Veterinary Ophthalmology (2013) 1–11                                                                                DOI:10...
2 famoseinterference, which is compared with light reflected on a            (14 cases), conjunctival grafts (eight cases),...
sd-oct evaluation of canine and feline cornea 3capture A-scans horizontally on a table or vertically, held            rela...
4 famose                                                                                     Figure 3. Corneal modification...
sd-oct evaluation of canine and feline cornea 5                                                      (a1)                 ...
6 famose   The three corneal foreign bodies (Fig. 6) were charac-               Three cases of major increase of the strom...
sd-oct evaluation of canine and feline cornea 7                                                      (a1)                 ...
8 famose(a1)                                  (a2)                                                                        ...
sd-oct evaluation of canine and feline cornea 9                                                      (a1)                 ...
10 famoselimitation could also be handled by the use of UBM that            investigative field that is comparable to the e...
sd-oct evaluation of canine and feline cornea 11                                                                         1...
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OCT cornea dogs and cats

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Article décrivant l'aspect OCT des principales affections cornéennes du chien et du chat

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OCT cornea dogs and cats

  1. 1. Veterinary Ophthalmology (2013) 1–11 DOI:10.1111/vop.12028Assessment of the use of spectral domain optical coherencetomography (SD-OCT) for evaluation of the healthy andpathological cornea in dogs and catsFrank FamoseService d’Ophtalmologie, Clinique vetrinaire des Acacias, Blagnac, France ´eAddress communications to: AbstractF. Famose Purpose Morphologic evaluation of the cornea is based on the slit-lamp examination.Tel.: +33 5 61712402 In human ophthalmology, optical coherence tomography (OCT) has opened a newFax: +33 5 61716552 field in the clinical approach to anterior segment disorders and more specificallye-mail: frankfamose@gmail.com the cornea. The aim of our study is to describe spectral domain OCT examination of the cornea in dogs and cats in clinical practice conditions. Material and methods One hundred eyes were examined from 52 dogs and 41 cats pre- sented to a private practice referral center with an Optovue iVue SD-OCT device. Sixteen healthy animals were used as control group, and the others were examined for various corneal conditions. All animals were examined after sedation or anesthesia. Results Normal and pathological aspects of canine and feline cornea were described for various conditions such as corneal ulcers, microbial keratitis, corneal sequestrum, infiltrations, foreign bodies, corneal dystrophies, and surgical conditions. Conclusion SD-OCT examination of normal and pathological corneal conditions in dogs and cats gave an accurate evaluation of each component of the cornea. The advantage of the technique is the in vivo, real-time evaluation of all corneal layers with the absence of corneal contact. Constraints included the necessity of sedation for precise focus and the low quality of images obtained with too pigmented or thickened corneas. Key Words: cats, cornea, dogs, keratitis, optical coherence tomography, spectral domain segment spectral domain OCT (SD-OCT) has been theINTRODUCTION subject of more than 500 scientific articles over the lastSeveral imaging methods exist for the evaluation of 5 years. The application of SD-OCT for medical andcorneal morphology. The most frequently used method is surgical purposes has been specifically described for theslit-lamp biomicroscopy, but visualization of deeper cor- structural analysis of tear meniscus, normal and pathologi-neal structures can be limited by light absorption and scat- cal cornea, and iridocorneal angle, as well as evaluation oftering through the cornea, particularly in case of corneal the anterior chamber, iris, and lens.5–16 OCT has alsoedema. The application of new technologies including been compared with slit-lamp examination and with Sche-high-frequency ultrasound (ultrasound biomicroscopy impflug imaging for corneal endothelial evaluation.17[UBM]), confocal microscopy, Scheimpflug imaging, and Spectral domain optical coherence tomography functionoptical coherence tomography (OCT) has led to improved is similar to ultrasonography with a