Incidence of corneal pigmented arc and factors associated with its appearance in orthokeratology*

Exploring the Location of Corneal Pigmented Arc and Myopia Control Efficacy in Orthokeratology-Treated Children Using Pentacam Measurements

OBJECTIVES

To determine the location and intensity of the corneal pigmented arc in orthokeratology (ortho-k)-treated children and its relationship with annual axial length (AL) change using Pentacam.

METHODS

This retrospective cohort study enrolled children aged 9 to 15 years who had been followed up for at least one year after ortho-k treatment for myopia control. A Pentacam was used to determine the location and intensity of pigmented arc after lens wear. Annual AL changes were further used as the outcome measurement to determine their relationships with the location and intensity of pigmented arc using generalized estimating equations (GEE).

RESULTS

In total, 62 eyes from 33 patients (mean age 10.9 years) were included in our final analysis. The mean follow-up time was 30.6 months. The mean annual AL changes were 0.10 mm. Age statistically correlated with annual AL change (GEE, P= 0.033). In addition, the annual AL change was negatively associated with the relative vertical distance of the lowest density of pigmented arc point based on the visual center, pupil center, and corneal thinnest point after adjustment with age ( P =0.005, P =0.004, and P< 0.001, respectively).

CONCLUSIONS

Pentacam could be a useful tool for evaluating the location and intensity of the corneal pigmented arc. In addition, there was a negative correlation between the vertical distance of the pigmented arc and annual AL change. These findings may provide important information regarding myopia control, next-generation ortho-k design, and prescription.

[Mineral dysmetabolism in corneal diseases]

Functional status and biological properties of connective tissues significantly depend on the mineral elements involved in their metabolism. Connective tissue portion of the corneal stroma makes up most of its thickness; pathological changes in collagen fibers and the stroma can cause a range of corneal diseases, some of which are specifically associated with disorders of mineral metabolism. The article considers impairments of mineral metabolism as possible pathophysiological mechanisms in certain diseases and disorders of the cornea, and describes in detail the abnormalities associated with mineral dysmetabolism observed in patients with keratoconus.

Myopia management in the Netherlands

PURPOSE

A trend that myopia is becoming gradually more common is shown in studies worldwide. Highest frequencies have been found in East Asian urban populations (96.5%) but also a study in Europe shows that nearly half of the 25-29 year olds has myopia. With the increase in prevalence, high myopia, i.e. a spherical equivalent of -6 or more and an axial length of 26 mm or more is also on the rise. High myopia particularly carries a significant risk of ocular pathology related to the long axial length. This highlights the need for myopia management in children with progressive myopia, in particular progression to high myopia.

RECENT FINDINGS

During the last decade, many intervention studies for myopia progression have emerged. Although lifestyle adjustments are effective, pharmacological and optical interventions have shown the highest efficacy on reduction of eye growth. High concentration atropine (0.5%-1.0%) shows the most reduction in axial length progression, but has drawbacks of light sensitivity and loss of accommodation. Nevertheless, when these side effects are mitigated by multifocal photochromatic glasses, the long-term adherence to high dose atropine is high. Lower concentrations of atropine are less effective, but have less side effects. Studies on optical interventions have reported reduction of progression for Ortho-K and multifocal contact lenses, but are in need for replication in larger studies with longer duration.

SUMMARY

The field of myopia management is rapidly evolving, and a position on the best approach for daily clinics is desirable. Over the last 10 years, our team of clinical researchers has developed a strategy which involves decision-making based on age, axial length, position on the axial length growth chart, progression rate, risk of high myopia, risk profile based on lifestyle and familial risk, side effects, and individual preference. This personalised approach ensures the most optimal long-term myopia control, and helps fight against visual impairment and blindness in the next generations of elderly.

