Acta Ophthalmologica 2015
Epidemiology and outcomes in refractive lens exchange surgery Oscar Westin, Timo Koskela and Anders Behndig Department of Clinical Sciences/Ophthalmology, Ume a University Hospital, Ume a, Sweden
ABSTRACT. Purpose: To assess demographics and refractive outcomes in patients undergoing refractive lens exchange surgery (RLE), with a population of cataract patients as a reference. Methods: A RLE cohort from a private eye clinic (n = 675) and a cataract cohort from the outcome registration of the Swedish National Cataract Register were studied and compared from an epidemiological perspective regarding age, gender, preoperative refraction and postoperative refractive outcome. Results: The RLE patients were younger (52.1 7.7 versus 73.84 9.32 years) with a smaller percentage of women (45.28% versus 60.46%; p < 0.001) and were more often myopic than the cataract patients. Astigmatism and hyperopia did not differ between the cohorts. Uncorrected visual acuity after RLE equalled the best corrected visual acuity in best cases after cataract surgery. The absolute biometry prediction was more accurate in RLE (0.17 0.27 D versus 0.40 0.58 D; p < 0.001), particularly in patients given a customized toric IOL (0.12 0.27 D; p < 0.05). In cataracts, the Haigis’ formula showed higher accuracy than the SRK/T formula (0.39 0.53 D versus 0.43 0.61 D; p < 0.01). Postoperatively after RLE, Laser Epithelial Keratomileusis was performed in 9.04% and Yttrium Aluminium Garnet capsulotomy in 7.41% of the eyes. Other reoperations were performed in three cases, and five postoperative retinal detachments occurred after RLE. Conclusion: Compared with patients undergoing cataract surgery, we see many similarities, but also many interesting differences in patients undergoing RLE. Basic information about the growing population choosing to undergo RLE can help us plan future ophthalmic care. Key words: cataract – complications – refractive lens exchange – refractive outcome – results
Acta Ophthalmol. 2015: 93: 41–45 ª 2014 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd
doi: 10.1111/aos.12460
Introduction With a total of 105 479 procedures performed in 2012 (C. Zetterstrom, et al. (2013), personal communication), lens exchange surgery is the most frequent surgical procedure in Sweden, as in many developed countries worldwide (Haigis 2012). Today, a growing part of the population in developed countries
with refractive errors and/or presbyopia chooses to undergo refractive lens exchange (RLE), a privately financed procedure that can be employed also where other refractive surgical treatments (e.g. excimer laser procedures or phakic intra-ocular lens implantation) are not suitable or not sufficient (Hoffman et al. 2004; Fong 2007; Kohnen et al. 2008). RLE is becoming an
increasingly popular procedure, and with 10 585 procedures performed in Sweden in 2012 according to a survey from the Swedish National Cataract Register (NCR), (C. Zetterstrom, et al. (2013), personal communication) it accounts for 10.0% of all lens exchange procedures in Sweden today. Monofocal and non-toric intra-ocular lenses (IOLs) are still vastly dominant in Swedish routine cataract surgery (Behndig et al. 2011). With 43.0% of Swedish cataract patients achieving emmetropia without significant residual astigmatism, and an additional 8% achieving a reading myopia, a substantial part of the patients undergoing cataract surgery in Sweden will still need spectacle correction for far and near vision (Behndig et al. 2011). In RLE, a multifocal IOL has become a standard option today, and different types of monovision solutions are rarely used (Barisic et al. 2010). The refractive results achieved with RLE are likely to be more stable than those achieved through other refractive surgery techniques, as RLE removes the crystalline lens, the structure within the eye that changes the most with age (Hoffman et al. 2004). Obviously, RLE eliminates the eventual need for future cataract surgery, but the procedure can also potentially lead to various complications that need to be taken care of by the public ophthalmic health care, such as posterior capsule opacification (PCO), retinal detachment (RD) and late dislocations of IOLs. RLE is becoming increasingly popular and the aim of this study was to compare patients choosing to undergo RLE with those currently undergoing cataract
41
Acta Ophthalmologica 2015
surgery and to roughly estimate possible effects on future cataract surgery and other types of ophthalmic care. In addition, basic data on refractive outcomes in the two procedures were compared.