few major differences.resolution and complementary evaluation of corneal Ultrasonography uses ultrasound waves emitted by a probeconditions.1–3 OCT, developed in 1990, was initially dedi- in contact with the tissue to be studied, whereas SD-OCTcated to evaluation of the retina in human ophthalmol- uses infrared (IR) light emitted at a distance from the cor-ogy.4 The use of OCT for the examination of the anterior nea, making contactless image acquisition possible.1 Whilesegment of the eye, a practice started in the early 2000s, optical transparency is not required for ultrasound, thehas opened a new field in the clinical and experimental use of IR light in OCT requires transparent media. Theapproaches to evaluating these structures.1–3 Anterior light passing through different ocular media experiences© 2013 American College of Veterinary Ophthalmologists
  2. 2. 2 famoseinterference, which is compared with light reflected on a (14 cases), conjunctival grafts (eight cases), corneal seques-reference mirror at the same working distance. Scanning tra (five cases), corneal foreign body (three cases), cornealthe reference mirror through a range of distances allows dystrophy (three cases), chronic superficial keratitis (threegeneration of an axial image (A-scan). A series of axial sec- cases), Florida keratopathy (two cases), stromal hemor-tions are combined to produce a composite image, similar rhage (one case), glaucoma with marked corneal edemato the standard two-dimension (B-scan) image produced (two cases), and bullous keratopathy (one case). All ani-in ultrasonography. SD-OCT images have an axial resolu- mals were examined after consent was obtained from theirtion of 2–4 lm and a lateral resolution of 20–25 lm. As a owner. All procedures were performed in accordance withcomparison, the axial resolution of 50-MHz ultrasonogra- the French guidelines for animal care.phy is 50 lm.12 Additional information about technicalfeatures of SD-OCT can be found elsewhere.1,4 Anesthesia Heavy and costly SD-OCT devices were initially lim- All animals examined were sedated or under general anes-ited to specialized human ophthalmology centers or thesia. Cats were anesthetized with 0.01 mg/kg medetomi-research centers. But now, lighter and more affordable dine (Domitorâ, Pfizer, NY, USA) and 5 mg/kg ketaminemodels have become available. The use of SD-OCT for (Imalgene 1000â, Merial, Lyon, France) via intramuscularthe morphological analysis of the cornea of dogs and cats administration. Dogs were anesthetized with 300 lg/m²in healthy and pathological conditions has yet to be medetomidine and 5 mg/kg ketamine delivered intrave-described. Our study aims to evaluate spectral domain nously followed by 0.5–2% isoflurane (Isoflurane Bela-OCT for corneal imaging in dogs and cats in clinical montâ, Nicholas Piramal Ltd, London, UK) in oxygenpractice conditions. after endotracheal intubation. Ophthalmologic examinationMATERIAL AND METHODS All animals were submitted to a thorough ophthalmologicAnimals examination including slit-lamp examination, SchirmerOne hundred eyes were examined in 93 animals. The test, and tonometry. In cases where bacterial infection wasgroup studied included 52 dogs and 41 cats examined suspected, samples were submitted for a bacteriologicbetween July and November 2011 at the Acacias Veteri- analysis in a local laboratory dedicated to veterinary bacte-nary Clinic Ophthalmology department. The healthy ani- riology (Laboratoire Meynaud, Toulouse, France).mal control group included eight dogs and eight cats.Control animals did not have any ocular lesions and were Imaginganesthetized for minor operations with no ocular involve- Imaging was performed using an iVue SD-OCT systemment. The remaining animals (44 dogs and 33 cats) were (Optovue EBC Medical, Paris, France) connected to aanesthetized prior to an examination or ocular surgery for computer interface and a laptop (Fig. 1). The system func-the following conditions: chronic superficial corneal ulcers tions at 840 nm, which is in the IR radiation range, and(13 cases), deep corneal ulcers (10 cases), anterior uveitis can perform 26 000 A-scans per second. The imaging unit(three cases), bacterial keratitis (10 cases), corneal wound has a working distance of 13 mm and can be positioned to (a) (b) Figure 1. The OCT device (a) and the animal in examination position (b). © 2013 American College of Veterinary Ophthalmologists, Veterinary Ophthalmology, 1–11
