Simultaneous Topography-Guided Photorefractive Keratectomy Followed by Corneal Collagen Cross-linking for Keratoconus




Purpose


To present the long-term results after simultaneous photorefractive keratectomy followed by corneal collagen cross-linking for keratoconus.


Design


Prospective, interventional, consecutive case series.


Methods


In this study, 26 patients (31 eyes) with progressive keratoconus were included. All patients underwent customized topography-guided photorefractive keratectomy immediately followed by corneal collagen cross-linking with the use of riboflavin and ultraviolet A irradiation. Epithelium was removed by transepithelial phototherapeutic keratectomy in all cases.


Results


Mean follow-up was 19.53 ± 3.97 months (range, 12 to 25 months). Mean preoperative spherical equivalent was −2.3 ± 2.8 diopters (D), whereas at the last follow-up examination, it was significantly ( P < .001) reduced to −1.08 ± 2.41 D. Logarithm of the minimal angle of resolution uncorrected and best-corrected visual acuity were reduced significantly by 0.46 and 0.084 ( P < .001), respectively, at the last follow-up examination. Finally, mean steep and flat keratometry readings were reduced by 2.35 ( P < .001) and 1.18 ( P = .013) at the last follow-up examination.


Conclusions


Simultaneous photorefractive keratectomy followed by corneal collagen cross-linking seems to be a promising treatment alternative in our series of keratoconic patients.


Corneal ectatic disorders, the most common of which is keratoconus, represent a group of conditions characterized by a bilateral state of tectonic corneal weakness that can lead to thinning of the cornea, production of myopia and irregular astigmatism, and visual acuity deterioration.


Treatment options comprise 2 general approaches: first, vision restoration by means of spectacles or rigid gas permeable contact lenses, and second, restoration of the tectonic integrity of the cornea by means of intracorneal ring segments and corneal collagen cross-linking (CXL). In advanced cases of keratoconus, lamellar or penetrating keratoplasty are considered essential treatment possibilities to improve patients’ quality of life.


CXL is a minimally invasive technique using riboflavin and ultraviolet A irradiation for the enhancement of corneal rigidity. In particular, CXL augments the biomechanical strength of the cornea by inducing interfibrillar cross-links of the stroma, resulting in the stabilization of the disorder. Results are extremely promising, but poor vision quality in patients remains largely unchanged, with minimal improvement.


Several combined procedures have been proposed to optimize the CXL result (such as conductive keratoplasty followed by CXL ), but it seems that the most effective is the combined topography-guided photorefractive keratectomy (PRK) followed by CXL. In this case series, we present the long-term results of simultaneous customized topography-guided surface ablation followed by CXL in patients with keratoconus.


Methods


In this study, 26 patients (31 eyes; consecutive series), 18 men and 8 women, with progressive keratoconus were included. Mean age was 29.3 ± 8.5 years (range, 19 to 49 years). Inclusion criteria were progressive keratoconus (keratoconus was described as progressive when there was an increase in the cone apex keratometry of −0.75 diopters [D] or an alteration of −0.75 D in the spherical equivalent refraction in the last 6 months), expected corneal thickness at the apex of the cone after PRK more than 400 μm, and no other corneal pathologic signs.


Clinical Evaluation


Preoperative evaluation consisted of general and ocular health history assessment; corneal topography (iTrace; Tracey Tech, Houston, Texas, USA); assessment of uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), and manifest refraction; scotopic pupillometry; central ultrasound pachymetry (Corneo-Gage Plus; Sonogage, Inc, Cleveland, Ohio, USA) and slit-lamp examination of the anterior and posterior segments of the eyes. Patients’ preoperative and postoperative data are shown in the Table .



TABLE

Preoperative and Last follow-up Refractive, Visual, and Keratometric Data in Keratoconic Patients after Combined Topography-Guided Photorefractive Keratectomy and Corneal Collagen Cross-linking


















































MRSE (D) UCVA (logMAR) BCVA (logMAR) Steep and Flat Keratometry (D)
Preoperative data
Mean ± SD –2.3 ± 2.8 0.21 ± 0.18 0.81 ± 0.65 49.8 ± 5.3
Range 1.63 to −12.88 0.54 to −0.06 2 to 0.1 67.7 to 42.7
Mean refraction (range) –2.06/–0.48@77° 20/33 20/131 44.39 ± 4.8 (62.75 to 37.1)
Postoperative data (mean follow-up, 19.53 ± 3.97 mos; range, 12 to 25 mos)
Mean ± SD –1.08 ± 2.41 0.12 ± 0.15 0.35 ± 0.36 47.46 ± 4.3
Range 2.5 to −8.75 0.46 to −0.04 1.2 to −0.04 53 to 37.48
Mean refraction (range) –0.81/–0.54@74° 20/27 20/46 43.21 ± 3.4 (53 to 37.48)

BCVA = best-corrected visual acuity; D = diopters; K = keratometrics; logMAR = logarithm of the minimal angle of resolution; mos = months; MRSE = manifest refraction spherical equivalent; SD = standard deviation; UCVA = uncorrected visual acuity.


