Confocal microscopic observations of stromal keratocytes during extended contact lens wear

CLEAR - Effect of contact lens materials and designs on the anatomy and physiology of the eye

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.

Keratocyte biology

The study of corneal stromal keratocytes is motivated by its strong association with corneal health and visual function. They play a dominant role in the maintenance of corneal homeostasis and transparency through the production of collagens, proteoglycans and corneal crystallins. Trauma-induced apoptosis of keratocytes and replacement by fibroblasts and myofibroblasts disrupt the stromal matrix organization, resulting in corneal haze formation and vision loss. It is, therefore, important to understand the biology and behaviours of keratocytes and the associated stromal cell types (like fibroblasts, myofibroblasts, stromal stem cells) in wound healing, corneal pathologies (including keratoconus, keratitis, endothelial disorders) as well as different ophthalmic situations (such as collagen crosslinking/photodynamic treatment, keratoplasty and refractive surgery, and topical medications). The recent development of ex vivo propagation of keratocytes and stromal stem cells, and their translational applications, either via stromal injection or incorporated in bioscaffold, have been shown to restore the corneal transparency and regenerate native stromal tissue in animal models of corneal haze and other disorders.

Variables associated with corneal confocal microscopy parameters in healthy volunteers: implications for diabetic neuropathy screening

AIM

Corneal confocal microscopy is a promising screening method for diabetic neuropathy. Although much research in this field has been accomplished, we aimed to determine and confirm the known clinical and eyewear variables associated with the parameters of corneal confocal microscopy specifically in healthy volunteers, in particular associations with corneal nerve fibre length.

METHODS

Clinical characteristics, electrophysiological examination and a general clinical eye history were collected from 64 healthy volunteers. Corneal confocal microscopy was performed to determine corneal nerve fibre length, corneal nerve branch density, corneal nerve fibre density and tortuosity coefficient. Univariate and multivariate linear regression analysis was used to determine clinical variables associated with corneal nerve fibre length parameters.

RESULTS

We observed that corneal nerve fibre length has a broad distribution in healthy volunteers (18 ± 4 mm/mm(2), 95% confidence interval, 12.3-25.7 mm/mm(2)). Multivariate regression analysis demonstrated that HbA(1c) was the only independent clinical factor to account for variations in corneal nerve fibre length, independent of age and status of contact lens wear.

CONCLUSIONS

This study does not provide convincing evidence that corneal nerve fibre length is independently associated with age or the wearing of contact lenses, and that these factors are therefore unlikely to hinder valid screening for polyneuropathies such as diabetic neuropathy. Furthermore, the strong inverse association of corneal nerve fibre length with glycaemic exposure may support the use of this parameter to detect subclinical pre-diabetic nerve injury.

Confocal microscopic observations of stromal keratocytes in soft and rigid contact lens wearers

PURPOSE

To determine the density of corneal stromal cells in wearers of soft contact lenses (SCLs) and rigid gas-permeable (RGP) contact lenses (CLs).

METHODS

The keratocyte density (KD) was measured at different depths of the stroma by confocal microscopy. In study 1, 32 wearers of rigid gas-permeable (RGP) lenses and 30 wearers of SCLs were studied. Forty volunteers with no history of CL wear were studied as controls. In study 2, 16 volunteers with no history of CL wear were divided into 2 groups; 7 subjects wore RGP lenses (oxygen transmissibility, Dk/L, 35) and 9 subjects wore SCLs (Dk/L, 34). All subjects were asked to wear the CLs daily for 6 months.

RESULTS

In study 1, the KDs in the anterior stroma (AST) and the posterior stroma (PST) of the cornea were significantly lower in the RGP lens group than in the control group. The KD in the SCL group was significantly lower at all depths of the cornea than that of the control group. In study 2, the KD in the AST of the RGP lens group was significantly lower after 1 month of CL wear. The KD in the AST and PST of the SCL group was decreased significantly at 1 month, and all layers were decreased by 10% to 20% 6 months after wearing CLs. At 5 weeks after discontinuation of SCL wear, the KD in all layers was not significantly different from that at the baseline.

