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Crouzet E, He Z, Ben Moussa O, Mentek M, Isard P, Peyret B, Forest F, Gain P, Koizumi N, Okumura N, Thuret G. Tissue engineered endothelial keratoplasty in rabbit: tips and tricks. Acta Ophthalmol 2021; 100:690-699. [PMID: 34967128 DOI: 10.1111/aos.15081] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2021] [Accepted: 12/07/2021] [Indexed: 12/20/2022]
Abstract
PURPOSE To report a detailed surgical procedure of tissue engineered endothelial keratoplasty (TEEK) in a rabbit model and its postoperative evaluation. METHODS TEEKs were prepared 7 days before transplantation by seeding human or rabbit corneal endothelial cells on either femtosecond laser-cut ultrathin human stromal lamellae (fs-UTSL) or femtosecond laser-cut human anterior lens capsule (fs-HALC). Thirty transplantations were performed on aphakic eyes. Recombinant tissue plasminogen activator (rTPA) was used throughout the surgery. The native endothelium was removed by full-surface scraping and central descemetorhexis. The transplantation was performed as a human Descemet's membrane endothelial keratoplasty. Controls included Descemetorhexis only and transplantation of carrier alone. Postoperative follow-up was performed by slit lamp and optical coherence tomography, followed by histology. RESULTS Controls remained oedematous. No fibrin occurred during surgery. All but three TEEKs adhered immediately. One/6 fs-UTSL and 9/16 fs-HALC cleared perfectly (p = 0.161). All failures could be explained by at least one of the following causes intraoperative bleeding, vitreous prolapsus, early partial detachment, postoperative irido corneal synechiea/angle closure. Presumed immune rejection was observed in three rabbits only after 4 weeks. Immunostaining with anti-human CD166 allowed to perfectly differentiate human cells from rabbit cells. In successful TEEK at 3 or 4 weeks, human cells formed a normal endothelium and started migrating outside the carrier. CONCLUSION Though the transplantation of a TEEK in rabbits is a complex model with many causes of failure, established procedure including use of rTPA allows reliable preclinical study. In addition, we suggest that fs-HALC might be a potential carrier for TEEK.
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Affiliation(s)
- Emmanuel Crouzet
- Corneal Graft Biology, Engineering and Imaging Laboratory BiiGC, EA2521 Health & innovation campus Faculty of Medicine Jean Monnet University Saint‐Etienne France
| | - Zhiguo He
- Corneal Graft Biology, Engineering and Imaging Laboratory BiiGC, EA2521 Health & innovation campus Faculty of Medicine Jean Monnet University Saint‐Etienne France
| | - Olfa Ben Moussa
- Corneal Graft Biology, Engineering and Imaging Laboratory BiiGC, EA2521 Health & innovation campus Faculty of Medicine Jean Monnet University Saint‐Etienne France
| | - Marielle Mentek
- Corneal Graft Biology, Engineering and Imaging Laboratory BiiGC, EA2521 Health & innovation campus Faculty of Medicine Jean Monnet University Saint‐Etienne France
| | | | - Benjamin Peyret
- Corneal Graft Biology, Engineering and Imaging Laboratory BiiGC, EA2521 Health & innovation campus Faculty of Medicine Jean Monnet University Saint‐Etienne France
| | - Fabien Forest
- Corneal Graft Biology, Engineering and Imaging Laboratory BiiGC, EA2521 Health & innovation campus Faculty of Medicine Jean Monnet University Saint‐Etienne France
- Pathology Department University Hospital Saint‐Etienne France
| | - Philippe Gain
- Corneal Graft Biology, Engineering and Imaging Laboratory BiiGC, EA2521 Health & innovation campus Faculty of Medicine Jean Monnet University Saint‐Etienne France
- Ophthalmology Department University Hospital Saint‐Etienne France
| | - Noriko Koizumi
- Department of Biomedical Engineering Faculty of Life and Medical Sciences Doshisha University Kyotanabe Japan
| | - Naoki Okumura
- Department of Biomedical Engineering Faculty of Life and Medical Sciences Doshisha University Kyotanabe Japan
| | - Gilles Thuret
- Corneal Graft Biology, Engineering and Imaging Laboratory BiiGC, EA2521 Health & innovation campus Faculty of Medicine Jean Monnet University Saint‐Etienne France
- Ophthalmology Department University Hospital Saint‐Etienne France
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Varshney T, Goel S, Bafna RK, Sharma N. Rapid spontaneous resolution of corneal hydrops in post-CXL keratitis. BMJ Case Rep 2021; 14:e246141. [PMID: 34848420 PMCID: PMC8634271 DOI: 10.1136/bcr-2021-246141] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/04/2021] [Indexed: 11/04/2022] Open
Abstract
An 11-year-old boy presented with right eye post-Corneal Collagen Cross-Linking (CXL) keratitis, which was complicated by acute corneal hydrops (CH). Keratitis was managed by topical antibiotics, and CH was managed conservatively. Cornea was monitored with serial anterior segment optical coherence tomography (ASOCT) scans. Spontaneous resolution of CH usually takes 8-12 weeks, but in this case it completely resolved in 3 weeks. Rapid resolution of CH after post-CXL keratitis could be attributed to a thinner cornea, increased interlamellar cohesive strength between collagen fibrils of corneal stroma coupled with normal functioning endothelial pump.
