Pellucid Marginal Degeneration: An Overview Of The Clinical Features Of The Disease And Its Treatment Options

The main aim of this project is to provide a synopsis of the clinical features of pellucid marginal degeneration (PMD) and provide a summary of the available surgical treatment options, including penetrating keratoplasty, full-thickness crescentic wedge resection (FTCWR), deep anterior lamellar keratoplasty (DALK), crescentic lamellar wedge resection (CLWR), crescentic lamellar keratoplasty, tuck-in lamellar keratoplasty (TILK), toric phakic intraocular lens (PIOL) implantation, intrastromal corneal ring segment implantation (ICRS), corneal collagen cross-linking (CXL), and combined therapies.

1) Ophthalmology Department, Royal Bournemouth Hospital, University Hospitals Dorset NHS Trust

2) Ophthalmology Department, University Hospitals Southampton, NHS Trust

A retrospective literature search was conducted using the following electronic platforms: i)Pubmed ii) Mendeley iii) Scopus and iv) Google Scholar.  The literature search did not yield any large prospective double-blind randomized control trials specifically designed for PMD. All reviewed published manuscripts had major weaknesses, namely their retrospective nature, limited number of recruited eyes and limited post-operative follow-up periods. Ideally, large multicentre double-blind prospective studies should be conducted to elucidate the optimum surgical management of PMD. It is acknowledged by the author that such a task will be very challenging to accomplish due to the paucity in numbers of PMD patients.

Reported data for each surgical option is reported. Corneal perforation can be treated either with corneal gluing or with emergency tectonic graft. PK is used as last resort. It is effective but is not free of complications. DALK reduces the risk of immune-mediated rejection but is more technically challenging than PK. FTCWR induces large astigmatic drift. CLWR, CLK and TILK show good results, but they are also technically challenging without long-term results. Toric IOLs correct astigmatism but fail to halt disease progression. ICRS may improve vision and contact lens fit but fail to stop disease progression. CXL and combination of the above techniques seem promising, but current data are limited to confirm their efficacy and safety.

In the modern and rapidly evolving world of refractive surgery, all eye specialists must be aware of this condition, as it may go undetected at early stages and may complicate the outcomes of laser refractive surgery. Currently, there is no unanimity with regards to the optimum surgical treatment of PMD. Novel treatment modalities seem to improve visual outcomes and reduce the rate of complications at the same time. Based on the currently available data, combined treatments seem promising and larger studies are required to fully validate their efficacy and safety. Finally, improving screening tools may reduce the need for surgical intervention in most PMD cases.