Materials and Methods Patients
This study comprised two cohorts of patients; one cohort underwent RLE and the other underwent cataract surgery. Preoperative patient data in the RLE cohort were collected prospectively and postoperative results were retrieved retrospectively from patient journals at Koskelas Eye Clinic in Lule a, Sweden from September 2011, when the clinic opened, until July 2013. Data from all consecutive patients were included in the analyses. Inclusion criteria were all patients attending the clinic and where RLE was deemed a suitable procedure during the time period 2011–2013. All operations were bilateral and simultaneous and were performed by a single surgeon (AB), and a single doctor (TK) did all postoperative controls. Temporal 2.2-mm clear corneal incisions were used in all RLE cases. Limbal relaxing incisions for astigmatism reduction were not used. Patient data in the cataract cohort were collected from the Swedish National Cataract Register (NCR). NCR registers all cataract surgeries performed in Sweden (Behndig et al. 2011). During the month of March each year, both public and private eye clinics are asked by the NCR to report the outcomes of performed cataract surgeries. This outcome registry is estimated to cover about 10% of the total cataract surgeries performed in Sweden annually (Behndig et al. 2011) (94 894 procedures for 2012). Patient data in the cataract cohort of this study were collected from NCR’s outcome registry of March 2013. Data from all patients were included in the analyses; for some analyses, cases without ocular comorbidity – ‘best cases’ – were used. The study was approved by Regional Ethical Review Boards of Ume a University, Ume a, Sweden. The NCR data collection was approved by the ethical committee in the South region of Sweden according to the Declaration of Helsinki and was also approved by the Swedish Data Inspection Board.
42
Registered variables
The registered variables for the RLE cohort were: age, gender, date for preoperative examination, preoperative subjective refraction and visual acuity; uncorrected (UDVA) and corrected distance visual acuity (CDVA), preoperative refractive and corneal astigmatism, axial length, IOL power calculation formula, planned refraction, date for surgery, date for final postoperative examination, postoperative refraction and visual acuity (UDVA and CDVA). History of any previous refractive interventions as well as eventual additional postoperative interventions: Yttrium Aluminium Garnet (YAG) laser capsulotomy or Laser Epithelial Keratomileusis (LASEK) was noted. Finally, complications such as RD and IOL dislocation were noted. All RLE patients received the Lentis LU-313 MF aspheric, plate-haptic, nonrotational symmetric multifocal IOL or the corresponding MFT toric multifocal IOL (Oculentis GmbH, Berlin, Germany). The limit for choosing the toric IOL was consequently set to ≥0.75 D of corneal astigmatism. The registered variables for the NCR cohort were: age, gender, preoperative visual acuity, axial length, IOL power calculation formula, postoperative refraction and visual acuity, and ocular comorbidities. To assess the preoperative refraction, which is not a registered variable in the NCR, the refraction of the unoperated fellow eye in first eye surgeries was used as previously detailed (Behndig et al. 2012). Preoperative refraction measurements in RLE patients were made by autorefractometer-assisted subjective refraction. Postoperatively, this type of multifocal IOL renders unreliable autorefractometer values, and the postoperative refractive status was therefore obtained by standard subjective refraction. The methods of refraction in the cataract cohort may have varied between clinics, but autorefractometerassisted subjective refraction is a common approach.
Calculations
Absolute biometry prediction error was calculated as the absolute value of the postoperative spherical equivalent (SE) minus the planned SE. Statistical calculations were performed the SPSS
statistics v. 20.0 (IBM North America, New York, NY, USA) or MICROSOFT EXCEL v. 14.1.4 (Microsoft Inc., New York, NY, USA). Statistical analyses
For statistical analyses, groups were compared using the Student paired and unpaired t-test, as appropriate. For nominal data, e.g. gender, chi-squared test was used. A p < 0.05 was considered statistically significant.
