Edward Lum

Myopia control during orthokeratology lens wear in children using a novel study design.

PURPOSE To investigate the effect of overnight orthokeratology (OK) contact lens wear on axial length growth in East Asian children with progressive myopia. DESIGN A prospective, randomized, contralateral-eye crossover study conducted over a 1-year period. PARTICIPANTS We enrolled 26 myopic children (age range, 10.8-17.0 years) of East Asian ethnicity. METHODS Subjects were fitted with overnight OK in 1 eye, chosen at random, and conventional rigid gas-permeable (GP) lenses for daytime wear in the contralateral eye. Lenses were worn for 6 months. After a 2-week recovery period without lens wear, lens-eye combinations were reversed and lens wear was continued for a further 6 months, followed by another 2-week recovery period without lens wear. Axial eye length was monitored at baseline and every 3 months using an IOLMaster biometer. Corneal topography (Medmont E300) and objective refraction (Shin-Nippon NVision-K 5001 autorefractor) were also measured to confirm that OK lens wear was efficacious in correcting myopia. MAIN OUTCOME MEASUREMENTS Axial length elongation and myopia progression with OK were compared with conventional daytime rigid contact lens wear. RESULTS After 6 months of lens wear, axial length had increased by 0.04±0.06 mm (mean±standard deviation) in the GP eye (P=0.011) but showed no change (-0.02±0.05 mm) in the OK eye (P=0.888). During the second 6-month phase of lens wear, in the OK eye there was no change from baseline in axial length at 12 months (-0.04±0.08 mm; P=0.218). However, in the GP eye, the 12-month increase in axial length was significant (0.09±0.09 mm; P<0.001). The GP lens-wearing eye showed progressive axial length growth throughout the study. CONCLUSIONS These results provide evidence that, at least in the initial months of lens wear, overnight OK inhibits axial eye growth and myopia progression compared with conventional GP lenses. Apparent shortening of axial length early in OK lens wear may reflect the contribution of OK-induced central corneal thinning, combined with choroidal thickening or recovery due to a reduction or neutralization of the myopiogenic stimulus to eye growth in these myopic children.

Mapping the corneal sub-basal nerve plexus in orthokeratology lens wear using in vivo laser scanning confocal microscopy.

PURPOSE This study was designed to map the sub-basal nerve plexus (SBNP) in the cornea of orthokeratology (OK) lens wearers. METHODS Laser scanning confocal microscopy (LSCM) was performed in vivo on three subjects: a non-lens wearer and two OK lens wearers. Scans were performed on the right eye while the left eye fixated a moving target. A total of 575, 430, and 676 contiguous images of the SBNP were taken from the non-lens wearing and the OK lens wearing subjects, respectively, and used to construct maps of the central to mid-peripheral SBNP. RESULTS In the non-lens wearing eye, nerves radiated towards a whorl-like complex centered nasally and inferiorly in an overall pattern consistent with previously reported studies. In the OK lens wearing eyes, this whorl pattern was absent, replaced by a tortuous network of nerve fibers centrally, and thicker curvilinear fibers mid-peripherally, particularly in the nasal, inferior, and temporal regions. CONCLUSIONS This study maps the corneal SBNP in OK lens wearers and provides compelling evidence that OK lens wear alters the normal SBNP distribution observed in healthy, non-lens wearing eyes.

Performance standards for toric soft contact lenses.

