Ophthalmology · Grand Rounds Clinical Case Presentation

Title of Case

Bilateral pellucid marginal degeneration with cortical cataract: intraocular lens power selection in extreme against-the-rule astigmatism

A woman in her late 50s with three years of progressive, painless diminution of vision in both eyes — and a cornea that defies the biometer.

+8.51 D

ΔK · Right Eye

+10.90 D

ΔK · Left Eye

6/36 · 6/18

BCVA with contact lens RE · LE

Cornea & Cataract Services · Tertiary Eye Care Centre Presented by Rohan Sonawane

02 · Summary02 / 23

The case in 150 words

A woman in her late 50s presented with three years of painless, progressive diminution of vision in both eyes, right worse than left. Corrected acuity was 2/60 and 4/60 with high compound myopic against-the-rule astigmatism. Slit-lamp examination revealed bilateral inferior peripheral corneal thinning sparing the limbus, without vascularisation or ulceration, together with cortical cataract in both eyes. Tomography and anterior segment optical coherence tomography confirmed bilateral pellucid marginal degeneration. Biometry showed keratometric astigmatism of +8.51 D and +10.90 D. A semi-scleral contact lens trial improved vision, confirming the corneal contribution. Cataract surgery of the right eye was planned with a monofocal intraocular lens, with power selection guided by the Barrett Universal II formula and a planned staged approach to the residual irregular astigmatism.

2

Pathologies per eye — ectasia + cataract

Combined surgical problem

3 yrs

Painless progressive visual decline

Near and distance

53.36 D

Steepest keratometry recorded

Right eye · K2 @ 174°

Pellucid Marginal Degeneration · Cortical CataractBMJ Case Report Structure

03 · Background03 / 23

Why this case matters

Pellucid marginal degeneration is a rare, idiopathic, non-inflammatory ectatic disorder — a crescentic band of inferior peripheral corneal thinning, classically 1–2 mm from the limbus, with the point of maximal protrusion above the band of thinning.
The topographic signature is the “crab-claw” pattern: inferior steepening with flattening of the vertical meridian, producing severe against-the-rule astigmatism.
Presentation is usually in the 2nd–5th decade with slowly progressive blurring; pain, photophobia or hydrops are uncommon.

When PMD coexists with visually significant cataract, every step of cataract surgery becomes contested territory: keratometry is unreliable, formulas disagree, and toric or multifocal lenses may harm rather than help.
This case illustrates a reasoned pathway — confirm the ectasia, prove the corneal contribution with a contact lens trial, then plan lens power and refractive target conservatively.

Non-inflammatory Peripheral Corneal EctasiaBackground

04 · Case Presentation — History04 / 23

Three years of quiet decline

Three years before presentation

Apparently well, then noticed diminution of vision in both eyes, right worse than left — for both near and distance.

Course

Gradually progressive and painless — no redness, watering, photophobia, or history of trauma.

At presentation

Vision inadequate for daily activities despite spectacles; referred to a tertiary eye care centre.

Relevant negatives

Past illness — no history of any systemic disease.
Previous operations — no history of any ocular surgery.
Allergies — none reported.
Family history — no similar complaints in the family; no eye rubbing or atopy elicited.

History — Anonymised per BMJ GuidanceCase Presentation

05 · Case Presentation — Examination05 / 23

Systemically well; visually crippled

General physical examination

General health	Good; afebrile; no pallor
Pulse / Resp	78 /min · 16 /min
Blood pressure	145/88 mm Hg
Random glucose	7.9 mmol/L (142 mg/dL)
Systemic exam	Cardiovascular, respiratory, gastrointestinal and nervous systems grossly within normal limits

Visual acuity & refraction

	Right eye	Left eye
Unaided (distance)	1/60	3/60
With spectacles	2/60	4/60
Best accepted refraction	−2.0 DS / −7.5 DC × 90° → 4/60	−1.0 DS / −9.0 DC × 90° → 5/60
BCVA with contact lens	6/36	6/18
Near (with +1.5 add)	N8	N6
Pattern	Compound myopic against-the-rule astigmatism, both eyes

