April 2012
Volume 53, Issue 4
Free
Cornea  |   April 2012
Mapping the Corneal Sub-Basal Nerve Plexus in Orthokeratology Lens Wear Using in vivo Laser Scanning Confocal Microscopy
Author Notes
  • From the School of Optometry and Vision Science, University of New South Wales, Sydney, Australia. 
  • Corresponding author: Prof. Helen A. Swarbrick, School of Optometry and Vision Science, University of New South Wales, Sydney, NSW 2052, Australia; h.swarbrick@unsw.edu.au
Investigative Ophthalmology & Visual Science April 2012, Vol.53, 1803-1809. doi:10.1167/iovs.11-8706
  • Views
  • PDF
  • Share
  • Tools
    • Alerts
      ×
      This feature is available to authenticated users only.
      Sign In or Create an Account ×
    • Get Citation

      Edward Lum, Blanka Golebiowski, Helen A. Swarbrick; Mapping the Corneal Sub-Basal Nerve Plexus in Orthokeratology Lens Wear Using in vivo Laser Scanning Confocal Microscopy. Invest. Ophthalmol. Vis. Sci. 2012;53(4):1803-1809. doi: 10.1167/iovs.11-8706.

      Download citation file:


      © ARVO (1962-2015); The Authors (2016-present)

      ×
  • Supplements
Abstract

Purpose.: This study was designed to map the sub-basal nerve plexus (SBNP) in the cornea of orthokeratology (OK) lens wearers.

Methods.: Laser scanning confocal microscopy (LSCM) was performed in vivo on three subjects: a non–lens wearer and two OK lens wearers. Scans were performed on the right eye while the left eye fixated a moving target. A total of 575, 430, and 676 contiguous images of the SBNP were taken from the non–lens wearing and the OK lens wearing subjects, respectively, and used to construct maps of the central to mid-peripheral SBNP.

Results.: In the non–lens wearing eye, nerves radiated towards a whorl-like complex centered nasally and inferiorly in an overall pattern consistent with previously reported studies. In the OK lens wearing eyes, this whorl pattern was absent, replaced by a tortuous network of nerve fibers centrally, and thicker curvilinear fibers mid-peripherally, particularly in the nasal, inferior, and temporal regions.

Conclusions.: This study maps the corneal SBNP in OK lens wearers and provides compelling evidence that OK lens wear alters the normal SBNP distribution observed in healthy, non–lens wearing eyes.