Results The patient numbers, ages, gender, follow-up time, pre- and postoperative refraction and visual acuity together with other registered variables and the missing data, are presented in Table 1. Of 974 putative RLE patients examined at the clinic, 675 underwent the procedure. The patients who chose not to undergo surgery were younger (50.9 7.9 versus 52.6 7.5; p = 0.002), but did not differ regarding gender, IOL power, refractive status, etc. The AbsBPE was significantly smaller in the RLE group, 0.17 0.27 D compared with 0.40 0.58 D in the NCR group, p < 0.001. Eyes implanted with toric IOLs (n = 538; 39.9%) had significantly smaller AbsBPE than when a spheric IOL was used (n = 806; 59.7%), 0.12 0.27 D versus 0.21 0.26 D; p < 0.001. This difference was still significant, albeit smaller, if a planned postoperative refraction of 0.0 D was assumed for the spheric IOL group (0.15 0.32 D, p = 0.049). Accordingly, eyes implanted with spheric IOLs were more often subject to postoperative LASEK enhancement treatment (p < 0.001, chi-squared test). The total frequency of postoperative LASEK was 9.04% (Table 1). In eyes subjected to postoperative LASEK, the treatment improved the UDVA significantly (from 0.65 0.20 to 0.92 0.14; p < 0.001) and reduced the AbsBPE to 0.14 0.23 D (p < 0.001). While the uncorrected visual acuity improved with LASEK, the CDVA actually worsened slightly after LASEK (0.97 0.09 versus 0.98 0.08; p < 0.001). Postoperative YAG capsulotomy was performed in 7.41% of the eyes operated (Table 1). Three cases of posterior capsule rupture occurred in the RLE material. One toric IOL rotation
Acta Ophthalmologica 2015
Table 1. Comparison of the cohorts. Variable
RLE
Cataract
Number of eyes operated 1350 6712 Number of patients operated 675 – Total number of patients 974 – Age 52.1 7.7* 73.8 9.3 Gender Male, total 533 (54.7%) – Male, operated 384 (56.9%)* 2652 (39.5%) Female, total 441 (45.3%) – Female, operated 291 (43.1%)* 4059 (60.46%) Visual acuity Uncorrected preoperative 0.32 0.30 – Spectacle corrected preoperative 1.0 0.03* 0.44 0.21 Uncorrected postoperative Total 0.91 0.16 – Toric IOL 0.91 0.18 – Spheric IOL 0.92 0.16 – Spectacle corrected postoperative 0.98 0.08* 0.84 0.22 Uncorrected postoperative, post-LASEK 0.92† – – Spectacle corrected postoperative, 0.97 0.09† post-LASEK Best case spectacle corrected – 0.91 0.15 postoperative Preoperative refraction Emmetropia, % 15.6%* 43.5% Hyperopia, % 36.9% 38.3% Myopia, % 47.6%* 18.2% Astigmatism, % 38.7%* 30.3% Preoperative K-values, D K1 42.98 1.56* 43.42 1.68 43.85 1.60* 44.37 1.77 K2 Kmean 43.41 1.64* 43.90 1.79 Preoperative corneal astigmatism, D 0.73 0.80 0.71 0.78 Absolute biometry prediction error (BPE), D Total 0.17 0.27* 0.40 0.58 Toric IOL 0.12 0.27† – Spheric IOL 0.21 0.26† – BPE post-LASEK 0.14 0.23† – Haigis’ formula – 0.39 0.53 (n = 2951)† SRK/T – 0.43 0.61 (n = 3241)† Best case & Haigis’ formula – 0.35 0.48† Time to follow up 153 148 days, 40 31 days, range 3–713 days range 0–219 days History of previous corneal excimer 13 Data not available laser treatment Ocular comorbidities, % of all patients Total 2.46%* 32.7% Glaucoma 0* 7.87% Macular degeneration 0* 16.51% Diabetes retinopathy 0* 3.77% Other 2.46%* 6.91% Postoperative treatment: eyes and patients, respectively YAG 80 (5.9%); 50 (7.4%) – LASEK 122 (9.0%); 78 (11.6%) – The table compares a cohort of bilateral refractive lens exchange (RLE) procedures to a cohort of cataract procedures. Visual acuity after RLE is presented for eyes operated with a Lentis LU-313 MF spheric multifocal IOL and the corresponding MFT toric multifocal IOL separately. Hyperopia is defined as a spherical equivalent exceeding +0.5 D; myopia as a spherical equivalent below 0.5 D. Astigmatism is defined as a corneal astigmatism of >0.75 D. Best cases are cataract patients without ocular comorbidities. K1 is the flattest keratometry reading, K2 the steepest and Kmean the mean of the two. The absolute biometry prediction error was calculated as the absolute value of the postoperative spherical equivalent minus the preoperative spherical equivalent. IOL, intra-ocular lenses; LASEK, Laser Epithelial Keratomileusis; YAG, Yttrium Aluminium Garnet * Signifies a p-value of
Epidemiology and outcomes in refractive lens exchange surgery Oscar Westin, Timo Koskela and Anders Behndig Department of Clinical Sciences/Ophthalmology, Ume a University Hospital, Ume a, Sweden
