Central and peripheral corneal thickness measurement in normal and keratoconic eyes using three corneal pachymeters

Repeatability of corneal pachymetry and epithelial thickness measurements with spectral-domain optical coherence tomography (SD-OCT) and correlation to ocular surface parameters

PURPOSE

To assess the repeatability of corneal pachymetry and epithelial thickness measurements with spectral-domain optical coherence tomography (SD-OCT) and identify correlations between epithelial thickness and ocular surface parameters.

METHODS

Adults who happened to have prolonged computer use were recruited, excluding those with conditions interfering with corneal measurements or tear production. All subjects filled in the ocular surface disease index (OSDI) questionnaire. Three consecutive measurements of central and peripheral corneal and epithelial thickness were performed with SD-OCT (RTVue XR). Schirmer test I and tear film break-up time (TBUT) were performed. Repeatability was evaluated with intraclass correlation coefficient (ICC), coefficient of variation and repeatability limit. Spearman correlation was used for non-parametric variables.

RESULTS

113 eyes of 63 subjects were included in the study. ICC was ≥ 0.989 for all corneal and ≥ 0.944 for all epithelial pachymetry segments. The best repeatability was found centrally and the worst superiorly both for corneal and epithelial measurements. Central epithelial thickness was weakly correlated with Schirmer test I (rho = 0.21), TBUT (rho = 0.02), OSDI symptoms and OSDI score (rho <|0.32|). OSDI symptoms and OSDI score were weakly correlated with Schirmer test I (rho <|0.3|) and TBUT (rho <|0.34|).

CONCLUSION

RTVue XR measurements of corneal and epithelial thickness are highly repeatable in all segments. The lack of correlation between epithelial thickness and ocular surface parameters could suggest the assessment of epithelial integrity with reliable methods such as SD-OCT.

Prevalence and characteristics of dry eye disease in Parkinson's disease: a systematic review and meta-analysis

We investigated and characterized the prevalence of dry eye disease (DED) in Parkinson's disease (PD). PubMed and EMBASE databases were searched for relevant studies between January 1, 1979 and March 10, 2022. Quality was assessed using the Joanna Briggs Institute Critical Appraisal Checklist. Study-specific estimates were combined using the DerSimonian-Laird random-effects model. Prevalence of subjective DED symptoms in patients with PD and mean differences in blink rate, corneal thickness, tear film breakup time, and tear secretion volume on Schirmer test I were compared to those in controls. Of 383 studies, 13 (1519 patients with PD) and 12 were included in qualitative and quantitative syntheses, respectively. Meta-analysis revealed a 61.1% prevalence of subjective DED symptoms in PD and that, compared with controls, patients with PD had significantly lower blink rate, thinner corneal thickness, shorter tear film breakup time, and lower tear secretion volumes on Schirmer test I, without and with anesthesia.

The Underlying Relationship between Keratoconus and Down Syndrome

Keratoconus (KC) is one of the most significant corneal disorders worldwide, characterized by the progressive thinning and cone-shaped protrusion of the cornea, which can lead to severe visual impairment. The prevalence of KC varies greatly by ethnic groups and geographic regions and has been observed to be higher in recent years. Although studies reveal a possible link between KC and genetics, hormonal disturbances, environmental factors, and specific comorbidities such as Down Syndrome (DS), the exact cause of KC remains unknown. The incidence of KC ranges from 0% to 71% in DS patients, implying that as the worldwide population of DS patients grows, the number of KC patients may continue to rise significantly. As a result, this review aims to shed more light on the underlying relationship between KC and DS by examining the genetics relating to the cornea, central corneal thickness (CCT), and mechanical forces on the cornea, such as vigorous eye rubbing. Furthermore, this review discusses KC diagnostic and treatment strategies that may help detect KC in DS patients, as well as the available DS mouse models that could be used in modeling KC in DS patients. In summary, this review will provide improved clinical knowledge of KC in DS patients and promote additional KC-related research in these patients to enhance their eyesight and provide suitable treatment targets.

