Radial keratotomy: background and how to manage these patients nowadays.

In this review, we presented the principles of radial keratotomy (RK), its evolution, enhancement, and complications, and strategies to manage the consequences of RK in the present day. It is essential to understand the RK procedure f, the theoretical background that supported this surgery, the current effect on the cornea, and how to approach patients needing vision improvement. These patients are developing cataracts that need to be handled well, from the IOL calculation to the surgical procedure. Guided keratorefractive surgery is the most accurate procedure to improve these patient's vision and life. Nevertheless, some patients may need other approaches, such as sutures, penetrating keratoplasty, corneal rings, and pinhole implants, depending on the degree of irregularity of the cornea, ablation depth for guided surgery or if the sutures are open.

Comparison of endothelial cell loss in diabetic patients after conventional phacoemulsification and femtosecond laser-assisted cataract surgery.

PURPOSE: This study aims to comparatively evaluate the morphological changes of the cornea after phacoemulsification (PHACO) and femtosecond laser-assisted cataract surgery (FLACS) without intercurrences in patients with type 2 diabetes mellitus. METHODS: A total of 95 diabetic patients with moderate cataracts (N2 + and N3+), 47 undergoing PHACO and 48 undergoing FLACS, were selected randomly for the study. Surgeries were performed by a single surgeon between July 2021 and December 2021. Cumulative dissipated energy (CDE) and total balanced saline solution (BSS) data were obtained at the end of each surgery. Changes in corneal endothelial cell density (ECD) and central corneal thickness (CCT) at three months postoperatively were investigated. RESULTS: After three months, evidence is lacking between groups in the CCT measures; the difference was neither statistically nor clinically relevant. However, for ECD, a significant and clinically significant difference was found; if all patients were treated with laser, the mean ECD would be 423.55 greater (RSE: 86.09; p-value < 0.001; 95% CI: 254.81-592.29) than the ECD potential means of 1656.423 among the conventional group (RSE: 74.90; p-value < 0.001; 95% CI: 1509.62-1803.23). CONCLUSIONS: Diabetic patients under treatment with moderate cataracts may predispose themselves to a more significant loss of endothelial cells after conventional phacoemulsification than femtosecond laser-assisted cataract surgery. TRIAL REGISTRATION: It was registered at The Brazilian Registry of Clinical Trials (ReBEC) with the code RBR-6d8whb5 (UTN code: U1111-1277-6020) on 17/05/2022.

New Device for the Correction of Aphakia Without Capsular Support.

PURPOSE: This study describes a prototype developed for aphakia without capsular support (AWCS) and its proof of concept. METHODS: This descriptive study used a 3D software to create and analyze virtual prototypes before manufacturing. A nylon-6/nylon-6.6 copolymer filament and a 3D printer were used for prototyping. A device implantation technique was developed using a 23-gauge hypodermic needle. Two opposing markings, 2 mm posterior to the limbus, were made to determine the location of the scleral punctures and the final position of the device. After adequate centralization and positioning of the device, its haptics were cut and cauterized to generate thermal modeling of the extremity and allow the thickening of the tips (flange), serving as an anchoring mechanism to the sclera. The efficacy and adequacy of the technique and device were then evaluated. RESULTS: Vitreous tissue extrusion was not observed during the sclerotomy. The device was well fixed to the sclera; however, adequate IOL stability and centralization still needed to be achieved. The surgeon evaluated the adequacy of all the other devices' characteristics. CONCLUSIONS: The development of a technology prototype for correcting AWCS was possible. Although the proposed prototype met most of the established concept guidelines, the stability of the IOL position remains challenging.

Ultraviolet-A absorbance analysis in thin porcine corneas pre-and post-crosslinking.

