Anterior Segment Dysgenesis Cat

8/3/2019 Anterior Segment Dysgenesis Cat

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Introduction

Anterior segment dysgeneses have been described in differentspecies of animals (cattle, horses, mice, dogs and cats). Theycommonly present as corneal opacities which can be asso-ciated with the presence of a residual pupillary membraneand cause varying degrees of visual disturbances.[3,5,7,8,12,13,15-19,21,22].

In human ophthalmology, a spectrum of congenital ano-malies of the anterior segment has been described, includingPeters anomaly, congenital or infantile glaucoma, iris hypo-plasia, Axenfeld-Rieger syndrome, endothelial dysplasia,sclerocornea, megalocornea, keratoconus and posteriorembryotoxon. [2,5,9,10,20] . Glaucoma is a frequent association.

These malformations arising during embryogenesis involvethe ocular tissues derived from the migration and differentiationof the cells of the cephalic neural crest and, in the most complexcases are associated with the adhesion of the lens to the cornealendothelium. [2,5,9,10].

This paper describes the case of an anterior segment dys-genesis of the left eye in an 18-month-old, one-eyed, domesticshorthair cat with a complex clinical presentation similar toPeters anomaly.

Clinical history

The 5 kg castrated male domestic shorthair cat was referredby a colleague, as an emergency, for a suspected anteriorluxation of the left lens associated with a corneal ulcer. Thecat had undergone an enucleation of the right eye at 8 monthsof age for an unknown reason; the condition was describedby the owners as similar to the one now affecting the left eye.

The cat was in good general condition and had no previoushistory of ocular trauma. Vision appeared normal.

No sign of ocular pain could be detected and there was noperiorbital inflammation. Pupillary light reflex was present.The globe was of normal size. Intraocular pressure, measuredusing a rebound tonometer (Tonovet, Icare Finland Oy,Espoo, Finland), was 19 mmHg. Examination of the corneaand anterior chamber using a biomicroscope (SL15, KowaEurope GmbH, Dsseldorf, Germany), revealed no signs ofinflammation or neovascularisation. The cornea was of normal

size and convexity. The peripheral cornea was normal. Theintermediate zone was translucent. A full thickness greyopacity 6 mm in diameter was present in the paracentralregion surrounding a small central ectatic opalescent zone,with the epithelium covering the cortex of the lens. Punctuate

SUMMARY

A case of anterior segment dysgenesis in an 18-month-old, one-eyed,domestic shorthair cat is reported. This congenital anomaly presented witha central corneal coloboma, a microspheric lens with a partial cataract,

pupillary membrane remnants and goniodysgenesis. Treatment consisted oflens removal by phacoemulsification and a corneal graft using a porcinesmall intestinal submucosa biomaterial (Vet BioSISt) to repair the corneaand preserve the vision. Intraocular pressure remained within the normalrange.Features of this case warrant classification as Peters anomaly, first inhumans in 1887 and which consists of defective development of the posteriorcornea caused by abnormal migration and differentiation of neural crest cellsimpeded by the late separation of the lens vesicle from the surface ectoderm.

Keywords: Anterior segment dysgenesis, cat, coloboma,

Peters anomaly, biomaterial graft.

RSUM

Un cas rare de dysgnsie du segment antrieur chez un chat europen

Lauteur dcrit un cas de dysgnsie du segment antrieur chez un chat europen

monophtalme, g de 18 mois. Cette anomalie congnitale associait un colo-bome cornen central accol une microsphrophakie partiellement cata-racte, des rsidus de membrane pupillaire et une goniodysplasie. Lexrsedu cristallin par phacomulsification suivie de la reconstruction de la cornepar greffe multilamellaire dun biomatriau (Vet BioSiSt) a permis deconserver la vision. La pression intraoculaire est reste normale.Cette dysgnsie fline est rapprocher de lanomalie congnitale de Petersdcrite, pour la premire fois, chez lHomme en 1887 et caractrise par laprsence dopacits cornennes dues labsence des plans stromal et endothlio-descemtique. Elle est associe un dfaut de migration et de diffrentiationdes cellules embryonnaires issues de la crte neurale. Labsence de sparationdu cristallin de lectoderme cphalique superficiel nest pas de rgle maisest considre par les diffrents auteurs comme un facteur aggravant le pro-nostic visuel, de mme que la survenue plus ou moins tardive dun glaucomeprimaire.

Mots cls : Dysgnsie du segment antrieur, chat, colo-

bome, anomalie de Peters, greffe de biomatriau.

