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Niazi S, Gatzioufas Z, Doroodgar F, Findl O, Baradaran-Rafii A, Liechty J, Moshirfar M. Keratoconus: exploring fundamentals and future perspectives - a comprehensive systematic review. Ther Adv Ophthalmol 2024; 16:25158414241232258. [PMID: 38516169 PMCID: PMC10956165 DOI: 10.1177/25158414241232258] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2023] [Accepted: 01/22/2024] [Indexed: 03/23/2024] Open
Abstract
Background New developments in artificial intelligence, particularly with promising results in early detection and management of keratoconus, have favorably altered the natural history of the disease over the last few decades. Features of artificial intelligence in different machine such as anterior segment optical coherence tomography, and femtosecond laser technique have improved safety, precision, effectiveness, and predictability of treatment modalities of keratoconus (from contact lenses to keratoplasty techniques). These options ingrained in artificial intelligence are already underway and allow ophthalmologist to approach disease in the most non-invasive way. Objectives This study comprehensively describes all of the treatment modalities of keratoconus considering machine learning strategies. Design A multidimensional comprehensive systematic narrative review. Data sources and methods A comprehensive search was done in the five main electronic databases (PubMed, Scopus, Web of Science, Embase, and Cochrane), without language and time or type of study restrictions. Afterward, eligible articles were selected by screening the titles and abstracts based on main mesh keywords. For potentially eligible articles, the full text was also reviewed. Results Artificial intelligence demonstrates promise in keratoconus diagnosis and clinical management, spanning early detection (especially in subclinical cases), preoperative screening, postoperative ectasia prediction after keratorefractive surgery, and guiding surgical decisions. The majority of studies employed a solitary machine learning algorithm, whereas minor studies assessed multiple algorithms that evaluated the association of various keratoconus staging and management strategies. Last but not least, AI has proven effective in guiding the implantation of intracorneal ring segments in keratoconus corneas and predicting surgical outcomes. Conclusion The efficient and widespread clinical translation of machine learning models in keratoconus management is a crucial goal of potential future approaches to better visual performance in keratoconus patients. Trial registration The article has been registered through PROSPERO, an international database of prospectively registered systematic reviews, with the ID: CRD42022319338.
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Affiliation(s)
- Sana Niazi
- Translational Ophthalmology Research Center, Tehran University of Medical Sciences, Tehran, Iran
- Ophthalmic Research Center, Research Institute for Ophthalmology and Vision Science, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Zisis Gatzioufas
- Department of Ophthalmology, University Eye Hospital Basel, Basel, Switzerland
| | - Farideh Doroodgar
- Translational Ophthalmology Research Center, Tehran University of Medical Sciences, Tehran Province, Tehran, District 6, Pour Sina St, P94V+8MF, Tehran 1416753955, Iran
- Negah Aref Ophthalmic Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Oliver Findl
- Department of Ophthalmology, Hanusch Hospital, Vienna Institute for Research in Ocular Surgery (VIROS), Vienna, Austria
| | - Alireza Baradaran-Rafii
- Department of Ophthalmology, Morsani College of Medicine, University of South Florida, Tampa, FL, USA
| | - Jacob Liechty
- Department of Ophthalmology, Morsani College of Medicine, University of South Florida, Tampa, FL, USA
| | - Majid Moshirfar
- John A. Moran Eye Center, University of Utah, Salt Lake City, UT, USA
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Xiao J, Li M, Wang C, Pi J, He H. Design and research of a robotic system for ultrasonic‐assisted lamellar keratoplasty. COGNITIVE COMPUTATION AND SYSTEMS 2021. [DOI: 10.1049/ccs2.12020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Affiliation(s)
- Jingjing Xiao
- School of Computer and Information Engineering Xiamen University of Technology Xiamen China
| | - Mengqiong Li
- Xiamen Eye Center Xiamen University Xiamen China
| | - Chiming Wang
- School of Computer and Information Engineering Xiamen University of Technology Xiamen China
| | - Jun Pi
- School of Mechanical and Energy Engineering Jimei University Xiamen China
| | - Hui He
- Eye Institute Medical College Xiamen University Xiamen China
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Abstract
In recent years, there has been a considerable interest regarding the concept of lamellar keratoplasty (LK), which contributed in spreading the use of this procedure in the treatment of keratoconus. This is a new frontier in corneal surgery that minimizes trauma on the recipient patient since it works on a "closed bulb". The LK surgery, in fact, aims to selectively replace diseased corneal stroma, leaving the healthy endothelium. The main advantage of LK is to avoid major causes of failure of penetrating keratoplasty as immunological rejection, and the late mismatch in the transplanted cornea, thus increasing the life of transplantation. In the last decade, several techniques of LK have been proposed, depending on how the anterior portion of the recipient cornea is removed. This article, through a literary research reviews the various emerging techniques of anterior lamellar surgery for the management of keratoconus, analyzing their indications, visual outcomes, and rate of complications.
