Review Article Clinical Applications Of Anterior Segment .
Hindawi Publishing CorporationJournal of OphthalmologyVolume 2015, Article ID 605729, 12 pageshttp://dx.doi.org/10.1155/2015/605729Review ArticleClinical Applications of Anterior SegmentOptical Coherence TomographySu-Ho Lim1,21Department of Ophthalmology, Yeungnam University College of Medicine, Daegu, Republic of KoreaDepartment of Ophthalmology, Daegu Veterans Health Service Medical Center, 60 Wolgok-ro, Dalseo-Gu, Daegu 704-802, Republicof Korea2Correspondence should be addressed to Su-Ho Lim; mdshlim@gmail.comReceived 20 December 2014; Accepted 21 February 2015Academic Editor: Edward MancheCopyright 2015 Su-Ho Lim. This is an open access article distributed under the Creative Commons Attribution License, whichpermits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Anterior segment optical coherence tomography (AS-OCT) was recently developed and has become a crucial tool in clinicalpractice. AS-OCT is a noncontact imaging device that provides the detailed structure of the anterior part of the eyes. In this review,the author will discuss the various clinical applications of AS-OCT, such as the normal findings, tear meniscus measurement,ocular surface disease (e.g., pterygium, pinguecula, and scleromalacia), architectural analysis after cataract surgery, post-LASIKkeratectasia, Descemet’s membrane detachment, evaluation of corneal graft after keratoplasty, corneal deposits (corneal dystrophiesand corneal verticillata), keratitis, anterior segment tumors, and glaucoma evaluation (angle assessment, morphological analysis ofthe filtering bleb after trabeculectomy, or glaucoma drainage device implantation surgery). The author also presents some interestingcases demonstrated via AS-OCT.1. IntroductionOptical coherence tomography (OCT) is a noncontact opticaldevice that provides cross-sectional images and quantitativeanalysis of the ocular tissues, mainly the posterior segment[1]. In 1994, Izatt et al. [2] presented the first report of theOCT image of the corneal and anterior segment. Anteriorsegment OCT (AS-OCT) has become a crucial tool in clinicalpractice. In this review, the author discussed the variousclinical applications of AS-OCT and its limitations.the contrary, a longer-wavelength system provides deeperpenetration, and a 1310 nm wavelength is strongly absorbedby water in ocular media, and as such, a small amount of thelight reaches the retina.Figure 1 shows the horizontal OCT section of the normalcornea using frame-averaged images. The ophthalmologistcan distinguish a highly reflective tear film over epithelium(a), Bowman’s layer (b), corneal stroma layer (c), Descemet’smembrane (d), and endothelium (e).3. Tear Meniscus Measurement2. Devices and Normal FindingsAnterior-segment OCT systems are categorized by wavelength of light sources; dedicated systems using 1310 nm(Zeiss Visante, Heidelberg SL-OCT, Tomey CASIA, etc.)and systems converted from a retinal scanner using 830 nm(Optovue RTvue, Optovue iVue, Zeiss Cirrus, HeidelbergSpectralis, etc.) [3]. Due to the different light sources, thereare some differences between the two groups. A shorterwavelength (830 nm, near infrared) system provides a higheraxial resolution, but its imaging depth is limited. OnTear film instability with potential damage of the ocularsurface is an important concept in relation to the dry-eyesyndrome [4]. Majority of the conventional tests, however,including the Schirmer test or staining, have the disadvantageof invasiveness, which influences the results [5]. Thus, variousmodalities have been investigated to evaluate the tear film,including AS-OCT.Tear meniscus measurement via AS-OCT seems to beeffective for the quantitative tear evaluation and diagnosis ofthe dry-eye syndrome or of patients with excessive tearing
