Lee Hall

The Influence of Corneoscleral Topography on Soft Contact Lens Fit

PURPOSE To evaluate the influence of peripheral ocular topography, as evaluated by optical coherence tomography (OCT), compared with traditional measures of corneal profile using keratometry and videokeratoscopy, on soft contact lens fit. METHODS Ocular surface topography was analyzed in 50 subjects aged 22.8 years (SD ±5.0) using videokeratoscopy (central keratometry, corneal height, and shape factor) and OCT to give both full sagittal cross-sections of the cornea and cross-sections of the corneoscleral junctions. Corneoscleral junction angle, corneal diameter, corneal sagittal height, and scleral radius were analyzed from the images. Horizontal visible iris diameter and vertical palpebral aperture were analyzed from digital slit lamp images. Lens fit was graded after 30 minutes wear of a -2.50 D commercially available standard hydrogel (etafilcon A, modulus 0.30 MPa) and silicone hydrogel (galyfilcon A, 0.43 MPa) design of similar geometries (8.30-mm base curve, 14.0-mm diameter). RESULTS The mean horizontal corneal diameter was 13.39 mm (SD ±0.44). In many cases, there was a tangential transition at the corneoscleral junction. The corneoscleral shape profile analyzed from cross-sectional OCT images contributed significantly (P < 0.001) to the prediction of soft contact lens fit compared with keratometry and videokeratoscopy, accounting for up to 24% of the variance in lens movement. The fit of the stiffer material silicone hydrogel lens was better able to be predicted and was more varied than the hydrogel contact lens. CONCLUSIONS The extra peripheral corneoscleral data gained from OCT characterization of ocular surface architecture provide valuable insight into soft contact lens fit dynamics.

Factors affecting corneoscleral topography

PURPOSE To evaluate factors affecting corneoscleral profile (CSP) using anterior segment optical coherence tomography (AS-OCT) in combination with conventional videokeratoscopy. METHODS OCT DATA WERE COLLECTED FROM 204 SUBJECTS OF MEAN AGE 34.9 YEARS (SD: ±15.2 years, range 18-65) using the Zeiss Visante AS-OCT and Medmont M300 corneal topographer. Measurements of corneal diameter (CD), corneal sagittal height (CS), iris diameter (ID), corneoscleral junction angle (CSJ), and scleral radius (SR) were extracted from multiple OCT images. Horizontal visible iris diameter (HVID) and vertical palpebral aperture (PA) were measured using a slit lamp graticule. Subject body height was also measured. Associations were then sought between CSP variables and age, height, ethnicity, sex, and refractive error. RESULTS Significant correlations were found between age and ocular topography variables of HVID, PA, CSJ, SR, and ID (P < 0.0001), while height correlated with HVID, CD, and ID, and power vector terms with vertical plane keratometry, CD, and CS. Significant differences were noted between ethnicities with respect to CD (P = 0.0046), horizontal and vertical CS (P = 0.0068 and P = 0.0095), and horizontal ID (P = 0.0010). The same variables, with the exception of vertical CS, also varied with sex; horizontal CD (P = 0.0018), horizontal CS (P = 0.0018), and ID (P = 0.0012). Age accounted for the greatest variance in topography variables (36%). CONCLUSIONS Age is the main factor influencing CSP; this should be taken into consideration in contact lens design, IOL selection, and in the optimization of surgical procedures. Ocular topography also varied with height, sex, ethnicity, and refractive error.