CONCLUSIONS

The change in the KD was greater in CL wearers than in volunteers with no history of CL wear and also greater in SCL wearers than in RGP lens wearers. Analysis of the KD by confocal microscopy may be a useful method for evaluating the effect of CL wear.

In vivo confocal microscopy: corneal changes of hydrogel contact lens wearers

To evaluate the corneal findings in hydrogel contact lens wearers by in vivo confocal scanning microscopy. One hundred and forty-two eyes of 71 myopic contact lens wearers (group 1) and 142 eyes of 71 non-contact lens wearers (group 2), whose age, gender and refractive error matched, were enrolled in order to detect the corneal changes by in vivo confocal microscopy through the central cornea. The average age was 25.5 ± 5.7 (16-52) and 25.6 ± 5.6 (17-49) in groups 1 and 2, respectively. The mean duration of contact lens wear was 43.9 ± 15.3 (6-240) months. Anterior keratocyte density was 667.5 ± 128.3 cells/mm(2) in group 1 and 821.4 ± 136.7 cells/mm(2) in group 2 (P = 0.001). Posterior keratocyte densities of groups 1 and 2 were 540.2 ± 87.6 cells/mm(2) and 628.2 ± 72.4 cells/mm(2), respectively (P < 0.001). Endothelial cellular density was 2611.2 ± 298.4 cells/mm(2) in group 1 and 2643 ± 218.2 cells/mm(2) in group 2 (P = 0.52). Ratio of polymegethism was 44.6 ± 8.8% in group 1 and 31.3 ± 4.7% in group 2 (P < 0.001). Epithelial cellular enlargement was observed in eyes wearing contact lenses with a mean Dk/t ratio of 26.5 × 10(-9) ± 5.9 (8.9-32 × 10(-9)). Stromal microdots occurred with contact lenses with a mean Dk/t ratio of 13.2 × 10(-9) ± 17.5 × 10(-9) (8.9-20 × 10(-9)). In vivo examination of the cornea with confocal microscopy revealed a number of changes. These changes can be attributed both to the mechanical and the hypoxic effects of soft contact lenses. In soft contact lenses with a high Dk/t ratio, these changes would be less frequent.

The Glenn A. Fry award lecture 2010: Ophthalmic markers of diabetic neuropathy

Diabetic peripheral neuropathy (DPN) is a debilitating condition that affects about 50% of diabetic patients. The symptoms of DPN include numbness, tingling, or pain in the arms and legs. Patients with numbness may be unaware of foot trauma, which could develop into a foot ulcer. If left untreated, this may ultimately require amputation. Currently, the only method of directly examining peripheral nerves is to conduct skin punch or sural/peroneal nerve biopsies, which are uncomfortable and invasive. Indirect methods include quantitative sensory testing (assessing responses to heat, cold, and vibration) and nerve electrophysiology. Here, I describe research undertaken in my laboratory, investigating the possibility of using a range of ophthalmic markers to assess DPN. Corneal nerve structure and function can be assessed using corneal confocal microscopy and non-contact corneal esthesiometry, respectively. Retinal nerve structure and visual function can be evaluated using optical coherence tomography and perimetry, respectively. These techniques have been used to demonstrate that DPN is associated with morphological degradation of corneal nerves, reduced corneal sensitivity, retinal nerve fiber layer thinning, and peripheral visual field loss. With further validation, these ophthalmic markers could become established as rapid, painless, non-invasive, sensitive, reiterative, cost-effective, and clinically accessible means of screening for early detection, diagnosis, staging severity, and monitoring progression of DPN, as well as assessing the effectiveness of possible therapeutic interventions. Looking to the future, this research may pave the way for an expanded role for the ophthalmic professions in diabetes management.

Assessment of keratocyte density in patients with keratoconus not using contact lenses

PURPOSE

To assess the keratocyte density (KD) in the cornea of patients with keratoconus not using contact lenses.