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Affiliation(s)
- Leopoldo Spadea
- Department of Biotechnology and Medical Surgical Sciences, Sapienza University of Rome, Latina, Italy. E-mail.
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Henein C, Nanavaty MA. Systematic review comparing penetrating keratoplasty and deep anterior lamellar keratoplasty for management of keratoconus. Cont Lens Anterior Eye 2016; 40:3-14. [PMID: 27802912 DOI: 10.1016/j.clae.2016.10.001] [Citation(s) in RCA: 59] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2016] [Revised: 09/27/2016] [Accepted: 10/07/2016] [Indexed: 12/13/2022]
Abstract
AIM Perception of reduced incidence of graft rejection after deep anterior lamellar keratoplasty (DALK) has attracted many surgeons towards this technique in keratoconus. This review aims to compare the visual, refractive and graft outcomes after penetrating keratoplasty (PK) and DALK for keratoconus. METHODS Electronic searches of PubMed, MEDLINE, EMBASE, Latin American and Caribbean Health Sciences Literature database (LILACS), metaRegister of Controlled Trials (mRCT), ClinicalTrial.gov and the WHO International Clinical Trials Registry Platform (ICTRP) were performed. We included randomized control trials (RCTs) and comparative studies to assess primary and secondary outcomes after PK and DALK in eyes with keratoconus. Primary outcome was best-corrected visual acuity (BCVA) LogMAR at ≥6 months. Secondary outcomes included number of patients with BCVA≥0 LogMAR, uncorrected visual acuity (UCVA) LogMAR, spherical equivalent (SE), refractive and keratometric astigmatism, endothelial cell density (ECD) cell/mm2, graft rejection and graft survival. RESULTS Eighteen studies (including 2 RCTs) compared DALK (965 eyes) and PK (2402 eyes) for keratoconus. There was strong evidence through RCTs suggesting better LogMAR BCVA at ≥6 months and better LogMAR UCVA with PK; reduced refractive astigmatism and rejection with DALK and no difference in SE and keratometric astigmatism. Moreover, there was weak evidence to suggest better BCVA≥0 LogMAR after PK and no difference in ECD between the two techniques. CONCLUSIONS Despite the popularity of DALK amongst corneal surgeons for keratoconus, there is a paucity of high quality RCTs. The existing limited evidence confirms reduced rejection and refractive astigmatism with DALK but better visual outcomes with PK. Internationally agreed data sets and follow-up protocol are warranted.
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Affiliation(s)
- Christin Henein
- Sussex Eye Hospital, Brighton & Sussex University H ospitals NHS Trust, Eastern Road, Brighton, BN6 5BF, United Kingdom
| | - Mayank A Nanavaty
- Sussex Eye Hospital, Brighton & Sussex University H ospitals NHS Trust, Eastern Road, Brighton, BN6 5BF, United Kingdom.
