Optical coherence tomography to evaluate the interaction of different edge designs of four different silicone hydrogel lenses with the ocular surface

Using clinical optical coherence tomography to characterise contact lens edge shape and base curve radius

CLINICAL RELEVANCE

Clinical optical coherence tomography devices are widely used in optometry and ophthalmology and may be used to measure contact lens base curvature radius and visualise contact lens edge shape.

BACKGROUND

Knowledge of contact lens geometry facilitates fitting, while optical coherence tomography provides a powerful means of measuring geometrical form. This study evaluates the performance of a clinical optical coherence tomography device (3D OCT-1000) in characterising contact lens edge shape and measuring the back optic zone radius of rigid gas-permeable contact lenses in vitro.

METHODS

First, an opto-mechanical optical coherence tomography contact lens adaptor was designed and 3D-printed to facilitate a contact lens being imaged using a commercial optical coherence tomography device. Second, several image-processing algorithms and a simple calibration method were developed to measure the back optic zone radius in optical coherence tomography B-scans. Finally, based on the findings of two experiments, B-scan performance was evaluated in terms of 1) capacity to differentiate between contact lens edge geometries, and 2) capacity to obtain accurate and repeatable back optic zone radius measurements. Statistical and graphical analyses were performed to characterise reliability and reproducibility.

RESULTS

The 3D OCT-1000 and adaptor combination was capable of acquiring images of sufficient quality to discriminate between soft and rigid contact lens edge geometries. Additionally, statistical analysis of the rigid contact lens measurements demonstrated satisfactory back optic zone radius measurement accuracy and reproducibility.

CONCLUSION

This study demonstrates that a 3D OCT-1000 fitted with an opto-mechanical adaptor combination can be used to assess contact lens edges in vitro and that this clinical optical coherence tomography device, combined with image processing and linear calibration of the B-scans, is capable of obtaining back optic zone radius measurements of rigid gas-permeable contact lenses that are close to the ISO 18,369-2:2018 manufacturing tolerance range (±0.05 mm).

Effects of Medium-Term Soft Contact Lens Fitting on Dry Eye: Analyses Using Ultra-High Resolution Optical Coherence Tomography and Digital Slit-Lamp Biomicroscopy

Purpose

This study aimed to evaluate the medium-term fit of soft contact lenses (SCLs) and its effects on dry eye by using ultra-high-resolution optical coherence tomography (UHR-OCT) and digital slit-lamp biomicroscopy (DSLB) and identify factors indicating a better contact lens fit.

Methods

A total of 14 participants (7 men, 7 women; mean age, 23.1 years) were recruited. Temporal lag and conjunctival coverage were imaged by UHR-OCT. DSLB was used to assess lens decentration and blink-induced movement. In addition, dry eye indices, including ocular surface disease index (OSDI), tear break-up time (TBUT), and Schirmer I test scores, were measured at baseline and 1 day, 1 week, 1 month, 3 months, and 6 months after wearing.

Results

Good repeatability was found in the assessments of lens fit characteristics by two researchers and in the assessments by one researcher at different follow-up times. There were no significant differences in lens fit characteristics, TBUT and Schirmer I test scores at each checkpoint (P >0.05). However, the OSDI was significantly higher than baseline after wearing (P <0.05). Changes in the temporal lag were positively correlated with changes in TBUT (r =0.544, P =0.044) and negatively correlated with changes in OSDI (r = -0.629, P =0.016). Changes in blink-induced movement were positively correlated with changes in OSDI, Schirmer I test scores, and TBUT (P <0.05).

Conclusions

UHR-OCT and DSLB can be used to comprehensively and quantitatively evaluate SCL fit. Both the contact lenses and ocular surface conditions are almost stable within 6 months of SCL wear. Temporal lag and blink-induced movement have a strong correlation with dry eye parameters in SCL wearers.

CLEAR - Evidence-based contact lens practice

Evidence-based contact lens -->practice involves finding, appraising and applying research findings as the basis for patient management decisions. These decisions should be informed by the strength of the research study designs that address the question, as well as by the experience of the practitioner and the preferences and environment of the patient. This reports reviews and summarises the published research evidence that is available to inform soft and rigid contact lens history and symptoms taking, anterior eye health examination (including the optimised use of ophthalmic dyes, grading scales, imaging techniques and lid eversion), considerations for contact lens selection (including the ocular surface measurements required to select the most appropriate lens parameter, lens modality and material selection), evaluation of lens fit, prescribing (teaching self-application and removal, adaptation, care regimen and cleaning instructions, as well as -->minimising risks of lens wear through encouraging compliance) and an aftercare routine.

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.

Clinical significance of contact lens related changes of ocular surface tissue observed on optical coherence images

PURPOSE

To investigate the relationship between the real contact lens imprint into the conjunctival tissue, observed by optical coherence tomography (OCT) and conjunctival staining and contact lens wearing comfort.