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Affiliation(s)
- Toshit Varshney
- Dr Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, Delhi, India
| | - Siddhi Goel
- Dr Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, Delhi, India
| | - Rahul Kumar Bafna
- Dr Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, Delhi, India
| | - Namrata Sharma
- Dr Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, Delhi, India
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Morgan PB, Murphy PJ, Gifford KL, Gifford P, Golebiowski B, Johnson L, Makrynioti D, Moezzi AM, Moody K, Navascues-Cornago M, Schweizer H, Swiderska K, Young G, Willcox M. CLEAR - Effect of contact lens materials and designs on the anatomy and physiology of the eye. Cont Lens Anterior Eye 2021; 44:192-219. [PMID: 33775377 DOI: 10.1016/j.clae.2021.02.006] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Accepted: 02/01/2021] [Indexed: 12/19/2022]
Abstract
This paper outlines changes to the ocular surface caused by contact lenses and their degree of clinical significance. Substantial research and development to improve oxygen permeability of rigid and soft contact lenses has meant that in many countries the issues caused by hypoxia to the ocular surface have largely been negated. The ability of contact lenses to change the axial growth characteristics of the globe is being utilised to help reduce the myopia pandemic and several studies and meta-analyses have shown that wearing orthokeratology lenses or soft multifocal contact lenses can reduce axial length growth (and hence myopia). However, effects on blinking, ptosis, the function of Meibomian glands, fluorescein and lissamine green staining of the conjunctiva and cornea, production of lid-parallel conjunctival folds and lid wiper epitheliopathy have received less research attention. Contact lens wear produces a subclinical inflammatory response manifested by increases in the number of dendritiform cells in the conjunctiva, cornea and limbus. Papillary conjunctivitis is also a complication of all types of contact lenses. Changes to wear schedule (daily disposable from overnight wear) or lens materials (hydrogel from SiHy) can reduce papillary conjunctivitis, but the effect of such changes on dendritic cell migration needs further study. These changes may be associated with decreased comfort but confirmatory studies are needed. Contact lenses can affect the sensitivity of the ocular surface to mechanical stimulation, but whether these changes affect comfort requires further investigation. In conclusion, there have been changes to lens materials, design and wear schedules over the past 20+ years that have improved their safety and seen the development of lenses that can reduce the myopia development. However, several changes to the ocular surface still occur and warrant further research effort in order to optimise the lens wearing experience.
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Affiliation(s)
- Philip B Morgan
- Eurolens Research, Division of Pharmacy and Optometry, University of Manchester, UK.
| | - Paul J Murphy
- University of Waterloo, School of Optometry and Vision Science, Waterloo, Canada
| | - Kate L Gifford
- School of Optometry and Vision Science, Queensland University of Technology, Brisbane, Australia
| | - Paul Gifford
- School of Optometry and Vision Science, UNSW Sydney, Australia
| | | | - Leah Johnson
- CooperVision Specialty EyeCare, Gilbert, AZ, United States
| | - Dimitra Makrynioti
- School of Health Rehabilitation Sciences, University of Patras (Aigio), Greece
| | - Amir M Moezzi
- Centre for Ocular Research and Education, University of Waterloo, Canada
| | - Kurt Moody
- Johnson & Johnson Vision Care, Jacksonville, FL, United States
| | | | | | - Kasandra Swiderska
- Eurolens Research, Division of Pharmacy and Optometry, University of Manchester, UK
| | | | - Mark Willcox
- School of Optometry and Vision Science, UNSW Sydney, Australia
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Patel S, Tutchenko L. The refractive index of the human cornea: A review. Cont Lens Anterior Eye 2019; 42:575-580. [PMID: 31064697 DOI: 10.1016/j.clae.2019.04.018] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2018] [Revised: 04/14/2019] [Accepted: 04/30/2019] [Indexed: 10/26/2022]
Abstract
The refractive index of the cornea and overlying tear film are key factors affecting refraction and overall optical properties of the eye. A figure of 1.376 is often quoted for the refractive index of the human cornea over the visible spectrum. In the 19th century estimates for the average refractive index of the human cornea ranged from 1.335 to 1.4391. Over the last two decades data obtained from either ex or in vivo corneas (under local anaesthesia with or without stromal resection) by contact Abbé refractometry show the refractive index of the cornea changes along its' depth undulating from around 1.400 at the epithelium to 1.380 at Bowman's layer, a low of 1.369 in the mid stroma and 1.373 at the endothelium. The mean refractive index of harvested tear samples is 1.337 rising to 1.482 for the overlying lipid layer. Contemporary measurements obtained in vivo by non-invasive methods reveal the average, or equivalent, refractive index of the tear film-cornea complex along the antero-posterior direction ranges from 1.423 to 1.436. Over the last 200 years calculations, with respect to the optics of the human eye, were based on values for the refractive index of the cornea obtained from invasive techniques. The refractive index of the cornea and overlying tear film appears to be higher than previously accepted and varies from case to case.
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Affiliation(s)
- Sudi Patel
- NHS National Services Scotland, Edinburgh, United Kingdom.
| | - Larysa Tutchenko
- Department of Ophthalmology, Shupyk National Medical Academy of Postgraduate Education, Kyiv, Ukraine; Kyiv City Clinical Ophthalmological Hospital "Eye Microsurgical Center", Kyiv, Ukraine
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Optical Coherence Tomography Assessment of the Cornea During Corneal Swelling: Should the Term "Descemet Membrane Folds" Be Reconsidered? Cornea 2019; 38:754-757. [PMID: 30844840 DOI: 10.1097/ico.0000000000001908] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
PURPOSE Previous work has suggested that Descemet membrane (DM) folds arise in response to corneal swelling. However, their origin has not been closely explored. In this study, we used optical coherence tomography to evaluate whether DM folds arise secondary to folds in the middle stroma. METHODS Serial optical coherence tomography images of donor cornea pairs in deionized water were taken for each of the following corneal manipulations: 1) untreated, 2) DM and the endothelium removed, 3) excised in the region of the deep middle/posterior stroma, and 4) excised in the middle stroma. RESULTS For intact corneas, increasing duration in deionized water was marked by a progressive increase in corneal thickness and number of folds along the posterior surface. With DM and the endothelium removed, a similar phenomenon was observed. In the third set of corneas, the plane of resection created a structural separation in the region of the deep middle/posterior stroma. Folds were seen originating anterior to the resection plane. For corneas with the posterior and part of the middle stroma removed, the typical folds on the posterior surface as seen in the previous conditions were not observed. Instead, less numerous and smaller irregularities of the posterior surface of the resection plane were present. CONCLUSIONS Folds in DM associated with corneal edema originate in the middle and posterior stroma and are secondarily transmitted into DM. On the basis of the stromal origin of these anatomic changes, "stromal folds" should be considered a more accurate term to replace "Descemet membrane folds."
