[Confocal microscopy of the cornea in patients with diabetes]

Diabetic Retinopathy: Soluble and Imaging Ocular Biomarkers

Diabetic retinopathy (DR), the most common microvascular complication of diabetes mellitus, represents the leading cause of acquired blindness in the working-age population. Due to the potential absence of symptoms in the early stages of the disease, the identification of clinical biomarkers can have a crucial role in the early diagnosis of DR as well as for the detection of prognostic factors. In particular, imaging techniques are fundamental tools for screening, diagnosis, classification, monitoring, treatment planning and prognostic assessment in DR. In this context, the identification of ocular and systemic biomarkers is crucial to facilitate the risk stratification of diabetic patients; moreover, reliable biomarkers could provide prognostic information on disease progression as well as assist in predicting a patient's response to therapy. In this context, this review aimed to provide an updated and comprehensive overview of the soluble and anatomical biomarkers associated with DR.

Mechanistic investigations of diabetic ocular surface diseases

With the global prevalence of diabetes mellitus over recent decades, more patients suffered from various diabetic complications, including diabetic ocular surface diseases that may seriously affect the quality of life and even vision sight. The major diabetic ocular surface diseases include diabetic keratopathy and dry eye. Diabetic keratopathy is characterized with the delayed corneal epithelial wound healing, reduced corneal nerve density, decreased corneal sensation and feeling of burning or dryness. Diabetic dry eye is manifested as the reduction of tear secretion accompanied with the ocular discomfort. The early clinical symptoms include dry eye and corneal nerve degeneration, suggesting the early diagnosis should be focused on the examination of confocal microscopy and dry eye symptoms. The pathogenesis of diabetic keratopathy involves the accumulation of advanced glycation end-products, impaired neurotrophic innervations and limbal stem cell function, and dysregulated growth factor signaling, and inflammation alterations. Diabetic dry eye may be associated with the abnormal mitochondrial metabolism of lacrimal gland caused by the overactivation of sympathetic nervous system. Considering the important roles of the dense innervations in the homeostatic maintenance of cornea and lacrimal gland, further studies on the neuroepithelial and neuroimmune interactions will reveal the predominant pathogenic mechanisms and develop the targeting intervention strategies of diabetic ocular surface complications.

Corneal Keratocyte Density and Corneal Nerves Are Reduced in Patients With Severe Obesity and Improve After Bariatric Surgery

Purpose

Obesity is associated with peripheral neuropathy, which bariatric surgery may ameliorate. The aim of this study was to assess whether corneal confocal microscopy can show a change in corneal nerve morphology and keratocyte density in subjects with severe obesity after bariatric surgery.

Methods

Twenty obese patients with diabetes (n = 13) and without diabetes (n = 7) underwent assessment of hemoglobin A1c (HbA1c), lipids, IL-6, highly sensitive C-reactive protein (hsCRP), and corneal confocal microscopy before and 12 months after bariatric surgery. Corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), corneal nerve fiber length (CNFL), and keratocyte density (KD) from the anterior, middle, and posterior stroma were quantified. Twenty-two controls underwent assessment at baseline only.

Results

CNFL (P < 0.001), CNBD (P < 0.05), and anterior (P < 0.001), middle (P < 0.001), and posterior (P < 0.001) keratocyte densities were significantly lower in obese patients compared to controls, and anterior keratocyte density (AKD) correlated with CNFL. Twelve months after bariatric surgery, there were significant improvements in body mass index (BMI; P < 0.001), HDL cholesterol (P < 0.05), hsCRP (P < 0.001), and IL-6 (P < 0.01). There were significant increases in CNFD (P < 0.05), CNBD (P < 0.05), CNFL (P < 0.05), and anterior (P < 0.05) and middle (P < 0.001) keratocyte densities. The increase in AKD correlated with a decrease in BMI (r = -0.55, P < 0.05) and triglycerides (r = -0.85, P < 0.001). There were no significant correlations between the change in keratocyte densities and corneal nerve fiber or other neuropathy measures.

