Menu

  1. Home
  2. /
  3. Cornea–III
  4. /
  5. FP1105 : IOL Power Calculation Changes Before and After Collagen Crosslinking in Keratoconus Patients

Share this post

Dr. Namitha V G, N20197, Dr. Poorvi Garg

ABSTRACT

PURPOSE:To find the IOL power calculation changes before and after collagen cross linking (CXL) in keratoconus.

METHODS: Thirty- five eyes of 25 patients who underwent CXL were included. Out of 35 eyes, there were conventional CXL (n=16), accelerated CXL (n=7), contact lens assisted CXL (CACXL) (n=9),accelerated CACXL(n=3).  All underwent IOL MASTER and corneal topography using ORBSCAN II preoperatively and 1year post CXL. Keratometry was determined from ORBSCAN II. Change in Best Corrected Visual Acuity(BCVA), axial length (AL), keratometry(K), anterior chamber depth(ACD) and IOL power were analyzed

RESULTS: There was no significant change in IOL power (p.0.05) at the end of 1 year. BCVA showed a significant increase (p<0.01).keratometry showed a significant flattening(p=0.001).At the end of 1 year ACD and  AL showed insignificant change

CONCLUSION: CXL doesn’t affect IOL power calculation at end of 1 year. However significant change in keratometry was noted.

KEYWORDS: Collagen Cross linking, Keratoconus , IOL Power

INTRODUCTION

Keratoconus is a non-inflammatory degenerative disorder of the cornea, and is associated with corneal steepening, irregular astigmatism and reduced visual acuity. It begins in puberty and progresses until about 40 years with an incidence of 50-130/100,000[1-2].CXL is one of the most recent treatment procedure that targets the disease pathology and in turn helps in halting the disease progression[3-9]. It strengthens the cornea by photopolymerization of collagen fibers in the stroma using UV-A light and Riboflavin. The most consistent finding of observational and randomised controlled studies has been that corneal collagen crosslinking induces a reduction in keratometry values, that tend to be maintained over at least a year. But, there are only a few studies that document post CXL changes in ACD and AL.  These parameters are the cornerstone of IOL power calculation.So all those patients who develop cataract after 20-30 years need IOL power calculation. This study’s aim is to identify the probable dioptric change after CXL at a young age using IOL MASTER(Carl Zeiss IOL Master Advanced Technology V.5.2.1).

METHODS

This prospective observational study was conducted for a period of 2 years(June 2015 to May 2017 ) and adhered to the tenets of the Declaration of Helsinki. Prior institutional review board approval was obtained and written informed consent forms were taken.35 eyes of 25 patients with ages above 18 years with progressive keratoconus confirmed by ORBSCAN II with minimum corneal thickness greater than 350 microns after epithelial removal were included. Patients with  scarred cornea,central corneal dystrophy,  who were pregnant, and  or postop complications were excluded from study. All patients underwent best corrected visual acuity, subjective refraction, detailed anterior segment and posterior segment evaluation. Corneal topography recorded by Orbscan (OrbscanΙΙz; Bausch & Lomb, Rochester, NY) ultrasound –guided pachymetry (Pachette; DCHTechnology,Exton, PA) was used to measure the corneal thickness. Based on the above investigations, we determined the suitable candidates for the procedure. All these suitable candidates  were subjected to IOL Master (Carl Zeiss IOL Master Advanced Technology V.5.2.1). During the procedure, for all the candidates whose  eyes had an axial length less than 22mm, we used HOFFER Q, 22-26.5mm – SRK/T, > 26.5 – Holladay II formula. For all the patients, an ultrasound A constant of 118 was used and emmetropic IOL power was determined in phakic mode.From the IOL MASTER, axial length (AL),  anterior chamber depth(ACD) and IOL power were analysed. Keratometry value was determined using ORBSCAN.

Out of 35 eyes,16 patients underwent standard CXL, 7- Accelerated CXL,9- Contact lens Assisted CXL(CACXL),and 3-Contact lens  Assisted Accelerated CXL.

Cross-linking was performed in a daycare facility. After topical anaesthesia using propracaine hydrochloride 0.5% eye drops , the epithelium was abraded using a blunt spatula in a 9.0 mm diameter area . 0.1%drops of riboflavin sulphate in 20% dextran (Ribolink; Aurolab, Madurai, India) was applied at intervals of 1-5 minutes for 15-30 minutes, until riboflavin was seen in anterior chamber of the eye using a blue filter on slit lamp examinations.

