Pellucid marginal degeneration (PMD) is an uncommon condition in which a band of the cornea becomes thinner, usually near its lower edge. The resulting change in shape can cause irregular astigmatism and blurred or distorted vision. Glasses may help in milder cases; custom contact lenses can become useful when glasses no longer provide adequate clarity. 1
At Vision Camberwell, we bring corneal assessment, contact lens fitting and ongoing monitoring together. Whether PMD has been diagnosed or is still suspected, we will explain the findings, assess your vision options and arrange ophthalmology input where needed.
Contents
What does PMD mean for your vision?
The cornea is the clear front surface of the eye. In PMD, thinning typically forms a crescent near the lower periphery, with protrusion above it. This differs from the more localised cone and thinning usually associated with keratoconus. 1
Tell us if you notice ghost images, increasing blur, glare around lights or repeated prescription changes. We will also ask how these affect reading, computer work and driving. Symptoms alone cannot establish PMD, so the assessment needs to identify the cause rather than assume that every visual change comes from the cornea.
PMD and keratoconus: why the distinction matters
A “crab-claw” scan is a clue, not a diagnosis
A crab-claw or butterfly-shaped curvature map can occur in both PMD and inferior keratoconus. In one comparative study, researchers identified this pattern in 47 eyes from a larger group of people with corneal ectasia. Clinical assessment classified 11 eyes as PMD and 36 as inferior keratoconus. That finding explains why the map alone is insufficient; it is not a population-wide estimate of your likelihood of either condition. 2
Looking beyond the front-surface map
The location and distribution of thinning, the front and back corneal surfaces and findings on slit-lamp examination help distinguish the conditions. A previous diagnosis of suspected keratoconus may therefore need refinement as more information becomes available. Age can provide context, but cannot settle the diagnosis. 2
How we assess PMD at Vision Camberwell
Your history and visual needs
We start with your symptoms, current glasses or lenses, previous scans and any ophthalmology reports. We want to understand both the clinical history and what you need your vision to do each day.
Corneal topography, tomography and examination
We use corneal topography and tomography as clinically indicated to assess corneal shape and thickness. The assessment also includes slit-lamp examination, prescription testing and an eye-health assessment. Particular attention is given to the peripheral cornea, where PMD-related thinning may lie.
We will explain whether the findings support PMD, suggest another condition or need further investigation. One scan does not necessarily establish how the cornea is changing.
Establishing a baseline
Previous measurements help us distinguish longstanding findings from possible progression. We will recommend a review interval based on your findings and available history, and tell you which changes should prompt an earlier appointment. Where appropriate, we will coordinate the assessment with your ophthalmologist.
Glasses and contact lens options for PMD
Glasses and soft lenses
Glasses or suitable soft lenses may remain useful when they provide adequate vision. The decision to move to a different lens is based on your actual vision and fit, not the diagnosis alone. 1
Corneal RGP and other custom designs
Corneal rigid gas permeable (RGP) lenses are another option. Their suitability depends on the corneal shape and whether the lens can achieve useful vision, stability and comfort. A diagnostic fitting helps us decide whether a corneal design or a lens that bridges over the cornea is the better starting point. 1
Scleral lenses
A scleral lens bridges over the cornea and rests on the conjunctival tissue overlying the white of the eye. Before insertion, its bowl is filled with sterile preservative-free saline. The rigid lens and fluid reservoir create an optical system that helps mask the irregular corneal surface. 3
A PMD-specific study by Dutta and colleagues found improvements in corrected vision, contrast sensitivity and several measures of optical distortion with scleral lenses. These findings support their use, but do not establish that every patient will achieve the same result or that scleral lenses are always superior to every other design. 3
The fitting needs to accommodate your individual corneal shape, including its peripheral changes. We assess clearance, the landing area, vision and the eye’s response to wear. Lens diameter alone does not determine whether the fit is suitable.
What to expect from fitting
We will discuss what the trial lens shows and what remains uncertain. Refinements may be needed before the final design is settled. Your ability to insert, remove and care for the lenses is part of the plan, alongside comfort and vision.
Tell us if a previous lens was uncomfortable, unstable or difficult to handle. That experience helps guide the next fitting. We will explain the proposed costs and review arrangements before you proceed; our scleral lens fitting and fees page provides further information.
Monitoring and treatment of progression
Clearer vision does not mean PMD has stopped changing
Contact lenses improve the optics while worn. They do not strengthen the cornea or replace monitoring for progression. If your findings suggest change, ophthalmology assessment may be needed even when you see well in lenses. 1, 4
Can cross-linking help?
Corneal cross-linking may be considered for selected eyes with progressive PMD. Its evidence base is smaller than for keratoconus, and the peripheral location of thinning makes treatment planning important. In a retrospective study of 40 treated eyes followed for at least five years, steep keratometry was stable in 25 eyes, improved in seven and worsened in eight. These observational results support consideration of treatment, but not a guarantee of stabilisation. 4
We refer for an ophthalmologist’s assessment of suitability, including corneal thickness, the affected area and documented progression. Do not wait for contact lenses to “fail” before investigating progression.
