Changes in Corneal Sensation and Ocular Surface in Patients With Asymmetrical Keratoconus

Corneal cross-linking effects on ocular surface parameters and corneal topographic and optical characteristics in progressive keratoconus cases: a prospective single-arm study

OBJECTIVE

This study aims to evaluate the effects of epithelial-off corneal cross-linking (CXL) on the ocular surface and corneal topographic and optical parameters in progressive keratoconus (KCN) cases.

STUDY DESIGN

Prospective single-arm interventional study.

METHODS

Thirty eyes of 25 progressive KCN cases needing corneal CXL entered the study. All the included eyes underwent an epi-off corneal CXl procedure following the Dresden protocol. The ocular surface parameters, including tear break-up time (TBUT), Schirmer I test, and Ocular surface disease index (OSDI), were evaluated at baseline, one and 6 months after the procedure. The corneal imaging with Pentacam (Oculus Inc.) was conducted at these visits, measuring topographic parameters (e.g., Kmax, K1, K2, and corneal thickness), indices (e.g., ISV, IVA, KI IHA), and aberrations.

RESULTS

The median age of the patients was 24.0 (IQR:21.0-26.5) with a baseline BCVA of 0.045 LogMAR (IQR:0.000-0.301). The BCVA had no significant change in the last follow-up (p:1.000). The baseline median values for TBUT, Schirmer test, and OSDI were 11.0s, 13.0mm, and 28.12, demonstrating a significant ocular surface malfunction. These ocular surface parameters showed no significant change 6 months after CXL (p: 0.662, 0.534, and 0.372, respectively). The K1 and K2 values decreased significantly at the last follow-up compared to the baseline (44.4 vs. 45.6 (p:0.019) and 48.0 vs. 48.1 (p:0.008), respectively). The only topographic indices that improved 6 months after CXL was the index of surface variance (ISV) (70.50 vs. 61.70, p:0.036). The corneal front surface higher-order aberrations, including spherical aberration, coma, and trefoil, showed no significant change 6 months after CXL.

CONCLUSION

Progressive KCN cases cope with some ocular surface problems, such as dry eye, but the corneal CXL is safe for these cases without causing any deterioration in the ocular surface problems. The corneal CXL might not improve the topographic indices and corneal aberrations 6 months after the procedure.

Age-Related Changes in Corneal Sensitivity

PURPOSE

The aim of this prospective cross-sectional cohort study was to clinically test whether corneal sensation decreases with age, based on subject feedback (psychophysical method), and whether it correlates with general pain perception.

METHODS

Subjects were recruited from 2 equally large age groups: group A (18-30 years) and group B (50-70 years; n = 45 per group). The inclusion criteria were healthy eyes, Ocular Surface Disease Index ≤13, and no contact lens wear. Corneal sensitivity threshold (CST) measurements were performed twice during each of the 2 visits, with the aid of the new Swiss liquid jet esthesiometer for corneal sensitivity (SLACS) and Cochet-Bonnet (CB) esthesiometer. A general pain sensitivity score was obtained from all participants.

RESULTS

Ninety subjects completed the study (n = 45 per age group, average age in group A: 24.2 ± 2.94 years, group B: 58.5 ± 5.71 years). Statistically higher CSTs for age group B were only observed for SLACS (mean difference: 1.58 dB, P < 0.001). No correlation was observed between the pain score and the CSTs obtained with either esthesiometry method (r = 0.11, P = 0.25 for liquid jet and r=-0.076, P = 0.61 CB).

CONCLUSIONS

A statistically significant decrease in corneal sensitivity was observed for the older age group with SLACS in this study, with CB however only a trend in the same direction was noted. General pain perception was not found to correlate with ocular surface sensation.

Morphological and functional assessment of the tear film and meibomian glands in keratoconus

PURPOSE

To evaluate morphological and functional state of the meibomian glands (MG) in keratoconus patients.

METHODS

One hundred eyes of 100 keratoconus patients and 100 eyes of 100 age-matched control subjects were included into this study. Ocular Surface Disease Index (OSDI) scores, non-invasive break up time (NIBUT), findings of meibography, staining with fluorescein of the ocular surface, tear film break-up time (TBUT), and Schirmer I test were documented in all patients' eyes and control eyes and were compared between the groups .

