The Association of Astigmatism and Spherical Refractive Error in a High Myopia Cohort

Verification of a nationwide population-based myopia growth chart in a large longitudinal cohort of 1155 Korean children

OBJECTIVE

To evaluate predictive value of the myopia growth chart based on population-based health survey data using longitudinal cohorts.

METHODS

Patients aged from 5 to 18 years and underwent two or more cycloplegic refraction (CR) exams with at least one year of interval were included. Percentile deviation was calculated by subtracting percentile at final exam from the percentile at initial exam based on the chart. Spherical equivalent (SE) deviation was calculated by SE at final CR subtracted from predicted SE based on initial CR using the chart.

RESULTS

2310 eyes from 1155 subjects were included. There were 1344 eyes (58.2%) categorized as inliers, where both initial and final CR were within the 2nd to 99th percentile. Mean percentile and SE deviations were + 11.0 ± 22.9 percentiles and -0.60 ± 1.33 diopters, each. Outliers, those except the inliers, were 966 eyes (41.8%). Most outliers (709 eyes, 73.4%) were outside the chart for both initial and final exam. The rest of the outliers (257 eyes, 26.2%) were within the 2 to 99 percentile range on the chart at least once, either at initial or final exams; most of those (202 eyes, 78.6%) progressed toward myopia more than predicted.

CONCLUSIONS

In our large cohorts, both inliers and outliers tended to progress toward more myopia than predicted from the chart. This suggests the chart predicts childhood myopia rather conservatively. The myopia growth chart may be useful as a screening tool in detecting children at high risk of developing high myopia.

Effects of atropine 0.01% on refractive errors in children with myopia

Background

Little is known about changes in astigmatism during atropine treatment. We aimed to explore the effects of atropine 0.01% eye drops on both spherical and cylindrical refractive errors in myopic children.

Methods

Children aged 6-14 years with myopia ≥ -6.00 D and < -0.50 D, and total astigmatism > -2.00 D in at least one eye were enrolled. Subjects were randomised either to receive atropine 0.01% once nightly with single-vision lenses or simply to wear single-vision lenses and were followed up at 3-month intervals. Cycloplegic refraction and axial length were measured. The magnitude and direction of total astigmatism (TA), corneal astigmatism (CA), and residual astigmatism (RA) were evaluated.

Results

Overall, 119 eyes (69 eyes in the atropine group and 50 eyes in the control group) were included in the final analyses after 9 months. Atropine-treated eyes showed significantly less progression of myopia than did control eyes (spherical equivalent: -0.35 ± 0.33 vs. -0.56 ± 0.49 D, p = 0.001; axial length: 0.20 ± 0.19 vs. 0.33 ± 0.19 mm, p < 0.001). Compared with control eyes (-0.04 ± 0.23 D), a significant increase in TA was observed in the atropine-treated eyes (-0.14 ± 0.29 D); this was mainly attributed to the increase in CA (-0.17 ± 0.26 D) rather than the minor decrease in RA (0.02 ± 0.32 D).

Conclusions

Atropine 0.01% was effective in preventing myopia progression, whereas 9 months of atropine treatment resulted in a clinically small, but statistically significant increase in TA in myopic Chinese children.

Epidemiology and Burden of Astigmatism: A Systematic Literature Review

SIGNIFICANCE

This is the first literature review to report the epidemiology, patient burden, and economic burden of astigmatism in the general adult population. The unmet needs of astigmatism patients with coexisting ocular conditions (cataract, glaucoma, dry eye, presbyopia, or macular degeneration) and risks associated with untreated astigmatism are also reviewed and reported.

PURPOSE

This study aimed to identify, report, and summarize the published literature on epidemiology, patient burden, and economic burden of astigmatism using a systematic literature review.

METHODS

MEDLINE, EMBASE, and Cochrane Library databases were searched (January 1996 to May 2021). Search results were limited to the English language. Proceedings (2018 to 2021) from ophthalmology congresses were searched along with gray literature using the Google Scholar platform.

RESULTS

The literature search yielded 6804 citations, of which 125 met the inclusion criteria (epidemiology, 68; patient burden, 60; economic burden, 6). Astigmatism prevalence in the general population varied from 8 to 62%, with higher rates in individuals 70 years or older. The prevalence of with-the-rule astigmatism was higher in individuals 40 years or younger, whereas rates of against-the-rule and oblique astigmatism increased with age. Astigmatic patients experienced decreased vision quality, increased glare (53 to 77%), haloes (28 to 80%), night-time driving difficulties (66%), falls, and spectacle dependence (45 to 85%). Astigmatic patients performed vision-related tasks slower (1 D, 9% slower; 2 D, 29% slower) and made more errors (1 D, 38% more errors; 2 D, 370% more errors) compared with fully corrected individuals. In cataract patients with astigmatism, the annual mean per-patient productivity loss costs ranged from €55 ($71) to €84 ($108), and mean informal care costs ranged from €30 ($39) to €55 ($71) with a mean of 2.3 to 4.1 hours spent on informal care.

CONCLUSIONS

Uncorrected astigmatism decreases patients' vision-related quality of life, decreases productivity among working-age adults, and poses an economic burden on patients and their families.

Characterizing Astigmatism in the United States

PURPOSE

To study astigmatism and astigmatism rule by 1) determining changes in prevalence in the United States between 1971-1975 and 1999-2008 and 2) identifying associations with demographic factors.

SETTING

National survey.

DESIGN

Retrospective cross-sectional study.

METHODS

Participants of the 1971-1975 and 1999-2008 National Health and Nutrition Examination Survey (NHANES) aged 20-74 years representing the United States population. The 1971-1975 NHANES measured astigmatism in individuals using an algorithm based on presenting visual acuity, lensometry and objective refraction. We implemented similar methods using 1999-2008 NHANES data for comparison. We identified prevalence of clinically significant astigmatism (≥1.0 D) and used logistic regression models to assess demographic associations with rule of astigmatism.