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Assessment of modifications in thickness, curvatures, and volume upon the cornea caused by disposable soft contact lens wear. Eur J Ophthalmol 2015; 25:385-90. [PMID: 25790813 DOI: 10.5301/ejo.5000592] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/13/2015] [Indexed: 11/20/2022]
Abstract
PURPOSE To assess the effect of different disposable soft contact lenses on several corneal parameters-thickness, anterior and posterior curvature, and volume-by means of a Scheimpflug imaging-based device (Pentacam HR). Diurnal variations of these parameters were taken into account. METHODS Twenty-one young, healthy subjects wore 4 different types of daily disposable soft contact lenses on 4 different days: Dailies AquaComfort Plus, SofLens, Dailies Total1, and Acuvue TruEye. The lenses had different material and water content. Pachymetry and curvature maps and corneal volume values were obtained using the Pentacam HR twice a day: one before putting the lens on and one after an 8-hour period of contact lens wear. Measurements were also taken without any contact lenses being worn. RESULTS Regarding corneal thickness, the lens with the most similar behavior to the naked eye scenario was the Dailies Total1, causing a thickening of 0.2 ± 0.1% in the central zone and 0.6 ± 0.2% in the periphery. All 4 lenses caused a slight but not significant flattening in the anterior corneal curvature, whereas the posterior corneal curvature only experienced a significant but small steepening with the SofLens. The use of these lenses increased corneal volume slightly. CONCLUSIONS Variations in corneal parameters seem to depend on the type of contact lens used (material, oxygen transmissibility, water content). However, the magnitude of the changes introduced by the use of soft contact lenses over the 8-hour period was small and probably not large enough to influence either visual acuity or comfort.
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Abstract
PURPOSE To compare an objective (VCH-1) with a manual subjective Abbé refractometer (MSAR) and evaluate the refractive index (RI)-hydration (H) relationship for the corneal stroma. METHODS Epithelial and endothelial layers were removed from a fresh postmortem ovine corneal buttons. RI was measured at both surfaces using (i) MSAR then (ii) VCH-1. The sample was weighed, slowly dehydrated under controlled conditions (2 h), and RI measures were repeated. Sample was oven dried (90°C) for 3 d to obtain dry weight and hydration at each episode of RI measurement. RESULTS Average difference between individual pairs of measurements obtained using the two refractometers (ΔRI) was 0.00071 (standard deviation ± 0.0029, 95% confidence interval ± 0.0058). Root mean square difference between measurements obtained by the refractometers was 0.0024. There was no relationship between ΔRI and the mean of each measurement pair (r = 0.201, n = 40, p = 0.214). Linear regression revealed a significant relationship between RI and reciprocal of H at both surfaces as follows: anterior (i) RI = 1.355 + 0.111/H (r = -0.852, n = 20, p = <0.001), (ii) RI = 1.357 + 0.105/H (r = -0.849, n = 20, p = <0.001) and posterior (i) RI = 1.353 + 0.085/H (r = -0.882, n = 20, p = <0.001), (ii) RI = 1.350 + 0.088/H (r = -0.813, n = 20, p = <0.001). CONCLUSIONS VCH-1 measurements are in good agreement with MSAR. RI at the anterior stroma was consistently higher suggesting hydration is lower by 1.10 units (6%) compared with the posterior stroma. Dehydration increased RI at both surfaces by similar rates. Current hypothetical models are useful for predicting RI from H for the posterior, but not the anterior, stroma.
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Olszewski J, Marzec E, Kulza M, Samborski W. Implications of the alpha dispersion for studies on interaction of tobacco smoke--corneal tissue. Colloids Surf B Biointerfaces 2012; 90:109-12. [PMID: 22037475 DOI: 10.1016/j.colsurfb.2011.10.007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2011] [Accepted: 10/05/2011] [Indexed: 12/11/2022]
Abstract
In this work, we have carried out a dielectric study to determine the effect of tobacco smoke on the rat corneal function. Measurements were performed over the frequency range of 500 Hz-100 kHz in air and at the temperature of 35°C. The frequency dependencies of the loss tangent for both healthy and smoky cornea exhibit two peaks with different width occurring as a narrow at 2 kHz and a broad at around 16 kHz. The distribution parameter α at 2 kHz has a value of about 0.3, which increases to 0.6 at 16 kHz. The magnitude of the permittivity decrement at 2 and 16 kHz is about two and four times higher, respectively, for the smoky cornea than that for the healthy one. These dielectric studies indicate that the present method is useful in detection of the effect of tobacco smoke exposure on the corneal behavior.
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Affiliation(s)
- J Olszewski
- Department of Bionics and Bioimpedance, Poznań University of Medical Sciences, Poznań, Poland
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Henriksson JT, Bron AJ, Bergmanson JP. An explanation for the central to peripheral thickness variation in the mouse cornea. Clin Exp Ophthalmol 2011; 40:174-81. [PMID: 21745264 DOI: 10.1111/j.1442-9071.2011.02652.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
BACKGROUND The mouse corneal stroma varies in thickness across its diameter. The purpose of the present study was to explain this variation and to advance our understanding of stromal lamellar architecture in the mammalian cornea. METHODS Eight C57BL/6 mice were killed, eyes enucleated, immersed in 2% glutaraldehyde fixative, processed and sectioned transversely for light and transmission electron microscopy. Transmission electron micrographs were assembled into montages and printed at 5000× magnification and used for lamellar counts and thickness assessments. RESULTS The mouse cornea had an average of 49.8±2.4 lamellae centrally averaging 2.1µm in thickness versus 35.5±3.0 lamellae, averaging 1.9µm in thickness peripherally. The central to peripheral decrease in number lamellae and lamellar thickness measured utilizing the transmission electron microscope was statistically significant (P<0.005). CONCLUSIONS This study demonstrated that the thickness difference between the thicker central and thinner peripheral mouse cornea is explained primarily by the number of lamellae present and that the peripheral lamellar dropout occurred in the anterior 2/3 of stroma. The decreased lamellar count towards the periphery suggested that not all lamellae cross the cornea limbus to limbus. These findings may be relevant to the thickness variation of the human cornea.
