|Year : 2020 | Volume
| Issue : 2 | Page : 630-635
Higher order aberration after wavefront-guided laser in-situ keratomileusis vs wavefront-guided photorefractive keratectomy
Hany A Khairy1, Mohammed S Abd-Alaziz1, Marwa M Ahmed Meliha2
1 Department of Ophthalmology, Faculty of Medicine, Menoufia University, Menoufia, Egypt
2 Department of Ophthalmology, Tanta Ophthalmology Hospital, Tanta, Egypt
|Date of Submission||24-Nov-2019|
|Date of Decision||22-Dec-2019|
|Date of Acceptance||31-Dec-2019|
|Date of Web Publication||27-Jun-2020|
Marwa M Ahmed Meliha
Source of Support: None, Conflict of Interest: None
The aim was to assess visual outcome and higher order aberrations between wavefront-guided laser in-situ keratomileusis (LASIK) and wavefront-guided photorefractive keratectomy (PRK).
LASIK is the most popular and commonly performed procedure in the field of corneal refractive surgery. Laser refractive surgery works on the principle of modification of corneal refractive power by means of photoablation of the stromal tissue.
Patients and methods
A total of 30 patients (60 eyes) with errors of refraction and higher order aberration underwent wavefront-guided LASIK and wavefront-guided PRK. Follow-up was performed on the first day, fifth day, first week, first month, third month, and 6 months postoperatively, and wavefront ocular analysis was performed at the first month, third months, and 6 months postoperatively.
This study included 60 eyes of 30 patients. The patients were divided into two groups: A and B. Wavefront-customized LASIK was performed on patients in group A, whereas patients in group B received wavefront-customized PRK. The age of the participants in group A ranged from 18 to 35 years. On the contrary, group B patients' age ranged from 19 to 36 years. Total higher order aberration root mean square in LASIK showed nonsignificant increase from 0.37 ± 0.15 (P = 0.922) preoperatively to 0.57 ± 0.17 (P = 0.764) postoperatively. It also showed nonsignificant increase in PRK from 0.38 ± 0.15 preoperatively to 0.59 ± 0.18 postoperatively.
The study showed significant improvement in visual acuity and refractive result, with increase of total higher order aberration root mean square.
Keywords: higher order aberrations, laser in-situ keratomileusis, photorefractive keratectomy, wavefront-guided laser in-situ keratomileusis, wavefront-guided photorefractive keratectomy
|How to cite this article:|
Khairy HA, Abd-Alaziz MS, Ahmed Meliha MM. Higher order aberration after wavefront-guided laser in-situ keratomileusis vs wavefront-guided photorefractive keratectomy. Menoufia Med J 2020;33:630-5
|How to cite this URL:|
Khairy HA, Abd-Alaziz MS, Ahmed Meliha MM. Higher order aberration after wavefront-guided laser in-situ keratomileusis vs wavefront-guided photorefractive keratectomy. Menoufia Med J [serial online] 2020 [cited 2020 Jul 13];33:630-5. Available from: http://www.mmj.eg.net/text.asp?2020/33/2/630/287787
| Introduction|| |
Two of the most common methods of refractive surgery are photorefractive keratectomy (PRK) and laser in-situ keratomileusis (LASIK). The rapid improvement in vision and lack of postoperative pain associated with LASIK has made this procedure the preferred option for patients compared with PRK, which has greater postoperative discomfort and longer recovery time of visual acuity. Laser refractive surgery works on the principle of modification of corneal refractive power by means of photoablation of the stromal tissue. Earlier surgical procedures like radial keratotomy, arcuate keratotomy, and PRK proved to be successful in quantitative improvement of refractive error; however, it was noticed that they degrade the quality of vision by reducing night vision clarity and increasing glare and halos.
Studies have shown that higher order aberrations (HOAs) are responsible for these postoperative visual complaints,. The introduction of wavefront technology has brought revolution in the field of corneal refractive surgery because of predictability and increased accuracy. The reliable results of wavefront-guided refractive surgical procedures has not only resulted in increasing the number of patients being benefitted but also the expansion of surgical indications,,.
HOAs (spherical aberrations, coma, and trefoil) are small optical irregularities of the ocular refractive media. Unlike low order aberrations (myopia, hypermetropia, and simple astigmatism), they cannot be corrected with spectacles or contact lenses. They are commonly described in terms of Zernike polynomials and measured by aberrometer, which measures the root mean square (RMS) value in micrometers,.
