OCT cornea dogs and cats

Assessment of the use of spectral domain optical coherencetomography (SD-OCT) for evaluation of the healthy andpathological cornea in dogs and cats

Frank FamoseService d’Ophtalmologie, Clinique vet�erinaire des Acacias, Blagnac, France

Address communications to:

F. Famose

Tel.: +33 5 61712402

Fax: +33 5 61716552

e-mail: [email protected]

AbstractPurpose Morphologic evaluation of the cornea is based on the slit-lamp examination.In human ophthalmology, optical coherence tomography (OCT) has opened a new

field in the clinical approach to anterior segment disorders and more specificallythe 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 examinedfor various corneal conditions. All animals were examined after sedation or anesthesia.

Results Normal and pathological aspects of canine and feline cornea were describedfor 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. Theadvantage 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 forprecise focus and the low quality of images obtained with too pigmented or thickenedcorneas.

Key Words: cats, cornea, dogs, keratitis, optical coherence tomography, spectraldomain

INTRODUCTION

Several imaging methods exist for the evaluation ofcorneal morphology. The most frequently used method isslit-lamp biomicroscopy, but visualization of deeper cor-neal structures can be limited by light absorption and scat-tering through the cornea, particularly in case of cornealedema. The application of new technologies includinghigh-frequency ultrasound (ultrasound biomicroscopy[UBM]), confocal microscopy, Scheimpflug imaging, andoptical coherence tomography (OCT) has led to improvedresolution and complementary evaluation of cornealconditions.1–3 OCT, developed in 1990, was initially dedi-cated to evaluation of the retina in human ophthalmol-ogy.4 The use of OCT for the examination of the anteriorsegment of the eye, a practice started in the early 2000s,has opened a new field in the clinical and experimentalapproaches to evaluating these structures.1–3 Anterior

segment spectral domain OCT (SD-OCT) has been thesubject of more than 500 scientific articles over the last5 years. The application of SD-OCT for medical andsurgical purposes has been specifically described for thestructural analysis of tear meniscus, normal and pathologi-cal cornea, and iridocorneal angle, as well as evaluation ofthe anterior chamber, iris, and lens.5–16 OCT has alsobeen compared with slit-lamp examination and with Sche-impflug imaging for corneal endothelial evaluation.17

Spectral domain optical coherence tomography functionis similar to ultrasonography with a few major differences.Ultrasonography uses ultrasound waves emitted by a probein contact with the tissue to be studied, whereas SD-OCTuses infrared (IR) light emitted at a distance from the cor-nea, making contactless image acquisition possible.1 Whileoptical transparency is not required for ultrasound, theuse of IR light in OCT requires transparent media. Thelight passing through different ocular media experiences

© 2013 American College of Veterinary Ophthalmologists

Veterinary Ophthalmology (2013) 1–11 DOI:10.1111/vop.12028

interference, which is compared with light reflected on areference mirror at the same working distance. Scanningthe reference mirror through a range of distances allowsgeneration of an axial image (A-scan). A series of axial sec-tions are combined to produce a composite image, similarto the standard two-dimension (B-scan) image producedin ultrasonography. SD-OCT images have an axial resolu-tion of 2–4 lm and a lateral resolution of 20–25 lm. As acomparison, the axial resolution of 50-MHz ultrasonogra-phy is 50 lm.12 Additional information about technicalfeatures of SD-OCT can be found elsewhere.1,4

Heavy and costly SD-OCT devices were initially lim-ited to specialized human ophthalmology centers orresearch centers. But now, lighter and more affordablemodels have become available. The use of SD-OCT forthe morphological analysis of the cornea of dogs and catsin healthy and pathological conditions has yet to bedescribed. Our study aims to evaluate spectral domainOCT for corneal imaging in dogs and cats in clinicalpractice conditions.