All data were analyzed for normality. Because not all variables followed normal distribution, the Wilcoxon signed-rank paired test (PASW Statistics 18; SPSS, Inc, Chicago, Illinois, USA) was used. All diagrams and frequency analyses were performed by Microsoft Excel 2007 (Microsoft, Inc, Redmond, Washington, USA). Harris notation was used to calculate the mean values of refractions in the Table .


Surgical Procedure


All procedures were performed in our institution by the same surgeon (G.D.K.) under sterile conditions. After topical anesthesia with tetracaine 1% and oxybuprocaine 0.4% eyedrops, the epithelium was removed by transepithelial phototherapeutic keratectomy (PTK). The transepithelial PTK ablation was performed in an 8.0-mm zone in an intended depth of 50 μm. A solid-state laser with a wavelength of 213 nm (Pulzar Z1; CustomVis, Perth, Washington, USA) was used for the PRK procedure. The wavelength is generated using a major neodymium:yttrium–aluminum–garnet laser system of 1064 nm, and through special cultivated crystals, the 213 nm is used finally. The customization was performed based on the topographic data obtained by the iTrace technology. System software allows using a percentage of customization from 0% to 100%. Because of continuous flattening after CXL, as shown in previous studies, the relevant attempted correction was up to 60% of sphere and cylinder of patient refractive error, whereas customization was adjusted from 0% to 100%. Using 0% would be equivalent to a conventional laser treatment, and 100% would be equivalent to a full customized treatment. Adjusting this percentage could lower the maximum depth of tissue removed (upper limit, 50 μm). Treatment modifications (attempted correction and percentage of customization) were based on preoperative corneal pachymetry, corrected distance visual acuity, and manifest refraction to arrive to a maximum ablation depth of 50 μm.


Next, riboflavin (0.1% solution of 10 mg riboflavin-5-phosphate in 10 mL dextran-T-500 20% solution) was applied every 3 to 5 minutes for approximately 30 minutes until the stroma was penetrated completely and aqueous was stained yellow (riboflavin shielding). A commercially available ultraviolet A system (UV-X illumination system, version 1000; IROC AG R&D, Zürich, Switzerland) with Koehler optics was used for ultraviolet A irradiation. Before treatment, the intended 3-mW/cm 2 surface irradiance (5.4 J/cm 2 surface dose after 30 minutes) was calibrated using the ultraviolet A meter YK-34UV (Lutron Electronic Enterprise CO, LTD, Taipei, Taiwan), which is supplied with the UV-X device. During treatment, riboflavin solution was applied every 3 to 5 minutes to ensure saturation.


After the treatment, a bandage contact lens was applied until the epithelium healed completely, followed by application of fluorometholone 0.1% eyedrops (FML Liquifilm; FALCON pharmaceuticals, Ltd, Fort Worth, Texas, USA) twice daily for 2 weeks.




Results


All values are expressed as mean ± standard deviation and range. Visual acuity is expressed as logarithm of minimal angle of resolution (logMAR) visual acuity. All values presented statistically significant differences between preoperative and last postoperative period. Patient postoperative data at the last follow-up examination are shown in the Table .


Mean follow up was 19.53 ± 3.97 months (range, 12 to 25 months). Mean preoperative spherical equivalent was −2.3 ± 2.8 D, whereas at the last follow-up examination, it was reduced significantly ( P < .001) to −1.08 ± 2.41 D. LogMAR UCVA and BCVA were reduced significantly by 0.46 and 0.084 logMAR units ( P < .001) at the last follow-up examination. There were no intraoperative or postoperative complications.


Regarding the method’s safety, 48% (15/31) of eyes gained 1 line or more of UCVA at the last follow-up examination ( Figure 1 ). At the last follow-up examination, 10% (3/31) of eyes lost 1 line of BCVA. As shown in Figure 2 , 58% (18/31) of eyes were had UCVA of 20/100 (Snellen) or better after surgery, whereas at the last follow-up, 87% (27/31) of eyes had UCVA of 20/100 (Snellen) or better. Mean steep and flat keratometry readings were reduced by 2.35 D ( P < .001) and 1.18 D ( P = .013), respectively ( Figure 3 ). The stabilization of uncorrected distance and corrected distance visual acuity is demonstrated in Figure 4 . Additionally, spherical equivalent refractive changes in the follow-up period can be seen in Figure 5 . Patient topographic improvement can be seen using the iTrace technology ( Figure 6 ).




FIGURE 1


Bar graph showing change in best-corrected visual acuity (BCVA; safety) before and after photorefractive keratectomy followed by corneal collagen cross-linking for keratoconus confirming that approximately 50% of patients gained 1 line or more of BCVA at the last follow-up examination. PostOp = after surgery.

Jan 16, 2017 | Posted by in OPHTHALMOLOGY | Comments Off on Simultaneous Topography-Guided Photorefractive Keratectomy Followed by Corneal Collagen Cross-linking for Keratoconus
Premium Wordpress Themes by UFO Themes