Zernike polynomials are divided into several orders, low-order aberrations ( first and second order) and high-order aberrations (third order onwards),. Studies have shown that wavefront-optimized LASIK though corrects the refractive error, it increases the HOAs,. The rationale of conducting this study is to analyze the induced change in HOAs by wavefront-optimized LASIK in myopic patients, as there has been no study of this kind conducted in our population.
| Patients and Methods|| |
This prospective comparative interventional study was carried out on 60 eyes (30 patients) at Refractive Surgery Department from October 2018 to May 2019. Approval by the Ethical Committee Menoufia University was obtained before initiating this study. Written informed consents were taken from all patients. Patients were divided into two groups (A and B). Each group has thirty eyes each. Wavefront-customized LASIK was performed on patients in group A, whereas patients in group B received wavefront-customized PRK treatment by Dr Mohammed Samy Abd-Alaziz, Lecturer of Ophthalmology, Menoufia University.
We included patient with errors of refraction with high-order aberrations, age of patients between 18 and 38 years, best-corrected visual acuity of 6/6, stable refraction for 1 year, stop soft contact lens for minimum 14 days before operation, and preoperative central corneal thickness of at least 500 μm in LASIK and in PRK, and estimated residual stromal bed thickness of at least 300 μm in patients undergoing wavefront-guided PRK.
Patients were subjected to history taking and complete ophthalmic examination: visual acuity by Snellen chart and decimal best-corrected visual acuity, anterior segment examination with slit-lamp biomicroscopy using direct diffuse illumination and transillumination techniques, measurement of intraocular pressure by applanation tonometry, fundus examination, corneal topography by pentacam and wavefront ocular analysis using VISX star S4 (AMO Manufacturing USA, LLC, 510 Cottonwood Dr, Milpitas, California, USA), which measures HOAs using technique based on the Schering principle. The wavelight analyzer sends a grid or spot pattern of light rays (10 × 10 mm) on the cornea that focus in front of the retina, forming a pattern. This pattern is captured by indirect ophthalmoscopy, and each spot position of the retinal image is compared with its ideal spot position. Any deviations or aberrations from the ideal spot position are then analyzed to determine the wavefront error present in the optical system. These data are then combined with the input of measured keratometry value and clinical refraction. A wavefront-guided ablation profile is calculated and displayed. Wavefront testing done at the time of surgery allows the surgeon to modify the target refraction and adjust the size of the optical zone and transition zone on the spot. Wavefront evaluation using VISX star S4 is approved for patients with myopia up to −11 D (maximum ware – front refraction sphere –11.75 D) with or without astigmatism up to 3.00 D (maximum WR cylinder 3.75 D). Mixed astigmatism from 1.00 to 5.00 D of cylinder can now be treated with CustomVue. Wavefront-guided LASIK is approved for patients with hyperopia and uses a 6.0 mm optical zone and an 8.0 mm treatment zone for the reduction or elimination of hyperopia and hyperopic astigmatism up to +3.00 D sphere (maximum WRSE +3.75 D) with cylinder 2.00 D (maximum WR cylinder +2.75 D) up to a maximum MR SE of +3.00 (maximum WRSE +3.75 D).
Regarding preoperative instructions and medications, all patients were instructed to use moxifloxacin 0.5% eye drops every 4 h starting 1 day before surgery, all patients were instructed to stop using contact lenses (if they are using) at least 2 weeks before surgery, and all patients were asked to sign an informed consent including general information, advantages, and disadvantages of laser refractive surgeries.
Regarding surgical technique, in LASIK, preparation of the field was done, followed by topical anesthesia with benoxinate hydrochloride 0.4% eye drops (Benox; Egyptian Int. Pharmaceutical Industries, El Obour city, Cairo, Egypt) and insertion of eye speculum. Microkeratome flap creation was done using the Moria M2 mechanical microkeratome (Moria Inc., Antony, France), and lifting of the flap and laser treatment was done. Irrigation of the stromal bed was done using balanced salt solution, followed by flap reposition and tobramycin 0.3% and dexamethasone 0.1% combination eye drops (Tobradex; Alcon, Fort Worth city, Texas state, USA).
In PRK, preparation of the field was done, followed by topical anesthesia with benoxinate hydrochloride 0.4% eye drops and insertion of eye speculum. Marking of the area was done, from which the corneal epithelium was be removed according to the ablation area. Epithelium removal was done manually by hockey knife, followed by wavefront optimized laser treatment, contact lens insertion, and tobramycin 0.3% and dexamethasone 0.1% combination eye drops.
Regarding postoperative medications, all patients were given the following medications: moxifloxacin 0.5% eye drops QID for 7 days, tobramycin 0.3% and Dexamethasone 0.1% combination eye drops QID for 3 weeks, hyaluronic acid 0.2%, preservative-free eye drops every 2 h during the day for at least three months, and vitamin C 1 g tablets once per day for1 week (PRK patients). Follow-up clinical examination visits were on the first day, fifth day, and first week postoperatively, then follow-up investigational visits were done at 1 month, 3 months, and 6 months postoperatively.