ABSTRACT. Purpose: To assess demographics and refractive outcomes in patients undergoing refractive lens exchange surgery (RLE), with a population of cataract patients as a reference. Methods: A RLE cohort from a private eye clinic (n = 675) and a cataract cohort from the outcome registration of the Swedish National Cataract Register were studied and compared from an epidemiological perspective regarding age, gender, preoperative refraction and postoperative refractive outcome. Results: The RLE patients were younger (52.1 7.7 versus 73.84 9.32 years) with a smaller percentage of women (45.28% versus 60.46%; p < 0.001) and were more often myopic than the cataract patients. Astigmatism and hyperopia did not differ between the cohorts. Uncorrected visual acuity after RLE equalled the best corrected visual acuity in best cases after cataract surgery. The absolute biometry prediction was more accurate in RLE (0.17 0.27 D versus 0.40 0.58 D; p < 0.001), particularly in patients given a customized toric IOL (0.12 0.27 D; p < 0.05). In cataracts, the Haigis’ formula showed higher accuracy than the SRK/T formula (0.39 0.53 D versus 0.43 0.61 D; p < 0.01). Postoperatively after RLE, Laser Epithelial Keratomileusis was performed in 9.04% and Yttrium Aluminium Garnet capsulotomy in 7.41% of the eyes. Other reoperations were performed in three cases, and five postoperative retinal detachments occurred after RLE. Conclusion: Compared with patients undergoing cataract surgery, we see many similarities, but also many interesting differences in patients undergoing RLE. Basic information about the growing population choosing to undergo RLE can help us plan future ophthalmic care. Key words: cataract – complications – refractive lens exchange – refractive outcome – results
Acta Ophthalmol. 2015: 93: 41–45 ª 2014 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd
doi: 10.1111/aos.12460
Introduction With a total of 105 479 procedures performed in 2012 (C. Zetterstrom, et al. (2013), personal communication), lens exchange surgery is the most frequent surgical procedure in Sweden, as in many developed countries worldwide (Haigis 2012). Today, a growing part of the population in developed countries
with refractive errors and/or presbyopia chooses to undergo refractive lens exchange (RLE), a privately financed procedure that can be employed also where other refractive surgical treatments (e.g. excimer laser procedures or phakic intra-ocular lens implantation) are not suitable or not sufficient (Hoffman et al. 2004; Fong 2007; Kohnen et al. 2008). RLE is becoming an
increasingly popular procedure, and with 10 585 procedures performed in Sweden in 2012 according to a survey from the Swedish National Cataract Register (NCR), (C. Zetterstrom, et al. (2013), personal communication) it accounts for 10.0% of all lens exchange procedures in Sweden today. Monofocal and non-toric intra-ocular lenses (IOLs) are still vastly dominant in Swedish routine cataract surgery (Behndig et al. 2011). With 43.0% of Swedish cataract patients achieving emmetropia without significant residual astigmatism, and an additional 8% achieving a reading myopia, a substantial part of the patients undergoing cataract surgery in Sweden will still need spectacle correction for far and near vision (Behndig et al. 2011). In RLE, a multifocal IOL has become a standard option today, and different types of monovision solutions are rarely used (Barisic et al. 2010). The refractive results achieved with RLE are likely to be more stable than those achieved through other refractive surgery techniques, as RLE removes the crystalline lens, the structure within the eye that changes the most with age (Hoffman et al. 2004). Obviously, RLE eliminates the eventual need for future cataract surgery, but the procedure can also potentially lead to various complications that need to be taken care of by the public ophthalmic health care, such as posterior capsule opacification (PCO), retinal detachment (RD) and late dislocations of IOLs. RLE is becoming increasingly popular and the aim of this study was to compare patients choosing to undergo RLE with those currently undergoing cataract
41
Acta Ophthalmologica 2015
surgery and to roughly estimate possible effects on future cataract surgery and other types of ophthalmic care. In addition, basic data on refractive outcomes in the two procedures were compared.