  3. 3. sd-oct evaluation of canine and feline cornea 3capture A-scans horizontally on a table or vertically, held relatively low reflectivity compared with the pre-cornealin place by an adjustable support for use in the operating tear film and anterior stroma. The stromal layer is thickerroom. For this study, the image capture unit was posi- and appears heterogeneous with an intermediate reflectiv-tioned vertically (Fig. 1a). ity. In the deepest layer, Descemet’s membrane and the The iVue device is designed to examine the retina and endothelium combine as a thin, dense line.the anterior segment. There are two operating modes for The average corneal thickness was 535 lm in dogsimaging the anterior segment, both of which require (interval of values 500–620 lm) and 600 lm in cats (inter-installation of an additional corneal-anterior module (or val of values 540–660 lm). In cats, the heterogeneouslyCAM) at the end of the image capture unit. The ‘pachy- organized anterior stroma was distinguishable from themetry’ mode images eight, 6-mm wide radial sections of posterior stroma where the homogeneous organization ofthe cornea, with the focus line positioned in the center of collagen lamellae was visible (Fig. 2b).the cornea. The ‘angle’ mode images a section along a line In the healthy animals, the average measured epithelialchosen to correspond with the area or interest. thickness was 55 lm in dogs (interval of values 50–60 lm) Animals were placed in dorsal recumbency, with the and 60 lm in cats (interval of values 55–65 lm). Thehead supported by a vacuum cushion (Fig. 1b). The image average measured stromal thickness was 480 lm in dogscapture unit, supported by an articulated arm, was brought (450–560 lm) and 540 lm in cats (485–595 lm). Theclose to the eye and then focused using an adjustment number of healthy animals imaged was not sufficient toknob. Care was taken to humidify the corneal surface with perform a statistical analysis on these parameters, and theartificial tears during imaging to avoid desiccation artifact. endothelio-Descemet layer was not thick enough to beImages were captured using a foot control and converted measured in healthy animals.to two-dimensional B-scans on which it was possible to Although care was taken to humidify the corneal surfacedraw, write, and measure with calipers. Image analysis was during examination, artifact lesions due to superficial cor-performed in the same manner as ultrasound image analy- neal desiccation were observed and appeared as a notch insis and covered three aspects: structure identification, the corneal thickness, with a reduction in epithelial thick-description of lesions by analysis of light interference areas ness (Fig. 3a,b).(increased or reduced reflection), and measurements. Thesame operator (Frank Famose) performed image examina- Epithelial and subepithelial disorderstion and processing. Thirteen chronic epithelial ulcers were examined. The main features observed in both species were an increase in the thickness and reflectivity of the epithelial layer, accom-RESULTS panied by epithelial detachment and a clearly visibleNormal cornea increase in anterior stromal reflectivity (Fig. 4a2). Epithe-Examination in ‘pachymetry’ mode reveals the different lial thickness at the margins of the ulcer ranged from 80layers in the cornea (Fig. 2a,b). The cornea appears as a to 150 lm.composite of three layers of varying reflectivity and thick- Three cases of canine chronic superficial keratitis withness. The epithelial layer appears homogeneous with a corneal melanosis were examined. In all cases, we observed (a)Figure 2. Normal cornea of dog (a) and cat (b)in pachymetric mode. The values in greenrepresent the total thickness of the cornea and (b)that of the epithelium.© 2013 American College of Veterinary Ophthalmologists, Veterinary Ophthalmology, 1–11
  4. 4. 4 famose Figure 3. Corneal modification due to desiccation. The red arrow represents the section area on the macroscopic view (a). OCT (b) revealed reduced epithelial thickness (white(a) (b) arrows). (a1) (a2) Figure 4. Epithelial and subepithelial conditions. The red arrow represents the section area. (a1,a2) Chronic epithelial erosion in a dog. Hyperplastic epithelium is shown by green arrows. Yellow (b1) (b2) arrows show epithelial detachment. Stromal increased density is shown by the white arrows. (b1,b2) Superficial corneal melanosis. The presence of melanocytes is shown by increased superficial reflectivity (yellow arrows). Stromal image is homogeneously attenuated. (c1,c2) Presumed lipid and/or calcic degeneration. Presumed lipid and/or calcic deposits are identified by high reflectivity in the anterior stroma (green arrows). Posterior stroma is unchanged. Epithelium thickness is heterogeneous. Melanosis (yellow arrows) and a (c1) (c2) corneal blood vessel (red arrow) are visible.a sharp