Data were collected, revised, coded, and entered into the statistical package for social science (IBM SPSS; SPSS Inc., Chicago, Illinois, USA), version 20 (IBM Corporation, Somers, New York, USA) software. Paired t-test was used to detect the difference between preoperative and postoperative data in the study group. Significance was considered at P less than 0.05.
Student t-test as used to test the probability, where P greater than 0.05 = statistically insignificant, P less than 0.05 = statistically significant, and P less than 0.01 = highly significant.
| Results|| |
This study included 60 eyes of 30 patients who came for refractive surgery consultation at the refractive surgery department. Patients were divided into two groups: A and B. Wavefront-customized LASIK was performed on patients in group A, whereas patients in group B received wavefront-customized PRK treatment. The age of the participants in A group ranged from 18 to 35 years (mean: 25.47 ± 5.95 years). No statistically significant differences were recorded between both groups ([Table 1] and [Table 2]).
In our study, decimal best-corrected visual acuity (BCVA) was 0.83 ± 0.16 in LASIK preoperatively, and it was 0.9 ± 0.1 in PRK preoperatively. Postoperative decimal BCVA improved in LASIK at 1 month to 0.83 ± 0.16, to 0.89 ± 0.13 at 3 months, and to 0.89 + 0.13 at 6 months. However, in PRK, decimal BCVA improved at 1 month to 0.74 ± 0.12, at 3 months to 0.81 ± 0.10, and to 0.94 ± 0.06 at 6 months [Table 3].
|Table 3: Preoperative and postoperative logMAR best-corrected visual acuity|
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In our study, the cylinder value was significantly improved from − 1.84 ± 1.00 and − 2.55 ± 1.09 preoperatively (P = 0.074) to –0.33 ± 0.29 and 0.39 ± 0.29 postoperatively (P = 0.488) in LASIK and in PRK, respectively [Table 4].
The sphere value significantly improved from − 1.69 ± 1.54 and − 1.11 ± 1.95 preoperatively (P = 0.375) to 0.23 ± 0.15 and 0.15 ± 0.30 postoperatively(P = 0.364) in LASIK and PRK, respectively [Table 5],[Table 6],[Table 7],[Table 8].
|Table 6: Comparison of preoperative and postoperative root mean square between the studied groups|
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|Table 7: Correlation between CCT, K reading and variables in laser in-situ keratomileusis|
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|Table 8: Correlation between CCT, K reading, and variables in photorefractive keratectomy|
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In our study, there was significant increase in total HOARMS from 0.37 ± 0.15 and 0.38 ± 0.15 preoperatively (P = 0.922) to 0.57 ± 0.17 and 0.59 ± 0.18 postoperatively(P = 0.764) in LASIK and PRK, respectively [Figure 1] and [Figure 2]).
|Figure 1: Preoperative and postoperative decimal best-corrected visual acuity.|
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| Discussion|| |
Refractive surgery is one of the most commonly performed elective procedures and will likely maintain its popularity as ablation techniques become more refined and our understanding of corneal wound healing improves. Two of the most common methods of refractive surgery are PRK and LASIK. The rapid improvement in vision and lack of postoperative pain associated with LASIK has made this procedure the preferred option for patients, compared with PRK, which has greater postoperative discomfort and longer recovery time of visual acuity.
Wavefront technology is the mainstay of refractive laser surgery, and it is supposed to improve the quality of vision. Wavefront or 'customized' LASIK is a variation on conventional treatment where the excimer laser ablates a pattern based on measurement from aberrometer reading. This treats aberrations other than sphere and cylinder, known as HOAs.
In this series, we studied the custom LASIK and PRK visual and refractive outcome in 60 eyes of 30 patients with refractive errors. In our study, the decimal BSCVA improved in Lasik significantly from 0.83 ± 0.16 preoperative to 0.83 ± 0.13 at 1 months, to 0.89 ± 0.13 at 3 months, and to 0.89 ± 0.13 at 6 months. In PRK, the decimal BSCVA deteriorated from 0.90 ± 0.10 preoperatively to 0.74 ± 0.12 at 1 month, slightly improved at 3 months to 0.81 ± 0.10, and improved to 0.94 ± 0.06 at 6 months.
Bissen-Miyajima et al. reported that uncorrected visual acuity (UCVA) was 6/6 in 58 (85.3%) eyes and 6/9 in 68 (100%) eyes.
