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Contact Lens & Anterior Eye 34 (2011) 56–63 Contents lists available at ScienceDirect Contact Lens & Anterior Eye journal homepage: www.elsevier.com/locate/clae Review Pellucid corneal marginal degeneration: A review Amit Jinabhai, Hema Radhakrishnan, Clare O’Donnell The University of Manchester, England, UK article info Keywords: PMD Clinical features Histopathology Differential diagnosis Management abstract Pellucid marginal corneal degeneration (PMD) is a rare ectatic disorder which typically affects the inferior peripheral cornea in a crescentic fashion. The condition is most commonly found in males and usually appears between the 2nd and 5th decades of life affecting all ethnicities. The prevalence and aetiology of this disorder remain unknown. Ocular signs and symptoms of patients with PMD differ depending on the severity of the condition. Unless corneal topography is evaluated, early forms of PMD may often be undetected however, in the later stages PMD can often be misdiagnosed as keratoconus. Visual signs and symptoms include longstanding reduced visual acuity or increasing against-the-rule irregular astig- matism leading to a slow reduction in visual acuity. In rare cases, patients may present with a sudden loss of vision and excruciating ocular pain due to corneal hydrops or spontaneous perforation. The vast majority of PMD patients are managed using spectacles and contact lenses. Several surgical procedures have been used in an attempt to improve visual acuity when spectacles and contact lenses do not provide adequate vision correction. Since patients with PMD make poor candidates for laser vision correction, an awareness of the topographical and slit-lamp features of PMD will be useful to clinicians screening for signs of corneal abnormality before corneal refractive surgery. This review describes the clinical features of PMD, its differential diagnosis and various management strategies presently available. © 2010 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved. 1. Introduction 1.1. Definition Pellucid marginal corneal degeneration (PMD) is a rare idio- pathic, thinning disorder of the peripheral cornea most usually affecting the inferior quadrant in a crescentic fashion. The word ‘pellucid’, meaning clear, was first used by Schlaeppi [1] to denote the clarity of the cornea in this condition despite the presence of ectasia. The condition may also have been previously identified in early European studies under several other names such as pellucid marginal degeneration [2–4] or pellucid marginal dystrophy [1,5]. This review describes the clinical features of PMD, its differential diagnosis and the options for management. 1.2. Aetiology At present, the exact aetiology of PMD is unclear and it is not known whether PMD, keratoconus, and keratoglobus are distinct diseases or phenotypic variations of the same disorder [6–8]. Nev- ertheless, several authors [2,3,9,10] have proposed that PMD is a Corresponding author at: The University of Manchester, Faculty of Life Sciences, Manchester M60 1QD, UK. Tel.: +44 161 306 3872; fax: +44 161 306 3969. E-mail address: Clare.O’[email protected] (C. O’Donnell). peripheral form of keratoconus. In agreement with this sugges- tion, other studies have reported the occurrence of keratoconus with PMD [11–13]. Kayazawa et al. [13] report that 17 out of 20 patients with PMD also showed concomitant keratoconus in the same eye. Varley et al. [12] describe that 8 out of 12 patients with PMD also displayed corneal features suggestive of keratoconus. Finally Sridhar et al. [11] report that PMD was associated with ker- atoconus in 12 out of 166 eyes evaluated. In agreement with the findings of Karabatsas and Cook [14], Sridhar et al. [11] also reveal that PMD was associated with keratoglobus in 15 out of 155 eyes investigated. Fogla and colleagues [15] have discovered induced PMD in two subjects who had undergone laser in situ keratomileusis (LASIK). The authors discuss that an inherent weakness in the biome- chanical properties of the cornea is most likely in PMD and that performing LASIK in eyes with any topographical signs of corneal abnormality may inadvertently induce this form of keratectasia. This in agreement with other reports [16–18]. 1.3. Epidemiology To date, no bio-statistical studies have evaluated either the inci- dence or prevalence of PMD; however, the general consensus in the literature is that PMD is a rare condition, less common than other ectatic diseases such as keratoconus [6–8], but more common than either keratoglobus [19] or posterior keratoconus [19]. 1367-0484/$ – see front matter © 2010 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.clae.2010.11.007

Pellucid corneal marginal degeneration: A review

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Page 1: Pellucid corneal marginal degeneration: A review

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Contact Lens & Anterior Eye 34 (2011) 56–63

Contents lists available at ScienceDirect

Contact Lens & Anterior Eye

journa l homepage: www.e lsev ier .com/ locate /c lae

eview

ellucid corneal marginal degeneration: A review

mit Jinabhai, Hema Radhakrishnan, Clare O’Donnell ∗

he University of Manchester, England, UK

r t i c l e i n f o

eywords:MDlinical featuresistopathologyifferential diagnosisanagement

a b s t r a c t

Pellucid marginal corneal degeneration (PMD) is a rare ectatic disorder which typically affects the inferiorperipheral cornea in a crescentic fashion. The condition is most commonly found in males and usuallyappears between the 2nd and 5th decades of life affecting all ethnicities. The prevalence and aetiologyof this disorder remain unknown. Ocular signs and symptoms of patients with PMD differ dependingon the severity of the condition. Unless corneal topography is evaluated, early forms of PMD may oftenbe undetected however, in the later stages PMD can often be misdiagnosed as keratoconus. Visual signsand symptoms include longstanding reduced visual acuity or increasing against-the-rule irregular astig-matism leading to a slow reduction in visual acuity. In rare cases, patients may present with a sudden