PURPOSE: To determine the absorbance coefficient of the thin porcine cornea to ultraviolet-A radiation (365 nm) submitted for crosslinking. METHODS: This in vitro, benchtop experiment using cadaver tissue study analyzed 12 porcine corneal lamellas, which were obtained using a microkeratome after mechanical de-epithelization and separated into three thickness groups: 180, 300, and 360 µm. The corneal thickness values were measured by anterior-segment optical coherence tomography. All lamellas had ultraviolet-A (365 nm) absorbance measured with a 96-well plate spectrophotometer using an ultraviolet transparent microplate before riboflavin instillation and preand post-crosslinking according to the Dresden protocol. RESULTS: The ultraviolet absorbance profiles of the 180, 300, and 360 µm groups were obtained as α-coefficients of 12.85, 76.55, and 120.27, respectively. A theoretical formula was calculated though a statistical analysis that demonstrated the correlation between stromal lamellar thickness and ultraviolet absorbance. CONCLUSIONS: Corneal thickness and ultraviolet-A spectral absorbance of corneal lamellas showed linear correlation. These findings can potentially contribute to the optimization of ultraviolet-A application during crosslinking, making the treatment of corneas with thickness <400 µm safe and personalized energy delivery for each corneal thickness.

Vision-Related Quality of Life in Patients With Keratoconus With Enantiomorphic Topography After Bilateral Intrastromal Corneal Ring Implantation.

PURPOSE: The aim of this study was to evaluate the quality of life (QOL) after intrastromal ring implantation in patients with keratoconus. METHODS: This was a prospective, randomized, interventional study. We analyzed 60 eyes of 30 patients aged 16 to 35 years who were treated at the Department of Ophthalmology and Visual Sciences, Federal University of São Paulo, Brazil. The Visual Function Questionnaire (VFQ-25) and Short-Form 36 Questionnaire (SF-36) were used before intracorneal ring segment (ICRS) implantation and at 3, 6, and 12 months after surgical intervention. RESULTS: The mean corrected visual acuity improved from a mean of 0.32 ± 0.2 logMAR (20/40) preoperatively to 0.14 ± 0.11 logMAR (20/25) 1 year postoperatively ( P = 0.001). The mean spherical equivalent varied from -7.24 ± 3.47 preoperatively to -4.13 ± 2.41 postoperatively ( P = 0.001). The overall composite score for the VFQ-25 improved from 55.1 preoperatively to 80.4 1 postoperatively ( P = 0.001). SF-36 showed statistically significant improvement in all scores. When analyzing the correlation between visual acuity and VFQ composite score, a significant correlation was found between both variables (Pearson correlation coefficient of -0.40, P = 0.001). CONCLUSIONS: Patients with keratoconus had increased psychological symptoms and lower QOL and improved psychosocial criteria associated with corneal remodeling and decreased visual dependence on others after surgery. Extrapolation of these data to the whole keratoconus population suggests that ICRS implantation could improve QOL in these patients.

Automated Capsular Decompression to Avoid Argentinian Flag Sign in Intumescent Cataract.

Purpose: We describe an alternative automated technique that consists of simultaneous anterior capsule puncture and decompression of the capsular bag by using an insulin needle attached to the aspiration tubing of the phacoemulsification device to prevent the occurrence of the "Argentinian Flag sign" during capsulorhexis in intumescent cataract. Setting: Instituto de Olhos de Assis and Center of Specialties Hoftalmed, located in the state of São Paulo, Brazil. Design: Prospective interventional study. Methods: Eighty-eight eyes of 88 patients with white or intumescent cataracts were included in this study. Routine clear cornea incision, capsule staining with trypan blue, intracameral anesthesia, and ophthalmic viscoelastic device were used before the procedure. A 26-gauge needle was connected to the phacoemulsification aspiration tubing using a double male Luer connector for irrigation, and aspiration was inserted into the anterior chamber through a new paracentesis incision with the bevel facing down. Immediately after insertion, automated aspiration of the liquefied cortex was performed to remove anterior intralenticular material and achieve capsular decompression. Compression of the nucleus with the needle tip was performed to remove any liquefied material trapped between the posterior surface of the nucleus and the posterior capsule. All surgeries were performed using the same phacoemulsification and parameters. The rate of complete continuous capsulorhexis was observed and noted. Results: No complications were observed in any of the cases. A single-stage, continuous, and well-centered capsulorhexis was achieved in 100% of cases. Conclusion: We conclude that a simultaneous puncture and decompression of the capsular bag using an insulin needle attached to the aspiration tubing of the phacoemulsification machine effectively avoided the "Argentinian Flag sign" in intumescent cataract surgery.