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Affiliation(s)
- Johanna Tukler Henriksson
- Texas Eye Research and Technology Center, University of Houston College of Optometry, Houston, Texas 770204-2020, USA
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Kwon RO, Price MO, Price FW, Ambrósio R, Belin MW. Pentacam Characterization of Corneas with Fuchs Dystrophy Treated with Descemet Membrane Endothelial Keratoplasty. J Refract Surg 2010; 26:972-9. [DOI: 10.3928/1081597x-20100212-08] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2009] [Accepted: 12/09/2009] [Indexed: 11/20/2022]
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Martin R, Izquierdo M, Saber A. Investigation of posterior corneal curvature in CL-induced corneal swelling. Cont Lens Anterior Eye 2009; 32:288-93. [PMID: 19592292 DOI: 10.1016/j.clae.2009.06.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2008] [Revised: 06/07/2009] [Accepted: 06/11/2009] [Indexed: 11/26/2022]
Abstract
PURPOSE To evaluate Orbscan II measurements without contact lens (CL) removal to monitor in vivo posterior corneal curvature in CL (hypoxia)-induced corneal swelling during extended wear (EW). METHODS Orbscan II corneal topographer was used to measure posterior corneal curvature 1 week before CL wearing and during 1 week of EW. Central corneal thickness (CCT) was also measured during the 2-week study with OCT to determine the corneal swelling percentage. High Dk (lotrafilcon A) and low Dk (etafilcon A) soft CL were randomly fitted in EW in the right and left eyes of 20 subjects with normal ocular health. Orbscan and OCT were also performed without CL removal after 3 and 7 days of wear. RESULTS Low Dk lenses induced significantly higher corneal swelling (2.41+/-2.65%), as compared to the high Dk lenses (0.17+/-2.28%; P<0.05 repeated measures ANOVA (Re-ANOVA and paired t-test) measures with OCT. The low Dk lens induced a significantly posterior corneal flattening compared to the high Dk lens (0.036+/-0.06mm versus 0.006+/-0.04mm; P<0.05 Re-ANOVA and paired t-test). High repeatability for Orbscan-measured posterior best fit sphere (BFS) radii with (r(2)=0.15, 95% limits of agreement (LoA)=0.10 to -0.06) and without (r(2)=0.00, 95% LoA=0.08 to -0.08) CL removal was also observed and suggest that posterior corneal changes was not due to Orbscan variability. CONCLUSIONS Orbscan is a non-invasive and reproducible technique to evaluate and monitoring posterior corneal curvature in vivo in CL (hypoxia)-induced corneal swelling during EW.
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Affiliation(s)
- Raul Martin
- IOBA-Eye Institute and School of Optometry, Department of Physics and Optics, University of Valladolid, Camino del Cementerio s/n E-47011 Valladolid, Spain.
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Abstract
PURPOSE Given the refractive importance of the human cornea, surprisingly little attention has been directed to the study of local variation in corneal refractive-index. This in vitro and in vivo study measures the refractive-index of different portions of the bovine and human cornea. METHODS Fifty fresh bovine corneas (obtained from an abattoir) and 10 human subjects were used for the study. The refractive-index of the central, nasal, and temporal corneal epithelium was measured with a bench-top Abbe refractometer in the case of bovine corneas and with a hand-held refractometer with humans. RESULTS The mean (+/-standard deviation) refractive-indices of the central, nasal, and temporal bovine corneal epithelium were 1.3760 (+/-0.003), 1.3757 (+/-0.002), and 1.3746 (+/-0.002), respectively. Refractive-indices of the anterior and posterior bovine corneal stroma were 1.3731 (+/-0.002) and 1.3708 (+/-0.004), respectively. The mean (+/-standard deviation) refractive-index in the central, nasal, and temporal periphery of the human cornea epithelium were 1.3970 (+/-0.001), 1.3946 (+/-0.001), and 1.3940 (+/-0.001), respectively. CONCLUSION There are small local differences in the refractive-index of the bovine and human corneal epithelium and the refractive-index of the epithelium is higher than that of the anterior and posterior stroma of the bovine cornea.
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Akhtar S, Bron AJ, Salvi SM, Hawksworth NR, Tuft SJ, Meek KM. Ultrastructural analysis of collagen fibrils and proteoglycans in keratoconus. Acta Ophthalmol 2008; 86:764-72. [PMID: 18422999 DOI: 10.1111/j.1755-3768.2007.01142.x] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
PURPOSE To investigate ultrastructural alterations in the distribution of collagen fibrils (CFs) and proteoglycans (PGs) in the keratoconus cornea. METHODS Four normal corneas (donor age 24-75 years) and four severe and one mild keratoconus corneas (donor age 24-47 years) were fixed in 2.5% glutaraldehyde containing 0.05% cuprolinic blue dye for electron microscopy. Analyses were carried out on approximately 39 000 CF and 66 000 PG filaments in the anterior, middle and posterior stroma, using analySIS soft imaging software. RESULTS In severe keratoconus, stromal lamellae were seen to undulate in most regions, whereas in mild keratoconus only the middle and posterior lamellae were affected. In keratoconus corneas the mean diameter and interfibrillar spacing of CFs was reduced in all zones (p < 0.0001) and the CF and PG number density and area fractions were significantly increased (p < 0.0001) compared with in normal corneas and were higher (p < 0.0001) in the corneas with severe keratoconus than in that with mild keratoconus. The lamellae contained microfibrils (8-9 nm wide) and, in addition, PGs embedded within CFs. Degenerate keratocytes containing PGs were found in all keratoconus corneas. CONCLUSIONS These studies suggest that as keratoconus progresses, the PG content of the stroma increases, whereas fibril diameter is reduced. The altered stromal content of PGs may influence CF diameters and their organization in keratoconus, weakening lateral cohesion and resulting in significant disorder of CF packing.
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Affiliation(s)
- Saeed Akhtar
- School of Optometry and Vision Sciences, Cardiff University, Cardiff, UK.