RESULTS

The mean TBUT and NIBUT were significantly lower, corneal staining and OSDI scores were statistically greater in the keratoconus group (p < 0.05). The mean meiboscore, partial gland, gland dropout and gland thickening scores for upper/lower eyelids were significantly greater in keratoconus patients than controls (p < 0.05). The NIBUT measurements significantly correlated with MG loss in upper/lower eyelids (p < 0.05). The severity of keratoconus seemed to correlate with meiboscore, partial gland, gland thickening scores in upper/lower eyelids.

CONCLUSION

Our data suggests that corneal ectasia in keratoconus is related with alterations in ocular surface, tear film function and MG morphology. Early screening and treatment of MG dysfunction may improve ocular surface quality and allow better disease management in keratoconus patients.

Integrative transcriptomics analysis and experimental validation reveal immunomodulatory patterns in keratoconus

Keratoconus is a progressive disorder of the cornea and is typically considered a noninflammatory disease. However, increasing evidence indicates that immune disorders play an essential role in keratoconus progression, but the immune-related etiology remains elusive. Here, we comprehensively utilized bioinformatics approaches and experimental methods to explore the potential immunoregulatory mechanism of keratoconus progression. Transcriptomics data containing two keratoconus patient groups was derived from the public dataset GSE151631. The intersection of genes and known immunological genes was used to obtain differentially expressed immune-related genes. We utilized various protein clustering algorithms to screen out and validated the hub immune-related genes, and further explored their potential biological functions via gene annotation and pathway enrichment analyses. Moreover, the underlying immune landscape and drug targets were predicted by immune cell infiltration analysis and drug-gene interaction analysis. Furthermore, keratoconus-related immunoregulatory competitive endogenous RNA networks were constructed and experimentally validated. After filtering and experimental validation, nine keratoconus-associated immune-related genes were credible. Infiltrated monocytes might play an essential role in the progression of keratoconus. Moreover, eleven intersecting drugs targeting four genes, CCR2, CCR5, F2RL1, and ADORA1, were considered as potential druggable molecular targets for keratoconus. Furthermore, in the competitive endogenous RNA network, we identified several lncRNAs and miRNAs as critical noncoding RNAs regulating the hub genes. Overall, our data indicated that the immunomodulatory patterns had undergone changes in the pathogenesis of keratoconus, which might facilitate the understanding of keratoconus-related immune processes and provide novel insights into developing new immunotherapies for keratoconus.

Diagnosis of keratoconus in a young male by electrophysiological test findings: A case report

RATIONALE

The purpose of this report was to describe the diagnostic process of a case of keratoconus (KCN) after electrophysiological examination.

PATIENT CONCERNS

A 23-year-old male army officer presented with decreased visual acuity (VA) in the left eye for 5 months. Best-corrected VA was 20/20 in the right eye and 20/300 in the left eye. The cornea and lens were clear in both eyes with a normal anterior chamber. No specific abnormalities were found on fundus photography, optical coherence tomography, fundus fluorescein angiography (FFA), indocyanine green angiography (ICGA), or full-field electroretinography (ffERG) of both eyes. Pattern visual-evoked potentials (PVEP) detected a reduced amplitude and delayed peak time of the P100-wave in both eyes, which was more severe in the left eye. The amplitude and peak time of the P2-wave in flash VEP (FVEP) were comparable in both eyes and were within the normal ranges.

DIAGNOSIS

Corneal topography was performed, and KCN was diagnosed by the presence of an asymmetrical bowtie pattern in both eyes, which was worse in the left eye.

INTERVENTIONS

Transepithelial corneal collagen cross-linking was performed.

OUTCOMES

The BCVA of both eyes remained stable after treatment at follow-up.

LESSONS

KCN should be suspected in cases of unimproved VA and significant irregular stigmatism, while no obvious lesions exist in other parts of the eyes. The evidence of lesion location by electrophysiological examinations could sometimes be of favor in diagnosing KCN.

Evaluation of corneal topography, tear film function and conjunctival impression cytology after long-term scleral contact lens wear in keratoconus patients