METHOD

In this pilot study, the eyes (n = 68) of 35 patients with the diagnosis of keratoconus, who did not use contact lenses and the eyes(n = 70) of 35 healthy controls were prospectively examined using the Heidelberg Retinal Tomography Rostock cornea module (HRT3/RCM). The cases with keratoconus and controls were compared with regard to KD in the anteroposterior stromal layers.

RESULTS

Of the cases with keratoconus, 15 (42.9%) were men and 20 (57.1%) were women. The mean age was 21.1 ± 11.1 (range =14-41) years. Of the controls, 26 (73.9%) were men and 9 (26.1%)were women. The mean age was 23.9 ± 12.9 (range = 14-35) years.Of the 68 eyes with keratoconus, 22 (28.2%) had mild keratoconus, 23 (35.9%) had moderate keratoconus, and 23 (35.9%) had severe keratoconus. The mean anterior stromal KD was 651.4 ± 89 cells per square millimeter in cases with keratoconus and 879.4 ± 75 cells per square millimeter in controls (P < 0.05). The mean anterior stromal KD decreased by 25.9% in corneas with keratoconus. The mean posterior stromal KD was found to be 363.6 ± 74 cells per square millimeter in cases with keratoconus and 469.7 ± 56 cells per square millimeter in controls (P< 0.01). The mean posterior stromal KD decreased by 22.6% in corneas with keratoconus. The anterior stromal KD was higher than the posterior stromal KD (P < 0.001). No significant relationships were found between the stromal KD data and central corneal thickness or steepest keratometric.

CONCLUSIONS

The KD in the anterior and posterior corneal stroma was decreased in patients with keratoconus, but without the use of contact lens, compared with healthy controls. This density difference was independent from the central corneal thickness and the stage of keratoconus.

Indirect evaluation of corneal apoptosis in contact lens wearers by estimation of nitric oxide and antioxidant enzymes in tears

BACKGROUND

Contact lens induced trauma to the corneal epithelium results in increased release of inflammatory mediators. The keratocyte apoptosis is directly related to epithelial injury and has been correlated with increased production of nitric oxide. Potent antioxidant enzymes protect cells from oxidative damage by inactivating reactive oxygen species and thus inhibiting apoptosis. This study aims at determination of total nitric oxide and antioxidant enzymes in tears which will be an indirect criteria for assessing apoptosis.

MATERIALS AND METHODS

Nitric oxide and antioxidant enzymes were estimated in tears of 25 soft contact lens wearers and compared with 25 age and sex matched controls.

RESULTS

Statistically significant increase of nitric oxide (P<0.001), superoxide dismutase (P<0.001) and glutathione peroxidase (P<0.001) levels was seen in tears of contact lens wearers as compared to controls. There was also statistically significant increase in the levels of antioxidant enzymes, superoxide dismutase (P<0.05) and glutathione peroxidase (P<0.01), with increase in the total duration of contact lens wear in years.

CONCLUSIONS

Increase in the level of nitric oxide and antioxidant enzymes in tears of contact lens wearers suggested that contact lens wear suppresses the process of apoptosis. However, it was also postulated that the increased levels of nitric oxide balances the anti-apoptotic activities of increased levels of antioxidant enzymes by its pro-apoptotic activity leading to protective outcomes in contact lens wearers.

Automated assessment of keratocyte density in stromal images from the ConfoScan 4 confocal microscope

Purpose. To develop a program to determine cell densities in images from the ConfoScan 4 (Nidek, Inc., Freemont, CA) confocal microscope and compare the densities with those determined in images obtained by the Tandem Scanning confocal microscope (Tandem Scanning Corp., Reston, VA). Methods. A program was developed that used image-processing routines to identify stromal cell nuclei in images from the ConfoScan 4 confocal microscope. Cell selection parameters were set to match cell densities from the program with those determined manually in 15 normal corneas of 15 volunteers. The program was tested on scans from 16 other normal volunteers and 17 volunteers 3 years after LASIK. Cell densities were compared to densities determined by manual assessment and to those in scans by the Tandem Scanning confocal microscope in the same corneas. Results. The difference in cell density between the automatic and manual assessment was -539 +/- 3005 cells/mm(3) (mean +/- SD, P = 0.11) in the 16 test corneas. Densities estimated from the ConfoScan 4 agreed with those from the Tandem Scanning confocal microscope in all regions of the stroma except in the anterior 10%, where the ConfoScan 4 indicated a 30% lower density. Conclusions. Differences in anterior stromal cell density between the ConfoScan 4 and the Tandem Scanning confocal microscope can be explained by the different optical designs. The lower spatial resolution of the ConfoScan 4 limits its ability to resolve thin layers. The adaptation of our earlier cell-counting program to the ConfoScan 4 provides a timesaving, objective, and reproducible means of determining stromal cell densities in images from the ConfoScan 4.