Partitioning and Spatial Distribution of Drugs in Ocular Surface Tissues

Ocular drug absorption after eye drop instillation has been widely studied, but partitioning phenomena and spatial drug distribution are poorly understood. We investigated partitioning of seven beta-blocking drugs in corneal epithelium, corneal stroma, including endothelium and conjunctiva, using isolated porcine tissues and cultured human corneal epithelial cells. The chosen beta-blocking drugs had a wide range (-1.76-0.79) of n-octanol/buffer solution distribution coefficients at pH 7.4 (Log D_7.4). In addition, the ocular surface distribution of three beta-blocking drugs was determined by matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) after their simultaneous application in an eye drop to the rabbits in vivo. Studies with isolated porcine corneas revealed that the distribution coefficient (K_p) between the corneal epithelium and donor solution showed a positive relationship and good correlation with Log D_7.4 and about a 50-fold range of K_p values (0.1-5). On the contrary, K_p between corneal stroma and epithelium showed an inverse (negative) relationship and correlation with Log D_7.4 based on a seven-fold range of K_p values. In vitro corneal cell uptake showed a high correlation with the ex vivo corneal epithelium/donor K_p values. Partitioning of the drugs into the porcine conjunctiva also showed a positive relationship with lipophilicity, but the range of K_p values was less than with the corneal epithelium. MALDI-IMS allowed simultaneous detection of three compounds in the cornea, showed data in line with other experiments, and revealed uneven spatial drug distribution in the cornea. Our data indicate the importance of lipophilicity in defining the corneal pharmacokinetics and the K_p values are a useful building block in the kinetic simulation models for topical ocular drug administration.

Limbal Metabolic Support Reduces Peripheral Corneal Edema with Contact-Lens Wear

Purpose

To assess the influence of limbal metabolic support on corneal edema during scleral-lens (SL) and soft-contact-lens (SCL) wear for healthy lens wearers.

Methods

A two-dimensional (2D) model of the cornea and sclera was designed on Comsol Multiphysics 5.4 along with SL and SCL architectures to mimic lens-wear induced hypoxia. The cornea is suffused with oxygen and metabolites from the limbus and aqueous humor. Air oxygen is supplied from and carbon dioxide is expelled to the atmosphere. Lens-oxygen permeability (Dk) was adjusted to investigate lens-wear safety against edema in different wear conditions. The 2D concentrations of oxygen, carbon dioxide, bicarbonate, lactate, sodium, chloride, glucose, and pH are quantified. Central-to-peripheral swelling of the cornea is determined by the change in stromal hydration caused by changing metabolite concentrations at the endothelium during hypoxia.

Results

The metabolic model assesses central-to-peripheral corneal swelling with different types of lenses, and oxygen Dks. Limbal metabolic support reduces edema from the periphery to approximately 1 mm away from the central cornea. Despite thicker lens designs, the peripheral cornea exhibits practically zero swelling due to limbal metabolic support.

Conclusions

The metabolic model accurately predicts central-to-peripheral corneal edema with various contact-lens designs, post-lens tear-film thicknesses, and lens oxygen Dk values. Despite the thicker periphery of most contact-lens designs, lactate and bicarbonate support from the limbus significantly reduces peripheral and mid-peripheral corneal edema, whereas oxygen has a lesser effect.

Translational Relevance

By utilizing metabolic kinetics, we provide a 2D computational tool to predict oxygenation safety across the entire cornea with various types and designs of contact lenses.

Peripheral Cornea Crosslinking Before Deep Anterior Lamellar Keratoplasty

Since Cornea crosslinking (CXL) has been proven to halt progression and biomechanically stabilize keratoconus, we hypothesized that CXL of the corneal periphery 3 months prior to corneal transplantation can reduce the incidence of recurrent ectasia by strengthening the peripheral corneal tissue and causing apoptosis of diseased peripheral host keratocytes. Thus, the aim of this case-report was to propose a novel peripheral CXL technique prior to keratoplasty and evaluate its safety. A 22-year-old woman was admitted with advanced right keratoconus and corrected distance visual acuities of 20/30 in the right eye and 20/200 in the left eye with a manifest refraction of -3.00D/ -8.00D × 36° and -17.00D/ -11.50D × 90°, respectively. The proposed treatment involved crosslinking of peripheral corneal tissue (6.5-9.5mm), sparing the central cornea and limbus, three months prior to corneal transplantation as a means of biomechanically strengthening the peripheral cornea tissue. This procedure was feasible and safe with repopulation of the peripheral cornea with keratocytes, no significant endothelial cell loss and a routine postoperative course following CXL and DALK. This method might reduce or eliminate the need for repeat corneal transplantation in patients with recurrent ectasia. Further studies are needed to confirm the results.

Towards seeing the visual impairments in Parkinson's disease: protocol for a multicentre observational, cross-sectional study

Background

Visual disorders are common in Parkinson’s disease (PD) but their exact frequency and severity are unknown. Good visual functioning is crucial for patients with PD, because of their need to compensate for loss of automated motor control and their postural instability, forcing patients to guide their movements visually. Here, we describe the study design of a cross-sectional, multi-centre study aiming to: (1) validate the Visual Impairment screening questionnaire (VIPD-Q, which aims to identify PD patients who should be referred to an ophthalmologist for further assessment); (2) study the prevalence of visual disorders in PD; (3) study the severity and clinical impact of different types of visual disorders in PD; and (4) explore treatment options for ophthalmologic disorders in PD, as a basis for future guideline development.