Introduction
The human cornea is the most densely innervated surface tissue in the human body. 12 The rich supply of nerve fibers controlling the sensory and trophic functions is located mainly in the anterior layers of the cornea. 3 The arrangement of these nerves is highly complex 1 and not yet completely known. However, it is important from a clinical perspective to understand and further investigate the architecture of these nerves because of recent studies showing a relationship between nerve morphology and ocular and systemic disease, 415 as well as nerve damage following refractive surgery. 1617  
The nerve fibers located between the basal epithelium and Bowman's layer are known as the sub-basal nerve plexus (SBNP). 18 They are detected relatively easily using contemporary in vivo laser scanning confocal microscopy (LSCM) and consequently are a main focus for evaluation of corneal nerve morphology. 1920 Patel and McGhee were the first to map a significant portion of the SBNP in normal subjects, describing the neural architecture of the central to mid-peripheral cornea as having a whorl-like pattern. 21 In a follow-up study, 22 they perform repeated scans on the same subject one week apart and found dramatic changes in the SBNP, concluding that it is a highly dynamic structure. 
Orthokeratology (OK) is a clinical technique that uses specially designed rigid lenses to reshape the corneal contour. Lenses are worn during sleep and removed on waking to temporarily correct refractive error, thereby providing clear, unassisted vision throughout the day. 23 Many studies have shown that OK-induced changes to the corneal contour are the result of changes in the epithelial layer 2427 ; however, no studies have investigated the effects of OK treatment on the SBNP. Furthermore, several researchers have suggested that sub-basal nerves and epithelial cells migrate in tandem, 21,2829 so an investigation of SBNP changes during OK treatment may increase our understanding of epithelial layer changes during this modality of contact lens wear. In addition, two previous case reports 2930 suggest that the appearance of fibrillary lines at the onset of OK treatment may represent altered nerve fibers in the SBNP, 31 but this has yet to be proven. Therefore, the purpose of this study was to investigate the corneal nerves in healthy human eyes by mapping the SBNP in OK lens wear using in vivo LSCM and thereby better understand epithelial layer changes as well as the origins of fibrillary lines during OK treatment. 
Methods
The research described in this paper followed the tenets of the Declaration of Helsinki 1975, as revised in 2000. After approval for the study had been obtained from the University of New South Wales Human Research Ethics Committee, three subjects were recruited for this study, a short-term OK lens wearer (STOK) of approximately 1-year experience, a long-term OK lens wearer (LTOK) of approximately 9-years experience, and a non–contact lens wearer (NC). The STOK, LTOK, and NC subjects were all healthy Asian females aged 21, 29, and 28 years, respectively. 
Laser scanning in vivo confocal microscopy was performed with the use of a corneal module (Heidelberg Retina Tomograph II [HRT], Rostock Corneal Module [RCM]; Heidelberg Engineering GmbH, Heidelberg, Germany) on the right eye of each subject. The instrument was set up using standard techniques described previously. 2021 The mapping of the SBNP was based on the technique developed at the laboratory of Professor Nathan Efron (Queensland University of Technology, Brisbane, Australia). 32 During the examination, all subjects were asked to fixate on an LCD screen that displayed a meandering white spot on a black background. This spot followed a motion path tracing out a line pattern as illustrated in Figure 1a. The overall dimensions of the line pattern on the screen were 11 cm × 13 cm (height [h] × width [w]). This screen was positioned at 70 cm perpendicular to the contralateral eye and corresponded to a scan area of approximately 2.5 mm × 3 mm (h × w) on the corneal surface (Fig. 1b). All subjects were emmetropic during the examinations and hence could clearly see the fixation spot with the contralateral eye. The HRT RCM was set on “sequence mode” to scan several sets of 100 high-quality contiguous images of the SBNP, taking approximately 40 seconds to capture each set of images. The position of the RCM probe was adjusted between each set of scans in order to target different areas of the cornea. Nine, 18, and 22 sets of scans were taken over 3, 5, and 7 visits for the NC, STOK, and LTOK subjects, respectively. Each visit lasted approximately 20 minutes, with a total confocal exposure time of less than 10 minutes. Hence, the subjects and operator did not exceed the manufacturer's imposed limit of 50 minutes of total exposure to the HRT laser at any single visit. 
Figure 1.
 
Fixation target (meandering white dot) and line pattern followed by contralateral eye during a single “sequence mode” scan of the sub-basal nerve plexus (A). Setup of subject and LCD screen at 70 cm perpendicular to fixating eye (B). The LCD screen displayed the moving fixation target for the contralateral eye.
Figure 1.
 
Fixation target (meandering white dot) and line pattern followed by contralateral eye during a single “sequence mode” scan of the sub-basal nerve plexus (A). Setup of subject and LCD screen at 70 cm perpendicular to fixating eye (B). The LCD screen displayed the moving fixation target for the contralateral eye.
The scanned images for each subject were arranged into a wide-field montage using Photoshop Elements 9 (Adobe Systems Inc., San Jose, CA). Some images required brightness correction before inclusion into the montage. Any blurred or duplicate images were discarded. A total of 575, 430, and 676 images were acquired for the NC, STOK, and LTOK subjects, respectively. All nerves on the montage were then manually traced on a Wacom Graphics Tablet (Wacom Co., Saitama, Japan) using a grip pen to outline the overall pattern of the nerve map. The overall dimensions (h and w) of the final montage were calculated using Image-Pro Analyser 7.0 (Media Cybernetics Inc., Bethesda, MD). 
There were no adverse effects following any examination session other than slight distance vision blur lasting approximately 5 minutes in the NC and LTOK subjects. This was due to temporary distortion of the corneal surface by the instrument probe. A Fischer-Schweitzer mosaic was also seen in the same subjects following the scan and persisted for approximately the same period as the blurred vision. 
The OK lens wearing subjects wore standard reverse geometry lenses. The parameters of the lenses were measured using standard lens metrology techniques, and these details are described in Table 1. A computerized corneal topography map was taken of each OK subjects' right eye using a Medmont E-300 corneal topographer (Medmont Pty. Ltd., Melbourne, Australia) to describe the profile of the cornea. Standard digital slit-lamp photography was used to record the presence of fibrillary lines in the corneal mid-periphery. 
Table 1.
 