Exploring the optimum step size for defocus curves

Purpose To evaluate the effect of reducing the number of visual acuity measurements made in a defocus curve on the quality of data quantified. Setting Midland Eye, Solihull, United Kingdom. Design Evaluation of a technique. Methods Defocus curves were constructed by measuring visual acuity on a distance logMAR letter chart, randomizing the test letters between lens presentations. The lens powers evaluated ranged between +1.50 diopters (D) and −5.00 D in 0.50 D steps, which were also presented in a randomized order. Defocus curves were measured binocularly with the Tecnis diffractive, Rezoom refractive, Lentis rotationally asymmetric segmented (+3.00 D addition [add]), and Finevision trifocal multifocal intraocular lenses (IOLs) implanted bilaterally, and also for the diffractive IOL and refractive or rotationally asymmetric segmented (+3.00 D and +1.50 D adds) multifocal IOLs implanted contralaterally. Relative and absolute range of clear‐focus metrics and area metrics were calculated for curves fitted using 0.50 D, 1.00 D, and 1.50 D steps and a near add‐specific profile (ie, distance, half the near add, and the full near‐add powers). Results A significant difference in simulated results was found in at least 1 of the relative or absolute range of clear‐focus or area metrics for each of the multifocal designs examined when the defocus‐curve step size was increased (P<.05). Conclusion Faster methods of capturing defocus curves from multifocal IOL designs appear to distort the metric results and are therefore not valid. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

The influence of end of day silicone hydrogel daily disposable contact lens fit on ocular comfort, physiology and lens wettability

PURPOSE To quantify the end-of-day silicone-hydrogel daily disposable contact lens fit and its influence of on ocular comfort, physiology and lens wettability. METHODS Thirty-nine subjects (22.1±3.5 years) were randomised to wear each of 3 silicone-hydrogel daily-disposable contact lenses (narafilcon A, delefilcon A and filcon II 3), bilaterally, for one week. Lens fit was assessed objectively using a digital video slit-lamp at 8, 12 and 16h after lens insertion. Hyperaemia, non-invasive tear break-up time, tear meniscus height and comfort were also evaluated at these timepoints, while corneal and conjunctival staining were assessed on lens removal. RESULTS Lens fit assessments were not different between brands (P>0.05), with the exception of the movement at blink where narafilcon A was more mobile. Overall, lag reduced but push-up speed increased from 8 to 12h (P<0.05), but remained stable from 12 to 16h (P>0.05). Movement-on-blink was unaffected by wear-time (F=0.403, P=0.670). A more mobile lens fit with one brand did not indicate that person would have a more mobile fit with another brand (r=-0.06 to 0.63). Lens fit was not correlated with comfort, ocular physiology or lens wettability (P>0.01). CONCLUSIONS Among the lenses tested, objective lens fit changed between 8h and 12h of lens wear. The weak correlation in individual lens fit between brands indicates that fit is dependent on more than ocular shape. Consequently, substitution of a different lens brand with similar parameters will not necessarily provide comparable lens fit.

Objective analysis of contact lens fit.

PURPOSE To assess the validity and repeatability of objective compared to subjective contact lens fit analysis. METHODS Thirty-five subjects (aged 22.0±3.0 years) wore two different soft contact lens designs. Four lens fit variables: centration, horizontal lag, post-blink movement in up-gaze and push-up recovery speed were assessed subjectively (four observers) and objectively from slit-lamp biomicroscopy captured images and video. The analysis was repeated a week later. RESULTS The average of the four experienced observers was compared to objective measures, but centration, movement on blink, lag and push-up recovery speed all varied significantly between them (p<0.001). Horizontal lens centration was on average close to central as assessed both objectively and subjectively (p>0.05). The 95% confidence interval of subjective repeatability was better than objective assessment (±0.128 mm versus ±0.168 mm, p=0.417), but utilised only 78% of the objective range. Vertical centration assessed objectively showed a slight inferior decentration (0.371±0.381 mm) with good inter- and intrasession repeatability (p>0.05). Movement-on-blink was lower estimated subjectively than measured objectively (0.269±0.179 mm versus 0.352±0.355 mm; p=0.035), but had better repeatability (±0.124 mm versus ±0.314 mm 95% confidence interval) unless correcting for the smaller range (47%). Horizontal lag was lower estimated subjectively (0.562±0.259 mm) than measured objectively (0.708±0.374 mm, p<0.001), had poorer repeatability (±0.132 mm versus ±0.089 mm 95% confidence interval) and had a smaller range (63%). Subjective categorisation of push-up speed of recovery showed reasonable differentiation relative to objective measurement (p<0.001). CONCLUSIONS The objective image analysis allows an accurate, reliable and repeatable assessment of soft contact lens fit characteristics, being a useful tool for research and optimisation of lens fit in clinical practice.