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Zhang C, Liu L, Tang M, Li Y, Chamberlain W, Huang D. Laboratory Evaluation of Femtosecond Laser Lamellar Cuts in Gamma-Irradiated Corneas. Cornea 2016; 34:1499-503. [PMID: 26382890 DOI: 10.1097/ico.0000000000000614] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
PURPOSE To evaluate the stromal interface quality after femtosecond laser full lamellar cuts in gamma-irradiated corneas (VisionGraft sterile cornea) and to determine the limits of the cut depth using the VisionGraft as donor corneas for laser-assisted lamellar anterior keratoplasty. METHODS Fourteen VisionGraft corneas underwent full lamellar cuts using the femtosecond laser. The percent cut depth was 17% to 21% (100 μm, n = 2), 31% to 35% (n = 3), 38% to 40% (n = 3), 45% to 48% (n = 3), and 50% (n = 3) of the total stromal thickness (not including the epithelium). The cap and stromal bed surfaces were imaged with a scanning electron microscope. The quality of cut surfaces was graded by 2 masked observers based on two indices: ridge and roughness. Ridge grading indicated macroscopic irregularity. Roughness grading indicated microscopic irregularity. The grading was done on a subjective integer scale of 1 to 5 (1 = best and 5 = worst), which was used in a previous study of cut quality in fresh corneas. RESULTS The ridge grading ranged from 1.5 for the shallowest cut to 2.2 for the deepest cut and weakly (r = 0.279) but significantly (P = 0.037) correlated with the percent cut depth. The roughness grading ranged from 2.63 to 2.56 and showed no trend with the percent cut depth (r = 0.006, P = 0.968). CONCLUSIONS Compared with previously published results of fresh corneas, in which ridge grading exceeded 3 for cuts deeper than 31%, cut quality was better for the VisionGraft. Even at depths up to 48% of the total stromal thickness, ridge grading was not worse than shallow cuts. Thus, gamma-irradiated corneas could provide a smoother interface than do fresh eye bank corneas for laser-assisted lamellar anterior keratoplasty.
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Affiliation(s)
- Chenxing Zhang
- *Center for Ophthalmic Optics and Lasers, Casey Eye Institute, Portland, OR; †Department of Ophthalmology, Oregon Health and Science University, Portland, OR; ‡Department of Ophthalmology, Southwest Eye Hospital, Third Military Medical University, Chongqing, China; and §Department of Ophthalmology, Peking Union Medical College Hospital, Beijing, China
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Li WJ, Hu YK, Song H, Gao XW, Zhao XD, Dong J, Guo YL, Cai Y. Observation on ultrastructure and histopathology of cornea following femtosecond laser-assisted deep lamellar keratoplasty for acute corneal alkaline burns. Int J Ophthalmol 2016; 9:481-6. [PMID: 27162716 DOI: 10.18240/ijo.2016.04.01] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Accepted: 12/24/2015] [Indexed: 01/20/2023] Open
Abstract
AIM To demonstrate the changes in ultrastructure and histopathology of the cornea in acute corneal alkaline burns after femtosecond laser-assisted deep lamellar keratoplasty. METHODS The New Zealand white rabbits treated with alkaline corneal burn were randomized into two groups, Group A (16 eyes) with femtosecond laser-assisted deep lamellar keratoplasty 24h after burn and Group B (16 eyes) without keratoplasty as controls. All eyes were evaluated with transmission electron microscopy (TEM) at 1, 2, 3, and 4wk follow-up, then all corneas were tested by hematoxylin and eosin staining histology. RESULTS The corneal grafts in Group A were transparent, while those in Group B showed corneal stromal edema and loosely arranged collagen fibers. One week after treatment, TEM revealed the intercellular desmosomes in the epithelial layers and intact non-dissolving nuclei in Group A. At week 4, the center of the corneas in Group A was transparent with regularly arranged collagen fibers and fibroblasts in the stroma. In Group B, squamous cells were observed on the corneal surface and some epithelial cells were detached. CONCLUSION Femtosecond laser-assisted deep lamellar keratoplasty can suppress inflammatory responses, prevent toxic substance-induced injury to the corneal endothelium and inner tissues with quicker recovery and better visual outcomes.
