{"id":27352,"date":"2024-09-11T17:18:48","date_gmt":"2024-09-11T15:18:48","guid":{"rendered":"https:\/\/eyelaser.at\/crosslinking-for-pellucid-marginal-degeneration-pmd\/"},"modified":"2025-08-07T23:08:42","modified_gmt":"2025-08-07T21:08:42","slug":"crosslinking-for-pellucid-marginal-degeneration-pmd","status":"publish","type":"post","link":"https:\/\/eyelaser.at\/en\/crosslinking-for-pellucid-marginal-degeneration-pmd\/","title":{"rendered":"Crosslinking for pellucid marginal degeneration (PMD)"},"content":{"rendered":"<p><span style=\"font-weight: 400;\">Pellucid marginal degeneration (PMD) is a rare, degenerative disease of the cornea that leads to thinning and deformation of the inferior cornea. It shares some similarities with keratoconus, but differs in several important aspects. <\/span><\/p>\n<h2><span style=\"font-weight: 400;\">Features of PMD<\/span><\/h2>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Thinning of the cornea:<\/b><span style=\"font-weight: 400;\"> In PMD, the thinning of the cornea typically occurs in the lower (inferior) area, often close to the corneal border.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Change in shape:<\/b><span style=\"font-weight: 400;\"> This thinning leads to a flattening of the upper cornea and a steepening of the lower cornea, resulting in a characteristic &#8220;crow&#8217;s wing&#8221; shape when looking at the corneal topography.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Visual impairment:<\/b><span style=\"font-weight: 400;\"> The irregular shape of the cornea causes significant distortion and vision loss, similar to keratoconus, but the pattern of distortion is different.<\/span><\/li>\n<\/ul>\n<h2><span style=\"font-weight: 400;\">Differences between PMD and keratoconus<\/span><\/h2>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Localization of the dilution:<\/b>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><b>PMD:<\/b><span style=\"font-weight: 400;\"> Thinning occurs mainly in the lower part of the cornea, near the edge.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><b>Keratoconus:<\/b><span style=\"font-weight: 400;\"> The thinning is more central or paracentral and often forms a cone-shaped protrusion.<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Form of deformation:<\/b>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><b>PMD:<\/b><span style=\"font-weight: 400;\"> Leads to a flattening of the upper cornea and a steepening of the lower cornea.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><b>Keratoconus:<\/b><span style=\"font-weight: 400;\"> Leads to a generalized cone-shaped protrusion of the cornea.<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Onset and progression:<\/b>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><b>PMD:<\/b><span style=\"font-weight: 400;\"> Often develops later in life and progresses more slowly.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><b>Keratoconus:<\/b><span style=\"font-weight: 400;\"> Typically begins in adolescence or young adulthood and may progress more rapidly.<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Diagnosis:<\/b>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><b>PMD:<\/b><span style=\"font-weight: 400;\"> Diagnosed by corneal topography and characteristic patterns of corneal deformation showing inferior peripheral thinning.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><b>Keratoconus:<\/b><span style=\"font-weight: 400;\"> Also diagnosed by corneal topography, but shows a central or paracentral cone-shaped protrusion.<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<h2><span style=\"font-weight: 400;\">Treatment of PMD<\/span><\/h2>\n<p><span style=\"font-weight: 400;\">Crosslinking (CXL) is a proven method for the treatment of keratoconus and can also be used in PMD to stabilize the cornea and slow the progression of the disease.  <\/span><\/p>\n<h3><b>Preparation and implementation of crosslinking with PMD<\/b><\/h3>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Preliminary examination:<\/b><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">A thorough examination of the cornea using corneal topography and pachymetry (measurement of corneal thickness) is necessary to determine the exact extent and localization of the thinning.<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Anesthesia:<\/b><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">Local anesthetic eye drops are used to numb the eye during the procedure.<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Epithelial management:<\/b><\/li>\n<\/ul>\n<p><b>Epi-off crosslinking:<\/b><span style=\"font-weight: 400;\"> The epithelium (the top layer of the cornea) is removed to allow better penetration of the riboflavin.<\/span><\/p>\n<p><b>Epi-on Crosslinking:<\/b><span style=\"font-weight: 400;\">  The epithelium remains intact. However, this method is used less frequently for PMD, as the penetration of the riboflavin may be less effective. <\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Riboflavin application:<\/b><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">Riboflavin (vitamin B2) is dripped onto the cornea and must be allowed to act for a sufficiently long time so that it can penetrate deep into the cornea. This usually takes 20-30 minutes. <\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>UV irradiation:<\/b><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">The cornea is irradiated with UV-A light. This irradiation activates the riboflavin, which leads to a hardening of the collagen fibers in the cornea. The irradiation lasts about 30 minutes.  <\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Conclusion:<\/b><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">After radiotherapy, a therapeutic contact lens is used to protect the eye and promote healing. Antibiotic and anti-inflammatory eye drops are also prescribed. <\/span><\/p>\n<h3><b>Special considerations in the treatment of PMD<\/b><\/h3>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Localization of thinning:<\/b><span style=\"font-weight: 400;\"> As PMD usually affects the inferior cornea, it is important to ensure that the riboflavin penetrates this area evenly and that the UV irradiation is strong enough to treat the entire affected region.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Corneal thickness:<\/b><span style=\"font-weight: 400;\">  In the case of very thin corneas, the thickness must be carefully monitored, as a cornea that is too thin increases the risk of complications during UV irradiation. In such cases, special techniques can be used to temporarily thicken the cornea. <\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Long-term monitoring:<\/b><span style=\"font-weight: 400;\"> After crosslinking, regular check-ups are necessary to monitor the stability of the cornea and to detect possible complications at an early stage.<\/span><\/li>\n<\/ul>\n<h2><span style=\"font-weight: 400;\">Alternative treatment methods for PMD  <\/span><\/h2>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Special contact lenses:<\/b><\/li>\n<\/ul>\n<p><b>Scleral lenses:<\/b><span style=\"font-weight: 400;\"> These large contact lenses bridge the irregular cornea and provide an even, smooth surface.<\/span><\/p>\n<p><b>Hybrid lenses:<\/b><span style=\"font-weight: 400;\"> Combine a firm, gas-permeable central area with a soft outer zone for improved comfort.<\/span><\/p>\n<p><b>RGP lenses (Rigid Gas Permeable):<\/b><span style=\"font-weight: 400;\"> Hard, gas permeable lenses that can provide better vision correction.<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Intrastromal corneal rings (intacs):<\/b><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">Small, semi-circular rings that are implanted into the cornea to change its shape and stabilize it.<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Corneal transplantation:<\/b><\/li>\n<\/ul>\n<p><b>Lamellar keratoplasty:<\/b><span style=\"font-weight: 400;\"> A partial corneal transplant in which only the affected layers of the cornea are replaced.<\/span><\/p>\n<p><b>Penetrating keratoplasty:<\/b><span style=\"font-weight: 400;\"> A complete corneal transplant in which the entire cornea is replaced.<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Phakic intraocular lenses (PIOLs):<\/b><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">Lens implants that are inserted into the eye in addition to the natural lens to improve visual acuity.<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Therapeutic eye injections:<\/b><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">Injections of medication to reduce inflammation and improve corneal stability.<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Corneal topography-guided photorefractive keratectomy (PRK):<\/b><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">A laser treatment to correct corneal deformation and improve the quality of vision.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">These alternative methods can be used depending on the severity of the PMD and individual patient needs.<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"<p>What is keratoconus? Dr. Victor Derhartunian explains what keratoconus is and what treatment options are available. Read more&#8230; <\/p>\n","protected":false},"author":9,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[141],"tags":[142],"class_list":["post-27352","post","type-post","status-publish","format-standard","hentry","category-faqs-en","tag-crosslinking-glossary-en"],"acf":[],"_links":{"self":[{"href":"https:\/\/eyelaser.at\/en\/wp-json\/wp\/v2\/posts\/27352","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/eyelaser.at\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/eyelaser.at\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/eyelaser.at\/en\/wp-json\/wp\/v2\/users\/9"}],"replies":[{"embeddable":true,"href":"https:\/\/eyelaser.at\/en\/wp-json\/wp\/v2\/comments?post=27352"}],"version-history":[{"count":0,"href":"https:\/\/eyelaser.at\/en\/wp-json\/wp\/v2\/posts\/27352\/revisions"}],"wp:attachment":[{"href":"https:\/\/eyelaser.at\/en\/wp-json\/wp\/v2\/media?parent=27352"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/eyelaser.at\/en\/wp-json\/wp\/v2\/categories?post=27352"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/eyelaser.at\/en\/wp-json\/wp\/v2\/tags?post=27352"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}