loss of vision and excruciating ocular pain due to corneal hydrops or spontaneous perforation. The vastmajority of PMD patients are managed using spectacles and contact lenses. Several surgical procedureshave been used in an attempt to improve visual acuity when spectacles and contact lenses do not provideadequate vision correction. Since patients with PMD make poor candidates for laser vision correction, anawareness of the topographical and slit-lamp features of PMD will be useful to clinicians screening forsigns of corneal abnormality before corneal refractive surgery. This review describes the clinical features

agnosBriti

of PMD, its differential di© 2010

. Introduction

.1. Definition

Pellucid marginal corneal degeneration (PMD) is a rare idio-athic, thinning disorder of the peripheral cornea most usuallyffecting the inferior quadrant in a crescentic fashion. The word

pellucid’, meaning clear, was first used by Schlaeppi [1] to denotehe clarity of the cornea in this condition despite the presence ofctasia. The condition may also have been previously identified inarly European studies under several other names such as pellucidarginal degeneration [2–4] or pellucid marginal dystrophy [1,5].

his review describes the clinical features of PMD, its differentialiagnosis and the options for management.

.2. Aetiology

At present, the exact aetiology of PMD is unclear and it is notnown whether PMD, keratoconus, and keratoglobus are distinctiseases or phenotypic variations of the same disorder [6–8]. Nev-rtheless, several authors [2,3,9,10] have proposed that PMD is a

∗ Corresponding author at: The University of Manchester, Faculty of Life Sciences,anchester M60 1QD, UK. Tel.: +44 161 306 3872; fax: +44 161 306 3969.

E-mail address: Clare.O’[email protected] (C. O’Donnell).

367-0484/$ – see front matter © 2010 British Contact Lens Association. Published by Elsoi:10.1016/j.clae.2010.11.007

is and various management strategies presently available.sh Contact Lens Association. Published by Elsevier Ltd. All rights reserved.

peripheral form of keratoconus. In agreement with this sugges-tion, other studies have reported the occurrence of keratoconuswith PMD [11–13]. Kayazawa et al. [13] report that 17 out of 20patients with PMD also showed concomitant keratoconus in thesame eye. Varley et al. [12] describe that 8 out of 12 patients withPMD also displayed corneal features suggestive of keratoconus.Finally Sridhar et al. [11] report that PMD was associated with ker-atoconus in 12 out of 166 eyes evaluated. In agreement with thefindings of Karabatsas and Cook [14], Sridhar et al. [11] also revealthat PMD was associated with keratoglobus in 15 out of 155 eyesinvestigated.

Fogla and colleagues [15] have discovered induced PMD in twosubjects who had undergone laser in situ keratomileusis (LASIK).The authors discuss that an inherent weakness in the biome-chanical properties of the cornea is most likely in PMD and thatperforming LASIK in eyes with any topographical signs of cornealabnormality may inadvertently induce this form of keratectasia.This in agreement with other reports [16–18].

1.3. Epidemiology

To date, no bio-statistical studies have evaluated either the inci-dence or prevalence of PMD; however, the general consensus in theliterature is that PMD is a rare condition, less common than otherectatic diseases such as keratoconus [6–8], but more common thaneither keratoglobus [19] or posterior keratoconus [19].

evier Ltd. All rights reserved.

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Sridhar and collaborators’ [11] study is the largest investigationf PMD to date, the authors evaluated 116 eyes from 58 patients andound a higher incidence of PMD in males (77.6% of their subjects).hese findings are in agreement with an early study by Kompellat al. [20], who found that 12 out of 15 patients examined withMD were male. Most recently, Tzelikis et al. [21] found that 30 outf the 45 patients they evaluated with PMD were male. However,rior to these three studies the literature had reported no genderredilection [6–8,22].

Krachmer et al. [6] explain that PMD is a slowly progressive con-ition, classically discovered between the second and fifth decadesf life. Sridhar and co-workers’ [11] study concurs with Krachmert al.’s [6] report and shows that the average age for presentationith PMD was 34 ± 15 years. Similarly, Kompella et al. [20] report

he average age of presentation with the condition as 39 ± 14 years.n the other hand, Tzelikis et al. [21] report a still higher averagege for presentation of 48 ± 12 years. The current literature sug-ests that PMD affects all ethnicities and shows no geographicalredisposition [6–8,19,22].

.4. Heredity

To date, there is no evidence that PMD is genetically inherited.nly Santo and Kara-Jose [23] describe topographical evidence oforneal ectasia in asymptomatic family members of a patient withlassic PMD. Unilateral cases however, usually manifest topograph-cal evidence of PMD in the contralateral eye or reveal the presencef other ectatic disorders [14]. Other authors have revealed mod-rate to high astigmatism in asymptomatic family members ofatients with PMD [4,24,25].

