Lens Base Curve Research Articles

Daily disposable soft lens sagittal depth and other lens parameter changes measured at room temperature (20 °C) and on-eye temperature (34 °C)

PurposeTo investigate the differences in contact lens sagittal depth (CL-SAG), base curve (BC), and overall lens diameter (OAD) of daily disposable (DD) SCLs at room temperature (20 °C) and on-eye (34 °C) temperature. MethodsTwelve different spherical daily SCLs were analyzed (labeled power −3.00 D) at 20 °C and 34 °C. The posterior CL-SAG, BC, and OAD were measured directly using a spectral domain OCT-based instrument (Optimec is830). ResultsThe CL-SAG range for the daily disposable lenses measured at 20 °C was 3468–4016 µm. At 34 °C, the DD CL-SAG of all lenses individually decreased compared to 20 °C (t = 7.78, p < 0.001), ranging from 3385 to 3913 µm. On average at the higher temperature, the measured overall lens diameter was smaller (t = 8.18, p < 0.001) and the BC was marginally steeper (t = 2.11, p = 0.058). ConclusionsSoft lens parameters change when equilibrated from room temperature (20 °C) to on-eye temperature (34 °C). All lenses shrink when going to on-eye temperature (both lens diameter and CL-SAG decreases), compared to lenses measured at room temperature by ISO standards. Higher water content materials tend to have greater changes to the lens parameters compared to lower water content material lenses.

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

ABSTRACT 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).

Novel deep learning approach to estimate rigid gas permeable contact lens base curve for keratoconus fitting

IntroductionRigid gas permeable contact lenses (RGP) are the most efficient means of providing optimal vision in keratoconus. RGP fitting can be challenging and time-consuming for ophthalmologists and patients. Deep learning predictive models could simplify this process. ObjectiveTo develop a deep learning model to predict the base curve (R0) of rigid gas permeable contact lenses for keratoconus patients. MethodsWe conducted a retrospective study at the Rothschild Foundation Hospital between June 2012 and April 2021. We included all keratoconus patients fitted with Menicon Rose K2® lenses. The data was divided into a training set to develop the model and a test set to evaluate the model's performance. We used a U-net architecture. The raw matrix of anterior axial curvature in millimeters was extracted from Scheimpflug examinations for each patient and used as input for the model. The mean absolute error (MAE) between the prediction and the prescribed R0 was calculated. Univariate and multivariate analyses were conducted to assess the model's errors. ResultsThree hundred fifty-eight eyes from 202 patients were included: 287 eyes were included in the training dataset, and 71 were included in the testing dataset. Our model's Pearson coefficient of determination (R2) was calculated at 0.83, compared to 0.75 for the manufacturer's recommendation (mean keratometry, Km). The mean square error of our model was calculated at 0.04, compared to 0.11 for Km. The predicted R0 MAE (0.16 ± 0.13) was statistically significantly different from the Km MAE (0.23 ± 0.23) (p = 0.02). In multivariate analysis, an apex center outside the central 5 mm region was the only factor significantly increasing the prediction absolute error. ConclusionOur deep learning approach demonstrated superior precision in predicting rigid gas permeable contact lens base curves for keratoconus patients compared to the manufacturer's recommendation. This approach has the potential to be particularly beneficial in complex fitting cases and can help reduce the time spent by ophthalmologists and patients during the process.

Investigation of the relationship between contact lens design parameters and refractive changes in Ortho-K

