Pellucid marginal degeneration

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Pellucid marginal degeneration
Other namesPMD
The eye & I.jpg
Pellucid corneal degeneration with hydrops and detachment of Descemet's membrane
Specialty Ophthalmology
Symptoms Vision loss
Complications Corneal perforation [1]
Diagnostic method Corneal topography
Differential diagnosis Keratoconus
TreatmentVision correction (eyeglasses or contact lenses)
FrequencyVery rare

Pellucid marginal degeneration (PMD) is a degenerative corneal condition, often confused with keratoconus. It typically presents with painless vision loss affecting both eyes. Rarely, it may cause acute vision loss with severe pain due to perforation of the cornea. It is typically characterized by a clear, bilateral thinning (ectasia) in the inferior and peripheral region of the cornea, although some cases affect only one eye. The cause of the disease remains unclear.

Contents

Pellucid marginal degeneration is diagnosed by corneal topography. Corneal pachymetry may be useful in confirming the diagnosis. Treatment usually consists of vision correction with eyeglasses or contact lenses. Intacs implants, corneal collagen cross-linking, and corneal transplant surgery are additional options. Surgery is reserved for individuals who do not tolerate contact lenses.

The term "pellucid marginal degeneration" was first coined in 1957 by the ophthalmologist Schalaeppi. [2] The word "pellucid" means clear, indicating that the corneas retain clarity in pellucid marginal degeneration. [1] The condition is rare, though the exact prevalence and incidence are unknown.

Signs and Symptoms

Pain is not typically present in pellucid marginal degeneration, and aside from vision loss, no symptoms accompany the condition. However, in rare cases, PMD may present with sudden onset vision loss and excruciating eye pain, which occurs if the thinning of the cornea leads to perforation. [1] While PMD usually affects both eyes, some unilateral cases have been reported. [3] [4]

PMD is characterized by bilateral thinning (ectasia) in the inferior and peripheral region of the cornea. The distribution of the degeneration is crescent or arcuate shaped. The cornea just above the region of thinning is of normal thickness, and may protrude anteriorly, which creates an irregular astigmatism. [5] This is described as a "beer belly" appearance since the greatest protrusion occurs below the horizontal midline (unlike keratoconus). Normally, PMD does not present with vascularization of the cornea, scarring, or any deposits of lipid. [3]

Pathophysiology

PMD is an idiopathic, [2] non-inflammatory condition. The thinning of the corneas may approach 20% of normal thickness. There may be an increase in the number of mucopolysaccharides in the corneal stroma. The Bowman's layer of the cornea may be absent, irregular, or have ruptured areas.[ citation needed ]

Diagnosis

The center of the cornea shows normal thickness, with an intact central epithelium, but the inferior cornea exhibits a peripheral band of thinning, to about 1–2 mm. The portion of the cornea that is immediately adjacent to the limbus is spared, usually a strip of about 1–2 mm. [6] In PMD we can see high against the rule astigmatism [6] along with horizontal bow ties. The inferior peripheral thinning is seen between the 4 o'clock and 8 o'clock positions. [7]

PMD lacks apical corneal scarring, Rizutti's phenomenon, Munson's sign, and the central corneal thickness is usually normal. [1]

The gold standard diagnostic test for PMD is corneal topography. [1] However, it may not be as specific as corneal pachymetry, because corneal topography only evaluates the degree and distribution of surface irregularities on the cornea, not the thickness of the cornea. [5] Corneal topography may show a "crab claw-like" appearance, a finding that is seen in both keratoconus and in pellucid marginal degeneration. Thus, if corneal topography is used for diagnosis, it should be in conjunction with clinical findings of peripheral, inferior corneal thinning. [8]

Treatment

Eye glasses

Most people can be treated non-surgically with eyeglasses, or contact lenses. [9]

Contact lenses

The early stages of pellucid marginal degeneration may also be managed with soft contact lenses. [1] Success has been shown with the use of rigid gas permeable contact lenses combined with over-refraction. People wearing contacts don't report increased problems with glare and contrast sensitivity, but it is not clear if this is due to the corneal disease, or the contact lenses themselves.[ citation needed ]

New studies found that the use of Scleral contact lens, a type of rigid gas permeable (RGP) lens, may be a good option for most people with PMD. Most of these lenses are in the range of 15.5mm to 18.0mm in diameter. Regardless of the lens size, it is thought that the larger the RGP lens will in most cases be more comfortable then standard rigid corneal lenses, and at times more comfortable than soft lenses, regardless of the fact that it is a rigid lens. The highlight to the scleral design and the correction of eye disorders such as pellucid marginal degeneration is that vision with these types of lenses is exceptional when fit correctly.[ citation needed ]