. Clinical features

Both Sridhar et al. [11] and Krachmer et al. [6] agree that PMD isbilateral condition, whereas other authors have also described

he occurrence of unilateral cases [26–29]. The condition mostommonly involves the inferior cornea [6–8,11,22] however, othereports have shown that the site of involvement can also includehe superior [11,25,30–33], nasal [30] and temporal [30] quadrantsf the cornea. Classically, PMD is characterised by a typical nar-ow, clear band of corneal thinning around 1 or 2 mm in widthhich extends from the 4-o’clock position to the 8-o’clock position

7,8,11]. Robin et al. [8] explain that the degree of thinning is usu-lly severe, resulting in up to 80% stromal tissue loss. Between thehinned band-like region and the limbus there is typically a 1–2-

m wide region of uninvolved, normal cornea which is usuallylear [8,10,22]. The corneal protrusion in PMD is most marked just

ig. 1. The corneal side-profile appearance of early-stage (A) and more advanced pellucimbus in either image, the inferior peripheral cornea shows a protruding appearance. Thives some indication of how pellucid marginal corneal degeneration may progress over

nterior Eye 34 (2011) 56–63 57

superior to the area of thinning, where the thickness of the centralcorneal is usually normal [6–8,11,34].

The gold standard in detecting corneal ectasia is undoubtedlycorneal topography. The very first computer-based topographers,such as the TMS-1 device (Tomey Technology, Waltham, MA, US),used the Placido rings method. More recently, the Orbscan II(Bausch & Lomb, Rochester, NY, US) has been developed whichutilises both slit-scanning (stereo-triangulation) and Placido ringsreflection to capture topographical and corneal thickness data.Alternatively, the Pentacam device (OCULUS, Wetzlar, Germany)uses Scheimpflug photography to determine corneal topogra-phy and pachymetry. Recent instrumentation such as the VisanteOmni (Carl Zeiss Meditec, Dublin California, USA), combines bothPlacido ring and optical coherence tomography techniques toderive corneal topography and thickness information in addition toproviding highly detailed images of the anterior segment. The useof such instruments allows the detection of early and subclinicalectasia which is essential in pre-operative corneal laser refractivesurgery assessment, because performing these procedures in earlyor known PMD [15] or keratoconus [35] patients can exacerbatethe progression of these conditions.

The hallmarks of PMD are corneal topographical abnormali-ties above the thinned zone which show an obvious flatteningof the cornea along the vertical meridian and “against-the-rule”astigmatism [6–8]. When viewed from the side, several authorsclassically describe that the inferior-central cornea in PMD appearsto show the side-profile contour of a “beer-belly” [36–38], as shownin Fig. 1(B). Although not diagnostic of any given ectatic condi-tion, the corneal side-profile appearance may be used alongsidecorneal topography, central thickness measurements and cornealslit-section observations in the differentiation of PMD from ker-atoconus and keratoglobus. In advanced cases of PMD, Krachmer[7] reports that the ectatic zone steepens abruptly (from the cen-tre downwards towards the periphery) with increases in curvatureof as much as 20 D. Topographical investigations have shown thatthis inferior peripheral steepening extends into the mid-peripheral,inferior oblique corneal meridians in a classic “crab-claw”, “but-terfly” or “kissing doves” appearance [11,14,34,39–41] as shownin Fig. 2(B). However, Lee et al. [42] have discussed that a “claw-shaped” pattern on corneal topography is not diagnostic of PMD andthat such patterns may also be found in keratoconus. The authorssuggest that slit-lamp signs as well as pachymetry maps must beconsidered in conjunction with corneal topography for a reliable

diagnosis.

As summarised in Table 1, corneas with PMD usually show nosigns of Fleischer’s ring, corneal infiltration, scarring or vascularisa-tion [6]. No obvious cone can be recognised and there are no signsof lipid deposition [8]. In addition, these corneas do not exhibit

id marginal corneal degeneration (B). When comparing the inferior and superioris classic “beer-belly” contour is more pronounced in image B than in image A, andtime.

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58 A. Jinabhai et al. / Contact Lens & Anterior Eye 34 (2011) 56–63

Fig. 2. The corneal topography of a normal eye (A), an eye with pellucid marginal corneal degeneration (B) and an eye with moderate keratoconus (C). Note the classic“kissing doves” appearance in image B. The scale bar values are in mm, the red colours represent steeper corneal curvatures whereas the green/blue colours represent flattercA dmontt

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orneal curvatures.ll three images were captured using the Medmont E300 corneal topographer (Me

his figure legend, the reader is referred to the web version of the article.)

unson’s sign (a V-shaped deformation of the lower eyelid whenhe eye is looking downwards) or Rizutti’s phenomenon (a sharplyocussed beam of light near the nasal limbus produced by lateralllumination of the temporal limbus) [42]. Descemet’s folds mayevelop and are usually found to be concentric with the inferior

imbus; such folds disappear when pressure is applied to the cornea6,43].