increase in the reflectivity of the epithelial layer, thickness was 380 and 530 lm, respectively, presumedwith a homogeneous attenuation of the stromal image lipid and/or calcic deposit depth ranged from 80 to(Fig. 4b1,b2). This increased anterior reflectivity is due to 250 lm. Melanosis, and corneal blood vessels were clini-the presence of melanocytes, including melanic pigments, cally present and visible on OCT scans.which absorb light in the IR range. In the two cases of presumed lipid and/or calcium cor- Stromal disordersneal degeneration, we observed increased anterior stromal Ten cases of suspected bacterial keratitis were evaluated.reflectivity with no modification of the posterior stroma. Positive cultures confirmed the diagnosis in eight of theVariations of the epithelial thickness were observed and ten cases. SD-OCT analysis revealed a reduction inwere associated with the density of the presumed lipid stromal thickness localized to the anterior stroma (Fig. 5).and/or calcium deposits (Fig. 4c1,c2). Total corneal The center of the lesion appeared either as a homoge- © 2013 American College of Veterinary Ophthalmologists, Veterinary Ophthalmology, 1–11
  5. 5. sd-oct evaluation of canine and feline cornea 5 (a1) (a2) (b1) (b2) (c1) (c2)Figure 5. Infectious keratitis and deep ulcers.The red arrow represents the section area. (a1,a2) (d1) (d2)infection with loss of surface substance (greyarrows) in a homogeneous stroma. (b1,b2) deepkeratitis with an area of collagenolysis (yellowarrows) and increased peripheral stromalreflectivity. (c1,c2) deep corneal ulceration. Areaof stromal densification (white arrows) and debris(pink arrow) are visible. Residual stromalthickness can be measured. (d1,d2) deep keratitiswith loss of stromal continuity and centralelevation of deep stroma (green arrows). (e1,e2)Predescemetic lesion. The residual corneal (e1) (e2)thickness is 50 lm.neous loss of stroma or as a heterogeneous association of Spectral domain optical coherence tomography evalua-high- and low-reflectivity zones. High-reflectivity zones tion of deep corneal ulcers revealed a homogeneouscorresponding to cellular infiltration surrounded these increase in stromal reflectivity surrounding the ulceratedlesions. The epithelial layer was partially absent, and in area and the presence of debris at the bottom of the ulcer.some cases of deep stromal destruction, Descemet’s Analysis allowed measurement of the ulcer depth, infor-membrane was pushed forward by intraocular pressure. mation that is critical to choosing the appropriate surgicalResidual stromal thickness was measurable. treatment.© 2013 American College of Veterinary Ophthalmologists, Veterinary Ophthalmology, 1–11
  6. 6. 6 famose The three corneal foreign bodies (Fig. 6) were charac- Three cases of major increase of the stromal thicknessterized by the presence of a posterior cone-shaped shadow were observed. In two cases of glaucoma with an intenserelated to their opacity. Depending on the penetration corneal edema, corneal structure was maintained, but thedepth, an endothelial reaction was visible. Localization of spacing of collagen lamellae was altered (Fig. 9a1,a2). Inthe end of the foreign body was challenging, and serial the other case, a feline bullous keratopathy, the normalscans were required to identify perforations. stromal architecture was severely disrupted, and pockets of We also examined two cases of Florida keratopathy liquid among highly modified stromal structures were(Fig. 7a1,a2). In SD-OCT images, these lesions were observed (Fig. 9b1,b2). Corneal thickness could not becharacterized by a clear increase in superficial and deep measured in either case due to the size of the cornea,stroma reflectivity. This increased reflectivity was deeper which was not entirely visible on the screen.than that observed in the case of stromal hemorrhage(Fig. 7b1,b2). The lesions were not accompanied by epi- Endothelial disordersthelial alteration, an increase in stromal thickness, or In a case of persistent pupillary membrane with localizedincreased IR light reflexion behind the lesions. endothelial dystrophy (Fig. 10a1,a2), a localized endothe- Spectral domain optical coherence tomography imaging lial hyper-reflectivity was observed supported by a sus-of feline corneal sequestrum was challenging. In the five pended structure in the anterior chamber. Filaments werecases examined, sequestrum appeared as an intense, local- difficult to highlight in two-dimensional scans, and serialized light reflection in the anterior stroma. IR light reflec- scans were required to monitor the filament trajectory.tion varied according to the density and thickness