Purpose: To investigate the impact of long-term scleral contact lens (ScCL) wear on corneal curvature, corneal thickness, tear film function, and ocular surface in patients with keratoconus.Methods: Sixteen keratoconus patients wearing ScCLs for 6 months were enrolled in the study. Corneal topography, tear osmolarity test, Schirmer 1 test, tear film break-up time (TBUT) test, and impression cytology analysis were assessed at baseline and follow-up examinations.Results: There were no significant differences in visual acuity, keratometric and pachymetric values after 6 months of ScCL wear compared to baseline (p>0.05 for all). Tear osmolarity, Schirmer 1 test, and TBUT test results showed no significant change during follow-up (p>0.05 for all). Median goblet cell density and grade of squamous metaplasia did not differ significantly at 1-month. However, there was a gradual deterioration in goblet cell density and Nelson grade until the third-month visit compared to baseline (p for goblet cell, p=0.003; p for Nelson grade, p=0.003). These impaired cytological features observed at 3-month visit persisted at 6-month visit (p for goblet cell, p=0.008; p for Nelson grade, p<0.001).Conclusion: Six months of ScCL wear did not induce any changes in corneal curvature and thickness and also did not affect tear function tests in keratoconic eyes. The only significant changes observed were a decrease in goblet cell density and metaplastic changes in conjunctival epithelium in impression cytology analysis. Further investigations may be needed to better understand the cause of impairment in cytological features of ocular surface and its clinical implications.

Current perspectives in the management of keratoconus with contact lenses

Our aim is to review current and significant articles on contact lens wear in keratoconus patients. A comprehensive literature search of PubMed was performed for the following topics on contact lens wear in keratoconus patients: (1) characteristics of contact lens wearers, (2) safety and efficacy, (3) complications, (4) fitting techniques, (5) contact lens wear after procedures/surgeries, (6) patient satisfaction. A total of 104 studies were finally selected and reviewed. Gas permeable (GP) lens wear provided significantly better vision than glasses. Special cone design lenses had better patient comfort levels though there was no difference in best corrected visual acuity among the GP lenses. Soft lenses showed good efficacy for the treatment of mild-to-moderate keratoconus with newer designs improving visual performance such as customised hydrogel and novel pinhole lenses. Scleral and hybrid lenses provide good visual acuity and comfort for keratoconic patients previously intolerant to RGP lenses. RGP lens wear post-cross linking (CXL) is relatively well-tolerated. Contact lenses may still be required post intrastromal corneal ring procedures and post keratoplasty. Scheimpflug imaging and anterior segment optical coherent tomography (ASOCT) are useful in contact lens fitting. Computerized contact lens fitting techniques could reduce the chair time of lens fitting as well as improve comfort and visual performance. Contact lenses play an important role in the visual rehabilitation of keratoconus patients. New contact lens designs and materials have significantly expanded the available fitting options for keratoconus patients. Imaging technology can be utilized to guide contact lens fitting.

Effect of rigid gas permeable contact lens on keratoconus progression: a review

The prevalence of keratoconus is 1/2000 in the general population and is high in adolescents. Keratoconus is a progressive disease, which has a great impact on patients' quality of life and mental health. It can be managed by surgical and non-surgical means, rigid gas permeable (RGP) contact lens as its main non-surgical method is widely used in clinic. The efficacy of wearing RGP contact lens has been confirmed to some extent, but some studies have found that wearing RGP contact lens has adverse effects, which may promote disease progression. In this paper, the advantages and disadvantages of RGP contact lens in controlling keratoconus were reviewed to provide more suggestions and references for the clinical application of RGP contact lens.

Mechanisms of Collagen Crosslinking in Diabetes and Keratoconus

Collagen crosslinking provides the mechanical strength required for physiological maintenance of the extracellular matrix in most tissues in the human body, including the cornea. Aging and diabetes mellitus (DM) are processes that are both associated with increased collagen crosslinking that leads to increased corneal rigidity. By contrast, keratoconus (KC) is a corneal thinning disease associated with decreased mechanical stiffness leading to ectasia of the central cornea. Studies have suggested that crosslinking mediated by reactive advanced glycation end products during DM may protect the cornea from KC development. Parallel to this hypothesis, riboflavin-mediated photoreactive corneal crosslinking has been proposed as a therapeutic option to halt the progression of corneal thinning by inducing intra- and intermolecular crosslink formation within the collagen fibrils of the stroma, leading to stabilization of the disease. Here, we review the pathobiology of DM and KC in the context of corneal structure, the epidemiology behind the inverse correlation of DM and KC development, and the chemical mechanisms of lysyl oxidase-mediated crosslinking, advanced glycation end product-mediated crosslinking, and photoreactive riboflavin-mediated corneal crosslinking. The goal of this review is to define the biological and chemical pathways important in physiological and pathological processes related to collagen crosslinking in DM and KC.

Tear function and ocular surface changes following corneal collagen cross-linking treatment in keratoconus patients: 18-month results

PURPOSE

To investigate the long-term effects that CXL has on the tear function and ocular surface in keratoconus.

