keratoconus is a greek word ( kerato : cornea ; konos : cone ) meaning cone - shaped protrusion of the cornea . keratoconus is a condition with noninflammatory , progressive thinning and steepening of the central and/or paracentral cornea . it is the most common primary ectasia and usually occurs in the second decade of life and affects both genders and all ethnicities . recent research suggests that keratoconus somehow accelerates the process of keratocyte apoptosis , which is the programmed death of corneal cells that occurs following injury . minor external traumas , such as poorly fitted contact lenses , ocular allergies , and eye rubbing mostly due to atopy   can release cytokines from the epithelium that stimulate keratocyte apoptosis . early studies demonstrated elevated levels of collagenolytic and gelatinolytic activities in keratoconic corneas . although thought to be a non - inflammatory disease , inflammatory molecules , such as interleukins and tumor necrosis factor , have been shown to be elevated in keratoconus , and these inflammatory molecules may mediate production and activation of proteases . genetics may play a role in the etiology of keratoconus , in that some patients may have a genetic predisposition . genetic heterogeneity consists of allelic heterogeneity ( different mutations in the same locus ) and/or locus heterogeneity with different loci producing the same phenotype . to date linkage analysis and association studies are the two main approaches used to identify the causative genes . linkage analysis identifies chromosomal region(s ) associated with the disease and the gene(s ) mapped to that regions   in complex disease , where more than one gene is considered , gene - gene interaction should also be investigated . one of the attempts to present the disease more realistically in a linkage analysis is a method allowing for analyzing two distinct loci simultaneously . such analysis performed in an australian pedigree by burdon et al . although the majority of patients presenting to ophthalmologists with keratoconus have a sporadic form of the disease , there is growing evidence of familial keratoconus and the involvement of genetic factors . ninety percent of pedigrees with familial keratoconus display an autosomal dominant inheritance with reduced penetrance . numerous loci have been mapped in keratoconus families , and research is ongoing to identify causative genes involved in keratoconus development and progression , such as a locus for autosomal dominant keratoconus was mapped in finnish families to 16q22.3q23.1 . more than two dozen syndromes are associated with keratoconus , including down syndrome , connective tissue disorders , including osteogenesis imperfecta , and some subtypes of ehlers - danlos syndrome . identification of genetic factors might allow to develop both specific diagnostic tests and keratoconus gene therapy in the future . early degeneration of basal epithelial cells can be followed by disruption of the basement membrane . the stroma has normal - sized collagen fibers but low numbers of collagen lamellae , which results in stromal thinning . the irregular superficial opacities and scars at or near the apex of the cone represent structural breaks in bowman 's layer . vogt 's striae are fine , and parallel striations stress lines of the stroma might be present . finally if there is a spontaneous tear in descemet 's membrane , aqueous flows into stroma creates acute corneal edema called  hydrops . soft contact lenses have limited role in correcting corneal irregularity , as they tend to drape over the surface of the cornea and result in poor visual acuity . early in the disease , soft lenses with toric design may be adequate to correct myopia and regular astigmatism . however , soft lenses designed specifically for keratoconus ( e.g. , kerasoft ) have a useful role in early keratoconus or where a patient may be intolerant of rgp . rigid gas permeable ( rgp ) lenses are required as the condition progresses in order to correct the irregular astigmatism . all keratoconus contact lenses should be ordered in a moderate to high dk rigid gas permeable material to avoid epithelial hypoxia and corneal erosion during the long wearing schedule of keratoconus patient . the three - point - touch design is the most popular and the most widely fitted design for keratoconic patients . three - point - touch actually refers to the area of apical central contact and two other areas of bearing or contact at the midperiphery in the horizontal direction . apical clearance : in this type of fitting technique , the lens vaults the cone and clears the central cornea , resting on the paracentral cornea . however , the disadvantages are causing a poor tear film , corneal oedema , and poor visual acuity as a result of bubbles under the lens . the apical bearing technique : the weight of the lens is supported by the area on the apex of the cornea but not elsewhere on the cornea . the advantage of this fit is that patients may have good visual acuity obtained as a result of apical touch . but it also may accelerate the corneal scarring due to touch . in some keratoconic patients , the steepness of the corneal apex and the radical