Advances in Anterior Segment Optical Coherence Tomography

Dear Eye Care Professional,

Scientific congresses around the world continue to demonstrate the importance of OCT in anterior segment applications. While the technology was originally conceived for retinal applications, it quickly became apparent that the unique advantages of tomography could also be applied to the anterior segment.

The cornea is essentially a transparent shell bathed on the posterior side in aqueous humor, and on the anterior side in air, both of which present challenges. Corneal Topography, the current gold standard for providing information about the shape of the cornea only provides information about the anterior surface, but not about the tissue itself. Understanding the shape of the posterior surface is fundamental to optimizing refractive surgery, and anterior segment OCT (AS-OCT) provides this information non-invasively, and with an unparalleled level of precision due to the inherent optical resolution of OCT. AS-OCT can also separate the epithelial layer from the stromal layer thereby providing valuable information about keratoconus, refractive surgery outcomes and dry eye disease. Finally, the information it provides about the tissue allows for calculations, measurements and visualization of the structural angles essential for monitoring glaucoma.

Our heritage of innovation in AS-OCT applications dates to the early days of Optovue. In 2007, shortly after introducing the RTVue OCT system, the original Optovue OCT system still in use today, we became the first manufacturer to add AS-OCT capabilities to a retinal imaging OCT system. As the clinical adoption of AS-OCT continued, we added Total Cornea Power (TCP) to help anterior segment surgeons calculate the required intraocular lens (IOL) power for post-laser vision correction patients to optimize surgical outcomes. TCP calculations are now a standard part of the American Society of Cataract and Refractive Surgeons online IOL calculator. The addition of epithelial thickness mapping (ETM) in 2012 allowed eye care professionals a non-invasive, fast and accurate way to assess for early ocular surface changes, and to separate pachymetry into individual stromal and epithelial measurements.

Innovation will not stop here. As OCT speeds increase, it will allow for increases in calculation accuracy such that topographical maps can be created without need of a separate instrument. Additionally, OCT angiography (OCTA) applications of the anterior chamber, although still nascent, are very promising for diseases such as diabetic retinopathy (DR), a disease of the periphery. DR can be assessed with retinal OCTA technology; however, peripheral assessment remains limited. AS-OCTA may very well overcome this limitation by allowing assessment of the blood vessels on the back of the iris.

As with any innovation, strong partners are the cornerstone of success. We would not be able to continue our heritage of innovation without our key opinion leaders and others in the scientific community with whom we regularly collaborate. We acknowledge their contributions with heartfelt appreciation, many of which are showcased in this compendium on AS-OCT applications.

Best,

Jay Wei Founder and CEO Optovue, Inc.

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Table of Contents

Anterior segment imaging: an overview

A brief history of anterior segment imaging

The benefits of AS-OCT

AS-OCT imaging modes

AS-OCT clinical applications

AS-OCT in refractive surgery

AS-OCT in cataract surgery.

AS-OCT in glaucoma diagnosis and management

AS-OCT in keratoconus diagnosis and management

AS-OCT in dry eye diagnosis and management

Case studies

AS-OCT for LASIK enhancement candidate

AS-OCT in post-refractive surgery IOL power calculation

AS-OCT in keratoconus evaluation

AS-OCT in dry eye disease treatment monitoring

Bibliography

A comprehensive listing of peer-reviewed articles related to AS-OCT

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Anterior segment imaging: an overviewThe anterior segment (AS) of the human eye consists of the structures in front of the vitreous humor including the crystalline lens, iris and cornea. These structures govern important aspects of the optical system and significant-ly impact vision. Indeed, pathologic changes in the AS can drastically decrease visual acuity and even lead to blindness.

The development of instruments for characterizing the AS has a long and colorful history. In the early 17th cen-tury, Schiener compared reflections on the corneal surface to those on a series of different-sized glass marbles to assess corneal topography.1 In the 19th century, Placido’s disc proved a major advancement — so much so that some contemporary systems still apply its principle of assessing the reflection of a concentric set of white rings to abet scanning-slit topography or Scheimpflug imaging.

One of the latest additions to the AS imaging armamentarium was optical coherence tomography (OCT). First developed in 1990 for use in an in vivo human eye, OCT is a noncontact imaging technology that produces detailed cross-sectional images (tomography) using low-coherence interferometry in biological tissues.2 OCT has been most widely applied to imaging of the posterior segment, however, anterior segment OCT (AS-OCT) imaging, first reported in 1994, ultimately became commercially available in 2001.3 AS-OCT is now employed worldwide and has become a crucial tool in many clinical practices for anterior chamber biometry, corneal pachymetric mapping, angle evaluation and high-resolution cross-sectional imaging.

Subject Plane

Lens Plane

Image Plane

Scheimpflug Intersection

Some commercially available AS imaging systems still use Placido disc techniques to enhance image analysis.

Scheimpflug imaging derives from a method for correcting aerial distortion in perspective photographs developed prior to WWI by Theodor Scheimpflug.4

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The benefits of AS-OCTAmong contemporary methods for AS imaging, AS-OCT is experiencing a pronounced increase in utilization in clinics around the world—becoming for many physicians a first-line AS imaging modality. There are compelling technological and practical reasons for this trend.

