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Color Light Emitting Diode Reflection Topography- Clinical Applications

Purpose: Report pre and post arcuate keratotomy (AK) values, guided by laser emitting diode (LED) topography, for residual astigmatism in pseudophakia, laser in situ keratomileusis( LASIK), and ingrowth patients. Setting: Private clinical practice in Barcelona, Spain. Methods: Prospective, interventional study using LED topography anterior keratometric map for post-surgical AK. Pre and post-operative variables included uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), subjective sphere, astigmatism, and axis, LED and Orscan topography cylinder, SimK, and axis (steep). Data reported as mean and standard deviation, student ttest to assess statistical significance, Pearson correlation, and linear regression analysis were calculated. Bonferroni adjustment for p values. Results: AK performed on pseudophakic (45 eyes), LASIK (10 eyes), and ingrowth patients (5 eyes). Pre and post AK mean astigmatism results, respectively, for pseudophakia were: subjective: 0.82 ± 0.4/0.2 ± 0.3D; p<0.001, LED 1.1 ± 0.5/0.8 ± 0.4D; p<0.0001, Orbscan 1.2 ± 0.7/0.7 ± 0.6D, LASIK: subjective: 0.75 ± 0.2/0.2 ± 0.3D; p<0.001, LED 0.8 ± 0.4D/0.61 ± 0.4D; p<0.05, Orbscan 0.78 ± 0.45/0.49 ± 0.2D; p>0.05, and ingrowth subjective: 1.2 ± 0.2/0.6 ± 0.4D; p>0.05, LED 2.1 ± 0.6/2.1 ± 0.4D; p<0.01, Orbscan 1.9 ± 0.9/1.1 ± 0.4D; p>0.05. Pseudophakia LED vs. Orbscan astigmatism R2=0.60, p<0.0001 and SimK values R2=0.90, p<0.0001. Correlation between topographers for LASIK was R2=0.60, p<0.0001 for SimK and R2=0.86, p<0.0001 for axis values, while for ingrowth values were R2=0.87, p>0.01 for SimK and R2=0.85, p>0.01 for axis values. Subjective vs. topography axis correlation for LASIK was R2=0.83, p>0.05 for Orbscan and R2=0.81, p>0.05, for LED. For ingrowth, values were R2=0.81, p>0.01 for Orbscan and R2=0.91, p>0.05 for LED. Conclusion: LED topography guided AK significantly improved UCVA in pseudophakic, LASIK, and ingrowth residual astigmatism. Strong correlation for astigmatism and SimK values between LED and Orbscan values in pseudophakic eyes.


Introduction
Recent articles have shown that new color light emitting diode (LED) reflection topographers offer a true elevation based topography analysis, are very precise in measuring corneal astigmatism, particular large values, and have improved axis and keratometry repeatability [1][2][3][4][5]. LED topography not only has the potential for toric intraocular lens calculation (IOL), but has been also tested for cylinder assessment in pseudophakia, keratoconus and corneal scars [1,3,[5][6][7]. Its clinical applications could also include other cases involving astigmatism correction, like post-surgical residual astigmatism.
Arcuate keratotomy (AK) safely and effectively reduces astigmatism and improves visual acuity in post cataract or LASIK cases with residual astigmatism [8][9][10][11]. Ferreira et al. reported that astigmatism value was better assessed with LED topography in pseudophakic eyes [4].
We report results after LED topography guided paired AK for treating post phacoemulsification and monofocal IOL or multifocal IOL (MF-IOL) implantation, laser in situ keratomileusis (LASIK), or stable epithelial ingrowth residual astigmatism and comparing values with Orbscan topography.

