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Modulation transfer function and critical flicker frequency in high-myopia patients.

BACKGROUND AND PURPOSE: Critical flicker frequency (CFF) decreases due to optic nerve and retinal damage in patients with optic neuritis or glaucoma. Because retinal degeneration is also found in high myopia, we investigated whether the modulation transfer function (MTF) and CFF are altered in patients with high myopia. METHODS: Forty-six patients with high myopia (< -8 diopters, D) were recruited from our outpatient department. The control group comprised 21 young volunteers with myopia of 0 to -2 D. The myopic and control groups were similar in terms of age and sex. RESULTS: At all frequencies tested, the myopic group had lower CFF and higher modulation values than the control group. The mean CFF was significantly lower in myopic patients (46.8 +/- 9.0 Hz) than in control subjects (52.5 +/- 4.4 Hz). Patients with extremely high myopia (< -10 D) had significantly greater modulation values at 5, 10, 15, 55 and 60 Hz than those with moderately high myopia (-8 D to -10 D). The CFF did not differ significantly between those with extremely high (46.3 +/- 8.8 Hz) and those with moderately high (49.0 +/- 6.9 Hz) myopia. CONCLUSIONS: The findings of this study support that the CFF decreases and MTF increases in patients with high myopia, and that the alternation of MTF is related to the degree of myopia. CFF and MTF may, therefore, have potential as indexes to evaluate the severity of retinal degeneration in patients with high myopia.

Adolescent↗

Twenty-four-hour pattern of intraocular pressure in young adults with moderate to severe myopia.

PURPOSE: To characterize the 24-hour change of intraocular pressure (IOP) in young adults with moderate to severe myopia. METHODS: Nineteen young adults, ages 18 to 25 years, with moderate to severe myopia (myopia group) and 17 age-matched volunteers with emmetropia or mild myopia (control group) were housed for 1 day in a sleep laboratory. An 8-hour accustomed sleep period was assigned to each volunteer. Twelve measurements of IOP, axial length, blood pressure, and heart rate were taken at 2-hour intervals. In the wake period, blood pressure and heart rate were measured after a 5-minute bed rest. Axial length and IOP were measured in supine volunteers. Volunteers then sat for 5 minutes, after which IOP was measured. In the sleep period, measurements were taken in supine volunteers in bed. RESULTS: In both the myopia and control groups, the average supine IOP in the sleep period was higher than the average sitting IOP in the wake period. However, the magnitude of this IOP elevation at night was significantly less in the myopia group. In the sleep period, IOP was less in the myopia group than in the control group. When only the 24-hour supine IOP data were considered, the trough occurred at 1:30 AM, and the peak occurred around noon in the myopia group. In the control group, the trough was at 9:30 PM, and the peak at 5:30 AM. Least-square cosine fits showed 24-hour rhythms of supine IOP in both groups, but their phase timings were different. Axial length remained unchanged throughout the day and night in both groups. There was no difference in the 24-hour rhythms of mean blood pressure and heart rate between the two groups. CONCLUSIONS: Considering habitual body positions, IOP increases at night in young adults with moderate to severe myopia, but the magnitude of the increase is significantly less than that in the age-matched control subjects. There is a 24-hour rhythm of supine IOP in the myopic group, but the phase timing is different from that in the control subjects. These variations of IOP in young adults with moderate to severe myopia are not related to changes in cardiovascular parameters.

Adolescent↗

Prevalence of myopia in Taiwanese schoolchildren: 1983 to 2000.