2Journal of Ophthalmology5. Architectural Analysis of Cataract Surgery:Cornea, Lens, and Biometry(a) (b)(c)(d) (e)Figure 1: Horizontal OCT section of the normal cornea: epithelium(a), Bowman’s layer (b), corneal stroma layer (c), Descemet’s membrane (d), and endothelium (e).with punctal stenosis [5–7]. Tear meniscus measurementwas recommended for taking an image immediately afterblinking, and three parameters were usually measured: thetear meniscus height (TMH), tear meniscus depth (TMD),and tear meniscus area (TMA) [5] (Figure 2). Sizmaz et al.[8] reported that the tear meniscus height was lower inthe patients with Grave’s diseases compared to the normalcontrol, which suggests that the tear function is significantlydisturbed in Grave’s diseases.After the installation of an artificial tear [7] or punctalocclusion [9], AS-OCT was able to quantify a dramaticincrease in tear meniscus. On the contrary, the tear meniscus height was decreased after the four-snip punctoplastyprocedure [6] or dacryocystorhinostomy in the patientswith epiphora [10]. In summary, OCT can be a valuablenoninvasive and quick clinical tool for the evaluation of a tearfilm [9].4. Pterygia, Pinguecula, andScleromalacia after SurgeryAS-OCT can provide high-resolution images of the anatomical relationship between the corneal tissues and pterygiumand the pinguecula [11–13]. Soliman and Mohamed [11]reported that the primary pterygium revealed the elevationof the corneal epithelium by a wedge-shaped mass separatingthe epithelium from the underlying Bowman’s membrane(Figures 3(a) and 3(b)). The image of the pseudopterygiumshowed that the overgrowing membrane was not reallyattached to the underlying cornea (Figure 3(c)). On the contrary, the OCT images of the pinguecula stopped at the limbalarea (Figure 3(d)) [11]. The quantitative data obtained via ASOCT also allow the accurate evaluation of the conjunctivalchanges over time after pterygium surgery with conjunctivalautograft [14] and argon photocoagulation of the pinguecula[12].Besides the results of the previous studies [11–14], theinterpretation of the AS-OCT may be helpful for predictingthe residual corneal opacity after surgery and the difficultyduring tissue dissection (Figures 3(a) and 3(c)). Moreover, thescleral thinning or scleromalacia after surgery can be repairedusing a preserved scleral graft with or without amnioticmembrane transplantation [15]. Fortunately, with the aid ofAS-OCT, the surgeon can consider the residual stromal-bedthickness and can estimate the graft thickness when planningsurgery such as lamellar scleral graft or amniotic-membranetransplantation (Figure 4).AS-OCT was also used to image the clear corneal incisionafter cataract surgery [16–18]. On OCT, radial scans may beperformed at the corneal incision site to analyze the followingparameters: the curvilinear length (the total length betweenthe internal and external wound openings), the linear length(the line between the internal and external wound openings),the angle between the corneal surface tangents, the architectural deformation, and the external depth of the incision[17]. In particular, the OCT image after cataract extractioncan show the detailed wound architecture, including theplane of incision, Descemet’s membrane detachment (DMD),endothelial misalignment, loss of coaptation, and endothelialor epithelium gaping (Figure 5).With regard to the complications, the microaxial cataractsurgery group had slightly fewer undesirable effects on theincision site compared to the biaxial group [16], and thefemtosecond-laser-generated corneal incision had a significantly lower endothelial gaping and endothelial misalignment compared to keratome incision [18].Recently, Nagy et al. [19] reported that AS-OCT imagingwas able to detect the tissue changes within the lens afterfemtosecond laser capsulorhexis and nuclear fragmentation,and there was a case report demonstrating posterior capsularrent in posterior polar cataract detected via AS-OCT [20].In vivo three-dimensional (3D) biometry before and aftercataract surgery was reported by Ortiz and colleagues [21].In conclusion, AS-OCT provides sufficient informationon the wound architecture