MATERIAL AND METHODS

AnimalsOne hundred eyes were examined in 93 animals. Thegroup studied included 52 dogs and 41 cats examinedbetween July and November 2011 at the Acacias Veteri-nary Clinic Ophthalmology department. The healthy ani-mal control group included eight dogs and eight cats.Control animals did not have any ocular lesions and wereanesthetized for minor operations with no ocular involve-ment. The remaining animals (44 dogs and 33 cats) wereanesthetized prior to an examination or ocular surgery forthe following conditions: chronic superficial corneal ulcers(13 cases), deep corneal ulcers (10 cases), anterior uveitis(three cases), bacterial keratitis (10 cases), corneal wound

(14 cases), conjunctival grafts (eight cases), corneal seques-tra (five cases), corneal foreign body (three cases), cornealdystrophy (three cases), chronic superficial keratitis (threecases), Florida keratopathy (two cases), stromal hemor-rhage (one case), glaucoma with marked corneal edema(two cases), and bullous keratopathy (one case). All ani-mals were examined after consent was obtained from theirowner. All procedures were performed in accordance withthe French guidelines for animal care.

AnesthesiaAll animals examined were sedated or under general anes-thesia. Cats were anesthetized with 0.01 mg/kg medetomi-dine (Domitor�, Pfizer, NY, USA) and 5 mg/kg ketamine(Imalgene 1000�, Merial, Lyon, France) via intramuscularadministration. Dogs were anesthetized with 300 lg/m²medetomidine and 5 mg/kg ketamine delivered intrave-nously followed by 0.5–2% isoflurane (Isoflurane Bela-mont�, Nicholas Piramal Ltd, London, UK) in oxygenafter endotracheal intubation.

Ophthalmologic examinationAll animals were submitted to a thorough ophthalmologicexamination including slit-lamp examination, Schirmertest, and tonometry. In cases where bacterial infection wassuspected, samples were submitted for a bacteriologicanalysis in a local laboratory dedicated to veterinary bacte-riology (Laboratoire Meynaud, Toulouse, France).

ImagingImaging was performed using an iVue SD-OCT system(Optovue EBC Medical, Paris, France) connected to acomputer interface and a laptop (Fig. 1). The system func-tions at 840 nm, which is in the IR radiation range, andcan perform 26 000 A-scans per second. The imaging unithas 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

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capture A-scans horizontally on a table or vertically, heldin place by an adjustable support for use in the operatingroom. For this study, the image capture unit was posi-tioned vertically (Fig. 1a).

The iVue device is designed to examine the retina andthe anterior segment. There are two operating modes forimaging the anterior segment, both of which requireinstallation of an additional corneal-anterior module (orCAM) at the end of the image capture unit. The ‘pachy-metry’ mode images eight, 6-mm wide radial sections ofthe cornea, with the focus line positioned in the center ofthe cornea. The ‘angle’ mode images a section along a linechosen to correspond with the area or interest.

Animals were placed in dorsal recumbency, with thehead supported by a vacuum cushion (Fig. 1b). The imagecapture unit, supported by an articulated arm, was broughtclose to the eye and then focused using an adjustmentknob. Care was taken to humidify the corneal surface withartificial tears during imaging to avoid desiccation artifact.Images were captured using a foot control and convertedto two-dimensional B-scans on which it was possible todraw, write, and measure with calipers. Image analysis wasperformed in the same manner as ultrasound image analy-sis and covered three aspects: structure identification,description of lesions by analysis of light interference areas(increased or reduced reflection), and measurements. Thesame operator (Frank Famose) performed image examina-tion and processing.

RESULTS

Normal corneaExamination in ‘pachymetry’ mode reveals the differentlayers in the cornea (Fig. 2a,b). The cornea appears as acomposite of three layers of varying reflectivity and thick-ness. The epithelial layer appears homogeneous with a

relatively low reflectivity compared with the pre-cornealtear film and anterior stroma. The stromal layer is thickerand appears heterogeneous with an intermediate reflectiv-ity. In the deepest layer, Descemet’s membrane and theendothelium combine as a thin, dense line.

The average corneal thickness was 535 lm in dogs(interval of values 500–620 lm) and 600 lm in cats (inter-val of values 540–660 lm). In cats, the heterogeneouslyorganized anterior stroma was distinguishable from theposterior stroma where the homogeneous organization ofcollagen lamellae was visible (Fig. 2b).

In the healthy animals, the average measured epithelialthickness was 55 lm in dogs (interval of values 50–60 lm)and 60 lm in cats (interval of values 55–65 lm). Theaverage measured stromal thickness was 480 lm in dogs(450–560 lm) and 540 lm in cats (485–595 lm). Thenumber of healthy animals imaged was not sufficient toperform a statistical analysis on these parameters, and theendothelio-Descemet layer was not thick enough to bemeasured in healthy animals.