METHODS

Twenty-one consecutive patients (24 eyes) with progressive keratoconus scheduled for CXL were included. All patients underwent the following procedures: conjunctival impression cytology analysis, ocular surface disease index (OSDI) score, tear osmolarity test, Schirmer test, tear film breakup time (TBUT), ophthalmic surface fluorescein (Fl) staining, and topographical corneal evaluation before as well as 3 and 18 months after accelerated CXL.

RESULTS

There was no change in the median OSDI score, tear osmolarity test, Schirmer test, and the Fl staining score after CXL. The median TBUT increased from 9.00 s at baseline to 12.00 s at 18 months postoperative (P < 0.001). The cytological features of the temporal and superior bulbar conjunctiva deteriorated at 3 months post-CXL (P < 0.001). An improvement in impression cytology analysis of the temporal conjunctiva was noted at 18-month follow-up (P < 0.001). Significant improvements in the median maximum keratometry and mean keratometry (K-mean) readings were also noted 18 months after CXL (P < 0.001). The changes in the K-mean correlated significantly with the changes in TBUT levels at 18-month follow-up as compared to baseline (r =  - 0.688, P < 0.001).

CONCLUSIONS

The improvement in TBUT, conjunctival squamous metaplasia, and the goblet cell density indicates a favorable effect of CXL on the ocular surface and tear film in keratoconus, presumably due to the reduced corneal irregularity after CXL.

Advanced anterior segment imaging in keratoconus: a review

Advances in anterior segment imaging have enhanced our ability to detect keratoconus in its early stages and characterize the pathologic changes that occur. Computerized corneal tomography has elucidated the alterations in shape of the anterior and posterior corneal surfaces and alterations in thickness as the disease progresses. Automated screening indices such as the keratoconus screening index were developed to assist in detecting keratoconus in suspicious cases. In vivo assessment of keratoconic corneas has revealed that compromised corneal biomechanics can now be measured clinically. Optical coherence tomography has demonstrated alterations in corneal epithelial thickness and distribution in keratoconus, has a role in assessing Descemet's membrane detachment in acute corneal hydrops (ACH) and the depth of the demarcation line following corneal collagen cross-linking. In vivo confocal microscopy has exhibited cellular changes that occur in keratoconus and provided insight into cellular events that may be related to the development of neovascularization in ACH.

Effects of the rigid gas permeable contact lense use on tear and ocular surface among keratoconus patients

PURPOSE

To investigate changes in tear and ocular surface of patients with keratoconus using rigid gas permeable contact lenses (RGPCL) and compare them against keratoconus patients who were not using lenses as well as a control group of healthy subjects.

METHODS

24 keratoconus patients using RGPCL (Group 1) 22 patients who were not using lenses (Group 3) and 21 healthy subjects (Group 3) were included in the study. Subjective complaints about the subjects' eyes have been investigated using the ocular-surface disease index (OSDI). After the control of best-corrected visual acuity, anterior chamber and fundus examinations were performed.

RESULTS

Schirmer (p-value=0.01) and tear break up mean comparison tests (p-value=0.002) revealed significant differences across different groups but tear osmolarity analysis did not (p-value >0.05). Oxford and OSDI scores were compatible with Schirmer and tear break up test comparisons. (for both p-value=0.001) Moreover, no statistical differences were seen in impression cytology measures between groups. (p-value >0.05) CONCLUSIONS: The erosion in the tear film stability is in line with the erosion in the ocular surface epithelium. Taking into account the statistical indifference between the impression cytology measures across groups, the break up time differences may be attributed to the collagen destruction in tear.

Analysis of the Pathogenic Factors and Management of Dry Eye in Ocular Surface Disorders

The tear film represents the interface between the eye and the environment. The alteration of the delicate balance that regulates the secretion and distribution of the tear film determines the dry eye (DE) syndrome. Despite having a multifactorial origin, the main risk factors are female gender and advanced age. Likewise, morphological changes in several glands and in the chemical composition of their secretions, such as proteins, mucins, lipidics, aqueous tears, and salinity, are highly relevant factors that maintain a steady ocular surface. Another key factor of recurrence and onset of the disease is the presence of local and/or systemic inflammation that involves the ocular surface. DE syndrome is one of the most commonly encountered diseases in clinical practice, and many other causes related to daily life and the increase in average life expectancy will contribute to its onset. This review will consider the disorders of the ocular surface that give rise to such a widespread pathology. At the end, the most recent therapeutic options for the management of DE will be briefly discussed according to the specific underlying pathology.