Measured Lens Parameters of OK Lenses Worn by Subjects
Table 1.
 
Measured Lens Parameters of OK Lenses Worn by Subjects
Parameter Short-Term Wearer Long-Term Wearer
Lens diameter (mm) 11.0 10.6
Optic zone diameter (mm) 6.00 5.75
Base curve (mm) 8.97 8.30
Back vertex power (D) +0.75 +0.50
Results
Two-dimensional maps of the SBNP were reconstructed from the scanned images (Figs. 2a–c) and were approximately 6.4 mm × 6.7 mm, 5.8 mm × 7.2 mm, and 6.8 mm × 8.5 mm (h × w) in dimension for the NC, STOK, and LTOK eyes, respectively. In the non–lens wearing eye, nerves converged radially from the outer edges of the map towards a clockwise whorl-like complex, centered inferior-nasally approximately 1 mm below the corneal center. The tracing of the nerves in Figure 3a shows this pattern more clearly. In the OK lens wearing eyes, the whorl-like complex was absent, replaced by a tortuous network of less dense and fewer interconnected nerve fibers centrally, and curvilinear fibers mid-peripherally, particularly in the nasal, inferior, and temporal regions, shown more clearly in the nerve tracing in Figures 3b and 3c. These curvilinear nerves in the mid-periphery were located approximately 2.5 to 3 mm from the center of the cornea and were thicker than the surrounding nerves in the LTOK eye. There appeared to be a reduction in the density of nerve fibers in the central region of the map and an increase in density in the mid-periphery in both OK subjects compared with the non–lens wearing eye. 
Figure 2.
 
Two-dimensional maps of the sub-basal nerve plexus reconstructed from 575 scanned images of the non–contact lens wearing eye (A), 430 scanned images of a short-term OK lens wearing eye (B), and 676 scanned images of a long-term OK lens wearing eye (C). Bar = 1 mm.
Figure 2.
 
Two-dimensional maps of the sub-basal nerve plexus reconstructed from 575 scanned images of the non–contact lens wearing eye (A), 430 scanned images of a short-term OK lens wearing eye (B), and 676 scanned images of a long-term OK lens wearing eye (C). Bar = 1 mm.
Figure 3.
 
Nerve tracings of the sub-basal nerve plexus map from a non–contact lens wearing eye (A), short-term (B) and long-term (C) OK lens wearing eye. Bar = 1 mm.
Figure 3.
 
Nerve tracings of the sub-basal nerve plexus map from a non–contact lens wearing eye (A), short-term (B) and long-term (C) OK lens wearing eye. Bar = 1 mm.
Figure 4 shows the nerve tracings of the SBNP from the OK subjects superimposed (to scale) upon computerized corneal topography maps of the same eye. The areas of reduced nerve fiber density over the central cornea corresponded with the area of relative corneal flattening on the topography maps. The curvilinear nerves in the mid-periphery arcing beneath the central corneal zone appeared to coincide with the outer edges of the area of relative corneal flattening, as well as the mid-peripheral areas of relatively no change and slight steepening in corneal curvature. 
Figure 4.
 
Nerve tracing of the SBNP superimposed upon a computerized corneal topography map (tangential power) in the same eye of a short-term (A) and long-term (B) OK lens wearing subject.
Figure 4.
 
Nerve tracing of the SBNP superimposed upon a computerized corneal topography map (tangential power) in the same eye of a short-term (A) and long-term (B) OK lens wearing subject.
Fibrillary lines following a curvilinear pattern were observed in the mid-periphery of the nasal, inferior, and temporal cornea of the LTOK eye using slit-lamp biomicroscopy. Photographic images of these lines from the nasal region are shown in Figures 5a and 5b. The pattern of these lines closely matches the scanned nerves from the SBNP in the same region as shown in Figure 5c. There were no such lines observed in the NC or STOK eyes. 
Figure 5.
 