Although care was taken to humidify the corneal surfaceduring examination, artifact lesions due to superficial cor-neal desiccation were observed and appeared as a notch inthe corneal thickness, with a reduction in epithelial thick-ness (Fig. 3a,b).

Epithelial and subepithelial disordersThirteen chronic epithelial ulcers were examined. Themain features observed in both species were an increase inthe thickness and reflectivity of the epithelial layer, accom-panied by epithelial detachment and a clearly visibleincrease in anterior stromal reflectivity (Fig. 4a2). Epithe-lial thickness at the margins of the ulcer ranged from 80to 150 lm.

Three cases of canine chronic superficial keratitis withcorneal melanosis were examined. In all cases, we observed

(a)

(b)

Figure 2. Normal cornea of dog (a) and cat (b)

in pachymetric mode. The values in green

represent the total thickness of the cornea and

that of the epithelium.


s d - o c t e v a l u a t i on o f c an i n e and f e l i n e c o rn e a 3

a sharp increase in the reflectivity of the epithelial layer,with a homogeneous attenuation of the stromal image(Fig. 4b1,b2). This increased anterior reflectivity is due tothe presence of melanocytes, including melanic pigments,which absorb light in the IR range.

In the two cases of presumed lipid and/or calcium cor-neal degeneration, we observed increased anterior stromalreflectivity with no modification of the posterior stroma.Variations of the epithelial thickness were observed andwere associated with the density of the presumed lipidand/or calcium deposits (Fig. 4c1,c2). Total corneal

thickness was 380 and 530 lm, respectively, presumedlipid and/or calcic deposit depth ranged from 80 to250 lm. Melanosis, and corneal blood vessels were clini-cally present and visible on OCT scans.

Stromal disordersTen cases of suspected bacterial keratitis were evaluated.Positive cultures confirmed the diagnosis in eight of theten cases. SD-OCT analysis revealed a reduction instromal thickness localized to the anterior stroma (Fig. 5).The center of the lesion appeared either as a homoge-

(a) (b)

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

arrows).

(a1) (a2)

(b1) (b2)

(c1) (c2)

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

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

corneal blood vessel (red arrow) are visible.


4 f amo s e

neous loss of stroma or as a heterogeneous association ofhigh- and low-reflectivity zones. High-reflectivity zonescorresponding to cellular infiltration surrounded theselesions. The epithelial layer was partially absent, and insome cases of deep stromal destruction, Descemet’smembrane was pushed forward by intraocular pressure.Residual stromal thickness was measurable.

Spectral domain optical coherence tomography evalua-tion of deep corneal ulcers revealed a homogeneousincrease in stromal reflectivity surrounding the ulceratedarea and the presence of debris at the bottom of the ulcer.Analysis allowed measurement of the ulcer depth, infor-mation that is critical to choosing the appropriate surgicaltreatment.

(a1)

(b1) (b2)

(c2)

(d2)

(e2)

(a2)

(c1)

(d1)

(e1)

Figure 5. Infectious keratitis and deep ulcers.

The red arrow represents the section area. (a1,a2)

infection with loss of surface substance (grey

arrows) in a homogeneous stroma. (b1,b2) deep

keratitis with an area of collagenolysis (yellow

arrows) and increased peripheral stromal

reflectivity. (c1,c2) deep corneal ulceration. Area

of stromal densification (white arrows) and debris

(pink arrow) are visible. Residual stromal

thickness can be measured. (d1,d2) deep keratitis

with loss of stromal continuity and central

elevation of deep stroma (green arrows). (e1,e2)

Predescemetic lesion. The residual corneal

thickness is 50 lm.



The three corneal foreign bodies (Fig. 6) were charac-terized by the presence of a posterior cone-shaped shadowrelated to their opacity. Depending on the penetrationdepth, an endothelial reaction was visible. Localization ofthe end of the foreign body was challenging, and serialscans were required to identify perforations.