Patients presenting with PMD most typically complain of a grad-al, progressive reduction in vision or longstanding poor visualcuity; both symptoms most commonly result from large mag-itudes of irregular, against-the-rule astigmatism [7,22]. Rarerymptoms experienced in PMD include sudden scleral injection,

cute pain, a sudden reduction in vision and photophobia as aesult of acute hydrops and/or spontaneous corneal perforation7,25,44–55]. Corneal hydrops is also found in patients with ker-toconus; similarly, the presenting signs for patients with PMDre corneal oedema with an identifiable break in Descemet’s

able 1summary of the differences in clinical signs between pellucid marginal corneal degener

Feature Keratoconus

Best corrected spectacle visual acuity Becomes reduced even at the mild stage

‘Scissors’ retinoscopic reflex Present in all severitiesPosition of maximum protrusion Equivalent to the area of thinning

Location of corneal thinning Can be centrally or just inferior to the visu

Video-keratography appearance (A) An increased area of corneal power suconcentric areas of decreasing power(B) Inferior–superior power asymmetry(C) Skewing of the steepest radial axes abthe horizontal meridian

Central corneal thickness Reduced compared to normalFleischer’s ring Usually present around the base of the coApical corneal scarring Usually present in the moderate and seveRizutti’s phenomenon Usually present in the moderate and seveMunson’s sign Usually present in the moderate and seve

, Camberwell, Victoria, Australia). (For interpretation of the references to colour in

membrane. The occurrence of corneal hydrops reflects a cornealresponse to progressive thinning. Sridhar et al. [11] evaluated 7eyes with hydrops due to PMD and reported that the sites of thebreaks in Descemet’s membrane were all above the area of thinning.In patients with superior PMD, Taglia and Sugar [25] and Lucarelliet al. [47] describe corneal perforation at the inferior crescent. Dur-ing the recovery from acute hydrops, corneal vascularisation andscarring has been found to occur in patients with PMD [7,22].

3. Classification

Owing to the rarity of the disorder, no clearly defined guidelineshave been proposed to help categorise the severity of the condi-tion. However, the literature reports that early [37,56,57], moderate[28,58,59] and advanced [11,60,61] stages of the condition exist andthat the ectatic process advances over time [7].

ation and keratoconus.

Pellucid marginal corneal degeneration (PMD)

Generally only becomes significantly reduced in theadvanced stageUsually only seen in advanced casesTypically – superior to the thinned zone [6–8,11,22]Atypically – inferior to the thinned zone [11,25,30–33]

al axis Typically – in a narrow band of approximately 1–2 mm,located around 1.5 mm above the inferior limbus; the bandis concentric to the limbus in a crescent-like shape,extending from the 4 o’clock to the 8 o’clock position[6–8,11,22]Atypically – in a narrow band of approximately 1–2 mm,located around 1.5 mm below the superior limbus; theband is concentric to the limbus in a crescent-like shape,extending from the 10 o’clock to the 2 o’clock position[11,25,30–33]

rrounded by Classic “kissing doves” or “crab-claw” patterndemonstrating irregular, against-the-rule astigmatism

ove and below

Usually normalne Absentre stages Absentre stages Absentre stages Absent

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. Histopathology

Zucchini [2] carried out the first histopathological study ofMD and found that even though Bowman’s layer was absent,he epithelium was normal. In addition, Zucchini reports anncrease in the stromal mucopolysaccharides. No abnormalitiesf Descemet’s layer or the endothelium were noted in thisnvestigation. Francois et al. [3] performed further detailed light-

icroscopy investigations and also discovered an increase intromal mucopolysaccharides as well as an irregular Bowman’sayer with ruptures in places. Interestingly, Francois et al. alsoescribe epithelial oedema and irregularity, folds in Descemet’s

ayer and stromal thinning in their study. Pouliquen et al. [9]onducted the first electron microscopy study of PMD and alsoevealed breaks in Bowman’s layer, an irregular arrangement of thetroma with the presence of extracellular, granular electron-denseeposits. Zucchini [2], Francois et al. [3] and Pouliquen et al. [9] allote the absence of inflammatory cells in their studies. Rodriguest al. [10] used scanning electron microscopy to evaluate corneasith PMD and revealed unusual electron-dense areas of fibrous

ong-spacing (FLS) collagen with a periodicity of 100–110 nm in theeripherally thinned areas, scattered in amongst regions of mostlyormal collagen which had a periodicity of 60–64 nm. Rodriguest al. [10] report that they had observed such FLS collagen in casesf advanced keratoconus with scarring.

Other conditions reported in patients with PMD include chronicpen-angle glaucoma [62], retinitis pigmentosa [20], retinal lat-ice degeneration [20] scleroderma (a progressive, multi-systemonnective tissue disorder) [39], kerato-conjunctivitis [63], eczema3,5] and hyperthyroidism [1,64]; however, none of these condi-ions have been proven to show an obvious pathogenic associationith PMD.