RESULTS

Main outcomes were prevalence estimates of astigmatism and odds ratios estimating associations with demographic characteristics. There was an increase in astigmatism from the 1970's to 2000's [14% (95% CI: 13.2-14.5) vs. 24% (22.8-24.6)], which was more pronounced in men [12% (10.8-12.7) vs. 23% (21.9-24.2)] than women [16% (14.9-16.8) vs. 24% (23.0-25.7)]. In adjusted analysis of the 2000's cohort, myopes had 8.34 (CI: 7.30-9.54) times greater odds of astigmatism than non-myopes. In the 2000's, there was increased odds of ATR astigmatism in males (OR, 1.4; 95% CI: 1.1-1.8) compared to females, non-myopes (OR, 2.3; 95% CI: 1.7-3.1) compared to myopes, and 60-74 year olds (OR, 3.7; 95% CI: 2.7-5.1) compared to 20-39 year olds.

CONCLUSIONS

There is greater prevalence of astigmatism and against-the-rule astigmatism in 1999-2008 compared to 30 years prior. Factors associated with against-the-rule astigmatism were being male, white, and nonmyopic.

Evaluation of preoperative corneal astigmatism using swept-source optical biometry in Chinese cataract surgery candidates with high myopia: a prospective, comparative observational study

Background

High myopia and cataracts are major causes of blindness in East and Southeast Asia. Corneal astigmatism is a major contributor to uncorrected poor vision after cataract surgery in patients with high myopia. The purpose of the present study was to evaluate the demographic characteristics and distribution of preoperative corneal astigmatism in Chinese cataract surgery candidates with high myopia.

Methods

Swept-source optical coherence tomography-based optical biometry was performed preoperatively in consecutive cataract surgery candidates who were classified by axial length (AL) into a high myopia group (defined as AL ≥26.0 mm) and a control group (normal ALs). The demographics, ALs, and keratometry values were recorded.

Results

Among 15,063 cataract surgery candidates (15,063 eyes), 1,921 patients (12.8%, 1,921 eyes) in the high myopia group and 11,880 patients (11,880 eyes) in the control group were enrolled. In the high myopia group, the mean age was 59.8±12.6 (standard deviation) years, which was younger than that in the control group (69.1±11.0 years, P<0.001). In the high myopia group, the mean corneal astigmatism was 1.20±0.83 dioptre (D), which was greater than that in the control group (0.93±0.69 D, P<0.001). In the high myopia group, 82.2% had corneal astigmatism ≥0.50 D, 51.4% ≥1.00 D, 27.4% ≥1.50 D and 14.4% ≥2.00 D, all of which were higher than the respective proportions in the control group (P<0.001 for all). In the high myopia group, 66.8% had moderate to high corneal astigmatism, and 42.8% had “with-the-rule” astigmatism, and both of these proportions were higher than the respective proportions in the control group (P<0.001 for both). In the high myopia group, corneal astigmatism tended to increase with increasing age (r =0.134, P<0.001) after the age of 50, which was consistent with the tendency in the control group.

Conclusions

A significant burden of preoperative corneal astigmatism was observed in Chinese cataract surgery candidates with high myopia. Moderate to high corneal astigmatism was more common in highly myopic eyes than in normal AL eyes.

Early Astigmatism Can Alter Myopia Development in Chickens

Purpose

To determine the effects of optically imposed astigmatism on myopia development in chickens.

Methods

Chicks were randomly assigned to wear either spherical (-10D, "LIM", n = 14) or sphero-cylindrical lenses (n ≥ 19 in each group) monocularly for a week from 5 days of age. All lenses imposed the same magnitude of spherical-equivalent hyperopic defocus (-10D), with the two astigmatic magnitudes (-8D or -4D) and four axes (45°, 90°, 135°, or 180°) altered to simulate four subtypes of clinical astigmatism. At the end of the treatment, refractive state was measured for all birds, whereas ocular axial dimensions and corneal curvature were measured for subsets of birds.

Results

Sphero-cylindrical lens wear produced significant impacts on nearly all refractive parameters (P < 0.001), resulting in myopic-astigmatic errors in the treated eyes. Compared to LIM, the presence of astigmatic blur induced lower myopic error (all except L180 group, P < 0.001) but with higher refractive astigmatism (all P < 0.001) in birds treated with sphero-cylindrical lenses. Distributions of the refractive, axial, and corneal shape parameters in the sphero-cylindrical lens-wear groups indicated that the astigmatic blur had directed the eye growth toward the least hyperopic image plane, with against-the-rule (ATR) and with-the-rule (WTR) astigmatisms typically inducing differential biometric changes.

Conclusions

The presence of early astigmatism predictably altered myopia development in chicks. Furthermore, the differential effects of WTR and ATR astigmatisms on anterior and posterior segment changes suggest that the eye growth mechanism is sensitive to the optical properties of astigmatism.

Anterior and Posterior Segment Manifestations of Pathological Myopia: A Clinical Study from Turkish Aegean Region

Background and Objective:

Myopia is one of the most prevalent vision conditions caused by a mismatch between the refractive power and axial length of the eyeball. High myopia may have a degenerative disorder, including cornea, sclera, choroid, optic disc, vitreous, macula, and peripheral retina. Although there are few studies regarding clinical features of pathological myopia, especially in the far-eastern countries where myopia is common, but are no comprehensive data in our region. This study was aimed to demonstrate both anterior and posterior ocular segment manifestations of pathological myopia.

Methods:

One hundred forty eyes of 82 patients who met the pathological myopia criteria were enrolled in this prospective study. Measurements of Central Corneal Thickness (CCT), endothelial cell parameters, Anterior Chamber Depth (ACD), Axial Length (AL) and Subfoveal Choroidal Thickness (SFCT) were performed in all patients. Presence of posterior segment pathologies such as peripapillary atrophy, tilted disc, Lacquer's crack, foveoschisis, myopic maculopathy, Choroidal Neovascularization (CNV), and peripheral retinal degeneration was recorded.