We also examined two cases of Florida keratopathy(Fig. 7a1,a2). In SD-OCT images, these lesions werecharacterized by a clear increase in superficial and deepstroma reflectivity. This increased reflectivity was deeperthan that observed in the case of stromal hemorrhage(Fig. 7b1,b2). The lesions were not accompanied by epi-thelial alteration, an increase in stromal thickness, orincreased IR light reflexion behind the lesions.

Spectral domain optical coherence tomography imagingof feline corneal sequestrum was challenging. In the fivecases examined, sequestrum appeared as an intense, local-ized light reflection in the anterior stroma. IR light reflec-tion varied according to the density and thickness of thesequestrum. In two cases, the posterior stroma remainedvisible (Fig. 8a1,a2), making it possible to measure thethickness of the necrotic area before making a decisionconcerning an operation. In the three remaining cases, thispre-operative evaluation was not possible due to highlesion reflectivity (Fig. 8b1,b2).

Three cases of major increase of the stromal thicknesswere observed. In two cases of glaucoma with an intensecorneal edema, corneal structure was maintained, but thespacing of collagen lamellae was altered (Fig. 9a1,a2). Inthe other case, a feline bullous keratopathy, the normalstromal architecture was severely disrupted, and pockets ofliquid among highly modified stromal structures wereobserved (Fig. 9b1,b2). Corneal thickness could not bemeasured in either case due to the size of the cornea,which was not entirely visible on the screen.

Endothelial disordersIn a case of persistent pupillary membrane with localizedendothelial dystrophy (Fig. 10a1,a2), a localized endothe-lial hyper-reflectivity was observed supported by a sus-pended structure in the anterior chamber. Filaments weredifficult to highlight in two-dimensional scans, and serialscans were required to monitor the filament trajectory.

In the three cases of anterior uveitis, precipitates behindthe cornea appeared in SD-OCT imaging as highly reflec-tive wide-based lesions on the endothelium (Fig. 10b1,b2).A diffuse inhomogeneous granular reflectivity of the ante-rior chamber was observed. Anterior synechia appeared asdense lesions attached to the endothelium in continuitywith the anterior face of the iris (Fig. 10c1,c2).

(a1)

(b1)

(c1)

(a2)

(b2)

(c2)

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 (***). Endothelialreaction (yellow arrows) is visible. Serial scans

(a1–c2) show total corneal perforation.


6 f amo s e

Surgical disordersCorneal structure was evaluated after conjunctival grafts ineight animals using SD-OCT (Fig. 11a1,a2). The imagesobtained showed a conjunctival structure covered with anepithelium and embedded in the stroma. The conjunctivalstructure was recognizable due to higher density and thepresence of blood vessels.

In the 14 cases of corneal wounds, the images obtaineddid not identify the precise area of perforation. However,images did show the presence of fibrin and blood in theanterior chamber (Fig. 11b1,b2). Evaluation of cornealincisions (Fig. 11c1,c2) to check the wound edge junctionwas possible, although assessment of deep sections of thestroma was difficult because of the IR absorption relatedto the corneal edema.

DISCUSSION

The goal of this study was to test the feasibility of usingSD-OCT to image the cornea in cats and dogs in com-mon practice situations. Our results confirm that thistechnique is applicable to the evaluation of the cornea inhealthy and pathological conditions. For most cases stud-ied, SD-OCT evaluation provides reliable and accurateadditional information to the standard examination usinga slit lamp for corneal disorders. Through the study ofmany different conditions, we were able to underline diag-nosis- and image-related advantages and limitations ofSD-OCT.

This study is one of the first evaluations of SD-OCTfor corneal diseases in private practice conditions. This

(a1)

(b1)

(a2)

(b2)

Figure 7. Diffuse stromal lesions. The red arrow

represents the section area. (a1,a2) Florida spots

with stromal cellular infiltration (white arrows).

(b1,b2) stromal hemorrage (green arrows).

(a1) (a2)

(b1) (b2)

Figure 8. Feline corneal sequestrum. The red

arrow represents the section area. (a1,a2) corneal

sequestrum (grey arrow) with deterioration of

stromal signal. (b1,b2) corneal sequestrum with

total signal absorption (yellow arrows).



means, we have evaluated the pathological conditions thatcame through our clinic during the time of the study.Although a wide range of conditions has been examined,many other conditions such as extended endothelialdystrophies or eosinophilic keratitis were not evaluatedbecause we were not presented with those conditionsduring the study.