PurposeTo investigate the relationship between Ortho-K contact lens design parameters and refractive power change of the eye through a parametric mathematical representation. MethodsThe current study utilises fully anonymized records of 249 eyes, 132 right eyes, and 117 left eyes from subjects aged 14.1 ± 4.0 years on average (range 9–38 years) which were selected for secondary analysis processing. The data were split into 3 groups (G1 up to 35 days wear, from 10 to 35 days, G2 up to 99 days wear, more than 35–99 days & G3 more than 100 days wear) according to the length of time, in days, that the lenses were worn. Corneal shape was measured before and after contact lens wear using the Medmont E300 topographer, from which height and distance files were read by a custom-built MATLAB code to construct the corneal anterior surface independently. Changes in refractive power pre and post-Ortho-K wear were determined using constructed tangential refractive power maps from which both centrally flattened and annular steepened zones were automatically bounded, hence used to determine the refractive power change. ResultsOn average, flat Sim-K and steep Sim-K were reduced after Ortho-K lens wear by 1.6 ± 1.3 D and 1.3 ± 1.4 D respectively. The radius of the base curve was correlated with the mean central flattened zone power change strongly in G1 (R = 0.7, p < 0.001) and moderately in G2 (R = 0.4) and G3 (R = 0.4, p < 0.001). Hence, a strong correlation with the base curve was recorded in group G1 and moderate in G2 and G3. The reverse curve was very strongly correlated to the mean central flattened zone power change in G1 (R = 0.8, p < 0.001) and strongly correlated with G2 (R = 0.6, p < 0.001) and G3 (R = 0.7, p < 0.001). The reverse curve was also strongly correlated with the mean annular steepened zone power change among all groups G1, G2, and G3 (R = 0.7, R = 0.6 and R = 0.6) respectively (p < 0.001). ConclusionsAlthough the central corneal refractive power change was strongly correlated to the Ortho-K lens base curve, it characterized only 50% of the target power change. However, the annular steepened zone refractive power change appears to be a clearer predictor of target power change, as there appears to be a one-to-one inverse relationship with the target refractive power correction. Differences between these results and the literature may be a result of the topography software smoothing effect.

Profile of pediatric aphakics over 10 years in a tertiary eye care – A retrospective study

AimTo investigate the outcome of contact lens (CL) fitting in aphakic children following lensectomy for congenital cataract. MethodRetrospective data of 205 aphakic children who visited for CL fitting following lensectomy from 2008 to 2018 were collected. Data includes the demographic details, CL parameters in first and last visit, hours of CL wear, reason for discontinuation of CL, surgical procedures underwent and years of follow up. Results205 (148 unilateral and 57 bilateral) aphakic children comprised of age group, < 1 month (n = 48), 1–3 months (n = 37), 3–6 months (n = 68), 6–12 months (n = 10), >12 months (n = 42). 173/205(84.39%) children were fitted with rigid gas permeable (RGP) and 32/205(15.6%) were fitted with soft CL at their first visit. 10 children had shifted to soft CL in their follow-up visits due to intolerance to RGP. 97/205(47.32%) children continued CL (55RGP, 42SCL) till the last follow-up for 2.17 ± 2.36 years and wore lens for 3.7 ± 3.65 h per day. Number of lenses replaced was 2 lenses (median) and maximum of 9 lenses over a period of 1–8 visits. The maximum visual acuity achieved was up to 0.2 log Mar units at the youngest age of 4 years on successful CL wear. 60/205(29.26%) children discontinued lenses at different follow-up visits due to IOL implantation(n = 28),using spectacles due to handling difficulty, child uncooperative to lens wear and lens fitting issues(n = 32). 48/205(23.41%) were lost to follow-up after the first visit. The average K (7.46 ± 0.43 mm) showed significant correlation to lens base curve in first visit (7.48 ± 0.41 mm) whereas flat K (7.71 ± 0.38 mm) showed significant correlation in the last visit (7.46 ± 0.39 mm) (p < 0.005). This was well described by a significant diameter change of 8.68 ± 0.31 mm to 9.42 ± 1.77 mm (p < 0.005) at the first and last visit respectively. The refractive error showed a significant difference between first (27.96 ± 5.33D) and last visit (21.97 ± 6.85D) (p < 0.005). ConclusionThis study witnessed successful contact lens wear in only half of the children. The visual rehabilitation following lensectomy depends on right CL choice and close follow-up.

