In vivo confocal microscopy for evaluation of wound healing following corneal refractive surgery

doi:10.1016/S1350-9462(02)00064-2

Progress in Retinal and Eye Research

Volume 22, Issue 3, May 2003, Pages 339-358

https://doi.org/10.1016/S1350-9462(02)00064-2 Get rights and content

Abstract

Understanding of corneal wound healing plays an important role, not only in management of corneal infections, but especially in refractive surgery. A better control of wound healing mechanisms might improve the results of such resculpturing techniques and help to avoid complications arising from these procedures. While studies have been focused in different aspects of corneal wound healing, our knowledge has increased greatly during the last years. Many problems associated with corneal healing also contribute to clinical pathology following corneal surgery. Understanding of such conditions has been augmented by the continuously developing corneal imaging techniques. We have used in vivo confocal microscopy (IVCM) for assessing corneas subjected to refractive surgery as well as corneas with common complications resulting from such procedures. IVCM has become a powerful tool for examining corneal cells, nerves, inflammations and infections. It allows information to be acquired repeatedly and at subbiomicroscopic levels that earlier had been obtainable only by invasive microscopic methods. Pre-examining corneas preoperatively by IVCM in order to reveal diseases or conditions in which elective refractive surgical procedures should not be undertaken or to select the ideal operation technique may help to avoid complications in the future. Measurement of the thickness of corneal sublayers or estimation of the thickness of a laser in situ keratomileusis flap or wound bed are other applications in which confocal microscopy may be valuable.

In this article we attempt to describe the in vivo confocal findings of common refractive procedures and their complications, and discuss their biology in light of the existing knowledge on wound healing phenomena.

Section snippets

History of in vivo imaging of the cornea

The development of the slit lamp by Gullstrand (Duke-Elder, 1962) for biomicroscopy of cornea and deeper ocular structures was a major benchmark (Cavanagh et al (1990), Cavanagh et al (1993), Cavanagh et al (1995), Cavanagh et al (2000); Masters and Farmer, 1993; Masters et al. (2001), Masters et al. (2002); Petroll et al., 1998) of corneal imaging. The microscope uses a narrow slit to remove part of the scattered light from adjacent tissue structures enabling a degree of optical sectioning,

Basic parameters of the cornea

Tear film: Prydal and Campbell (1992) have used TSCM to measure the thickness of tear film. However, the applanating objective and use of Goniosol^® gel may disturb estimation of tear characteristics.

Epithelium: Irrespective of the type of the microscope, both superficial (Fig. 2A) and basal epithelial cells are easily visualised (Fig. 2B). The impact of limbal stem cell deficiency on corneal healing has also been assessed by IVCM (Cho et al., 1998). Bowman's layer appears as a cell free area,

Radial keratectomy (RK)

RK was the first procedure widely used to alter corneal refractive power. It is based on incision wounds (Jester et al., 1992b), the histology of which has been reviewed in this journal (Jester et al., 1999b). Briefly, an incision wound is first filled by epithelial cells sliding into the wound cleft. Subsequently, these cells form an epithelial plug (at 7 days) that is later replaced by activated keratocytes adapting myofibroblast-like phenotype (at 14 days). These cells accomplish

Nerve regeneration after refractive surgery

Both PRK (Campos et al., 1992; Ishikawa et al., 1994; Trabucchi et al., 1994; Kohlhaas et al., 1995; Perez-Santonja et al., 1999; Benitez-del-Castillo et al., 2001) and LASIK (Kanellopoulos et al., 1997; Chuck et al., 2000, Perez-Santonja et al., 1999; Matsui et al., 2001; Linna et al., 2000a; Ang et al., 2001) severe corneal nerves and lead to a loss of corneal sensitivity.

PRK ablates Bowman's layer and the subepithelial nerve plexus. The Bowman's layer shows only minimal if any regeneration

Interphase debris

Vesaluoma et al. (2000a) showed that there are about 600 (mean) particles per square milllimeter 3 days after LASIK. The particles (Fig. 16A) presumably include cells, cell fragments (apoptotic bodies), debris, metal particles, and salt presipitates from tear film. One month post-operatively the particle count was lower. Improved cleaning procedures adopted after that study seem to have decreased the particle counts. The significance of interphase particles to LASIK complications, such as DLK

Other possibilities in corneal imaging

Means of imaging corneal or other tissues in the eye are being constantly developed. Optical Coherence Tomography (OCT; Humphrey-Zeiss Medical Systems) developed for imaging of retina and optic nerve can also be used for imaging of the cornea and estimation of central corneal thickness (Bechmann et al., 2001; Muscat et al., 2002; Wirbelauer et al., 2002; Neubauer et al., 2002). Nidek EAS-100 anterior segment analysis system also enables imaging of the whole anterior segment including the