Fibrillary lines (arrows) in the nasal mid-periphery of a long-term OK lens wearer (A, B), and the corresponding map of the SBNP from the same subject (C).
Figure 5.
 
Fibrillary lines (arrows) in the nasal mid-periphery of a long-term OK lens wearer (A, B), and the corresponding map of the SBNP from the same subject (C).
Discussion
Although this study only reported the appearance of the SBNP in two OK subjects, the obvious differences between the nerve map for a non–lens wearer compared with the OK lens wearers provide compelling evidence that overnight OK lens wear alters the normal nerve pattern observed in healthy, non–lens wearing eyes. 
This study also supports previous suggestions 2931 that the appearance of fibrillary lines during OK treatment are altered nerve fibers in the SBNP. This is seen in the matched patterns between the fibrillary lines observed using slit-lamp biomicroscopy with those of the thick, curvilinear nerves in the mid-peripheral SBNP using LSCM in the LTOK subject (Fig. 5). Alterations in the thickness of these nerves may have made visible the fibers that are normally invisible using slit-lamp biomicroscopy. This suggestion is further supported by the absence of fibrillary lines in the STOK subject, where the thickness of mid-peripheral, curvilinear nerves appeared equal to surrounding nerves. 
The mechanism underlying these OK-induced alterations in the nerve map is unknown. We speculate that the forces exerted by the OK lens during eye closure to produce corneal profile change 33 are somehow responsible for the reorganization of the SBNP. This is supported by our nerve/topography map overlays (Fig. 4), which illustrated how the apparent reduction in nerve fiber density centrally coincided with the area of relative corneal flattening, thereby suggesting that the positive force or pressure exerted by the OK lens on the corneal surface may have been responsible for the reduction in nerve density. In addition, the apparent increase in nerve fiber density and thickness mid-peripherally occurred in an area of no profile change or slight corneal steepening, suggesting this region of neutral or negative pressure under the OK lens, otherwise known as the return zone area, may have played a role in the increase in nerve density. Furthermore, the curvilinear mid-peripheral nerves appear to follow a similar curvature as the return zone area, suggesting that pressure from the lens has manipulated the orientation of these nerves. Therefore, the unique balance of positive, neutral, and negative pressures exerted by an OK lens during overnight wear is possibly the cause for the distinctive pattern seen in the SBNP of the OK lens wearers. 
The cause of the apparent increase in nerve fiber thickness in the mid-periphery of the LTOK subject is unknown. Many studies have reported the enlargement of corneal nerves in eye diseases, with some investigators suggesting that increases in the myelination of nerves contributes to their enlargement and consequently thickening. 34 However, Patel and McGhee reported that illumination intensity of the HRT confocal microscope affects the apparent thickness of corneal nerves, particularly as they approach the limits of resolution. 35 In this study, the illumination intensity was constantly set on automatic mode. Consequently, if the background of a single scan appeared underexposed to the instrument, an automatic increase in the illumination intensity occurred, thereby potentially increasing the apparent thickness of the nerve fibers. Hence, the thickness change may be an artifact created by the LSCM. Alternatively, these thicker curvilinear nerves may represent compressed bundles of separate nerve fibers running closely together rather than an actual thickening of a single fiber. This is suggested in Figures 3c and 5c, where nerve fibers from the periphery appear to converge to create a single line, which becomes large enough to be resolved using slit-lamp biomicroscopy. Thus, fibrillary lines may well be a compressed bundle of separate nerves running very closely together. 