Results:

The mean age was 54.1 ± 14.2 years. 43 (52.4%) of the patients were female. One hundred patients (71.4%) were phakic and 40 (28.6%) were pseudophakic. The mean CCT, corneal endothelial cell density, ACD, AL, and SFCT were 548.91 ± 43.44 µm, 2335.89 ± 374.38 cells/mm2, 3.93 ± 0.79 mm, 28.75 ± 2.20 mm, and 94.56 ± 73.11 µm, respectively. Tilted disc, peripapillary atrophy and posterior staphyloma were detected in 89 (63.6%), 119 (85%) and 78 (55.7%) eyes, respectively. Normal fundus, tessellated fundus, diffuse chorioretinal atrophy, focal chorioretinal atrophy and macular atrophy were seen in 13 (9.3%), 59 (42%), 26 (18.6%), 14 (10%), and 28 (20%) eyes, respectively. Lacquer crack, CNV, and Fuchs spot were observed in 11 (7.9%), 39 (27.9%), and 47 (33.6%) eyes, respectively.

Conclusion:

This study reported clinical characteristics of eyes with pathological myopia in a retina specialty clinic at a tertiary referral center from the Turkish Aegean Region. Pathological myopia may affect both anterior and posterior ocular segments. However, posterior segment manifestations may be associated with lesions that threaten vision. Therefore, periodic follow-up in patients with pathological myopia is critical.

Astigmatismus

Der Astigmatismus ist der weltweit häufigste Refraktionsfehler vor Hypermetropie und Myopie. Man unterscheidet den äußeren vom inneren Astigmatismus. Der äußere Astigmatismus kann weiter in „mit der Regel“, „gegen die Regel“ und „schräg“ unterteilt werden. Die Summierung des äußeren und inneren Astigmatismus ergibt den refraktiven Zylinder. Astigmatismus wurde lange als zweidimensionales Phänomen gesehen, doch erst die dreidimensionale Betrachtung hat den Blick auf bestehende Analyseverfahren (Topo- und Tomographie) erweitert. Die Vektoranalyse nach Alpins ist hierbei eine bekannte Methode zur Therapieplanung. Zur Therapie des Astigmatismus stehen konservative Optionen wie Brille oder torische Kontaktlinse sowie unterschiedlichste chirurgische Verfahren wie photorefraktive Keratektomie, Femtosekundenlaser-assistierte Keratotomie, Laser-in-situ-Keratomileusis, „small-incision lenticule extraction“ und die Implantation torischer Intraokularlinsen zur Verfügung.

Origins of Refractive Errors: Environmental and Genetic Factors

Refractive errors are the product of a mismatch between the axial length of the eye and its optical power, creating blurred vision. Uncorrected refractive errors are the second leading cause of worldwide blindness. One refractive error currently attracting significant scientific interest is myopia, mostly owing to the recent rise in its prevalence worldwide and associated ocular disease burden. This increase in myopia prevalence has also been rapid, suggesting environmental influences in addition to any genetic influences on eye growth. This review defines refractive errors, describes their prevalence, and presents evidence for the influence of genetic and environmental factors related to refractive error development.

[Astigmatism]

Astigmatism is the most frequent refractive error worldwide followed by hyperopia and myopia. Internal astigmatism has to be differentiated from external astigmatism. Furthermore, external astigmatism can be divided into "with the rule", "against the rule" and "oblique". The summation of internal and external astigmatism results in the refractive cylinder. Astigmatism has for a long time been regarded as a two-dimensional phenomenon; however, only a three-dimensional consideration expanded the view on existing analytical methods (topography and tomography). Alpins' vector analysis is a commonly used method for treatment planning. Multiple options exist for treatment of astigmatism with conservative approaches, such as eyeglasses or toric contact lenses as well as various surgical procedures, such as photorefractive keratectomy, femtosecond laser-assisted keratotomy, laser in-situ keratomileusis, small incision lenticule extraction and toric intraocular lens implantation.

Enantiomorphism and rule similarity in the astigmatism axes of fellow eyes: A population-based study

PURPOSE

To evaluate the relationship patterns between astigmatism axes of fellow eyes (rule similarity and symmetry) and to determine the prevalence of each pattern in the studied population.

METHODS

This population-based study was conducted in 2015 in Iran. All participants had tests for visual acuity, objective refraction, subjective refraction (if cooperative), and assessment of eye health at the slit-lamp. Axis symmetry was based on two different patterns: direct (equal axes) and mirror (mirror image symmetry) or enantiomorphism. Bilateral astigmatism was classified as isorule if fellow eyes had the same orientation (e.g. both eyes were with-the-rule) and as anisorule if otherwise.

RESULTS

Of the total cases of bilateral astigmatism, 80% were isorule, and in the studied population, the prevalence of isorule and anisorule astigmatism was 14.89% and 3.53%, respectively. The prevalence of isorule increased with age (p<0.001). The prevalence of both isorule and anisorule increased at higher degrees of spherical ametropia (p<0.001). Median inter-ocular axis difference was 10° in mirror symmetry and 20° in direct symmetry with no significant difference between two genders (p>0.288). Both symmetry patterns reduced with age (p<0.001). Among cases of bilateral astigmatism, 15.5% and 19.8% had exact direct and mirror symmetry, respectively.

CONCLUSION

Bilateral astigmatism is mainly isorule in the population and anisorule astigmatism is rare. The enantiomorphism is the most common pattern in the population of bilateral astigmatism.

Rotational Stability and Visual Outcomes of V4c Toric Phakic Intraocular Lenses

PURPOSE

To investigate the clinical outcomes and rotational stability following implantation of V4c toric implantable collamer lenses (ICLs) (STAAR Surgical Company, Monrovia, CA) and to analyze the factors that influence rotational stability.

METHODS

In this prospective observational case series, the authors analyzed the visual outcomes and rotational stability in 52 eyes of 52 patients immediately and 3 and 6 months after implantation. Postoperative rotation was defined as the angle between the adjusted axis and alignment axis. Central vaulting of the ICL was measured in a non-accommodative state using Visante optical coherence tomography (Carl Zeiss Meditec, Jena, Germany). Vector analysis of refractive astigmatism was performed. Regression analysis was used to investigate the association between the degree of rotation 6 months postoperatively and the associated variables.