Acknowledgements

Acknowledge is extended to the collaborators and mentors, who have instructed either of the writers into the field of confocal microscopy or corneal refractive surgery or participated in the creation of the results presented. Starting from the beginning, discussions with Stephen Trokel, inventor of PRK and Steven E Wilson, a good friend and prominent scientist in the field of corneal wound healing are to be acknowledged. The authors are also grateful for Professor Wilson for reading and

References (160)

L. Battat et al.
Effects of laser in situ keratomileusis on tear production, clearance, and the ocular surface
Ophthalmology
(2001)
A. Behrens et al.
Experimental evaluation of two current-generation automated microkeratomesthe Hansatome and the Supratome
Am. J. Ophthalmol.
(2000)
M.W. Belin et al.
Elevated intraocular pressure-induced interlamellar stromal keratitis
Ophthalmology
(2002)
J. Berlau et al.
Depth and age-dependent distribution of keratocytes in healthy human corneas
J. Cataract Refract. Surg.
(2002)
M. Böhnke et al.
Confocal microscopy of the cornea
Prog. Retinal Eye Res.
(1999)
J. Buhren et al.
Diffuse lamellar keratitis after laser in situ keratomileusis imaged by confocal microscopy
Ophthalmology
(2001)
M. Campos et al.
Corneal sensitivity after photorefractive keratectomy
Am. J. Ophthalmol.
(1992)
R.S. Chuck et al.
Corneal sensation after laser in situ keratomileusis
J. Cataract Refract. Surg.
(2000)
M.S. Chung et al.
Confocal microscopic findings in a case of delayed-onset bilateral diffuse lamellar keratitis after laser in situ keratomileusis
J. Cataract Refract. Surg.
(2002)
A. El-Maghraby et al.
Randomized bilateral comparison of excimer laser in situ keratomileusis and photorefractive keratectomy for 2.50 to 8.00 diopters of myopia
Ophthalmology
(1999)

(1998)

Duke-Elder, S., 1962. System of Ophthalmology. Kimpton, London, pp....

W.J. Dupps et al.

Effect of acute biomechanical changes on corneal curvature after photokeratectomy

J. Refract. Surg.

(2001)

J.C. Erie et al.

Keratocyte density in vivo after photorefractive keratectomy in humans

Trans. Am. Ophthalmol. Soc.

(1999)

G.J. Florakis et al.

Scanning slit confocal microscopy of fungal keratitis

Arch. Ophthalmol.

(1997)

B.E. Frueh et al.

In vivo confocal microscopy after photorefractive keratectomy in humansa prospective, long-term study

Arch. Ophthalmol.

(1998)

Cited by (94)

