You will be presented with the full text of a biomedical research paper. Please write an abstract for this paper. Your response should include the abstract and no additional text.

Paper text:
removal of the corneal epithelium is an essential component of riboflavin - ultraviolet - a ( uva ) corneal collagen cross - linking ( cxl ) therapy to permit the penetration of riboflavin into the corneal stroma .
failure to achieve adequate stromal absorption of riboflavin may impair the efficacy of the cross - linking process ; until now epithelial removal is performed mechanically .
excimer laser phototherapeutic keratectomy ( ptk ) is a well - known surgical technique that has successfully been used in the management of superficial corneal pathology , such as anterior corneal dystrophies , degenerations , and the treatment of keratoconus nodules .
transepithelial ptk ( t - ptk ) uses an excimer laser ablation in order to remove the epithelium and smooth the anterior irregular cornea . in this paper , we present a case of a keratoconic patient who underwent epithelial removal with t - ptk using a solid - state laser system followed by cxl treatment with riboflavin and uva irradiation .
a twenty - four - year - old male with progressive keratoconus presented to our institute for consultation . at the time of the examination , uncorrected visual acuity ( ucva ) was 20/25 in the right and 20/63 in the left eye and best spectacle - corrected visual acuity ( bscva ) was 20/20 ( manifest refraction plano1.00  15 ) in the right eye and 20/40 ( manifest refraction1.25    4.00  125 ) in the left eye . a trial with a rigid gas - permeable contact lens demonstrated improvement in visual acuity of 20/20 in his left eye .
keratometric readings were 42.60  24/43.52  114 at the right and 47.51  46/ 56.98  136 at the left eye . in order to assess corneal thickness ,
a pachymetric map measurement was performed in the right ( 481  m central , 639 nasal , 550 temporal , 587 superior , and 547 inferior ) and left ( 462  m central , 581 nasal , 569 temporal , 611 superior , and 541 inferior ) eye by ultrasound pachymetry ( sonogage , cleveland , ohio , usa ) .
epithelial thickness at the apex of the cone was 41  m in the left eye .
a solid - state laser system with a wavelength of 213  nm ( pulzar z1 , customvis , perth , wa ) was used for the procedure .
the wavelength is generated using a major nd : yag laser system of 1064  nm , and through special cultivated crystals the 213  nm is finally used .
the t - ptk ablation was performed in an 8.0  mm zone in an intended depth of 50  m . there was a correlation between the localized ablated stroma and the preoperative topography ( figure 1 ) .
after t - ptk , riboflavin 0.1% solution was instilled every 3 minutes for approximately 30 minutes .
penetration of the cornea and presence of riboflavin in the anterior chamber ( riboflavin shielding ) were monitored by slit - lamp examination .
uva irradiation was performed using a commercially available uva optical system ( uv - x illumination system version 1000 , zurich , switzerland ) with a light source consisting of an array of uv diodes ( 365  nm ) with a potentiometer in series to allow regulation of voltage .
before treatment , intended irradiance of 3.0  mw / cm ( 5.4  j / cm surface dose after 30 minutes ) was calibrated using the uv - a light meter yk-34uv ( lutron electronic ) which is supplied with the uv - x device .
irradiance was performed for 30 minutes , corresponding to a dose of 5.4  j / cm . during treatment ,
riboflavin solution was applied every 5 minutes to saturate the cornea with riboflavin . at the end of the procedure ,
a silicon - hydrogel bandage contact lens ( lotrafilcon b , air optix , ciba vision14.0  mm diameter , 8.6 base curvature , and dk = 140 barrers ) was applied until full reepithelialization .
postoperative medication included diclofenac sodium 0.1% ( denaclof , novartis ) for 2 days as well as antibiotic / corticosteroid ( tobramycin / dexamethasone ) drops ( tobradex , alcon laboratories , inc . )
contact lens was removed at the fifth postoperative day , and no signs of edema or inflammation were cited by slit - lamp biomicroscopy . after the removal of the contact lens , the patient received corticosteroid drops ( fml , fluorometholone 0.1% ,   falcon pharmaceuticals ) , tapering for the next 15 days , and he was encouraged to use artificial tears at least six times per day for 3 months postoperatively .   
one month after the combined t - ptk and cxl procedure , both ucva and bscva were improved at 20/32 and 20/25 , respectively ( manifest refraction 0.50    2.00  135 ) .
corneal topography revealed a significant improvement ( figure 2 ) which remained stable during the six - month follow - up period .
excimer laser phototherapeutic keratectomy ( ptk ) is a well - known surgical technique that has successfully been used in the management of superficial corneal pathology , such as anterior corneal dystrophies and degenerations .
demonstrated the safety and efficacy of ptk in the treatment of keratoconus nodules and the improvement of contact lens tolerance in these patients .
t - ptk uses an excimer laser ablation to remove the epithelium and smooth the anterior irregular cornea . in this paper ,
the patient underwent t - ptk using a solid - state laser system before cxl with riboflavin and uva irradiation .
the aim of t - ptk was epithelial removal and anterior cornea smoothening in order to decrease the irregular astigmatism .
reinstein has reported that in a study of 38 keratoconic eyes , an inferotemporal region of thin epithelium surrounded by epithelial thickening was found ; a pattern coincided with the cone on topography . according to this keratoconic pattern ,
an intended ablation depth of 50  m has been chosen in order to use the patient 's own epithelium as a masking agent allowing laser ablation to take place on the apex of the cone to regularize the stromal surface ( figure 1 ) .  
the significant improvement in visual acuity , especially in ucva , from the first postoperative month should be the result of t - ptk which decreases corneal irregularities as shown at the topography one month postoperatively ( figure 2 ) .
cxl after mechanical epithelial removal could potentially improve patient 's ucva but not at the first postoperative month and in this amplitude .
a possible limitation of this approach could be the decrease of corneal tissue by t - ptk at the cone apex before cxl .
in conclusion , epithelial removal with t - ptk before cxl could improve patient 's visual outcomes .
longer follow - up is necessary in order to evaluate the outcomes of this combined procedure .
purpose . to present a case of a keratoconic patient who underwent epithelial removal with transepithelial phototherapeutic keratectomy ( t - ptk ) using a 213-nm solid - state laser system followed by corneal collagen cross - linking ( cxl ) with riboflavin and ultraviolet - a ( uva ) irradiation 
 . methods . case report . results . a twenty - four - year - old male with keratoconus underwent cxl treatment after epithelial removal with t - ptk using a solid - state laser system . 
 no intra- or early postoperative complications were found . 
 one month postoperatively , uncorrected visual acuity ( ucva ) improved from 20/63 to 20/32 while best spectacle- corrected visual acuity ( bscva ) improved from 20/40 to 20/25 . 
 corneal topography revealed a significant improvement which remained stable during the six - month followup period . conclusions . 
 epithelial removal with t - ptk before cxl could improve patient 's visual outcome .