Visual rehabilitation after LASIK complication: flap amputation, topo-guided surgery, and phacoemulsification.

We present a case of a patient complaining of monocular diplopia due to a decentered ablation after LASIK. The patient underwent a wavefront-guided retreatment, which resulted in an epithelial ingrowth complication. Additionally, the patient developed cataract, with cataract surgery requiring reliable biometric measurements. Therefore, we opted for corneal treatment and corneal surface regularization. Although we attempted to lift the flap and wash the interface initially, the procedure proved unsuccessful, thereby necessitating immediate flap amputation. Once the corneal surface was regularized in the seventh postoperative month, transepithelial photorefractive keratectomy was successfully performed to homogenize the ocular surface, thereby significantly improving the patient's corrected visual acuity and resolving monocular diplopia. The surface and corneal curvature stabilized by the fifth month after the procedure. Phacoemulsification was then performed along with the implantation of a toric monofocal lens, which was selected using an appropriate formula, resulting in an excellent uncorrected visual acuity.

Comparison of visual outcomes of bilateral dual-technology diffractive intraocular lens vs blended enhanced monofocal with dual-technology intraocular lens.

PURPOSE: To compare clinical outcomes after implantation of TECNIS Synergy (ZFR00V) intraocular lenses (IOLs) in both eyes and implantation of the TECNIS Synergy and TECNIS Eyhance (ICB00) combination in patients undergoing cataract surgery. SETTING: Department of Cataract, Hospital Oftalmológico de Brasilia (HOB), Brasília, Brazil. DESIGN: Prospective, interventional, randomized, parallel-group study. METHODS: Patients were categorized into 2 groups: Group 1: ZFR00V IOL was implanted in both eyes. Group 2: An ICB00 IOL was implanted in the dominant eye, and a ZFR00V IOL was implanted in the nondominant eye. RESULTS: Visual acuity was similar between the 2 groups (95% CI <0.1 logMAR). A superior visual acuity of ≥ 20/25 (at -2.00 to -2.50 diopters [D]) was achieved in Group 1 (bilateral ZFR00V) than in Group 2 (combination of ZFR00V/ICB00). The binocular defocus curve demonstrated better visual acuity at 40 cm (-2.00 D) and 50 cm (-2.50 D) in Group 1 than in Group 2 ( P < .05). Similar contrast sensitivity values were observed between the 2 groups. Patients in Group 1 reported higher satisfaction (completely satisfied) than those in Group 2 ( P < .05). However, halos and glare were more pronounced in Group 1 than in Group 2 ( P < .05). CONCLUSIONS: Both presbyopia-correcting IOL combinations showed similar binocular visual acuity results. Group 1 demonstrated enhanced visual acuity in the defocus curve at 40 cm (-2.00 D) and 50 cm (-2.50 D). Comparable contrast sensitivity outcomes were observed in both groups. Patients were more completely satisfied in Group 1 than in Group 2, despite the higher frequency of postoperative nighttime halos and glare.

Results of Fibrin Glue Applied Over the Corneal Surface Immediately After Pterygium Surgery: A Novel Pain Relief Technique.

