Pellucid Marginal Degeneration (PMD) Treatment & Management

Updated: Oct 30, 2017
  • Author: Jean Deschênes, MD, FRCSC; Chief Editor: Hampton Roy, Sr, MD  more...
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Treatment

Medical Care

Spectacle correction usually fails early in the course of pellucid marginal degeneration (PMD), as the degree of irregular astigmatism increases. In early-to-moderate cases, contact lenses are beneficial in providing visual rehabilitation.

Spectacles and toric hydrophilic contact lenses are useful in mild pellucid marginal degeneration.

Spherical hydrophilic contact lenses cannot correct the astigmatism associated with this condition.

Hybrid contact lenses, which are easier than other lenses to fit to the ectatic cornea, may provide good vision for some patients; however, their poor oxygen permeability often leads to corneal neovascularization, which may adversely affect the prognosis for future corneal transplantation.

Rigid gas-permeable contact lenses provide excellent oxygen transmission to the cornea but are harder than the other lenses to fit. Problems in fitting result from the flattening of the superior cornea and the high degree of against-the-rule astigmatism that often causes the lens to dislocate inferiorly. The upper eyelid may support large-diameter rigid lenses with a high edge lift, but they often cause marked irritation and move excessively with movements of the eyelids, causing the patient's vision to periodically blur. Rigid gas-permeable contact lenses may improve the vision of patients with pellucid marginal degeneration, as in those with keratoconus. However, evidence that these lenses have any effect on the progression of the disease is lacking.

Scleral rigid contact lenses or "mini scleral" contact lenses made from gas-permeable materials are an excellent alternative if fitted by a skilled practitioner. [13, 14]

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Surgical Care

In patients who cannot tolerate contact lenses or in those who do not achieve adequate visual acuity with rigid contact lenses because of the degree of ectasia, surgery may be considered.

A number of surgical procedures have been performed to provide visual rehabilitation. Standard-sized penetrating keratoplasty may produce poor results because the inferior edge of the transplant has to be sutured to an abnormally thin cornea, causing a high degree of postkeratoplasty astigmatism in the short- and long-term period. Continued thinning of the host cornea in the inferior aspect produces a situation similar to the situation that indicated surgery.

Large-diameter grafts have been tried to remove as much of the affected cornea as possible, with good success. However, because of the proximity to the limbus and its blood vessels, these grafts may be prone to rejection. Regular-sized grafts that are deliberately decentered in the inferior aspect also work poorly. The degree of astigmatism is large because of the decentering, and the incidence of rejection is high because of the proximity to the limbus. Thermokeratoplasty and epikeratophakia are of only historical interest because the results obtained with these techniques are extremely poor.

Excision of a crescentic wedge of corneal tissue from the inferior cornea, followed by tight suturing, has been reported to reduce the corneal ectasia. [7]  The procedure is usually well tolerated; however, the effect is typically short lived, and thinning and ectasia recur. In addition, this procedure may be hazardous in inexperienced hands. Several instances of wound dehiscence and resultant flat anterior chambers with its attendant problems have been reported with attempts of this procedure. Crescentic lamellar keratoplasty, in which a crescentic transplant is performed to reinforce the area of thinning, has been described, but it may result in a high degree of astigmatism that necessitates subsequent central penetrating keratoplasty.

Modified intrastromal lamellar sclerokeratoplasty incorporating a scleral tunnel and perioperative optical coherence tomography (OCT) mapping is a novel technique developed to correct both corneal thinning and induced corneal astigmatism. Corneal thinning is mapped using OCT. Then, through a scleral tunnel, an intrastromal pocket is created via stromal lamellar dissection under OCT guidance. A 300-μm-thick stromal lamellar graft was inserted in the pocket before closure of the sclera to increase vertical median keratometry. [15]

Currently, the combination of peripheral lamellar crescentic keratoplasty, followed by a central penetrating keratoplasty after a few months is a favored surgical treatment. The lamellar transplant restores normal thickness to the inferior cornea and enables good edge-to-edge apposition at the time of penetrating keratoplasty, reducing the possibility of high postkeratoplasty astigmatism. Furthermore, the central graft that is now sutured to normal-thickness host tissue can be treated with videokeratography-guided selective removal of sutures and astigmatic keratotomy in the usual way to reduce any residual astigmatism.

Ophthalmologists have begun performing the 2 operations in the same sitting, with encouraging results, though this approach is technically difficult. Performing 2 keratoplasty procedures at different times necessitates the use of 2 separate corneas. By performing the 2 procedures in the same sitting, tissue from the same donor may be used, potentially reducing the antigenic load. Because a central graft almost always is needed, performing both procedures at the same time significantly decreases the time needed to attain best-corrected acuity; this is shown in the image below. This consideration is important, as patients are often young and in the active and working phase of their lives.

Image shows simultaneous central penetrating kerat Image shows simultaneous central penetrating keratoplasty and inferior peripheral lamellar keratoplasty performed to treat pellucid marginal degeneration.

The femtosecond laser has also been used to make lamellar dissections to place Intacs and Intracorneal ring segments. [16, 17]

Corneal collagen cross linkage (CXL) also may be of benefit in preventing progression. A 2016 study showed an improvement in visual acuity and reduction of K1 and K2 parameters after CXL. [18]

A case of successful sliding keratoplasty combined with I-CXL was reported in 2016 and was shown to be safe and effective in the treatment of advanced PMD. [19]

Long-term follow-up is required to assess the efficacy of these newer procedures.

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Consultations

Treatment of pellucid marginal degeneration with either contact lenses or surgery requires considerable experience. A cornea specialist should be consulted to ensure the best visual outcome.

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