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ORIGINAL ARTICLE
Year : 2014  |  Volume : 3  |  Issue : 2  |  Page : 103-106

Outcome of same day topographic guided photorefractive keratomileusis and corneal cross-linkage in patients with subclinical keratoconus


Department of Ophthalmology, Taif University Medical College, Taif, Saudi Arabia

Date of Web Publication20-Jun-2014

Correspondence Address:
Talal Abdulrahman Althomali
Department of Surgery, College of Medicine, Taif University, PO Box 888, Taif, 21974
Saudi Arabia
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2278-0521.134864

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  Abstract 

Purpose: To evaluate the outcome of same day topographic-guided photorefractive keratomileusis (PRK) and corneal cross-linkage in patients with subclinical keratoconus. Materials and Methods: A total of 20 patients with subclinical keratoconus were treated with topographic-guided PRK and same day corneal collagen cross-linkage with riboflavin. Inclusion criteria was low grade myopia of up to 3 diopter spherical equivalent, corneal thickness more than 475 microns, maximum keratometry reading K max less than 50 D. Results: Median preoperative spherical equivalent refraction was −2.25 D. At final follow-up visit at 1 year spherical equivalent was statistically significantly reduced to −0.25 D (P < 0.001). Median preoperative uncorrected visual acuity was 0.25 and best corrected visual acuity was 0.60. Median postoperative uncorrected visual acuity was 0.90 and best corrected visual acuity was 1.0. Median steepest K reading preoperatively was 46.25 D and it was 43.62 D at final follow-up visit. Conclusion: Same day topographic-guided PRK and corneal cross-linkage is a safe treatment offering good vision in subclinical cases of keratoconus.

Keywords: Cross-linkage, keratoconus, myopia, photo-refractive keratomileusis, topography


How to cite this article:
Althomali TA, Khaliq J. Outcome of same day topographic guided photorefractive keratomileusis and corneal cross-linkage in patients with subclinical keratoconus. Saudi J Health Sci 2014;3:103-6

How to cite this URL:
Althomali TA, Khaliq J. Outcome of same day topographic guided photorefractive keratomileusis and corneal cross-linkage in patients with subclinical keratoconus. Saudi J Health Sci [serial online] 2014 [cited 2021 Jul 24];3:103-6. Available from: https://www.saudijhealthsci.org/text.asp?2014/3/2/103/134864


  Introduction Top


Keratoconus is characterized by progressive corneal stromal thinning accompanied by unstable myopic astigmatic refractive error. It is the corneal biomechanical weakness that is responsible for corneal bulging and refractive error. [1],[2]

To correct the refractive error glasses, contact lenses, intrastromal corneal rings are used. [3],[4] Penetrating keratoplasty has been the gold standard for the ultimate visual and anatomical rehabilitation of keratoconus in severe and advanced cases.

To halt the progression of keratoconus, corneal collagen cross-linkage has been used with success. [5],[6] It results in stability of biomechanical architecture but leave the refractive error unchanged.

Photorefractive keratectomy (PRK) has been widely used for correction of refractive error. This procedure removes the tissue so it can potentially weaken the cornea. Doing PRK in eyes having keratoconus that is still subclinical is a procedure that can accelerate the disease process.

Myopic cases that show evidence of keratoconus on topography, demand special attention. While PRK can address refractive error but it removes stroma and cornea is left with less tissue to give structural support. If there was progression of the disease, then it would be already thinned cornea to resist it. We must seek some way of strengthening the cornea if we are going to subject it to iatrogenic tissue loss.

Doing corneal collagen cross-linkage in cornea with subclinical keratoconus can give structural support to resist the onset and progression of clinical disease.

Combining PRK with corneal collagen cross-linkage can result in anatomically strong cornea with more regular surface and less refractive error.