Effect of Wearing Different Soft Contact Lens Material &amp; Base Curve on the Objective Refraction

Purpose : The study investigated the effect of different soft contact lens material & Base curve on over-refraction using ARK and corneal topography measurement. Methods : 20 participants with mean corneal curvature of 7.77±0.24 mm (mean age = 24.73 ±2.52 years) volunterred. Each participant worn –3.00 D of hydrogel contact lenses and silicone hydrogel lenses with BC 9.0 mm & 8.5 mm in random order. The refraction (KR-8100P) and corneal topography measurement (Oculus Keratograph 5M) were conducted and difference of before and while wearing the lenses were analysed after –3.00 D compensation. Results : There were no statistically significant for ARK and topography measurmenet among 4 lenses (ARK p=0.691, Topography p=0.438). Differences by material were 0.05±0.05 for hydrogel and 0.12±0.04 for silicone hydrogel (p=0.327). Difference by BC were 0.06±0.05 for BC 9.0 and 0.11±0.05 for BC 8.5 (p=0.482). For Topography measurement, differences by material were 0.30±0.05 D for hydrogel and 0.38±0.05 D for silicone hydrogel (p=0.298). Difference by BC were 0.36±0.04 D or BC 9.0 and 0.32±0.06 D for BC 8.5 (p=0.537). Conclusion : Material and BC did not make any difference on the objective refraction, however corneal topography showed more than 0.25 D map changes, therefore cautious approaches needs to be made when prescribing contact lens.

Age-based Estimation of Contact Lens Base Curve in Filipino Infants

Objective. To create an age-based formula to estimate the base curve needed for contact lens fitting using measured central corneal curvature (CCC) with a handheld auto keratometer from ophthalmologically normal infants. Methods. This is a prospective cross-sectional study involving 70 ophthalmologically normal full-term infants aged 0 to 12 months. The infants were divided into four groups: 0–3 months, &gt;3–6 months, &gt;6–9 months and &gt;9–12 months. CCC was measured with a handheld auto keratometer and was used to compute for the base curve. Differences in CCC between the four groups were measured and linear regression models were used for formula creation. Results. The mean CCC was highest in group 1 at 45.5 ±2.4 diopters (D). These values slowly decreased as age increased. A formula predictive of the base curve based on the infants age was derived using linear regression analysis. It predicted that for every month increase in age, there is a 0.063 millimeter increase in the base curve (p&lt;0.001). Conclusion. Infant CCC is highest at birth and gradually decreases as age increases. The formula can predict the base curve needed for contact lens fitting in infants without the need for a handheld autokeratometer.

Novel Method to Determine Target Refraction in Cataract Surgery for Patients Dependent on Therapeutic Scleral Lenses.

Objectives:To evaluate a novel approach to determine the refractive target for patients undergoing cataract surgery who are dependent on therapeutic scleral lenses, to avoid the need for postoperative scleral lens replacement.Methods:Retrospective single-surgeon case series. The target refraction for intraocular lens selection was determined by considering the effective scleral lens system power. This was calculated by adding the known scleral lens spherical power to the difference between the scleral lens base curve and the average keratometry value.Results:Six eyes from three patients with moderate myopia or emmetropia with ocular graft versus host disease dependent on therapeutic scleral lenses underwent cataract surgery with intraocular lens selection based on this method. All six eyes had corrected visual acuities of 20/30 or better while wearing their previous scleral lenses at the postoperative week 1 visit. All six eyes resumed full-time scleral lens use 1 week after phacoemulsification and did not require scleral lens replacement.Conclusions:Using this method, patients requiring therapeutic scleral lenses can quickly experience optimal vision, comfort, and ocular surface protection 1 week after cataract surgery. These patients can continue to use their existing scleral lenses and avoid the costs and burdens associated with lens replacement.

Multi-view deep learning for rigid gas permeable lens base curve fitting based on Pentacam images.

Many studies in the rigid gas permeable (RGP) lens fitting field have focused on providing the best fit for patients with irregular astigmatism, a challenging issue. Despite the ease and accuracy of fitting in the current fitting methods, no studies have provided a high-pace solution with the final best fit to assist experts. This work presents a deep learning solution for identifying features in Pentacam four refractive maps and RGP base curve identification. An authentic dataset of 247 samples of Pentacam four refractive maps was gathered, providing a multi-view image of the corneal structure. Scratch-based convolutional neural network (CNN) architectures and well-known CNN architectures such as AlexNet, GoogLeNet, and ResNet have been used to extract features and transfer learning. Features are aggregated through a fusion technique. Based on a comparison of means square error (MSE) of normalized labels, the multi-view scratch-based CNN provided R-squared of 0.849, 0.846, 0.835, and 0.834 followed by GoogLeNet, comparable with current methods. Transfer learning outperforms various scratch-based CNN models, through which proper specifications some scratch-based models were able to increase coefficient of determinations. CNNs on multi-view Pentacam images have enabled fast detection of the RGP lens base curve, higher patient satisfaction, and reduced chair time. Graphical abstract The Pentacam four refractive maps is learned by the proposed scratch-based and transfer learning-based CNN methodology. The deep network-based solutions enable identification of rigid gas permeable lens for patients with irregular astigmatism.