Omega-3 polyunsaturated fatty acids and corneal nerve health: Current evidence and future directions
2023, Ocular Surface
Citation Excerpt :
These procedures, by removing or transecting the corneal epithelium and laser photoablation, directly cause corneal nerve injury and disrupt ocular surface homeostasis [2]. The extent of denervation and rate of recovery depends on several factors, including the procedure used, the zone of treatment, and the degree of refractive error [113]. Dry eye disease is a common complication of refractive surgery [114].
Corneal nerves play a key role in maintaining ocular surface integrity. Corneal nerve damage, from local or systemic conditions, can lead to ocular discomfort, pain, and, if poorly managed, neurotrophic keratopathy. Omega-3 polyunsaturated fatty acids (PUFAs) are essential dietary components that play a key role in neural development, maintenance, and function. Their potential application in modulating ocular and systemic inflammation has been widely reported. Omega-3 PUFAs and their metabolites also have neuroprotective properties and can confer benefit in neurodegenerative disease. Several preclinical studies have shown that topical administration of omega-3 PUFA-derived lipid mediators promote corneal nerve recovery following corneal surgery. Dietary omega-3 PUFA supplementation can also reduce corneal epithelial nerve loss and promote corneal nerve regeneration in diabetes. Omega-3 PUFAs and their lipid mediators thus show promise as therapeutic approaches to modulate corneal nerve health in ocular and systemic disease. This review discusses the role of dietary omega-3 PUFAs in maintaining ocular surface health and summarizes the possible applications of omega-3 PUFAs in the management of ocular and systemic conditions that cause corneal nerve damage. In examining the current evidence, this review also highlights relatively underexplored applications of omega-3 PUFAs in conferring neuroprotection and addresses their therapeutic potential in mediating corneal nerve regeneration.
Management of late traumatic LASIK flap dislocation related to dog scratch 16 Years postoperatively
2022, American Journal of Ophthalmology Case Reports
This report details a case of an unusual late dislocation of a laser in situ keratomileusis (LASIK) flap due to animal-related trauma 16 years after the initial surgery.
A 59-year-old woman with history of LASIK surgery on both eyes 16 years prior, and uncomplicated cataract surgery on the left eye (oculus sinister; OS) 3 years prior, arrived at our institution with sudden painful visual loss 3 hours after receiving a scratch on OS from her dog. Corneal examination revealed a completely displaced nasally hinged LASIK flap folded irregularly over the hinge, with multiple creases over its entire thickness. The flap was intact but edematous and opaque, with detritus present both on the flap surface and stromal face. Treatment was initiated with topical moxifloxacin and oral clindamycin. The next morning, the flap was refloated, and debris was removed from both sides of the flap while irrigating with preservative-free moxifloxacin. The flap was repositioned and a bandage contact lens placed. Postoperative topical medication included moxifloxacin, prednisolone acetate, and sodium hyaluronate. At the final follow-up visit, the patient was asymptomatic, with a measured uncorrected distance visual acuity (UDVA) of 20/25 OS.
This uncommon case highlights the longest reported interval—16 years— between initial surgery and traumatic LASIK flap displacement, caused by animal-related trauma. Patients experiencing LASIK surgery complications, including contaminated trauma many years after the original ablation, can still recover excellent visual acuity when managed appropriately and in a timely fashion.
Corneal nerves in health and disease
2019, Progress in Retinal and Eye Research
Citation Excerpt :
Laser refractive surgery has focused intense attention on corneal innervation and consequence of damage to corneal nerves that is inevitable with any type of laser refractive surgery both by the incisions made to prepare a corneal flap mechanically with a blade or with femtosecond laser; and by the excimer laser applied to achieve the refractive change. It has been reported that procedures like radial keratotomy, photorefractive keratectomy, and LASIK produce localised injury of thick stromal nerves and the sub-basal plexus resulting in transient mild to severe epithelial changes with neurotrophic and/or dry eye features (Tervo and Moilanen, 2003; Wilson, 2001; Wilson and Ambrosio, 2001). Several studies have been conducted to investigate the exact mechanism by which the corneal nerve fibres maintain a healthy cornea and promote wound healing after corneal injuries.
The cornea is the most sensitive structure in the human body. Corneal nerves adapt to maintain transparency and contribute to corneal health by mediating tear secretion and protective reflexes and provide trophic support to epithelial and stromal cells. The nerves destined for the cornea travel from the trigeminal ganglion in a complex and coordinated manner to terminate between and within corneal epithelial cells with which they are intricately integrated in a relationship of mutual support involving neurotrophins and neuromediators. The nerve terminals/receptors carry sensory impulses generated by mechanical, pain, cold and chemical stimuli. Modern imaging modalities have revealed a range of structural abnormalities such as attrition of nerves in neurotrophic keratopathy and post-penetrating keratoplasty; hyper-regeneration in keratoconus; decrease of sub-basal plexus with increased stromal nerves in bullous keratopathy and changes such as thickening, tortuosity, coiling and looping in a host of conditions including post corneal surgery. Functionally, symptoms of hyperaesthesia, pain, hypoaesthesia and anaesthesia dominate. Morphology and function do not always correlate. Symptoms can dominate in the absence of any visible nerve pathology and vice-versa. Sensory and trophic functions too can be dissociated with pre-ganglionic lesions causing sensory loss despite preservation of the sub-basal nerve plexus and minimal neurotrophic keratopathy. Structural and/or functional nerve anomalies can be induced by corneal pathology and conversely, nerve pathology can drive inflammation and corneal pathology. Improvements in accuracy of assessing sensory function and imaging nerves in vivo will reveal more information on the cause and effect relationship between corneal nerves and corneal diseases.