Conclusions

Corneal confocal microscopy demonstrates early small fiber damage and reduced keratocyte density in obese patients. Bariatric surgery leads to weight reduction and improvement in lipids and inflammation and an improvement in keratocyte density and corneal nerve regeneration.

Pathogenic Role of PPARα Downregulation in Corneal Nerve Degeneration and Impaired Corneal Sensitivity in Diabetes

The purpose of this study was to investigate the protective role of peroxisome proliferator-activated receptor α (PPARα) against diabetic keratopathy and corneal neuropathy. Corneal samples were obtained from human donors with and without diabetes. Streptozotocin-induced diabetic rats and mice were orally treated with PPARα agonist fenofibrate. As shown by immunohistochemistry and Western blotting, PPARα was downregulated in the corneas of humans with diabetes and diabetic rats. Immunostaining of β-III tubulin demonstrated that corneal nerve fiber metrics were decreased significantly in diabetic rats and mice, which were partially prevented by fenofibrate treatment. As evaluated using a Cochet-Bonnet aesthesiometer, corneal sensitivity was significantly decreased in diabetic mice, which was prevented by fenofibrate. PPARα ^-/- mice displayed progressive decreases in the corneal nerve fiber density. Consistently, corneal sensitivity was decreased in PPARα ^-/- mice relative to wild-type mice by 21 months of age. Diabetic mice showed increased incidence of spontaneous corneal epithelial lesion, which was prevented by fenofibrate while exacerbated by PPARα knockout. Western blot analysis revealed significantly altered neurotrophic factor levels in diabetic rat corneas, which were partially restored by fenofibrate treatment. These results indicate that PPARα protects the corneal nerve from degeneration induced by diabetes, and PPARα agonists have therapeutic potential in the treatment of diabetic keratopathy.

Keratocyte Density Is Reduced and Related to Corneal Nerve Damage in Diabetic Neuropathy

Purpose

The purpose of this study was to assess the relationship between corneal keratocyte density (KD) and corneal nerve damage in patients with and without diabetic peripheral neuropathy.

Methods

Eighty-six patients with type 1 and type 2 diabetes and 21 age-matched control subjects underwent assessment of the neuropathy disability score, quantitative sensory testing, electrophysiology, and corneal confocal microscopy and were divided into those without (DN-) (n = 22) and with (DN+) (n = 64) diabetic neuropathy. Corneal sub-basal nerve parameters and KD in the anterior, mid, and posterior stroma were quantified.

Results

Anterior, mid, and posterior stromal KD were significantly reduced in DN- (P = 0.02, P = 0.009, P = 0.01, respectively) and DN+ (all P < 0.0001) subjects compared to controls. Corneal nerve branch density (CNBD) (P < 0.0001, P < 0.0001) and corneal nerve fiber length (CNFL) (P = 0.03, P < 0.0001) were significantly reduced in DN- and DN+ subjects, respectively, and corneal nerve fiber density (CNFD) (P < 0.0001) was significantly reduced only in DN+ subjects compared to controls. Anterior, mid, and posterior stromal KD correlated significantly with CNFD (P = 0.008, P = 0.005, P = 0.01), CNBD (P = 0.01, P = 0.006, P = 0.001), and CNFL (P = 0.04, P = 0.008, P = 0.003), respectively.

Conclusions

This study demonstrates a reduction in anterior, mid, and posterior KD, which is associated with corneal sub-basal plexus nerve damage in patients with diabetes.

Corneal microstructural changes in nerve fiber, endothelial and epithelial density after cataract surgery in patients with diabetes mellitus

PURPOSE

The aim of this study was to analyze microstructural corneal changes following phacoemulsification of cataract with intraocular lens insertion in diabetes mellitus (DM).

