Pauline Cho

The Longitudinal Orthokeratology Research in Children (LORIC) in Hong Kong: A Pilot Study on Refractive Changes and Myopic Control

Purpose: Myopia is a common ocular disorder, and progression of myopia in children is of increasing concern. Modern overnight orthokeratology (ortho-k) is effective for myopic reduction and has been claimed to be effective in slowing the progression of myopia (myopic control) in children, although scientific evidence for this has been lacking. This 2 year pilot study was conducted to determine whether ortho-k can effectively reduce and control myopia in children. Methods: We monitored the growth of axial length (AL) and vitreous chamber depth (VCD) in 35 children (7–12 years of age), undergoing ortho-k treatment and compared the rates of change with 35 children wearing single-vision spectacles from an earlier study (control). For the ortho-k subjects, we also determined the changes in corneal curvature and the relationships with changes of refractive errors, AL and VCD. Results: The baseline spherical equivalent refractive errors (SER), the AL, and VCD of the ortho-k and control subjects were not statistically different. All the ortho-k subjects found post-ortho-k unaided vision acceptable in the daytime. The residual SER at the end of the study was –0.18 ± 0.69 D (dioptre) and the reduction (less myopic) in SER was 2.09 ± 1.34 D (all values are mean ± SD). At the end of 24 months, the increases in AL were 0.29 ± 0.27 mm and 0.54 ± 0.27 mm for the ortho-k and control groups, respectively (unpaired t test; p = 0.012); the increases in VCD were 0.23 ± 0.25 mm and 0.48 ± 0.26 mm for the ortho-k and control groups, respectively (p = 0.005). There was significant initial corneal flattening in the ortho-k group but no significant relationships were found between changes in corneal power and changes in AL and VCD. Conclusion: Ortho-k can have both a corrective and preventive/control effect in childhood myopia. However, there are substantial variations in changes in eye length among children and there is no way to predict the effect for individual subjects.

The performance of four different corneal topographers on normal human corneas and its impact on orthokeratology lens fitting.

Purpose. To evaluate the performances of Humphrey Atlas 991, Orbscan II, Dicon CT200, Medmont E300 on young Chinese adults. Methods. Three sets of corneal topography measurements were obtained from each topographer from 22 subjects—two sets by the same examiner and one set by another examiner on the same day. Results. There were no significant within-examiner and between-examiner differences for any of the parameters tested for each topographer. However, only the repeatability and reproducibility (of apical radius[Ro], eccentricity, and elevation) of the Humphrey and Medmont were good. There was no statistically significant between-topographer difference in Ro, but significant differences in eccentricity and elevation values were found. The number of repeated readings that should be taken for a precision of 2 &mgr;m (elevation) were 12 for the Humphrey and 2 for the Medmont. Conclusions. The performance of both the Humphrey and the Medmont was very good. Roand eccentricity values of different topographers cannot be used interchangeably, but the agreement in elevation values was good for these topographers. The number of repeated readings required for maximum precision varies with the topographer used, and they are not interchangeable.

Microbial contamination of contact lenses and lens care accessories of soft contact lens wearers (university students) in Hong Kong

Purpose:  This study aimed to examine the rates of microbial contamination, and identify contaminants associated with contact lenses and lens care accessories used by a group of young contact lens wearers.

Review of the tear break-up time and a closer look at the tear break-up time of Hong Kong Chinese

The technique of assessing tear stability using the fluorescein instillation technique has been widely used in the clinical diagnosis of “dry eye” and in the screening of potential contact lens wearers. Various inconsistencies in the application of the tear break-up time (TBUT) techniques and the results obtained were noted in the literature and this review summarizes the differences and the conclusions of various investigators. The reliability of this technique using two different methods of observation was examined and the mean TBUT of Hong Kong Chinese subjects (HK-Chinese) was determined. We conclude that the TBUT can be measured reliably using either the scanning or full beam method in most patients. The mean TBUT of HK-Chinese is approximately 8 s and about 70% of HK-Chinese have TBUTs less than 10 s.