In conventional CXL,  an ultraviolet –A meter calibrated with an intended radiance of 3mw/cm2 and supplied with an ultraviolet light source of 370 nm was applied for 30 min. (cumulative dose of 5.4J/cm²). Throughout the procedure ,riboflavin drops were instilled every 2 to 3 minutes to make the corneal surface dry and to make the corneal stromal bed more than 400-micronthick[10]. In an accelerated CXL, instead of following the Dreseden Dresden protocol[11], overall cumulative dose of 5.4J/cm2was  achieved by using 10mw/cm2of irradiance for 9 minutes[12].

Patients, whose thinnest pachymetry was less than 400 microns after epithelial removal were subjected to contact lens assisted collagen crosslinking. After epithelial removal, isotonic riboflavin 0.1% in dextran T500 was applied every 3 minutes for 30 minutes. At the same time a daily disposable soft contact lens, (14mm diameter and 8.6mm basal curvature – Bausch And Lomb of 90μm thickness made of Hilafilcon B without UV filter), was immersed in 0.1% riboflavin in dextran for 30mins. The riboflavin soaked contact lens was then applied on the surface of the cornea and the thickness was measured. Once pachymetry was confirmed to be more than 400μm , the treatment was continued as per the conventional protocol or accelerated protocol13.  A bandage contact lens was applied at the end of procedure. The patients were instructed to use 0.5% moxifloxacin eye drops , four times a day till the epithelial healing  followed by Fluromethalone 1% drops in a tapering dose for 2 weeks along with tear substitutes ,and followed up .

In this study, the follow- up  of 25patients (corresponding to 35 eyes), who underwent collagen cross linking procedure was additionally conducted after 1 year. On these patients, the best corrected visual acuity, subjective refraction, and IOL master tests and Orbscan II were performed.Statistical analysis was carried out using a computer based statistical programme, Microsoft Excel 2007 and statistical package, SPSS v.20. All categorical data were summarized using frequency and percentages. All continuous data was described using mean and standard deviation. To study the difference of clinical parameters between the groups, Independent sample t-test was applied for the continuous measurements after checking normality assumption. A P-value <0.05 was considered significant.

RESULTS

Thirty five eyes of 25patients were studied out of which 18 were males (25 eyes) and 7 were females (10 eyes). Mean age at the time of presentation was 22.22years (range18-30 years). 10 patients had bilateral involvement, thus both their eyes have been included in the study. However, the remaining 15 had unilateral involvement. Among the total 35 eyes, which were included in this study, standard CXL was done for16 patients (45.72%) Contact lens assisted CACXL was performed for 9 patients (25.71%), accelerated CXL was done in7 patients (20%), accelerated CACXL was done for 3(8.57%)patients. The mean preoperative BCVA in decimal was 0.16±0.15. (vision was recorded by Snellen’s and converted to decimal format for statistical calculations). Mean preoperative axial length , ACD and IOL power measured using CARL ZEISS IOL master were 23.9± 1.44 ,,3.49± 0.28 and 14.01± 4.78 respectively & keratometry  measured using orbscan was 48.83±2.98.

One year postop BCVA in decimal(0.09±0.10), axial length (24.00±1.52), keratometry mean(48.15±2.90), ACD(3.49±0.25), IOLpower(13.27±5.67).

BCVA: we found a statistically significant improvement in BCVA (p=0.0058) at the end of 1 year. Mean preop BCVA increased from 0.137±.11 to .091±.10, 1 year after the procedure. (table1)

KERATOMETRY: The  keratometry value measured using ORBSCAN II was found to be statistically significant (p = 0.0010) with a change from 48.83 ± 2.99 to 48.15 ±2.91.(table2)

ANTERIOR CHAMBER DEPTH(ACD):The change in the ACD  was found to be statistically insignificant with a change  from3.492 ± 0.280 to 3.498 ± 0.25  (p = .747) in our study.(table3)

AXIAL LENGTH: the change in the axial length was found to be statistically insignificant (23.90±1.44 to 24.00±1.51) ( p =0.26).(table4)

IOL POWER:The change in the IOL POWER   was found to be statistically insignificant (p= .08) at the end of 1 year post procedure. (14.01±4.77 to 13.27 ± 5.67).(table5)

DISCUSSION

Outcome of a cataract surgery is determined by an accurate IOL power calculation.To meet patient’s satisfaction, the formula for IOL power calculation had been modified over years from the first FYODOROVs formula till the late Hill RBF formula[13].Collagen cross linking is a revolutionary technique introduced in late 1998 by Theo seilor to address the problems of progressive corneal ectasia.We analysed the changes in these variables required for IOL power calculation,and IOL power 1 year after this procedure .