SpeedIn recent years, OCT image-acquisition speeds have increased several times over. This has in turn dramatically augmented AS imaging performance and diagnostics.

Image qualityThe inherently high image resolution of OCT enables accurate, reproducible AS measurements. Compared with most imaging modalities, OCT has a higher depth resolution. Its spatial resolution also is excellent (on the order of 5 µm), making it ideal for imaging small eye structures.5

Detailed mappingOCT produces highly detailed pachymetry, epithelial thickness and stromal thickness maps that aids in early detection and better management of keratoconus, ectasia, dry eye and corneal thinning conditions. The OCT corneal scan and mapping enables examiners to assess:6

• Thickness of the cornea • Degree of epithelial hyperplasia • Corneal degeneration • Depth of corneal opacities • Scleral melts • Corneal scars and dystrophies

Patient easeAS-OCT is a non-contact methodology that uses infrared wavelengths that do not dazzle the patient. Image capture does not require water immersion or direct probe contact to the eye, averting image distortion and patient discomfort. AS-OCT system speed also ensures fast exams, so patients are in and out in minutes.

The infrared light in an OCT system is broken into two arms—a sample arm and a reference arm. The combination of reflected light from the two produces a high-resolution profile of the sample.

The Optovue Avanti® OCT system captures 70,000 A-scans per second, detecting signals from the entire depth range in parallel, rather than serially—without sacrificing signal-to-noise ratio.7

Computer

Spectrometer

Fiber Coupler

BiomicroscopeOcular

DiffractionGrating

Collimator

LensCCD

DichroicMirror Image

Plane

OcularLens

ScanningMirror

ReferenceMirror

DensityFilter

Glass Block

ScanLens

xz

SLD Light Source

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AS-OCT imaging modesEpithelial thickness mapping (ETM™)ETM is an Optovue technology innovation that is opening new doors in AS diagnosis. It is derived via a radial scan pattern of the cornea, whereby eight meridians are scanned at a scan length of 6mm with a scan density of 1024 A-scans per meridian. Automatic segmentation of the cornea occurs through detection of three boundaries:

• Corneal anterior surface boundary • Epithelial posterior boundary • Corneal posterior surface boundary

The resultant maps of the epithelium and stroma, which are highly detailed, provide subtle insights into patient AS health. Thus it holds the potential to help eyecare practitioners assess AS pathologies sooner than previously possible.8

PachymetryCorneal pachymetry precisely characterizes point-to-point corneal thickness. With the growth of refractive surgical techniques, corneal pachymetry helps determine good candidates for ablation procedures. Pachymetry is also important in evaluating and managing ocular hypertension and glaucoma. AS-OCT pachymetry can discern sub-layer detail and may be able to characterize corneas with pathology that could hinder other imaging techniques.9

ETM involves the scanning of eight meridians at a scan length of 6mm with a scan density of 1024 A-scans per meridian. The scan of each meridian is repeate four times for reliability and accuracy.

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Epithelial thickness map images contrasting a normal eye (L) and one with keratoconus (R).

Pachymetry and epithelial thickness mapping enable precise monitoring of dry eye disease progression.

Baseline Follow-up

Pachymetry change analysis

Epithelial thickness mapping

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Total cornea power (TCP™)Reduced accuracy of IOL power calculation in eyes that have undergone previous corneal refractive surgery is a clinical challenge. Historically, IOL power in such cases has been postulated through statistical averaging. TCP on the other hand computes corneal power from five preoperative measurements: axial length (AL); anterior chamber depth (ACD); net corneal power; posterior corneal power; and central corneal thickness.10 The resul-tant TCP value enables very precise IOL power determination.

Cornea line-scanDifferent AS-OCT applications require different scan protocols. The two principal ones are radial (multiple B-scans in a radial pattern) and high-resolution single-line B-scans. Radial scans enable evaluation of corneal curvature and thickness. A single-line B-scan, however, is the protocol of choice when a high-quality image of an anterior structure (e.g., the anterior chamber angle) is required.

Anterior chamber angle (ACA) scanOCT has become an important tool for assessing ACA and angle closure. Improvement in image resolution and scan speed has facilitated more detailed and comprehensive analyses of the ACA including Schwalbe’s line and Schlemm’s canal.11

AS-OCT can provide a highly detailed depiction of anterior chamber angle anatomy.

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TCP measurement enables precise IOL power determination based on actual measurements rather than postulated values.

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AS-OCT in refractive surgeryPre-surgical planning AS-OCT gives physicians valuable information that aids in the planning of refractive procedures. Optovue’s AS-OCT module provides standard functionality such as high-resolution line scans and radial scans of the cornea as well as proprietary features that include non-contact measuring and mapping of the corneal epithelium and stroma.