RESULTS

The mean efficacy index and safety index 6 months postoperatively were 1.35 ± 0.19 and 1.38 ± 0.22, respectively. In vector analysis, the magnitude of error was -0.20 diopters (D), indicating slight undercorrection. Absolute degree of rotation was 2.81° ± 1.87° immediately after the operation and 3.75° ± 2.92° and 3.87° ± 3.07° at 3 and 6 months postoperatively, respectively (P = .009). Bonferroni-adjusted post-hoc comparison showed that the absolute degree of rotation immediately after the operation was significantly smaller than that after 3 (P = .043) and 6 (P = .023) months, with barely any change after 3 months. No explanatory variable relevant to the absolute degree of rotation was discovered.

CONCLUSIONS

The V4c toric ICL is predictable, safe, and effective in correcting low and high levels of astigmatism, showing relatively good postoperative rotational stability. [J Refract Surg. 2018;34(7):489-496.].

Astigmatism and its components in 12-year-old Chinese children: the Anyang Childhood Eye Study

Purpose

To determine prevalence of refractive (RA), corneal (CA) and internal astigmatism (IA), including variation with gender and spherical equivalent refraction (SE), in a population of 12-year-old Chinese children.

Methods

A total of 1783 students with a mean age of 12.7 years (range 10.0–15.6 years) completed comprehensive eye examinations in the Anyang Childhood Eye Study. Data of cycloplegic refraction and corneal curvature were analysed.

Results

Prevalences of RA, CA and IA ≥1.0 D were 17.4% (95%CI 15.6% to 19.2%), 52.8% (50.5% to 55.1%)%) and 20.9% (19.0% to 22.8%), respectively. With different limits of astigmatism axes classification, including ±15°, ±20° and ±30°, RA and CA axes were mainly ‘with-the-rule’ (WTR) (ie, correcting axis of negative cylinders at or near 180°), while those for IA axes were mainly ‘against-the-rule’ (ATR) (ie, correcting axis of negative cylinders at or near 90°). RA was not different between the genders, but girls had higher prevalence and greater means of CA and IA. RA and CA increased in students with higher ametropia (more myopia and more hyperopia) and were the highest in a high myopic group (SE≤−6 D), while IA was stable across refraction groups. Children with RA higher than 0.50 D were more likely to have lens corrections (51%, 57%, 61% and 69% for magnitudes of ≥0.50 D, ≥0.75 D, ≥1.0 D and ≥1.5 D, respectively).

Conclusions

Prevalence of RA in the Chinese 12-year-old children was relatively high compared with other studies. RA and CA had mainly ‘WTR’ astigmatism, while IA was mainly ATR and partially compensated for CA. Girls had greater means and prevalences of CA and IA than did boys. Both RA and CA, but not IA, increased with refractive errors away from emmetropia.

Astigmatism in Chinese primary school children: prevalence, change, and effect on myopic shift

PURPOSE

To study the prevalence, type, and progression of astigmatism in primary school children, and its effect on myopic shift.

STUDY DESIGN

A prospective study carried out in a primary school in southern Taiwan.

METHODS

The study was performed on a subset of children, one year after initial examination. Refractive error measured by cycloplegic autorefraction was the main study outcome. Astigmatism was recorded as negative cylinder form, and we defined clinical significant astigmatism (CSA) as cylinder refraction -1.0 D or greater. Myopia was defined as a spherical equivalent refraction (SER) of -0.50 D or greater.

RESULTS

Three hundred sixty-two children, mean age was 8.97 y/o (SD 1.41; range 7 to 11 y/o) participated in the study. One hundred nineteen (32.9 %) subjects had CSA at the initial screening. The mean cylinder refraction was -0.80 + 0.84 diopters (D) (-5.25 D to 0.00 D), with predominant with rule astigmatism (69.7%). In the 183 children studied longitudinally, the mean cylinder refraction was reduced from -0.74 D to -0.58 D (p< 0.05). The cylinder refraction in the initial CSA group was not associated with SER change (p=0.99) or axial length change (p=0.55). Compared to the initial non-CSA group, the initial CSA group had no significant difference in axial length elongation (p=0.20).

CONCLUSION

The prevalence of astigmatism was not low in the Chinese primary school children and with-the-rule astigmatism was predominant. The astigmatism decreased during the 1 year follow-up. The CSA was not associated with myopia progression (p=0.99).

Non-Orthogonal Corneal Astigmatism among Normal and Keratoconic Brazilian and Chinese populations

PURPOSE

To investigate the prevalence of non-orthogonal astigmatism among normal and keratoconic Brazilian and Chinese populations.

METHODS

Topography data were obtained using the Pentacam High Resolution (HR) system ^® from 458 Brazilian (aged 35.6 ± 15.8 years) and 505 Chinese (aged 31.6 ± 10.8 years) eyes with no history of keratoconus or refractive surgery, and 314 Brazilian (aged 24.2 ± 5.7 years) and 74 Chinese (aged 22.0 ± 5.5 years) keratoconic eyes. Orthogonal values of optical flat and steep powers were determined by finding the angular positions of two perpendicular meridians that gave the maximum difference in power. Additionally, the angular positions of the meridians with the minimum and maximum optical powers were located while being unrestricted by the usual orthogonality assumption. Eyes were determined to have non-orthogonal astigmatism if the angle between the two meridians with maximum and minimum optical power deviated by more than 5° from 90°.

RESULTS

Evidence of non-orthogonal astigmatism was found in 39% of the Brazilian keratoconic eyes, 26% of the Chinese keratoconic eyes, 29% of the Brazilian normal eyes and 20% of the Chinese normal eyes.

CONCLUSIONS

The large percentage of participants with non-orthogonal astigmatism in both normal and keratoconic eyes illustrates the need for the common orthogonality assumption to be reviewed when correcting for astigmatism. The prevalence of non-orthogonality should be considered by expanding the prescription system to consider the two power meridians and their independent positions.