  Materials and methods Top


A total of 20 patients with subclinical keratoconus in both eyes were enrolled in this study after taking detailed consent regarding procedure. Inclusion criteria were a documented subclinical keratoconus, corneal thickness of at least 475 μm at the thinnest point in the worse eye, and age older than 18 years. The diagnosis of subclinical keratoconus was made based on corneal topography results. Exclusion criteria included corneal scarring or Vogt striae, any history of other ocular disease, eye surgery, trauma, any systemic disease, and pregnancy.

Preoperative evaluation consisted of general and ocular health history assessment; autorefractometry and autokeratometry corneal topography assessment of uncorrected visual acuity, best-spectacle corrected visual acuity, manifest and cycloplegic refraction; scotopic pupillometry; central ultrasound pachymetry and slit-lamp examination of the anterior and posterior segments of the eye.

All procedures were performed by the same surgeon. After topical anesthesia with 0.5% proparacaine and eye drops, the epithelium was mechanically removed within an 8.5-mm diameter. Topographic-guided PRK was performed. Riboflavin 0.1% solution was applied every 3 minutes for approximately 20 minutes until the stroma was completely penetrated and the aqueous was stained yellow. Ultraviolet A irradiation was applied for 30 minutes. During treatment, riboflavin solution was applied every 5 min to ensure saturation. After treatment, a bandage contact lens was applied until the epithelium healed completely, followed by application of 0.1% fluorometholone eye drops and 0.3% ofloxacin eye drops, QID daily for 2 weeks.

Age was analyzed by simple descriptive statistics as mean and standard deviation. Gender was represented as frequency. Visual acuity was recorded by Snellen's chart and it was converted into decimal notion. Central corneal thickness, visual acuity, refractive error in spherical equivalent, and steepest keratometry reading were presented as ''median'' as the data was not normally distributed in nature. For nonnormal data, Wilcoxon signed-ranked test was used.


  Results Top


There were 40 eyes from 20 patients included in this study. Eleven (55%) males and nine (45%) females. Mean age was 25.22 ± 4.30 years.

In [Table 3] which is based on wilcoxon signed rank test Unaided preoperative median visual acuity was 0.25 decimal that improved to 0.9 decimal that is statistically significant (P < 0.001) shown in [Table 4]. Best corrected preoperative median visual acuity was 0.6 decimal that improved to 1.0 decimal at final follow up visit at 1 year [Table 3]. This difference was statistically significant (P < 0.001) [Table 4]. Median spherical equivalent shown in [Table 3] at baseline was -2.25 D that was reduced to 0.25 D at 1 year. This difference was statistically significant (P < 0.001) [Table 4]. Median preoperative central corneal thickness was 500.5 μ that was reduced to 450 μ at 1 year follow up [Table 3]. Median steepest keratometric reading at base line was 46.25 D. At 1 year follow up median keratometric reading was 43.62 D [Table 3]. The difference was statistically significant (P < 0.001). Median preoperative central corneal thickness was 500.5 μ which was reduced to 450 μ after 1 year follow-up. Median steepest keratometric reading at base line was 46.25 D. At 1 year follow-up, median keratometric reading was 43.62 D. The difference was statistically highly significant (P < 0.001).


  Discussion Top


The issue involved in the surgical treatment of patients with subclinical keratoconus, having myopic refractive error, was to treat the refractive error and at the same time, keep the corneal biomechanical stable. The aim of our study was to evaluate the role of simultaneous PRK and corneal collagen cross-linkage in order to offer functional vision and mechanical stability of cornea at the same time.

Corneal collagen cross-linkage has been used for achieving stability of progressive ectatic corneal disorders, but it does not result in much refractive improvement. [7]

In forme fruste keratoconus surface laser ablation has been used with success. Several studies reported successful use of PRK for the correction of spherical cylindrical refractive error. It has been proven that successful use of PRK in cases of subclinical keratoconus showed no progression of the disease even after 10 years of the treatment [8] Other investigators successful treatment subclinical keratoconus with spherical and cylindrical refractive error. [9] Likewise, others had very good experience in treating cases of subclinical keratoconus with refractive error. [10]

Topographic-guided PRK not only flattens the apex of the cone but also broadens the base of the cone, so it allows a more stable pedestal. The new corneal architecture is more stable mechanically and more functional optically. [11],[12] But as surface ablation removes the corneal tissue, it always puts the cornea at the verge of progression of the keratoconus. There must be some way that at least counter acts the weakening effect of PRK. Corneal collagen cross-linkage here gives an answer. It has been shown to stiffen the cornea and does halt the disease progression.