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Affiliation(s)
- Wen-Jing Li
- Department of Ophthalmology, the 474th Hospital of the Chinese People's Liberation Army, Urumchi 830011, Xinjiang Autonomous Region, China
| | - Yu-Kun Hu
- Department of Ophthalmology, the 474th Hospital of the Chinese People's Liberation Army, Urumchi 830011, Xinjiang Autonomous Region, China
| | - Hui Song
- Department of Ophthalmology, the 309th Hospital of the Chinese People's Liberation Army, Beijing 100000, China
| | - Xiao-Wei Gao
- Department of Ophthalmology, the 474th Hospital of the Chinese People's Liberation Army, Urumchi 830011, Xinjiang Autonomous Region, China
| | - Xu-Dong Zhao
- Department of Ophthalmology, the 474th Hospital of the Chinese People's Liberation Army, Urumchi 830011, Xinjiang Autonomous Region, China
| | - Jing Dong
- Department of Ophthalmology, the 474th Hospital of the Chinese People's Liberation Army, Urumchi 830011, Xinjiang Autonomous Region, China
| | - Yun-Lin Guo
- Department of Ophthalmology, the 474th Hospital of the Chinese People's Liberation Army, Urumchi 830011, Xinjiang Autonomous Region, China
| | - Yan Cai
- Department of Ophthalmology, the 474th Hospital of the Chinese People's Liberation Army, Urumchi 830011, Xinjiang Autonomous Region, China
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Correlation Between Corneal Button Size and Intraocular Pressure During Femtosecond Laser-Assisted Keratoplasty. Cornea 2016; 35:383-7. [PMID: 26751991 DOI: 10.1097/ico.0000000000000717] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
PURPOSE To evaluate changes in intraocular pressure (IOP) in recipient and donor eyes during femtosecond laser-assisted keratoplasty (FLAK) and to assess for differences in the diameter of trephinated corneal buttons according to changes in pressure. MATERIALS AND METHODS Twenty porcine whole eyes (recipient model) and 20 porcine-corneoscleral rims (donor model) were prepared, and anterior chamber pressures were measured using a fiberoptic sensing device (Opsens, Quebec, Canada) during the femtosecond laser corneal cutting process. To determine the diameter of corneal buttons, 10 porcine whole eyes (recipient model) and 12 corneoscleral rims (donor model) of each baseline IOP were cut with the femtosecond laser programmed to the following pattern: "vertical side cut"; 1200 μm (depth), 8 mm (diameter). Digital photographs were obtained using microscopy and subsequently analyzed. RESULTS The IOP (mean ± SD) for the recipient model was 10.2 (±0.9) mm Hg at baseline and ranged from 96.6 (±4.5) to ∼138.4 (±3.8) mm Hg during the corneal cutting process. This shows that the maximum IOP during FLAK increased 13.5 times compared with baseline. In the donor model, the mean pressure elevation from baseline artificial anterior chamber (AAC) pressure to corneal cutting was 15.8 (±5.4) mm Hg. This showed a positive correlation with baseline IOP [correlation coefficient (CC) = 0.827, P = 0.006]. As the baseline IOP in the recipient eye increased, trephinated corneal button size was reduced by up to 3.9% in diameter (CC = -0.945, P = 0.015). In addition, in donor eyes, the diameter was decreased by up to 11.7% as the baseline AAC pressure increased (CC = -0.934, P = 0.006). CONCLUSIONS During the FLAK procedure, the IOP increases in both recipient and donor eyes. The diameter of the trephinated donor and recipient corneal buttons was decreased as the initial baseline IOP increased. Ophthalmic surgeons can determine the AAC pressure based on the baseline IOP in the recipient patient.