High fat diet induces pre-type 2 diabetes with regional changes in corneal sensory nerves and altered P2X7 expression and localization
2018, Experimental Eye Research
Type 2 diabetes is one of the leading pathologies that increases the risk of improper wound healing. Obesity has become a major risk factor for this disease that is now considered to be the 4th highest cause of preventable blindness according to the World Health Organization. The cornea is the most densely innervated structure in the human body and senses even the slightest injury. In diabetes, decreased corneal sensitivity secondary to diabetic peripheral neuropathy can lead to increased corneal abrasion, ulceration, and even blindness. In this study, a diet induced obesity (DIO) mouse model of pre-Type 2 diabetes was used to characterize changes in sensory nerves and P2X7, a purinoreceptor, a pain receptor, and an ion channel that is expressed in a number of tissues. Since our previous studies demonstrated that P2X7 mRNA was significantly elevated in diabetic human corneas, we examined P2X7 expression and localization in the DIO murine model at various times after being fed a high fat diet. Fifteen weeks after onset of diet, we found that there was a significant decrease in the density of sub-basal nerves in the DIO mice that was associated with an increase in tortuosity and a decrease in diameter. In addition, P2X7 mRNA expression was significantly greater in the corneal epithelium of DIO mice, and the increase in transcript was enhanced in the central migrating and peripheral regions after injury. Interestingly, confocal microscopy and thresholding analysis revealed that there was a significant increase in P2X7 distal to the injury, which contrasted with a decrease in P2X7-expressing stromal sensory nerves. Therefore, we hypothesize that the P2X7 receptor acts to sense changes at the leading edge following an epithelial abrasion, and this fine-tuned regulation is lost during the onset of diabetes. Further understanding of the corneal changes that occur in diabetes can help us better monitor progression of diabetic complications, as well as develop new therapeutics for the treatment of diabetic corneal dysfunction.
The effect of previous soft contact lens wear on corneal refractive surgery outcomes
2017, Contact Lens and Anterior Eye
To examine the influence of previous soft contact lens (SCL) wear on corneal refractive surgery (CRS) outcomes when SCL wear is ceased for two weeks versus twenty-four hours, and also when compared to no wear, prior to CRS.
A retrospective examination of CRS patient records was carried out for two groups of patients- who ceased SCL wear for two weeks (n = 45) and for twenty-four hours (n = 49) prior to CRS and compared to a non-contact lens (NCL) control group (n = 45 and n = 49, respectively). CRS outcomes (efficacy, predictability, visual acuity and refractive error) were compared pre-operatively and one and six months post-operatively.
One month post-operative results found unaided distance visual acuity (UDVA) was significantly better for LASEK/PRK patients who had ceased SCL wear for two weeks prior to CRS (−0.05 ± 0.09), compared with the NCL group (0.02 ± 0.09; p = 0.04). Furthermore, six month post-operative results found UDVA was significantly better for both LASIK and LASEK/PRK patients who had ceased SCL wear for two weeks prior to CRS, and for LASEK/PRK patients who had ceased SCL wear for twenty-four hours prior to CRS compared with the NCL group.
Given the current setup and methods followed, it was concluded that previous SCL wear had no negative impact on visual outcomes following CRS compared with a NCL control group, regardless of previous SCL cessation time prior to CRS.
The impact of lens care solutions on corneal epithelial changes during daily silicone hydrogel contact lens wear as measured by in vivo confocal microscopy
2017, Contact Lens and Anterior Eye
To assess corneal epithelial microstructure via confocal microscopy and determine if cellular changes are associated with lens care solutions during daily wear of silicone hydrogel contact lenses.
Corneal in vivo confocal microscopy with the Nidek ConfoScan4 was performed at baseline and after 5 months of lotrafilcon A daily contact lens wear. Enrolled participants were randomized to use either a polyhexamethylene biguanide (PHMB) preserved multipurpose care solution (MPS) or a peroxide based solution system. Lens and storage case bioburden were assessed with aerobic culture methods. Univariate and multivariable analyses were done to evaluate the association between solution use, or solution-related clinical covariates, and morphologic differences (hyper-reflectivity) in the superficial epithelial cells and epithelial basal cell density.
Data on 139 participants were available for analysis of superficial epithelial cells while data on 92 participants were available for epithelial basal cell density. Five months after randomization to the solution groups, 33% of participants had visible hyper-reflective cells. More participants using MPS had ≥1 hyper-reflective cells compared to peroxide users at 5 months (44% vs. 22%; p = 0.006). Similarly at 5 months, more participants with solution-induced corneal staining (SICS) had ≥1 hyper-reflective cells compared to non-SICS participants (57% vs. 29%; p = 0.010). The adjusted odds ratios (ORs) for risk of presenting with hyper-reflective cells in MPS users or SICS participants was 2.7 (95% CI; 1.27–5.65) and 3.4 (95% CI; 1.29–8.97), respectively. Basal cell density decreased by over 350 cells/mm² over time (about 6%) in participants who had substantial bioburden on their lenses or in their storage case.
The confocal microscope can detect epithelial cellular changes in vivo during contact lens wear. Hyper-reflective superficial epithelial cells are associated with a PHMB preserved solution and decreases in basal epithelial cell density may be associated with bacterial bioburden.

View all citing articles on Scopus

View full text