Methods

This study consists of two phases. In phase one, 750 PD patients and 250 healthy controls will be recruited to complete the VIPD-Q. In phase two, a subgroup of responders (n = 100) (with the highest and lowest scores on the VIPD-Q) will be invited for an extensive neurological and ophthalmological assessment. The in-depth ophthalmologic examination will serve as the “gold standard” for validating the VIPD-Q. Moreover, these assessments will be used to study associations between visual disorders and clinical presentation, in order to gain more insight in their clinical impact.

Discussion

Our study will heighten the awareness of visual problems in PD and offers a robust starting point to systematically approach this subject. In current daily practice, the association between visual problems and PD is far from obvious to both patients and clinicians. Consequently, patients may not adequately report visual problems themselves, while clinicians miss potentially treatable visual disorders. Routinely asking patients to complete a simple screening questionnaire could be an easy solution leading to timely identification of visual problems, tailored treatment, restored mobility, greater independence and improved quality of life.

Trial registration

Dutch Trial Registration, NL7421, Registered on 4 December 2018 – Retrospectively registered.

Electronic supplementary material

The online version of this article (10.1186/s12883-019-1365-8) contains supplementary material, which is available to authorized users.

A contralateral eye study comparing characteristics of corneal endothelial cells in bilateral keratoconus patients with unilateral corneal Vogt's striae

Purpose

The aim of this study was to analyze and compare corneal endothelial cell morphology and characteristics in bilateral keratoconus (KCN) patients with unilateral Vogt's striae.

Methods

Fifty patients aged 20–38 years were recruited in this cross-sectional contralateral eye study. In this study, corneal endothelial cell parameters were evaluated in patients with bilateral KCN and unilateral Vogt's striae using the Topcon SP2000P specular microscope (Topcon, Tokyo, Japan).

Results

In the current study, there were no significant differences in corneal endothelial cell parameters including endothelial cell density (ECD), hexagonal cell ratio (HEX), and coefficient of variance of cell size (CV) between the KCN groups with and without Vogt's striae, [(2968.34 ± 276.65 vs. 2980.05 ± 253.30, P = 0.618), (51.88 ± 13.57 vs. 53.24 ± 9.31, P = 0.658), and (32.50 ± 5.40 vs. 32.97 ± 4.07, P = 0.467), respectively]. Also, among study groups with and without Vogt's striae, ECD did not correlate with anterior chamber depth (ACD) [(P = 0.564, r = 0.09), (P = 0.219, r = −0.18), respectively], maximum keratometry (Kmax) [(P = 0.215, r = 0.18), (P = 0.898, r = 0.02), respectively], and central corneal thickness (CCT) [(P = 0.989, r = −0.02), (P = 0.643, r = −0.07), respectively].

Our results showed significant differences in corrected and uncorrected distance visual acuity (UDVA), cycloplegic refractive error components (calculated by vectorial analysis), CCT, and Kmax between two study groups (all P < 0.05) except for J₄₅ (Jackson cross cylinder, axes at 45 and 135°) (P = 0.131).

Conclusions

We were not able to find the statistically significant differences in ECD, HEX, and CV between KCN eyes with and without Vogt's striae. Despite clinical and tomographic results, it seems that Vogt's striae cannot cause deterioration in the corneal endothelial morphology.

Anatomy of cornea and ocular surface

Important functions of cornea in the eye include protecting the structures inside the eye, contributing to the refractive power of the eye, and focusing light rays on the retina with minimum scatter and optical degradation. Considerable advances have taken place in understanding the organization of collagen in the corneal stroma and its clinical significance. In this review, the structure and function of various components of cornea and ocular surface are presented.

Anterior segment ultrasound biomicroscopy image analysis using ImageJ software: Intra-observer repeatability and inter-observer agreement

PURPOSE

In this novel study, we demonstrate a standardized imaging and measurement protocol of anterior segment (AS) structures with reliability analysis using ultrasound biomicroscopy (UBM) and ImageJ software.

METHODS

Ten pediatric and young adult patients undergoing examination under anesthesia for AS pathology were imaged using UBM. Four trained observers analyzed 20 images using ImageJ. Forty-five structural parameters were measured. Those that relied on the trabecular-iris angle (TIA) as a reference landmark were labeled TIA-dependent (TD) and all others were labeled non-TIA dependent (NTD). Intra-observer repeatability (IOR) and inter-observer agreement (IOA) of measurements were determined using coefficient of variation (CV) and intra-class correlation (ICC) followed by assessment of Bland-Altman plots (BAP) for each pair of observers, respectively.