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Patel S, Alió JL, Javaloy J, Perez-Santonja JJ, Artola A, Rodriguez-Prats J. Human Cornea Before and After Refractive Surgery Using a New Device: VCH-1. Cornea 2008; 27:1042-9. [DOI: 10.1097/ico.0b013e318172fc40] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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Mergler S, Pleyer U. The human corneal endothelium: new insights into electrophysiology and ion channels. Prog Retin Eye Res 2007; 26:359-78. [PMID: 17446115 DOI: 10.1016/j.preteyeres.2007.02.001] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The corneal endothelium is a monolayer that mediates the flux of solutes and water across the posterior corneal surface. Thereby, it plays an essential role to maintain the transparency of the cornea. Unlike the epithelium, the human endothelium is an amitotic cell layer with a critical cell density and the risk of corneal decompensation. The number of endothelial cells subsequently decreases with age. Moreover, the endothelial cell loss is accelerated after various impairments such as surgical trauma (e.g. cataract extraction) and following corneal transplantation. This cell loss is associated with programmed cell death (apoptosis) and changed ion channel activity. However, little is known about the electrophysiology and ion channel expression (in particular Ca2+ channels) in corneal endothelial cells. This article reviews our current knowledge about the electrophysiology of the corneal endothelium. It highlights ion channel expression, which may have a major role in corneal cell physiology and pathological events. A better understanding of the (electro)physiological function of the cornea may lead to the development of clinical relevant new therapeutic and preventive measures.
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Affiliation(s)
- Stefan Mergler
- Department of Ophthalmology, Charité-University Medicine Berlin, Campus Virchow-Clinic, Augustenburger Platz 1, 13353 Berlin, Germany.
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Suwan-Apichon O, Reyes JMG, Griffin NB, Barker J, Gore P, Chuck RS. Microkeratome versus femtosecond laser predissection of corneal grafts for anterior and posterior lamellar keratoplasty. Cornea 2006; 25:966-8. [PMID: 17102676 DOI: 10.1097/01.ico.0000226360.34301.29] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
PURPOSE To compare 2 different techniques for predissection of human anterior and posterior lamellar corneal grafts for eye bank storage. METHODS A mechanical microkeratome (group 1, N = 5) and a femtosecond laser (group 2, N = 5) were used to dissect intended 350-microm-deep lamellar planes in deepithelialized donor corneas mounted on an artificial anterior chamber. These corneas were replaced in Optisol GS at 4 degrees C postoperatively and examined 2 days later to simulate a clinical scenario. Ultrasonic pachymetry of corneal lamellar sections was measured before and after separation of the lamellar grafts. Group 1 sections were separated by the mechanical microkeratome, whereas group 2 sections were manually separated 2 days after laser dissection. Endothelial cell viability was evaluated in posterior grafts. RESULTS Total corneal thicknesses immediately before dissection were 559 +/- 61 (group 1) and 578 +/- 79 microm (group 2; P = 0.46). Immediate postdissection anterior and posterior graft thicknesses were 361 +/- 68 and 203 +/- 74 microm (group 1), respectively. Achieved anterior and posterior graft thicknesses 2 days later were 282 +/- 44 and 413 +/- 35 microm (group 1) and 324 +/- 112 and 397 +/- 51 microm (group 2), respectively. Percentage of devitalized endothelial cells were 3.4% +/- 1.6% (group 1) and 1.6% +/- 1.2% (group 2; P = 0.35). CONCLUSIONS Centralized predissection by both techniques, cold storage, and shipping by airmail results in viable grafts without significant endothelial cell loss 2 days later.
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Affiliation(s)
- Olan Suwan-Apichon
- Wilmer Ophthalmological Institute, Johns Hopkins University, Baltimore, MD 21287-9278, USA
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Suwan-Apichon O, Reyes JMG, Griffin NB, Barker J, Gore P, Chuck RS. Microkeratome Preparation of Lamellar Corneal Grafts. Eye Contact Lens 2006; 32:248-9. [PMID: 16974159 DOI: 10.1097/01.icl.0000219364.21999.e4] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
PURPOSE To evaluate the thickness and viability of microkeratome-prepared lamellar corneal grafts in cold storage. METHODS Ten human corneas were sectioned with a mechanical microkeratome with a 350-microm depth head and stored in Optisol GS at 4 degrees C for 2 days to simulate an eye bank scenario. Central corneal thickness before and after mechanical microkeratome sectioning was measured by ultrasonic pachymetry. Endothelial cell viability was evaluated by trypan blue and alizarin red staining. RESULTS Total corneal thickness immediately before microkeratome dissection was 562 +/- 51 microm. Anterior and posterior graft thicknesses were 296 +/- 111 microm and 270 +/- 74 microm, respectively, immediately after dissection, and 282 +/- 38 microm and 429 +/- 31 microm, respectively, 2 days after storage. There was significant swelling in the posterior (P=0.005) but not the anterior grafts (P=0.386). The percentage of devitalized endothelial cells was 3.0% +/- 1.2%. CONCLUSIONS Corneal lamellar grafts may possibly be precut in a centralized facility and stored cold before further distribution.
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Affiliation(s)
- Olan Suwan-Apichon
- Wilmer Ophthalmological Institute, Johns Hopkins University, Baltimore, MD 21287-9278, USA
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19
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Lu F, Simpson T, Fonn D, Sorbara L, Jones L. Validity of Pachymetric Measurements by Manipulating the Acoustic Factor of Orbscan II. Eye Contact Lens 2006; 32:78-83. [PMID: 16538128 DOI: 10.1097/01.icl.0000174760.95482.9c] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
PURPOSE To assess the validity of pachymetric measurements by examining the constancy of the acoustic factor (AF) of the Orbscan II (Orbtek, Bausch & Lomb, Rochester, NY) after overnight rigid gas-permeable (RGP) contact lens wear. METHODS Twenty participants wore CRT (Paragon Vision Sciences, Mesa, AZ) HDS 100 contact lenses on one eye and control lenses on the contralateral eye for one night while sleeping. Another 24 participants wore CRT lenses on both eyes for one night. Central corneal thickness was measured using optical coherence tomography and Orbscan II on the night before lens use, immediately after lens removal on the following morning, and 1, 3, 6, and 12 hours later. By using optical coherence tomography as a reference, the adjusted AF was calculated by using a least squares method over time. RESULTS The adjusted AF depended on the corneal thickness in normally hydrated corneas. The adjusted AF and the percentage change of the adjusted AF varied before and after overnight lens wear. There was a strong and significant correlation between the corneal swelling and the percentage change of the adjusted AF (all r at least 0.91, P<0.05). CONCLUSIONS The adjusted AF is a variable, not a constant. The AF is a function of the corneal thickness and its alteration with, for example, corneal swelling. The validity of the adjusted Orbscan II pachymetric measures using a single AF is untenable.