METHODS

Prospective study of consecutive patients undergoing phacoemulsification with intraocular lens insertion, over a period of 6 months. Age, gender, serum glycosylated hemoglobin A1c levels, and effective phacoemulsification time were recorded. Anterior segment optical coherence tomography and corneal in vivo confocal microscopy were performed preoperatively and 1-month postoperatively. Subbasal nerve plexus (SBN) density, basal epithelial cell density, and endothelial cell density (ECD) were quantitatively analyzed.

RESULTS

Twenty-eight patients with type 2 DM (71.2 ± 7.6 years) and 23 healthy controls (mean age, 74.4 ± 7.4 years) were recruited. Mean hemoglobin A1c level was 7.5% in patients with DM and 5.7% in the control group (P < 0.0001). A significant reduction in SBN density was noted postoperatively in both DM (P < 0.0001) and non-DM groups (P < 0.0001). Patients with DM had a lower mean SBN density compared with non-DM group, before (P < 0.0001) and after surgery (P < 0.0001). Longer effective phacoemulsification time correlated with a greater decrease in ECD postoperatively in the whole cohort (P < 0.0001), and in the control (P = 0.002) and DM (P = 0.039) groups independently. There was no significant difference in preoperative ECD between the DM group (2254 +/- 426 cells/mm(2)) and non-DM group (2384 +/- 438 cells/mm(2); P = 0.2). [corrected].

CONCLUSIONS

Subbasal nerve density is reduced after cataract surgery in patients with and without DM. However, lower initial SBN density in patients with DM may predispose them to develop diabetic keratopathy. DM does not predispose to greater endothelial loss following phacoemulsification.

Sensory nerve regeneration after epithelium wounding in normal and diabetic cornea

The cornea is the most densely innervated mammalian tissue. The sensory nerves are responsible for sensations of dryness, temperature, touch, and pain, and play important roles in the blink reflex, wound healing, and tear production. Many ocular and systemic diseases can adversely affect corneal sensory nerve and consequently impair their function. One of such systemic diseases is diabetes mellitus (DM) which causes sensory degeneration, neurotrophic keratopathy (DNK), and delayed wound healing. In this review, we summarize recent discoveries revealing mechanisms underlying the pathogenesis of DNK and the impairment of sensory nerve regeneration in post wound diabetic corneas in using animal model of human diabetes. Because it is generally believed that common mechanisms are operative in the pathogenesis of diabetic peripheral neuropathy in different tissues, the findings in the corneas have implications in in other tissues such as the skin, which often leads to foot ulceration and amputation in diabetic patients.

The effect of donor diabetes history on graft failure and endothelial cell density 10 years after penetrating keratoplasty

OBJECTIVE

To examine the long-term effect of donor diabetes history on graft failure and endothelial cell density (ECD) after penetrating keratoplasty (PK) in the Cornea Donor Study.

DESIGN

Multicenter, prospective, double-masked, controlled clinical trial.

PARTICIPANTS

One thousand ninety subjects undergoing PK for a moderate risk condition, principally Fuchs' dystrophy or pseudophakic or aphakic corneal edema, were enrolled by 105 surgeons from 80 clinical sites in the United States.

METHODS

Corneas from donors 12 to 75 years of age were assigned by 43 eye banks to participants without respect to recipient factors. Donor and recipient diabetes status was determined from existing medical records. Images of the central endothelium were obtained before surgery (baseline) and at intervals for 10 years after surgery and were analyzed by a central image analysis reading center to determine ECD.

MAIN OUTCOME MEASURES

Time to graft failure (regraft or cloudy cornea for 3 consecutive months) and ECD.

RESULTS

There was no statistically significant association of donor diabetes history with 10-year graft failure, baseline ECD, 10-year ECD, or ECD values longitudinally over time in unadjusted analyses, nor after adjusting for donor age and other significant covariates. The 10-year graft failure rate was 23% in the 199 patients receiving a cornea from a donor with diabetes versus 26% in the 891 patients receiving a cornea from a donor without diabetes (95% confidence interval for the difference, -10% to 6%; unadjusted P=0.60). Baseline ECD (P=0.71), 10-year ECD (P>0.99), and changes in ECD over 10 years (P=0.86) were similar comparing donor groups with and without diabetes.