In 2011, Keir et al. reported UCVA at 6 months was 20/20 in 54 (87.1%) eyes and was 20/40 in 60 (96.8%) eyes. Chen et al. showed that 3-month UCVA was 20/20 in 13 (66.7%) eyes and was 20/25 in 17 (88.9%) eyes. In 2010, Moshirfar et al. reported, UCVA was 20/20 in 40 (91%) eyes and 20/15 in 26 (59%) eyes. In a study done by O'BRART, 100% in the wavefront-optimized group achieved a UCVA of 1 ± 00 at 3 months. Dijk found that after wavefront-optimized treatment, 67% of eyes had a corrected distance visual acuity of 1.25 and 93% of eyes had a corrected distance visual acuity of 1 ± 00.
In our study, the cylinder value showed significant improvement. It significantly improved from −1.84 ± 1.00 and −1.55 ± 1.09 (P = 0.074) preoperatively to −0.33 ± 0.29 and −0.39 ± 0.29 (P = 0.488) postoperatively in LASIK and PRK, respectively. The sphere value significantly improved from −1.69 ± 1.54 and −1.11 ± 1.95 (P = 0.375) preoperatively to 0.23 ± 0.15 and 0.15 ± 0.30 postoperatively in LASIK and PRK, respectively.
Bissen-Miyajima et al. reported in a prospective contralateral eye study to compare conventional and wavefront-guided LASIK that MRSE was within +0.52 D of emmetropia in 62 (91.2%) eyes and within +0.75 D in 68 (100%) eyes. Koch showed that MRSE was within +0.50 D of emmetropia in 50 (93%) eyes. Keir et al. reported that MRSE was within +1.00 D in 60 (96.8%) eyes and +0.50 D in 44 (71%) eyes. Chen et al. reported within 3 months the MRSE was within +1.00 D of emmetropia in 17 (88.9%) eyes. Piccinini et al. reported that in LASIK group at 6 months the MRSE was within +0.50 D in 67 (97%) eyes and +1.00 D in 68 (100%) eyes. Roe et al. found that at 3 months postoperatively, 74.1% of eyes in the mechanical microkeratome group were within 0.5 D of emmetropia compared with 64.3% of eyes in the intralase group. Abd Allah et al. found a steepening in the hinge meridian when LASIK flaps were created by microkeratome.
Excimer laser wavefront-guided ablation was developed and introduced in clinical practice with the aim of individualizing the outcomes obtained with keratorefractive procedure. Several studies have shown that this type of procedure is effective in correcting the spherocylindrical error and minimizing HOA in eyes without previous surgeries,.
The study of higher order aberrations in our study showed a significant increase in total HOARMS. In LASIK, it showed a significant increase from 37 ± 0.15 (P = 0.922) to 0.57 ± 0.17 (P = 0.764) postoperatively. However, in PRK, it showed significant increase from 0.38 ± 0.15 preoperatively to 0.59 ± 0.18 postoperatively. Coma aberration showed significant increase in LASIK from 0.22 ± 0.13 (P = 0.967) preoperatively to 0.29 ± 0.14 (P = 0.752) postoperatively, and in PRK, coma showed significant increase preoperatively from 0.22 ± 0.10 to 0.31 ± 0.10 postoperatively. Spherical aberrations showed significant increase in LASIK from 0.08 ± 0.07 preoperatively to 0.24 ± 0.23 postoperatively, whereas in PRK, spherical aberration showed significant increase preoperatively from 0.9 ± 0.21 preoperatively to 0.22 ± 0.18 postoperative. Trefoil aberration showed significant increase in LASIK from 0.19 ± 0.09 preoperatively to 0.24 ± 0.13 postoperatively, and in PRK, trefoil showed significant increase from 1.19 ± 0.10 preoperatively to 0.28 ± 0.08 postoperatively.
Few studies have compared wavefront-guided LASIK and wavefront-guided PRK. Our results were in contrast to a previous study by Moshirfar et al., who showed that wavefront-guided PRK induced fewer HOAs than wavefront-guided LASIK in a bilateral prospective randomized clinical trial. Aǧca et al. also showed a lower mean HOA in PRK eyes compared with LASIK eyes.
The difference observed between our study and the aforementioned studies can be explained by the follow-up period, which was larger in our study (6 months) than their studies (3 months). Hosseini et al. showed that wavefront-guided Lasik was superior to wavefront-guided PRK with respect to the increase in total HOAs at postoperative month 1. At 3 months postoperatively, however, this different was not statistically significant. In a prospective comparative, contralateral study, Hosseini et al. did not find a significant difference between PRK and thin flap LASIK in terms of the increase in HOA.
The absence of postoperative pain and rapid visual recovery are the advantages for LASIK. PRK dominates complications related to the corneal flap and reduces the risk of iatrogenic ectasia. The results of the present study and other studies indicate that PRK and LASIK are comparable in visual outcomes and alterations in HOAs.
| Conclusion|| |
Our study showed significant improvement in visual acuity and refractive result with increase of total HOARMS.
The data sets used and analyzed during the current study are available from the corresponding author on reasonable request.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8]