An image processing approach for rigid gas-permeable lens base-curve identification

This research is aimed at accurate identification of base-curve in rigid gas-permeable (RGP) lens based on supervised image processing and classification of Pentacam four refractive maps in irregular astigmatism cases. Base-curve, is typically identified based on expert’s opinion of the corneal structure of the eye. Studies have applied time-consuming methods, focusing on manual and device-based techniques. For the identification of the base-curve of a lens, image analysis is proposed. As each map in the four refractive maps is of a singular view, multi-view learning is recommended to provide a single representation. To this end, an authentic dataset consisting of 247 labeled Pentacam four refractive maps was gathered in which labels were verified manually. We have proposed two novel feature extraction techniques in this domain: quantization-based radial–sectoral segmentation (QRSS) in image processing and deep convolutional neural networks. Feature fusion is applied and RGP base-curve is identified by the regression layer of a neural network. A combination of QRSS and multilayered perceptron delineates the best result, achieving a coefficient of determination of 0.9642 and satisfactory mean square error (0.0089) which is acceptable by the experts. The proposed multi-view model could improve base-curve detection accuracy, with less trial and error and patient visits in the lens fitting process.

Simulated optical performance of soft contact lenses on the eye.

PurposeTo evaluate the impact of soft contact lens eye-fit on optical power by computational modelling and to produce correction maps for reversing this impact during the design process.MethodsFinite element models of spherical and toric hydrogel contact lenses at varying nominal powers of -20 D to +20 D, base curves radii (R1b) of 8.2, 8.5, 8.8 mm, and overall diameters (d3) of 14.5, 15.0, 15.5 mm were generated. Lenses were fitted to computational eye models generated with human eyes’ topography data. Combined eye-lens simulations were run under the boundary conditions of the tears’ surface tension between the contact lens and the eye in addition to the eyelid blink pressure. Lens optical zone power changes were calculated through computational light-ray tracing methods following each simulation.ResultsEffective power changes (EPC) were affected negatively for all toric simulated lenses with power varying from -20 D to +20 D. Spherical lenses demonstrated similar behaviour, however with some positive EPC over the power range from -20 D to -10 D for spherical power (SPH) lenses. EPC assessment was between +0.25 D and -0.5 D for most lenses, however, lenses with prescriptions from +10 D to +20 D incurred EPC outside this range. The spherical lenses showed a maximum effective power change of +1.046 ± 0.338 D (Average Eye), and a minimum of -3.278 ± 0.731 D (Steep Eye). Similarly, the toric lenses showed a maximum of +1.501 ± 0.338 D (Average Eye), and a minimum of -3.514 ± 0.731 D (Steep Eye). EPC trends, along with minimum and maximum power, generally increased negatively as nominal lens prescription increased positively. Contact lens base curve selection affected the assessed effective power change for both spherical and toric lenses. The effect from lens total diameter for spherical lenses was less substantial than that for toric lenses.ConclusionsThis study considered the impact of soft contact lens design parameters on effective optical power changes (EPC) after eye-fit. Spherical lenses experienced more EPC of clinical significance (>0.25 D) than toric lenses. Both types of lenses, spherical and toric (simple astigmatism), demonstrated similar trends in EPC on fitting from -20 D to +20 D, with lenses in the extremely positive and the extremely negative prescriptions demonstrating the highest EPCs. The lens base curve impacted the extent of EPC observed, with flatter base curves experiencing less power change. Diameter proved to impact toric lenses more than spherical ones, however generally the diameter has less effect on power change than base curve selection.