IMI Prevention of Myopia and Its Progression

The prevalence of myopia has markedly increased in East and Southeast Asia, and pathologic consequences of myopia, including myopic maculopathy and high myopia-associated optic neuropathy, are now some of the most common causes of irreversible blindness. Hence, strategies are warranted to reduce the prevalence of myopia and the progression to high myopia because this is the main modifiable risk factor for pathologic myopia. On the basis of published population-based and interventional studies, an important strategy to reduce the development of myopia is encouraging schoolchildren to spend more time outdoors. As compared with other measures, spending more time outdoors is the safest strategy and aligns with other existing health initiatives, such as obesity prevention, by promoting a healthier lifestyle for children and adolescents. Useful clinical measures to reduce or slow the progression of myopia include the daily application of low-dose atropine eye drops, in concentrations ranging between 0.01% and 0.05%, despite the side effects of a slightly reduced amplitude of accommodation, slight mydriasis, and risk of an allergic reaction; multifocal spectacle design; contact lenses that have power profiles that produce peripheral myopic defocus; and orthokeratology using corneal gas-permeable contact lenses that are designed to flatten the central cornea, leading to midperipheral steeping and peripheral myopic defocus, during overnight wear to eliminate daytime myopia. The risk-to-benefit ratio needs to be weighed up for the individual on the basis of their age, health, and lifestyle. The measures listed above are not mutually exclusive and are beginning to be examined in combination.

Orthokeratology with increased compression factor (OKIC): study design and preliminary results

OBJECTIVE

To present the study design and the baseline data of a prospective cohort study investigating the safety, refractive correction and effectiveness of myopia control in subjects fitted with orthokeratology (ortho-k) lenses of different compression factors.

METHODS AND ANALYSIS

This study is a 2-year longitudinal, double-masked, partially randomised study. Myopic children aged between 6 and 10 years are recruited and they may choose to participate in either the ortho-k or spectacle-wearing group. Subjects in the ortho-k group are randomly assigned to wear ortho-k lenses of either conventional compression factor (CCF, 0.75 D) or increased compression factor (ICF, 1.75 D). For the ortho-k subjects, the time and between-group effects within the first month of lens wear were analysed.

RESULTS

Sixty-nine ortho-k subjects (CCF: 34; ICF: 35) and 30 control subjects were recruited. There were no significant differences in baseline demographic data among the three groups of subjects (p>0.19). At the 1-month visit, the first fit success rates were 97% and 100% in the CCF and ICF ortho-k group, respectively. A higher percentage of ICF subjects could achieve full correction (CCF: 88.2%; ICF: 94.3%). The change in axial length was significantly higher in the ICF group (CCF, 0.003 mm; ICF, -0.031 mm) (p<0.05). No significant between-group differences in daytime vision or in the coverage and depth of corneal staining between the two ortho-k groups (p>0.05) were observed at any visit.

CONCLUSION

ICF did not compromise the corneal integrity and the lens centration within the first month of lens wear. The preliminary performance of ortho-k lenses with ICF of 1.00D shows that it was safe to be used in the longer term for the investigation of myopia control.

TRIAL REGISTRATION NUMBER

NCT02643342.

Correlation of corneal pigmented arc with wide epithelial thickness map in orthokeratology-treated children using optical coherence tomography measurements

PURPOSE

To determine the intensity of corneal pigmented arc in orthokeratology (ortho-k)-treated children and its correlation with wide epithelial thickness map (ETM) obtained through anterior segment optical coherent tomography (AS-OCT).

METHODS

This retrospective case series reviews medical records of children who received ortho-k treatment for myopia control. Intensity of ortho-k-associated pigmented arc after wearing ortho-k lens more than 12 months and its correlation with each sector/zone of wide ETM obtained by AS-OCT was explored. Pigmented arcs were further divided into apparent and unapparent groups, and the clinical differences between groups were determined.

RESULTS

This study included 57 eyes of 29 children (mean age, 11.4 years, range 9-15); after initiating ortho-k treatment, the incidence of the corneal pigmented arc was 91.2% with mean lens wear duration of 26.1 months. Intensity of pigmented arc was significantly correlated with lens wear duration, target power, baseline degree of myopia, C zone and sectors I2, I3 and IT3 on wide ETM. Comparison between apparent and unapparent groups showed the same significant results except for C zone. After adjusting for lens wear duration and target power, sector I2 has the highest association with pigmented arc severity.

CONCLUSION

Children treated with ortho-k are likely to develop ortho-k-associated pigmented arcs. The new wide ETM of AS-OCT can provide important information regarding the intensity of pigmented arc in these children. This can support customized pigmented arc-free ortho-k treatment for children in the future.