In Vivo Confocal Microscopy of Corneal Nerves in Health and Disease

In vivo confocal microscopy (IVCM) is becoming an indispensable tool for studying corneal physiology and disease. Enabling the dissection of corneal architecture at a cellular level, this technique offers fast and noninvasive in vivo imaging of the cornea with images comparable to those of ex vivo histochemical techniques. Corneal nerves bear substantial relevance to clinicians and scientists alike, given their pivotal roles in regulation of corneal sensation, maintenance of epithelial integrity, as well as proliferation and promotion of wound healing. Thus, IVCM offers a unique method to study corneal nerve alterations in a myriad of conditions, such as ocular and systemic diseases and following corneal surgery, without altering the tissue microenvironment. Of particular interest has been the correlation of corneal subbasal nerves to their function, which has been studied in normal eyes, contact lens wearers, and patients with keratoconus, infectious keratitis, corneal dystrophies, and neurotrophic keratopathy. Longitudinal studies have applied IVCM to investigate the effects of corneal surgery on nerves, demonstrating their regenerative capacity. IVCM is increasingly important in the diagnosis and management of systemic conditions such as peripheral diabetic neuropathy and, more recently, in ocular diseases. In this review, we outline the principles and applications of IVCM in the study of corneal nerves in various ocular and systemic diseases.

Signs and Symptoms of Dry Eye in Keratoconus Patients Before and After Intrastromal Corneal Rings Surgery

PURPOSE

Based on the relationship between keratoconus and dry eye, the aim of this study was to evaluate changes in signs and symptoms of dry eye in keratoconus patients before and after intrastromal corneal ring surgery.

METHODS

Fifteen keratoconus patients were enrolled in Fundación Jiménez-Díaz of Madrid and University Clinic of Optometry of the Universidad Complutense de Madrid (Madrid, Spain). Tear break up time (TBUT), Schirmer test without anesthesia, corneal staining, diadenosine tetraphosphate (Ap₄A) concentration, and ocular surface disease index (OSDI) were evaluated. Impression cytology combined with laser confocal microscopy was performed to evaluate goblet cell density, mucin cloud height (MCH), and cell layer thickness (CLT). All measurements were performed before (pre) surgery, 1 month (post) and 6 months after surgery (post6m).

RESULTS

We found no statistical differences in time in Schirmer test, TBUT, and corneal staining. OSDI scores were 44.96  ±  8.65, 26.30 ± 6.79, and 19.31 ± 4.28 for (pre), (post), and (post6m) surgery, respectively (p < 0.001). Impression cytology showed a decrease in cell density at (post6m) compared with presurgery (47.36 ± 35.15 cells/mm² and 84.88 ± 32.08 cells/mm², respectively, p = 0.04). At post6m, the MCH increased compared with presurgery values (13.97 ± 4.26 µm and 6.77 ± 2.51 µm, respectively, p < 0.001). There was a statistically significant increase in CLT in time. Ap₄A tear concentrations were lower post6m than presurgery (1.02  ±  0.65 and 2.56   ± 1.10  µM, respectively, p < 0.001).

CONCLUSION

Intrastromal corneal ring surgery induces changes improving dry eye symptoms but no changes were found in signs of dry eye after surgery in keratoconus patients except for the MCH that increases drastically. More studies are needed to clarify the reason of its improvement.

Short-term Effect of Scleral Lens on the Dry Eye Biomarkers in Keratoconus

PURPOSE

To evaluate the most important signs of dry eye, such as osmolarity, inflammation, and diadenosine tetraphosphate (Ap(4)A) concentration before and after wearing scleral lenses for 8 h in keratoconus patients.

METHODS

A pilot, experimental, short-term study involved 26 keratoconus patients (average age, 36.95 ± 8.95 years). They voluntarily enrolled in the study at the Optometry Clinic of the Faculty of Optics and Optometry in the University Complutense of Madrid. They were divided into two groups: patients with intrastromal corneal ring, the ICRS group, and patients without ICRS, the keratoconus (KC) group. Ocular Surface Disease Index questionnaire, the Schirmer test without anesthesia, tear break-up time, matrix metalloproteinase 9 (MMP-9) concentration, osmolarity, and Ap4A concentration were evaluated before and after wearing a scleral lens for 8 h.