Materials and Methods Patients
This study comprised two cohorts of patients; one cohort underwent RLE and the other underwent cataract surgery. Preoperative patient data in the RLE cohort were collected prospectively and postoperative results were retrieved retrospectively from patient journals at Koskelas Eye Clinic in Lule a, Sweden from September 2011, when the clinic opened, until July 2013. Data from all consecutive patients were included in the analyses. Inclusion criteria were all patients attending the clinic and where RLE was deemed a suitable procedure during the time period 2011–2013. All operations were bilateral and simultaneous and were performed by a single surgeon (AB), and a single doctor (TK) did all postoperative controls. Temporal 2.2-mm clear corneal incisions were used in all RLE cases. Limbal relaxing incisions for astigmatism reduction were not used. Patient data in the cataract cohort were collected from the Swedish National Cataract Register (NCR). NCR registers all cataract surgeries performed in Sweden (Behndig et al. 2011). During the month of March each year, both public and private eye clinics are asked by the NCR to report the outcomes of performed cataract surgeries. This outcome registry is estimated to cover about 10% of the total cataract surgeries performed in Sweden annually (Behndig et al. 2011) (94 894 procedures for 2012). Patient data in the cataract cohort of this study were collected from NCR’s outcome registry of March 2013. Data from all patients were included in the analyses; for some analyses, cases without ocular comorbidity – ‘best cases’ – were used. The study was approved by Regional Ethical Review Boards of Ume a University, Ume a, Sweden. The NCR data collection was approved by the ethical committee in the South region of Sweden according to the Declaration of Helsinki and was also approved by the Swedish Data Inspection Board.
42
Registered variables
The registered variables for the RLE cohort were: age, gender, date for preoperative examination, preoperative subjective refraction and visual acuity; uncorrected (UDVA) and corrected distance visual acuity (CDVA), preoperative refractive and corneal astigmatism, axial length, IOL power calculation formula, planned refraction, date for surgery, date for final postoperative examination, postoperative refraction and visual acuity (UDVA and CDVA). History of any previous refractive interventions as well as eventual additional postoperative interventions: Yttrium Aluminium Garnet (YAG) laser capsulotomy or Laser Epithelial Keratomileusis (LASEK) was noted. Finally, complications such as RD and IOL dislocation were noted. All RLE patients received the Lentis LU-313 MF aspheric, plate-haptic, nonrotational symmetric multifocal IOL or the corresponding MFT toric multifocal IOL (Oculentis GmbH, Berlin, Germany). The limit for choosing the toric IOL was consequently set to ≥0.75 D of corneal astigmatism. The registered variables for the NCR cohort were: age, gender, preoperative visual acuity, axial length, IOL power calculation formula, postoperative refraction and visual acuity, and ocular comorbidities. To assess the preoperative refraction, which is not a registered variable in the NCR, the refraction of the unoperated fellow eye in first eye surgeries was used as previously detailed (Behndig et al. 2012). Preoperative refraction measurements in RLE patients were made by autorefractometer-assisted subjective refraction. Postoperatively, this type of multifocal IOL renders unreliable autorefractometer values, and the postoperative refractive status was therefore obtained by standard subjective refraction. The methods of refraction in the cataract cohort may have varied between clinics, but autorefractometerassisted subjective refraction is a common approach.
Calculations
Absolute biometry prediction error was calculated as the absolute value of the postoperative spherical equivalent (SE) minus the planned SE. Statistical calculations were performed the SPSS
statistics v. 20.0 (IBM North America, New York, NY, USA) or MICROSOFT EXCEL v. 14.1.4 (Microsoft Inc., New York, NY, USA). Statistical analyses
For statistical analyses, groups were compared using the Student paired and unpaired t-test, as appropriate. For nominal data, e.g. gender, chi-squared test was used. A p < 0.05 was considered statistically significant.