Global and regional estimates of prevalence of refractive errors: Systematic review and meta-analysis

Purpose

The aim of the study was a systematic review of refractive errors across the world according to the WHO regions.

Methods

To extract articles on the prevalence of refractive errors for this meta-analysis, international databases were searched from 1990 to 2016. The results of the retrieved studies were merged using a random effect model and reported as estimated pool prevalence (EPP) with 95% confidence interval (CI).

Results

In children, the EPP of myopia, hyperopia, and astigmatism was 11.7% (95% CI: 10.5–13.0), 4.6% (95% CI: 3.9–5.2), and 14.9% (95% CI: 12.7–17.1), respectively. The EPP of myopia ranged from 4.9% (95% CI: 1.6–8.1) in South–East Asia to 18.2% (95% CI: 10.9–25.5) in the Western Pacific region, the EPP of hyperopia ranged from 2.2% (95% CI: 1.2–3.3) in South-East Asia to 14.3% (95% CI: 13.4–15.2) in the Americas, and the EPP of astigmatism ranged from 9.8% in South-East Asia to 27.2% in the Americas. In adults, the EPP of myopia, hyperopia, and astigmatism was 26.5% (95% CI: 23.4–29.6), 30.9% (95% CI: 26.2–35.6), and 40.4% (95% CI: 34.3–46.6), respectively. The EPP of myopia ranged from 16.2% (95% CI: 15.6–16.8) in the Americas to 32.9% (95% CI: 25.1–40.7) in South-East Asia, the EPP of hyperopia ranged from 23.1% (95% CI: 6.1%–40.2%) in Europe to 38.6% (95% CI: 22.4–54.8) in Africa and 37.2% (95% CI: 25.3–49) in the Americas, and the EPP of astigmatism ranged from 11.4% (95% CI: 2.1–20.7) in Africa to 45.6% (95% CI: 44.1–47.1) in the Americas and 44.8% (95% CI: 36.6–53.1) in South-East Asia. The results of meta-regression showed that the prevalence of myopia increased from 1993 (10.4%) to 2016 (34.2%) (P = 0.097).

Conclusion

This report showed that astigmatism was the most common refractive errors in children and adults followed by hyperopia and myopia. The highest prevalence of myopia and astigmatism was seen in South-East Asian adults. The highest prevalence of hyperopia in children and adults was seen in the Americas.

Comparison between toric and spherical phakic intraocular lenses combined with astigmatic keratotomy for high myopic astigmatism

BACKGROUND

To compare the outcomes of a toric phakic intraocular lens (PIOL) and a spherical PIOL combined with astigmatic keratotomy (AK) for the correction of high myopic astigmatism.

METHODS

This study enrolled patients with high myopic astigmatism, including 30 eyes (22 patients) that received a toric PIOL implantation (TICL group), and 32 eyes (24 patients) that received combined AK and a spherical PIOL implantation (AK+ ICL group). The outcomes were compared between the two groups before surgery, and at the following time points after surgery: 1 week, 1, 3, 6 months, and 1, 2 years.

RESULTS

Preoperatively, the mean manifest spherical equivalent (SE) was -14.14 ± 2.12 D in the TICL group and -14.83 ± 2.79 D in the AK + ICL group (P = 0.28), and the mean manifest refractive cylinder, -2.87 ± 1.09 D and -2.58 ± 0.85 D, respectively (P = 0.28). Two years postoperatively, the mean safety index was 1.53 ± 0.55 in the TICL group and 1.60 ± 0.70 in the AK + ICL group (P = 1.00), and the mean efficacy index, 1.18 ± 0.45 and 1.38 ± 0.52, respectively (P = 0.86). The mean manifest refractive cylinder correction was 1.94 ± 1.07 D in the TICL group and 1.39 ± 0.71 D in the AK + ICL group (P = 0.02). The mean changes in SE and refractive cylinder from 1 week to 2 years were less than 0.50 D in both groups.

CONCLUSIONS

Both TICL implantation and AK + ICL implantation are a good alternative for correction of astigmatism in addition to high myopia. TICL implantation has better predictability in correction of high myopic astigmatism.

TRIAL REGISTRATION

NCT03202485.

Astigmatism among myopics and its changes from childhood to adult age: a 23-year follow-up study

PURPOSE

To study the prevalence of and changes in astigmatism from the onset of myopia at school age.

METHODS

Two hundred and forty myopic schoolchildren (mean age 10.9 years), with no previous spectacles, were recruited during 1983-1984 to a randomized 3-year clinical trial of bifocal treatment of myopia. Three annual examinations with subjective cycloplegic refraction were performed for 237-238 subjects. Subsequent examinations were performed at the mean ages of 23.2 and 33.9 years for 178 and 163 subjects, and the last examination, including data from prescriptions of different ophthalmologists, for 32 subjects. Corneal topography was studied at baseline, at the 3-year follow-up and at the two adulthood follow-ups. Prevalence and changes in refractive astigmatism (RA), in its polar values J0 and J45, and corneal astigmatism (CA) were studied.

RESULTS

Mean RA of the right eye increased during follow-up from 0.26 D (SD) ± 0.30 to 0.79 D ± 0.74. Mean CA was 1.07 D ± 0.74 at study end. The prevalence of RA ≥0.25 or ≥1.00 D increased from 54.9 and 3.8% to 83.4 and 34.4%, respectively. The main direction of the axis of RA and its polar value J0 and CA changed mainly through sphericity, from against the rule (ATR) to with the rule during the follow-up. There was a negative correlation between RA and spherical refraction in the ATR group at end of follow-up. Changes in RA were associated with increase in myopia and with changes in CA.

CONCLUSIONS

The prevalence and mean amount of RA associated with CA increased, and the axis of astigmatism changed among myopics during the 23-year follow-up.

[The cornea in high axial myopia]

PURPOSE

To compare corneal characteristics of eyes with high myopia with those of eyes with no spherical ametropia using Orbscan and ultrasonic pachymetry.