The SD-OCT imaging resolution was excellent at alldepths, and we were able to measure the central corneathickness with a resolution of 5 lm. This measurementrequired the device to be positioned axially in the centerof the cornea. The results obtained in the ‘pachymetry’mode were compatible with available data.18,19 However,statistical analysis of these data was not the aim of this

(a1) (a2)

(b1) (b2)

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

‘pockets’ of fluid.

(a1) (a2)

(b1) (b2)

(c1) (c2)

Figure 10. Endothelial alterations. (a1,a2)

persistent pupillary membrane with endothelial

attachment (grey arrows). (b1,b2) retrokeratic

precipitates (green arrows) with heterogeneity of

anterior chamber. (c1,c2) anterior synechia (green

arrows).


8 f amo s e

study and has not been performed. The influence of thecorneal curvature on the pachymetry value is known inhumans,20 but has not been measured in this study. As isthe case with humans, the central trajectory of IR illumi-nation was accompanied by a central reflection that coulddisturb tissue analysis. This reflection was not systematicand was related to the perpendicular position of the inci-dent light in relation to the corneal surface.7

In all pathological cases studied, qualitative and quanti-tative analyses of the lesions were possible usingSD-OCT. In the case of chronic superficial corneal ulcer-ation, we were able to detect both epithelial detachmentand hyperplasia, as well as the increased reflectivity of theanterior stroma. The analysis of bacterial keratitis high-lighted the presence and the intensity of cellular infiltra-tion, corneal edema, and tissue destruction. Measurementsmade on the different compartments of the cornea allowedus to monitor the development of these lesions over time.Our observations were similar to those performed inhuman ophthalmology for which SD-OCT is now a usefuladditional technique in the evaluation of bacterial kerati-tis.21,22 However, in some cases, the hyper-reflectivity oflesions limited the assessment of deep corneal areas, andas a result, evaluation of the entire stroma was not alwayspossible.

Images of corneal dystrophy and degeneration were cor-related with available histologic data by identifying areas

of high reflectivity in the anterior stroma.23 We were ableto measure the thickness of these high-density regions invivo using SD-OCT. These observations were similar tohuman data produced from analysis of presumed calcifiedlesions.24,25 Precise localization in the subepithelialstroma, specific reflectivity, and evaluation of the depositsthickness provided a noninvasive confirmation of clinicaldiagnosis. The deepest stromal lesions, Florida spots, werealso characterized by the presence of an infiltrating com-ponent without any epithelial modification. SD-OCTimaging of major stromal changes such as complete cor-neal edema and bullous keratopathy produced spectacularpictures showing profound changes in the stromal archi-tecture that could not be evaluated by slit-lamp examina-tion. What we call feline bullous keratopathy is named, inhuman ophthalmology, corneal hydrops, a condition asso-ciated with endothelial rupture or detachment.26 SD-OCTexamination failed to show endothelial structures in bul-lous keratopathy because it was not technically possible tohave the entire corneal thickness on the same scan, soresults could, therefore, not be compared with humandata.27 Similarly, when imaging endothelial lesions, theSD-OCT examination provided an accurate evaluation aslong as the corneal thickness was <1300 lm, and thus,absorption was minimal. This limitation can be furtherinvestigated by imaging endothelial dystrophies anddegenerations, which were not included in our study. This

(a1) (a2)

(b1) (b2)

(c1) (c2)

Figure 11. Surgical disorders. The red arrow

represents the section area. (a1,a2) conjunctival

graft in a dog. The conjunctiva (green arrows) is

denser 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

edge coaptation is shown by white arrows.



limitation could also be handled by the use of UBM thatuses high-frequency ultrasound, which does not dependon corneal transparency. UBM can scan extremely thickcorneas but with a lower resolution than OCT.6

We also used SD-OCT for evaluation and follow-up ofsurgical procedures. The preoperative analysis of cornealsequestra in cats was not reliable. Our aim was to antici-pate the choice of the surgical technique and of the prog-nosis by preoperative evaluation. In two cases, the size andposition of the lesion were accurately measured, while inother cases, the reflectivity of the pigmented lesion pro-duced a posterior shadow that made analysis of the deepstroma impossible. However, this lack of informationabout the depth of the sequestrum did not change eitherthe treatment choice or the outcome of the surgical proce-dure. OCT was used after the keratectomy to measure thecorneal thickness and to detect residual hyper-reflectiveareas. The shadow effect was also observed in the evalua-tion of corneal foreign bodies. Serial scans were requiredto overcome this difficulty and accurately quantify thedepth of penetration.