of the In the three cases of anterior uveitis, precipitates behindsequestrum. In two cases, the posterior stroma remained the cornea appeared in SD-OCT imaging as highly reflec-visible (Fig. 8a1,a2), making it possible to measure the tive wide-based lesions on the endothelium (Fig. 10b1,b2).thickness of the necrotic area before making a decision A diffuse inhomogeneous granular reflectivity of the ante-concerning an operation. In the three remaining cases, this rior chamber was observed. Anterior synechia appeared aspre-operative evaluation was not possible due to high dense lesions attached to the endothelium in continuitylesion reflectivity (Fig. 8b1,b2). with the anterior face of the iris (Fig. 10c1,c2). (a1) (a2) (b1) (b2) Figure 6. Corneal foreign body. The red arrow represents the section area. Corneal foreign body (FB) appears with a strong IR absorption with posterior cone-shaped shadow (***). Endothelial (c1) (c2) reaction (yellow arrows) is visible. Serial scans (a1–c2) show total corneal perforation. © 2013 American College of Veterinary Ophthalmologists, Veterinary Ophthalmology, 1–11
  7. 7. sd-oct evaluation of canine and feline cornea 7 (a1) (a2)Figure 7. Diffuse stromal lesions. The red arrowrepresents the section area. (a1,a2) Florida spotswith stromal cellular infiltration (white arrows). (b1) (b2)(b1,b2) stromal hemorrage (green arrows). (a1) (a2)Figure 8. Feline corneal sequestrum. The redarrow represents the section area. (a1,a2) cornealsequestrum (grey arrow) with deterioration ofstromal signal. (b1,b2) corneal sequestrum with (b1) (b2)total signal absorption (yellow arrows).Surgical disorders DISCUSSIONCorneal structure was evaluated after conjunctival grafts ineight animals using SD-OCT (Fig. 11a1,a2). The images The goal of this study was to test the feasibility of usingobtained showed a conjunctival structure covered with an SD-OCT to image the cornea in cats and dogs in com-epithelium and embedded in the stroma. The conjunctival mon practice situations. Our results confirm that thisstructure was recognizable due to higher density and the technique is applicable to the evaluation of the cornea inpresence of blood vessels. healthy and pathological conditions. For most cases stud- In the 14 cases of corneal wounds, the images obtained ied, SD-OCT evaluation provides reliable and accuratedid not identify the precise area of perforation. However, additional information to the standard examination usingimages did show the presence of fibrin and blood in the a slit lamp for corneal disorders. Through the study ofanterior chamber (Fig. 11b1,b2). Evaluation of corneal many different conditions, we were able to underline diag-incisions (Fig. 11c1,c2) to check the wound edge junction nosis- and image-related advantages and limitations ofwas possible, although assessment of deep sections of the SD-OCT.stroma was difficult because of the IR absorption related This study is one of the first evaluations of SD-OCTto the corneal edema. for corneal diseases in private practice conditions. This© 2013 American College of Veterinary Ophthalmologists, Veterinary Ophthalmology, 1–11
  8. 8. 8 famose(a1) (a2) Figure 9. Major stromal alterations. (a1,a2) intense corneal edema due to glaucoma in a cat. Collagen lamellae are separated by aqueous hyporeflective material. (b1,b2) Feline Bullous keratopathy. Stromal structure is replaced by(b1) (b2) ‘pockets’ of fluid. (a1) (a2) (b1) (b2) Figure 10. Endothelial alterations. (a1,a2) persistent pupillary membrane with endothelial attachment (grey arrows). (b1,b2) retrokeratic precipitates (green arrows) with heterogeneity of (c1) (c2) anterior chamber. (c1,c2) anterior synechia (green arrows).means, we have evaluated the pathological conditions that The SD-OCT imaging resolution was excellent at allcame through our clinic during the time of the study. depths, and we were able to measure the central corneaAlthough a wide range of conditions has been examined, thickness with a resolution of 5 lm. This measurementmany other conditions such as extended endothelial required the device to be positioned axially in the centerdystrophies or eosinophilic keratitis were not evaluated of the cornea. The results obtained in the ‘pachymetry’because we were not presented with those conditions mode were compatible with available data.18,19 However,during the study. statistical analysis of these data was not the aim of this © 2013 American College of Veterinary Ophthalmologists, Veterinary Ophthalmology, 1–11