When screening patients for a refractive procedure, it is critical to identify those at risk for developing post-oper-ative ectasia. Corneal topography has long been the gold standard for identifying at-risk eyes; however, patients with normal topographical readings and no other risk factors have still developed ectasia following refractive surgery. In these cases, additional information is needed to help to identify patients who may have very early kera-toconus or other ectasias that would put them at risk for a poor surgical outcome. AS-OCT, and more specifically, epithelial thickness mapping (ETM), may provide the needed information. Studies have shown that the epithelial layer demonstrates an irregular thickness pattern in eyes with subclinical keratoconus, indicating that ETM may give the refractive surgeon another means by which to identify patients at risk for post-operative ectasia.12

Assessment of stromal thickness alongside epithelial thickness also provides important information in pre-surgical planning. It has been well documented that the epithelium is highly responsive to changes in the stroma, and that epithelial irregularities may affect surgical outcomes.13 Quantifying the thickness of both the epithelium and stroma before surgery may help the surgeon to select and plan the refractive surgery procedure.

AS-OCT is useful when planning an enhancement procedure as well. AS-OCT cornea line scans with caliper tools can often allow the physician to measure the depth of the previous flaps to properly place the enhancement flaps.

Pentacam image v. epithelial thickness map of eye with subclinical keratoconus. Whereas Pentacam imaging depicts a normal front surface curvature and elevation, pachymetry and epithelial thickness mapping reveal a pattern consistent with early keratoconus.

Pentacam image ETMTM

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Post-surgical managementETM is a valuable tool in the management of post- refractive surgery patients, as it gives the physician a method to quantify epithelial remodeling. Research has shown that the epithelium thickens after refractive surgery, and that the amount of thickening corresponds to the amount of correction.14 Another study demonstrated that epithelial thickness changes are statistically significant three months post-operatively, but that no further significant changes were identified nine months post-operatively. This finding validates the widespread practice of waiting at least three months before performing an enhancement procedure.13

When refractive surgery outcomes are other than expected, ETM may provide information on the cause of the sub-optimal acuity. Epithelial hyperplasia may be present, which should be taken into consideration when planning an enhancement procedure. Lack of epithelial remodeling and abnormal epithelial remodeling after surgery are also measurable via AS-OCT and can guide the surgeon in post-operative decision-making.

AS-OCT may enable visualization and measurement of LASIK flaps without lifting, which can help in the planning of enhancement procedures.

Epithelial thickness map of post-myopic PRK eye shows that epithelial remodeling corresponds to the ablation zone.

ETMTM

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AS-OCT in cataract surgeryCataract challenges in post-refractive surgery patientsMore than 20 million people worldwide15 have undergone laser refractive surgery since the first procedure was performed in the late 1980s. As these patients age and begin to develop cataracts, ophthalmologists are faced with an influx of patients who challenge traditional methods of IOL power calculation in cataract surgery.

These traditional methods are based on a ratio of posterior to anterior corneal curvature; however, this ratio does not always hold true when the front surface of the cornea has been altered by laser vision correction (LVC). Alterna-tively, IOL power may be calculated based on corneal power before refractive surgery and the change in manifest refraction induced by the procedure. Unfortunately, this type of historical data is not always available or completely accurate. These challenges become even greater because post-LVC patients tend to have high vision expectations as evidenced by their decision to have elective vision correction surgery. In this patient cohort, suboptimal visual outcomes following cataract surgery are not well accepted.

Improving accuracy through Total Cornea Power (TCP®)An exclusive feature of the Optovue Avanti OCT system is its Total Cornea Power application, which provides a new way to calculate IOL powers in post-LVC patients by measuring both the front and back surface of the cornea. The OCT-based measurements are then entered into the ASCRS Post-Refractive IOL Calculator to obtain the recommended IOL power.

Several studies have demonstrated that the OCT-based formula provides an accurate IOL power recommendation for post-LVC patients. For example, a 2013 study by David Huang’s group at Casey Eye Institute compared the OCT-based formula to two “no-history” methods that use regression analysis to estimate the corneal power from standard keratometric readings. The re-searchers found that IOL power calculations based on OCT data were within 0.5D of the predicted refraction for 61% of eyes, whereas 46% of post-LVC eyes fell within 0.5D of the predicted refraction when the “no-history” meth-ods were used.16 A 2016 study by Li Wang and associates from the Cullen Eye Institute evaluated the OCT-based method alongside four “no-history” methods and an average of all five formulas used in the study. The OCT-based method resulted in 68.3% of eyes falling within 0.5D of the predicted refraction, while the “no-history” methods produced less accurate results. The percent of eyes falling within 0.5D of the predicted refraction was 58.7% for the Barrett True-K No History; 50% for the Wang-Koch-Maloney; 52.9% for the Shammas; and 55.8% for the Haigis-L. When the outcomes from all five formulas were averaged, 67.3% of eyes fell within 0.5D of the predicted refraction, indicating that the most accurate method of calculating IOL power in post-LVC patients was the OCT-based formula.17

Additional utility of AS-OCT in cataract surgeryAS-OCT may also be used to evaluate cataracts before surgery and to assess corneal incisions and IOL placement following cataract surgery. The cornea line scan and 3D cornea scan provide cross-sectional images of the cornea and measurement tools that enable quantitative analysis.

AS-OCT Total Cornea Power measurements are entered into the ASCRS Post-Refractive IOL Calculator to obtain the recommended IOL power.

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The Optovue Avanti OCT system TCP application calculates IOL powers in post-LVC patients by measuring the front and back surface of the cornea.

Cornea line scan for IOL monitoring reveals posterior capsule opacification, which may affect visual acuity.