Materials and Methods
We designed a prospective, longitudinal study involving patients with postoperative residual astigmatism, phacoemulsification with monofocal or MF-IOL implantation, post LASIK, or treated epithelial ingrowth who underwent treatment with AK. The study adhered to the tenets of the Declaration of Helsinki and all patients read and signed an informed consent form. Orbscan and LED reflection topography (Cassini, i-Optics, The Hague, The Netherlands), was performed by one technician (SB) before and one month post AK. With the patient in a sitting upright position, horizontal axis was marked with the Robomarker® (Surgilūm,Wilmington, N.C., USA). Eye was fixed using a FINE-THORTON 13Ø fixation ring (CARL TEUFEL, Liptingen, Germany), and one surgeon (JRST) performed paired AK with a disposable slit angled 3.2 ophthalmic knife (MANI, Park Utsunomiya, Tochigi, Japan) on the steepest angles, using LED reflection topography axial map. Treatment with topical 3 mg/ml tobramycin and For each patient group (pseudophakia, LASIK, ingrowth), pre and post AK data included uncorrected VA (UCVA), best corrected VA (BCVA), subjective sphere, subjective astigmatism, Orbs can and LED topographic astigmatism, SimK, and axis (steep meridian). Data was recorded on a spreadsheet (Microsoft Office Excel 97-2013) and reported as mean and standard deviation. Student t-test to assess statistical significance (paired), Pearson correlation, and linear regression analysis were calculated for pre and post AK data. Statistical significance was set at p ≤ 0.05 with Bonferroni adjustment to correct for type II errors. Bonferroni adjustment for multiple pair comparisons error was calculated at ά=0.03 for statistical significance in pseudophakic group, ά=0.005 for LASIK group, and ά=0.01 for ingrowth group. Table 1 summarizes patient´s characteristics for each study group.   In the pseudophakic group, mean pre AK subjective axis (87 ± 54º) compared to topography values, LED (93 ± 49°; R 2 =0.3) and Orbscan (100 ± 50º; R 2 =0.2).

Results
Mean post AK axis values for Orbscan was 75.3 ± 49.8º (p ≤ 0.05) and 75.1 ± 38° for LED topography. Pre and post results were p<0.03 for Orbscan axis and p>0.03 for LED axis.
Linear regression analysis for topographic cylinder and SimK values ares depicted on Figure 8 (pseudophakic) and Figure 9 (LASIK and ingrowth eyes).

Pseudophakic
•Results   Reports have concluded that the LED topographer provides highly repeatable corneal power and astigmatism measurements, while values are comparable to other commonly used devices [1][2][3][4][5]. It provides higher keratometry values than Placido and Scheimpflug based devices and axis value agrees well with the latter [4]. Recently, additional clinical applications for the Cassini LED topographer have been reported for keratoconus, corneal scars, toric IOL calculations and in pseudophakia [1,[3][4][5][6][7]. For the latter, LED topography seems to be a better technique for astigmatism assessment, compared to Placido or multiple measuring points based topography, and correlates with subjective astigmatism [4].   Post AK mean UCVA increased in all groups, significantly for the pseudophakic (p ≤ 0.001) and LASIK (p ≤ 0.03) groups; Ingrowth eyes (p ≥ 0.01).

•Number
As expected, for pseudophakic patients undergoing LED topography guided AK for residual astigmatism, we recorded significant decrease in subjective astigmatism and sphere values [8][9]. Mean UCVA also significantly improved for all groups, with this technique, however, unlike reports from Akura et al., BCVA improvement was not significant [9]. Post AK sphere also decreased for all groups, significantly solely for pseudophakic eyes [11]. LED and Orbscan topography cylinder values also significantly decreased, however SimK values decreased non-significantly.
Our results differ from those reported by Ferreira, regarding poor subjective astigmatism correlation with LED and Orbscan topography values. They recruited patients with at least 3 months after surgery, while our patients had at least 2 weeks and many had postoperative dry eye syndrome that could explain these results. Significant more variability in keratometry and astigmatism measurements have been reported in dry eye syndrome [12,13]. In addition, most patients had multifocal IOL implantation, which usually requires earlier emmetropia for improving visual satisfaction. We also used the earlier software, which required a learning curve for our technician and patients while Ferreira et al. had 2 technicians.