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Wan KHN, Yiu EPF, Young AL. Corneal transplantation: Beyond the horizon. World J Ophthalmol 2015; 5:36-44. [DOI: 10.5318/wjo.v5.i2.36] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Revised: 03/04/2015] [Accepted: 04/02/2015] [Indexed: 02/06/2023] Open
Abstract
Evolving techniques in keratoplasty have undoubtedly led to thinner corneal grafts. These newer iterations of keratoplasty aim to reduce graft rejections, improve visual acuity and visual rehabilitation. Each technique poses its own advantages and disadvantages; the surgeon should select patients suitable for a particular technique while accounting for their surgical competency given the learning curve associated with these newer techniques. Alternatives to corneal transplant may have a role in addressing the shortages of corneal graft, these bioengineered material and medical treatment still need further studies to demonstrate its clinical applicability.
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Zhang C, Bald M, Tang M, Li Y, Huang D. Interface quality of different corneal lamellar-cut depths for femtosecond laser-assisted lamellar anterior keratoplasty. J Cataract Refract Surg 2015; 41:827-35. [PMID: 25747165 DOI: 10.1016/j.jcrs.2014.08.031] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2014] [Revised: 07/31/2014] [Accepted: 08/19/2014] [Indexed: 11/30/2022]
Abstract
PURPOSE To evaluate the interface quality of different corneal lamellar-cut depths with the femtosecond laser and determine a feasible range of depth for femtosecond laser-assisted lamellar anterior keratoplasty. SETTING Casey Eye Institute, Portland, Oregon, USA. DESIGN Experimental study. METHODS Full lamellar cuts were made on 20 deepithelialized human cadaver corneas using the femtosecond laser. The cut depth was 17% to 21% (100 μm), 31%, 35%, 38% to 40%, and 45% to 48% of the central stromal thickness. Scanning electron microscopy images of the cap and bed surfaces were subjectively graded for ridge and roughness using a scale of 1 to 5 (1 = best). The graft-host match was evaluated by photography and optical coherence tomography in a simulated procedure. RESULTS The ridge score was correlated with the cut depth (P = .0078, R = 0.58) and better correlated with the percentage cut depth (P = .00024, R = 0.73). The shallowest cuts had the fewest ridges (score 1.25). The 31% cut depth produced significantly fewer ridges (score 2.15) than deeper cuts. The roughness score ranged from 2.19 to 3.08 for various depths. A simulated procedure using a 100 μm host cut and a 177 μm (31%) graft had a smooth interface and flush anterior junction using an inverted side-cut design. CONCLUSIONS The femtosecond laser produced more ridges in deeper lamellar cuts. A depth setting of 31% stromal thickness might produce adequate surface quality for femtosecond laser-assisted lamellar anterior keratoplasty. The inverted side-cut design produced good edge apposition even when the graft was thicker than the host lamellar-cut depth. FINANCIAL DISCLOSURE Proprietary or commercial disclosures are listed after the references.
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Affiliation(s)
- Chenxing Zhang
- From the Center for Ophthalmic Optics & Lasers (Zhang, Bald, Tang, Li, Huang), Casey Eye Institute and Department of Ophthalmology, Oregon Health & Science University, Portland, Oregon, USA; the Southwest Eye Hospital (Zhang), Third Military Medical University, Chongqing, China
| | - Matthew Bald
- From the Center for Ophthalmic Optics & Lasers (Zhang, Bald, Tang, Li, Huang), Casey Eye Institute and Department of Ophthalmology, Oregon Health & Science University, Portland, Oregon, USA; the Southwest Eye Hospital (Zhang), Third Military Medical University, Chongqing, China
| | - Maolong Tang
- From the Center for Ophthalmic Optics & Lasers (Zhang, Bald, Tang, Li, Huang), Casey Eye Institute and Department of Ophthalmology, Oregon Health & Science University, Portland, Oregon, USA; the Southwest Eye Hospital (Zhang), Third Military Medical University, Chongqing, China
| | - Yan Li
- From the Center for Ophthalmic Optics & Lasers (Zhang, Bald, Tang, Li, Huang), Casey Eye Institute and Department of Ophthalmology, Oregon Health & Science University, Portland, Oregon, USA; the Southwest Eye Hospital (Zhang), Third Military Medical University, Chongqing, China
| | - David Huang
- From the Center for Ophthalmic Optics & Lasers (Zhang, Bald, Tang, Li, Huang), Casey Eye Institute and Department of Ophthalmology, Oregon Health & Science University, Portland, Oregon, USA; the Southwest Eye Hospital (Zhang), Third Military Medical University, Chongqing, China.