IMI - Interventions Myopia Institute: Interventions for Controlling Myopia Onset and Progression Report

Myopia has been predicted to affect approximately 50% of the world's population based on trending myopia prevalence figures. Critical to minimizing the associated adverse visual consequences of complicating ocular pathologies are interventions to prevent or delay the onset of myopia, slow its progression, and to address the problem of mechanical instability of highly myopic eyes. Although treatment approaches are growing in number, evidence of treatment efficacy is variable. This article reviews research behind such interventions under four categories: optical, pharmacological, environmental (behavioral), and surgical. In summarizing the evidence of efficacy, results from randomized controlled trials have been given most weight, although such data are very limited for some treatments. The overall conclusion of this review is that there are multiple avenues for intervention worthy of exploration in all categories, although in the case of optical, pharmacological, and behavioral interventions for preventing or slowing progression of myopia, treatment efficacy at an individual level appears quite variable, with no one treatment being 100% effective in all patients. Further research is critical to understanding the factors underlying such variability and underlying mechanisms, to guide recommendations for combined treatments. There is also room for research into novel treatment options.

Correlation between pigmented arc and epithelial thickness (COPE) study in orthokeratology-treated patients using OCT measurements

PURPOSE

To determine the intensity of corneal pigmented arc in orthokeratology (ortho-k)-treated children, and its correlation with key epithelial thickness measurements obtained by anterior segment optical coherence tomography (AS-OCT).

METHODS

This study is a retrospective case series. Medical records of children who received ortho-k treatment for myopia control in our hospital were reviewed. Intensity of ortho-k-associated pigmented arc and its correlation with key epithelial thickness parameters in the central 7-mm-diameter zone obtained by AS-OCT was examined. The subjects were further divided into apparent and unapparent pigmented arc groups for severity comparison.

RESULTS

The mean age of children was 11.4 years, and the incidence of corneal pigmented arc was 92.2% after lens wear for a mean duration of 21.2 months. Intensity of pigmented arc was found to be significantly correlated with key epithelial thickness parameters, including maximum and minimum epithelial thickness (Spearman's rank correlation coefficient (rs) = 0.404, P = 0.003; rs = - 0.426, P = 0.002, respectively), the difference between them (Min-Max) (rs = -0.624, P < 0.001) and standard deviation (rs = 0.659, P < 0.001). Significant correlation between intensity of pigmented arc and ortho-k target power (rs = 0.454, P = 0.001) was found. Comparison between the two groups showed significant difference in the same key epithelial thickness parameters.

CONCLUSIONS

Children receiving ortho-k treatment tended to develop pigmented arcs. Significant correlation between intensity of pigmented arc and key epithelial thickness parameters was observed. AS-OCT can be a useful tool for predicting intensity of pigmented arc in ortho-k-treated children.

[Abnormal distribution of trace elements in keratoconic corneas]

Our understanding of etiology and pathogenesis of many disorders, corneal included, greatly relies on existing knowledge in human biochemistry and biophysics. This study was aimed at chemical mapping of normal and keratoconic corneas.

MATERIAL AND METHODS

Modern methods of analytical chemistry, such as X-ray fluorescence and energy-dispersive X-ray spectroscopy on the basis of scanning electron microscopy, were adapted to the needs of cornea research. Normal human corneas obtained postmortem and corneal buttons obtained during penetrating keratoplasty were analyzed.

RESULTS

In keratoconus, abnormal accumulation of iron, copper, and zinc was found in the periphery of the buttons, i.e. in the zone of visible pigmentation (Fleischer ring), while the center - the ectatic zone - demonstrated a total deficiency of trace elements. This data suggests that keratoconus pathogenesis is associated with impaired mineral metabolism and formation of a physicochemical barrier in corneal tissues with subsequent keratectasia. The authors discuss several possible vicious circles involved.

High myopia-partial reduction ortho-k: a 2-year randomized study

PURPOSE

To investigate if the combination of partial reduction (PR) orthokeratology (ortho-k) and spectacles for residual refractive errors in the daytime was effective to slow myopic progression in high myopic children.