The Relation between Invasive and Noninvasive Tear Break-Up Time

TBUT and NITBUT (tear break-up time and noninvasive tear break-up time, respectively) were measured on four groups of subjects from different countries (two groups of Caucasians, two groups of Chinese). No significant difference was found in either TBUT or NITBUT values among the four groups of subjects. Gender of the subjects was not a factor affecting the TBUT or NITBUT values. The distributions of both NITBUT and TBUT were non- Gaussian and the median value of either parameter was lower than those previously reported. The NITBUT values were significantly higher than the TBUT values in both Caucasian and Chinese subjects. An investigation into the extent of agreement between the TBUT and NITBUT methods of assessing tear stability indicated that these methods do not agree sufficiently closely (that is, tear stability values measured with the NITBUT technique do not agree with those measured with the TBUT technique); short average tear break-up values are associated with small differences between the measures, whereas long average tear break-up values are associated with large differences between the measures.

Reliability of the tear break-up time technique of assessing tear stability and the locations of the tear break-up in Hong Kong Chinese

The measurement of tear break-up time (TBUT) in assessing stability of the tear film is somewhat controversial, even though the technique is widely used. We examined reliability of the technique within and among examiners and conclude that measurements of TBUT can be made reliably; full-beam observation of the cornea is preferable to scanning the cornea with a narrow slit in making the measurements. There may be differences in TBUT measurements made in the same subjects among examiners, but these differences are smaller with more experienced practitioners. In the Hong Kong Chinese (HK-Chinese), tear break-up appears to be more likely to first occur in the inferior periphery of the cornea. In this population mean TBUT is about 7.20 s; assuming a Gaussian distribution of TBUT values, 2.1 s should be adopted as the lower limit for normal TBUT in HK-Chinese.

Endothelial cells analysis with the TOPCON specular microscope SP-2000P and IMAGEnet system

Purpose. Corneal endothelium plays an important role in the maintenance of corneal transparency and stability. The purpose of this study was to evaluate the performance of the TOPCON SP-2000P and IMAGEnet system in terms of (a) the difference in results between automated endothelial cell analysis and retraced cell analysis, (b) the differences in the endothelial cell analysis when using the first image and the clearest of three images taken with the SP-2000P, (c) the repeatability and reproducibility of the IMAGEnet system in the determination of corneal endothelial cell variables, and (d) the repeatability and reproducibility of the SP-2000P in capturing endothelial cell images for endothelial cell analysis. Methods. Two experiments were performed. Twenty male subjects participated in the first experiment in which endothelial images were captured by examiner SWC and endothelial cell analysis was performed by two examiners, SWC (twice on two different days) and PC (once only). Nineteen male subjects participated in the second experiment in which endothelial cell images were captured by examiners SWC and PC on Visit 1 and by examiner SWC on Visit 2. Endothelial cell analysis was performed by examiner SWC only. The 95% limits of agreements (95%LA) and the intraclass correlation coefficient (ICC) between tested parameters were determined. Results. Automated cell analysis significantly underestimated average cell size (ACS) and hexagonality, and overestimated endothelial cell density (ECD) and coefficient of variance of cell size (CV) (p < 0.05). No statistically significant differences were found in the endothelial cell variables between the first and the clearest images (p > 0.05). There were no statistically significant intra- or inter-examiner differences in any of the endothelial variables determined (p > 0.05). For a set of endothelial cell images, the reproducibility and repeatability of the endothelial cell variables determined with the IMAGEnet system were good, with ICC > 0.9. No significant inter-visit or inter-examiner differences were found (p > 0.05). Reliability was good for the determination of ECD and ACS (ICC > 0.9) but poor or average for the determination of CV and hexagonality (ICC: 0.4–0.8). Conclusions. We suggest the use of the clearest image with the retraced method for endothelial cell analysis with the IMAGEnet system, as the variability in hexagonality results between the first and the clearest images can be clinically significant. For the same set of images captured by one examiner, the TOPCON IMAGEnet system was reliable in determining ECD and ACS, and was fairly reliable in determining hexagonality and CV. When images were captured on different days or by different examiners, the TOPCON SP-2000P with the IMAGEnet system gives repeatable and reproducible values for ECD and ACS only. Caution should therefore be exercised when using CV and hexagonality to monitor endothelial changes in comparative studies.