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Abstract
Corneal transplantation is one of the most common types of human transplant surgery. By removing a scarred or damaged host cornea and replacing it with a clear and healthy donor transplant, this procedure helps to restore vision in a variety of corneal diseases. The traditional technique for corneal transplantation, penetrating keratoplasty (PKP), involves transplantation of all corneal layers. Over the past decade though, there has been a trend away from PKP as surgeons have developed partial thickness transplant procedures, such as deep anterior lamellar keratoplasty and Descemet stripping automated endothelial keratoplasty. These partial thickness transplant procedures selectively replace diseased host corneal tissue, while conserving healthy and functioning tissue. This review describes current surgical techniques in the field of corneal transplantation, with special emphasis on indications for transplantation and postoperative outcomes.
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Affiliation(s)
- Grace E Boynton
- Department of Ophthalmology and Visual Sciences, University of Michigan Medical School, Kellogg Eye Center, 1000 Wall St., Ann Arbor, MI 48105, USA
| | - Maria A Woodward
- Department of Ophthalmology and Visual Sciences, University of Michigan Medical School, Kellogg Eye Center, 1000 Wall St., Ann Arbor, MI 48105, USA
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Abstract
PURPOSE OF REVIEW To describe trends in corneal transplantation surgery, including indications for surgery, evolution of lamellar keratoplasty, current surgical techniques, and future directions. RECENT FINDINGS Over the past decade, anterior and posterior lamellar keratoplasty have begun to supplant penetrating keratoplasty. Surgical techniques continue to change and improve outcomes. In recent years, Descemet membrane endothelial keratoplasty (DMEK) has gained interest as it eliminates the corneal stromal interface, which may limit visual acuity after Descemet stripping automated endothelial keratoplasty. Despite the promising results with improved visual acuity and decreased rejection, the technical challenges associated with DMEK have limited widespread acceptance. With technical refinements and more eye banks providing precut tissue for both Descemet stripping automated endothelial keratoplasty and DMEK, it is likely both procedures will continue to increase over time. SUMMARY Corneal transplantation has evolved rapidly over the past decade, from full-thickness penetrating keratoplasty towards lamellar keratoplasty to only remove and replace damaged layers of the cornea. Achieving minimal induced astigmatism with excellent visual acuity remains a challenge in corneal transplantation. Further refinements in surgical technique may help improve technical challenges and visual outcomes. In this article, we review changing trends in corneal transplantation and highlight developing medical treatments that may be available in the future.