and the biometric parameters,and thus surgeons can consider the structural stability of thecataract wound incision and can monitor the occurrence ofcomplications.6. Refractive Surgery and Ectatic DisordersKeratectasia is a significant concern for refractive surgery.Therefore, many refractive surgeons have tried to minimizethe incidence of post-LASIK ectasia. The ectasia risk factorscore system provides a screening strategy to help minimizethe risk and suggested that abnormal topography (formefruste keratoconus), residual stromal-bed thickness, age, andpreoperative corneal thickness are important factors [22]. Therecommended residual stromal-bed thickness is 250–325 𝜇m[22, 23].High-resolution OCT is helpful in the visualization offlap thickness, flap interface (flap-stroma relationship), andflap displacement [24]. Reinstein et al. [25] reported that theresidual stromal thickness measured via OCT was thickerthan that measured through very high-frequency ultrasoundin many eyes with insufficient residual stromal thickness.Zhang et al. [26] demonstrated that flaps creased by femtosecond laser were more accurate, reproducible, and uniformcompared to those creased by microkeratome. Timing forchecking the LASIK flap thickness is also important. At oneweek, the surgically induced corneal changes were mostlyresolved, and the interface can be easily seen via OCT. Thus,
Journal of Ophthalmology3TMATMHTMD(a)(b)(c)Figure 2: Tear meniscus measurement by AS-OCT. Normal (a), dry eye syndrome (b), three parameters that were usually measured (c); tearmeniscus height (TMH), tear meniscus depth (TMD), and tear meniscus area (TMA).(a)(b)(c)(d)Figure 3: AS-OCT images of pterygium and pinguecula. Pterygium with corneal opacity (a), pterygium without corneal opacity (b), pseudopterygium (c), and pinguecula (d).(a)(b)Figure 4: Anterior segment photography (a) and OCT image (b) of scleral thinning after surgery.
4Journal of Ophthalmology(a)(b)(c)(d)Figure 5: Architectural analysis of cataract surgery. Well apposed corneal wound (1 plane) (a), loss of cooptation with minimal endothelialmisalignment (2 plane) (b), minimal Descemet’s membrane detachment with epithelial gap (2 plane) (c), and loss of cooptation withendothelial gap (3 plane) (d).Li et al. [27] suggested that this time is best for measuring theflap thickness.The detection of an ectatic change also has clinical pitfalls.Li et al. [28] provided several parameters for detecting theasymmetry and global or focal thinning, as follows: (1) I-S(the difference between the average thickness of the inferioroctant and that of the superior octant) 31 𝜇m; (2) IT-SN(the difference between the inferotemporal octant and thesuperonasal octant) 48 𝜇m; (3) minimum 492 𝜇m; (4)minimum-maximum 63 𝜇m; and (5) the thinnest regionof the cornea is located outside the central 2 mm area. Theysuggested that one abnormal parameter provides suspectkeratoconus, and two or more abnormal parameters providea definite diagnosis (Figure 6).The qualitative and quantitative evaluation of the corneavia AS-OCT before implantation of the intrastromal ringsegment may offer safer surgery [29].Corneal collagen cross-linking (CXL) has emerged as apromising technique to increase corneal stiffness and stabilizethe ectatic corneal leading to inhibition of progression forkeratoconus and postoperative LASIK ectasia [30]. A cornealstromal demarcation line indicates the transition zone (at adepth of approximately 300 𝜇m) between the cross-linkedanterior corneal stroma and the untreated posterior stromaafter CXL [30–33]. AS-OCT can visualize the demarcationline as hyperreflective line and evaluate the depth of theline which is correlated with the effective depth of the CXLtreatment [31–33]. In recent comparative study, both confocalmicroscopy and AS-OCT have similar results in evaluatingthe depth of corneal demarcation line after CXL (confocal306.2 𝜇m versus AS-OCT 300.7 𝜇m) [31]. Yam et al. measureddemarcation line using AS-OCT and showed that it maydecrease