. Differential diagnosis of PMD

PMD is most frequently misdiagnosed as the more commonorneal ectatic disorder keratoconus [19,42]. Keratoconus, is theerm used to describe the condition where the cornea takes onsteepened, conical profile at the same position as the maximal

tromal thinning [6,65]. The disease process of keratoconus is non-nflammatory, showing no signs of either vascularisation or cellularnfiltration [6]. The condition is usually bilateral and involves theentral two-thirds of the cornea, with the cone apex most usuallyisplaced inferior to the visual axis [66]. Keratoconus classicallyauses mild to marked impairment of visual function [19]. Typicaligns of keratoconus include a “scissors” retinoscopic reflex, an “oil-rop” ophthalmoscopic reflex, Fleischer’s ring [67], Vogt’s striae68] and stromal tissue thinning with conical protrusion [69,70].ater signs of keratoconus include Munson’s sign, Rizutti’s phe-omenon and apical corneal scarring [71,72].

In moderate cases, Rabinowitz [66] explains that PMD can beistinguished from keratoconus by slit-lamp biomicroscopic exam-

nation, due to the classic location of the region of corneal thinning.owever, in early cases of PMD the cornea may look relativelyormal, and in severe cases PMD may be difficult to differenti-te from keratoconus because the corneal thinning may involvehe majority, if not all of the inferior cornea [8]. In both theseases corneal topography is most valuable in order to differentiateetween the two conditions, as they generally show distinctly dif-erent topographic patterns [14,34,73], as highlighted in Fig. 2(C).

his example of a moderately keratoconic cornea shows a classi-al inferior-central cone where the steepening extends towardshe inferior limbus [73]. Rabinowitz and McDonnell [74] have alsoeported that keratoconic corneas characteristically show steepen-ng of the inferior cornea compared with the superior cornea, which

nterior Eye 34 (2011) 56–63 59

is more prominent temporally. Lee et al. [42] have also advocatedthe use of pachymetry maps to make the most reliable identifica-tion. A differential diagnosis of PMD from keratoconus is desirablesince the prognosis and management can vary between the twoconditions [75].

The differential diagnosis of PMD also includes the rare, bilateralectatic condition keratoglobus. Keratoglobus is typically charac-terised by limbus-to-limbus thinning causing the cornea to assumea globular profile [76], where keratometry measurements canoften be as high as 60–70 D [77]. As opposed to in keratoconus,corneas with keratoglobus are usually diffusely thinned (to approx-imately one-third to one-fifth of the normal thickness [77]) at themid-peripheral cornea [78,79]. Vogt’s striae, sub-epithelial scar-ring, Fleischer’s ring, lipid deposition and corneal vascularisationare rarely found in corneas with keratoglobus [77,78]. However,the cornea can become opaque and oedematous from breaks inDescemet’s membrane [19].

Other peripheral corneal thinning disorders misdiagnosed withPMD include Mooren’s ulcer and Terrien’s marginal degeneration.Mooren’s ulcer is an idiopathic condition characterised by eitherunilateral or bilateral painful, inflammatory thinning and ectasia ofthe peripheral cornea [8]. Slit-lamp examination signs of Mooren’sulcer classically include perilimbal corneal infiltrates, epithelialdefects within the ulcerated region and finally the developmentof a shallow furrow at the edge of the ulcer [80]. Usually the siteof involvement is the inferior limbus, with the ulceration thenspreading circumlimbally and then centrally, eventually involvingthe entire cornea. Vascularisation occurs during the healing pro-cess which can last up to 12–18 months [81]. Chow and Foster [81]report that at the end-stages of Mooren’s ulcer, a scarred and vascu-larised cornea is typically found with stromal thinning to less thanhalf of the original corneal thickness.

Terrien’s marginal degeneration is a non-inflammatory condi-tion characterised by slowly progressive, bilateral, marginal cornealectasia typically beginning superiorly which can then progresscircumferentially [8]. Terrien’s marginal degeneration most com-monly affects males in their mid-twenties [82]. Forstot [82] reportsthat early slit-lamp examination signs include marginal opacifica-tion with peripheral vascularisation. Marginal thinning then beginsto occur parallel to the limbus, forming a “gutter-like furrow” in theclear gap between the opacification and the limbus. This furrowdoes not ulcerate and the epithelium remains fully intact how-ever, lipid deposition occurs as the furrow deepens [8]. Goldmanand Kaufman [83] have previously reported that pseudo-pterygiamay develop near the furrowed area. As the process continuesthe thinning may extend to the inferior cornea, sparing the inter-palpebral periphery [8]. Very few cases of central ectasia havebeen reported in association with Terrien’s marginal degeneration[84,85]. The corneal topography of Terrien’s disease is characterisedby corneal flattening over the areas of peripheral thinning pro-duced by the disorder [86,87]. When the thinning is restricted tothe superior and/or inferior areas of the peripheral cornea only, arelative steepening of the inter-palpebral peripheral cornea can befound, resulting in large magnitudes of against-the-rule or obliqueastigmatism [86]. Perforation of the ectatic regions may occur withocular trauma or even spontaneously [8]. Terrien’s marginal degen-eration progresses very slowly, frequently taking several years.Increases in irregular astigmatism cause a subsequent diminutionof best-corrected visual acuity. Very rarely does Terrien’s marginaldegeneration cause acute ocular inflammation with pain [88,89],with the vast majority of patients complaining of mild, intermittent

ocular irritation [82].

