Pellucid Marginal Degeneration
Encyclopedia
Pellucid Marginal Degeneration (PMD; keratotorus), is a degenerative cornea
l condition, often confused with keratoconus
. It is typically characterized by a bilateral thinning (ectasia
) in the periphery of the cornea, that is non-inflammatory, although unilateral cases have been reported. The term was first coined in 1957 by the ophthalmologist Schalaeppi.
, and causing a distortion in vision. Deterioration can become severe over time.
Like keratoconus, PMD rules a patient out for refractive surgery
. Due to the thinning of the cornea, procedures such as LASIK
and PRK
would make the patient a poor candidate.
. Patients wearing contacts 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.
However new studies show that the use of a "GP" or Scleral contact lens
has shown promise for most patients that exhibit Pellucid Marginal Degeneration. 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 GP lens, regardless of the fact that it is a rigid lens, will in most cases be more comfortable then standard rigid corneal lenses, and at times more comfortable than soft lenses. 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.
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...
l condition, often confused with keratoconus
Keratoconus
Keratoconus , is a degenerative disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape than its normal gradual curve....
. It is typically characterized by a bilateral thinning (ectasia
Ectasia
Dilation or distention of a tubular structure. It occurs as part of a pathophysiological process.-Specific conditions:* Duct ectasia of breast, a dilated milk duct...
) in the periphery of the cornea, that is non-inflammatory, although unilateral cases have been reported. The term was first coined in 1957 by the ophthalmologist Schalaeppi.
Incidence
Incidence of PMD is rare, but it is unknown how many cases occur each year, due in part to the confusion of the condition with keratoconus.Symptoms
Unlike keratoconus, pain is not normally present, and aside from the visual deterioration, no symptoms accompany the condition. Normally, PMD does not present with vascularization of the cornea, scarring, or any deposits of lipid.Signs and diagnosis
Upon examination by an optometrist or ophthalmologist, the patient exhibits normal corneal thickness in the center, with an intact central epithelium, but the inferior cornea exhibits a peripheral band of thinning.In pmd we can see high against the rule astigmatism along with horizontal bow ties and inferior peripheral thinning seen in between 7 and 4 o'clock meridian.Epidemiology
Although there has been only one reported association of PMD and scleroderma, no other identifiable factors have been found to link to race, sex, or age, although most cases present early in life, in the age group of 20-40. No known cause for the disease has been found.Prognosis
Visual function declines as a result of the irregular corneal shape, resulting in astigmatismAstigmatism
An optical system with astigmatism is one where rays that propagate in two perpendicular planes have different foci. If an optical system with astigmatism is used to form an image of a cross, the vertical and horizontal lines will be in sharp focus at two different distances...
, and causing a distortion in vision. Deterioration can become severe over time.
Like keratoconus, PMD rules a patient out for refractive surgery
Refractive surgery
Refractive eye surgery is any 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 or cataract surgery. The most common methods today use excimer lasers to...
. Due to the thinning of the cornea, procedures such as LASIK
LASIK
LASIK or Lasik , commonly referred to simply as laser eye surgery, is a type of refractive surgery for correcting myopia, hyperopia, and astigmatism...
and PRK
PRK
PRK could refer to:*Phase Reversal Keying, see BPSK*Photorefractive keratectomy, a laser eye surgery procedure*ISO 3166-1 alpha-3 code, International Olympic Committee country code, and FIFA country code for North Korea...
would make the patient a poor candidate.
Contact lenses
Visual acuity can not usually be corrected with the use of corrected lenses, but success has been shown with the use of rigid contact lenses combined with over-refractionRefraction
Refraction is the change in direction of a wave due to a change in its speed. It is essentially a surface phenomenon . The phenomenon is mainly in governance to the law of conservation of energy. The proper explanation would be that due to change of medium, the phase velocity of the wave is changed...
. Patients wearing contacts 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.
However new studies show that the use of a "GP" or Scleral contact lens
Scleral lens
A scleral lens is a large lens that rests on the Sclera and creates a Tear-filled vault over the Cornea. Scleral lenses are designed to treat a variety of eye conditions, many of which do not respond to other forms of treatment.- Design :...
has shown promise for most patients that exhibit Pellucid Marginal Degeneration. 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 GP lens, regardless of the fact that it is a rigid lens, will in most cases be more comfortable then standard rigid corneal lenses, and at times more comfortable than soft lenses. 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.
Intacs
The use of intacs implants has been tested as a treatment for PMD, with slight improvement in visual acuity noted after eleven months, and intacs have been used with keratoconus with success.See also
- KeratoconusKeratoconusKeratoconus , is a degenerative disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape than its normal gradual curve....
- OptometryOptometryOptometry is a health care profession concerned with eyes and related structures, as well as vision, visual systems, and vision information processing in humans. Optometrists, or Doctors of Optometry, are state licensed medical professionals trained to prescribe and fit lenses to improve vision,...
- OphthalmologyOphthalmologyOphthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems...
- Terrien's marginal degeneration
External links
- Keratotorus (Pellucid Marginal Degeneration) - Atlas of ophthalmology