with the severity of ectasia and age [32]. And themean depth measured by AS-OCT after CXL treatmentis greater centrally in comparison to nasal and temporaldepths (310.7 𝜇m centrally, 212.1 𝜇m nasally, and 218.0 𝜇mtemporally) [33]. In summary, AS-OCT may also providesufficient monitoring of the depth of the corneal demarcationafter CXL as with confocal microscopy.7. Assessment of Descemet’sMembrane: Descemet’s MembraneDetachment and KeratoplastyDescemet’s membrane detachment (DMD) is considered asevere complication after intraocular surgery and trauma[34, 35]. Some DMDs, however, reattach spontaneouslywith a good prognosis, and a few corneas do not clear inspite of surgical treatment [31]. AS-OCT can demonstratedifferent statuses of the DMD, including planar/nonplanar,local/extensive detachment, and rupture [34–36]. AS-OCT isalso a valuable tool for selecting the appropriate treatmentand for monitoring the treatment outcomes when cornealedema is present [35] (Figure 7).AS-OCT can also provide detailed information on thecornea after various keratoplasty operations, including penetrating keratoplasty (PKP), Descemet’s membrane endothelial keratoplasty (DMEK), and Descemet’s membrane stripping automated endothelial keratoplasty (DSAEK). The previous study [37] suggested that AS-OCT is an effective toolfor the detection of an early graft detachment after DMEK,to determine if secondary intervention is indicated or is to be
Journal of Ophthalmology56 mm 6 mm800780S740700STSN660620580 0.13 1.130.91540TN500460420182FT 189RSB ry statistics within central 5 mm zoneSN-I(2–5 mm):SN-IT(2–5 mm): 149450 91Min:Min-median:Location Y:Min–max:87 760 191Min thickness at ( 1.668 mm, 0.760 mm) indicated as (c)Figure 6: AS-OCT image of post-LASIK keratectasia. Horizontal OCT section demonstrating flap thickness (FT) and residual stromal bedthickness (RSB) (a), pachymetry map (b), and asymmetry parameters (c).1 day1 week1.47 mm 199 𝜇m2.16 mm 327 6 mm 6 mmSNTNITINI(a)2 weeks800780740700660620580540500460420380340300S 6 mm 6 80340300SST6 mm 6 mmSNTNITINI(c)Figure 7: Spontaneous resolution of a detachment of Descemet’s membrane following phacoemulsification. Optical coherence tomography(OCT) images at 1 day after cataract surgery (a) demonstrated superior planar type DMD with diffuse corneal edema. OCT images atpostoperative 1 week (b) and 2 weeks (c) revealed spontaneous resolution of DMD without descemetopexy.
6Journal of Ophthalmologyavoided. Yeh et al. [38] also reported that the one-hour ASOCT scan showed the best predictive value of the six-monthgraft adherence status after DMEK.The wound interface pattern can be shown by AS-OCTduring DSAEK [36] or after PKP. Miyakoshi et al. [39]suggested that AS-OCT is useful for detecting the interfacefluid between the host cornea and the graft during a DSAEK.Similarly, Sung and Yoon [40] showed that the alignmentpattern of the wound interface after PKP differed accordingto the clinical diagnosis before surgery.(a)8. Explanatory Text, Figure 7A 84-year-old male patient with benign prostate hypertrophyhad underwent cataract surgery. During phacoemulsification, posterior capsular rupture was occurred because ofsevere intraoperative floppy iris syndrome. Thus, sulcusplacement of single-piece acrylic IOL with anterior vitrectomy was performed.On 1 day after surgery, slit-lamp examination revealeddiffuse stromal and epithelial edema (central corneal thickness, CCT 704 𝜇m). Optical coherence tomography (OCT)demonstrated superior Descemet’s membrane detachment(DMD, base height, 2.16 mm 327 𝜇m) and stromal thickening. The uncorrected visual acuity (UCVA) was 20/200with no pinhole improvement and IOP was 14 mmHg. However, he deferred intracameral gas injection.On postoperative 1 week, slit-lamp and OCT showedpartial resolution of DMD (1.47 mm 199 𝜇m). On twoweeks after surgery, slit-lamp and OCT displayed uniformattachment of the DMD without any folds or gaps betweenDescemet’s membrane and corneal stroma (CCT 574 𝜇m).The UCVA