Intacs

The use of intacs implants has been tested as a treatment for PMD, with slight improvement in visual acuity noted after eleven months, [10] and intacs have been used with keratoconus with success. [11]

Corneal collagen cross-linking

There is evidence suggesting corneal collagen cross-linking may be beneficial for patients with pellucid marginal degeneration. [12] [13] [14] Research shows some promising results by combining collagen cross linking with photorefractive keratectomy, or with topography-guided transepithelial surface ablation. [7]

Surgery

Corneal transplant surgery may be difficult due to the peripheral thinning of the cornea, even with large and off-center grafts. [9] Therefore, surgery is usually reserved for people that do not tolerate contact lenses. Several different surgical approaches may be taken, and no one approach is currently established as the standard. Examples of surgical procedures used for PMD include: wedge resection, lamellar crescentic resection, penetrating keratoplasty, lamellar keratoplasty, epikeratoplasty and intracorneal segments. Transplantation of the entire thickness of the cornea (penetrating keratoplasty) may be performed if there is enough normal tissue present. However, if there is not enough normal tissue present, then attaching the graft is difficult. New surgical techniques are in evaluation such as Intrastromal lamellar Keratoplasties and Sclerocorneal Intrastromal Lamellar Keratoplasty (SILK), these techniques allow thickening of the inferior peripheral cornea and steepening of the vertical meridien. [15] [16]

Due to the thinning of the cornea, people with PMD are poor candidates for procedures such as LASIK and photorefractive keratectomy. [17]

Prognosis

Visual function declines as a result of the irregular corneal shape, resulting in astigmatism, and causing a distortion in vision. Deterioration can become severe over time. [2]

Epidemiology

The incidence and prevalence of PMD are unknown, and no studies have yet investigated its prevalence or incidence. However, it is generally agreed that PMD is a very rare condition. [1] Some uncertainty regarding the incidence of PMD may be attributed to its confusion with keratoconus. PMD is not linked to race or age, although most cases present early in life, between 20 and 40 years of age. [17] While PMD is usually considered to affect men and women equally, some studies suggest that it may affect men more frequently. [1]

Several diseases have been observed in people with PMD. However, no causal relationships have been established between any of the associated diseases and the pathogenesis of PMD. Such diseases include: chronic open angle glaucoma, retinitis pigmentosa, retinal lattice degeneration, scleroderma, [18] kerato-conjunctivitis, eczema, and hyperthyroidism.

See also

Related Research Articles

<span class="mw-page-title-main">Keratoconus</span> Medical condition involving the eye

Keratoconus (KC) is a disorder of the eye that results in progressive thinning of the cornea. This may result in blurry vision, double vision, nearsightedness, irregular astigmatism, and light sensitivity leading to poor quality-of-life. Usually both eyes are affected. In more severe cases a scarring or a circle may be seen within the cornea.

<span class="mw-page-title-main">Cornea</span> Transparent front layer of the eye

The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is approximately 43 dioptres. The cornea can be reshaped by surgical procedures such as LASIK.

<span class="mw-page-title-main">Farsightedness</span> Eye condition in which light is focused behind instead of on the retina

Far-sightedness, also known as long-sightedness, hypermetropia, and hyperopia, is a condition of the eye where distant objects are seen clearly but near objects appear blurred. This blur is due to incoming light being focused behind, instead of on, the retina due to insufficient accommodation by the lens. Minor hypermetropia in young patients is usually corrected by their accommodation, without any defects in vision. But, due to this accommodative effort for distant vision, people may complain of eye strain during prolonged reading. If the hypermetropia is high, there will be defective vision for both distance and near. People may also experience accommodative dysfunction, binocular dysfunction, amblyopia, and strabismus. Newborns are almost invariably hypermetropic, but it gradually decreases as the newborn gets older.

<span class="mw-page-title-main">LASIK</span> Corrective ophthalmological surgery

LASIK or Lasik, commonly referred to as laser eye surgery or laser vision correction, is a type of refractive surgery for the correction of myopia, hyperopia, and an actual cure for astigmatism, since it is in the cornea. LASIK surgery is performed by an ophthalmologist who uses a laser or microkeratome to reshape the eye's cornea in order to improve visual acuity.

<span class="mw-page-title-main">Refractive surgery</span> Surgery to treat common vision disorders

Refractive surgery is optional eye surgery used to improve the refractive state of the eye and decrease or eliminate dependency on glasses or contact lenses. This can include various methods of surgical remodeling of the cornea (keratomileusis), lens implantation or lens replacement. The most common methods today use excimer lasers to reshape the curvature of the cornea. Refractive eye surgeries are used to treat common vision disorders such as myopia, hyperopia, presbyopia and astigmatism.