CONCLUSIONS

The study results do not suggest an association between donor diabetes and PK outcome. However, the assessment of donor diabetes was imprecise and based on historical data only. The increasing frequency of diabetes in the aging population in the United States affects the donor pool. Thus, the impact of donor diabetes on long-term endothelial health after PK or endothelial keratoplasty, or both, warrants further study with more precise measures of diabetes and its complications.

Corneal nerve fibre damage precedes diabetic retinopathy in patients with type 2 diabetes mellitus

AIMS

To quantify the morphological alterations in corneal nerve fibres and cells in patients with type 2 diabetes mellitus in relation to the severity of diabetic retinopathy.

METHODS

One hundred and thirty-two eyes of 132 patients with type 2 diabetes and 32 eyes of 32 healthy control subjects were evaluated with in vivo corneal confocal microscopy. Patients with diabetes were classified into three groups: patients without diabetic retinopathy, patients with non-proliferative diabetic retinopathy and patients with proliferative diabetic retinopathy. Anterior and posterior stromal keratocyte, endothelial cell and basal epithelial cell densities and sub-basal nerve fibre structure were evaluated.

RESULTS

Significant reductions in basal epithelial cell, anterior stromal keratocyte and endothelial cell densities were observed only in patients with diabetic retinopathy. However, nerve fibre density, nerve branch density and nerve fibre length were reduced in patients without diabetic retinopathy and worsened progressively with increasing severity of retinopathy.

CONCLUSIONS

Corneal cell pathology occurs in patients with diabetic retinopathy, but corneal nerve fibre damage seems to precede the development of diabetic retinopathy.

Corneal confocal microscopy: a new technique for early detection of diabetic neuropathy

Corneal confocal microscopy (CCM) is a noninvasive method for the study of human cornea in vivo. It has increasingly been used to assess the morphology of the sub-basal corneal nerve plexus. CCM has good reproducibility and may contribute to the early diagnosis of diabetic polyneuropathy. It may also be useful to document favorable changes in nerve fiber structure early after therapeutic intervention. Corneal nerve pathology is more pronounced in patients with diabetic polyneuropathy and is associated with its clinical severity. The sensitivity and specificity of CCM for the diagnosis of polyneuropathy is moderate to high. CCM now merits further use in large longitudinal studies to provide more information on the natural history of diabetic neuropathy and effects of treatment. Moreover, there is a need for a larger normative database. Finally, technical progress is expected to enable visualization of larger corneal areas and improve nerve fiber quantification, increasing diagnostic accuracy.

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.

In vivo confocal microscopy of corneal small fiber damage in diabetes mellitus

BACKGROUND

Advanced diabetic keratopathy includes impaired corneal sensation, reduced tear secretion, conjunctival squamous metaplasia, and goblet cell loss, as well as susceptibility to corneal erosions and ulcerations. It is thought to be a form of generalized diabetic neuropathy. Early diagnosis of nerve fiber degeneration is essential to prevent further damage.

METHODS

We examined the corneal innervation pattern of patients with diabetes mellitus type 1 and 2 of various durations by in vivo confocal microscopy, and correlated our findings to the severity of diabetic retinopathy, corneal sensation, peripheral diabetic neuropathy in the lower limb, and nephropathy.

RESULTS

Nerve fiber length (NFL) was significantly different between patients without diabetic retinopathy and controls (p = 0.028). In patients with non-proliferative diabetic retinopathy (NPDR) and patients with proliferative diabetic retinopathy (PDR), nerve fiber parameters including density (NFD), NFL, and corneal nerve branching (NB) showed a difference with increasing significance compared to healthy persons. A history of nephropathy and/or peripheral neuropathy (all p < 0.001), decreased corneal sensation (all p < or = 0.03), and pathological vibration sensation (p < or = 0.04) were significantly associated with a decrease in NFD, NFL, and NB (except vibration sensation). Unexpectedly, diabetic patients with normal corneal and vibration sensation demonstrated significant changes in NFD (p = 0.005), NFL, and NB (both p = 0.001) compared to healthy volunteers with intact corneal and vibration sensation.