Image courtesy of Adil Maftouhi, OD; Centre Rabelais, Lyon, France.

3D cornea scan of a cataract with phacosclerosis helps physicians quantify the level of cataract involvement in decreased vision.

Image courtesy of Adil Maftouhi, OD; Centre Rabelais, Lyon, France.

3D Cornea

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AS-OCT in glaucomaAssessment of the anterior segment is a critical component of the glaucoma workup. Anterior segment exams provide valuable information on angle structure and corneal thickness, both potential indicators of glaucoma. Gonioscopy is the gold standard for visualizing the iridocorneal angle; however, this technique is highly depen-dent on the examiner’s skill and the patient’s cooperation with the exam. A shortfall in either results in subjective outcomes and poor reproducibility. Furthermore, gonioscopy is most often performed at the slit lamp, and slit lamp illumination may cause pupil constriction, which introduces another source of error.18

Highly precise visualization of angle structureAnterior segment OCT (AS-OCT) has become an increasingly popular method of assessing the angle in glauco-ma suspects. Scans are easily captured, do not require contact with the patient and do not cause the pupil to dilate or constrict. AS-OCT enables precise visualization of the angle structure, which some studies suggest may provide information that helps the clinician determine the mechanism of angle closure.19 AS-OCT also allows measurement of the angle opening distance (AOD) and trabecular-iris space area (TISA) to aid in glaucoma diagnosis and assess response to treatment. Most anterior segment OCT systems are also capable of performing pachymetry, which enhances their usability in the diagnosis of glaucoma.18

The AS-OCT angle scan allows detailed study of the anterior chamber angle with quantification of TISA and AOD.

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AS-OCT in glaucoma surgery planningResearchers have also investigated the role of AS-OCT in planning for glaucoma surgery. Sung and associates looked at the anterior chamber angle structure of patients planning to undergo laser peripheral iridotomy (LPI). They found that patients with a thin peripheral iris and less AOD had better outcomes from LPI, whereas pa-tients with a thicker peripheral iris experienced fewer positive effects from the procedure.20 Recently, minimally invasive glaucoma surgery (MIGS) procedures have grown in popularity and resulted in another application of AS-OCT.19 MIGS procedures attempt to reduce IOP by targeting the trabecular meshwork, which is responsible for the majority of outflow of aqueous humor from the eye. As a result, physicians need to be able to clearly visualize the trabecular meshwork, which is possible with spectral domain AS-OCT.

AS-OCT in post-surgical management of glaucoma patientsFinally, AS-OCT plays an important role in the management of glaucoma patients after surgery. Angle assess-ment is important to determine whether a procedure has successfully increased the AOD. AS-OCT also enables physicians to visualize drainage devices to determine their position and assess their functionality.18 For patients who have undergone trabeculectomy, AS-OCT may be used to assess the filtering bleb, and researchers have shown that bleb morphology (specifically, wall uniformity and internal reflectivity on AS-OCT) are directly cor-related to IOP control.19

AS-OCT provides valuable and reliable information to clinicians diagnosing glaucoma as well as surgeons who treat glaucoma patients. Furthermore, AS-OCT is often used to educate patients on their condition, explain the importance of compliance with glaucoma medications and describe surgical procedures and outcomes.

AS-OCT enables visualization of stent placement to assess position and patency.21

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AS-OCT in keratoconusThe importance of early diagnosisKeratoconus is a progressive disorder without a cure, However, the FDA’s clearance of corneal collagen cross-linking (CXL) has provided physicians with a new treatment aimed at halting this degenerative condition, thus it is imperative to diagnose keratoconus in its earliest stages, before vision loss has occurred.

Corneal topography is generally accepted as the standard diagnostic test for keratoconus; however, new re-search into the role of AS-OCT in detecting keratoconus indicates that corneal and epithelial thickness changes may occur in ectatic disease before topographical changes are noted.

Epithelial thickness as a “red-flag” indicatorLi, et al. studied the pachymetric, epithelial and stromal pattern standard deviation (PSD) in normal eyes and eyes with subclinical keratoconus, defined as eyes with normal slitlamp findings, CDVA of 20/20 or better and topographical readings consistent with keratoconus. In normal eyes the epithelium was thickest at the center and thinner superiorly. In contrast, the eyes with subclinical keratoconus showed inferotemporal thinning and supero-nasal thickening. Although all the PSD variables demonstrated high diagnostic accuracy, the authors concluded that epithelial PSD had the greatest potential in the diagnosis of subclinical keratoconus.22

Epithelial (top) and stromal (bottom) thickness maps of a normal eye.

Epithelial (top) and stromal (bottom) thickness maps of an eye with keratoconus show noticeable thinning in the location of the cone.