INTRODUCTION: To determine time trends in myopia over a 20-year period in Taiwan, we conducted 5 nationwide surveys pertaining to the ocular refraction of schoolchildren in 1983, 1986, 1990, 1995 and 2000. MATERIALS AND METHODS: The sampling technique used herein involved the assessment of stratified systematic clusters, with the unweighted myopic rate being represented using data derived from different sectors of the population, such as metropolitan, city, town, and aboriginal. The mean values for the spherical equivalent of the cycloplegic refractive status and the dimension of corneal radii as determined by the autorefractometer were used for the calculation. RESULTS: In our review of 5 nationwide myopia surveys, we found that the mean prevalence of myopia among 7 year olds increased from 5.8% in 1983 to 21% in 2000. At the age of 12, the prevalence of myopia was 36.7% in 1983 increasing to 61% in 2000, corresponding figures for 15-year-olds being 64.2% and 81%, respectively. The prevalence of myopia increased from 74% in 1983 to 84% in 2000 for children aged between 16 and 18 years, and, in addition, the prevalence of high myopia (over -6.0 D) increased from 10.9% in 1983 to 21% of 18-year-old students of Taiwan in 2000. The mean refractive status at the age of 12 deteriorated from -0.48 D in 1983 to -1.45 D in 2000, and from -1.49 D to -2.89 D for children aged 15, whilst for individuals aged 18, it deteriorated from -2.55 D in 1983 to -3.64 D in 2000. The mean ocular refraction began to progress to a myopic condition at the age of 11 in 1983, this becoming an age of 8 years in 2000. There appeared to be significant difference in both the prevalence and the degree of myopia between study participants residing in cities and villages. CONCLUSIONS: We conclude that the cause of the relative increasing severity of myopia among the schoolchildren was due to the onset of myopia at a very young, and progressively-decreasing, age over the study period. Thus, to reduce the prevalence and severity of myopia, we should pay more attention to the eye care of pre-schoolchildren.

Adolescent↗

The epidemiology of myopia in Hong Kong.

INTRODUCTION: The prevalence of myopia amongst the Chinese has escalated in recent decades. While this refractive error was previously a little more than an inconvenience and a source of unwanted expense to the affected individuals, it is now sufficiently prevalent to warrant national concern. Myopia is also a major cause of low vision. This review aims to provide information on the prevalence of myopia in the Chinese community in Hong Kong. MATERIALS AND METHODS: Based on a number of studies carried out mainly at the Centre for Myopia Research in The Hong Kong Polytechnic University, myopia in the Chinese community in Hong Kong is described. RESULTS: Infants in Hong Kong appear to have refractive errors similar to infants of European descent; however, by the age of 7 years myopia is already prevalent. The annual incidence of myopia thereafter averages 11% to 12%; by the age of 17 years more than 70% are myopic, and this prevalence is greater than in people of European descent. In Hong Kong, myopia is much less prevalent in the older generation. CONCLUSION: The increase in prevalence of myopia over a short period of time is postulated to be due to environmental factors. Children of Chinese descent have a susceptibility to environmental factors which cause myopia.

Astigmatism↗

The TGFbeta1 gene codon 10 polymorphism contributes to the genetic predisposition to high myopia.

PURPOSE: Transforming growth factor-beta (TGFbeta), a multifunctional growth factor that plays a key role in the remodeling of scleral tissue, may be involved in the predisposition and pathophysiology of high myopia. Our aim was to examine the association between myopia and the polymorphisms within codon 10 of the TGFbeta1 gene. METHODS: This was a case control study. The study group contained participants who had high myopia and a spherical equivalent greater than -6.00 D. The control group was composed of medical students whose spherical equivalent was less then -0.5 D. All volunteers in this study were over 16 years old and had never undergone ocular surgery. Genotyping was conducted by restriction fragment length polymorphism, and the results were compared between myopia patients and control subjects. RESULTS: The frequency of the CC genotype in TGFbeta1 codon 10 differed significantly between patients in the high myopia group (n=201) and individuals in the control group (n=86; p<0.001). People with either the CT or TT genotype had a lower probability of having high myopia with a spherical equivalent greater than -6.00 D than those with the CC genotype. Furthermore, there was a higher frequency of the C allele in the high myopia group than with the control group (p<0.001, OR=1.83, CI=1.27-2.63). CONCLUSIONS: The frequency of the CC homozygote in the high myopia group was much higher than in the control group, indicating people with the CC homozygote may be at a higher risk of developing high myopia. Varied expression of this gene may contribute to the genetic predisposition to high myopia in Chinese Taiwanese.

Adolescent↗

[Photorefractive keratectomy by excimer laser for correcting myopia and myopic astigmatism].