CONCLUSION

Confocal microscopy is a valuable tool for demonstrating subtle corneal nerve alterations in vivo. It is capable of demonstrating diabetic nerve fiber damage earlier than corneal sensation testing and vibration perception assessment in the lower limb.

Corneal endothelium in patients with diabetes mellitus: a historical cohort study

PURPOSE

Retinopathy is the major cause of ocular morbidity in patients with diabetes mellitus. Chronic hyperglycemia spares no organ and can affect the morphology and function of the various corneal layers, compromising its transparency. This study was conducted to associate the status of corneal endothelium to diabetes mellitus (DM) and identify risk factors of compromised corneal endothelium.

METHODS

A total of 220 eyes of randomly selected patients (110 diabetic and 110 nondiabetic) were subjected to detailed slitlamp and fundus evaluation. Corneal endothelial status was evaluated using the Nidek Confoscan 2. Cell density, percentage polymegathism, and pleomorphism were calculated. The findings in diabetic patients were compared to those without disease. The outcome was correlated to diabetic retinopathy (DR). The effects of hypertension, hyperlipidemia, age, gender, type, duration, glycemic control, and grades of DR was also considered.

RESULTS

The mean corneal endothelial cell density was -175 cells/mm2 (95% CI -317 to -33 cells/mm2) less in eyes of diabetic patients. The number of endothelial cells with polymegathism was significantly greater among eyes of diabetic patients. There were less corneal endothelial cells with pleomorphism in nondiabetic patients. Polymegathism and pleomorphism of corneal endothelial cells seems to be positively associated with DM type II. Cell density was significantly lower in eyes with DR than those without DR.

CONCLUSIONS

Corneal endothelium in diabetic patients seems to be compromised. Evaluation of corneal endothelium should be part of protocol for eye care of diabetic patients.

Morphologic alterations of both the stromal and subbasal nerves in the corneas of patients with diabetes

PURPOSE

To evaluate the subbasal and the stromal nerves of the corneas of patients with type 2 diabetes with in vivo confocal microscopy and to compare them with those of nondiabetic patients.

METHODS

Thirty-five corneas of patients with type 2 diabetes and 24 corneas of age-matched control subjects were included in the study. Patients with diabetes were further classified with respect to the stage of retinopathy. Subbasal and stromal nerve plexus morphology and thickness were evaluated with in vivo confocal microscopy. Subbasal long nerve fiber (LNF) and total nerve branch (NB) densities were calculated.

RESULTS

The mean stromal nerve thickness was significantly higher in patients with diabetes (8.99 +/- 2.32 microm) than that of the control subjects (5.69 +/- 1.49 microm; Mann-Whitney U test; P < 0.001). The proportion of curved stromal nerves in patients with diabetes (45.7%) was also higher than that of normal subjects (20.8%; chi(2), P = 0.05). Subbasal LNF and NB densities were found to significantly lower in the corneas of patients with diabetes (28.3 +/- 10.4 and 39.7 +/- 13.2 nerve/mm(2), respectively) than those of the control subjects (34.1 +/- 5.7 and 58.5 +/- 12.4 nerve/mm(2), respectively; Mann-Whitney, P = 0.012 and P < 0.001). In addition, the subbasal nerve plexus of patients with diabetes appeared significantly thicker and more tortuous than those of the control subjects (Mann-Whitney, P = 0.002 and P = 0.001).

CONCLUSION

Both stromal and subbasal nerves appear abnormal in the corneas of patients with diabetes. Patients with proliferative diabetic retinopathy show more pronounced nerve alterations than patients who do not have diabetic retinopathy.

Diabetes and corneal cell densities in humans by in vivo confocal microscopy

PURPOSE

Diabetes is accompanied by an increased autofluorescence of the cornea, probably because of accumulation of advanced glycation end products (AGEs). The pathogenic mechanism is still unknown. This study aimed to quantify differences in corneal cell densities between diabetic patients and healthy controls.