METHODS

High myopic children (aged 8 to 11 years) with spherical equivalent refraction at least -5.75 diopters (D) and myopia -5.00 D or more myopic were recruited and randomly assigned into PR ortho-k and control groups. Subjects in the PR ortho-k group were fitted with custom made four-zone ortho-k lenses with target reduction of 4.00 D for both eyes, and the residual refractive errors were corrected with single-vision spectacles for clear vision in the daytime. Control subjects were fully corrected with single-vision spectacles. Axial length of each eye of all subjects was measured with the IOLMaster at 6-month intervals by a masked examiner. This study was registered at www.clinicaltrial.gov with the identifier NCT00977236.

RESULTS

Fifty-two subjects were recruited and randomized to the PR ortho-k and control groups. Twelve PR ortho-k and 16 control subjects completed the study. Compared with the residual refractive errors at the 1-month visit (after stabilization of ortho-k treatment), the median increase in noncycloplegic residual myopia at the 24-month visit was 0.13 D. In the control group, the median increase in myopia was 1.00 D at the end of the study. The mean ± SD increases in axial length were 0.19 ± 0.21 mm in the PR ortho-k group and 0.51 ± 0.32 mm in the control group (95% confidence interval, -0.55 to -0.12; unpaired t test, p = 0.005).

CONCLUSIONS

This single-masked randomized study showed that PR ortho-k effectively slowed myopic progression in high myopes. Axial length elongation was 63% slower in PR ortho-k-treated children compared with children wearing spectacles.

High myopia-partial reduction orthokeratology (HM-PRO): study design

PURPOSE

To report the study design and preliminary results of a pilot study, High Myopia-Partial Reduction Orthokeratology study.

METHODS

Children with myopia of 6.00D or above and who satisfied the recruitment criteria were randomly assigned to partial reduction orthokeratology (PR ortho-k) and spectacle-wearing control groups. The myopia of the PR ortho-k children were partially reduced using custom made 4-zone ortho-k lenses of target 4.00D. Residual refractive errors were corrected with single vision spectacles. Control subjects were fully corrected with single vision spectacles. PR ortho-k subjects were also required to return for assessment after the first overnight lens wear, and one week and one month after lens wear.

RESULTS

Fifty-two eligible subjects were randomly assigned to PR ortho-k group (n=26) and control group (n=26). The median age of each group was 10.00 years. The median (range) subjective myopia of the right eye at baseline was 6.41D (5.00-8.00D) and 6.22D (6.00-8.00D) for PR ortho-k and spectacle groups, respectively (p>0.05). Nineteen (79%) PR ortho-k subjects achieved successful lens fit at the one month visit and the median myopic reduction was 3.75D in the right eye. The incidence of (mild) corneal staining in PR ortho-k subjects reduced from 30% at the first overnight lens wear to 16% at the 1-month visit. Corneal pigmented arc was observed in 32% of PR ortho-k subjects at the 1-month visit.

CONCLUSIONS

PR ortho-k was successfully applied to high myopic children with no significant changes in ocular health/best corrected visual acuity after one month of lens wear.

Do fenestrations affect the performance of orthokeratology lenses?

PURPOSE

To investigate the effect of lens fenestrations on the performance of orthokeratology lenses.

METHODS

Twenty-two subjects (aged 11 to 31 years) were fitted with identical reverse geometry orthokeratology lenses in the two eyes. One eye was randomly designated to wear a lens with three 0.20 mm fenestrations at 120° intervals placed at the junction of the reverse and alignment curves. The lens for the other eye was not fenestrated. Subjects were reviewed at 1 week, 1 month, 3 months, 6 months, and 1 year after fitting. Data were collected on refraction, visual performance, incidences and severity of corneal staining, lens binding, and corneal pigmented arc.

RESULTS

Fifteen subjects achieved full correction in OU. There were no statistically significant differences in refractive and corneal changes, visual performance, incidences and severity of corneal staining and corneal pigmented arc formation between the two eyes. The incidence of lens binding was consistently higher in eyes wearing non-fenestrated lenses but was not statistically significant. Severity of lens binding, however, was statistically significant at the 1-, 3-, 6- and 12-month visits, with the non-fenestrated lenses causing more severe binding.

CONCLUSIONS

The addition of fenestrations to orthokeratology lenses has no effect on the efficacy of the treatment or outcomes in low to moderate myopic subjects. However, the severity of lens binding is reduced. Fenestrating reverse geometry lenses may be of assistance in cases where lens binding is a problem.

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.