Development of Silicone Hydrogel Antimicrobial Contact Lenses with Mel4 Peptide Coating.

This study investigated the development of an antimicrobial coating on silicone hydrogel contact lenses that may have the capacity to reduce contact lens-related infection and inflammatory events. The purpose of this study was to develop an effective antimicrobial coating for silicone hydrogel contact lenses by attachment of Mel4 peptide. Lotrafilcon A, comfilcon A, somofilcon A, senofilcon A, and lotrafilcon B silicone hydrogel contact lenses were plasma coated with acrylic acid followed by Mel4 antimicrobial peptide immobilization by covalent coupling. Peptide immobilization was quantified by x-ray electron spectroscopy. Contact lens diameter, base curve, center thickness, and lens surface wettability were measured by captive-bubble contact-angle technique. Antimicrobial activity of the lenses was determined against Pseudomonas aeruginosa and Staphylococcus aureus by viable plate count and also after soaking with artificial tears solution for 1 day. In vivo safety and biocompatibility were determined in an animal model for 1 week. Mel4 peptide-coated silicone hydrogel contact lenses were associated with high antimicrobial inhibition (>2 log), except for lotrafilcon B and senofilcon A. Lotrafilcon B did not exhibit any activity, whereas senofilcon A showed 1.4- and 0.7-log inhibition against P. aeruginosa and S. aureus, respectively. X-ray electron spectroscopy revealed significant increases in the lens surface-bound amide nitrogen in all contact lenses except for lotrafilcon B. All contact lens parameters remained unchanged except for the base curve and center thickness for senofilcon A. Mel4 immobilization was associated with a decrease in contact angle. Mel4-coated contact lens wear was not associated with any signs or symptoms of ocular irritation in a rabbit model study. Reduced antimicrobial activity was observed with all the lenses after soaking with artificial tears solution or rabbit wear. Mel4 antimicrobial coating may be an effective option for development of antimicrobial silicone hydrogel contact lenses.

Inter-relationship of Soft Contact Lens Diameter, Base Curve Radius, and Fit.

To evaluate the inter-relationship of soft contact lens base curve radius (BC), diameter, and lens fit using a mathematical model. 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. 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. 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.

Mathematical model for evaluating soft contact lens fit.

To evaluate the effect of varying lens and ocular topography parameters on soft contact lens (SCL) fit, using a novel computer spreadsheet model. Although SCLs are worn by more than 100 million ametropes, the factors governing their fitting characteristics are poorly understood. A spreadsheet-based computer model used a novel ellipto-conical corneal model coupled with population data on corneoscleral topography obtained in a previous clinical study. The model calculated lens edge strain (circumferential elongation) as a predictor of lens tightness. The following parameters were systematically varied: corneal curvature, corneal diameter, corneal shape factor, corneoscleral junction angle, lens base curve (BC), and diameter. The ellipto-conical corneal model showed closer concordance with actual measurements of corneal sagittal height than a simple elliptical model (limits of agreement, ±0.20 vs. ±0.25 mm; p = 0.0015). For an eye with average ocular parameters wearing a typical SCL design (BC, 8.60; diameter, 14.2 mm), the model calculated an edge strain of 2.7%. For the same SCL, the tightest fit (8.5% strain) was found with the eye showing the combination of smallest, flattest, most aspheric cornea. Conversely, the loosest fitting (-2.6%) was found with the eye showing the combination of largest, steepest, least aspheric cornea. A change in BC of 0.4 mm typically resulted in changes in edge strain of less than 2.5%, whereas a change in diameter of 0.5 mm resulted in a change of less than 2%. Using the typical SCL design and average corneal model, wide variations in corneoscleral junction angle did not critically affect lens fit. More extreme combinations of SCL and ocular parameters resulted in edge strain likely to result in a tight (>6%) or loose fit (<0%). A novel ellipto-conical corneal model in conjunction with spreadsheet mathematical modeling proved to be a useful tool for attempting to understand the factors governing SCL fit.