Comparison of Cornea Module and DermaInspect for noninvasive imaging of ocular surface pathologies

Minimally invasive imaging of ocular surface pathologies aims at securing clinical diagnosis without actual tissue probing. For this matter, confocal microscopy (Cornea Module) is in daily use in ophthalmic practice. Multiphoton microscopy is a new optical technique that enables high-resolution imaging and functional analysis of living tissues based on tissue autofluorescence. This study was set up to compare the potential of a multiphoton microscope (DermaInspect) to the Cornea Module. Ocular surface pathologies such as pterygia, papillomae, and nevi were investigated in vivo using the Cornea Module and imaged immediately after excision by DermaInspect. Two excitation wavelengths, fluorescence lifetime imaging and second-harmonic generation (SHG), were used to discriminate different tissue structures. Images were compared with the histopathological assessment of the samples. At wavelengths of 730 nm, multiphoton microscopy exclusively revealed cellular structures. Collagen fibrils were specifically demonstrated by second-harmonic generation. Measurements of fluorescent lifetimes enabled the highly specific detection of goblet cells, erythrocytes, and nevus-cell clusters. At the settings used, DermaInspect reaches higher resolutions than the Cornea Module and obtains additional structural information. The parallel detection of multiphoton excited autofluorescence and confocal imaging could expand the possibilities of minimally invasive investigation of the ocular surface toward functional analysis at higher resolutions.

In vivo confocal microscopy for the evaluation of corneal microstructure in keratoconus

PURPOSE

To evaluate the corneal microstructure in keratoconus with in vivo confocal microscopy (IVCM).

METHODS

Unscarred corneas of 68 patients with keratoconus and 22 controls were evaluated with slit lamp examination, corneal topography, and IVCM (Confoscan 3.0, Vigonza, Italy). One eye was randomly chosen for analysis. Keratocyte, endothelial cell and basal epithelial densities, sub-basal and stromal nerve structure, and severity of stromal haze were evaluated.

RESULTS

Compared with corneas of control subjects, patients with keratoconus had a significantly lower anterior stromal keratocyte density (1279+/-197 cells/mm(2) vs. 1132+/-178 cells/mm(2), p=0.002), lower midstromal keratocyte density (904+/-213 cells/mm(2) vs. 770+/-120 cells/mm(2), p<0.001), lower posterior stromal keratocyte density (935+/-113 cells/mm(2) vs. 725+/-113 cells/mm(2), p<0.001), lower endothelial cell density (2924+/-300 cells/mm(2) vs. 2719+/-279 cells/mm(2), p=0.004), lower basal epithelial cell density (5987+/-699 cells/mm(2) vs. 4365+/-537 cells/mm(2), p<0.001), lower sub-basal long nerve density (32.0+/-6.5 nerves/mm(2) vs. 19.6+/-6.5 nerves/mm(2), p<0.001), thicker sub-basal (3.2+/-0.4 microm vs. 3.7+/-1.1 microm, p=0.01) and stromal nerves (5.0+/-1.2 microm vs. 8.0+/-2.9 microm, p<0.001), and higher proportion of corneas with haze (40.9% vs. 92.6%, p<0.001). A history of contact lens use (n=12) was not associated with lower keratocyte, endothelial cell, or basal epithelial cell counts.

CONCLUSIONS

Corneal microstructure is abnormal in patients with keratoconus. Keratocyte and endothelial cell loss appears to be present in keratoconic corneas.