was improved to 20/32.9. Corneal Deposits: Corneal Dystrophies andCorneal Verticillata (En-Face OCT)When corneal opacities obscure the clinical differentiationbetween the anterior and deep infiltrates, OCT may determine the layers of the accumulation [41]. OCT measurementwas reported to be highly repeatable: 2.1 𝜇m centrally and1.2 𝜇m pericentrally [42]. Thus, AS-OCT provides usefulinformation for the selection and planning depth of surgicalprocedures such as phototherapeutic keratectomy for removing corneal opacities with granular corneal dystrophy [43, 44](Figure 8).Other corneal deposits can also be demonstrated byAS-OCT. To the best of the authors’ knowledge, there hasbeen no case report with amiodarone-induced keratopathydemonstrated by AS-OCT. In a previous study with in vivoconfocal microscopy [45], there were highly reflective andbright intracellular inclusions in the epithelial layers, andthese findings were more evident within the basal cell layerin the patients with amiodarone keratopathy [44–46]. SomeOCT machines can provide particular scan modes, such asen-face scan, which offers a new view of the different layers oftissue, like confocal microscopy [47]. In this patient, highlyreflective and bright intracellular inclusions were observed(b)Figure 8: Anterior segment photography. En-face and horizontalOCT images of corneal deposits. Granular corneal dystrophy (a) andcorneal verticillata (b).mainly in the epithelial basal layer, and cornea verticillata wasalso detected easily in AS-OCT (en-face view) compared tothe conventional slit lamp examination (Figure 8).10. KeratitisIn clinical situations, the necrotic lesion and area of infiltration are not usually clear in microbial keratitis. Thus, itis easy for the cornea perforation and resection to becomeincomplete, and the recurrence of keratitis in severe casesneeded surgical intervention [48]. Fortunately, the use ofOCT allows the objective measurement of the corneal thickness and is an additional method for following microbialkeratitis with greater accuracy compared to biomicroscopyalone [49]. Soliman et al. [50] reported that fungal keratitisgrasped two unique patterns of early localized and diffusenecrotic stromal cystic spaces. Sun et al. [48] suggested thatthe removal of the necrotic tissue combined with conjunctivalflap under the guidance of AS-OCT in the treatment offungal keratitis is a safe and effective method. Similar toa previous report [49], in HSV keratitis with underlyinggranular corneal dystrophy, AS-OCT allowed the preciselocalization of microcystic edema and keratic precipitate inthe subject patient (Figure 9).11. TumorsAS-OCT is a relatively reliable, convenient, and noncontact method for detecting and measuring anterior-segmenttumors [51]. Image analysis [52] comparing UBM and ASOCT with 200 patients, however, revealed the adequate visualization of all tumor margins (95% versus 40%), posteriortumor shadowing (5% versus 72%), and high overall imagequality (80% versus 68%). UBM showed a better resolutionfor a pigmented tumor (66% versus 34%) and nonpigmentedtumors (61% versus 39%). In another study comparing OCTto UBM in a nonpigmented iris tumor, the images of theanterior tumor surface and internal tumor heterogeneitywere equivalent, but the posterior tumor surface was welldefined in 54% of the OCT images versus 100% of the UBM
Journal of Ophthalmology7(a)(b)Figure 9: Herpetic keratitis with granular corneal dystrophy. InHSV keratitis with underlying granular corneal dystrophy, AS-OCTimages (b) allowed the precise localization of microcystic edema(arrow head) and keratic precipitate (arrow) compared to baseline(a).images [53]. In conclusion, UBM showed the superior imagequality and reproducibility of the anterior
Review Article Clinical Applications of Anterior Segment Optical Coherence Tomography Su-HoLim 1,2 Department of Ophthalmology, Yeungnam University College of Medicine, Daegu, Republic of Korea
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