Both Rabinowitz [66] and Robin et al. [8] propose that PMDcan be differentiated from Mooren’s ulcer and Terrien’s marginaldegeneration because the area of thinning in PMD is always epithe-lialised, without lipid deposition, remaining avascular and clear.

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Table 1 summarises the subtle differences in clinical signsetween PMD and keratoconus which could allow clinicians toifferentiate between the two conditions.

. Management

.1. Non-surgical methods

Management of PMD is dependant on the severity of the disease.n the early stages of the condition, PMD is most commonly man-ged using spectacles [21,28,75]. Biswas et al. [28] achieved goodisual acuity in PMD patients with high astigmatism after prescrib-ng appropriate sphero-cylindrical spectacles with high refractivendex lenses. Kompella et al. [20], Mahadevan et al. [90] and Srid-ar et al. [11] all suggest that soft toric contact lenses can be useful,ut usually only before the progression of irregular astigmatismccurs. Other authors describe the successful use of hybrid contactenses for patients with PMD, including Saturn II lenses (Pilkingtonarnes-Hind Inc., Sunnyvale, CA, US) [91]; SoftPerm lenses (Pilk-

ngton Barnes-Hind Inc., Sunnyvale, CA, US) [92,93] and SynergEyesenses (SynergEyes Inc., Carlsbad CA, US) [94,95]. However, Saturn IIenses tended to tighten with time [96] and had low oxygen perme-bility (Dk = 14 × 10−11 (cm2/s) (ml O2/ml × mmHg)) resulting inorneal oedema and neovascularisation as common complications97]. SoftPerm lenses were manufactured with the same materialss the Saturn II lenses, but used a larger diameter with a modi-ed edge design to allow better tear circulation. Despite showing

ewer complications, both Maguen et al. [98] and Chung et al. [99]ound that SoftPerm lenses ripped easily between the RGP and softens junction during lens handling. Both authors also reported aigh rate of giant papillary conjunctivitis (GPC) in patients wearingoftPerm lenses.

Compared to Saturn II (1st-generation) and SoftPerm (2nd-eneration) hybrid lenses, SynergEyes lenses provide the benefitsf a stronger RGP-hydrogel junction as well as higher oxygen per-eability (Dk = 100 (cm2/s) (ml O2/ml × mmHg)). Nonetheless, Nau

95] found lens tightness and removal problems in patients usingynergEyes lenses, whilst Abdalla et al. [94] report the occurrencef GPC and allergies.

Moderate cases of PMD usually require fitting with rigid gas per-eable (RGP) contact lenses. In these patients, a common problemith standard-diameter, spherical RGP lens use is excessive inferior

dge stand-off. This is primarily due to large amounts of irregulargainst-the-rule astigmatism resulting in unstable lens centra-ion. Consequently, many authors have fitted larger-diameter RGPenses with successful results [20,21,28,100]. In these studies largeiameter RGP lenses were found to provide satisfactory lens stabil-

sation and lens tolerance with good visual acuity [20,21,28,100].n addition, Raizada and Sridhar [60] and Mahadevan et al. [90]ave described step-by-step methods to help practitioners obtaingood fit with large diameter spherical RGP lenses using a minimalumber of trial lenses.

‘Bi-toric’ RGP contact lenses have also been shown to be suc-essful in managing patients with PMD. Dominguez et al. [101],astl and Kirby [102] and Gruenauer-Kloevekorn et al. [40] haveescribed the successful correction of large amounts of cornealstigmatism using specialised back surface design lenses leading toood visual acuity. These authors all report satisfactory contact lensomfort and tolerance in patients wearing these specialised lenses,owever no evaluation of the average or maximum wearing times

as made in any of the three studies.

Liu et al. [64] describe the use of reverse-geometry lenses inpatient with early PMD to allow better peripheral lens align-ent where the cornea is steepest. However, such lenses may beost useful in patients with negative corneal eccentricities. PMD

nterior Eye 34 (2011) 56–63

patients, in general, only show negative eccentricities in the infe-rior quadrant of the cornea [40]. Therefore reverse-geometry lensescould potentially cause superior lens binding, resulting in inade-quate tear exchange and persistent epithelial damage.

Modern day RGP and soft contact lens materials can be specif-ically manufactured to offer “sector management control”; suchdesigns allow the peripheral lens geometry to be customised tocomplement the anterior surface of the ectatic cornea. White [103]has reported that these bespoke designs have been useful with softlens materials for keratoconic patients and has suggested that thistechnology may also be helpful for PMD patients.

As PMD progresses further to the advanced stages, adequate RGPlens centration can become very difficult to achieve as additionalcorneal steepening increases the possibility of lens dislocation withblinking. Several authors propose that RGP scleral contact lensesmay be of use in such situations [28,104–107]. Scleral lenses areadvantageous in that they are supported by the sclera thus reduc-ing lid sensation; they can vault the area of the cornea affectedby the disease making the irregular topography less of a problemto fit; they provide good centration meaning high-powered lensesremain static; they are unlikely to dislodge upon blinking andfinally there is less risk of foreign body entrapment. Scleral lensescan have several disadvantages such as poorer oxygen transmissionto the cornea; complicated manufacturing processes; difficultieswith application compared to corneal RGP lenses and lastly thatrelatively few practitioners are experienced in fitting such lenses.