METHODS

Orbscan and ultrasonic pachymetry values were prospectively recorded in a study group of 105 patients with high myopia (i.e., axial length greater than 26mm in both eyes) and in a control group of 105 patients with no spherical ametropia (absolute value of spherical equivalent less than 1.25D regardless of cylinder value). Astigmatism data were expressed by rectangular coordinates in a dioptric plane. Axis was decomposed in 2 components (WTR/ATR and oblique) which were analyzed by Cos2axis and Sin2axis trigonometric functions. Enantiomorphism (mirror-image symmetry) between fellow eyes was quantified by a Euclidean distance for the location of the thinnest point and by the difference (in absolute value) between 180° and the sum of both axes for astigmatism.

RESULTS

In the study group, the mean axial length and subjective spherical equivalent were, respectively, 27.82±2.14mm (26.00 to 34.06) and -9.00±3.46D (-4.71 to -19.82). The mean corneal astigmatism was +0.92D×91.3° in the study group and +0.65D×89.3° in the control group. The mean corneal cylinder was higher in the study group (1.44D versus 0.91D; P<0.001) whereas axis showed no significant differences between both groups. The mean maximal keratometry was steeper in the study group (44.53D versus 44.13D; P=0.03) whereas the mean keratometry and minimal keratometry displayed no significant differences between both groups. No significant differences in central corneal thickness (540.2μm versus 546.9μm; P=0.10), peripheral corneal thickness, corneal diameter, corneal irregularity, asphericity, and irregular astigmatism were found between both groups. There were no significant differences in enantiomorphism parameters between both groups. In the study group, correlation with axial length was significant only for spherical equivalent (r=-0.86; P<0.001) and corneal cylinder (r=0.16; P=0.04).

CONCLUSION

High myopia exhibits corneal characteristics similar to corneas of eyes with no spherical ametropia, except for toricity. While the posterior segment elongates, development of high myopia appears not to affect corneal characteristics. Corneal toricity may be associated with evolution toward high myopia by perturbing mechanisms of emmetropization.

Astigmatism and myopia in Tohono O'odham Native American children

PURPOSE

To describe change in spherical equivalent (M) in a longitudinal sample of Tohono O'odham students ages 3 to 18 years and to test the hypothesis that astigmatism creates complex cues to emmetropization, resulting in increased change in M in the direction of increasing myopia and increased occurrence of myopia.

METHODS

Subjects were 777 Tohono O'odham Native American children on whom cycloplegic right eye autorefraction was measured on at least two study encounters between ages 3 and 18 years (first encounter prior to age 5.5 years, final encounter ≥3 years later). Regression lines were fit to individual subjects' longitudinal M data to estimate rate of change in M (regression slope, D/yr). Regression was also used to predict if a subject would be myopic (≤-0.75 D M) by age 18 years. Analysis of covariance was used to assess the relation between M slope and magnitude of baseline M and astigmatism. Chi-square analyses were used to assess the relation between predicted myopia onset and magnitude of baseline M and astigmatism.

RESULTS

Mean M slope was significantly more negative for hyperopes (M ≥ +2.00) than for myopes (M ≤ -0.75) or for subjects neither hyperopic nor myopic (NHM, M > -0.75 and < +2.00), but there was no significant difference between the myopic and NHM groups. Chi-square analysis indicated that final myopia status varied across level of baseline astigmatism. Subjects with high astigmatism were more likely to be predicted to have significant myopia by age 18 years.

CONCLUSIONS

The association between greater shift in M towards myopia with age in subjects who were hyperopic at baseline is consistent with continued emmetropization in the school years. Results regarding predicted myopia development imply that degradation of image quality due to refractive astigmatism creates complex cues to emmetropization, resulting in increased occurrence of myopia.

The visual and functional impacts of astigmatism and its clinical management

PURPOSE

To provide a comprehensive overview of research examining the impact of astigmatism on clinical and functional measures of vision, the short and longer term adaptations to astigmatism that occur in the visual system, and the currently available clinical options for the management of patients with astigmatism.

RECENT FINDINGS

The presence of astigmatism can lead to substantial reductions in visual performance in a variety of clinical vision measures and functional visual tasks. Recent evidence demonstrates that astigmatic blur results in short-term adaptations in the visual system that appear to reduce the perceived impact of astigmatism on vision. In the longer term, uncorrected astigmatism in childhood can also significantly impact on visual development, resulting in amblyopia. Astigmatism is also associated with the development of spherical refractive errors. Although the clinical correction of small magnitudes of astigmatism is relatively straightforward, the precise, reliable correction of astigmatism (particularly high astigmatism) can be challenging. A wide variety of refractive corrections are now available for the patient with astigmatism, including spectacle, contact lens and surgical options.

CONCLUSION

Astigmatism is one of the most common refractive errors managed in clinical ophthalmic practice. The significant visual and functional impacts of astigmatism emphasise the importance of its reliable clinical management. With continued improvements in ocular measurement techniques and developments in a range of different refractive correction technologies, the future promises the potential for more precise and comprehensive correction options for astigmatic patients.

Practical applications to modify and control the development of ametropia

For many individuals, the developmental trend of lessening hyperopia from birth continues past emmetropia towards myopia during childhood. The global pattern for prevalence of refractive errors indicates that the prevalence of hyperopia is low; in contrast, the burden of myopia is on the rise because of rising prevalence and magnitude of myopia. This review highlights the need to lessen the global burden of myopia by intervening with the development and/or slowing the progression of myopia. Further, outcomes from human clinical trials of pharmaceutical, optical, and environmental approaches to control myopia will be summarised. Pharmaceutical treatments are effective in controlling eye growth but are associated with deleterious side effects. Optical strategies that induce myopic defocus at the retina such as peripheral defocus reducing lenses, simultaneous defocus lenses, bifocals, and orthokeratology as well as environmental influences such as increased outdoor activity show promise and provide a substantially risk-free environment in which to control eye growth.

Characteristics of astigmatism as a function of age in a Hong Kong clinical population

PURPOSE

To characterize astigmatism as a function of age in a Hong Kong clinical population.

