DR DINESH MITTALDR SONALEE MITTALDRISHTI EYE HOSP VIJAYNAGAR INDORE
Normal corneal layers
Noninflammatory Ectatic DisordersThey are keratoconus, pellucid marginal degeneration, keratoglobus, and posterior keratoconus. first three disorders may actually represent variations in phenotypic expression of same pathogenetic mechanism. Corneal thinning is a hallmark of these ectatic diseases. area of maximal thinning, relative to location of maximal corneal protrusion, is helpful in differentiating these conditions.
A KERATOCONUS B PMD C KERATOGLOBUS D POST KERATOCONUS
Noninflammatory Ectatic DisordersDistortion of the anterior corneal curvature occurs in keratoconus, pellucid marginal degeneration, and keratoglobus . The resultant reduction in visual function can vary from mild to severe. Computer-assisted topographical and pachymetric analyses have dramatically improved the sensitivity of detection of these ectatic disorders, particularly in the case of keratoconus. This has prompted debate on appropriate terminology for the patient .
Noninflammatory Ectatic Disorders debate on appropriate terminology for Pt with topographical evidence of inferior steepening, eccentric elevation or thinning, but without clinical signs of keratoconus. Keratoconus suspect or subclinical keratoconus are commonly used terms. Visual correction begins with glasses, followed by contact lens fitting. Failing these modalities, a surgical approach, designed to restore a more normal corneal contour, is planned.
Keratoconus is a condition in which cornea assumes a conical shape because of thinning and protrusion. Cellular infiltration and vascularization do not occur. It is usually b/l and, although it involves central two-thirds of cornea, apex of cone is usually centered just below visual axis. This results in mild to marked impairment of visual function.
Prevalence, distribution, & course50 to 230 per 100000 , occurs bilaterally. u/l cases occur 24% onset of keratoconus occurs at age of puberty. cornea begins to thin and protrude, resulting in irregular astigmatism. Typically, over a period of 10 to 20 years the process continues until progression gradually stops. If a faint, broad iron ring is present, it becomes a thinner, more discrete ring. rate of progression is variable. severity of disorder at time progression stops can range from very mild irregular astigmatism to severe thinning, protrusion, and scarring requiring keratoplasty
KC occurs with increased frequency with systemic and ocular conditions:1. Systemic disorders:Downs syndrome, Turner syndrome, Ehlers-Dunlos syndrome, Marfan syndrome,atopy, osteogenesis imperfecta, and mitral valve prolapse.
2. Ocular associations:Vernal disease, retinitis pigmentosa, blue sclera, aniridia, and ectopia lentis
onset is at puberty and progresses slowly thereafter, it may become stationary .The hallmark of KC is central or paracentral stromal thinning, apical protrusion,& irregular astigmatism. This results in impairment in both quantity and quality of vision because of the progressive nature of the disease.In advanced KC with corneal opacities , corneal grafting can be the only surgical alternative.modern managements have been developed to stop the progression of the disease
Clinical FindingsMunsons sign : When the patient is asked to look downward toward the floor, a V-shaped profile of the lower lid margin can be seen . Moderate-to severe KC tends to produce Munsons sign, while mild cases will not produce this sign .Rizzutis sign : This sign is observed by seeing a light on the nasal anterior sclera when the light is directed into the cornea from the temporal direction
Retinoscopy Signs scissoring effect of the retinal reflex seen with retinoscopy is highly diagnostic of KC (and of all forms of irregular astigmatism). It is best seen when the pupils are dilated. Unlike Munsons sign, scissoring effect is considered to be sensitive to even mild forms of KC
Slit Lamp Biomicroscopy SignsFocal thinning : focal thinning occurs at the cone apex,which is usually located inferior to the center of cornea; in pellucid marginal degeneration (PMD), this focal thinning is located in the lower third of the cornea. Fleischers ring : It is due to accumulation of ferritin particles in corneal basal epithelial cells. It encircles the base of the cone.
Vogts striae, hydrops cornea, and corneal scaringAs cornea continues to thin and bulge out,stretch marks may develop in form of thin,bright lines located deep in the stroma adjacent to Descemets membrane called Vogts striae . Vogts striae are a sign of corneal stretchingand protrusion. When cornea is depressed, Vogts striae often disappear. These striae are sometimes called stress lines.