The literature reviewed indicates that the vast majority ofpatients with PMD are managed using non-surgical methods[20,21]. Both Kompella et al. [20] and Tzelikis et al. [21] report thatapproximately 88% of their participants successfully used eitherspectacles or contact lenses to correct their visual difficulties, witharound 12% of patients opting for surgical intervention. The differ-ent surgical strategies used for PMD will now be discussed.

6.2. Surgical methods

Penetrating keratoplasty (PK) is considered for patients withPMD whose vision is inadequate with contact lenses or for patientswho are lens intolerant [12,28,108]. In general however, patientswith PMD are usually poor candidates for PK as the corneal thin-ning occurs close to the limbus. As a result large eccentric graftsare required and must be positioned very close to the limbusthus increasing the chances of graft rejection, suture-induced com-plications and corneal neovascularisation [7,11,66]. In addition,PK typically induces large amounts of post-operative astigmatismwhich may be difficult to correct due to variation in the graft-hostthickness [66]. Biswas et al. [28] found that 66 months after surgeryan average residual cylinder of 4.63 D still remained giving an aver-age best-corrected acuity of 6/15 in 3 eyes with PMD. On the otherhand, in deep anterior lamellar keratoplasty (DALK), the anteriorthird (to two thirds) of the cornea is replaced with donor tissue[50]. To date, only Millar and Maloof [50] have described the suc-cessful use of DALK in a PMD patient presenting with a sudden lossof vision due to spontaneous corneal perforation. The authors foundthat post-operative visual acuity remained stable at 6/6-2 even oneyear after surgery.

Earlier techniques used in treating PMD include lamellar cres-centic keratoplasty [109,110]. Biswas et al. [28] have also reportedconducting lamellar thermo-keratoplasty (LTK), an adaptation ofthe surgical technique described by Schanzlin et al. [109], for one

eye with PMD. This procedure involved thermal shrinkage of thehost lamellar bed, prior to the placement and suturing of thecrescent-shaped donor lamellar cornea. Biswas et al. [28] recordeda best-corrected visual acuity of 6/6 one year after surgery in spiteof 6 D of residual astigmatism.
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A. Jinabhai et al. / Contact Lens & Anterior Eye 34 (2011) 56–63 61

Table 2A summary of the non-surgical and surgical methods used to manage pellucid marginal corneal degeneration.

Non-surgical methods Surgical methods

Spectacles [21,28,75] Penetrating keratoplasty [12,28,108]Soft lenses [11,20,90,103] Deep anterior lamellar keratoplasty [50]Large diameter RGP lenses [20,21,28,60,90,100] Lamellar crescentic keratoplasty [109,110]Hybrid lenses [91–95] Lamellar thermo-keratoplasty [28]Bi-toric RGP lenses [40,101,102] Lamellar crescentic resection [59,112,113]Scleral lenses [28,104–107] Corneal wedge excision [114–116]

Epikeratoplasty [117]in lamstromen crphaki

gaaidpd

psop

trnciiw

pmfp

icc[

tstsiiatepaS[temvaaK

Tuck-Intra-CollagToric

Kremer et al. [111] had previously suggested a two-staged sur-ical procedure which firstly involves lamellar grafting followed bysmaller penetrating graft, with a view to avoid the complicationsssociated with large eccentric grafts and to achieve a topograph-cally satisfactory corneal surface. Rasheed and Rabinowitz [61]escribe using additional astigmatic keratotomy for some of theiratients in order to reduce large amounts of residual astigmatismuring the post-surgical follow-up period.

Lamellar crescentic resection (LCR) has also been carried out foratients with PMD [59,112,113]. The primary aim of LCR is the exci-ion of the abnormally thinned stroma and then re-approximationf the near-normal thickness edges. The major advantage to thisrocedure is that no donor tissue is required.

Corneal wedge excision (also referred to as corneal wedge resec-ion) is similar to LCR except it involves full corneal thickness tissueemoval followed by re-apposition of the remaining normal thick-ess cornea using sutures [114–116]. Busin et al. [115] coupledorneal wedge resection with two bevelled, sutureless, penetrat-ng relaxing incisions (at the 3 o’clock and 9 o’clock positions) tomprove long-term astigmatic stability in 10 eyes of 10 patients

ith PMD.Other rarer forms of surgery indicated in PMD are epikerato-

lasty. This is a form of on-lay lamellar keratoplasty in which a lensade of human corneal tissue is sutured onto the anterior sur-

ace of the cornea to change its anterior curvature and refractiveroperties [117].

More recent and novel surgical techniques used to treat PMDnclude “tuck-in” lamellar keratoplasty (TILK) [118], intra-stromalorneal segment ring (INTACS) inserts [36,56,58,119,120], andollagen cross-linking with riboflavin and UVA irradiation (CXL)121,122].