METHODS

All records from new clinical patients at a university optometry clinic in the year 2007 were used for the study. Only data from subjects with corrected visual acuity ≥6/9 in both eyes and with completed subjective refraction were analyzed. The subjects were divided into seven age groups by decade (i.e., 3 to 10 years, 11 to 20 years, …, >60 years). Refractive errors were decomposed into spherical-equivalent refractive error (M), J0, and J45 astigmatic components for analyses. Internal astigmatism was calculated by subtracting corneal astigmatism from refractive astigmatism (RA).

RESULTS

Of the 2759 cases that fulfilled our selection criteria, 58.9% had myopia (M ≥-0.75 D) and 28.4% had RA (Cyl ≥ 1.00 D). The prevalence of RA increased from 17.8% in the 3 to 10 years age group to 38.1% in the 21 to 30 years age group. It then dipped to 25.8% in 41 to 50 years age group but increased again to 41.8% in the >60 years age group. Among the astigmats, almost all 3- to 10-year-old children (92.6%) had with-the-rule (WTR) astigmatism, but a majority of the elderly (>60 years) had against-the-rule (ATR) astigmatism (79.7%). For a subset of subjects who had both subjective refraction and keratometric readings (n = 883), RA was more strongly correlated with corneal (r = 0.35 to 0.74) than with internal astigmatism (r = 0.01 to 0.35). More importantly, the magnitudes of both refractive and corneal J0 were consistent with synchronized decrements (-0.15 and -0.14 D per 10 years, respectively) after the age of 30 years, indicating that the shift toward more ATR astigmatism was related to corneal change.

CONCLUSIONS

In this Hong Kong Chinese clinical population, the prevalence rates of both myopia and astigmatism increased during the first three decades and shared a similar trend before the age of 50 years. The manifest astigmatism was mainly corneal in nature, bilaterally mirror symmetric in axis, and shifted from predominantly WTR to ATR with age.

[Relationships between refractive parameters: sphere, cylinder and axis]

PURPOSE

To analyze the relationships between refractive parameters as well as the relationship between fellow eyes in a normal population.

METHODS

Both subjective refraction and auto-refractometry data of 500 patients were prospectively recorded. Refraction data were analyzed on three rectangular coordinates in a dioptric space. WTR/ATR ratio of axis was quantified by the Cos2axis function. Enantiomorphism (mirror-image symmetry) between fellow eye axes was quantified by the absolute value of the difference between 180° and the sum of both axes.

RESULTS

Mean refraction and mean cylinder were -1.74D (+0.28D × 91.5°) and 0.81 ± 0.89D respectively. The spherical component had no significant influence on refractive astigmatism (r(s)≤ 0.07, P ≥ 0.07) except for high spherical ametropia. Eyes with spherical equivalent greater than 4D (in absolute value) demonstrated higher cylinder (1.15D vs 0.84D, P<0.001). Cylinder influenced the WTR/ATR ratio (r(s)=-0.25, P<0.001) and the enantiomorphism (r(s)=0.36, P<0.001). Age also influenced the WTR/ATR ratio (r(s)=0.27, P<0.001) and the enantiomorphism (r(s)=0.14, P<0.001). Axes were more likely WTR and enantiomorphic when the cylinder was high and the subject young. Oblique axes were less enantiomorphic (35.5° vs 20.6°, P<0.001) and were associated with lower cylinder (0.56D vs 0.98D, P<0.001). Correlation between fellow eyes was significant for cylinder (r(s)=0.66, P<0.001) and for spherical equivalent (r(s)=0.96, P<0.001). Gender had no significant influence on refraction (P>0.12) except for spherical equivalent (relative hyperopia of +0.17D, P=0.04 in females).

CONCLUSION

The spherical component of the refraction appears to be independent of the refractive astigmatism except for high spherical ametropia. Cylinder influences somewhat the WTR/ATR ratio of axis and the enantiomorphism. Relationships between refractive parameters are weak in comparison to the fellow eye relationships.

The influence of corneal astigmatism on retinal nerve fiber layer thickness and optic nerve head parameter measurements by spectral-domain optical coherence tomography

Background

To evaluate the influence of corneal astigmatism (CA) on retinal nerve fiber layer (RNFL) thickness and optic nerve head(ONH) parameters measured with spectral-domain optical coherence tomography (OCT) in high myopes patients before refractive surgery.

Methods

Seventy eyes of 35 consecutive refractive surgery candidates were included in this study. The mean age of the subjects was 26.42 ± 6.95 years, the average CA was −1.17 diopters (D; SD 0.64; range −0.2 to-3.3D), All subjects in this study were WTR CA. 34 eyes were in the normal CA group with a mean CA was −0.67 ± 0.28D, 36 eyes were in the high CA group with an average CA of −1.65 ± 0.49D. All subjects underwent ophthalmic examination and imaging with the Cirrus HD OCT.

Results

No significant difference was noted in the average cup-to-disk ratio, vertical cup-to-disk ratio and cup volume (all P values > 0.05). Compared with the normal CA group, the high CA group had a larger disc area and rim area, thinner RNFL thickness in the temporal quadrant, and the superotemporal and inferotemporal peaks were farther to the temporal horizon (All P values < 0.05). There were no significant differences between the two groups in global average RNFL thickness, as well as superior, nasal and inferior quadrant RNFL thickness (all P values > 0.05).

Conclusions

The degree of with-the-rule CA should be considered when interpreting ONH parameters and peripapillary RNFL thickness measured by the Cirrus HD OCT.