Clinical applications of corneal confocal microscopy

Corneal confocal microscopy is a novel clinical technique for the study of corneal cellular structure. It provides images which are comparable to in-vitro histochemical techniques delineating corneal epithelium, Bowman's layer, stroma, Descemet's membrane and the corneal endothelium. Because, corneal confocal microscopy is a non invasive technique for in vivo imaging of the living cornea it has huge clinical potential to investigate numerous corneal diseases. Thus far it has been used in the detection and management of pathologic and infectious conditions, corneal dystrophies and ecstasies, monitoring contact lens induced corneal changes and for pre and post surgical evaluation (PRK, LASIK and LASEK, flap evaluations and Radial Keratotomy), and penetrating keratoplasty. Most recently it has been used as a surrogate for peripheral nerve damage in a variety of peripheral neuropathies and may have potential in acting as a surrogate marker for endothelial abnormalities.

Automated assessment of keratocyte density in clinical confocal microscopy of the corneal stroma

Cell density in the corneal stroma is typically determined by counting the number of bright objects, presumably keratocyte nuclei, in images from clinical confocal microscopy. We present a program that identifies bright objects and counts those that most likely represent cells. Selection variables were determined from 125 normal corneas with cell densities that had been assessed manually. The program was tested on 17 corneas of patients before and at several intervals to 5 years after laser in situ keratomileusis (LASIK) surgery. In these corneas, which showed a decrease in cell density after surgery, the program identified cells as well as human observers did.

The impact of silicone hydrogel materials on overnight corneal swelling

PURPOSE

To identify the corneal swelling response associated with silicone hydrogel contact lens wear.

METHODS

Twenty-five subjects were recruited to participate in this single-center, controlled, single-masked, clinical trial. The corneal swelling response was evaluated by central corneal pachymetry after overnight wear of balafilcon A, etafilcon A, lotrafilcon A, senofilcon A, and no lens wear. More specifically, after 8 hours of closed-eye wear of each material, corneal thickness was measured immediately on eye opening, in addition to the first 4 hours of open-eye wear. Paired t tests were used to compare the swelling response from each condition to that associated with senofilcon A, and given the numerous statistical comparisons, a P value of <or=0.01 was considered significant.

RESULTS

At eye opening, there was no difference in the swelling response when comparing balafilcon A (1.35%), lotrafilcon A (1.22%), or no lens wear (0.77%) to senofilcon A (1.40%), although the swelling response associated with etafilcon A was significantly greater (P<0.001) than that associated with senofilcon A. There were no differences between balafilcon A, lotrafilcon A, and no lens wear compared to senofilcon A during the open-eye deswelling period. However, 1 hour after eye opening, corneal swelling remained significantly greater with etafilcon A than with senofilcon A (1.76% vs. -0.51%, respectively, P=0.01), although no other time-specific comparisons differed.

CONCLUSIONS

Silicone hydrogel lenses, with high oxygen transmissibilities, are associated with very little corneal swelling after overnight wear of the lenses.

Contact lens-induced changes in the anterior eye as observed in vivo with the confocal microscope

The availability of the confocal microscope over the past decade has allowed clinicians and researchers to refine their understanding of the physiological and pathological basis of the ocular response to contact lens wear, and to discover previously unknown phenomena. Mucin balls, which form in the tear layer in patients wearing silicone hydrogel lenses, can penetrate the full thickness of the epithelium, leading to activation of keratocytes in the underlying anterior stroma. Epithelial cell size increases in response to all forms of lens wear, with lenses of higher oxygen transmissibility (Dk/t) interfering least with the normal process of epithelial desquamation. A higher density of Langerhans' cells is observed in the layer of the sub-basal nerve plexus among contact lens wearers, suggesting that contact lens wear may be altering the immune status of the cornea. Dark lines and folds are observed in the oedematous cornea in response to contact lens wear. Mechanical stimulation of the corneal surface, due to the physical presence of a contact lens, and the consequent release of inflammatory mediators, is the likely cause of reduced keratocyte density associated with lens wear. Highly reflective stromal 'microdot deposits' are observed throughout the entire stroma in higher numbers in lens wearers. 'Blebs' in the endothelium have a bright centre surrounded by a dark annular shadow; this appearance is explained with the aid of an optical model. The confocal microscope has considerable clinical utility in diagnosing Acanthamoeba and fungal keratitis. At the limbus, contact lenses can induce structural changes such as increases in basal epithelial cell size. An increased number of rolling leucocytes is observed in limbal vessels in response to low Dk/t lenses. It is concluded that the confocal microscope has considerable utility in contact lens research and practice.