Best corrected visual acuity showed a statistically significant improvement from baseline at the end of one year in our study.Our study  findings were  similar to those of studies undertaken by Caporossi et al[5] ,Raiskup-Wolf[6] et al ,Wittig Silva et al[7], Hersh et al[8], Coskunsenen[9] et al etc.

It has previously been reported that the maximum corneal curvature regression is noted 1 year post CXL.We found a  statistically significant flattening at the  end of one year with a decrease of 0.7D  in Keratometry value .Wittig Silva et al in his study showed a decrease in Kmax by 0.74D at 3 months,0.92 at 6 months and 1.28D by 12 months.This was also supported by Hersh et al, Raiskup-Wolf et al6 ,Caporossi et al[5] in their studies .

In our study group , mean Axial length did not show any statistically significant change at the end of one year. A similar finding was noted in a study conducted  by De Bernado15 and Yakow Goldich16, where they  showed no statistically significant change at the end of 1 year.But as the follow up increased ,  it showed significant change. Our finding was contradicted in a study conducted by Nihat Polat17, where he showed AL increased significantly at end of 1 year.

Anterior chamber parameters were the least studied after collagen cross-linking. We studied ACD using IOL master .We found the change in  ACD at the end of 1 year was statistically insignificant. This was substantiated in a study conducted by Toprak and Yildrim[19],where they found a statistically insignificant change from baseline in 2 groups(p>.05).Another study by De Bernado[15]showed that there is no statistically significant change in ACD at end of 2 yrs  post CXL on progressive keratoconus. Another study conducted by Nihat polat [17] showed an increase in ACD at 6 months and 1 year in 45 eyes where he used scheimplug imaging to detect the parameters.

In our study , all the 35 eyes of 25 patients, after choosing proper IOL power calculation formulas based on their axial length,  underwent IOL master test preoperatively and postoperatively.We found there is no statistically significant change in IOL power( p=.08)at end of one year ,though a slight reduction in IOL power been noticed.

Limitations of our study include  1. small sample size and 2. short term followup.Comparison was between non uniform procedures(CXL.acceleratedCXL,cacxl,accelerated CACXL) although it has been done for same disease.

In conclusion,  corneal collagen crosslinking produces significant improvement in best correced visual acuity, significant reduction in  keratometry values but no change in anterior chamber depth and axial length at end of one year.Despite change in mean , keratometry there is no significant change in IOL power at end of one year.

We recommend extrapolation of our studies to large population with long follow up to further comment on the change in IOL power calculation after CXL.