METHODS

17 participants (mean age = 26.6 SD ± 3.6 years; 7 females) were fitted with three different contact lenses base curves of the same silicone hydrogel custom lens type (Visell 50; Hecht Contactlinsen, Au, Germany) in a randomised order. One lens was optimally fitted according to the manufacturer's recommendation, one fitted 0.4 mm flatter and one fitted 0.4 mm steeper. After 4 h of lens wear the contact lens edge in the area of the conjunctiva was imaged nasally and temporally using OCT (Optovue iVue SD-OCT). To correct the artefact due to optical distortion with OCT, the imprint of all worn lenses was measured on a glass plate afterwards. Conjunctival staining in the limbal region after 4 h of lens wear was classified using the CCLRU Grading Scale. Comfort scoring was based on visual analog scales from 0 (very poor) to 100 (excellent).

RESULTS

The mean conjunctival imprint of all contact lens edges was 32.0 ± 8.1 μm before and 7.3 ± 6.5 μm after distortion correction of the OCT images. The distortion corrected conjunctival imprint with the 0.4 mm steeper lens (11.5 ± 6.2 μm) was statistically significantly greater compared to the optimally fitted lens (6.5 ± 5.9 μm) (One-way ANOVA followed Tukey-test; p = 0.017) and greater compared to the 0.4 mm flatter lens (3.9 ± 5.3 μm) (p < 0.001). There was no statistically significant difference between the optimally fitted lens and the 0.4 mm flatter lens (p = 0.209). The nasally measured imprint (11.4 ± 9.0 μm) was significantly greater than the temporally measured (3.3 ± 7.6 μm) (p < 0.001). There was no statistically significant correlation between the amount of conjunctival imprint and the graded conjunctival staining (p = 0.346) or the wearer's comfort (p = 0.735).

CONCLUSIONS

Contact lens edges imaged by OCT exhibited displacement artefacts. The observed conjunctival imprints are a combination of real conjunctival compression and artefacts. A deeper imprint of the contact lens into the conjunctiva caused by a steeper base curve was not related to clinically significant staining or changes in comfort after 4 h of lens wear. The observed differences between nasal and temporal imprint are likely to be caused by variations of conjunctival thickness and the shape of the underlying sclera.

Fractal Features and Surface Micromorphology of Unworn Surfaces of Rigid Gas Permeable Contact Lenses

PURPOSE

The aim of this exploratory study was to investigate the micromorphology of surfaces of rigid gas permeable (RGP) contact lenses (CLs) using atomic force microscopy (AFM) followed by fractal analysis.

MATERIALS AND METHODS

In order to characterize in a quantitative manner the micromorphology of surfaces of new and unworn RGP CLs made of twelve different materials, AFM was taken and then analyzed using fractal methods. Surface topography was sampled in an intermittent-contact mode in air, on square areas of 5 × 5 µm² (MultiMode with Nanoscope V (Bruker). Spatial characteristics of 3-D surface texture were obtained using parameters defined in ISO 25178-2: 2012 norm.

RESULTS

The surface texture turned out to have complex 3-D nanoscale geometry. For quantitative characterization of the properties of surface geometry at nanometer level of CL on the global scale, a series of fractal parameters was used.

CONCLUSIONS

Statistical and fractal parameters of 3-D surfaces can be used by manufacturers to assess the micromorphology of CLs in order to improve their 3-D surface texture characteristics. These parameters can also be used in an elastic-plastic finite element model with contact elements to simulate the friction, wear and micro-elastohydrodynamic lubrication at a nanometer scale between the CL with the corneal surface.

Impact of Contact Lens Material, Design, and Fitting on Discomfort

OBJECTIVE

To review the effect of contact lens (CL) material, design, and fitting characteristics on CL discomfort.

METHODS

A PubMed search identified publications describing subjective comfort and CL material, fitting, and design parameters. The review included clinical signs associated with discomfort that may be a consequence of these parameters.

RESULTS

Reduced lens movement or more CL tightness were associated with improved comfort. Increased lens-induced paralimbal conjunctival staining and indentation, considered as quasi-indicators of CL fitting or edge design, were also associated with better comfort. No recent studies have evaluated varying CL design parameters and subjective comfort. Silicone hydrogel CLs are no different in comfort compared with hydrogel CLs. Lower equilibrium water content is associated with improved comfort in hydrogel CL wear. Coefficient of friction shows promise as a material factor potentially associated with comfort. Lid wiper epitheliopathy and lid-parallel conjunctival folds have been linked with comfort in established wearers.

CONCLUSIONS

Recent studies have confirmed the association between more mobile CLs and more discomfort, whereas closer conformity of the CL to the bulbar conjunctiva improved subjective comfort. There is no evidence to support the perceived comfort difference between silicone hydrogel and hydrogel CL. There has been limited progress in understanding the impact of varying specific CL design parameters. Although specific clinical signs may be predictive of discomfort, their role in the natural history of discomfort remains unclear. A better understanding of the relationship between coefficient of friction and comfort and strategies to improve lubricity may hold promise for limiting CL discomfort.