The procedure for INTACS implantation involves the incorpora-ion of two semi-circular plastic rings into the peripheral cornealtroma through a small radial incision. INTACS essentially flattenhe centre of the cornea from within the stroma using an “archortening” effect [123]. The procedure for placement of INTACSnserts is performed outside the central visual axis, and INTACSnserts can be removed or replaced if the required outcome is notchieved. In PMD, the ectatic corneal tissue has a thinner struc-ure and is potentially more easily flattened compared to in normalyes. INTACS inserts are useful in managing contact lens–intolerantatients with clear corneas and central thicknesses above 400 �ms an attempt to delay or perhaps avoid corneal transplantation.everal authors have revealed successful outcomes after surgery36,56,58,119,120]. Mularoni et al. [58] carried out INTACS inser-ion in 8 eyes of 8 patients with varying degrees of PMD. The authorsvaluated their patients for a minimum of 12 months after treat-

ent and report an improvement in the average best-corrected

isual acuity from 6/15 to 6/9 after surgery. Successful results havelso been described by Akaishi et al. [124], Barbara et al. [125], Ertannd Bahadir [126] and Pinero et al. [120]. Ertan and Bahadir [33] andubaloglu et al. [119] both adapted the surgical technique used in

ellar keratoplasty [118]al corneal segment rings [36,56,58,119,120,124–126]oss-linking [121,122]c intra-ocular lens [129]

the treatment by utilising a single INTACS insert. Ertan and Bahadir[33] used this method to treat a 26-year old patient with superiorPMD.

The technique of corneal collagen cross-linking consists ofthe photo-polymerisation of the stromal collagen fibres by thecombined action of a photosensitising substance (riboflavin, vita-min B2) and ultra-violet light from a solid-state UVA source[127]. Photo-polymerisation essentially increases the rigidity ofthe corneal collagen and its resistance to ectasia. The procedureinvolves epithelial debridement using a blunt spatula, followedby the application of topical riboflavin drops before beginning30 min of constant UVA irradiation. During the irradiation step,riboflavin drops are applied every 5 min. Spadea [121] and Kymio-nis et al. [122] have each described a case resulting in the successfulimprovement of best-corrected visual acuity in a patient with earlyPMD. Both groups of authors discuss that longer post-operativefollow-up is required to better understand the efficacy of CXL inpatients with PMD. At present the use of CXL has been studied inmore depth in patients with keratoconus [128].

De Vries et al. [129] have reported the use of toric phakic intra-ocular lens (TPIOL) implants in a patient with bilateral early-stagePMD which was less pronounced in the left eye. The TPIOL implantswere fixed onto the anterior iris (at the 3 and 9 o’clock positions)through a superior corneo-scleral incision. The authors elected touse this treatment as they could not rule out future increases inastigmatism owing to the progressive nature of the condition; theimplants used were removable should the patient’s prescriptionincrease dramatically over time. These results suggest that TPIOLimplantation can provide good acuity in the early stages of PMD.The authors discuss that due to the reversible nature of this surgerypatients may prefer to elect for this treatment over more perma-nent procedures such as a graft.

Table 2 summarises the non-surgical and surgical methodsavailable to manage PMD.

6.3. Acute management

As mentioned earlier, acute hydrops with corneal oedema maydevelop in patients with PMD [43]. As in keratoconus [130], themain cause of such an episode is a rupture in Descemet’s mem-brane [43,44], which may occur as the disease progresses. PMDpatients presenting with acute hydrops or corneal perforationmay be treated using a number of strategies which include theapplication of glue tissue adhesive [51–54], bandage soft contactlenses [48], crescentic lamellar keratoplasty [54], penetrating ker-atoplasty [47,51] and finally deep anterior lamellar keratoplasty[50].

7. Conclusion

PMD is a rare disorder that can often be misdiagnosed as otherforms of corneal ectasia. However, as the management and prog-

Page 7: Pellucid corneal marginal degeneration: A review

6 ns & A

ndamm‘

latnmca

D

A

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R

2 A. Jinabhai et al. / Contact Le

osis of these ectatic conditions can be very different, an accurateiagnosis is important. Topographical abnormalities in PMD char-cteristically show superior corneal flattening along the verticaleridian, with inferior peripheral steepening extending into theid-peripheral inferior oblique meridians in a classic ‘crab-claw’,

butterfly’ or ‘kissing doves’ pattern.PMD is most commonly managed using spectacles and contact

enses. Surgical methods have also been attempted when spectaclesnd contact lenses are unsuccessful. Although a number of surgicalechniques are available for patients with PMD, there is currentlyo consensus on which method provides the most effective treat-ent. However, since patients with PMD make poor candidates for

orneal laser refractive surgery, eye-care practitioners need to beware of the topographical and slit-lamp features of the condition.

eclaration

The authors have no funding or conflicts of interest to disclose.

cknowledgements

Amit Jinabhai is supported by a PhD studentship from theollege of Optometrists (UK). We would like to thank Dr Cindy Tro-ans, Consultant Optometrist at Manchester Royal Eye Hospital,

or providing us with the images displayed in Fig. 1.

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