PURPOSE: The aim of this study was to compare the use of fibrin glue on the corneal epitheliectomy site at the end of pterygium surgery versus conventional eye patch regarding pain levels, need for oral analgesic medications, number of days feeling pain, and awakening due to pain after surgery. METHODS: Forty-eight eyes of 24 patients with bilateral primary pterygium were included in this prospective, randomized, double-masked controlled trial. Each eye of the same patient was randomized to the intervention or control group. The intervention group received 2 drops of fibrin glue in the epitheliectomy site at the end of surgery and an eye patch, whereas the control group was only received an eye patch. Patients returned on the first and seventh days after surgery. Pain intensity (measured using the visual pain analog scale), need for oral analgesics, the number of days the pain lasted, and quality of sleep were assessed during follow-up visits and compared between groups. Comparison analysis accounted for sex, age, pterygium grading, and comorbidities. RESULTS: Visual analog pain scale after surgery was significantly lower in eyes receiving fibrin glue (-1.58; 95% confidence interval: -2.84 to -0.32; P = 0.014). In addition, the intervention group presented a 73% lower chance of using oral analgesics (OR: 0.27; 95% confidence interval: 0.07-0.95; P = 0.041). No difference in the awakenings at night was noted ( P = 0.240) nor the mean days of ocular pain in the first week after surgery ( P = 0.474). CONCLUSIONS: Fibrin glue at the end of pterygium surgery effectively reduces pain and the need for oral analgesics compared with conventional eye patching. This study is the first to describe the results of this strategy.

Spectrophotometric Analysis of Different Polymethyl Methacrylate Filters and their Importance in the Implantation of Corneal Rings.

PURPOSE: This study evaluated the luminous behavior applied to materials used in intraocular surgeries. METHODS: Discs of the different products were delivered in 19.00 mm × 3.00 mm. Each sample was fixed on support keeping it perpendicular to the spectrophotometer beam. Later, their analyses were carried out in the air/PMMA ratio. The graphs of individual profiles of the measurements along the length were constructed according to each of the filters from the spectrophotometric analysis. In addition, descriptive statistics of transmittance and absorbance for each wavelength presented were correlated for each filter. RESULTS: It is possible to observe that the minimum absorption measure was found in the Red Filter, especially in the blue and green light spectrum. CONCLUSION: Using filters in PMMA materials appears to improve visual quality in corneal implants, especially the red filter, due to greater absorbance of light leading to fewer light scattering phenomena through corneal rings. However, further studies comparing the effects of different filters on Intracorneal rings should be carried out to elucidate this field of study.

Measurement of the visual axis through two different methods: quantification and differences for measuring chord µ.

PURPOSE: To compare the differences between the apparent and actual chord µ. METHODS: In this prospective, comparative, non-randomized, and non-interventional study, imaging examinations using Pentacam and the HD Analyzer were performed in the same room under the same scotopic conditions. The inclusion criteria were patients aged 21-71 years, able to provide informed consent, myopia up to 4D, and anterior topographic astigmatism up to 1D. Patients using contact lenses, those with previous eye diseases or surgeries, corneal opacities, corneal tomographic changes, or suspected keratoconus were excluded. RESULTS: Altogether, 116 eyes of 58 patients were analyzed. The patients' mean age was 30.69 (±7.85) years. In the correlation analyses, Pearson's correlation coefficient of 0.647 indicates a moderate positive linear relationship between apparent and actual chord µ. The mean actual and apparent chord µ were 226.21 ± 128.53 and 278.66 ± 123.90 µm, respectively, with a mean difference of 52.45 µm (p=0.01). The analysis of mean pupillary diameter resulted in 5.76 mm using the HD Analyzer and 3.31 mm using the Pentacam. CONCLUSIONS: We found a correlation between the two measurement devices, and even though we found considerable differences, both can be used in daily practice. Given their differences, we should respect their peculiarities as well.

Ten-year follow-up of corneal cross-linking and refractive surface ablation in patients with asymmetric corneal topography.