References

  1. Hofstetter HW. A keratoscopic survey of 13,395 eyes. Am J Optom Arch Am Acad Optom. 1959; 36(1):3–11.
  2. Kennedy RH, Bourne WM, Dyer JA. A 48-year clinical and epidemiologic study of keratoconus. Am J Ophthalmol.1986;101(3):267–73.
  3. Copeland RA, Afshari NA, Dohlman CH. Copeland and Afshari’s principles and practice of cornea. NewDelhi: Jaypee-Highlights Medical Publishers, Inc; 2013. 1460 p.
  4. Wollensak G, Spoerl E, Seiler T. Riboflavin/ultraviolet-a-induced collagencrosslinking for the treatment of keratoconus. Am J Ophthalmol. 2003;135(5):620-7.
  5. Caporossi A, Baiocchi S, Mazzotta C, Traversi C, Caporossi T. Parasurgical therapy for keratoconus by riboflavin-ultraviolet type A rays induced cross-linking of corneal collagen: preliminary refractive results in an Italian study. J Cataract Refract Surg. 2006 ;32(5):837-45.
  6. Raiskup-Wolf F, Hoyer A, Spoerl E, Pillunat LE. Collagen crosslinking with riboflavin and ultraviolet-A light in keratoconus: long-term results. J Cataract Refract Surg. 2008 May;34(5):796-80.
  7. Wittig-Silva C, Whiting M, Lamoureux E, Lindsay RG, Sullivan LJ, Snibson GR. A randomized controlled trial of corneal collagen cross-linking in progressive keratoconus: preliminary results. J Refract Surg. 2008 ;24(7):S720-5.
  8. Hersh PS, Greenstein SA, Fry KL. Corneal collagen crosslinking for keratoconus and corneal ectasia: One-year results. J Cataract Refract Surg. 2011 ;37(1):149-60.
  9. Coskunseven E, Jankov MR 2nd, Hafezi F. Contralateral eye study of cornealcollagen cross-linking with riboflavin and UVA irradiation in patients withkeratoconus. J Refract Surg. 2009 ;25(4):371-6.
  10. Spoerl E, Hoyer A, Pillunat LE, Raiskup F. Corneal cross-linking and safety issues.Open Ophthalmol J. 11;5:14-6.
  11. Tomita M, Mita M, Huseynova T. Accelerated versus conventional corneal collagen crosslinking. J Cataract Refract Surg. 2014;40(6):1013-20.
  12. Jacob S, Kumar DA, Agarwal A, Basu S, Sinha P, Agarwal A. Contactlens-assisted collagen cross-linking (CACXL): A new technique for cross-linking thin corneas. J Refract Surg. 2014;30(6):366-72.
  13. Gökce SE, Zeiter JH, Weikert MP, Koch DD, Hill W, Wang L. Intraocular lenspower calculations in short eyes using 7 formulas. J Cataract Refract Surg. 2017;43(7):892-7.
  14. Shetty R. Keratoconus and corneal collagen cross-linking.Indian J Ophthalmol. 2013;61(8):380.
  15. De Bernardo M, Capasso L, Lanza M, Tortori A, Iaccarino S, Cennamo M, Borrelli M, Rosa N. Long-term results of corneal collagen crosslinking for progressive keratoconus. J Optom. 2015 ;8(3):180-6.
  16. Goldich Y, Marcovich AL, Barkana Y, Mandel Y, Hirsh A, Morad Y, Avni I, Zadok D. Clinical and corneal biomechanical changes after collagen cross-linking with riboflavin and UV irradiation in patients with progressive keratoconus: results after 2 years of follow-up. Cornea. 2012 ;31(6):609-14.
  17. Polat N, Gunduz A, Colak C. The influence of corneal collagen cross-linking on anterior chamber in keratoconus.Indian J Ophthalmol. 2017 ;65(4):271-275.
  18. Toprak I, Yildirim C. Scheimpflug parameters after corneal collagen crosslinking for keratoconus. Eur J Ophthalmol. 2013;23(6):793-8.

List of Tables

BCVA[1] N MEAN SD ‘P ‘VALUE*
PREOP 35 0.137 0.11 0.0058
POSTOP 1 YEAR 35 0.091 0.1

TABLE1: Analysis of  BCVA – pre and post CXL[2]

K [3]value N MEAN SD P VALUE*
PREOP 35 48.83 2.99 0.0010
POSTOP 1 YR 35 48.15 2.91

TABLE 2: Analysis of Keratometric value pre and post CXL

*paired ‘t’ test

TABLE3: Analysis of ACD pre and post CXL

 

ACD[4]

  

N

  

MEAN

  

SD

  

p Value*
 

PREOP

  

35

  

3.492

  

0.280

  

0.747
 

POSTOP 1 YR

  

35

  

3.498

  

0.253

*paired ‘t’ test

TABLE 4: Analysis of Axial length values pre and post CXL

AXIAL LENGTH N MEAN SD P VALUE*
PREOP 35 23.9 1.44 0.26
POSTOP 1 YEAR 35 24 1.51

 

 

IOL POWER[5]

  

N

  

MEAN

  

SD

  

P VALUE*
 

PREOP

  

35

  

14.01

  

4.78

  

 

0.08
 

POSTOP 1 YR

  

35

  

13.27

  

5.67

*paired ‘t’ test

TABLE 4: Analysis of IOL Power values pre and post CXL

*paired ‘t’ test

[1] Best Corrected Visual Acuity

[2]Collagen Cross linking

[3]Karetometry Value

[4]Anterior Chamber Depth

[5]IOL Power – Intra ocular lens

Leave a Comment