Preoperative and post-operative evaluation duringsuperficial keratectomies and conjunctival or biomaterial(such as porcine intestine submucosa) grafts was possiblewith SD-OCT. The thin graft material was transparentenough to allow unobstructed imaging of underlyingstructures and the measurement of their dimensions.These observations were similar to those made in humanswhere OCT is used frequently in the operative scope ofcorneal surgery to aid in choice of treatment strat-egy.2,5,7,11,25,28 Currently, more data are needed to supportthis kind of protocol, but we believe that increasinglywidespread use of OCT will improve treatment strategiesin the future. For example, the ability to accurately evalu-ate corneal thickness before or during the surgical proce-dure will allow the veterinary surgeon to use novelsurgical tools like lasers or corneal cross-linking, whichshould only be used when minimal residual corneal thick-ness can be guaranteed.

The analysis of corneal wounds proved more difficult.Perforation areas were not always visible in SD-OCTbecause they required the beam to be oriented accuratelyalong the axis of the wound. In addition, the IR absorp-tion due to corneal edema limited the imaging of deepstructures in most of the cases. In these conditions, theuse of SD-OCT adds little to no value to the slit-lampexamination.

The SD-OCT images of healthy corneas in carnivoreswere comparable to images of the human cornea, wheredifferent layers are easily distinguishable.6 These resultscorrelate strongly with a previous study performed on asmaller group.29 However, the SD-OCT image of Desc-emet’s membrane and the endothelium fades as the thick-ness of the cornea increases.

The use of SD-OCT for corneal evaluation in normaland pathological conditions in dogs and cats opens an

investigative field that is comparable to the existing fieldin human ophthalmology. In our study, the advantages ofthis technique were found in the ability of giving a quali-tative and quantitative evaluation of all cornea layers, invivo, in real time. The rapid acquisition time and theabsence of contact with the ocular surface make themethod insensitive to eye movements and compatiblewith the fragility of the cornea to be examined. Further-more, the production of quantitative images and measure-ments allows us to monitor clinical situations in anobjective manner, particularly in the context of microbialkeratitis.

However, we encountered three types of difficulties inthe application of SD-OCT to corneal evaluation. First,focusing must be very precise, and it was very difficult touse the device on conscious animals. This fact led us touse SD-OCT on sedated animals only, which added thenecessity of permission, from the owners, for repeatedsedations for follow-up imaging sessions. Additionally, dueto the fine focus requirements, small lesions were not eas-ily detected during the examination, as was the case forthe corneal wounds and foreign bodies. Serial scans wererequired to obtain useable evaluation images in such cases.Finally, for certain disorders, opacity of corneal structuresobscures image acquisition and interpretation, and thus,accurate analysis of corneal sequestra was difficult usingSD-OCT. In these cases, SD-OCT presented the samelimitations as slit-lamp examination. For highly edematouslesions, examination was limited by corneal thickness forwhich it was not possible, with our device, to scan theentire cornea. The use of UBM, which does not dependon corneal transparency but has a lower resolution thanOCT, could help to evaluate such corneal conditions.

We were driven to complete this study because of thepossibility of obtaining equipment that is compatible withveterinary practice. Here, we demonstrate the successfuluse of the SD-OCT technique for the imaging and evalua-tion of canine and feline cornea in clinical conditions for awide range of corneal diseases. This technique is notintended to replace careful slit-lamp examination. Theresults and images presented here show that SD-OCToptical analysis has a resolution comparable to low-magni-fication histologic images, and the images obtained are inagreement with available clinical and histologic data in theliterature. In most of the cases, images provided us withquantitative information that completed the slit-lampexamination. The major advantage of this technique isreal-time, in vivo, contactless evaluation of animal cornealstructures, and SD-OCT corneal evaluation in pathologi-cal and surgical conditions is very promising diagnostictool for therapeutic decision-making and for follow-up ofcorneal healing.

ACKNOWLEDGMENTS

None.


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