Virtual slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1148475676881895

Genome-wide meta-analysis of five Asian cohorts identifies PDGFRA as a susceptibility locus for corneal astigmatism

Corneal astigmatism refers to refractive abnormalities and irregularities in the curvature of the cornea, and this interferes with light being accurately focused at a single point in the eye. This ametropic condition is highly prevalent, influences visual acuity, and is a highly heritable trait. There is currently a paucity of research in the genetic etiology of corneal astigmatism. Here we report the results from five genome-wide association studies of corneal astigmatism across three Asian populations, with an initial discovery set of 4,254 Chinese and Malay individuals consisting of 2,249 cases and 2,005 controls. Replication was obtained from three surveys comprising of 2,139 Indians, an additional 929 Chinese children, and an independent 397 Chinese family trios. Variants in PDGFRA on chromosome 4q12 (lead SNP: rs7677751, allelic odds ratio = 1.26 (95% CI: 1.16-1.36), P(meta) = 7.87×10(-9)) were identified to be significantly associated with corneal astigmatism, exhibiting consistent effect sizes across all five cohorts. This highlights the potential role of variants in PDGFRA in the genetic etiology of corneal astigmatism across diverse Asian populations.

Axes of astigmatism in fellow eyes show mirror rather than direct symmetry

PURPOSE

Most astigmats have a similar level of astigmatism in each eye. However, there is controversy over whether the astigmatic axes in fellow eyes typically show direct or mirror symmetry. We carried out a statistical analysis designed to address this issue.

METHODS

The median absolute difference in the astigmatic axes of fellow eyes was calculated for a sample of 50 995 astigmats (subjects with at least 0.25 D of astigmatism in each eye). This was done, firstly, for a 'direct symmetry model' in which the difference in axis was calculated as |AxisR - AxisL| and secondly, for a 'mirror symmetry model' in which the difference in axis was calculated as |AxisR - (180 - AxisL)|.

RESULTS

Under the direct symmetry model, the median absolute difference in the axis of astigmatism between fellow eyes was 20 degrees. Under the mirror symmetry model, the median absolute difference in the axis of astigmatism between fellow eyes was significantly lower, at 10 degrees (p < 10e-100). Comparable results were found when the analysis was restricted to subjects with: lower levels of astigmatism (< or =1.00 D), higher levels of astigmatism (>1.00 D), against-the-rule astigmatism, with-the-rule astigmatism or oblique astigmatism (all p < 10e-100).

CONCLUSION

Our results show that mirror, rather than direct, symmetry is the norm.

Astigmatism in Children With Epiblepharon

PURPOSE

To study the relationship between astigmatism and epiblepharon in Taiwanese children that need surgical correction.

METHODS

In a retrospective case-control study, a total of 254 eyes in 134 children surgically treated for lower-lid epiblepharon were studied. A further 205 eyes in 104 children 4-7 years of age were included as controls. Data on age, sex, severity of preoperative corneal erosion, best-corrected visual acuity, and preoperative and postoperative refractive errors were recorded. The data of astigmatism were decomposed into P90 (at 90 degrees) and its oblique meridian Pobl. Nonparametric tests were used to compare the severity of astigmatism.

RESULTS

No significant difference between age group (<4, 4-7, >7 years) in P90 was shown in children with epiblepharon. Pobl was trivial in each group of epiblepharon. Children with epiblepharon 4-7 years of age had significantly (P < 0.001) greater P90 than controls (1.12 vs. 0.47 D). P90 and Pobl were not significantly changed postoperatively. In the same individual, the eye with the more severely affected cornea had greater astigmatism (P = 0.002), even after the corneal erosion healed.

CONCLUSIONS

Children with epiblepharon who needed surgery had greater with-the-rule astigmatism than controls. More severe corneal erosion was associated with higher astigmatism. Surgical correction of skinfold and promotion of reepithelialization did not attenuate astigmatism significantly.

A review of astigmatism and its possible genesis

Astigmatism is a refractive condition encountered commonly in clinical practice. This review presents an overview of research that has been carried out examining various aspects of this refractive error. We examine the components of astigmatism and the research into the prevalence and natural course of astigmatic refractive errors throughout life. The prevalence of astigmatism in various ethnic groups and diseases and syndromes is also discussed. We highlight the extensive investigations that have been conducted into the possible aetiology of astigmatism, however, no single model or theory of the development of astigmatism has been proven conclusively. Theories of the development of astigmatism based on genetics, extraocular muscle tension, visual feedback and eyelid pressure are considered. Observations and evidence from the literature supporting and contradicting these hypotheses are presented. Recent advances in technology such as wavefront sensors and videokeratoscopes have led to an increased understanding of ocular astigmatism and with continued improvements in technology, our knowledge of astigmatism and its genesis should continue to grow.

Potential Higher-Order Aberration Cues for Sphero-Cylindrical Refractive Error Development

PURPOSE

To investigate analytically whether higher-order wavefront errors comprising combinations of trefoil along 30 degrees (trefoil30), vertical coma, and spherical aberration could provide cues to sphero-cylindrical refractive error development.

METHODS

A total of 25 test wavefronts, subdivided into five different types and five levels of higher-order root mean square errors (HO-RMS), were created for the study. One type contained spherical aberration only, producing HO-RMS levels between 0.1 and 0.5 microm. Four wavefront types contained coma, trefoil, and spherical aberration of various sign combinations also producing HO-RMS levels between 0.1 and 0.5 microm. From the 25 wavefronts, refractive power maps were created and 2025 different sphero-cylindrical combinations were added to each refractive power map. For each sphero-cylinder combination, the visual Strehl ratio based on the modulation transfer function (VSMTF) was calculated. Retinal images and refractive power histograms were calculated for the refractive power maps corresponding to the peak of the VSMTF.

RESULTS

Spherical aberration affected the best focal plane thereby inducing spherical or defocus cues. The VSMTF produced by vertical coma and trefoil30, in combination with spherical aberration, could be improved with sphero-cylinders of various magnitudes and directions (i.e., with-the-rule, against-the rule, myopic astigmatism, or hyperopic astigmatism). Clinical significance of sphero-cylinders (i.e., >or=0.25 D) was reached at HO-RMS levels between 0.2 and 0.3 microm for a 5-mm pupil zone.

CONCLUSIONS

In the context of compensatory blur driven eye growth, commonly occurring combinations of the three considered higher-order aberrations have the potential to produce cues to eye growth resulting in myopia and with-the-rule astigmatism.