An uncommon case of anterior segment

dysgenesis in a domestic shorthair cat

P. LAZARD1* DVM, R.L. PEIFFER2 DVM, PHD, ACVO

1Clinique vtrinaire, 80 rue Preire, 78100 Saint-Germain-en-Laye, FRANCE.2Merck Research Laboratories, Merck and Co. WP45-226, PO Box 4, West Point, PA 19486, USA.

*Corresponding author: [email protected]


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174 LAZARD (P.) AND PEIFFER (R. L.)

fluorescein staining in the most central zone without extensioninto the adjacent tissues was observed.

The anterior chamber was of normal depth. The sphericallens, identified in the anterior chamber, was of small size.Multifocal opacities were observed in the anterior cortex andnucleus. The lens was centred on the optic axis with cornealadhesions at the zones of modified transparency, but did notcontact the iris. Strands of residual pupillary membrane werepresent on its surface. The pupil was normal in shape andvery mobile without any detectable synechia (Fig. 1).

Following pharmacologically induced mydriasis(Mydriaticum 0.5%, Tha, Clermont Ferrand, France), thevitreous and the retina had a normal appearance on direct andindirect ophthalmologic examination. Under sedation, exa-mination of the iridocorneal angle using a Barkan lens revea-led goniodysgenesis characterised by an open iridocornealangle and absence of the pectinate ligament fibers in many

regions. Ocular ultrasound (Philips HD 11XE, PhilipsUltrasound, Bothell, WA, USA) confirmed the small sizespherical lens and the absence of retinal detachment.

The young age of the subject, the absence of signs of priorinflammation or trauma, and the microspherophakia supportedthe diagnosis of a cleavage anomaly arising during embryo-genesis.

Treatment

Because of the increased risk of corneal perforation in itscentral zone, a corneal graft using a porcine small intestinalsubmucosa biomaterial (Vet BioSISt, Cook Inc., Hert-fordshire, UK) combined with partial lens removal was per-formed. The aim was to reconstruct the cornea whilst preserving

its transparency and conserving vision. The pre-anaestheticblood test (complete blood count, serum biochemistry andserum protein electrophoresis) showed no abnormalities.Serological and antiviral assays (Speed-Tests FELV-FIV-PIF, BVT-Virbac, La Seyne sur Mer, France) for felineimmunodeficiency virus (FIV), feline infectious peritonitis(FIP) and feline leukaemia virus (FeLV) were negative, as

was the bacteriological examination performed on a samplefrom the central zone of the cornea. Following a 4-day-courseof local antibioprophylaxis (ofloxacin ointment, Exocine,Laboratoire Allergan France SAS), surgery was performedunder isoflourane gaseous anaesthetic using an operatingmicroscope (Zeiss OPMI 6, Carl Zeiss S.A.S, Le Pecq,France).

Immediately prior to surgery, the anterior segment had asignificantly different appearance from that of the initial exa-mination 4 days previously. The lens had lost its sphericalappearance and appeared crumpled. There was an axial cor-neal defect with the base comprised of the anterior capsule of

the adherent lens The depth of the anterior chamber remainedunchanged, with the lens remaining adhered to the posteriorcorneal surface in the intermediate and paracentral zones (Fig. 2).

A lateral canthotomy was performed. The lens fragmentswere extracted by phacoemulsification (Universal II;Laboratoires Alcon S.A, Rueil- Malmaison, France) followinga keratotomy 1 cm from the central zone of the cornea directedin such a way as to penetrate directly into the lens. An ocu-tome probe (Atiop, Alcon France S.A) was used to aspirateand remove any part of the lens capsule which was not adheredto the cornea. The anterior lens capsule was left in place withthe exception of the perforated area. A high-density visco-elastic product (Healon GV, Amo, Mougins, France) wasused to fill the anterior chamber. The corneal epithelium wasthen removed beyond the limit of the 6 mm diameter para-central zone. To prepare the site for the biomaterial graftused to reconstruct the cornea, the underlying tissue and theexposed superficial layer of normal stroma of the interme-diate zone were excised by lamellar keratectomy

Two corneal grafts derived from porcine small intestinalsubmucosa (Vet BioSISt, Cook Inc., Hertfordshire, UK)were then superimposed using simple interrupted absorbablesutures (Vicryl 10/0, Ethicon, Janssen, Noisy-le-Grand,

France). The first graft, of 6 mm diameter, was sutureddirectly to the borders of the paracentral zone, and thesecond, of 8 mm diameter, to healthy corneal stroma and epi-thelium. The viscous product was then aspirated and theentry point for the phacoemulsification was closed using thesame suture material (Fig. 4).