In this study, a clockwise whorl-like nerve pattern was observed in the non–lens wearer's map, which is consistent with the findings from previous reports using a similar in vivo mapping technique in normal subjects, 21 and ex vivo microphotography techniques on normal cadaver eyes. 3637 Given that several researchers have suggested nerves and cells migrate in tandem in healthy human corneas, 21,2829 this nerve pattern suggests that in a normal eye cells migrate centripetally towards the inferior-central cornea. The whorl-like pattern, however, was absent in the OK lens wearers' maps, replaced by a tortuous network of nerves centrally, and a curvilinear pattern of nerves mid-peripherally, suggesting a disruption to the normal nerve and epithelial cell migration pattern. Hence, we speculate that the corneal contour changes occurring during OK treatment may not only be the result of epithelial thickness change but also a redistribution of epithelial cells. 
The nerve map pattern observed in the OK lens wearing subjects shows some similarity to the maps described by Patel and McGhee 8 in keratoconic corneas using the same in vivo LSCM technique. In their study, a similar reduction in nerve density is observed centrally. Patel and McGhee also observe nerve fiber bundles following a curvilinear pattern at the base of the cone, similar to what is seen in the mid-periphery of our OK subjects. However, keratoconus is a degenerative eye disease that results in an irregular corneal profile and is accompanied by other nerve morphology changes, which were not observed in the current study. In addition, changes due to keratoconus are permanent, whereas the corneal profile changes in OK are known to be reversible. Since the corneal profile returns to its original shape on cessation of lens wear, 38 we speculate that changes to the SBNP during OK treatment may likewise revert to the normal pattern when treatment ceases. This requires further investigation. 
There are three possible mechanisms underlying the apparent reduction in central nerve density and interconnections in the OK lens wearers: diversion of nerves from their usual trajectory, increased distance between nerves, or a loss of nerves, such as occurs in ocular disease. 414 First, from the nerve map, it appears that the paths of the nerves that originate from the outer limits were diverted from their normal trajectory, towards a new path within the mid-periphery. Hence, the nerves normally seen in the center appear to have been redistributed towards the mid-periphery. Second, the reshaping of the corneal profile causes compression of the epithelial cells centrally, 24,27 thereby increasing the en face surface area of each cell. Since fibers in the SBNP are thought to mainly run between neighboring epithelial cells, 18 the flattening of cells may increase the separation of nerves, thereby giving the impression of reduced nerve density. Third, the reduction in the nerve density centrally may be the result of nerve loss, which should have implications for the sensitivity of the cornea, particularly in relation to its regional variations. Hiraoka et al. 39 found an overall reduction in corneal sensitivity after 3 months of OK treatment. In that study, measurements are taken at five locations: at the corneal apex, and at 2 mm from the limbus in the superior, inferior, nasal, and temporal corneal locations, and no regional variations in sensitivity were found at baseline or at the 3-month visit. However, sensitivity was measured using the Cochet-Bonnet aesthesiometer with the thicker 0.12-mm diameter nylon monofilament, which has been demonstrated to have a truncated stimulus intensity range. 40 Therefore subtle differences across the cornea may not have been detected. A change in sensitivity would be expected with such marked changes in morphology as have been observed in this present study, as many studies involving subjects with eye 45,7,1112,14 and systemic disease, 1213 as well as following corneal surgery, 1617 show a relationship between changes in nerve morphology and corneal sensitivity. In addition, a reduction in nerve density may also have implications on corneal wound healing 4142 and the immune response to corneal infections. 15 Hence, the clinical implications of restructuring the SBNP on corneal sensitivity as well as the long-term health of human eyes treated with OK require further investigation. 