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Temstet, et al. studied form fruste keratoconus, a term they used to describe a topographically normal eye whose fellow eye has clinically diagnosed keratoconus. This study examined the role of AS-OCT in the identification of form fruste keratoconus and found that epithelial thickness mapping improved the detection of this manifestation of the disease. Specifically, they showed that both the thinnest part of the epithelium and the thinnest part of the cornea were located inferiorly in form fruste keratoconus eyes, whereas the epithelium was thinnest superotem-porally in normal eyes. Furthermore, they found that the thinnest area of the epithelium in form fruste keratoconus was significantly thinner than the thinnest area in normal eyes.23

Epithelial thickness patterns in keratoconic eyesKanellopoulos and Asimellis are among many who have published on epithelial thickness patterns in keratoconus. They describe keratoconic eyes as having overall increased epithelial thickness as well as greater variation in thickness distribution, or “(in simple terms, not only choppy waters, but high tide as well).” Due to the compensatory nature of the epithelium in response to stromal changes, the epithelium tends to form a donut-like pattern in keratoco-nus. Thinning is seen over the apex of the cone where the stroma has bulged and a thicker epithelium surrounds the base of the cone. Their research also found that thickness irregularities corresponded to the stage of the disease.24

For eye care professionals looking to identify keratoconus at its earliest stages and surgeons seeking to avoid operating on eyes at risk for ectasia, AS-OCT adds valuable information that aids in clinical decision-making.

Pentacam imaging (top) and epithelial thickness map (bottom) of keratoconus eye. In this case, keratoconus is assumed to be unilateral.

Pentacam imaging of fellow, normal eye does not indicate keratoconus, but the epithelial thickness map shows a pattern similar to the fellow, keratoconic eye.

Case and images courtesy of Barry Eiden, OD, FAAO.

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AS-OCT in dry eyeThe challenge of definitive DED diagnosisEye care professionals (ECPs) know that definitively diagnosing the cause of dry eye disease (DED) is a challenge confounded by a myriad of tests. Current diagnostic tests include subjective quality of life questionnaires, slit lamp evaluation, fluorescein staining and a range of tear-film assessments. The challenge is that none of these tests is the gold standard of DED diagnosis, nor can any of them independently confirm the cause of this common condition.

As diagnostic technology progresses, new tests for the diagnosis of DED are emerging. AS-OCT is among the promising advancements. Its primary feature used in the study of dry eye has been epithelial thickness mapping, available exclusively from Optovue. Although research into the effects of DED on the corneal epithelium is in its initial stages, investigators agree that the epithelial layer in dry eye patients differs from normal controls.

Effects of DED on the epithelial layerKanellopoulos and Asimellis were among the first to publish on the epithelial layer in DED. Their research found that both central epithelial thickness and average epithelial thickness was greater in DED and that the pattern of epithelial thickness showed greater variability than in normal eyes.25 Cui and associates reported that the epitheli-um thinned superiorly in DED and that the amount of thinning correlated to the severity of the disease. While their research found that central epithelial thickness was not significantly altered in dry eyes, they did find that epithelial thickness distribution was more varied in DED.26 Liang and his team of researchers looked at limbal and conjunc-tival epithelial thickness and reported that the epithelium thickened in the conjunctival region and thinned in the limbal region. Again, the amount of the thickening and thinning directly correlated to dry eye severity.27

Although more research is needed into the correlation between epithelial thickness distribution and DED, it is clear that the corneal epithelium shows greater irregularity with DED than in normal eyes. Given that AS-OCT is relatively quick and easy to perform, obtaining epithelial thickness maps on all dry eye suspects gives the clinician an objective measure of the ocular surface that may guide subsequent diagnostic tests.

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Epithelial thickness map of a dry eye (top) shows greater variability than the epithelial thickness pattern in a normal eye (bottom).

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AS-OCT for LASIK enhancement candidate A 54-year-old female underwent hyperopic LASIK in 2014. Her preoperative programmed refraction was +1.50–0.50X165 OD and +3.00–0.50X178 OS with an aim of –1.50 for monovision in the left eye.

She enjoyed good vision but returned in 2018 with a drift in her distance corrected manifest refraction to +1.25–0.50X5 OD and – 0.50–0.25X150 OS. Her lifestyle demanded better uncorrected near vision, while the overall uncorrected distance vision was acceptable.

Possible surgical options for improving her vision included:

• A relift LASIK enhancement in both eyes to reset the initial aim • HPRK enhancement in both eyes • A recut LASIK flap enhancement in both eyes • Early cataract surgery with a lens implant surgery

Epithelial thickness maps (ETM) acquired with the Avanti OCT showed greater epithelial thickening in the area of the LASIK flap OS, indicating that an HPRK enhancement would likely have a higher probability of post-operative regression and shorter term of visual improvement.

While surgery is still pending in this case, the information added by the ETM scan helped to narrow the surgical enhancement options in this case to a LASIK enhancement or lens implant.

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Case study

The Avanti OCT system’s ETM capabilities helped to narrow surgical options in this case.

Case study courtesy of Mihir Parikh, MD, NVISION Eye Center, San Diego, California.

AS-OCT in post-refractive surgery IOL power calculation A 68-year-old female had a history of myopic LASIK in the right eye. Her pre-LASIK refraction was – 6.25 + 1.50 x 165. Her LASIK was done in 1996, and she presented for a cataract surgery consultation in 2018. Her refraction was –1.75 sphere, and she reported glare and difficulty driving.

Her goal was to be clear with distance vision post-phacoemulsification, so my aim was – 0.75 sphere.

