram using the similarity of its surroundings to a reference set of model pixels from user-selected area(s). Operator intervention is required to assess the quality of segmentation. Thickness and distance maps from the segmented layers and their analysis are presented for healthy and pathological retinas.

Retinal imaging by spectral optical coherence tomography

PURPOSE

To demonstrate applicability of high speed spectral optical coherence tomography (SOCT) method for imaging retinal pathologies in clinical conditions.

METHODS

SOCT was performed in 67 eyes with different macular diseases. Examinations were carried out with the prototype SOCT instrument constructed in the Institute of Physics, Nicolaus Copernicus University, Toruń, Poland. A broadband superluminescent diode was used as a light source.

RESULTS

The disturbances of retinal layer structure concerning mainly outer segments of photoreceptors were observed in case of central serous chorioretinopathy and choroidal neovascularization in age-related macular degeneration. Large drusen were often related to significant changes of outer nuclear layer thickness and reflectivity.

CONCLUSIONS

SOCT detects small disturbances of the retinal structure and helps to precisely determine layers involved in different pathologies.

In vivo imaging of posterior capsule opacification using Spectral Optical Coherence Tomography

Three years after uneventful extracapsular cataract extraction with implantation of a poly(methyl methacrylate) (PMMA) intraocular lens (IOL) (MZ60BD, Alcon) in a 74-year-old man, the anterior segment of the right eye was photographed with a Canon EOS 300D digital camera and examined with a slitlamp and a prototype spectral optical coherence tomography (SOCT) instrument. Subsequently, a neodymium:YAG laser posterior capsulotomy was performed, followed by another examination. The quality of the SOCT images was adequate for detailed cross-sectional evaluation of the IOL, posterior capsule opacification (PCO), and morphological changes after laser capsulotomy. En face contour maps of PCO distribution were created from 3-dimensional SOCT data. The results presented indicate future applicability of SOCT technology in evaluating modern IOL designs and investigating the process of PCO formation.