Keratoconous: An Eye Disease

Keratoconous is derived from Greek word “Kerato” means cornea and “conus” means cone. It is a non-inflammatory eye disorder linked to the progressive thinning of corneal stroma, asymmetrical corneal distortion and protrusion. Visual acuity, headache, photophobia, monocular diplopia and glare are some of the symptoms associated to keratoconous. Light microscopy, confocal microscopy and optical coherence tomography are the techniques utilized to observe corneal changes in keratoconous. Intra stromal corneal ring segment, Corneal collagen cross linkages to stabilize the cornea, Corneal transplant are some of the treatment employed to treat KC.


Symptoms
Clinical symptoms of KC are reduced visual acuity, headache, photophobia, monocular diplopia and glare. Different ways of treatment are applied to reduce these symptoms [3].

Etiology
From many years scientists are working to find the actual cause of KC. But they come to know that this is multifactorial disease and associated with genetics and environment factors [4].

Genetic Factors
Majority of Keratoconous cases are sporadic, which did not have any family history. First degree relatives who suffered from Keratoconous have 15 to 67 times higher risk of developing keratoconous than normal population. In the familial cases the DOI: 10.26717/BJSTR.2020.30.004999 23663 pattern of inheritance is autosomal dominant. It is a complex non Mendelian disease. Mutation in MIR184 gene has been found to cause keratoconous, but the majority of mutation still remains to be identified. 5 to 10 % of patients have positive family history. In such case both autosomal dominant and recessive pattern of inheritance have been observed [5,6].

Environmental Factors
Most of the cases of Keratoconous are sporadic. Along with the genetic factors many environmental factors were also responsible for Keratoconous. These factors include vigorous eye rubbing and ultraviolent light exposure [7]. Keratoconous is positively linked to allergic immune disorder and autoimmune disease. In many studies negative association has been found between diabetes mellitus and Keratoconous [3].

Hormonal Changes in Keratoconous
Development of KC has been proposed to be correlated with hormonal changes that occur at puberty, pregnancy or menopause.
There was a reported case in which pregnancy has induced the progression of KC. Some studies have postulated that pregnancy may be considered a risk factor of KC. The hormonal Changes in pregnancy have negative impact on corneal biomechanics. During the gestation period women experienced significant progression in KC [3]. and light microscopy has been used to corneal tissue in vitro [3].

Structural Changes Associated with Keratoconous
Eye is made of different layers as shown in Figure 2

In Turkey
Different scientist worked to find out the type of mutation in VSX1gene responsible for keratocous. In Turkey the "VSX1" was studied in keratoconous patients. Scientists detected two missence mutations D144N and D295Y in exon 2 and exon 5of VSX1 gene respectively in affected patients by using generation sequence analysis. The pathogenic effect of these missence mutation protein function were also determined by bioinformatic analysis tools SIFT, Polyphen and Mutation Taster. These results explain that the D144N and D295Y mutation might have role in pathogenesis of keratoconous [10].

In Korea
Genetic analysis of VSX1 gene in Korean patients suggest that two novel missencesubstitution (Leu17Val and Val199Leu) and one substitution (Gly160Val) do not have significant role in the pathogenesity of keratoconous [11].

In Denmark
Under sophisticated experimental investigation it was observed that the occurrence of KC was 86 patients per 100 000 residents and the incidence at 1.3 per 100 000 per year. Whole experiment was concluded as KC is quite prevalent in Denmark, with approximately more than 4600 affected individuals [12].

Contact Lenses
In early stages glass may provide significant correction in image formation. Later on, cornea changes to irregular form, instead of glass "contact lens" is used as a treatment. Lens provides normal refractive surface and correct irregular astigmatism. Nature of contact lens depends upon the severity of disease as soft lens are used in early stage. At later stages due to the change in the cornea shape complex rigid gas permeable lens are used to provide mechanical support [1].

Deep Anterior Lamella Kerotoplasty
It is the method used to treat keratoconous. This method is followed when the inner layers (endothelium and Descent's membrane) are healthy. Only external layers of corneal, epithelium and stroma are transplanted only [1].

Corneal Transplant
It is also called as penetrating keratoplasty. This treatment is usually done for those patients who suffer from severe keratoconous. This gives 95% favorable results. Complications in this treatment include rejection of graft, intraocular damage, postoperative astigmatism and reoccurrence of keratoconous [1].

Corneal Collagen Cross Linkages to Stabilize the Cornea
It is method of treatment in which covalent bonds are increased with or between the molecules of extracellular matrix such as collagen proteoglycan as shown in Figure 3.This provides stiffness and rigidity to cornea and prevents protrusion of cornea [13] ( Figure 3).

Conclusion
Keratoconous is one of the major eye disorder which results into corneal distortion and protrusion. But now different test and treatment are available to analyze and treat a patient.