Purpose. To simplify the clinical assessment of toric soft contact lens (TSCL) on-eye behavior by establishing a set of standard clinical evaluation techniques. The likely performance range expected among the TSCL wearing population was determined for a series of lens designs and acceptable performance standards indicated for each variable. Methods. Four prism-ballast, two peri-ballast and one dynamic stabilization TSCL designs were each worn by groups of 20 subjects in a nondispensing study. After 20 min of lens wear, lenses were assessed, in right eyes only, for subjective comfort (100-point scale), lens mislocation (degrees deviation from vertical) and rotational recovery after deliberate 30° mislocation (degrees/10 blinks). The percentage of lenses orienting within ±10° of target orientation (zero rotation) and the variability of orientation (standard deviation of mislocation) were also calculated for each lens group. Results. Based on partitioning of the data distributions for each variable, performance was designated as excellent, acceptable or poor. Corresponding performance cut-offs were determined at ≥90, 89 to 80, and <80 for subjective comfort, ≤±6°, ±7° to 10°, and >±10° for mislocation, >10°/10 blinks, 10° to 6°/10 blinks, and <6°/10 blinks for rotational recovery. For groups of wearers the appropriate cut-offs were ≥90%, 89 to 70%, and <70% of lenses orienting within ±10° of target orientation and <±6°, ±6° to 10°, and >±10° for variability of orientation. Conclusion. Techniques suitable for the evaluation of TSCL clinical performance have been described and guidelines for the assessment of such lenses established. In the process, we have identified potential performance differences that may relate to variations in TSCL design.

Central and paracentral corneal curvature changes during orthokeratology.

Purpose To investigate regional changes in corneal curvature and power induced by overnight orthokeratology (OK) contact lens wear over a period of 2 weeks. Methods Corneal topography data (Medmont E300) from 21 myopes (12 M, 9F, 20 to 40 years), who had worn BE OK lenses manufactured in Boston XO material for 14 nights, were analyzed retrospectively. Enrollment criteria were myopia up to 4.50 D and corneal toricity up to 1.50 D. Custom MATLAB programs were used to determine sectorial tangential curvature and refractive power, and to investigate changes from baseline after 1 and 14 nights, and between 1 and 14 nights of lens wear in the central circular zone (CCZ) and surrounding paracentral annular zone (PCZ), with each zone subdivided into nasal, superior, temporal, and inferior sectors. Results After OK, significant asymmetry was found in tangential curvature across sectors. In the CCZ, by day 14 there was greater flattening in the temporal (−1.27 ± 0.62 D, p < 0.001) than nasal sector (0.05 ± 0.62 D, p = 0.893). In the PCZ, by day 14 there was greater steepening in the temporal (2.37 ± 1.09 D, p < 0.001) than nasal sector (0.30 ± 1.36 D, p = 0.326). In both zones, vertical sectors did not show any asymmetry. The variation in corneal curvature across sectors and the mirror asymmetry was also reflected in variations in the corneal refractive power. Conclusions OK induces non-uniform corneal changes to the central and paracentral regions. This non-uniformity may influence peripheral refraction profiles reported with OK that have been suggested to be influential in myopia control.

Corneal sensitivity with contact lenses of different mechanical properties.

Purpose To examine the changes in corneal sensitivity after overnight wear of contact lenses with different mechanical properties. Methods Twenty young-adult subjects wore a silicone hydrogel, rigid gas-permeable, or orthokeratology (OK) contact lens in randomized order for a single night of wear in the right eye only. All lenses were matched in Dk/t (∼46 ISO Fatt). Changes in corneal apical radius ro, asphericity Q, and corneal refractive power (Medmont E300) were measured. Changes in central corneal sensitivity were also measured by a masked investigator using two instruments: Cochet-Bonnet (COBO) aesthesiometer and Non-Contact Corneal Aesthesiometer (NCCA). Results There were significant differences in corneal topographic change from baseline between the lens types for ro, Q, and corneal refractive power. There were also significant differences in the change from baseline (mean ± SD) in corneal sensitivity between lens types using the COBO (silicone hydrogel, 0.02 ± 0.17 g/mm2; rigid gas-permeable, 0.03 ± 0.20 g/mm2; OK, 0.22 ± 0.33 g/mm2). A significant increase in threshold from baseline was only seen in the OK lenses (p = 0.006). There was no change in sensitivity thresholds from baseline for any lens type using the NCCA (p > 0.05). Conclusions Central corneal sensitivity is reduced after a single overnight wear of OK lenses, as measured using the COBO aesthesiometer. This suggests that the mechanical force exerted by contact lenses may influence corneal sensitivity.