Reconstruction of the lateral canthus of the eyelid was per-formed and the nictitating membrane was sutured to the lateralaspect of the upper lid. Finally, a blepharorrhaphy was per-formed for additional protection. Ten mg of marbofloxacin(Marbocyl, Vetoquinol, Lures, France) and 1.5 mg ofmeloxicam (Metacam, Boehringer Ingelheim, Paris,

France) were injected intravenously and subcutaneouslyrespectively.

An Elizabethan collar was fitted and the antibiotic wascontinued as a 10-day oral course (marbofloxacin at 2

FIGURE 1 : Photo of the left eye of a cat affected by anterior segmentdysgenesis (Peters anomaly). The cornea displays 4 distinct zonesindicated by coloured dots: green dot = peripheral cornea, of nor-mal appearance; white dot = equatorial zone of the lens; blue dot

= zone of adhesion between the microspheric lens and the posteriorcornea; black dot = the most fragile, central region, with the lensembedded in the defective cornea and covered by epithelium ; reddot = the paracentral zone, which is partially opaque. (Peters anomaly).


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mg/kg/day). After 20 days' isolation at the owners home, thesutures were removed from the eyelids and nictitating mem-brane. The anterior chamber was formed, and the biomaterialcorneal grafts were incorporated in a zone of corneal granu-lation. No anterior synechia were present. An indometacin-based anti-inflammatory treatment (Indocollyre 0.1%;Bausch & Lomb, Lab. Chauvin, Montpellier, France), and avitamin A ointment to promote healing (Faure, Laboratoires

Europhta, Monaco) were prescribed for 1 month.

At the end of this period, the eye was visually functional.The cornea presented with a small central opacity, which wasrelatively transparent and only slightly vascularised (Fig. 5).

Discussion

The congenital abnormalities of this eye present similaritieswith anterior segment dysgeneses described in both animalsand humans (corneal opacity, remnants of persistent pupillarymembrane, malformation of the iridocorneal angle, ectopicmicrospherophakia). [2,3,5,7-10,13,15-19,21,22] The corneal

coloboma and anterior chamber lesions were non-inflam-matory. [2,3,9,16,17] The central corneal perforation was notof traumatic or infectious origin. [2,9,16,] The presence ofmicrospherophakia adherent to the defective cornea couldnot be confused with the well-documented lens luxation of

FIGURE 2 : Photo taken during the operation. The enlarged image of theeye appears inverted due to the positioning of the animal. The mostcentral zone of the cornea had not been impermeable for 2 days.The lens has become crumpled. The coloured marker dots refer to

the same areas as described in the caption to Fig. 1.

FIGURE 4 : Photo taken during the operation: view of the eye at the endof surgery after suturing the 2 superimposed grafts of porcine smallintestinal submucosa (Vet BioSISt) and closure of the phacoe-

mulsification keratotomy.

FIGURE 5 : View of the eye 1 month after surgery. The anterior chamberhas a normal depth. The cornea is reconstructed and of satisfactorytransparency. Visual function has been conserved.

FIGURE 3 : Photo taken during the operation at the end of phacoemulsi-fication and after removal of the posterior lens capsule. The mostcentral zone of the cornea has been freed of all lens tissue and com-municates directly with the anterior chamber, filled with a visco-elastic

product. The surgical keratotomy is visible at the zone of adhesionof the lens at the 3 oclock position. The coloured marker dots referto the same areas as described in the caption to Fig. 1. The whitedot is no longer present because of the posterior capsulectomy.


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176 LAZARD (P.) AND PEIFFER (R. L.)

familial and congenital origin in the Siamese cat, [3,12,14]which is most commonly inflammatory in adult cats, anddegenerative in elderly cats. [4,11-13,15,19,24] This case issimilar to keratolenticular dysgenesis described by PEIFFERin 1983. In that case, a Persian kitten presented with a lens,containing a dumbbell-shaped partial cataract, embedded ina central keratoconus. Histology showed that the Descemets

membrane and anterior capsule of the lens were absent, causingthe corneal stroma and the lens cortex to be in closecontact.[16] A similar corneal coloboma was described in anewborn infant affected by a Peters anomaly, heart malfor-mation and hydrocephalus in 1996. [9]