<span class="mw-page-title-main">Corneal transplantation</span> Surgical procedure of repairing corneal tissue to treat corneal blindness

Corneal transplantation, also known as corneal grafting, is a surgical procedure where a damaged or diseased cornea is replaced by donated corneal tissue. When the entire cornea is replaced it is known as penetrating keratoplasty and when only part of the cornea is replaced it is known as lamellar keratoplasty. Keratoplasty simply means surgery to the cornea. The graft is taken from a recently deceased individual with no known diseases or other factors that may affect the chance of survival of the donated tissue or the health of the recipient.

<span class="mw-page-title-main">Fuchs' dystrophy</span> Medical condition

Fuchs dystrophy, also referred to as Fuchs endothelial corneal dystrophy (FECD) and Fuchs endothelial dystrophy (FED), is a slowly progressing corneal dystrophy that usually affects both eyes and is slightly more common in women than in men. Although early signs of Fuchs dystrophy are sometimes seen in people in their 30s and 40s, the disease rarely affects vision until people reach their 50s and 60s.

<span class="mw-page-title-main">Corneal cross-linking</span> Surgical procedure

Corneal cross-linking (CXL) with riboflavin (vitamin B2) and UV-A light is a surgical treatment for corneal ectasia such as keratoconus, PMD, and post-LASIK ectasia.

<span class="mw-page-title-main">Intrastromal corneal ring segment</span> Small device implanted in the eye to correct vision

An intrastromal corneal ring segment (ICRS) (also known as intrastromal corneal ring, corneal implant or corneal insert) is a small device surgically implanted in the cornea of the eye to correct vision. Two crescent or semi-circular shaped ring segments are inserted between the layers of the corneal stroma, one on each side of the pupil, This is intended is intended to flatten the cornea and change the refraction of light passing through the cornea on its way into the eye.

Corneal perforation is an anomaly in the cornea resulting from damage to the corneal surface. A corneal perforation means that the cornea has been penetrated, thus leaving the cornea damaged.
The cornea is a clear part of the eye which controls and focuses the entry of light into the eye. Damage to the cornea due to corneal perforation can cause decreased visual acuity.

Peter S. Hersh is an American ophthalmologist and specialist in LASIK eye surgery, keratoconus, and diseases of the cornea. He co-authored the article in the journal Ophthalmology that presented the results of the study that led to the first approval by the U.S. Food and Drug Administration (FDA) of the excimer laser for the correction of nearsightedness in the United States. Hersh was also medical monitor of the study that led to approval of corneal collagen crosslinking for the treatment of keratoconus.

Raymond Mark Stein, MD, FRCSC, DABO, is a Canadian ophthalmologist. He practices refractive and cataract surgery. He is the medical director of the Bochner Eye Institute in Toronto, Ontario and Chief of Ophthalmology at the Scarborough General Hospital.

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Jeewan Singh Titiyal is an Indian ophthalmologist, credited with the first live cornea transplant surgery by an Indian doctor. He was honoured by the Government of India, in 2014, by bestowing on him the Padma Shri, the fourth highest civilian award, for his services to the field of medicine.

Post-LASIK ectasia is a condition similar to keratoconus where the cornea starts to bulge forwards at a variable time after LASIK, PRK, or SMILE corneal laser eye surgery. However, the physiological processes of post-LASIK ectasia seem to be different from keratoconus. The visible changes in the basal epithelial cell and anterior and posterior keratocytes linked with keratoconus were not observed in post-LASIK ectasia.

Corneal ectatic disorders or corneal ectasia are a group of uncommon, noninflammatory, eye disorders characterised by bilateral thinning of the central, paracentral, or peripheral cornea.

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A corneal button is a replacement cornea to be transplanted in the place of a damaged, diseased or opacified cornea, normally approximately 8.5–9.0mm in diameter. It is used in a corneal transplantation procedure whereby the whole, or part, of a cornea is replaced. The donor tissue can now be held for days to even weeks of the donor's death and is normally a small, rounded shape. The main use of the corneal button is during procedures where the entirety of the cornea needs to be replaced, also known as penetrating keratoplasty.

<span class="mw-page-title-main">Corneal opacity</span> Medical condition

Corneal opacification is a term used when the human cornea loses its transparency. The term corneal opacity is used particularly for the loss of transparency of cornea due to scarring. Transparency of the cornea is dependent on the uniform diameter and the regular spacing and arrangement of the collagen fibrils within the stroma. Alterations in the spacing of collagen fibrils in a variety of conditions including corneal edema, scars, and macular corneal dystrophy is clinically manifested as corneal opacity. The term corneal blindness is commonly used to describe blindness due to corneal opacity.