Contemporary in vivo confocal microscopy of the living human cornea using white light and laser scanning techniques: a major review

In vivo confocal imaging of the cornea has evolved exponentially over the last few decades and it has increasingly emerged from the laboratory to be used in the clinical setting in relation to inherited corneal diseases, corneal infections, contact lens wear and the effects of corneal surgery. This evolution has led to significant enhancement of our knowledge of the living cornea in both its physiological and pathological states. A number of in vivo confocal microscope devices using white, and more recently coherent, light sources have been developed to provide non-invasive assessment of the corneal microstructure at a lateral resolution of 1-2 microm. The fundamental principles of in vivo confocal microscopy and the key differences between these devices are highlighted in this review. By providing a systematic review of the extensive literature on the human cornea, this perspective paper aims to provide an overview of how in vivo confocal microscopy has contributed to our greater understanding of the human cornea in health, in disease, and following surgery, with a particular emphasis on quantitative data. The utility and limitations of available data are highlighted as are possibilities for the future development of this innovative technology.

Study of the factors associated with the presence of white dots in the corneas of regular soft contact lens users from an Asian country

PURPOSE

: To investigate factors associated with the presence of microdot deposits or white dots (WDs) on confocal microscopy in regular soft contact lens (SCL) users.

METHODS

: This cross-sectional observational study investigated changes in the cornea in regular SCL users by using an in vivo slit-scanning microscope (ConfoScan 3). Images were analyzed by noting the presence of highly reflective WDs. Factors associated with WDs were analyzed by using an unpaired t test with Welch correction.

RESULTS

: There were 56 SCL wearers. Of these, a group of 10 had WDs (GWD) in various parts of the cornea. They had worn SCLs for 7 to 20 years and had a mean total duration of SCL wear of 13.6 +/- 4.4 years. Their mean age was 35.8 +/- 10.4 years. They were compared with a group of SCL wearers with no evidence of WDs (GNWD). The mean age of GNWD was 29.1 +/- 7.2 years, with a mean duration of SCL use of 8.17 +/- 5.1 years. The two groups were compared in terms of age, total duration of SCL wear (years), duration in hours per week, SCL water content (%), mean cell density in the endothelium and stroma, endothelial cell coefficient of cell size variation, and percentage of hexagonal cells. Only the duration of SCL wear was significantly associated with the presence of WDs (p=0.0042). WDs were most commonly found in the posterior stroma (n = 9). Two patients had WDs in the epithelium, with one of these having WDs in the endothelium. All patients except one with a hazy left eye scan had WDs bilaterally and symmetrically.

CONCLUSIONS

: Confocal microscopy allows visualization of WDs in the corneas of Asian regular SCL users. Patients with WDs have a longer history of SCL wear. WDs may represent an early stage of corneal disease or degeneration associated with alterations in cell behavior.

Clinical corneal confocal microscopy

Confocal microscopy allows non-invasive in vivo imaging of the ocular surface. Its unique physical properties enable microscopic examination of all layers of the cornea and have been used to investigate numerous corneal diseases: epithelial changes, numerous stromal degenerative or dystrophic diseases, endothelial pathologies, corneal deposits, infections, and traumatic lesions. It offers a new approach to study the physiological reactions of the cornea to different stimuli and the pathophysiologic events leading to corneal dysfunction in certain diseases. Confocal microscopy proves to be a powerful diagnostic tool and is especially of value in certain corneal diseases by allowing straightforward and non-invasive recognition of the pathologic conditions.