Two investigators adopted a two-step approach in which they first did corneal collagen cross-linkage and one year later, they performed topographic-guided.

PRK [13] Their results were encouraging with stabilization of the disease progression and optically, a better cornea. But in that approach there were few drawbacks; PRK was performed on cross-linked cornea, so beneficial effect was partially lost; PRK on stiffened corneas is not as predictable as on corneas that have not been treated with CXL, and thus there were more chances of having post-PRK haze in corneas that have already been treated with CXL. [7]

There is an alternative approach of doing PRK followed immediately by CXL. Advantages of this approach include, no ablation of CXL treated corneas, beneficial effect of CXL not wasted, CXL depletes the cornea of keratocytes and may prevent post PRK haze formation. [13]

We, however, prefer the second approach of doing topographic-guided PRK followed immediately by corneal collagen cross-linkage by riboflavin. To maintain a safety margin, we did perform procedure in eyes with mild myopic refractive error. Our ceiling for myopic error was −3.0 D spherical equivalent. To further make procedure safer, we opted not to ablate more than 50 microns of cornea. Our goal was to leave at least 400 microns of corneal tissue after PRK.

Unaided preoperative median visual acuity was 0.25 decimal and was improved to 0.9 decimal with high statistically significance, (P < 0.001). Best corrected preoperative median visual acuity was 0.6 decimal, which was improved to 1.0 decimal at final follow-up visit after 1 year. This difference was statistically significant (P < 0.001).

Median spherical equivalence at the baseline, was −2.25 D, reduced to 0.25 D after 1 year. This difference was statistically highly significant (P < 0.001) [Table 1]. Median preoperative central corneal thickness was 500.5 μ, which was reduced to 450 μ after 1 year, [Table 2]. Median steepest keratometric reading at base line was 46.25 D. After 1 year follow-up, median keratometric reading was reduced to 43.62 D. The difference was statistically significant (P < 0.001).

There were 30 (75%) eyes that attained 20/20 (1.0) visual acuity postoperatively. Out of 11 males, 8 had bilaterally 1.0 decimal visual acuity, while 3 had unilateral 1.0 decimal visual acuity. Out of 9 females, postoperative 1.0 decimal visual acuity was attained in three patients bilaterally and five patients unilaterally as seen in [Table 1].
Table 1: Postoperative visual acuity in the 1 year study period

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[Table 2] shows the few complication which happened postoperatively, delayed epithelial healing for 6 days in four cases (10%), mild corneal haze in three cases (7.5%).
Table 2: Postoperative complications

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{Table 3}{Table 4}

Which resolved slowly within 1 year, 3 (7.5%) cases regressed, and two cases (5%) get steroid response with elevation of intraocular pressure, returned to normal after stopping steroids.

These three figures which were taken by pentacam topography in left eye of the same patient of. [Figure 1], is a posterior elevation map showing subclinical keratoconus, and [Figure 2] in the same patient shows an anterior elevation map which is normal in subclinical keratoconus. [Figure 3] which was taken 1 year after the procedure shows stability and no progression.
Figure 1: Posterior elevation map showing subclinical keratoconus

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Figure 2: Same patient shows an anterior elevation map on pentacam which is normal in subclinical keratoconus

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Figure 3: Pentacam picture taken one year after procedure ,shows stability and no progression

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Topographic-guided photorefractive keratectomy followed by CXL offers a safe and effective way of treating refractive error in cases of subclinical keratoconus. This approach not only gives spectacle- and contact lens-free better vision, but also offers stability to the cornea against future progression of the disease.