In summary, this study reports the mapping of the corneal SBNP in OK lens wear. The apparent changes in these nerve maps compared with the map of a non–lens wearer appeared to coincide with the contour changes on the computerized topography maps. The nerve maps also provided evidence to suggest that the migration pattern of epithelial cells was altered during OK treatment, thereby adding to our understanding of the complex changes that occur to the epithelial layer during OK treatment. This study also confirmed previous suggestions that fibrillary lines observed during OK treatment are altered nerve fibers in the SBNP. Further studies are required to determine the onset and possible recovery of these changes in the SBNP, as well as whether functional changes such as altered corneal sensitivity reflect the morphologic changes seen in this study. 
Acknowledgments
The authors thank Dipika Patel, Nicola Pritchard, Xinjie Angela Lai, and Moneisha Gokhale for expert technical assistance with the LSCM and the nerve mapping technique, and Juliet Mar and Judith Flanagan for critical reading of the manuscript. 
References
Marfurt CF Cox J Deek S Dvorscak L . Anatomy of the human corneal innervation. Exp Eye Res. 2010;90:478–492. [CrossRef] [PubMed]
Müller LJ Marfurt CF Kruse F Tervo TMT . Corneal nerves: structure, contents and function. Exp Eye Res. 2003;76:521–542. [CrossRef] [PubMed]
Guthoff RF Wienss H Hahnel C Wree A . Epithelial innervation of human cornea: a three-dimensional study using confocal laser scanning fluorescence microscopy. Cornea. 2005;24:608–613. [CrossRef] [PubMed]
Benítez-Del-Castillo JM Acosta MC Wassfi MA Relation between corneal innervation with confocal microscopy and corneal sensitivity with noncontact esthesiometry in patients with dry eye. Invest Ophthalmol Vis Sci. 2007;48:173–181. [CrossRef] [PubMed]
Hamrah P Cruzat A Dastjerdi MH Corneal sensation and subbasal nerve alterations in patients with herpes simplex keratitis: an in vivo confocal microscopy study. Ophthalmology. 2010;117:1930–1936. [CrossRef] [PubMed]
Niederer RL Perumal D Sherwin T McGhee CNJ . Laser scanning in vivo confocal microscopy reveals reduced innervation and reduction in cell density in all layers of the keratoconic cornea. Invest Ophthalmol Vis Sci. 2008;49:2964–2970. [CrossRef] [PubMed]
Patel DV Ku JYF Johnson R Laser scanning in vivo confocal microscopy and quantitative aesthesiometry reveal decreased corneal innervation and sensation in keratoconus. Eye. 2009;23:586–592. [CrossRef]
Patel DV McGhee CNJ . Mapping the corneal sub-basal nerve plexus in keratoconus by in vivo laser scanning confocal microscopy. Invest Ophthalmol Vis Sci. 2006;47:1348–1351. [CrossRef] [PubMed]
Patel DV McGhee CNJ . In vivo confocal microscopy of corneal stromal nerves in patients with peripheral neuropathy. Arch Neurol. 2009;66:1179–1180. [CrossRef] [PubMed]
Patel DV McGhee CNJ . Laser scanning in vivo confocal microscopy demonstrating significant alteration of human corneal nerves following herpes zoster ophthalmicus. Arch Neurol. 2010;67:640–641. [PubMed]
Rosenberg ME Tervo TMT Gallar J Corneal morphology and sensitivity in lattice dystrophy type II (familial amyloidosis, Finnish type). Invest Ophthalmol Vis Sci. 2001;42:634–641. [PubMed]
Rosenberg ME Tervo TMT Immonen IJ Corneal structure and sensitivity in type 1 diabetes mellitus. Invest Ophthalmol Vis Sci. 2000;41:2915–2921. [PubMed]
Tavakoli M Quattrini C Abbott C Corneal confocal microscopy: a novel noninvasive test to diagnose and stratify the severity of human diabetic neuropathy. Diabetes Care. 2010;33:1792–1797. [CrossRef] [PubMed]
Tuisku IS Konttinen YT Konttinen LM Tervo TM . Alterations in corneal sensitivity and nerve morphology in patients with primary Sjögren's syndrome. Exp Eye Res. 2008;86:879–885. [CrossRef] [PubMed]
Cruzat A Witkin D Baniasadi N Inflammation and the nervous system: the connection in the cornea in patients with infectious keratitis. Invest Ophthalmol Vis Sci. 2011;52:5136–5143. [CrossRef] [PubMed]
Darwish T Brahma A O'Donnell C Efron N . Sub-basal nerve fiber regeneration after LASIK and LASEK assessed by noncontact esthesiometry and in vivo confocal microscopy: prospective study. J Cataract Refract Surg. 2007;33:1515–1521. [CrossRef] [PubMed]
Linna TU Vesaluoma MH Pérez-Santonja JJ Effect of myopic LASIK on corneal sensitivity and morphology of subbasal nerves. Invest Ophthalmol Vis Sci. 2000;41:393–397. [PubMed]
Müller LJ Pels L Vrensen GF . Ultrastructural organization of human corneal nerves. Invest Ophthalmol Vis Sci. 1996;37:476–488. [PubMed]