Pre-surgical exam • 20/40 OD • 2+ NS cataract • Glare 20/80 • Axial length: 26.62 • Tap 14 • K 40.15/41.01 x 90 • Well-healed LASIK scar

Without accounting for the prior LASIK, the IOL master called for a 17 diopter lens, which would have resulted in a significant hyperopic surprise.

Since I had no access to the pre-LASIK K’s, I ran the TCP scan and input the data into the ASCRS calculator. The calculator recommended an 18.5 diopter lens, which achieved the goal. Following surgery, the patient is –0.75 sphere with 20/20 acuity.

From IOL Master

ACD (mm) 3.48 Valid

AL (mm) 26.62 Valid

From OCT Scan #1 Scan #2

Net Corneal Power (D) 39.12 39.11

Anterior Corneal Power (D) 45.10 45.11

Posterior Corneal Power (D) – 6.08 – 6.10

Central Corneal Thickness (µm) 541.00 543.00

IOL Power Calculation Results

IOL Power (D) 18.38

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Case study

IOL power data was extracted from the corneal power measurements made by the Optovue Avanti OCT system.

Case study courtesy of Jason Bacharach, MD, North Bay Eye Associates, Petaluma, California.

Right/OD

Left/OS

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AS-OCT in keratoconus evaluationA 32-year old woman relocated and was referred for keratoconus care. Her right eye was clinically keratoconic and stable for a number of years. Her previous doctor had determined that the left eye was not keratoconic.

Pentacam imaging of the right eye shows classic feature of keratoconus including anterior and posterior abnor-malities. The left eye has normal front surface curvature and elevation, can be refracted to 20/20 and shows no slit lamp findings of keratoconus. However, Pentacam imaging of the left posterior cornea is abnormal. The pachymetry map shows thinning in both eyes along with pronounced epithelial thinning centrally surrounded by thickening, a pattern often seen with more advanced keratoconus.

Based on the irregular posterior cornea, pachymetry and epithelial thickness map, a diagnosis of keratoconus is made in the right eye.

Case study

Case study courtesy of Barry Eiden, OD, FAAO. North Suburban Vision Consultants, Deerfield, IL.

Pentacam image of the right eye shows abnormal front and back surface of the cornea and abnormal pachymetry map.

Pentacam image of the left eye shows a normal front surface elevation with abnormal back surface elevation and abnormal pachymetry map.

Pachymetry and epithelial thickness maps show irregularities OU.

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AS-OCT in dry eye disease treatment monitoring A patient presented with blepharitis due to Meibomian gland dysfunction (MGD). The epithelial thickness map demonstrated inferior epithelial hyperplasia likely caused by moderate dry eye with MGD. A daily regimen of warm compresses and lid scrubs to clean the eyelids was prescribed.

One week later, the epithelial thickness map showed a reduction in the epithelial hyperplasia indicating that the prescribed treatment was having an effect on the patient’s dry eye disease. Follow-up exams at one and three months confirmed the positive impact of the treatment.

Case study

Case study courtesy of Adil El Maftouhi, OD, Centre Rabelais , Lyon, France.

Baseline One month of dry eye treatment Three months of dry eye treatment

AS-OCT Bibliography2017

1. Voskresenskaya A, Pozdeyeva N, Vasilyeva T, Batkov Y, Shipunov A, Gagloev B, Zinchenko R. Clinical and morphological manifestations of aniridia-associated keratopathy on anterior segment optical coherence tomography and in vivo confocal microscopy. Ocul Surf. 2017 Jul 8. pii: S1542-0124(17)30103-9. doi: 10.1016/j.jtos.2017.07.001. [Epub ahead of print].

2. Mansoori T, Balakrishna N. Intrasession repeatability of pachymetry measurements with RTVue XR 100 optical coherence tomography in normal cornea. Saudi J Ophthalmol. 2017 Apr-Jun;31(2):65-68. Epub 2017 Apr 9.

3. Mansoori T, Balakrishna N. Repeatability and agreement of central corneal thickness measurement with non-contact methods: a comparative study. Int Ophthalmol. 2017 Apr 22. doi: 10.1007/s10792-017-0543-1. [Epub ahead of print].

4. Ang M, Devarajan K, Das S, Stanzel T, Tan A, Girard M, Schmeterer L, Mehta J. Comparison of anterior segment optical coherence tomogra-phy angiography systems for corneal vascularisation. Br J Ophthalmol. 2017 Sep 22. pii: bjophthalmol-2017-311072. [Epub ahead of print].

5. Pashtaev NP, Pozdeeva NA, Voskresenskaya AA, Gagloev BV, Shipunov AA. Comparative analysis of the value of information provided by anterior segment optical coherence tomography and confocal laser scanning microscopy for identifying the palisades of Vogt in normal limbus. [Article in Russian; Abstract available in Russian from the publisher]. Vestn Oftalmol. 2017;133(1):60-69.

6. Schallhorn JM, Tang M, Li Y, Louie DJ, Chamberlain W, Huang D. Distinguishing between contact lens warpage and ectasia: Usefulness of optical coherence tomography epithelial thickness mapping. J Cataract Refract Surg. 2017 Jan;43(1):60-66.

7. Chandapura RS, Shetty R, Shroff R, Shilpy N, Francis M, Sinha Roy A. OCT layered tomography of the cornea provides new insights on remod-eling after photorefractive keratectomy. J Biophotonics. 2017 Jul 12. doi: 10.1002/jbio.201700027. [Epub ahead of print].