Acuity Refractory to Spectacle CorrectionCase Presentation

06 · Case Presentation — Anterior Segment06 / 23

Slit-lamp: a thinning band, a quiet eye

Right eye

Cornea	Inferior thinning 3–8 o'clock, 1 mm inside the limbus; clear cornea above; tram-track lipid deposition at the edge; no vascularisation, no ulceration
Ant. chamber	Deep (Van Herick 4), regular; no cells or flare
Iris / pupil	Brown, no neovascularisation; 2→8 mm, central, brisk
Lens	Cortical cataract (worse than left); visual axis involved on retro-illumination
IOP	19 mm Hg

Left eye

Cornea	Inferior thinning 3–6 o'clock, sparing the limbus; lipid deposition at the edge; no vascularisation, no ulceration
Ant. chamber	Deep (Van Herick 4), regular; no cells or flare
Iris / pupil	Brown, no neovascularisation; 2→8 mm, central, brisk
Lens	Cortical cataract; vitreous clear
IOP	15 mm Hg

Both Corneas: Ectatic, Uninflamed, UnvascularisedCase Presentation

07 · Clinical Photographs — Right Eye07 / 23

The cornea in profile

Slit-lamp photograph of the right eye: broad optic section across the inferior cornea

Right eye · 01

Inferior peripheral thinning

Broad optic section across the inferior cornea — the section narrows toward the periphery while the cornea above stays clear.

Slit-lamp photograph of the right eye: tangential view of the corneal contour

Right eye · 02

Tangential view — the contour bows forward above the thinned band.

Slit-lamp photograph of the right eye: inferior peripheral cornea and limbus

Right eye · 07

Inferior periphery — thinning band inside a clear limbus.

What to look forA crescent of thinning 1 mm inside the limbus, 3–8 o'clock, with clear cornea above it — no vascularisation, no infiltrate.

Slit-lamp Photography · Right EyeClinical Photographs

08 · Clinical Photographs — Right Eye, Detail08 / 23

Periphery, limbus, and lens

03

Optic section crossing the inferior cornea.

Slit-lamp photograph of the right eye: peripheral optic section at the limbus

08

Peripheral section — the beam narrows toward the limbus.

Slit-lamp photograph of the right eye: adjacent peripheral section inside the limbal margin

09

Adjacent section — thinning stops short of the limbus.

Slit-lamp photograph of the right eye: diffuse view with optic section through the pupil

04

Diffuse view with section through the pupil.

Slit-lamp photograph of the right eye: optic section through the pupillary axis and lens

05

Section through the lens — opacity on the visual axis.

Slit-lamp photograph of the right eye: higher magnification of the pupillary area and lens

06

Higher magnification — cortical cataract in the pupillary area.

Two Pathologies in One Eye: Ectasia and CataractClinical Photographs

09 · Clinical Photographs — Left Eye09 / 23

The fellow eye, one step behind

Slit-lamp photograph of the left eye: optic section through the inferior cornea and pupil

Left eye · 10

Inferior thinning, 3–6 o'clock

Optic section through the inferior cornea and pupil — the same crescent of peripheral thinning, over a cortical cataract.

Left eye · 10Thinning spans a shorter arc than the right — 3–6 o'clock, sparing the limbus, with lipid deposition at the edge of the band.

6/18

Best-corrected acuity with contact lens

Right eye 6/36

15 mm Hg

Intraocular pressure

Right eye 19 mm Hg

+10.90 D

Keratometric astigmatism, ΔK @ 5°

Worse than the right eye

Bilateral, Asymmetric — Left Eye Less AdvancedClinical Photographs

10 · Case Presentation — Posterior Segment10 / 23

The fundus of a myopic eye

Media — clear beyond the cataract; good fundal glow both eyes.
Discs — cup–disc ratio asymmetry: recorded 0.5 : 0.3 on initial dark-room examination and 0.9 : 0.5 on dilated glaucoma evaluation with peripapillary atrophy — prompting a formal glaucoma workup.
Retina — dull foveal reflex; extensive chorioretinal degeneration in both eyes; arteriovenous ratio 1:2; an inferior pigmented lesion in the left eye, flat, without fluid.