RESULTS

The patients wore the scleral lenses from 6 to 9 h, with a mean of 7.59 ± 0.73 h. The mean scleral lens sag for all patients was 4310 ± 166.31 μm, ranging from 4200 μm to 4800 μm. No significant changes in the Schirmer test and tear break-up time were found for either group. Ocular Surface Disease Index scores were statistically lower after wearing scleral lenses for both groups (p < 0.05). A significantly lower osmolarity and a significant rise of MMP-9 concentration after wearing scleral lenses were found in both groups (p < 0.05). Diadenosine tetraphosphate concentration was lower after wearing the scleral lens in the KC group (p < 0.05) but no significant difference was found for the ICRS group (p > 0.05).

CONCLUSIONS

Short-term scleral lens wearing improves the symptomatology and some signs of dry eye, such as osmolarity and Ap4A concentration. The increase of MMP-9 concentration could be caused by tear film stagnation and use of preserved saline.

The influence of rigid gas permeable lens wear on the concentrations of dinucleotides in tears and the effect on dry eye signs and symptoms in keratoconus

PURPOSE

To evaluate the signs and symptoms of dry eye and dinucleotide secretion in tears of keratoconus patients (KC) and the potential effect of rigid gas permeable (RGP) contact lens wear.

METHODS

Twenty-three KC patients and forty control subjects were enrolled in this study. Signs of dry eye including tear volume, tear stability and corneal staining along with symptoms were assessed using the McMonnies questionnaire. Tears were collected using Schirmer strips, and dinucleotide concentrations in collected tears measured using high pressure liquid chromatography. Values obtained in KC and controls were compared. The effect of contact lens wear in KC was also assessed.

RESULTS

KC eyes showed a significantly lower tear volume compared to controls, shorter tear break up time (TBUT), higher corneal staining and higher McMonnies dry eye questionnaire scores (p<0.05). When compared with non-wearers, KC contact lens wearers showed significantly higher symptoms, lower Schirmer and TBUT values (p<0.05). Concentration of Ap4A (0.695±0.304μM vs. 0.185±0.178μM) and Ap5A (0.132±0.128μM vs. 0.045±0.036μM) were higher in KC compared to controls (p<0.001) and only Ap4A was statistically higher in RGP wearers compared to non-wearers (0.794±0.478μM vs. 0.417±0.313μM) (p<0.05).

CONCLUSION

Signs and symptoms of dry eye as well as concentrations of Ap4A and Ap5A were markedly increased in KC patients compared to controls. Moreover, Ap4A and symptoms of dry eye were statistically higher in RGP wearers compared to non-wearers. This seems to indicate that factors such as RGP contact lens wear might exacerbate the clinical condition of dry eye.

Tear film osmolarity and dry eye disease: a review of the literature

Objective

To evaluate the evidence in the peer-reviewed literature regarding the use of tear osmolarity as a physiological marker to diagnose, grade severity, and track therapeutic response in dry eye disease (DED). In addition, to review the evidence for the role of tear osmolarity in the pathophysiology of DED and ocular surface disease.

Methods

A literature review of all publications after the year 2000, which included the keywords “tear osmolarity”, was conducted. Relevant articles were graded according to quality of evidence and research, using the University of Michigan Practice Guideline and the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) rating systems. Articles were further categorized by the nature of any reported financial support and by the overall impression they provided related to tear osmolarity.

Results

A total of 164 articles were identified as relevant to the search criteria, although some were editorials, and some were written in a foreign language. Of the total, it was possible to grade 159, and an overall impression was generated for 163. A positive impression of tear osmolarity in DED diagnosis was evident in 72% (117/163) of all articles, with a neutral impression in a further 21% (35/163); 7% had a negative impression. The percentage of positive impressions appeared independent of the quality of research; 73% (38/52) of articles graded high/moderate quality supported the use of tear film osmolarity measurement in DED diagnosis. Impressions were also independent of the source of financial support, with 72% (75/104) of independent studies positive.

Conclusion

The literature broadly supports the use of tear film osmolarity as an objective numerical measure for diagnosing, grading severity, and managing treatment of DED.

Corneal Sensitivity and Dry Eye Symptoms in Patients with Keratoconus

PURPOSE

To investigate corneal sensitivity to selective mechanical, chemical, and thermal stimulation and to evaluate their relation to dry eye symptoms in patients with keratoconus.