flattening of the mid - peripheral and peripheral cornea limit the effective use of spherical lenses to correct irregularity . an aspheric lens with a high eccentricity value will become flatter quicker compared to a spherical curve . this allows you to select a relatively steep base curve radius to match the apex of the cornea and the highly aspheric posterior designs provide better alignment and weight distribution over a larger area of the cornea . the aim of aspheric lens fit should be good centration , central alignment or slight central bearing , good movement ( 1  mm ) , and peripheral clearance . the mcguire system : the mcguire system was first introduced in 1978 and consists of three diagnostic lens sets , nipple , oval , or globus . the rose k is a unique keratoconus lens design with complex computer - generated peripheral curves based on data collected by dr . paul rose of hamilton , new zealand . the system ( 26 lens set ) incorporates a triple peripheral curve system [ 17 , 18 ] . piggyback lenses are used for difficult cases , for instance in cases of rgp lens intolerance , proud nebulae in keratoconus , or apical dimpling or where there are areas of recurrent epithelial erosion . the system consists of a rigid lens fitted on top of a soft lens aiming to obtain same visual acuity as with a single lens . soft lens must be a silicone hydrogel lens with a high dk / t . hybrid lens system ; the softperm lens ( ciba vision ) is a hybrid lens with a rgp centre surrounded by a soft hydrophilic skirt . the synergeyes is relatively new and with a high dk hybrid lens , it could be used for early keratoconus due to its aspherical design . these lenses tend to be used in cases of rgp lens intolerance . a recent study performed by abdalla et al . scleral and semiscleral lenses have proven to be extremely beneficial for patients with highly irregular and/or asymmetric keratoconic corneas . these patients will benefit from a large diameter ( 13.5 to 16.0  mm ) semiscleral lens design . schornack et al . showed a dramatic improvement in visual acuity by using scleral lens in a study [ 21 , 22 ] . for keratoconus surgery might be considered when patients are no longer able to tolerate their gas - permeable contact lenses , when a successful contact lens fit is no longer possible or because of unresolving corneal hydrops . penetrating keratoplasty ( pk ) or full - thickness corneal transplant , historically has been the most common surgical correction for irregular astigmatism resulting from keratoconus . the corneal graft is susceptible to epithelial , stromal , and endothelial forms of inflammatory rejection from the host 's immune response . the purpose of deep anterior lameller keratoplasty ( dalk ) is to preserve host descemet 's membrane and endothelium . the main reason of decreased visual acuity after keratoplasty is most likely high astigmatism . generally , even after suture removal , residual astigmatism still cause visual problems . various types of treatment modalities are tried with contact lenses : sclerals , rigid gas permeable and reverse geometry hydrogel lenses , and silicone hydrogel soft toric contact lenses , in order to improve lens and optical stability , but no common consensus is approved yet [ 2325 ] . if postresidual astigmatism is under 4d , a hard gas permeable , large - diametered contact lens will be recommended , bearing in mind that donor cornea diameter should be smaller than contact lens diameter , eventually . if astigmatism is under 1d , soft contact lenses would be successful to correct refractive status . in a recent study , geerards et al . successfully fitted large - diameter ( 12  mm ) tricurve rigid gas - permeable contact lenses for 90 ( 47% ) of 190 penetrating keratoplasty patients with good tolerance . intralimbal rigid gas - permeable contact lenses are found effective in increasing visual acuity after penetrating keratoplasty , keratoconus and pellucid marginal degeneration as well . also special design contact lenses can improve visual acuity after penetrating keratoplasty . fitted 4 different types of special contact lenses in 28 eyes , and nearly in all patients visual acuity significantly improved . in conclusion , there are many contact lens options available to correct postkeratoplasty astigmatism before conducting any surgical method .
keratoconus is the most common corneal distrophy . 
 it 's a noninflammatory progressive thinning process that leads to conical ectasia of the cornea , causing high myopia and astigmatism . 
 many treatment choices include spectacle correction and contact lens wear , collagen cross linking , intracorneal ring segments implantation and finally keratoplasty . 
 contact lenses are commonly used to reduce astigmatism and increase vision . 
 there are various types of lenses are available . 
 we reviewed soft contact lenses , rigid gas permeable contact lenses , piggyback contact lenses , hybrid contact lenses and scleral - semiscleral contact lenses in keratoconus management . 
 the surgical option is keratoplasty , but even after sutur removal , high astigmatism may stil exists . 
 therefore , contact lens is an adequate treatment option to correct astigmatism after keratoplasty .