Treatment Zone Decentration During Orthokeratology on Eyes With Corneal Toricity.

Purpose To compare the magnitude of treatment zone decentration between eyes with minimally toric corneas (⩽1.50 DC, LoTor group) and eyes with moderately toric corneas (1.50 to 3.50 DC, HiTor group) after a single overnight wear of spherical orthokeratology lenses. Methods In the LoTor group, 21 participants (9 M, 12 F, 20–40 years) were fitted using a conventional fitting approach based on the flat corneal meridian. In the HiTor group, 12 participants (5 M, 7 F, 19–45 years) were fitted using the conventional fitting method in one eye (HiTor group I) and the other eye was fitted with a lens with slightly deeper sagittal height (HiTor group II). In all groups, BE spherical orthokeratology trial contact lenses (Boston XO) were used and corneal topography data (Medmont E300) were obtained at baseline and after a single overnight wear. The magnitude of treatment zone decentration relative to vertex normal was determined from corneal topography refractive power difference maps. Treatment zone parameters including magnitude and direction of decentration were analyzed and related to baseline corneal parameters. Results After a single overnight wear, the mean magnitude of treatment zone decentration was 0.48 ± 0.20 mm in the LoTor group, 1.06 ± 0.57 mm in HiTor group I, and 0.95 ± 0.44 mm in HiTor group II. Treatment zone decentration in the LoTor group was significantly different from HiTor group I (p < 0.001), both fitted using a conventional fitting method. Treatment zone decentration was not significantly different between HiTor group I and II (p = 0.606). The magnitude of treatment zone decentration was positively correlated with the amount of baseline corneal toricity (LoTor and HiTor group I combined, p = 0.048). Conclusions Eyes with higher amounts of corneal toricity give rise to increased amounts of treatment zone decentration in overnight orthokeratology.

Corneal Nerve Morphology and Tear Film Substance P in Diabetes

PURPOSE This work aims to characterize the relationship between tear film neuropeptide substance P and the structural integrity of the sub-basal nerve plexus in diabetes. METHODS Seventeen healthy control participants and nine participants with diabetes were recruited in this cross-sectional study. Total protein content and substance P concentrations were determined in the flush tears of participants. Corneal nerve morphology was assessed by capturing the corneal sub-basal nerve plexus using the Heidelberg Retinal Tomograph II with the Rostock Corneal Module (Heidelberg Engineering GmbH, Heidelberg, Germany) in the central cornea. Corneal nerve fiber density (CNFD) was measured using ACCMetrics (M.A. Dabbah, Imaging Science and Biomedical Engineering, Manchester, UK) on eight captured images. Comparisons between groups were made using independent samples t-tests. Correlations between parameters were analyzed using Pearsons correlations. RESULTS Substance P concentrations were significantly higher in the tears of the control group compared to participants with diabetes (4150 ± 4752 and 1473 ± 1671 pg/mL, respectively, P = .047). There was no significant difference in total protein content between the groups (3.4 ± 1.8 and 2.6 ± 1.7 mg/mL in the control and diabetes groups, respectively, P = .262). CNFD was significantly lower in the participants with diabetes compared to the control group (16.1 ± 5.7 and 21.5 ± 7.0 mm/mm, respectively, P = .041). There was a moderate correlation between substance P and CNFD (r = 0.48, P = .01). CONCLUSIONS Substance P is expressed at a significantly lower level in the tears of people with diabetes compared with healthy controls. The positive correlation between substance P and corneal nerve density indicates that substance P may be a potential biomarker for corneal nerve health.

Reduced Corneal Sensitivity and Sub-Basal Nerve Density in Long-Term Orthokeratology Lens Wear.