Glaucoma-suspect workup

Prior glaucoma clinic registration retrieved.
Gonioscopy — open angles, posterior trabecular meshwork visible; iris processes noted.
Humphrey visual fields 30-2 ordered both eyes; topical ocular hypotensive therapy initiated per glaucoma service.

Gonioscopy photograph: open angle with the trabecular meshwork in view

Gonioscopy · 01

Gonioscopy photograph: open angle with iris processes crossing the recess

Gonioscopy · 02

GonioscopyOpen angle with the posterior trabecular meshwork in view; iris processes bridge the recess.

Disc Asymmetry + Myopic Degeneration Shape the PrognosisCase Presentation

11 · Investigations — Corneal Imaging11 / 23

Confirming the ectasia

Scheimpflug tomography (Pentacam) — inferior steepening with the classic crab-claw pattern; maximal protrusion above the thinning band; both eyes affected, asymmetrically.
Anterior segment OCT (radial scans) — band of inferior peripheral stromal thinning with preserved central thickness; epithelium intact throughout; thinnest peripheral pachymetry ≈ 377 µm against a central ≈ 483 µm.
Macular OCT — performed to exclude macular pathology contributing to visual loss before surgical planning.

2280 · 2673

Specular endothelial count, cells/mm² (RE · LE)

Adequate for phacoemulsification

6/36 · 6/18

Best-corrected acuity with contact lens, right and left

Confirms corneal contribution · predicts rehabilitation

Tomography + ASOCT + Specular Microscopy + CL TrialInvestigations

12 · Investigations — AS-OCT, Right Eye12 / 23

The thinning, measured

Anterior segment OCT of the right eye: horizontal radial section with pachymetry annotations

Right eye · AS-OCT

377 µm · peripheral thinning

422 µm @ −0.47 mm

Pachymetry

422 µm

At −0.47 mm from the vertex

Near-central cornea

483 µm

At −4.58 mm from the vertex

Opposite mid-periphery

377 µm

Thinnest peripheral measurement

The band of ectatic thinning

Anterior segment OCT of the right eye: peripheral section with a 1.65 mm annotation

Right eye · 1.65 mm

Peripheral Stromal Thinning with a Preserved CentreInvestigations

13 · Investigations — Left Eye Imaging13 / 23

The same disease, less far along

Left eye · AS-OCT

Anterior segment OCT of the left eye: radial section with a 1.00 mm scale marker

Left eye · Δ 1.00 mm

Radial section of the left cornea — peripheral thinning present but less marked than the right; the centre is preserved.

Left eye · Scheimpflug overview

Pentacam general overview of the left eye: Scheimpflug section, densitometry and back elevation map

Left eye · Pentacam

Scheimpflug section with densitometry — astigmatism 10.6 D at a steep axis of 4.5°, thinnest location 442 µm.

Left Eye: Same Pattern, Lower MagnitudeInvestigations

14 · Investigations — Scheimpflug Tomography14 / 23

The crab-claw, on four maps

$Pentacam 4 Maps Refractive display of the right eye: axial curvature, front and back elevation, and corneal thickness$

Right eye · 4 Maps Refractive

Right eye · Cornea front

K1 / K2	45.0 D / 53.9 D
Km	49.0 D
Astigmatism	9.0 D · steep axis 176.5°
K max (front)	70.3 D
Thinnest location	428 µm
Q-value (8 mm)	0.63 — oblate
ACD / volumes	3.98 mm · cornea 41.9 mm³ · chamber 146 mm³

Inferior steepening with flattening of the vertical meridian — the butterfly of pellucid marginal degeneration, and a K max no keratometer would predict from the refraction.