METHODS

Corneal sensitivity to mechanical, chemical, and thermal thresholds were determined using a gas esthesiometer in 19 patients with keratoconus (KC group) and in 20 age-matched healthy subjects (control group). Tear film dynamics was assessed by Schirmer I test and by the non-invasive tear film breakup time (NI-BUT). All eyes were examined with a rotating Scheimpflug camera to assess keratoconus severity.

RESULTS

KC patients had significatly decreased tear secretion and significantly higher ocular surface disease index (OSDI) scores compared to controls (5.3±2.2 vs. 13.2±2.0 mm and 26.8±15.8 vs. 8.1±2.3; p<0.001). There was no significant difference in NI-BUT between the two groups (KC: 9.8±4.8 vs. control: 10.7±3.8; p>0.05). The mean threshold for selective mechanical (KC: 139.2±25.8 vs. control: 109.1±24.0 ml/min), chemical (KC: 39.4±3.9 vs. control: 35.2±1.9%CO2), heat (KC: 0.91±0.32 vs. control: 0.54±0.26 Δ°C) and cold (KC: 1.28±0.27 vs. control: 0.98±0.25 Δ°C) stimulation in the KC patients were significantly higher than in the control subjects (p<0.001, for all parameters). No correlation was found between age and mechanical, chemical, heat or cold thresholds in the patients with KC (p>0.05), whereas in the control subjects both mechanical (r = 0.52, p = 0.02), chemical (r = 0.47, p = 0.04), heat (r = 0.26, p = 0.04) and cold threshold (r = 0.40, p = 0.03) increased with age. In the KC group, neither corneal thickness nor tear flow, NI-BUT or OSDI correlated significantly with mechanical, chemical, heat or cold thresholds (p>0.05 for all variables).

CONCLUSIONS

Corneal sensitivity to different types of stimuli is decreased in patients with keratoconus independently of age and disease severity. The reduction of the sensory input from corneal nerves may contribute to the onset of unpleasant sensations in these patients and might lead to the impaired tear film dynamics.

Recovery of corneal sensitivity after collagen crosslinking with and without epithelial debridement in eyes with keratoconus

PURPOSE

To evaluate the changes in corneal sensitivity after corneal collagen crosslinking (CXL) with the epithelium off (epi-off) and with the epithelium on (epi-on) in eyes with keratoconus.

DESIGN

Prospective interventional case series.

SETTING

Eye Clinic, A. Fiorini Hospital, Terracina (Latina), Rome, Italy.

METHODS

On the basis of the corneal pachymetry at the area of topographic steepening, eyes treated with CXL were divided in 2 groups: those with a corneal thickness of 400 μm or more (epi-off) and those with a corneal thickness of less than 400 μm (epi-on). Corneal sensitivity was measured using a contact esthesiometer (Cochet-Bonnet) before treatment and 1 and 7 days and 1, 3, 6, 9, and 12 months after treatment.

RESULTS

The study evaluated 50 CXL-treated eyes in 50 patients (25 epi-on and 25 epi-off) from January 7, 2012, to December 15, 2012. In the epi-off group, corneal sensitivity was statistically significantly reduced for up to 3 months after CXL and gradually returned to normal levels. In the epi-on group, corneal sensitivity was statistically significantly reduced for up to 7 days but was not statistically significantly different from preoperative values at other measurement times. At 7 days, the corneal sensitivity was statistically significantly lower in the epi-off eyes than in the epi-on eyes.

CONCLUSIONS

Epi-off and epi-on CXL both caused hypoesthesia, but corneal sensitivity subsequently recovered completely. The corneal hypoesthesia was more pronounced in eyes in which the epi-off technique was used, and the recovery time was shorter for eyes treated using epi-on CXL.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Signs and Symptoms of Dry Eye in Keratoconus Patients: A Pilot Study

PURPOSE

To compare signs and symptoms of dry eye in keratoconus (KC) patients versus healthy subjects.

METHODS

A total of 15 KC patients (KC group, n = 15 eyes) and 16 healthy subjects (control group, 16 eyes) were enrolled in this study. The Schirmer I test with no anesthetic, tear break-up time (TBUT), corneal staining characteristics, and ocular surface disease index (OSDI) scores were evaluated for both groups. Impression cytology, combined with/scanning laser confocal microscopy (LCM), was performed to evaluate goblet cell density, mucin cloud height (MCH), and goblet cell layer thickness (CLT). Finally, tear concentrations of di-adenosine tetraphosphate (Ap4A) were assessed. Results were statistically analyzed using Shapiro-Wilk and non-parametric Wilcoxon rank sum tests. Statistical significance was set at p < 0.05.