Results The patient numbers, ages, gender, follow-up time, pre- and postoperative refraction and visual acuity together with other registered variables and the missing data, are presented in Table 1. Of 974 putative RLE patients examined at the clinic, 675 underwent the procedure. The patients who chose not to undergo surgery were younger (50.9 7.9 versus 52.6 7.5; p = 0.002), but did not differ regarding gender, IOL power, refractive status, etc. The AbsBPE was significantly smaller in the RLE group, 0.17 0.27 D compared with 0.40 0.58 D in the NCR group, p < 0.001. Eyes implanted with toric IOLs (n = 538; 39.9%) had significantly smaller AbsBPE than when a spheric IOL was used (n = 806; 59.7%), 0.12 0.27 D versus 0.21 0.26 D; p < 0.001. This difference was still significant, albeit smaller, if a planned postoperative refraction of 0.0 D was assumed for the spheric IOL group (0.15 0.32 D, p = 0.049). Accordingly, eyes implanted with spheric IOLs were more often subject to postoperative LASEK enhancement treatment (p < 0.001, chi-squared test). The total frequency of postoperative LASEK was 9.04% (Table 1). In eyes subjected to postoperative LASEK, the treatment improved the UDVA significantly (from 0.65 0.20 to 0.92 0.14; p < 0.001) and reduced the AbsBPE to 0.14 0.23 D (p < 0.001). While the uncorrected visual acuity improved with LASEK, the CDVA actually worsened slightly after LASEK (0.97 0.09 versus 0.98 0.08; p < 0.001). Postoperative YAG capsulotomy was performed in 7.41% of the eyes operated (Table 1). Three cases of posterior capsule rupture occurred in the RLE material. One toric IOL rotation
Acta Ophthalmologica 2015
Table 1. Comparison of the cohorts. Variable
RLE
Cataract
Number of eyes operated 1350 6712 Number of patients operated 675 – Total number of patients 974 – Age 52.1 7.7* 73.8 9.3 Gender Male, total 533 (54.7%) – Male, operated 384 (56.9%)* 2652 (39.5%) Female, total 441 (45.3%) – Female, operated 291 (43.1%)* 4059 (60.46%) Visual acuity Uncorrected preoperative 0.32 0.30 – Spectacle corrected preoperative 1.0 0.03* 0.44 0.21 Uncorrected postoperative Total 0.91 0.16 – Toric IOL 0.91 0.18 – Spheric IOL 0.92 0.16 – Spectacle corrected postoperative 0.98 0.08* 0.84 0.22 Uncorrected postoperative, post-LASEK 0.92† – – Spectacle corrected postoperative, 0.97 0.09† post-LASEK Best case spectacle corrected – 0.91 0.15 postoperative Preoperative refraction Emmetropia, % 15.6%* 43.5% Hyperopia, % 36.9% 38.3% Myopia, % 47.6%* 18.2% Astigmatism, % 38.7%* 30.3% Preoperative K-values, D K1 42.98 1.56* 43.42 1.68 43.85 1.60* 44.37 1.77 K2 Kmean 43.41 1.64* 43.90 1.79 Preoperative corneal astigmatism, D 0.73 0.80 0.71 0.78 Absolute biometry prediction error (BPE), D Total 0.17 0.27* 0.40 0.58 Toric IOL 0.12 0.27† – Spheric IOL 0.21 0.26† – BPE post-LASEK 0.14 0.23† – Haigis’ formula – 0.39 0.53 (n = 2951)† SRK/T – 0.43 0.61 (n = 3241)† Best case & Haigis’ formula – 0.35 0.48† Time to follow up 153 148 days, 40 31 days, range 3–713 days range 0–219 days History of previous corneal excimer 13 Data not available laser treatment Ocular comorbidities, % of all patients Total 2.46%* 32.7% Glaucoma 0* 7.87% Macular degeneration 0* 16.51% Diabetes retinopathy 0* 3.77% Other 2.46%* 6.91% Postoperative treatment: eyes and patients, respectively YAG 80 (5.9%); 50 (7.4%) – LASEK 122 (9.0%); 78 (11.6%) – The table compares a cohort of bilateral refractive lens exchange (RLE) procedures to a cohort of cataract procedures. Visual acuity after RLE is presented for eyes operated with a Lentis LU-313 MF spheric multifocal IOL and the corresponding MFT toric multifocal IOL separately. Hyperopia is defined as a spherical equivalent exceeding +0.5 D; myopia as a spherical equivalent below 0.5 D. Astigmatism is defined as a corneal astigmatism of >0.75 D. Best cases are cataract patients without ocular comorbidities. K1 is the flattest keratometry reading, K2 the steepest and Kmean the mean of the two. The absolute biometry prediction error was calculated as the absolute value of the postoperative spherical equivalent minus the preoperative spherical equivalent. IOL, intra-ocular lenses; LASEK, Laser Epithelial Keratomileusis; YAG, Yttrium Aluminium Garnet * Signifies a p-value of