Tomography Explains What Keratometry CannotInvestigations

15 · Investigations — Belin/Ambrósio Display15 / 23

Ectasia, objectively

Right eye

Left eye

9.13

Final D value · right eye

Abnormal beyond 1.6

7.25

Final D value · left eye

Bilateral disease, asymmetric

241 · 274

ART max, right and left

Thinnest point vs progression

428 · 442

Thinnest location, µm

Displaced inferiorly, both eyes

Both Eyes Flagged: Enhanced Ectasia Confirms the DiagnosisInvestigations

16 · Investigations — Biometry & IOL Calculation16 / 23

Where the numbers fight the formula

Optical biometry	Right eye	Left eye
Axial length	26.89 mm	25.81 mm
Flat K (K1)	44.84 D @ 84°	41.75 D @ 95°
Steep K (K2)	53.36 D @ 174°	52.65 D @ 5°
ΔK (astigmatism)	+8.51 D @ 174°	+10.90 D @ 5°
SE / TSE	48.73 / 48.84 D	46.57 / 46.56 D
ΔTK (total keratometry)	+8.55 D @ 174°	+11.01 D @ 5°
ACD / LT	3.93 / 3.89 mm	3.46 / 3.98 mm
White-to-white	11.3 mm	11.4 mm

Steep meridian near-horizontal in both eyes — biometric confirmation of against-the-rule ectatic astigmatism.
Lens thickness flagged by the biometer in both eyes — consistent with cortical cataract.
Barrett Universal II used for power selection: monofocal IOL ≈ +3.7 D for emmetropia (RE) and ≈ +8.6 D (LE) — unusually low powers driven by long axial length and steep mean keratometry.

Long Eye + Steep Irregular Cornea = Formula Stress-TestInvestigations

17 · Investigations — IOL Selection17 / 23

Choosing the implant

Optical biometry printout: IOL calculation sheet for both eyes

IOL calculation · both eyes

Optical biometry, both eyes — phakic, vitreous body, untreated. The sheet is stamped rechecked, with axial length measured again by hand.

Barrett Universal II · target emmetropia

Implant option	Right eye	Left eye
AcrySof IQ SN60WF — emmetropia	+3.70 D	+8.59 D
Power selected · predicted	+3.50 D → +0.13	+8.50 D → +0.11
AcrySof PanOptix TFN T00 — emmetropia	+3.72 D	+8.63 D
Power · predicted	+3.50 D → +0.13	+8.50 D → +0.08
Manual axial length, rechecked	26.80 mm	25.89 mm

Powers this low are driven by a long eye and a steep mean cornea — the two errors push in opposite directions, which is exactly why the sheet was rechecked. The diffractive option was calculated and deliberately not chosen: irregular ectatic astigmatism and multifocal optics do not belong in the same eye.

Monofocal Implant · Barrett Universal II · Conservative TargetInvestigations

18 · Differential Diagnosis18 / 23

Teasing out the thinning cornea

Considered	Why it was considered	Why it was excluded
Keratoconus	Ectasia with high astigmatism and progressive myopic shift	Thinning here is peripheral, not apical — protrusion sits above the band; no Fleischer ring, no Vogt striae, no cone on tomography
Terrien marginal degeneration	Peripheral thinning with lipid at the leading edge	Terrien is typically superior and vascularised; this band is inferior, avascular, with intact epithelium
Keratoglobus	Bilateral thinning with globular steep corneas	Thinning is limbus-to-limbus in keratoglobus; here the central cornea and the limbal margin are spared
Mooren / marginal ulcerative keratitis	Peripheral corneal thinning	No pain, no inflammation, no epithelial defect, no infiltrate — a quiet eye over three years

An inferior crescent of thinning 1 mm inside a clear limbus, steepest cornea above the band, and a crab-claw map — the diagnosis is pellucid marginal degeneration.

Location · Vascularity · Inflammation · TopographyDifferential Diagnosis

19 · Treatment19 / 23

A staged, conservative plan

Step 1 · Optical rehabilitation trial

Spectacle correction inadequate (4/60, 5/60). Semi-scleral contact lens trial improved acuity — confirming the corneal component and establishing the post-operative rehabilitation route.