RESULTS

KC patients had lower tear volumes and greater corneal staining than did healthy subjects (p < 0.05). OSDI scores were 44.96 ± 8.65 and 17.78 ± 6.50 for the KC and control groups, respectively (p < 0.05). We found no statistically significant differences in TBUT between groups. Impression cytology revealed lower goblet cell densities in KC group patients versus control group subjects (84.88 ± 32.98 and 128.88 ± 50.60 cells/mm,(2) respectively, p < 0.05). There was a statistically significant reduction in MCH and CLT in KC group patients compared with control group subjects. Ap4A tear concentrations were higher in KC group patients than in control group subjects (2.56 ± 1.10 and 0.15 ± 0.12 µM, respectively, p < 0.05).

CONCLUSIONS

The parameters evaluated in this study indicate that KC patients suffer greater symptoms of dry eye and greater tear instability, primarily due to the decreased mucin production in their tears, than do healthy patients with no KC.

Evaluation of subbasal nerve morphology and corneal sensation after accelerated corneal collagen cross-linking treatment on keratoconus

PURPOSE

The aim of this study was to report on the evaluation of corneal nerve fiber density and corneal sensation after accelerated corneal collagen cross-linking on keratoconus patients.

METHODS

The study was performed on 30 keratoconus eyes (30 participants: 16 M, 14 F; 17-32 years old) treated with accelerated collagen cross-linking for disease stabilization. Mean outcome measures were corneal sensation evaluation by Cochet-Bonnet esthesiometry and subbasal nerve fiber density assessment by corneal in vivo confocal microscopy. All corneal measurements were performed using scanning slit confocal microscopy (ConfoScan 4, Nidek Technologies, Padova, Italy).

RESULTS

The accelerated corneal collagen cross-linking procedure was performed on 30 eyes of 30 patients (19 right, 63.3%; 11 left, 27.7%). The mean age was 23.93 ± 4. The preoperative mean keratometry, apex keratometry and pachymetry values were 47.19 ± 2.82 D, 56.79 ± 5.39 and 426.1 ± 25.6 μm, respectively. Preoperative mean corneal sensation was 56.3 ± 5.4 mm (with a range from 40 to 60 mm), it was significantly decreased at 1st and 3rd month visit and increased to preoperative values after 6th month visit. Preoperative mean of subbasal nerve fiber density measurements was 22.8 ± 9.7 nerve fiber/mm(2) (with a range of 5-45 mm), it was not still at the preoperative values at 6th month (p = 0.0001), however reached to the preoperative values at 12th month (p = 0.914).

CONCLUSIONS

Subbasal nerve fibers could reach the preoperative values at the 12th month after accelerated corneal collagen cross-linking treatment although the corneal sensation was improved at 6th month. These findings imply that the subjective healing process is faster than the objective evaluation of the keratoconus patients' cornea treated with accelerated corneal collagen cross-linking.

Corneal sensitivity in keratoconus: a review of the literature

Corneal sensitivity has recently received much attention given the crucial role the corneal nerves play in maintaining normal corneal structure and function. An increased understanding of the corneal sensitivity and dry eye disease in keratoconus, including alterations of the conjunctival cells, may help explain the pathogenesis of this disorder. There is histological evidence of the involvement of corneal nerves in the pathology of keratoconus and it has been suggested that this plays a role in the pathophysiological features and progression of the disease. In this review, the impaired corneal sensitivity found on keratoconus and corneal sensitivity changes after cross-linking performed in patients with keratoconus are reported.

TearLab® Osmolarity System for diagnosing dry eye

Dry eye (DE) disease is an impairment of the lachrymal unit function and one the most frequent eye problems. A major challenge is to find accurate diagnostic criteria to be able to define DE severity, as symptoms poorly correlate with clinical signs. Tear osmolarity is considered a key factor in DE onset and perpetuation; its measurement is now possible in clinical setting by an innovative electrical impedance-based lab-on-a-chip technology. This article outlines the features of DE disease and the limitations of current clinical tests. The role of tear osmolarity in DE etiopathogenesis is surveyed, and the pitfalls in measurement are discussed. Diagnostic performance, accuracy and clinical applications of the technology in focus are critically reviewed. The instrument offers the possibility to measure tear osmolarity in a rapid and reliable way in daily practice. As scientific evidence grows, it is expected in the future that it will represent an objective indicator of ocular surface health in the management of DE disease and in clinical trials.