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Affiliation(s)
- Fenghe Lu
- Centre for Contact Lens Research, School of Optometry, University of Waterloo, Canada
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20
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Patel S, Illahi W, Davies A. Changes in water content of high plus hydrogel lenses worn on an extended wear basis in a geriatric aphakic population. Cont Lens Anterior Eye 2005; 28:127-34. [PMID: 16318843 DOI: 10.1016/j.clae.2005.06.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
PURPOSE To investigate the water content of hydrogel lenses of relatively high plus power hydrogel lenses after 3 months extended wear and compare values with unused lenses. METHOD Geriatric aphakic extended wear soft lens patients were fitted with one of four different brands of hydrogel lenses (A) Incanto 78 (Cantor and Nissel, UK), (B) PSL72 (Prospect lenses, UK), (C) ES70 (Ocular Sciences), (D) Proclear (Coopervision). After 3 months continuous wear the lens was removed and water content (WC) was determined at both lens surfaces using an Abbé refractometer. The water content was also measured for 40 unused lenses (+10 to +20D, 10 lenses per brand). RESULTS One hundred and thirty-two lenses were checked after 3 months extended wear. Mean (+/-S.D.) WC values for front (f) and back (b) surfaces of worn and unworn lenses were, respectively, (A) Worn (n=45): f 73.2(4.13) b 73.8(4.33); unworn f 80.5(0.68) b 81.1 (0.80). (B) Worn (n=37); f 70.5(4.49) b 70.9 (3.89); unworn f 72.5(0.94) b 72.3 (0.89). (C) Worn (n=34); f 68.3(3.18) b 68.4(3.63); unworn f 70.6 (0.48) b 71.1 (0.55). (D) Worn (n=16); f 63.4(3.68) b 63.3(3.19); unworn f 60.9 (1.56) b 61.5 (1.92). There was a significant correlation between WC measured from front and back surfaces (p < 0.01). In worn A-C lenses, front surface WC tended to be lower than back surface WC. For lenses A and C at both surfaces the WC of worn lenses was significantly lower than unworn lenses (p < 0.05). For lens D, mean WC of worn lenses was significantly higher than unworn lenses (p < 0.05). In 80% of B lenses, surface WC of worn lenses were significantly lower than WC of unworn lenses (p < 0.05). There was no relationship between WC and lens power. CONCLUSION On average, A and C lenses tended to desiccate but D lenses tended to swell as did 20% of B lenses. The front surface of worn lenses measured lower water content than the back surface suggesting the front surface is drier than the back. This apparent difference in water content between the surfaces could be an artefact emanating from differential rates of surface deposition.
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Affiliation(s)
- Sudi Patel
- Vissum/Instituto Oftalmológico de Alicante, Avda de Denia s/n, Edificio Vissum, 03016 Alicante, Spain.
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21
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Moezzi AM, Fonn D, Simpson TL, Sorbara L. Contact Lens-Induced Corneal Swelling and Surface Changes Measured with the Orbscan II Corneal Topographer. Optom Vis Sci 2004; 81:189-93. [PMID: 15017178 DOI: 10.1097/00006324-200403000-00011] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
PURPOSE The purpose of this study was to measure central and topographical corneal swelling in response to contact lens wear and eye closure, to determine whether the swelling induced by soft and polymethyl methacrylate (PMMA) lenses is different, and to determine whether the anterior and/or posterior corneal shape alters with corneal swelling. METHODS An Orbscan II corneal topographer was used to measure corneal swelling and the shape of the anterior and posterior corneal surfaces of 16 neophytes before and after wearing soft and PMMA contact lenses with near-zero oxygen transmissibility. The lens-wearing eye was patched for 3 h. RESULTS The mean 15.1% +/- 3.8% (+/- SD) central corneal swelling with soft lenses was significantly >12.6% +/- 4.1% with PMMA lenses. Topographical corneal swelling was significantly greater with soft vs. PMMA lenses. However, the difference between central and peripheral corneal swelling was much greater with PMMA lenses. With both lenses, the cornea swelled significantly more in the center than the periphery. The anterior best-fit sphere radius remained unchanged in response to soft lenses (0.00 +/- 0.04 mm) and steepened slightly but significantly with PMMA lenses (-0.04 +/- 0.05 mm). The posterior best-fit sphere radius flattened significantly with both lenses (0.12 +/- 0.07 mm with soft and 0.14 +/- 0.08 mm with PMMA lenses). CONCLUSIONS Corneal swelling (greater centrally than peripherally) flattens the posterior surface of the cornea and is independent of lens type. Although the anterior best-fit sphere radius steepened with PMMA, the magnitude is probably clinically unimportant. Both lens types produced greater central vs. peripheral corneal swelling. However, the soft lens induced significantly greater overall swelling than PMMA. Because their oxygen transmission was the same, these results suggest that there is lateral diffusion of oxygen from the peripheral area of the cornea (that is not covered by the lens) toward the center.
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Affiliation(s)
- Amir M Moezzi
- Centre for Contact Lens Research, School of Optometry, University of Waterloo, Waterloo, Ontario, Canada
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22
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González-Méijome JM, González-Pérez J, Cerviño A, Yebra-Pimentel E, Parafita MA. Changes in corneal structure with continuous wear of high-Dk soft contact lenses: a pilot study. Optom Vis Sci 2003; 80:440-6. [PMID: 12808404 DOI: 10.1097/00006324-200306000-00010] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
PURPOSE Despite numerous studies that have considered the effects of extended wear of high-Dk soft contact lenses on ocular physiology, little attention has been paid to the impact of such lenses on central or peripheral corneal thickness and curvature. The present study aims to report the time course of changes in corneal thickness and curvature that accompanies the 30-night continuous wear of new silicone hydrogel soft contact lenses in a neophyte population in a longitudinal study. METHODS Six subjects wore high-Dk lotrafilcon (Dk = 140) on a 30-night replacement schedule for 12 months. Only measurements from the right eye were considered for analysis. Topographical measurements of corneal thickness and curvature were taken. The same parameters were monitored for an additional period of 3 months after lens removal. RESULTS An almost homogenous increase in corneal radius of curvature was detected for all the locations studied, being statistically significant for the 4-mm cord diameter area. This effect was associated with a progressive thinning effect for the central cornea, whereas midperipheral and peripheral areas did not display such a thinning effect during continuous wear. These effects were still evident for the central cornea 3 months after contact lens wear discontinuation. CONCLUSIONS Continuous wear of high-Dk silicone hydrogel contact lenses is associated with clinically appreciable changes in topographical corneal curvature, whereas only a reduction in corneal thickness is appreciated in the central area. This effect seems to be a result of mechanical pressure induced by these hybrid hyperpermeable materials, characterized by a higher modulus of elasticity. The small sample size compromises the conclusions addressed from this study, and further work will be necessary to confirm the present results.