  9. 9. sd-oct evaluation of canine and feline cornea 9 (a1) (a2) (b1) (b2)Figure 11. Surgical disorders. The red arrowrepresents the section area. (a1,a2) conjunctivalgraft in a dog. The conjunctiva (green arrows) isdenser than the cornea and has blood vessels(yellow arrows). (b1,b2) traumatic cornea wound.Blood clot is present near the edge of the wound.(c1,c2) Surgical corneal wound in a cat. Wound (c1) (c2)edge coaptation is shown by white arrows.study and has not been performed. The influence of the of high reflectivity in the anterior stroma.23 We were ablecorneal curvature on the pachymetry value is known in to measure the thickness of these high-density regions inhumans,20 but has not been measured in this study. As is vivo using SD-OCT. These observations were similar tothe case with humans, the central trajectory of IR illumi- human data produced from analysis of presumed calcifiednation was accompanied by a central reflection that could lesions.24,25 Precise localization in the subepithelialdisturb tissue analysis. This reflection was not systematic stroma, specific reflectivity, and evaluation of the depositsand was related to the perpendicular position of the inci- thickness provided a noninvasive confirmation of clinicaldent light in relation to the corneal surface.7 diagnosis. The deepest stromal lesions, Florida spots, were In all pathological cases studied, qualitative and quanti- also characterized by the presence of an infiltrating com-tative analyses of the lesions were possible using ponent without any epithelial modification. SD-OCTSD-OCT. In the case of chronic superficial corneal ulcer- imaging of major stromal changes such as complete cor-ation, we were able to detect both epithelial detachment neal edema and bullous keratopathy produced spectacularand hyperplasia, as well as the increased reflectivity of the pictures showing profound changes in the stromal archi-anterior stroma. The analysis of bacterial keratitis high- tecture that could not be evaluated by slit-lamp examina-lighted the presence and the intensity of cellular infiltra- tion. What we call feline bullous keratopathy is named, intion, corneal edema, and tissue destruction. Measurements human ophthalmology, corneal hydrops, a condition asso-made on the different compartments of the cornea allowed ciated with endothelial rupture or detachment.26 SD-OCTus to monitor the development of these lesions over time. examination failed to show endothelial structures in bul-Our observations were similar to those performed in lous keratopathy because it was not technically possible tohuman ophthalmology for which SD-OCT is now a useful have the entire corneal thickness on the same scan, soadditional technique in the evaluation of bacterial kerati- results could, therefore, not be compared with humantis.21,22 However, in some cases, the hyper-reflectivity of data.27 Similarly, when imaging endothelial lesions, thelesions limited the assessment of deep corneal areas, and SD-OCT examination provided an accurate evaluation asas a result, evaluation of the entire stroma was not always long as the corneal thickness was 1300 lm, and thus,possible. absorption was minimal. This limitation can be further Images of corneal dystrophy and degeneration were cor- investigated by imaging endothelial dystrophies andrelated with available histologic data by identifying areas degenerations, which were not included in our study. This© 2013 American College of Veterinary Ophthalmologists, Veterinary Ophthalmology, 1–11
  10. 10. 10 famoselimitation could also be handled by the use of UBM that investigative field that is comparable to the existing fielduses high-frequency ultrasound, which does not depend in human ophthalmology. In our study, the advantages ofon corneal transparency. UBM can scan extremely thick this technique were found in the ability of giving a quali-corneas but with a lower resolution than OCT.6 tative and quantitative evaluation of all cornea layers, in We also used SD-OCT for evaluation and follow-up of vivo, in real time. The rapid acquisition time and thesurgical procedures. The preoperative analysis of corneal absence of contact with the ocular surface make thesequestra in cats was not reliable. Our aim was to antici- method insensitive to eye movements and compatiblepate the choice of the surgical technique and of the prog- with the fragility of the cornea to be examined. Further-nosis by preoperative evaluation. In two cases, the size and more, the production of quantitative images and measure-position of the lesion were accurately measured, while in ments allows us to monitor clinical situations in another cases, the reflectivity of the pigmented lesion pro- objective manner, particularly in the context of microbialduced a posterior shadow that made analysis of the