Oliveira-Soto L Efron N . Morphology of corneal nerves using confocal microscopy. Cornea. 2001;20:374–384. [CrossRef] [PubMed]
Stachs O Zhivov A Kraak R In vivo three-dimensional confocal laser scanning microscopy of the epithelial nerve structure in the human cornea. Graefes Arch Clin Exp Ophthalmol. 2007;245:569–575. [CrossRef] [PubMed]
Patel DV McGhee CNJ . Mapping of the normal human corneal sub-basal nerve plexus by in vivo laser scanning confocal microscopy. Invest Ophthalmol Vis Sci. 2005;46:4485–4488. [CrossRef] [PubMed]
Patel DV McGhee CNJ . In vivo laser scanning confocal microscopy confirms that the human corneal sub-basal nerve plexus is a highly dynamic structure. Invest Ophthalmol Vis Sci. 2008;49:3409–3412. [CrossRef] [PubMed]
Swarbrick HA . Orthokeratology review and update. Clin Exp Optom. 2006;89:124–143. [CrossRef] [PubMed]
Choo JD Caroline PJ Harlin DD Papas EB Holden BA . Morphologic changes in cat epithelium following continuous wear of orthokeratology lenses: a pilot study. Cont Lens Anterior Eye. 2008;31:29–37. [CrossRef] [PubMed]
Knappe S Stachs O Guthoff R . Corneal changes after wearing orthokeratology contact lenses: an investigation using in vivo, confocal laser scanning microscopy. Ophthalmologe. 2007;104:681–687. [CrossRef] [PubMed]
Matsubara M Kamei Y Takeda S Histologic and histochemical changes in rabbit cornea produced by an orthokeratology lens. Eye Contact Lens. 2004;30:198–204. [CrossRef] [PubMed]
Nieto-Bona A González-Mesa A Nieto-Bona MP Short-term effects of overnight orthokeratology on corneal cell morphology and corneal thickness. Cornea. 2011;30:646–654. [CrossRef] [PubMed]
Auran JD Koester CJ Kleiman NJ Scanning slit confocal microscopic observation of cell morphology and movement within the normal human anterior cornea. Ophthalmology. 1995;102:33–41. [CrossRef] [PubMed]
Cheung SW Cho P Bron AJ Chui V Chan B . Case report: the occurrence of fibrillary lines in overnight orthokeratology. Ophthalmic Physiol Opt. 2006;26:525–531. [CrossRef] [PubMed]
Lum E Swarbrick H . Fibrillary lines in overnight orthokeratology. Clin Exp Optom. 2007;90:299–302. [CrossRef] [PubMed]
Bron AJ . Superficial fibrillary lines: a feature of the normal cornea. Br J Ophthalmol. 1975;59:133–135. [CrossRef] [PubMed]
Efron N . The Glenn A. Fry award lecture 2010: ophthalmic markers of diabetic neuropathy. Optom Vis Sci. 2011;88:661–683. [CrossRef] [PubMed]
Mountford J Noack D . A mathematical model for corneal shape change associated with ortho-k. Contact Lens Spectrum. 1998;13:6.
Kim SK Dohlman CH . Causes of enlarged corneal nerves. Int Ophthalmol Clin. 2001;41:13–23. [CrossRef] [PubMed]
Patel DV McGhee CNJ . In vivo confocal microscopy of human corneal nerves in health, in ocular and systemic disease, and following corneal surgery: a review. Br J Ophthalmol. 2009;93:853–860. [CrossRef] [PubMed]
Al-Aqaba MA Fares U Suleman H Lowe J Dua HS . Architecture and distribution of human corneal nerves. Br J Ophthalmol. 2010;94:784–789. [CrossRef] [PubMed]
He J Bazan NG Bazan HEP . Mapping the entire human corneal nerve architecture. Exp Eye Res. 2010;91:513–523. [CrossRef] [PubMed]
Barr JT Rah MJ Meyers W Recovery of refractive error after corneal refractive therapy. Eye Contact Lens. 2004;30:247–251. [CrossRef] [PubMed]
Hiraoka T Kaji Y Okamoto F Corneal sensation after overnight orthokeratology. Cornea. 2009;28:891–895. [CrossRef] [PubMed]
Golebiowski B Papas E Stapleton F . Assessing the sensory function of the ocular surface: implications of use of a non-contact air jet aesthesiometer versus the Cochet-Bonnet aesthesiometer. Exp Eye Res. 2011;92:408–413. [CrossRef] [PubMed]
Beuerman RW Schimmelpfennig B . Sensory denervation of the rabbit cornea affects epithelial properties. Exp Neurol. 1980;69:196–201. [CrossRef] [PubMed]
Belmonte C Acosta MC Gallar J . Neural basis of sensation in intact and injured corneas. Exp Eye Res. 2004;78:513–525. [CrossRef] [PubMed]
Footnotes
 Disclosure: E. Lum, Bausch & Lomb (F), BE Enterprises Pty. Ltd. (F), and Capricornia Contact Lens Pty. Ltd. (F); B. Golebiowski, None; H. Swarbrick, Bausch & Lomb (F), BE Enterprises Pty. Ltd. (F), and Capricornia Contact Lens Pty. Ltd. (F)
Footnotes
 Supported by the Australian Research Council Linkage Project Scheme, with industry partners Bausch & Lomb, BE Enterprises Pty. Ltd., and Capricornia Contact Lens Pty. Ltd.
Figure 1.
 