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Baradaran-Rafii A, Hasani H. Different techniques for performing DALK: are they making a real difference? Br J Ophthalmol 2014; 98:1311-2. [PMID: 24682177 DOI: 10.1136/bjophthalmol-2013-304407] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Affiliation(s)
| | - Hamidreza Hasani
- Ophthalmic Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran
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Vestergaard AH. Past and present of corneal refractive surgery: a retrospective study of long-term results after photorefractive keratectomy and a prospective study of refractive lenticule extraction. Acta Ophthalmol 2014; 92 Thesis 2:1-21. [PMID: 24636364 DOI: 10.1111/aos.12385] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
UNLABELLED Surgical correction of refractive errors is becoming increasingly popular. In the 1990s, the excimer laser revolutionized the field of corneal refractive surgery with PRK and LASIK, and lately refractive lenticule extraction (ReLEx) of intracorneal tissue, using only a femtosecond laser, has become possible. Two new procedures were developed, ReLEx flex (FLEX) and ReLEx smile (SMILE). Until this thesis, only a few long-term studies of PRK with a relatively limited number of patients had been published; therefore, this thesis intended to retrospectively evaluate long-term outcomes after PRK for all degrees of myopia for a large number of patients. Furthermore, a prospective contralateral eye study comparing FLEX and SMILE, when treating high to moderate degrees of myopia, had not been performed prior to this study. This was the second aim of this thesis. In the first study, results from 160 PRK patients (289 eyes) were presented. Preoperative spherical equivalent ranged from -1.25 to -20.25 D, with 78% having low myopia (<-6 D). Average follow-up time was 16 years (range 13-19 years), making this the longest published follow-up study on PRK patients. Outcomes from eyes with low myopia were generally superior to outcomes from eyes with high myopia, at final follow-up. Seventy-two percent were within ± 1.00 D of target refraction, as compared to 47% of eyes with high myopia. However, results from a subgroup of unilateral treated PRK patients indicated that refraction at final follow-up was affected by myopic progression. Fifty percent of eyes with low myopia had uncorrected 20/20 distance visual acuity or better, as compared to 22% of eyes with high myopia. Haze did not occur if attempted corrections were <-4 D, and only eyes with high myopia lost two lines or more of CDVA (corrected distance visual acuity). Eighty-one per cent were satisfied or very satisfied with their surgery. CONCLUSION The results support the continued use of the excimer laser for corneal surface ablation as a treatment option for correction of low degrees of myopia, and as the treatment of choice for subgroups of refractive patients (thin corneas, etc.). The results also highlight that treatment of higher degrees of myopia with standard PRK should only be done today under special circumstances, due to low refractive predictability, and high risk of corneal haze. Technological advances since then should be taken into account when comparing these results with contemporary techniques. In the second study, 35 patients were randomized to receive FLEX in one eye and SMILE in the other. Preoperative spherical equivalent refraction ranged from -6 to -10 D with low degrees of astigmatism. A total of 34 patients completed the 6 month follow-up period. Refractive and visual outcomes were very similar for the two methods, as well as tear film measurements and changes in corneal biomechanics. Ninety-seven percent were within ± 1.00 D of target refraction, no eyes lost two lines or more of CDVA, and contrast sensitivity was unaffected after both procedures. The changes in higher-order aberrations were also very similar. There were also no differences in tear film parameters 6 months after surgery, although less postoperative foreign body sensation was reported within the first week after surgery in SMILE eyes. Corneal sublayer pachymetry measurements demonstrated equally increased epithelial thickness 6 months after surgery. Contrary to expectations, it was not possible to measure the theoretical biomechanical advantages of a small corneal incision in SMILE as compared to a corneal flap in FLEX. The main differences between FLEX and SMILE were found when the corneal nerves and intraoperative complications were evaluated. Thus, corneal sensitivity was better preserved and corneal nerve morphology was less affected after SMILE, but intraoperative complications occurred more frequently, although without visual sequela. Finally, 97% were satisfied or very satisfied with both their surgeries. CONCLUSION The results support the continued use of both FLEX and SMILE for treatment of up to high degrees of myopia. Overall, refractive and visual results for both procedures were good and similar, but from a biological point of view, the less invasive SMILE technique is more attractive, as demonstrated in this study, despite being slightly more surgically demanding than FLEX.
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Affiliation(s)
- Anders Højslet Vestergaard
- Faculty of Health Science; University of Southern Denmark; Odense Denmark
- Department of Ophthalmology; Odense University Hospital; Odense Denmark
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