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Affiliation(s)
- J M González-Méijome
- Department of Physics (Optometry), School of Sciences, University of Minho, Braga, Portugal
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Marchant JK, Zhang G, Birk DE. Association of type XII collagen with regions of increased stability and keratocyte density in the cornea. Exp Eye Res 2002; 75:683-94. [PMID: 12470970 DOI: 10.1006/exer.2002.2058] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The anterior avian cornea possesses several distinct cellular and extracellular regions including the epithelial basal lamina, Bowman's layer and the interfacial matrix that separates Bowman's layer from the stroma. These unique regions differ biochemically, physically and morphologically but all contain type XII collagen. Previously, the collagen fibrils of several of these interfacial regions were shown to be stable to thermal and enzymatic denaturation. We reasoned that type XII collagen, a fibril-associated collagen, would be a good candidate to confer such stabilizing properties. The studies described herein were performed to localize type XII collagen and to assess its role in the interfacial matrices (IM). Using antibodies that react with both the short and long type XII collagen isoforms and that react specifically with the long isoform, we demonstrate that it is the short isoform that is present in Bowman's layer and the associated interfacial matrix lying between Bowman's and the stroma proper. In situ hybridization analyses demonstrate that both the epithelial and endothelial cells synthesize type XII collagen. In vitro cell culture analyses, however, demonstrate that in addition to epithelial cell synthesis, the stromal fibroblasts are capable of synthesizing type XII collagen as well. Immunofluorescence analyses performed at elevated temperature demonstrate that type XII collagen is thermally stable in Bowman's layer, but not in the anterior interfacial matrix or Descemet's layer. In addition, we observed that the distribution of type XII collagen during the development of the anterior extracellular matrices correlates precisely with an elevated density of keratocytes populating the interfacial matrix just deep to Bowman's layer. We show that this cellular density is developmentally regulated and does not arise from a localized increase in cell proliferation. These data demonstrate that Bowman's layer and the anterior interfacial matrix have unique biochemical and morphologic properties. Type XII collagen is thermally stable in Bowman's layer and, as a surface component of type I collagen fibrils, may contribute to the stability of the fibrils in this region. Neither type XII nor type I collagen is stable in the adjacent interfacial matrix, suggesting that differences in the type I-XII collagen fibril organization may exist between Bowman's layer and IM.
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Affiliation(s)
- Jeffrey K Marchant
- Department of Anatomy and Cellular Biology, Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111, USA.
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Müller LJ, Pels E, Vrensen GF. The effects of organ-culture on the density of keratocytes and collagen fibers in human corneas. Cornea 2001; 20:86-95. [PMID: 11189011 DOI: 10.1097/00003226-200101000-00017] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
PURPOSE Keratocytes are important in regaining corneal transparency during wound healing after surgery or trauma. Hitherto, there are still controversies concerning the effects of organ culture on the density and integrity of keratocytes and collagen fibers. The current study aimed at a systematic analysis of the effects of organ-culture on the morphology and density of keratocytes and collagen fibers. METHODS Human corneas were organ-cultured in MEM for 7 (n = 17, 3 pairs), 14 (n = 18, 9 pairs) and 21 days (n = 18, 9 pairs). Of the pairs one cornea was processed in swollen condition and the fellow cornea after reversal of swelling in MEM plus Dextran. Eleven post-mortem corneas (PM) and 11 fresh corneas obtained from melanoma patients were used as controls. Stromal thickness, number of keratocyte profiles (corrected for swelling), number and diameter of collagen fibers were measured in light microscopical sections and electron micrographs. RESULTS Stromal swelling due to organ-culture resulted in large keratocyte profiles with many vacuoles and large distances between collagen fibers in the posterior stroma. In contrast both keratocytes and distances between collagen fibers were not affected in the anterior stroma. After reversed-swelling the posterior corneal stroma was similar to that in fresh controls, indicating that the swelling process is largely reversible. The initial decrease in keratocyte density (18%) in the early post-mortem period did not progress during 21 days of organ culture. CONCLUSION With respect to the morphology and density of keratocytes and collagen fibers it can be concluded that donor corneas remain suitable for transplantation up to at least 21 days after organ-culture.
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Affiliation(s)
- L J Müller
- Department of Morphology, Netherlands Ophthalmic Research Institute, Amsterdam
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Melles GR, Lander F, van Dooren BT, Pels E, Beekhuis WH. Preliminary clinical results of posterior lamellar keratoplasty through a sclerocorneal pocket incision. Ophthalmology 2000; 107:1850-6; discussion 1857. [PMID: 11013184 DOI: 10.1016/s0161-6420(00)00253-0] [Citation(s) in RCA: 164] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022] Open
Abstract
PURPOSE To report the preliminary results of a surgical technique for transplantation of posterior corneal tissue through a sclerocorneal pocket incision for corneal endothelial disorders. DESIGN Retrospective, noncomparative, interventional cases series. PARTICIPANTS AND INTERVENTION In seven sighted human eyes, a deep stromal pocket was created across the cornea through a 9.0-mm superior scleral incision. A 7.0- or 7.5-mm diameter, posterior lamellar disc was excised and replaced by a 'same size' donor posterior disc, without suture fixation. The scleral incision was sutured. MAIN OUTCOME MEASURES Intra- and postoperative complications, best spectacle-corrected visual acuity, keratometry, topography, biomicroscopy, pachymetry, and endothelial cell density were evaluated. RESULTS Six to 12 months after surgery, all transplants were clear and in position. Best spectacle-corrected visual acuity was limited by preexisting maculopathies in two eyes and varied from 20/80 to 20/20. Postoperative astigmatism averaged 1. 54 diopters (D; standard deviation [SD] +/- 0.81 D), pachymetry averaged 0.49 mm (SD +/- 0.09 mm), and postoperative endothelial cell density averaged 2520 cells/mm(2) (SD +/- 340 cells/mm(2)). In one eye, a microperforation occurred during stromal pocket dissection so that the procedure was converted into a penetrating keratoplasty. CONCLUSIONS Posterior lamellar keratoplasty through a sclerocorneal pocket incision is a feasible surgical approach to manage corneal endothelial disorders.