8. Tomilova EV, Nemsitsveridze MN, Panova IE. Effect of medicinal treatment on epithelial wound healing after phacoemulsification. [Article in Russian; Abstract available in Russian from the publisher]. Vestn Oftalmol. 2017;133(3):44-50. doi: 10.17116/oftalma2017133344-50.

9. Ishida T, Jonas JB, Ishii M, Shinohara K, Ikegaya Y, Ohno-Matsui K. Peripapillary Arterial Ring of Zinn-Haller in Highly Myopic Eyes as Detected by Optical Coherence Tomography Angiography. Retina. 2017 Feb;37(2):299-304.

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11. Kang AS, Welch RJ, Sioufi K, Say EAT, Shields JA, Shields CL. Optical coherence tomography angiography of iris microhemangiomatosis Am J Ophthalmol Case Reports. 2017 Feb;6:24-26. Epub 2017 Feb 13.

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20. Liu Q, Zhou YH, Zhang J, Zheng Y, Zhai CB, Liu J. Comparison of corneal flaps created by Wavelight FS200 and Intralase FS60 femtosec-ond lasers. Int J Ophthalmol. 2016 Jul 18;9(7):1006-10. eCollection 2016.

21. Eroglu FC, Karalezli A, Dursun R. Is optical coherence tomography an effective device for evaluation of tear film meniscus in patients with acne rosacea? Eye (Lond). 2016 Apr;30(4):545-52. Epub 2016 Jan 15.

22. Jung JW, Park SY, Kim JS, Kim EK, Seo KY, Kim TI. Analysis of Factors Associated With the Tear Film Lipid Layer Thickness in Normal Eyes and Patients With Dry Eye Syndrome. Invest Ophthalmol Vis Sci. 2016 Aug 1;57(10):4076-83.

23. Lang AJ, Holliday K, Chayet A, Barragán-Garza E, Kathuria N. Structural Changes Induced by a Corneal Shape-Changing Inlay, Deduced From Optical Coherence Tomography and Wavefront Measurements. Invest Ophthalmol Vis Sci. 2016 Jul 1;57(9):OCT154-61.

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26. Urs R, Lloyd HO, Reinstein DZ, Silverman RH. Comparison of very-high-frequency ultrasound and spectral-domain optical coherence tomog-raphy corneal and epithelial thickness maps. J Cataract Refract Surg. 2016 Jan;42(1):95-101.

27. Wasielica-Poslednik J, Lisch W, Bell K, Weyer V, Pfeiffer N, Gericke A. Reproducibility and Daytime-Dependent Changes of Corneal Epithelial Thickness and Whole Corneal Thickness Measured With Fourier Domain Optical Coherence Tomography. Cornea. 2016 Mar;35(3):342-9. Epub 2016 Jan 6.

28. Gunay M, Celik G, Yildiz E, Bardak H, Koc N, Kirmizibekmez H, Gunay BO, Yesiltepe Mutlu RG. Ocular Surface Characteristics in Diabetic Children. Curr Eye Res. 2016 Dec;41(12):1526-1531. Epub 2016 May 9:1-6.

29. Tang M, Li Y, Chamberlain W, Louie DJ, Schallhorn JM, Huang D. Differentiating Keratoconus and Corneal Warpage by Analyzing Focal Change Patterns in Corneal Topography, Pachymetry, and Epithelial Thickness Maps. Invest Ophthalmol Vis Sci. 2016 Jul 1;57(9):OCT544-9.

30. Kardes E, Sezgin Akçay BI, Unlu C, Ergin A. Choroidal Thickness in Eyes with Fuchs Uveitis Syndrome. Ocul Immunol Inflamm. 2016 Jan 14:1-8. [Epub ahead of print].

31. Allegrini D, Montesano G, Pece A. Optical Coherence Tomography Angiography in a Normal Iris. Ophthalmic Surg Lasers Imaging Retina. 2016 Dec 1;47(12):1138-1139.

32. Fernández-Vigo JI, De-Pablo-Gómez-De-Liaño L, Fernández-Vigo C, Sánchez-Guillén I, Santos-Bueso E, Martínez-de-la-Casa JM, García-Fei-jóo J, Fernández-Vigo JÁ. Quantification of trabecular-iris contact and its prevalence by optical coherence tomography in a healthy Caucasian population. Eur J Ophthalmol. 2016 Dec 16:0. [Epub ahead of print].

33. Skalet AH, Li Y, Lu CD, Jia Y, Lee BK, Husvogt L, Maier A, Fujimoto JG, Thomas CR, Huang D. Optical Coherence Tomography Angiogra-phy Characteristics of Iris Melanocytic Tumors. Ophthalmology. 2016;124(2):197-204. Epub 2016 Nov 14.

34. Li Y, Chamberlain W, Tan O, Brass R, Weiss JL, Huang D. Subclinical keratoconus detection by pattern analysis of corneal and epithelial thickness maps with optical coherence tomography. J Cataract Refract Surg. 2016 Feb;42(2):284-95.