The limitations of our study include small number of cases and a short follow-up period. It is thus recommended that the number of cases and follow-up period be increased in order to monitor progressions of the subclinical keratoconus.


  Conclusion Top


Same day topographic-guided PRK and corneal cross-linkage is a safe treatment offering good vision in subclinical cases of keratoconus.

 
  References Top

1.Krachmer JH, Feder RS, Belin MW. Keratoconus and related non-inflammatory corneal thinning disorders. Surv Ophthalmol 1984;28:293-322.  Back to cited text no. 1
[PUBMED]    
2.Rabinowitz Y. Keratoconus. Surv Ophthalmol 1998;42:297-319.  Back to cited text no. 2
    
3.Kymionis GD, Siganos CS, Tsiklis NS, Anastasakis A, Yoo SH, Pallikaris AI, et al. Long-term follow-up of Intacs in keratoconus. Am J Ophthalmol 2007;143:236-44.  Back to cited text no. 3
    
4.Coskunseven E, Kymionis GD, Tsiklis NS, Atun S, Arslan E, Jankov MR, et al. One-year results of intra-stromal corneal ring segment implantation (KeraRing) using femto-second laser in patients with keratoconus. Am J Ophthalmol 2008;145:775-9.  Back to cited text no. 4
    
5.Wollensak G, Spoerl E, Seiler T. Riboflavin/ultraviolet-a-induced collagen cross-linking for the treatment of keratoconus. Am J Ophthalmol 2003;135:620-7.  Back to cited text no. 5
    
6.Wollensak G, Spoerl E, Seiler T. Stress-strain measurements of human and porcine corneas after riboflavin-ultraviolet-A-induced cross-linking. J Cataract Refract Surg 2003;29:1780-5.  Back to cited text no. 6
    
7.Kymionis GD, Kontadakis GA, Kounis GA, Portaliou DM, Karavitaki AE, Magarakis M, et al. Simultaneous topography-guided PRK followed by corneal collagen cross-linking for keratoconus. J Refract Surg 2009;25:S807-11.  Back to cited text no. 7
    
8.Alpins N, Stamatelatos G. Customized photo-astigmatic refractive keratectomy using combined topographic and refractive data for myopia and astigmatism in eyes with forme fruste and mild keratoconus. J Cataract Refract Surg 2007;33:591-602.  Back to cited text no. 8
    
9.Koller T, Iseli HP, Donitzky C, Ing D, Papadopoulos N, Seiler T. Topography-guided surface ablation for forme fruste keratoconus. Ophthalmology 2006;113:2198-202.  Back to cited text no. 9
    
10.Cennamo G, Intravaja A, Boccuzzi D, Marotta G, Cennamo G. Treatment of keratoconus by topography-guided customized photo-refractive keratectomy: Two-year follow-up study. J Refract Surg 2008;24:145-9.  Back to cited text no. 10
    
11.Kanellopoulos AJ. Managing highly distorted corneas with topography-guided treatment. In: ISRS/AAO 2007 Subspecialty Day/Refractive Surgery Syllabus. Section II: Ablation Strategies. San Francisco: American Academy of Ophthalmology; 2007. p. 13-15.  Back to cited text no. 11
    
12.Kanellopoulos AJ. Comparison of sequential vs same-day simultaneous collagen cross-linking and topography-guided PRK for treatment of keratoconus. J Refract Surg 2009;25:S812-8.  Back to cited text no. 12
[PUBMED]    
13.Kymionis GD, Diakonis VF, Kalyvianaki M, Portaliou D, Siganos C, Kozobolis VP, et al. One-year follow-up of corneal confocal microscopy after corneal cross-linking in patients with post-laser in situ keratomileusis ectasia and keratoconus. Am J Ophthalmol 2009;147:774-8.  Back to cited text no. 13
    


    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2]



 

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