Inter-relationship of soft contact lens diameter, base curve radius, and fit

PURPOSE To evaluate the inter-relationship of soft contact lens base curve radius (BC), diameter, and lens fit using a mathematical model. METHODS A spreadsheet mathematical model was used to evaluate theoretical fitting characteristics for various combinations of soft lens BC and diameter. The designs were evaluated using ocular topography data collected from 163 UK subjects. The model evaluated lens tightness (edge strain) and on-eye diameter (horizontal corneal overlap) and assumed that acceptable values fell within the range 0 to 6% and 0.2 to 1.2 mm, respectively. Analyses were undertaken of various trends relating to soft lens fit, including (1) the effect of BC and diameter on fitting success; (2) the effect of lens asphericity, BC, and sag on lens diameter on the eye; and (3) the effect of lens diameter on lens tightness. RESULTS The highest overall success rate (90.2%) was achieved with an 8.60/14.2 mm (BC/diameter) design. Using this design on the sample population, the median edge strain value was 3.2% (IQR: 2.1%) whereas median corneal overlap was 0.62 mm (IQR: 0.35). There was a positive correlation (r = 0.37, P < .0001) between edge strain and corneal overlap. Edge strain showed significant correlations with each of the ocular topography variables, most notably corneal asphericity (-0.62, P < .0001). Corneal overlap showed significant correlations with corneal asphericity (r = -0.42, P < .0001) and corneal diameter (r = 0.92, P < .0001). For a 0.4 mm change in BC, it is necessary to change diameter by 0.2 mm to maintain similar on-eye diameter (arclength). When changing lens diameter, a change in BC of 0.2 mm is required to maintain similar tightness of fit. CONCLUSIONS Mathematical modeling is a useful technique for large-scale evaluation of the interactions of soft contact lens design and fit. The study has given useful insights into the general performance of soft lens designs.

Clinical comparison of optimum and large diameter soft contact lenses

PURPOSE To compare the clinical performance of large diameter lenses with optimally fit lenses in the same material and monocurve back surface design. METHOD In a four-visit, randomised, bilateral, crossover, study, 25 myopic subjects wore optimum diameter lenses (control) and large diameter lenses (test) in random succession for 1 week each. Both study lenses were made of methafilcon A and of an identical design. Trial fittings with Frequency 55 (Coopervision) lenses modified with a design algorithm were used to determine the appropriate custom-made study lenses. RESULTS The least squares mean scores (±SE) for overall comfort and end-of-day comfort (0-10 scale) were 7.57 ± 0.33 vs. 7.42 ± 0.33 (P = 0.59) and 7.00 ± 0.31 vs. 7.27 ± 0.32 (P > 0.05) for the optimum and large diameter lenses, respectively. There were no significant differences in mean (±SE) gradings for limbal hyperaemia (1.23 ± 0.11 vs. 1.19 ± 0.11, 0-4 scale, P = 0.60) and corneal staining (1.79 ± 0.25 vs. 2.04 ± 0.25, P = 0.39). Conjunctival staining was greater for the optimum lens: 1.80 ± 0.28 vs. 0.93 ± 0.28 (0-4 scale, P = 0.001). With regard to lens fit, the large diameter lenses showed significantly less post-blink movement (0.22 ± 0.01 vs. 0.16 ± 0.01 mm, P = 0.004), and greater total decentration (0.15 ± 0.02 vs. 0.21 ± 0.02 mm, P = 0.010). However, there was no significant difference in the key fit variable of tightness on push-up (46 ± 0.69% vs. 48 ± 0.69%, 0-100 scale, P = 0.12). DISCUSSION The findings suggest that larger than optimal soft lenses may be worn without detriment to either comfort or ocular physiology, provided an optimal fit is otherwise maintained.