Lens parameter changes under in vitro and ex vivo conditions and their effect on the conjunctiva

To quantify changes in contact lens parameters induced by lens wear and determine whether these changes are associated with contact lens-induced conjunctival staining (CLICS). In vitro: Lens diameter, sag, edge shape, base curve of six contact lens brands (balafilcon, comfilcon, etafilcon, lotrafilcon B, omafilcon and senofilcon) measured at 21°C and 35°C (eye temperature). Ex vivo: Diameter of lenses collected from a prospective, randomised, contra-lateral, cross-over clinical trial from 36 subjects wearing all lens types for 1 week daily wear, measured in 35°C PBS after removal. Ocular surface was examined for lens-induced conjunctival staining by masked examiner. In vitro: Changes in diameter and base curve outside ISO tolerance were found with etafilcon A and omafilcon A. Ex vivo: Comfilcon A and etafilcon A had greatest shrinkage in diameter (0.18mm) and base curve (0.11mm steeper) with temperature increase from 21°C to 35°C. Senofilcon A, lotrafilcon B and balafilcon A maintained most stable parameters between 21°C and 35°C. Changes in diameter and base curve from lens wear were not correlated with CLICS (p>0.49). Multivariate analysis showed significantly greater levels of lens induced staining were associated with lens modulus (p<0.001) and knife (p<0.001) and chisel (p<0.001) edge shapes. Parameter changes induced by lens wear were associated with increasing temperature, but these changes in lens diameter and base curve did not induce CLICS. Modulus and edge shape were associated with increased CLICS. The susceptibility of etafilcon A and omafilcon A lenses to parameter changes might be related to their high water content.

The Infant Aphakia Treatment Study Contact Lens Experience

We describe our experience correcting a cohort of infants with contact lenses in the Infant Aphakia Treatment Study. Fifty-seven infants 1-6 months of age were randomized to contact lens wear. An examination under anesthesia was performed at the time of enrollment and at approximately 1 year of age. A traveling examiner assessed visual acuity at approximately 1 year of age. Forty-two treated eyes (74 %) were fitted with silicone elastomer (SE) contact lenses; 12 eyes (21 %) with rigid gas permeable (RGP) contact lenses, and 3 eyes (5%) wore both lens types. Median visual acuity was +0.80 logMAR in both lens type-wearing groups. The mean (± SD) keratometric power of the treated eyes was 46.3±2.8 D at baseline and 44.6±2.3 D at 1 year of age for a mean decrease of 0.2±0.2 D/mo. Keratometric astigmatism of treated eyes was 1.98±1.37 D at baseline and 1.62±0.98 D at 1 year of age for a mean decrease of 0.05±0.2 D/mo. The mean RGP lens base curve at baseline was 47.62 D±2.62 D versus 47.00 D±3.50 D at 12 months after surgery. Children wearing SE lenses required a mean of 10.9 replacements (range 2-24) compared to 16.8 replacements (range 8-32) for children wearing RGP lenses. Three adverse events occurred. Contact lenses were worn successfully with relatively few adverse events by a cohort of infants with unilateral aphakia. The visual acuity results were identical independent of the contact lens material or modality. RGP lenses needed replacement more often than SE lenses.

Rigid contact lens fitting based on keratometry readings in keratoconus patients: predicting formula.

To find a simple mathematical correlation between the lens base curve (BC) and keratometry findings (krf). This retrospective study included 400 keratoconic eyes (350 patients) previously fit with rigid contact lenses at an academic eye center over a five year period. The patients were classified into five groups based on the keratometry findings (krf<7, krf:7-8, krf>8, krf-krs (difference between two keratometry; flat and steep)= 0.3-0.6, krf-krs >0.6mm as groups 1 to 5, respectively. Multivariate linear regression and Munro's correlation coefficient were employed to defer the formulas. A linear correlation could be found in all groups except for patients in group 3. For group 1, BC=0.211×krf+ 5.904. For group 2, BC=0.456×krf+4.160. For group 4, BC= 0.321×krf+5.219. For group 5, BC=0.337×krf+ 5.090. The development of new formulas for RGP fitting enables ophthalmologists to work with confidence and prevents unnecessary and frequent lens trials. The customary lens fitting methods are needed to be replaced by new formulas, which help to save time and costs.