In many species of animal, a persistent pupillary membraneis the most common manifestation of anterior segment dys-genesis. [4,13,17,21] More rarely, clinical signs associate, invarying degrees, anatomical defects affecting the optic axis.These can be found at the level of the corneal stroma andendothelium, the iris, and the anterior aspect of the lens Inall probability, this is the result of a defect in the separation

between the surface ectoderm and the lens vesicle.[3,8,9,16,18]

This anterior segment dysgenesis presents many similaritieswith Peters anomaly in humans. It is an irido-corneo-trabeculardysgenesis, which is normally bilateral, but can be unilateraland asymmetric. [2,5,10,14] It presents as a central cornealopacity caused by the absence of the endothelium andDescemets membrane. Iridocorneal adhesions arise from theiris collarette attaching to the periphery of the endothelialdeficit. Lesions of the iris can also be associated with this, aswell as defects of the iridocorneal angle occasionally asso-

ciated with a primary glaucoma of more or less early onset.[2,9,10,20] Malformations of the face, heart, genito-urinarytract, central nervous system spinal cord, and retardedgrowth can equally coexist and have a hereditary natureoften. [2,5,9,10,20] The association of a palpebral agenesisand an ocular anterior segment dysgenesis has been describedin a domestic cat. The genetic origin of these disorders hasnot been proven in this species. [13,19]

In human ophthalmology, dysgeneses of the ocular anteriorsegment are classified into either ocular anomalies caused bydefective migration or differentiation of cells of the cephalicneural crest, or more complex forms of dysgenesis, in which

the induction mechanisms of the lens, of ectodermal origin,are paramount. [10]

In the case under discussion, the abnormal conformation ofthe 2 central zones of the cornea may have resulted from ananomaly of embryogenesis of the corneal stroma, the originof which cannot be determined. The same applies to thedefective migration of the lens. Only histological examinationof the anterior segment would allow this hypophysis to betested, but this would have been incompatible with our aimof preserving a functioning eyeball.

In the cat, glaucoma is known to be principally secondary

to uveitis, lens luxation or neoplasms of the anterior segment.[11,19,24] Primary glaucoma is rare. [7,11-13,15,17,19,22]In a histological study of 131 cases, WILCOX et al. [24]found only 3 cases of goniodysgenesis responsible for ocularhypertension. A breed disposition to primary glaucoma has

been described in the Siamese and the Persian (pectinateligament dysplasia) and the Burmese (closed angle). [19] Nopublications have mentioned the angle anomalies describedin this clinical case. Today, the cat is 3 years older and hasshown no signs of increase in ocular pressure to date.

Phacoemulsification was chosen to excise the lens due tothe adhesions between the lens and the cornea. The keratotomywas performed on healthy cornea whilst taking the lens positioninto account so as to allow easy extraction of the lens fragments.The evacuation of the irrigation fluid was performed at thesame time by means of a hand piece, via the perforation inthe cornea, thus sparing the anterior chamber from ultra-sound waves and debris from the lens.

The preservation of the contact zone between the anteriorlens capsule and the cornea supported the application of thebiomaterial corneal graft, using a previously published tech-nique. [1,6,23] The superimposition of layers allowed a goodquality seal to be obtained. Due to the cats lively nature, the

operated zone was protected by suturing the nictitating mem-brane to the upper eyelid, followed by a supplementary ble-pharorrhaphy.

The central scar opacity had an undeniable transparency,unlike the leucomas observed by BUSSIERES and colleagues[1] in 2 cats with perforated corneal ulcers treated by excisionof necrotic tissue and the application of a porcine small intestinalsubmucosa graft. A pedunculated conjunctival graft had beenused to protect the operation site and could explain theappearance of a very opaque central leucoma. In the caseunder discussion, the biomaterial graft was replaced by tissuewhich re-covered the area with a functioning transparency,

and was sufficient to preserve the vision of this one-eyed cat.

Conclusion

Anterior segment dysgeneses are well known in humans.Their pathology is well understood and their origin has beenexplained using animal models. Their mode of transmissionand the genetic mutations responsible for these conditionshave been the subject of much research. In more than 70% ofcases, they are associated with congenital glaucoma, whichcarries a poor prognosis for vision. This clinical case closely

resembles Peters anomaly, first described in 1887. As far asthe author is aware, this is the first case describing an anteriorsegment dysgenesis with corneal perforation that was suc-cessfully treated with a biomaterial graft in the cat.

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Anterior Segment Dysgenesis Cat