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Affiliation(s)
- G R Melles
- The Netherlands Institute for Innovative Ocular Surgery, Rotterdam, The Netherlands.
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Patel S, Alio JL, Perez-Santonja JJ. A Model to Explain the Difference Between Changes in Refraction and Central Ocular Surface Power After Laser in situ Keratomileusis. J Refract Surg 2000; 16:330-5. [PMID: 10832982 DOI: 10.3928/1081-597x-20000501-06] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE After refractive surgery, changes in central ocular surface power are usually less than actual changes in refraction. The aim of this paper was to examine the theoretical changes in the radius of the epithelial-stromal interface and corneal stromal refractive index which could take place to account for some of the empirical findings. METHODS The parameters of an aspheric human eye model featuring gradient index optics was modified using data from a clinical study evaluating effects of laser in situ keratomileusis (LASIK) for correction of moderate to high myopia. Computations were performed to determine: 1) theoretical postoperative radius of the epithelial-stromal interface and hence distribution of epithelial thickness, and 2) refractive index of the stroma when the epithelium was of fixed uniform thickness. RESULTS Within the central 2-mm diameter refractive zone of the cornea after LASIK for myopia, either of two factors could account for the difference between changes in central ocular surface power and the actual change in ocular refraction: 1) a steepening of the epithelial-stromal interface resulting from a 400% centrifugal increase in epithelial thickness, or 2) a reduction in stromal refractive index from an average of 1.376 to 1.364. CONCLUSION The difference between the observed changes in refraction and central ocular surface power could be explained by reduction in stromal refractive index and this could be secondary to a 6.5% increase in water content of the stroma during the postoperative period. The epithelial-stromal interface after LASIK is unlikely to steepen by the extent predicted by our model. This surface is not the source of the difference between the change in refraction and change in central ocular surface power.
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Affiliation(s)
- S Patel
- Refractive Surgery Section, Instituto Oftalmologico de Alicante, University Miguel Hernandez de Elche School of Medicine, Spain.
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Gong H, Johnson M, Ye W, Kamm RD, Freddo TF. The non-uniform distribution of albumin in human and bovine cornea. Exp Eye Res 1997; 65:747-56. [PMID: 9441698 DOI: 10.1006/exer.1997.0382] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
In our previous studies, we noted a non-uniform distribution of protein tracer preferentially entering the anterior stromal lamellae of the cornea from the limbus. Given other differences reported previously between the anterior and posterior lamellae of the cornea, and the number of corneal disorders in which abnormalities are preferentially confined to either the anterior or posterior lamellae, we were prompted to examine the distribution of albumin in normal human and bovine cornea. The distribution of albumin in bovine and human cornea was studied immunohistochemically. Total soluble protein and albumin in the anterior 1/3 and posterior 2/3 of the central, middle and peripheral cornea of bovine eyes was measured biochemically. To aid in interpreting the findings, a theoretical model was developed based upon the combined effects of diffusive and convective transport. Using immunohistochemical methods, in both bovine and human eyes, intense staining of albumin was found in the anterior 1/3 of the corneal stroma. There was a gradual reduction in staining intensity from the limbus to the central cornea in the anterior corneal stroma. Less staining was found in the posterior 2/3 of corneal stroma. Additionally, a greater concentration of soluble protein and albumin was found in the anterior stroma than in the posterior stroma of the bovine eyes by biochemical analyses. The theoretical model demonstrated that this distribution of protein required a difference in excluded volume fraction between the anterior and posterior stroma and was consistent with a convective flux originating at the limbus and passing through the corneal stroma. The soluble proteins of the bovine and human cornea are preferentially concentrated in the anterior cornea and near the limbus. This distribution is likely due to differences in excluded volume fraction between the anterior and posterior stroma and a small convective flux passing through the cornea.
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Affiliation(s)
- H Gong
- Department of Ophthalmology, Boston University School of Medicine, MA 02118, USA
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Roy P, Petroll WM, McKinney AE, Chuong CJ. Computational models of the effects of hydration on corneal biomechanics and the results of radial keratotomy. J Biomech Eng 1996; 118:255-8. [PMID: 8738793 DOI: 10.1115/1.2795969] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- P Roy
- Joint Program in Biomedical Engineering, University of Texas Southwestern Medical Center, Arlington, USA
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Abstract
BACKGROUND The refractive index of the cornea must be determined to optically perfect keratorefractive procedures. There are very few empirical measurements of the human corneal refractive index described in the literature. Throughout its depth, the cornea demonstrates regional variations in physiological properties such as swelling/de-swelling characteristics. These properties suggest there may be a difference in the refractive index between the anterior and posterior corneal surfaces. METHODS The refractive index of the human corneal epithelium of 10 eyes was measured, in vivo, using a modified hand-held refractometer. The refractive indices of the anterior and posterior surfaces of the bare stroma of fresh human corneas were measured using a bench model Abbe refractometer. RESULTS The mean refractive index of the epithelium, stromal anterior and posterior surfaces were 1.401 (SD +/- 0.005), 1.380 (SD +/- 0.005), and 1.373 (SD +/- 0.001) respectively. CONCLUSIONS The refractive index of the cornea is not uniform. The calculated dioptric power of the corneal epithelium is approximately -1.40 diopters (D). The varying refractive index does not significantly affect the total dioptric power of the cornea. The varying refractive index of the cornea has the potential to significantly contribute to the overall optical performance of the eye in relation to refractive surgery. The results should be incorporated into mathematical models, comparing and contrasting the optical performance of the eye before and after surgery.
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Affiliation(s)
- S Patel
- Department of Vision Sciences, Glasgow Caledonian University, Scotland, United Kingdom
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