Quantitative analysis of corneal microstructure in keratoconus utilising in vivo confocal microscopy

PURPOSE

To establish and quantify the in vivo confocal microscopic features of moderate to advanced keratoconus.

METHODS

Nineteen keratoconus subjects were catergorised using Orbscan-derived corneal apex power and pachymetry as exhibiting moderate (n=7) and advanced (n=12) keratoconus. Control subjects included 23 noncontact lens wearers (Group A) and 15 contact lens wearers (Group B). All subjects underwent Confoscan slit scanning in vivo confocal microscopy.

RESULTS

Compared with Group A (4912+/-434 cells/mm(2)), basal epithelial density was significantly lower in both moderate (4592+/-414 cells/mm(2), P<0.05) and advanced keratoconus (4530+/-596 cells/mm(2), P=0.01). In comparison to Group A (761+/-118 cells/mm(2)), anterior stroma keratocyte density was significantly greater in both moderate keratoconus (883+/-111 cells/mm(2), P=0.001) and advanced keratoconus (952+/-122 cells/mm(2), P<0.001). Compared to Group A (504+/-80 cells/mm(2)) posterior stroma keratocyte density was also significantly greater in advanced keratoconus (599+/-97 cells/mm(2), P<0.001) and posterior stromal keratocyte density appeared to increase with increasing severity of keratoconus (P<0.05). However, comparing control Groups A and B, contact lens wear per se, was associated with significantly reduced (P=0.000) keratocyte density in the anterior stroma (609+/-66 cells/mm(2)) and demonstrated a trend (P=0.056) in the posterior stroma (470+/-63 cells/mm(2)). Keratoconic corneas (429+/-72 microm) were significantly thinner than control Groups A (508+/-77 mm) and B (495+/-80 microm). The presence of keratoconus did not affect the endothelial cell density (P=0.54).

CONCLUSION

In vivo confocal microscopy can provide insight into the microstructural changes that occur in keratoconus.

Assessment of stromal keratocytes and tear film inflammatory mediators during extended wear of contact lenses

PURPOSE

To monitor quantitative changes in stromal keratocyte density and the level of tear film inflammatory mediators following extended contact lens wear.

METHODS

Twenty-two subjects aged 32 +/- 11 years participated in this cross-sectional study. Eleven subjects had worn silicone hydrogel (Si-H) lenses on a 30-day continuous wear basis for 12 months. Eleven subjects had worn rigid gas permeable lenses on the same basis for 12 months. Eleven age-matched control subjects were also recruited. Ultrasound pachometry, confocal microscopy, and tear fluid sample collection were performed on all subjects. Tear samples were assayed for epidermal growth factor (EGF), hepatocyte growth factor (HGF) and interleukin (IL)-8.

RESULTS

Corneal thickness was similar for all subject groups. Total keratocyte density was not different between the 3 groups; however, keratocyte density was lower for rigid lens wearers in the anterior to mid stroma and lower for Si-H lens wearers in the posterior stroma compared with control subjects. Rigid lens wearers exhibited an irregular keratocyte distribution across the corneal stroma. EGF concentration and rate of release was greater in the tears collected from the rigid lens wearers and Si-H lens wearers, and IL-8 concentration was higher in the samples collected from the rigid lens wearers compared with the samples collected from the control subjects.

CONCLUSIONS

Mechanical stimulation of the corneal surface due to the physical presence of a contact lens and the consequent release of inflammatory mediators may account for a loss or redistribution of keratocytes.

The corneal stroma during contact lens wear

Recent technological advances have lead to novel descriptions of the microanatomy of the corneal stroma. In the first section of this review, these findings and the role they play in the maintenance of vital properties such as corneal transparency, mechanical strength, homeostasis, wound-healing response and metabolism are described. In the second part, contact lens induced stromal alterations such as acidosis, oedema, striae, thinning and opacities are reviewed as well as the more recently described phenomenon of microdot deposits and keratocyte loss with an emphasis on how lens wearing stromal effects can be minimised.