Objectives: To investigate changes in corneal sensitivity and nerve morphology in orthokeratology (OK) contact lens wear. Methods: In a cross-sectional study, 54 subjects (aged 18–45 years) were grouped into three categories: nonlens (NL), soft lens (SCL), and OK lens wearers. Corneal sensitivity was measured at the corneal apex and 2.5 mm temporal to the apex using the Cochet–Bonnet aesthesiometer. Corneal nerve morphology was assessed by sampling a 1 mm2 area of the corneal sub-basal nerve plexus using the Heidelberg Retinal Tomograph with Rostock Corneal Module at the corneal apex and 2.5 mm temporal to the apex. Nerve fiber density (NFD) was calculated by measuring the total length of nerve fibers per square millimeter using Image-Pro Analyser. Comparisons between groups were made using mixed analysis of variance and post hoc paired t tests with Bonferroni correction or the Kruskal–Wallis test and post hoc Mann–Whitney U tests as appropriate. Results: There was a significant difference in corneal sensitivity between the three groups (P=0.027). Central threshold was significantly higher in the OK than NL group (0.69±0.42 g/mm2 vs. 0.45±0.12 g/mm2; P=0.048). Mid-peripheral threshold was not different between the three groups (P>0.05). There was a significant difference in NFD between the three groups (P<0.001). Central NFD was significantly less in the OK than NL and SCL groups (OK: 17.89±4.42 mm/mm2, NL: 25.87±5.00 mm/mm2; SCL: 24.52±4.93 mm/mm2; P<0.001). Mid-peripheral NFD was not different between the three groups (P>0.05). Conclusions: Long-term OK lens wear is associated with a decrease in central corneal sensitivity and NFD. The mechanism underlying refractive change during OK treatment seems to impact both corneal sensitivity and nerve morphology.

Fibrillary lines in overnight orthokeratology.

This case report describes the appearance of fibrillary lines in the anterior stroma of a 39‐year‐old Asian woman wearing overnight orthokeratology (OK) lenses. The fibrillary lines were fine, slightly curved and sub‐epithelial, arranged in a band‐like annulus in the corneal mid‐periphery. The lines were not associated with epithelial staining, although a marked Fischer‐Schweitzer corneal mosaic was noted after blinking. Fibrillary lines are a relatively common finding in normal and keratoconic corneas and have been reported previously accompanying OK lens wear. Their origin is unknown and epithelial neural remodelling, corneal biomechanical stress and abrupt corneal curvature changes have been suggested as contributing factors. The appearance of fibrillary lines in our OK patient had no adverse consequences on vision or ocular health, at least in the medium term.

Effects of ambient humidity on the Cochet–Bonnet aesthesiometer

PurposeThe Cochet–Bonnet (COBO) aesthesiometer is the current standard in corneal sensitivity assessment. This study investigates the influence of ambient room humidity levels on the stimulus force exerted by the instrument.MethodsA COBO instrument (Luneau Opthalmologie) with 0.12 mm nominal nylon filament diameter was placed in an environment chamber (Electro-tech systems Inc. PA, USA) at 25 °C and relative humidity (%RH) set to either 20–80%, in 10% steps. After 12 h in the chamber at a chosen %RH level, the instrument was removed and exerted force measured by pressing the nylon filament onto the plate of an analytical microbalance (Mettler-Toledo AB265; precision ±0.0001 g) at a perpendicular angle, by a predetermined amount. Exerted force onto the microbalance was recorded in grams for a specified filament length. Procedure was repeated for filament lengths 10–60 mm, in 5 mm steps. The instrument was returned to the chamber and procedure repeated 5 times, before repeating at the next %RH setting (random order). Measurements at each filament lengths were compared using one-way ANOVA and post-hoc Tukey’s range test. A p-value < 0.05 denoted statistical significance.ResultsSignificant differences in exerted force were observed with alteration in %RH levels for each filament length (all p < 0.001). Exerted force decreased significantly with an increase in %RH for all filament lengths, with the average force decreasing by 15% with each 10% rise in %RH.ConclusionsThis study confirms previous suggestions that the rigidity of the COBO nylon filament is affected by ambient room humidity levels, with implications on the stimulus force delivered by the instrument. A conversion table is provided for converting filament lengths to pressure for a range of relative humidity levels.