Purpose: Compare the safety and efficacy of wavefront-guided photorefractive keratotomy (PRK) 6 months after cross-linking (CXL) to wavefront-guided PRK alone for refractive correction in patients with bilateral asymmetric corneal topography. Methods: Prospective randomized clinical trial with 16 patients (32 eyes). CXL with subsequent PRK after 6 months in one eye, and PRK alone was performed in contralateral eyes. The follow-up was 10 years. We analyzed visual outcomes, Scheimpflug topography, and corneal haze evaluation. Results: Eyes in the PRK group showed better results than in the CXL + PRK group. Mean postoperative CDVA was 0.044 logmar (SD, 0.073) in the PRK group and 0.1 logmar (SD, 0.21) in the CXL + PRK group, the mean sphere was + 0.21 (SD, 0.6) D in the PRK group and 0.87 (SD, 2.3) D in the CXL + PRK group, and mean SE was -0.35 (SD, 0.65) D in the PRK group and 0.62 (SD, 2.32) D in the CXL + PRK group. In one patient, a steepening of 2.5 D and a thinning of 17 µm occurred in PRK alone group. Two patients in the CXL + PRK group presented corneal haze. The overall complication rate was 18,75% (haze and ectasia). Conclusion: Non-simultaneous CXL and PRK procedures yielded good refractive results, but worse than those obtained with PRK alone. Although one patient in the PRK group developed corneal ectasia, the CXL + PRK group had a higher loss of vision lines, indicating less safety.

Donor graft harvesting with air in pterygium surgery.

PURPOSE: Report a new technique for improvement of pterygium surgery: donor graft harvesting with air. CASE REPORTS: We describe a technique that was used with 138 patients who underwent surgery that included a conjunctival autograft and fibrin glue with air injection to dissect the Tenon capsule from the conjunctiva. RESULTS: No complications occurred with this technique and all patients achieved good results. DISCUSSION: The surgical time with this new technique was similar to that reported in the literature. In addition, the graft thickness was close to that reported with femtosecond laser dissection and it was thinner than that reported with aesthetic/saline dissection (unable to determine statistical significance). CONCLUSIONS AND IMPORTANCE: With the injection of an air bubble, we could easily dissect the conjunctiva from the Tenon capsule and quickly acquire thin grafts without any additional costs or complications.

Vision Quality Questionnaire Assessment in Patients After Topography-Guided Photorefractive Keratectomy for Irregular Astigmatism Secondary to Radial Keratotomy.

Aim: To evaluate the vision-related quality of life with the National Eye Institute Refractive Error Quality of Life (NEI-RQL) questionnaire in patients with astigmatism secondary to radial keratotomy surgery who underwent topography-guided photorefractive keratectomy. Methods: Prospective non-randomized clinical trial. This study included 15 patients (30 eyes) aged > 21 years, mean age 55.1 (SD, 3.5) years, 53.3% female, with astigmatism ≤ - 6.00 D resulting from radial keratotomy, which could have been associated with hyperopia ≤ + 6.00 D. Photorefractive keratectomy with topography-guided custom ablation treatment was used in all cases. The patients answered the NEI-RQL questionnaire preoperatively and at 4 and 48 months after topography-guided photorefractive keratectomy. The following data were collected: age, sex and education level, pre-operative refraction data, visual acuity with or without correction, pachymetry, and keratometry. Results: There was a significant difference between pre-and postoperative NEI-RQL scores for the domains clarity of vision, near vision, far vision, diurnal fluctuation, activity limitations, glare, symptoms, correction dependence, appearance, and satisfaction with correction (p < 0.001). Conclusion: Topography-guided photorefractive keratectomy improved vision-related quality of life in patients with a history of irregular astigmatism secondary to radial keratotomy.

Pain response and symptoms in photorefractive keratectomy: mechanical de-epithelization compared with transepithelial ablation.