Contact lens assisted pharmacologically induced keratoshaping

PURPOSE

To retrospectively evaluate the effectiveness and describe the process of reducing hyperopia with a nonsteroidal antiinflammatory agent and a soft disposable contact lens in postoperative excimer laser patients with consecutive hyperopia.

SETTING

Private practice.

METHODS

This study includes a retrospective analysis of 14 eyes of 12 patients who underwent laser in situ keratomileusis or photorefractive keratectomy and experienced consecutive hyperopia. Patients were treated with a tightly fit, extended-wear contact lens in combination with the use of ketorolac tromethamine 0.5% (Acular) in an attempt to steepen the cornea. Uncorrected visual acuity, manifest refraction, and slitlamp examination were performed on a weekly basis until the desired outcome was achieved or until treatment was discontinued.

RESULTS

A total of 78.57% of eyes experienced a decrease in consecutive hyperopia (>or=0.50 diopters [D]) (P = 0.002). The mean dioptric change was 1.05D. A total of 88.89% of eyes experienced an increase in uncorrected visual acuity (>or=1 line) (P < 0.001). The mean increase was three lines of Snellen or Jaeger acuity. The mean number of weeks to see an effect was 1.71 weeks, and the mean number of weeks to achieve endpoint was 8.29 weeks (median, 6 weeks). CONCLUSIONS.: Contact lens-assisted pharmacologically induced keratoshaping is an effective treatment option for patients who experience consecutive hyperopia after laser in situ keratomileusis or photorefractive keratectomy.

Mechanical damage to corneal stromal cells by epithelial scraping

OBJECTIVE

Corneal epithelial scraping, a common clinical procedure, triggers a loss of underlying keratocytes. This study was conducted to examine whether the physical impact of epithelial scrape injury plays any role in the death of these cells.

METHODS

Epithelial debridement was carried out on the cornea of a freshly killed mouse either by mechanical scraping with a blunt spatula, as in the clinical scraping, or lifting by repeated touching with a gelatin-coated slide. Subsequently, nuclei, nuclear envelope, microtubules, microfilaments, and plasma membranes were examined with specific probes. Some corneas were fixed with alcohol before scrape injury. Fate of keratocytes after epithelial injury was investigated with isolated eyes ex vivo and living mice in vivo. Some of the procedures were performed with human donor corneas.

RESULTS

Within seconds of, or possibly simultaneous to, mechanical epithelial scraping, nuclei of underlying keratocytes became grossly deformed to assume extremely stretched morphology, accompanied by destruction of microfilaments and microtubules as well as compromised plasma membranes. These cells deteriorated gradually over several hours both ex vivo and in vivo. Nuclear deformation was observed even when the cornea was fixed with alcohol before epithelial scraping. When the epithelium was removed by gentle lifting, nuclei remained mostly intact. Similar results were obtained with human donor corneas.

CONCLUSION

Mechanical epithelial scraping can cause immediate damage to underlying anterior keratocytes by a physical impact, which appears to lead to degeneration of these cells.

In vivo confocal microscopy of the human cornea

AIMS

To describe the optics of in vivo confocal microscopy, its advantages over previous methods, and to summarise the literature that arose from its use for the observation of the human cornea. A critical review of the clinical usefulness of this new technology for the corneal examination is undertaken.

METHODS

Confocal microscopes obtain increased resolution by limiting the illumination and observation systems to a single point. Rapid scanning is used to reconstruct a full field of view and allows for "real time" viewing.

RESULTS

Coronal sections of the in situ epithelium, Bowman's membrane, stroma, and endothelium can be visualised at a resolution of 1-2 micro m. A backscattered light intensity curve allows objective measurements of sublayer thickness and corneal haze to be taken. In vivo confocal microscopy is therefore particularly useful in the areas of infective keratitis, corneal dystrophies, refractive surgery, and contact lens wear, where it aids in differential diagnosis and detection of subtle short and long term changes. Real time endothelial cell assessment can also be performed.

CONCLUSION

Because of their ability to visualise living tissue at cellular levels, confocal microscopes have proved useful additions to the current clinical tools.