METHODS

The left cornea of 15 patients with non-insulin-dependent diabetes mellitus (NIDDM) with level of retinopathy 20 according to the Early Treatment of Diabetic Retinopathy Study (ETDRS) and of 15 healthy controls were examined by noninvasive in vivo confocal microscopy in an observational prospective study. The cell densities in 6 corneal layers were determined along the optical axis of the cornea by using stereologic methods.

RESULTS

The average cell density per unit area in the superficial and basal epithelium and the endothelial layer was 725 +/- 171, 5950 +/- 653, and 2690 +/- 302 cells/mm in controls and 815 +/- 260, 5060 +/- 301, and 2660 +/- 364 cells/mm in diabetic patients. The cell density per unit volume in the anterior, mid-, and posterior stroma was 26,300 +/- 4090, 19,390 +/- 3120, and 25,700 +/- 3260 cells/mm in controls and 27,560 +/- 3880, 21,930 +/- 2110, and 25,790 +/- 3090 cells/mm in patients with diabetes. In both groups, the density in the midstroma was significantly lower than in both the anterior stroma and the posterior stroma (P < 0.02). The cell density in the basal layer of diabetic patients was significantly lower than in healthy controls (-15.0%, P < 0.0004). In the other layers, no significant differences between both groups (P > 0.07) were observed.

CONCLUSIONS

The lower basal cell density found in patients with diabetes may result from a combination of different mechanisms including decreased innervation at the subbasal nerve plexus, basement membrane alterations, and higher turnover rate in basal epithelial cells. The lower cell density in the midstroma of diabetic patients and healthy controls may be attributed in part to differences in oxygen concentration in the stromal layers (depths). Changes in cellular density did not seem to be responsible for the increased autofluorescence in diabetes.

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.

Apport de la microscopie confocale in vivo dans l’exploration de tumeurs limbiques

PURPOSE

To explore tumors of the limbus with a new in vivo confocal microscope and to compare the images to histology results.

METHODS

We evaluated three tumors in three patients with the Heidelberg Retina Tomograph II, Rostock Cornea Module. A diagnostic and therapeutic excision with adjunctive cryotherapy was performed for each individual. Confocal microscopy was compared to histopathologic sections.

RESULTS

Histology identified two dysplasias and one carcinoma in situ. The main pathological features were visible on our images: cytonuclear atypias, epithelial folds into an inflammatory and vascularized conjunctival stroma, fine vessels perpendicular to the surface, a clear limit with normal epithelium, papillomatous organization, and abnormal keratinization.

CONCLUSION

Our preliminary study showed that this type of limbal tumor could be explored using in vivo confocal microscopy. We were not able to determine whether there was a microinvasion. This new method could be a diagnostic aid, especially for atypical lesions and for follow-up because of frequent recurrences. Other studies are necessary to confirm our hypothesis.

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.

Confocal microscopy of the cornea

This paper provides the clinician and the researcher with an in-depth manual on the use of a scanning-slit confocal light microscope for the clinical examination and investigation of the living human cornea in vivo. The scope of the paper includes a thorough explanation of the principles of various types of confocal microscopes as well as their limitations, a comprehensive review of the development of biomicroscopy of the eye, and a comparison of confocal microscopy and other optical techniques such as optical coherence tomography. The early work of Ridley, Goldmann and others on point illumination in early confocal instruments is described. The main part of the paper describes and illustrates the clinical examination of the living human cornea with the confocal microscope. Figures (many in color) from the normal cornea, the cornea with known parthologies, and the postsurgical cornea are selected for their educational value. Photographs of standard light microscopy of fixed, human corneal sections are compared with confocal maicroscopic images. Where appropriate, slit lamp color photographs are compared with confocal microscopic images. The clinical scanning-slit confocal microscope is an evolving instrument for biomicroscopy of the living eye.