Fixation target (meandering white dot) and line pattern followed by contralateral eye during a single “sequence mode” scan of the sub-basal nerve plexus (A). Setup of subject and LCD screen at 70 cm perpendicular to fixating eye (B). The LCD screen displayed the moving fixation target for the contralateral eye.
Figure 1.
 
Fixation target (meandering white dot) and line pattern followed by contralateral eye during a single “sequence mode” scan of the sub-basal nerve plexus (A). Setup of subject and LCD screen at 70 cm perpendicular to fixating eye (B). The LCD screen displayed the moving fixation target for the contralateral eye.
Figure 2.
 
Two-dimensional maps of the sub-basal nerve plexus reconstructed from 575 scanned images of the non–contact lens wearing eye (A), 430 scanned images of a short-term OK lens wearing eye (B), and 676 scanned images of a long-term OK lens wearing eye (C). Bar = 1 mm.
Figure 2.
 
Two-dimensional maps of the sub-basal nerve plexus reconstructed from 575 scanned images of the non–contact lens wearing eye (A), 430 scanned images of a short-term OK lens wearing eye (B), and 676 scanned images of a long-term OK lens wearing eye (C). Bar = 1 mm.
Figure 3.
 
Nerve tracings of the sub-basal nerve plexus map from a non–contact lens wearing eye (A), short-term (B) and long-term (C) OK lens wearing eye. Bar = 1 mm.
Figure 3.
 
Nerve tracings of the sub-basal nerve plexus map from a non–contact lens wearing eye (A), short-term (B) and long-term (C) OK lens wearing eye. Bar = 1 mm.
Figure 4.
 
Nerve tracing of the SBNP superimposed upon a computerized corneal topography map (tangential power) in the same eye of a short-term (A) and long-term (B) OK lens wearing subject.
Figure 4.
 
Nerve tracing of the SBNP superimposed upon a computerized corneal topography map (tangential power) in the same eye of a short-term (A) and long-term (B) OK lens wearing subject.
Figure 5.
 
Fibrillary lines (arrows) in the nasal mid-periphery of a long-term OK lens wearer (A, B), and the corresponding map of the SBNP from the same subject (C).
Figure 5.
 
Fibrillary lines (arrows) in the nasal mid-periphery of a long-term OK lens wearer (A, B), and the corresponding map of the SBNP from the same subject (C).
Table 1.
 
Measured Lens Parameters of OK Lenses Worn by Subjects
Table 1.
 
Measured Lens Parameters of OK Lenses Worn by Subjects
Parameter Short-Term Wearer Long-Term Wearer
Lens diameter (mm) 11.0 10.6
Optic zone diameter (mm) 6.00 5.75
Base curve (mm) 8.97 8.30
Back vertex power (D) +0.75 +0.50
×
×

This PDF is available to Subscribers Only

Sign in or purchase a subscription to access this content. ×

You must be signed into an individual account to use this feature.

×