The effect of a compliance enhancement strategy (self-review) on the level of lens care compliance and contamination of contact lenses and lens care accessories

Purpose:  The aims were to determine the level of compliance of contact lens wearers, to identify which procedures have highest levels of non‐compliance and to study the effectiveness of a compliance enhancement strategy on the level of compliance.

Microbial flora of tears of orthokeratology patients, and microbial contamination of contact lenses and contact lens accessories.

Purpose. The purpose of this study is to determine if there are changes in the ocular flora of overnight orthokeratology (ortho-k) patients, and the levels of contamination of their lenses and lens accessories, and to correlate compliance with levels of contamination. Method. Normal ocular flora of 41 subjects was determined twice before commencing ortho-k lens wear by culture of the lower conjunctiva. Further specimens were collected on six follow-up visits after beginning lens wear, as were samples from their lenses, cases, and suction holders. A questionnaire on lens care was administered after the fifth visit. Results. Three subjects provided conjunctival samples yielding Staphylococcus aureus on one occasion before lens wear, one being positive for this organism after beginning lens wear. Of 38 subjects yielding no growth or only normal eye flora before use, 28 remained free of ocular pathogens after beginning lens wear. Only four subjects had positive cultures on more than one occasion after lens wear. There was no significant difference in isolation levels of pathogens with lens wear (p = 0.423). Lens culture of 54% of subjects yielded no growth or normal flora only; lenses of 16 subjects yielded potential pathogens, including three subjects contaminated on more than one occasion. Lens isolates did not match the organisms transiently colonizing the eye. Lens case, the most frequently contaminated item, was associated with lens contamination (p < 0.001), the same organism being isolated from both items in 11 subjects. Lens suction holder was less frequently contaminated. Neither lens case nor suction holder contamination was associated with isolates from the eye. Reported good compliance correlated with lack of contamination in all but one subject. The most frequent breaches in the lens care protocol were failure to clean, disinfect, and replace the lens case. Conclusion. Ocular flora was not altered by ortho-k lens wear over an extended period, and patients remained free of infection. Contaminants identified were generally of a transient nature. Most patients had significant contamination of at least one item, most frequently the lens case. Lens case isolates were significantly associated with those from the lens. The majority of patients reporting good compliance had low or no contamination of their lenses and accessories.

Myopia control using toric orthokeratology (TO-SEE study).

PURPOSE This nonrandomized clinical study aimed to investigate the effectiveness of toric orthokeratology (ortho-k) for myopia control in myopic children with moderate-to-high astigmatism METHODS We enrolled 80 subjects (aged 6-12 years; ortho-k, 43; control, 37) with myopia of 0.50 to 5.00 diopters (D), and with-the-rule astigmatism of -1.25 to -3.50 D, and unremarkable ocular and general conditions. Data collection, including visual acuity, subjective and objective refraction, axial length, corneal topography, and biomicroscopy examination, was performed every 6 months during the 24-month study period. Results from the right eye or the eye with higher astigmatism were reported. RESULTS A total of 35 ortho-k and 23 control subjects completed the study successfully. Subjects in both groups demonstrated axial elongation (P < 0.001). The average axial elongation at the end of study was 0.31 ± 0.27 and 0.64 ± 0.31 mm in the ortho-k and control groups, respectively (P < 0.001). At the end of 24 months, axial elongation in ortho-k subjects was 52% slower than that in the control group. Axial elongation was correlated significantly with the initial age of the subjects (P = 0.02) and treatment assigned (P = 0.04), but not with sex, initial myopia, initial refractive cylinder, or initial corneal toricity (P > 0.08). CONCLUSIONS Toric ortho-k lenses can slow axial elongation effectively in myopic children with moderate-to-high astigmatism. (ClinicalTrials.gov number, NCT00978692.).