deep keratitis.stroma impossible. However, this lack of information However, we encountered three types of difficulties inabout the depth of the sequestrum did not change either the application of SD-OCT to corneal evaluation. First,the treatment choice or the outcome of the surgical proce- focusing must be very precise, and it was very difficult todure. OCT was used after the keratectomy to measure the use the device on conscious animals. This fact led us tocorneal thickness and to detect residual hyper-reflective use SD-OCT on sedated animals only, which added theareas. The shadow effect was also observed in the evalua- necessity of permission, from the owners, for repeatedtion of corneal foreign bodies. Serial scans were required sedations for follow-up imaging sessions. Additionally, dueto overcome this difficulty and accurately quantify the to the fine focus requirements, small lesions were not eas-depth of penetration. ily detected during the examination, as was the case for Preoperative and post-operative evaluation during the corneal wounds and foreign bodies. Serial scans weresuperficial keratectomies and conjunctival or biomaterial required to obtain useable evaluation images in such cases.(such as porcine intestine submucosa) grafts was possible Finally, for certain disorders, opacity of corneal structureswith SD-OCT. The thin graft material was transparent obscures image acquisition and interpretation, and thus,enough to allow unobstructed imaging of underlying accurate analysis of corneal sequestra was difficult usingstructures and the measurement of their dimensions. SD-OCT. In these cases, SD-OCT presented the sameThese observations were similar to those made in humans limitations as slit-lamp examination. For highly edematouswhere OCT is used frequently in the operative scope of lesions, examination was limited by corneal thickness forcorneal surgery to aid in choice of treatment strat- which it was not possible, with our device, to scan theegy.2,5,7,11,25,28 Currently, more data are needed to support entire cornea. The use of UBM, which does not dependthis kind of protocol, but we believe that increasingly on corneal transparency but has a lower resolution thanwidespread use of OCT will improve treatment strategies OCT, could help to evaluate such corneal conditions.in the future. For example, the ability to accurately evalu- We were driven to complete this study because of theate corneal thickness before or during the surgical proce- possibility of obtaining equipment that is compatible withdure will allow the veterinary surgeon to use novel veterinary practice. Here, we demonstrate the successfulsurgical tools like lasers or corneal cross-linking, which use of the SD-OCT technique for the imaging and evalua-should only be used when minimal residual corneal thick- tion of canine and feline cornea in clinical conditions for aness can be guaranteed. wide range of corneal diseases. This technique is not The analysis of corneal wounds proved more difficult. intended to replace careful slit-lamp examination. ThePerforation areas were not always visible in SD-OCT results and images presented here show that SD-OCTbecause they required the beam to be oriented accurately optical analysis has a resolution comparable to low-magni-along the axis of the wound. In addition, the IR absorp- fication histologic images, and the images obtained are intion due to corneal edema limited the imaging of deep agreement with available clinical and histologic data in thestructures in most of the cases. In these conditions, the literature. In most of the cases, images provided us withuse of SD-OCT adds little to no value to the slit-lamp quantitative information that completed the slit-lampexamination. examination. The major advantage of this technique is The SD-OCT images of healthy corneas in carnivores real-time, in vivo, contactless evaluation of animal cornealwere comparable to images of the human cornea, where structures, and SD-OCT corneal evaluation in pathologi-different layers are easily distinguishable.6 These results cal and surgical conditions is very promising diagnosticcorrelate strongly with a previous study performed on a tool for therapeutic decision-making and for follow-up ofsmaller group.29 However, the SD-OCT image of Desc- corneal healing.emet’s membrane and the endothelium fades as the thick-ness of the cornea increases. ACKNOWLEDGMENTS The use of SD-OCT for corneal evaluation in normaland pathological conditions in dogs and cats opens an None. © 2013 American College of Veterinary Ophthalmologists, Veterinary Ophthalmology, 1–11
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