Keratoconus: An updated review

Abstract

Keratoconus is a bilateral and asymmetric disease which results in progressive thinning and steeping of the cornea leading to irregular astigmatism and decreased visual acuity. Traditionally, the condition has been described as a noninflammatory disease; however, more recently it has been associated with ocular inflammation. Keratoconus normally develops in the second and third decades of life and progresses until the fourth decade. The condition affects all ethnicities and both sexes. The prevalence and incidence rates of keratoconus have been estimated to be between 0.2 and 4,790 per 100,000 persons and 1.5 and 25 cases per 100,000 persons/year, respectively, with highest rates typically occurring in 20-to 30-year-olds and Middle Eastern and Asian ethnicities. Progressive stromal thinning, rupture of the anterior limiting membrane, and subsequent ectasia of the central/paracentral cornea are the most commonly observed histopathological findings. A family history of keratoconus, eye rubbing, eczema, asthma, and allergy are risk factors for developing keratoconus. Detecting keratoconus in its earliest stages remains a challenge. Corneal topography is the primary diagnostic tool for keratoconus detection. In incipient cases, however, the use of a single parameter to diagnose keratoconus is insufficient, and in addition to corneal topography, corneal pachymetry and higher order aberration data are now commonly used. Keratoconus severity and progression may be classified based on morphological features and disease evolution, ocular signs, and index-based systems. Keratoconus treatment varies depending on disease severity and progression. Mild cases are typically treated with spectacles, moderate cases with contact lenses, while severe cases that cannot be managed with scleral contact lenses may require corneal surgery. Mild to moderate cases of progressive keratoconus may also be treated surgically, most commonly with corneal crosslinking. This article provides an updated review on the definition, epidemiology, histopathology, aetiology and pathogenesis, clinical features, detection, classification, and management and treatment strategies for keratoconus.

Delayed Topographical and Refractive Changes Following Corneal Cross-Linking for Keratoconus

“…Keratoconus is the most common primary corneal ectasia, affecting both genders and all ethnicities [ 1 , 2 ]. It may result in progressive and severe loss of vision [ 1 , 3 ], with younger patients demonstrating the greater progression of their disease [ 2 ] Management options include spectacles, contact lenses, intracorneal ring segments, Corneal Collagen Crosslinking, and ultimately lamellar or penetrating keratoplasty [ 1 ].…”

Indications for keratoplasty in management of corneal ectasia

“…Spectacles are first-line therapy for mild disease. However, spectacles cannot accommodate for irregular astigmatism, where the angle between the principal power meridians are not separated by 90° [9 ▪▪ ,10]. A novel design for glasses that compensates for nonorthogonal astigmatism has been proposed, and it has been shown to improve best corrected visual acuity by one to four lines in limited reports [10].…”

“…Although rigid gas-permeable contact lenses can achieve higher levels of visual correction, they require special fitting techniques to improve tolerability [13 ▪▪ ]. They can accommodate for higher levels of irregular astigmatism through neutralization of the tear lens [9 ▪▪ ]. As its name suggests, gas-permeable lenses allow for higher oxygen permeability and tear exchange rate through materials such as silicone and fluorine.…”

Topographic Outcomes in Keratoconus Surgery: Epi-on versus Epi-off Iontophoresis Corneal Collagen Cross-Linking

“…Increased systemic levels of pro-inflammatory factors, including interleukin-6, tumor necrosis factor-α, and matrix metalloproteinase-9 were found, suggesting that KC may have an inflammatory component [ 1 ]. Nevertheless, the etiopathological mechanisms are still not completely elucidated [ 2 ]. Keratoconus is characterized by the thinning of the corneal stroma, which leads to the cornea taking a conical shape, generating irregular astigmatism, and increasing the level of higher-order aberrations, with the consequent progressive deterioration of vision [ 2 ].…”

“…Nevertheless, the etiopathological mechanisms are still not completely elucidated [ 2 ]. Keratoconus is characterized by the thinning of the corneal stroma, which leads to the cornea taking a conical shape, generating irregular astigmatism, and increasing the level of higher-order aberrations, with the consequent progressive deterioration of vision [ 2 ]. The typical onset of KC is puberty [ 3 , 4 ], with pediatric patients showing the highest rate and speed of progression [ 5 ].…”