Relationship Between Corneal Topographic Indices and Scleral Lens Base Curve

To determine whether parameters of anterior corneal contour as identified by topographic analysis (steep and flat simulated keratometry, reference sphere) predict the base curve of Jupiter scleral lenses in patients with dry eye syndrome and keratoconus. We identified 33 eyes with dry eye syndrome and 21 eyes with keratoconus that were fit with Jupiter scleral lenses of standard design between June 2006 and July 2009. Steep and flat simulated keratometry powers and shape factor from axial topographic maps, reference sphere from elevation maps, and base curve of the scleral lens prescribed for each eye were recorded. Correlations between topographic indices and base curve were evaluated by using the Pearson correlation coefficient, and significances were completed by using generalized estimating equation models. In dry eye syndrome, the base curve of the final scleral lens prescribed correlated with the steep keratometric power (r = 0.70, P = 0.05, n = 33), the flat keratometric power (r = 0.71, P<0.001, n = 33), and the reference sphere (r = 0.73, P = 0.002, n = 33). In eyes with keratoconus, base curve also correlated with the steep keratometric power (r = 0.72, P<0.001, n = 19), the flat keratometric power (r = 0.70, P<0.001, n = 19), and the reference sphere (r = 0.68, P<0.001, n = 21). There were no correlations between base curve and shape factor. In eyes with normal and abnormal ocular contour, base curve of scleral lenses correlates with reference sphere and steep and flat keratometric powers, but the predictive relationship is weak (r ∼0.50). Diagnostic fitting may be the most efficient method of fitting scleral lenses at present.

Corneal Topography and Soft Contact Lens Fit

To determine which ocular topography variables affect soft contact lens fit. Fifty subjects each wore three pairs of soft lenses in random succession (Vistakon Acuvue 2, Vistakon Acuvue Advance, Ciba Vision Night & Day), and various aspects of lens fit were evaluated. The steeper base curves of each type were worn in one eye and the flatter base curves in the other eye. Corneal topography data were collected using a Medmont E300 corneal topographer (Camberwell, Australia). Corneal curvature, shape factor (SF), and corneal height were measured over a 10 mm chord and also over the maximum measurable diameter. These were measured in the horizontal, vertical, steepest, and flattest meridians. With each lens type, the steeper base curve provided the best fit on the greatest proportion of eyes and the significant differences in various aspects of fit were noted between base curves. For each lens type, there was no significant difference in mean K-reading between those eyes best fit with the steeper base curve and those eyes best fit with the flatter base curve. Two of the lenses showed a positive correlation between centration and horizontal corneal height (maximum), whereas one lens showed a negative correlation between centration and horizontal SF (SF = e). Several lenses showed a positive correlation between post-blink movement and horizontal or vertical corneal SF. The measurement of corneal topography using current Placido disc instrumentation allows a better prediction of soft lens fit than by keratometry, but it is not reliable enough to enable accurate selection of the best fitting base curve. Some correlations are evident between corneal measurements; however, trial fitting remains the method of choice for selection of soft lens base curve.

The use of video-keratoscopy in predicting contact lens parameters for keratoconic fitting

The purpose of this report is to demonstrate the use the video-keratoscope in determining the type and size of the cone in keratoconus and PMD patients and the final back optic zone diameter (BOZD) and total lens diameter (LD). A retrospective review of one hundred clinical records including topographic maps, of keratoconic patients (randomly selected) was performed. Cone diameter and type and final contact lens base curve and diameter were recorded. The types or variations of keratoconus were determined with the use of the tangential map to be either: centred or nipple, early oval cones, moderate oval cones, severe cones or pellucid marginal degeneration (PMD). The size of the cone was dependent on the type and the stage of progression of the cone. Inventory sets for keratoconus that had progressively smaller BOZDs as the base curve or back optic zone radius (BOZR) steepened were found to fit best when prescribed for centred or nipple cones. Inventory sets or multicurve sets that had a constant BOZD with a certain lens diameter that did not vary with the BOZR were found to perform better on oval cones. Very large cones, as with PMD benefited from lenses with very large BOZDs. Matching the size of the BOZD (and in tandem the LD) to the size of the cone as determined with the tangential topographic map may be a useful tool in aiding in contact lens fitting to increase success.