References

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  2. 1 2 3 Karim Rasheed, MD (2005). "Pellucid Marginal Degeneration". WebMD. Retrieved September 3, 2007.
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  4. ↑ Kaushik, S; Jain, A K; Saini, J S (2003). "Unilateral pellucid marginal degeneration". Eye. 17 (2): 246–8. doi: 10.1038/sj.eye.6700301 . PMID   12640416.
  5. 1 2 Belin, Michael W.; Asota, Ijeoma M.; Ambrosio, Renato; Khachikian, Stephen S. (2011). "What's in a Name: Keratoconus, Pellucid Marginal Degeneration, and Related Thinning Disorders". American Journal of Ophthalmology. 152 (2): 157–162.e1. doi:10.1016/j.ajo.2011.03.028. PMID   21708379.
  6. 1 2 Krachmer, JH (1978). "Pellucid marginal corneal degeneration". Archives of Ophthalmology. 96 (7): 1217–21. doi:10.1001/archopht.1978.03910060051009. PMID   352310.
  7. 1 2 Hovakimyan, Marine; Guthoff, Rudolf F.; Stachs, Oliver (31 March 2011). "Collagen Cross-Linking: Current Status and Future Directions". Journal of Ophthalmology. 2012: 406850. doi: 10.1155/2012/406850 . PMC   3263643 . PMID   22288005.
  8. ↑ Lee, Brandon W.; Jurkunas, Ula V.; Harissi-Dagher, Mona; Poothullil, Antony M.; Tobaigy, Faisal M.; Azar, Dimitri T. (2007). "Ectatic Disorders Associated with a Claw-shaped Pattern on Corneal Topography". American Journal of Ophthalmology. 144 (1): 154–156. doi:10.1016/j.ajo.2007.02.032. PMID   17601448.
  9. 1 2 Tzelikis, PF; Cohen, EJ; Rapuano, CJ; Hammersmith, KM; Laibson, PR (2005). "Management of pellucid marginal corneal degeneration". Cornea. 24 (5): 555–60. doi:10.1097/01.ico.0000153555.82278.5b. PMID   15968160. S2CID   12137149.
  10. ↑ Kymionis, George D; Aslanides, Ioannis M; Siganos, Charalambos S; Pallikaris, Ioannis G (2004). "Intacs for early pellucid marginal degeneration". Journal of Cataract & Refractive Surgery. 30 (1): 230–233. doi:10.1016/S0886-3350(03)00656-4. PMID   14967293.
  11. ↑ Intacs (2005). "A new FDA approved option for keratoconus filling the gap between contact lenses and a corneal transplant". Intacs. Archived from the original on August 9, 2007. Retrieved September 3, 2007.
  12. ↑ Kozobolis, Vassilios; Labiris, G; Gkika, M; Sideroudi, H (2011). "Additional Applications of Corneal Cross Linking". The Open Ophthalmology Journal. 5: 17–8. doi: 10.2174/1874364101105010017 . PMC   3065117 . PMID   21448300.
  13. ↑ Kymionis, George D.; Karavitaki, Alexandra E.; Kounis, George A.; Portaliou, Dimitra M.; Yoo, Sonia H.; Pallikaris, Ioannis G. (2009). "Management of pellucid marginal corneal degeneration with simultaneous customized photorefractive keratectomy and collagen crosslinking". Journal of Cataract & Refractive Surgery. 35 (7): 1298–301. doi:10.1016/j.jcrs.2009.03.025. PMID   19545822.
  14. ↑ Spadea, Leopoldo (2010). "Corneal Collagen Cross-Linking with Riboflavin and UVA Irradiation in Pellucid Marginal Degeneration". Journal of Refractive Surgery. 26 (5): 375–7. doi:10.3928/1081597X-20100114-03. PMID   20128533.
  15. ↑ Guindolet D, Petrovic A, Doan S, Cochereau I, Gabison EE (June 2016). "Sclerocorneal Intrastromal Lamellar Keratoplasty for Pellucid Marginal Degeneration". Cornea. 35 (6): 900–3. doi:10.1097/ICO.0000000000000813. PMID   27055210. S2CID   7748765.
  16. ↑ Jabbarvand M, Hashemian H, Khodaparast M, Hassanpour N, Mohebbi M (January 2015). "Intrastromal lamellar keratoplasty in people with pellucid marginal degeneration". Journal of Cataract and Refractive Surgery. 41 (1): 2–8. doi: 10.1016/j.jcrs.2014.11.030 . PMID   25532629.
  17. 1 2 Ophthalmology Times (2006). "Signs of pellucid marginal degeneration should rule out refractive surgery". Ophthalmology Times. Archived from the original on September 27, 2007. Retrieved September 3, 2007.
  18. ↑ Sii, F; Lee, GA; Sanfilippo, P; Stephensen, DC (2004). "Pellucid marginal degeneration and scleroderma". Clinical & Experimental Optometry. 87 (3): 180–4. doi: 10.1111/j.1444-0938.2004.tb03172.x . PMID   15186210.
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