35. Rechichi M, Mazzotta C, Daya S, Mencucci R, Lanza M, Meduri A. Intraoperative OCT Pachymetry in Patients Undergoing Dextran-Free Riboflavin UVA Accelerated Corneal Collagen Crosslinking. Curr Eye Res. 2016 Oct;41(10):1310-1315. Epub 2016 Feb 16.

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49. El Sanharawi M, Sandali O, Basli E, Bouheraoua N, Ameline B, Goemaere I, Georgeon C, Hamiche T, Borderie V, Laroche L. Fouri-er-domain optical coherence tomography imaging in corneal epithelial basement membrane dystrophy: a structural analysis. Am J Ophthalmol. 2015 Apr;159(4):755-63. Epub 2015 Jan 9.

50. Girard MJ, Ang M, Chung CW, Farook M, Strouthidis N, Mehta JS, Mari JM. Enhancement of Corneal Visibility in Optical Coherence Tomography Images Using Corneal Adaptive Compensation. Invest Ophthalmol Vis Sci. 2015 May 15;4(3):3.

51. Liang H, Baudouin C, Tahiri Joutei Hassani R, Brignole-Baudouin F, Labbe A. Photophobia and corneal crystal density in nephropathic cystinosis: an in vivo confocal microscopy and anterior-segment optical coherence tomography study. Invest Ophthalmol Vis Sci. 2015 May;56(5):3218-25.

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52. Hekimoglu E, Erol MK, Toslak D, Turgut Coban D, Doğan B, Yucel O. Comparison of Measurement of Central Corneal Thickness with Spectral Domain Optical Coherence Tomography and Standard Ultrasonic Pachymeter in Premature Infants. J Ophthalmol. 2015;2015:129269. Epub 2015 Jul 22.

53. Bouheraoua N, Hrarat L, Parsa CF, Akesbi J, Sandali O, Goemaere I, Hamiche T, Laroche L, Borderie V. Decreased Corneal Sensation and Subbasal Nerve Density, and Thinned Corneal Epithelium as a Result of 360-Degree Laser Retinopexy. Ophthalmology. 2015 Oct;122(10):2095-102. Epub 2015 Jul 16.

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57. Temstet C, Sandali O, Bouheraoua N, Hamiche T, Galan A, El Sanharawi M, Basli E, Laroche L, Borderie V. Corneal epithelial thickness map-ping using Fourier-domain optical coherence tomography for detection of form fruste keratoconus. J Cataract Refract Surg. 2015 Apr;41(4):812-20.

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66. Kamal S, Ali MJ, Ali MH, Naik MN. Fourier Domain Optical Coherence Tomography With 3D and En Face Imaging of the Punctum and Vertical Canaliculus: A Step Toward Establishing a Normative Database. Ophthal Plast Reconstr Surg. 2015 Feb 3. [Epub ahead of print].

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68. Zheng Y, Zhou Y, Zhang J, Liu Q, Zhai C, Wang Y. Comparison of laser in situ keratomileusis flaps created by 2 femtosecond lasers. Cornea. 2015 Mar;34(3):328-33.

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73. Fernández-Vigo JI, Fernández-Vigo JÁ, Macarro-Merino A, Fernández-Pérez C, Martínez-de-la-Casa JM, García-Feijoó J. Determinants of anteri-or chamber depth in a large Caucasian population and agreement between intra-ocular lens Master and Pentacam measurements of this variable. Acta Ophthalmol. 2016 Mar;94(2):e150-5. Epub 2015 Aug 25.

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75. Kanellopoulos AJ, Georgiadou S, Asimellis G. Objective Evaluation of Planned Versus Achieved Stromal Thickness Reduction in Myopic Femto-second Laser-assisted LASIK. J Refract Surg. 2015 Sep;31(9):628-32.

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76. Bayhan HA, Aslan Bayhan S, Can I. Comparison of central corneal thickness measurements with three new optical devices and a standard ultrasonic pachymeter. Int J Ophthalmol. 2014 Apr 18;7(2):302-8.

77. Nowinska AK, Wylegala E, Teper S, Wróblewska-Czajka E, Aragona P, Roszkowska AM, Micali A, Pisani A, Puzzolo D. Phenotype and genotype analysis in patients with macular corneal dystrophy. Br J Ophthalmol. 2014;98:1514-1521. Published Online First 11 June 2014.

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79. Bouheraoua N, Jouve L, El Sanharawi M, Sandali O, Temstet C, Loriaut P, Basli E, Borderie V, Laroche L. Optical coherence tomography and confocal microscopy following three different protocols of corneal collagen-crosslinking in keratoconus. Invest Ophthalmol Vis Sci. 2014 Oct 28;55(11):7601-9.

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86. Liu YC, Lwin NC, Chan NS, Mehta JS. Use of anterior segment optical coherence tomography to predict corneal graft rejection in small animal models. Invest Ophthalmol Vis Sci. 2014 Sep 23;55(10):6736-41.

87. Liu YC, Teo EP, Adnan KB, Yam GH, Peh GS, Tan DT, Mehta JS. Endothelial approach ultrathin corneal grafts prepared by femtosecond laser for descemet stripping endothelial keratoplasty. Invest Ophthalmol Vis Sci. 2014 Dec 4;55(12):8393-401.

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