Anterior stromal scars may develop due to continuous protrusion of the cornea. These scars may be small or large . The size and location of the scars determines its impact on visual function. If stretching becomes excessive, the cornea may eventually tear in the Descemets membrane leadingto fluid accumulation within the stroma and therefore to hydrops cornea .
Corneal hydrops This intense stromal edema often results in an acutely blurred vision since the tears often occur centrally.When the endothelium migrates to cover the tear,edema resolves and a posterior scar may form. Tears can occur in corneal periphery which may have minimal impact on vision
Forme Fruste KeratoconusForme Fruste Keratoconus (FFKC) is a subclinical disease and is not a variant of KC. Although clinicians use many other terms such as mild KC, early KC, and subclinical KC, their exact meanings and applications are less certain. These terms are not universally accepted.The diagnosis of KC is a clinical one that is aided by topography, while the diagnosis of FFKC is topographic.
TWO OPINIONS REGARDING THEDEFINITION FFKC is a completely normal cornea with neither clinical nor topographical risk factors, but this cornea is able to develop KC when treated by laser. The fellow eye may be keratoconic or there may be a family history of KC
TWO OPINIONS REGARDING THEDEFINITION FFKC is an abnormal cornea. Corneal topography or corneal hysteresis or both are abnormal; i.e., there are risk factors but the case is still not a clinically obvious KC.
Pellucid Marginal Degeneration (PMD) & Pellucid-like Keratoconus (PLK)PMD is a b / l , non-inflammatory, peripheral corneal thinning disorder characterized by a peripheral band of thinning of the inferior cornea. The cornea in and adjacent to the thinned area is ectatic.The etiology of PMD has not been clearly established, but collagen abnormalities, as seen in KC, have been reported. Patients usually are aged 2040 years at the time of clinical presentation
KeratoglobusIt is a generalized thinning of cornea . thinning is marked at limbus, extending circumferentially for 360; this makes it different from the globus morphological pattern of the KC. The whole cornea protrudes, in contrast to the regional thinning seen in KC and the inferior paralimbal thinning in PMD.
Keratoglobus. A generalized bulging and thinning of the cornea
Terrien marginal degenerationIt affects an age group similar to that affected by PMD ,can be bilateral. Although this condition can be associated with large amounts of astigmatism, it can be differentiated from PMD because the superior cornea is predominantly affected & because the area of thinning is often associated with vascularization and lipid deposition.
Terrien marginal degeneration. Note the lipid deposition
Furrow degeneration:It has some features of PMD. An intact epithelium is present, and area of corneal thinning is not vascularized, at least in the acute phase. differentiating feature is that area of thinning is closer to limbus with virtually no intervening zone of normal cornea, unlike findings in PMD.
Peripheral corneal melting disorders, such as Mooren ulcer, or peripheral melting secondary to rheumatologic disorders are characterized by pain. This pain may be severe in cases of Mooren ulcer. Associated findings include an epithelial defect over the area of thinning and corneal vascularization adjacent to the area of thinning in the acute phase.
PathologyFragmentation of the Bowman's layer seen with scanning electron microscopy has been described as specific to keratoconus and an early change leading to the disease.A hallmark of keratoconus is the Fleischer ring found at the base of the cone . brown iron ring can be seen histopathologically. Light and electron microscopy reveal that ferritin particles accumulate within and between the epithelial cells, particularly in the basal epithelium
The Fleischer ring in keratoconus
Hemosiderin pigment deposited in basal epithelium
DiagnosisThe diagnosis of keratoconus depends first on the suspicion of the condition and then on careful evaluation employing various available diagnostic tools including biomicroscopy, keratometry, keratoscopy, pachymetry, and computer-assisted topography & tomography . an affected patient in the teens or twenties seeks consultation for symptoms of progressive visual blurring and/or distortion. Photophobia, glare, monocular diplopia, and ocular irritation are also presenting symptoms. Early in the course of the disease, visual acuity may be normal even in symptomatic patients.
DiagnosisContrast sensitivity measurement may, however, uncover visual dysfunction before Snellen visual acuity loss can be measured. High, irregular myopi