Step 2 · Cataract surgery, right eye first

Phacoemulsification with in-the-bag monofocal IOL (Barrett Universal II), right eye first as the worse eye; peribulbar anaesthesia with attention to the thinned peripheral cornea during incision planning.

Step 3 · Residual astigmatism managed off the cornea

Irregular ectatic astigmatism to be corrected with a scleral contact lens after surgery, not with a toric or multifocal implant.

Deliberate exclusions

No multifocal IOL — diffractive optics compound the higher-order aberrations of an irregular cornea.
No toric IOL — the astigmatism is irregular and potentially progressive; axis determination is unreliable, and a scleral lens would neutralise the front surface anyway.
No simultaneous corneal procedure — the ectasia was managed conservatively; the cataract is addressed first, the cornea rehabilitated optically.

Phacoemulsification + Monofocal IOL + Scleral Lens RehabilitationTreatment

20 · Outcome and Follow-up20 / 23

Outcome and surveillance

Immediate outcome

Right eye surgery completed uneventfully under peribulbar anaesthesia; pre-operative fasting and pre-anaesthetic orders followed.
[Editable] Post-operative day-1 findings: add vision, IOP, wound and IOL status here.
[Editable] Post-operative refraction and best-corrected acuity at 4–6 weeks: add here.

Planned follow-up

Scleral contact lens fitting once refraction stabilises; then second-eye surgery.
Glaucoma surveillance — Humphrey 30-2 fields, disc imaging, IOP review on therapy.
Ectasia surveillance — serial tomography to document stability of the peripheral thinning.
Retina review — the myopic chorioretinal degeneration and the flat pigmented lesion (left eye) kept under observation.

Press E to Edit — Add Post-operative Data When AvailableOutcome and Follow-up

21 · Discussion21 / 23

Cataract surgery on an ectatic cornea

Keratometry misleads. In PMD the measured Ks sample a grossly asymmetric cornea; standard formulas assume regularity. Reported strategies include using flatter or tomography-derived total keratometry, modern formulas (Barrett Universal II), and counselling for refractive surprise.
Long eyes add error. Axial myopia (26.89 mm here) compounds formula inaccuracy; a slightly myopic target is safer than emmetropic ambition.
The contact lens trial is diagnostic and prognostic — it separates corneal from lenticular blur and previews the achievable end-point.

Published experience is sparse. Case reports and small series of cataract surgery in PMD converge on the same choices made here: monofocal implant, astigmatism managed with rigid/scleral lenses, torics reserved for stable, regular-bowtie cases.
Comorbidity shapes prognosis. Disc asymmetry with a positive glaucoma history and myopic chorioretinal degeneration cap the visual ceiling — honest counselling belongs in the consent discussion.

Formula Choice · Refractive Target · Lens Strategy · CounsellingDiscussion

22 · Learning Points / Take Home Messages22 / 23

What to remember at the slit lamp

Extreme against-the-rule astigmatism deserves tomography — pellucid marginal degeneration hides behind a “high cylinder” refraction, and the thinning band is easy to miss without a deliberate look at the inferior periphery.
In ectatic corneas, standard keratometry cannot be trusted for IOL power; use modern formulas, tomography-informed keratometry, and set a conservative, slightly myopic target.
A rigid or scleral contact lens trial before surgery both proves the corneal contribution to visual loss and predicts the quality of post-operative rehabilitation.
Monofocal implants are the default in irregular corneas; multifocal optics are best avoided, and toric correction is unreliable when the astigmatism is irregular or progressive.
Complete the whole examination — coexisting glaucoma suspicion and myopic fundus degeneration change the counselling, the consent, and the follow-up plan.

Five Take-Home MessagesLearning Points

Ophthalmology · Grand Rounds Clinical Case Presentation

Thank you

Questions & discussion

Bilateral pellucid marginal degeneration with cortical cataract — presented in the structure of a BMJ case report.

Cornea & Cataract Services · Tertiary Eye Care Centre 23 / 23