RESULTS

For NTD parameters, non-ciliary body (CB) related measurements showed CV range 0.60-16.22% and ICC range 0.84-0.89, whereas CB-related parameters showed CV range 2.86-23.40% and ICC range 0.29-0.92. For TD parameters, parameters < 2 degrees removed from reference showed CV range 0.02-5.40% and ICC range 0.89-1.00, whereas parameters > 1 degree removed showed CV range 0.63-27.44% and ICC range 0.22-1.00. No systematic proportional bias was detected by BAPs.

CONCLUSIONS

Preplaced landmarks yielded good IOR and IOA in quantitative assessment of AS structures that were NTD and non-CB-related or less removed from the reference. CB-related NTD measurements varied greatly in IOR and IOA, indicating protocol modifications or CB qualitative assessments needed to improve accuracy. Variability in TD measurements increased the further removed from the reference, which supports implementation of a reliable reference landmark to minimize variation.

Corneal thickness measurements with Scheimpflug and slit scanning imaging techniques in keratoconus

PURPOSE

To determine the repeatability of corneal thickness measurements with Scheimpflug (Pentacam) and slit scanning (Orbscan) imaging techniques in different grades of keratoconus.

METHODS

This study was conducted as a cross-sectional research. Imaging with Orbscan and Pentacam was performed on patients with different grades of keratoconus. With each device, 3 measurements were taken at 10 min intervals. Repeatability indices in different grades of keratoconus were calculated for each device.

RESULTS

Seventy-four eyes of 42 keratoconus patients were enrolled. Repeatability index (RI) of central corneal thickness (CCT) measurements in keratoconus grade 1, 2, and 3, were 12.8, 9.9, and 24.2 with Pentacam, and 23.6, 26.3, and 59.3 with Orbscan, respectively. For the thinnest point, these figures were 9.6, 8.0, and 35.7 with Pentacam and 19.5, 16.6, and 26.8 with Orbscan, respectively. The 95% limit of agreement (LOA) between Pentacam and Orbscan in measuring CCT and thinnest point in grade 1 were -25.5-47.7 mic and -33.3-32.8 mic, respectively. These results for grade 2 were -9.8-50.6 mic and -26.2-43.7 mic, respectively. In grade 3, 95% LoA were -20-64.6 mic and -31.4-60.5 mic, respectively.

CONCLUSIONS

The results of this study showed that although repeated measurements of the CCT with Orbscan and Pentacam are strongly correlated, repeatability values of CCT measurements significantly decrease at more advanced grades of keratoconus. In all keratoconus grades, repeatability of CCT measurements was better with Pentacam than Orbscan. These findings indicate that corneal thickness readings have less validity in patients with advanced keratoconus.

Evaluation of Central Corneal Thickness Using Corneal Dynamic Scheimpflug Analyzer Corvis ST and Comparison with Pentacam Rotating Scheimpflug System and Ultrasound Pachymetry in Normal Eyes

Purpose. To assess the repeatability and reproducibility of central corneal thickness (CCT) measurements by corneal dynamic Scheimpflug analyzer Corvis ST in normal eyes and compare the agreement with Pentacam rotating Scheimpflug System and ultrasound pachymetry. Methods. 84 right eyes underwent Corvis ST measurements performed by two operators. The test-retest repeatability (TRT), within-subject coefficient of variation (CoV), and intraclass correlation coefficient (ICC) were used to evaluate the intraoperator repeatability and interoperator reproducibility. CCT measurements also were obtained from Pentacam and ultrasound pachymetry by the first operator. The agreement between the three devices was evaluated with 95% limits of agreement (LoA) and Bland-Altman plots. Results. Corvis ST showed high repeatability as indicated by TRT ≤ 13.0 μm, CoV < 0.9%, and ICC > 0.97. The interoperator reproducibility was also excellent. The CoV was <0.9%, and ICC was >0.97. Corvis ST showed significantly lower values than Pentacam and ultrasound pachymetry (P < 0.001). The 95% LoA between Corvis ST and Pentacam or ultrasound pachymetry were −15.8 to 9.5 μm and −27.9 to 12.3 μm, respectively. Conclusions. Corvis ST showed excellent repeatability and interoperator reproducibility of CCT measurements in normal eyes. Corvis ST is interchangeable with Pentacam but not with ultrasound pachymetry.