PURPOSE: To compare postoperative pain and discomfort between mechanical and transepithelial photorefractive keratectomies. METHODS: This prospective comparative study included 190 eyes of 95 patients with hyperopia (up to +4.00 D), astigmatism (up to -5.00 D), and myopia (up to -8.00 D) who underwent mechanical photorefractive keratectomy in one eye and transepithelial photorefractive keratectomy in the contralateral eye using Wavelight Allegretto EX500 excimer laser. The patients were unaware of the side treated with each technique. The interval between operations in the same patient was 15-30 days. Both eyes had similar refraction before surgery, with a maximum of 15-µm difference in ablation. Postoperative questionnaires were administered on days 1 and 7 to assess the patients' level of discomfort (0=no discomfort to 5=extreme discomfort) with the following symptoms: pain, burning sensation, itchiness, tearing, photophobia, eye redness, foreign body sensation, and eyelid swelling. Patients were also asked about which method they preferred. RESULTS: The sample consisted of 61 women (64.21%) and 34 men (35.79%). The mean (SD) patient age was 31.66 (6.69) years (range, 22-54 years). On postoperative day 1, the patients reported significantly less discomfort in terms of pain (1.9 ± 1.74 vs 2.5 ± 1.83; p=0.017), burning sensation (1.8 ± 1.56 vs 2.5 ± 1.68; p=0.004), tearing (2.3 ± 1.71 vs 3.1 ± 1.69; p=0.001), and foreign body sensation (1.9 ± 1.77 vs 2.5 ± 1.86; p=0.024) in the eye that received mechanical photorefractive keratectomy than in the eye that received transepithelial photorefractive keratectomy. No significant differences were found between the mechanical and transepithelial photorefractive keratectomies on postoperative day 7. Fifty-nine patients (62.10%) preferred mechanical photorefractive keratectomy, while 32 (33.68%) preferred transepithelial photorefractive keratectomy. Four patients (4.22%) expressed no preference. CONCLUSIONS: Our results showed that pain scores were significantly lower in the mechanical photorefractive keratectomy-treated eyes than in the transepithelial photorefractive keratectomy-treated eyes on postoperative day 1, which may have provided greater patient comfort after surgery and led patients to prefer the mechanical photorefractive keratectomy technique.

Association between keratoconus, ocular allergy, and sleeping behavior.

PURPOSE: To compare the severity and laterality of keratoconus according to allergic rhinitis, scratching and sleeping habits, and manual dexterity. METHODS: Objective assessments regarding allergic rhinitis, eye itching, and slee-ping position among patients with keratoconus (diagnosed based on corneal tomography) were conducted. Diagnostic criteria and classification were based on the Amsler-Krumeich classification. RESULTS: Ocular pruritus was reported by 29 of 34 participants (85.29%). Eighteen participants (62.07%) reported equal scratching of both eyes, six (20.69%) more on the right eye, and five (17.24%) more on the left eye. Comparison of the main sleeping position and the eye with more severe presentation of the disease using Fisher's exact test revealed some correlations (0.567 and 0.568 in the right and left eye, respectively). However, these correlations were not statistically significant. CONCLUSIONS: The association between higher keratometry values and sleeping position appears to be more significant than that reported between keratometry and itching, or manual dexterity.

Corneal densitometry in patients with keratoconus undergoing intrastromal Ferrara ring implantation.

OBJECTIVE: Evaluation of central corneal densitometry changes following Ferrara corneal ring segment implantation in patients with keratoconus, especially the correlation between corneal densitometry and keratometry. METHODS: Retrospective, non-comparative, interventional study based on the review of medical records of patients diagnosed with keratoconus who underwent Ferrara corneal ring segment implantation. Pre and post-operative corneal densitometry measurements obtained with Pentacam HR (Oculus, Wetzlar, Germany) were analyzed. The follow-up time was 3 months, and data comparison was made, using specific statistical analysis, with the data of 3 months postoperatively. RESULTS: The study sample consisted of 43 eyes of 36 patients. The mean corrected visual acuity improved from 0.82 LogMAR preoperatively (SD ± 0.33) to 0.19 LogMAR (SD ± 0.13) postoperatively. The mean spherical equivalent varied from -4.63 (SD ± 3.94) preoperatively to -2.16 (SD ± 2.63) postoperatively. Asphericity varied from -0.69 (SD ± 0.32) preoperatively to -0.27 (SD ± 0.31) postoperatively. The mean maximum K was 54.01D (SD ± 3.38) preoperatively and 51.50D (SD ± 2.90) postoperatively. The mean anterior densitometric value was 18.26 (SD ± 2.03) preoperatively and 17.66 (SD ± 1.84) postoperatively. CONCLUSION: Corneal densitometry is an interesting technology that should be studied in keratoconus patients. Our results suggest that the corneal densitometry in the cornea's anterior layer reduces after ICRS implantation and correlates with corneal keratometry. Further studies should be performed to increase the knowledge in this field.

