keratoconus is an idiopathic , progressive , non - inflammatory ectasia of the lower central cornea . its cause is unknown , although metabolic / chemical changes have been documented [ 3 , 4 ] . genetic factors may play an important role , as indicated by the association of keratoconus with genetic syndromes and gene mapping studies [ 5 , 6 , 7 , 8 , 9 ] . keratoconus has been associated with macular coloboma , leber 's congenital amaurosis , retinal aplasia , cone - rod dystrophy , central serous chorioretinopathy , and rarely myelinated retinal nerve fibers . myelination , which occurs in 1% of the population [ 16 , 17 ] , normally terminates shortly after birth at the level of the lamina cribrosa . it is usually non - progressive , although there are two cases in which progression has been confirmed [ 18 , 19 ] . a 39-year - old woman presented with a diagnosis of stage ii keratoconus in the right eye and stage i keratoconus in the left eye . the patient , characterized by eutocic childbirth , was on no general or local medication and had no history of any systemic illness or trauma , except for the detection of peripapillary myelinated retinal nerve fibers and amblyopia in her right eye during childhood . her best corrected visual acuity was 20/30 in the right eye , with refractive error of 1.502.50  90 , and 20/20 with 1  80 in the left eye . axial lengths were 24.35 mm in the right eye and 24.20 mm in the left eye . slit - lamp biomicroscopy revealed corneal steepening in the inferior paracentral area in the right eye , much more evident than in the left one , and absence of vogt 's striae and fleisher 's ring in both eyes . the fundus oculi demonstrated extensive papillary and peripapillary myelination in the right eye only ( fig . 1 ) : the patch was located at the superior - inferior sectors of the optic nerve head and along the superior - inferior retinal vascular arcades masking the lower vessels . corneal topography ( eye top cso , italy ) showed markedly irregular astigmatism and inferior - superior asymmetry in the right eye ( fig . the oct pachymetry map scans were acquired with a high - speed anterior segment oct prototype ( carl zeiss meditec inc . , our patient showed indications for treatment with the cross - linking in her right eye . thirty minutes before the procedure , 2% pilocarpine drops were instilled to reduce the amount of light rays potentially harmful to the lens and retina . after topical anesthesia with two applications of lidocaine hydrochloride drops 4% and benoxinate hydrochloride 0.2% ( oxybuprocaine hydrochloride ) , the corneal epithelium was abraded in a central , 9-mm - diameter area , using an amoil brush . before beginning ultraviolet a ( uva ) irradiation , photosensitizing riboflavin ( vitamin b2 ) 0.1% solution ( 10 mg riboflavin-5-phosphate in 10 ml dextran 20% solution ) was applied to the cornea every minute for 15 min to achieve adequate penetration of the solution . after the removal of the corneal epithelium and the application of riboflavin , the cornea underwent low - dose ( 3 mw / cm ) irradiation with uva lasting 30 min ; in the meantime , the use of riboflavin was repeated every 2.5 min . after exposure to uva the eye was medicated with antibiotic , mydriatic , anti - inflammatory eye drops and finally a bandage contact lens was inserted , which was removed at the follow - up visit after 4 days once epithelial healing was complete . postoperatively , topical levofloxacin was given 4 times daily for 10 days , flurbiprofen sodium drops 3 times daily for 20 days and hyaluronate sodium drops 0.15% 6 times daily for 45 days . in addition , our patient received oral aminoacid supplements for 10 days . during the 6-month follow - up period , biomicroscopic examination detected no abnormalities of corneal transparency ; the fundus oculi was unchanged from the pre - operative state . refractive and topographic control showed stabilization of the progression of keratoconus . in particular were evaluated best corrected visual acuity , apical keratometry , mean ks , apical curvature gradient and inferior - superior index , which were comparable to preoperative data . to the best of our knowledge , corneal cross - linking for the treatment of keratoconus has not been previously reported in a patient with the coexistence of abnormalities in the ipsilateral posterior segment such as myelinated retinal nerve fiber layer . an association between idiopathic keratoconus and myelinated retinal nerve fiber layer has been reported in the literature , although it does not provide an estimate of incidence . the onset of keratoconus occurs during puberty and the disorder progresses until the third to fourth decade of life , when it usually arrests . on the other hand , myelinated retinal nerve fibers are developmental anomalies that usually appear as congenital and stationary lesions , rarely described as being acquired or progressive . in the case of our patient , the diagnosis of keratoconus was made at the age of 27 years , whereas the detection of abnormal fundus examination dates back to her childhood . the patient also reported vision worsening since school age . the decision to refer the patient to treatment with cross - linking was also derived from the stability of objective examination of the ocular fundus evaluated by comparing the retinal performed in time . another aspect we considered was the poor visual acuity of the woman 's right eye since childhood . schmidt et al .   proposed that myelinated fibers could blur retinal images and induce visual deprivation . found that 10% of patients with myelinated nerve fibers have myopia , amblyopia and strabismus . the cause of amblyopia in patients with myelinated retinal nerve fibers is a matter of controversy . some authors believe in an organic etiology and postulate that myelinated nerve fibers result in elevation of the optic disc and disorganization of neural elements leading to amblyopia . an estimated amblyopia prevalence from 2 to 3% , which is mainly an anisometropic amblyopia , and a 0.9% prevalence of unilateral nerve fiber layer myelination , would lead to believe the combination of these findings is more frequent . in our case we can exclude anisometropic amblyopia as proved by the calculation of biometrics in the two eyes . in this case , keratoconus treatment was also intended to maintain stable visual acuity in the right eye , already reduced in relation to the presence of ipsilateral myelinated retinal nerve fibers . cross - linking of collagen with riboflavin 0.125% uva is recommended for all forms of keratoconus in refractive stage ( i and ii ) that are negatively progressing , that is to say keratoconus with a clinically , topographically , pachymetry - documented worsening over the last 6 months . it is for such considerations that our patient was subjected to treatment . since the pilot study by wollensak et al . published in january 2003 , there have been eight studies which have reported their efficacy results . the study methodology , in terms of inclusion and exclusion criteria , treatment parameters , outcome measures and analysis are very variable among the studies . all the studies have reported varying degrees of improvement in visual acuity , reduction in keratometry , with a progressive trend in improvement for the duration of follow - up , which was in some cases 3 years or longer . no major complications were noted , although some studies have claimed to have re - treated their non - responders . the post - operative results obtained in our case are similar to those demonstrated by studies with a minimum follow - up of 6 months that indicate stabilization of progressive keratoconus after collagen cross - linking . the progression of keratoconus and stability of ipsilateral myelination allowed corneal cross - linking in the right eye of our patient . corneal cross - linking in our patient was found to be non - invasive , safe and effective . it was also important to verify the absence of postoperative changes in the fundus oculi , this being the first case of keratoconus treated in a patient with myelinated retinal nerve fiber .
keratoconus associated with myelinated retinal nerve fibers is not frequent and the relationship between the two pathologies is difficult to explain , therefore studies and further investigation are required . 
 the etiology of each condition may suggest the role of genetic factors . 
 follow - up is important to evaluate the progression of keratoconus and myelination . 
 here we describe the unusual coexistence of keratoconus and ipsilateral myelinated retinal nerve fiber layer and , for the first time , the corneal cross - linking treatment in this condition .