When surgery is considered
Other corneal procedures may be considered when vision cannot be adequately rehabilitated or structural problems require intervention. The operation depends on the individual eye; there is no single surgical pathway for every person with PMD. 1
Before your appointment
Bring your glasses, contact lenses, lens case and care products, together with available scans, prescriptions and referral letters. Make a note of when symptoms started, whether one eye is more affected and which activities are difficult.
Ask our team whether to wear your lenses beforehand or leave them out for imaging. The instructions depend on your current lens and the purpose of the visit. Do not wear a painful lens simply to demonstrate the problem.
When symptoms need urgent attention
A sudden reduction in vision, pain, redness, marked light sensitivity or a newly cloudy cornea needs prompt assessment. Do not assume this is routine progression. If wearing contact lenses, remove them and seek urgent advice without reinserting them. If VCO is unavailable, seek urgent eye care elsewhere. 5
Questions patients often ask
Is PMD the same as keratoconus?
They are related corneal ectatic conditions with overlapping features, but the typical pattern of thinning differs. Examination and imaging are needed to distinguish PMD from inferior keratoconus. 2
Does a crab-claw pattern prove I have PMD?
No. The same curvature pattern can appear in inferior keratoconus. We assess the thickness distribution and clinical findings rather than label the condition from one image. 2
Do I automatically need scleral lenses?
No. We assess what glasses and different lens designs can achieve for your eye. Scleral lenses are an important option, but the fitting decision remains individual.
Will contact lenses stop progression?
No. Vision correction and assessment of corneal stability are separate parts of your care. Good vision in a lens is not a reason to skip monitoring or a recommended ophthalmology referral. 4
Will I need a corneal transplant?
A PMD diagnosis does not automatically mean a transplant. The next step is to assess your vision, corneal stability and response to non-surgical correction. Surgical decisions require an individual ophthalmology assessment. 1
Can you assess me if the diagnosis is uncertain?
Yes. Bring the reports and scans you have. We will review the findings and explain whether further investigation or ophthalmology input is needed, without assuming a single visit will answer every question.
Can you review contact lenses fitted elsewhere?
Yes. Bring your existing lenses and fitting details if available. We will assess what works, what needs attention and whether a refit is appropriate.
Do I need a GP referral?
No. You can contact us directly. Correspondence from your optometrist or ophthalmologist is helpful, particularly if PMD or progression has already been suspected.
Arrange a PMD assessment in Camberwell
Call (03) 9882 5666 and tell our team that PMD or an irregular cornea has been diagnosed or suspected. Mention whether you currently wear contact lenses so we can arrange the appropriate appointment.
Vision Camberwell Optometrists is at 784 Burke Road, Camberwell VIC 3124. We welcome patients from Camberwell, Hawthorn, Balwyn, Kew, Canterbury and across Melbourne. Consultations in Mandarin are available with Jue Wang; mention your language preference when booking.
References
- Tsatsos M, Koulotsiou K, Giachos I, et al. Pellucid Marginal Degeneration: A Comprehensive Review of Pathophysiology, Diagnosis, and Management Strategies. Journal of Clinical Medicine. 2025;14(15):5178.
- Koc M, Tekin K, Inanc M, et al. Crab claw pattern on corneal topography: pellucid marginal degeneration or inferior keratoconus? Eye. 2018;32(1):11–18.
- Dutta R, Iyer G, Srinivasan B, Iqbal A. Aberration change after scleral lens wear in eyes with pellucid marginal degenerations. Indian Journal of Ophthalmology. 2024;72(7):1037–1042.
- Irajpour M, Noorshargh P, Peyman A. Corneal Cross-Linking in Pellucid Marginal Degeneration: Evaluation after Five Years. Journal of Current Ophthalmology. 2022;34(2):229–233.
- US Food and Drug Administration. Contact Lens Risks. Accessed 5 October 2026.
Reviewed by Dr Shonit Jagmohan, Optometrist. Last reviewed October 2026.
Visit us in Camberwell
T. (03) 9882 5666
E. vision@visioncamberwell.com.au
Find Us at:
784 Burke Rd, Camberwell
Victoria 3124, Australia
Opening Hours:
Monday, Tuesday and Friday. 9am – 6pm
Wednesday. 9am – 5pm
Thursday. 10.30am – 7.30pm
Saturday. CLOSED
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T: (03) 9882 5666
Serving Camberwell and the Surrounding South Eastern Suburbs
An independent practice in Camberwell since 1951, we are experts in specialty contact lenses, including fittings after a corneal graft. We welcome patients from Hawthorn, Deepdene, Surrey Hills, Balwyn, Kew, Canterbury, Box Hill, Glen Iris, and across greater Melbourne.