Evaluation of keratoconus progression and visual improvement after intrastromal corneal ring segments implantation: A retrospective study.

OBJECTIVE: To investigate the role of ICRS in halting keratoconus progression in a large sample of patients. METHODS: A retrospective, non-comparative, interventional study based on the review of medical records of patients diagnosed with keratoconus who underwent Ferrara corneal ring segment implantation. A retrospective chart analysis study of 123 operated eyes with follow-up ranging from 3 to 16 years (mean 5.3 ± 3.6 years) was performed. This study was carried out at Ocular Surgery Unit, São Paulo, Brazil. All topographic data were obtained from Pentacam (Oculus, Arlington, USA). The same surgeon performed all surgeries, and the Ferrara ICRS nomogram was used for ICRS selection in all cases. RESULTS: Corrected distance visual acuity, keratometry, and topographic astigmatism improved in most cases, with statistical significance. In 42 eyes (53.8%), there was an increase in K1 or K2, and in 36 (46.2%), there was a reduction or maintenance in K1. Considering a difference higher than 1 D, between 3-month post-surgery and final visit (group 3), 32 eyes (41%) showed an increase, and 46 eyes (59%) ended equal or below this value. CONCLUSION: The implantation of ICRS showed improvement in visual and keratometric indexes. The majority of patients did not increase more than one diopter in keratometric values after ICRS implantation. ICRS may be effective for slowing disease progression, especially in older patients.

Centration in refractive surgery.

The point of centration for refractive surgery is a theme of great importance that generates considerable discussion among specialists and surgeons in the field. Notably, any changes in light can alter the size of the pupil, and the visual axis of the fixation line to the fovea is unique in each patient. A variety of options have been described in the literature with respect to centration in refractive surgery, and the results differ among these methods. No consensus has been established regarding the ideal refractive surgery technique for evaluation of centration in each patient that will yield a satisfactory surgical result.

Two-year follow-up of corneal cross-linking and refractive surface ablation in patients with asymmetric corneal topography.

AIMS: To evaluate the safety and efficacy of corneal cross-linking (CXL) followed by photorefractive keratectomy (PRK) for refractive correction in patients with bilateral asymmetric topography. METHODS: Forty-four patients (88 eyes) were enrolled in this prospective randomised clinical trial. CXL with subsequent PRK after 6 months was performed in one eye (study group), and PRK alone was performed in contralateral eyes (control group). Patients were followed for 24 months after PRK. Outcome measures investigated included visual acuity (VA), refraction, aberrometry, topography, pachymetry and endothelial cell count. Groups were compared with linear mixed regression and repeated measures logistic regression. Multiple comparison adjustment with the Holm procedure was performed. RESULTS: At baseline, the logMAR VA (best spectacle corrected) in study and control groups was 0.12±0.13 (mean±SD) and 0.08D±0.14, respectively, and axial inferior-superior index (IS) (topographic IS) in study and control groups were 0.59D±0.31D and 0.58D±0.32D, respectively. After 24 months, a mean under correction of -0.50D was observed in both groups. Change from baseline in logMAR VA in study and control groups was 0.00D±0.08D and -0.02D±0.10D, respectively. Frequency of haze at 30 months in study and control group eyes was, respectively, 18.2% and 4.6% (p=0.05). There was no statistical difference between groups in spherical aberration and coma after adjustment for multiple comparisons. CONCLUSIONS: Non-simultaneous CXL followed by PRK may be performed safely, and refractive results over a 2-year follow-up are highly similar in virgin and previously cross-linked corneas. Despite using mitomycin C, corneal haze can be significantly higher in the first year after PRK in eyes pretreated with CXL.