Photorefraction keratectomy (PRK) was carried out using Nidek EC-5000 eximer laser in patients with myopia of different degree and myopic astigmatism. After 12 months, visual acuity without correction was 0.6-1.0 diopters in all patients with slight myopia, 0.7-1.0 in 95% of patients with medium myopia, and 0.8-1.0 in 86% of patients with high myopia. A lower visual acuity in high myopia was caused by retinal complications of myopia. The results of refraction after PRK depended on the severity of myopia and patient's age. The degree of myopia regression depended on preoperative refraction and was more expressed in high myopia. Young patients developed a more expressed tendency to decrease of postoperative refraction. The results indicate that eximer laser is an effective and reliable tool for correcting myopia of different degree and myopic astigmatism.

Adolescent↗

Predictability of excimer laser treatment of myopia. Melbourne Excimer Laser Group.

OBJECTIVE: To prospectively examine the predictability of excimer laser photorefractive keratectomy and photoastigmatic refractive keratectomy for myopia that ranged from -1 to -18 diopters (D). METHODS: Patients were treated with an excimer laser and followed up prospectively for 12 months. Low myopia was treated in one ablation zone (6.0 mm), high myopia in two ablation zones (5.0 and 6.0 mm), and extreme myopia in three ablation zones (4.5, 5.0, and 6.0 mm) with a maximum treatment of 15 D. Data were analyzed to determine the distribution of the various postoperative outcomes by preoperative myopia. RESULTS: Two hundred seventy-four low myopes, 189 high myopes, and 41 extreme myopes were available for 12-month follow-up. The re-treatment rate increased with preoperative myopia. The predictability of refraction and uncorrected and best corrected visual acuity progressively decreased with increasing myopia. The likelihood of losing lines of best corrected visual acuity and corneal haze increased with increasing myopia. CONCLUSION: These data should help in the counseling of patients about the likely outcome if they have excimer laser surgery to correct myopia.

Adult↗

[Correction of myopia and astigmatism using topography-assisted laser in situ keratomileusis (TopoLink LASIK)].

PATIENTS AND METHODS: We treated 114 patients (eyes) with myopia of -1 to 6 D and astigmatism of 0 to -4 D (group 1), and 89 patients (eyes) with myopia of -6.1 to -12 D and astigmatism of 0 to -4 D (group 2). All treatments were calculated on the basis of corneal topography measured with the Orbscan II system. The Keracor 217 excimer laser and the Hansatome microkeratome were used. RESULTS: At 3 months, 51 patients in the low myopia group and 40 patients in the high myopia group were available for examination. In the low (high) myopia group, 96.1% (75.0%) were within +/- 0.50 D of emmetropia, and uncorrected visual acuity was 20/20 or better in 82.4% (62.5%), 20/25 or better in 98.0% (70.0%), and 20/40 or better in 100% (95.0%). A loss of two or more lines of spectacle-corrected visual acuity occurred in 3.9% of the low and 5.0% of the high myopia group. In low myopia, spectacle-corrected visual acuity was 20/12.5 or better in 5.9% preoperatively and in 13.7% at three months and 20/15 or better in 37.3% and 47.1%, respectively (P = 0.0002 and P = 0.01). CONCLUSIONS: LASIK based on corneal topography showed very high efficacy in low and moderate myopia with astigmatism, and maximal visual acuity could even be improved in some cases. There was somewhat less precision in high myopia with astigmatism.

Astigmatism↗

Prevalence of myopia and refractive changes in students from 3 to 17 years of age.

We investigated changes in the prevalence of myopia and mean changes in refractive errors in Japanese students from 3 to 17 years old from 1984 to 1996. Mass ophthalmologic surveys were performed annually during the course of the study. The age-specific frequency distribution of refractive errors remained similar for 6-year-old students (defined in this study as students in the first grade of primary school) during the 13-year period, but the distribution became gradually skewed toward myopia for 12-year-old students (defined in this study as students in the first grade of junior high school). Comparisons between 1984 and 1996 examinations showed a considerable increase in the incidence of myopia among those 7 years of age or older, and changes in mean refractive errors also demonstrated a greater shift toward myopia, especially in students older than 10 years, for whom the changes were statistically significant. In this 13-year period, the prevalence of myopia increased from 49.3% to 65.6% in 17-year-old students. In addition to the annual mass ophthalmologic examinations, we also performed a longitudinal 6-year study of 346 students who entered junior high school in 1989, 1990, or 1991. Among these students, the prevalence of myopia increased from 43.5% at 12 years of age to 66.0% at 17 years of age. These 346 students were divided into the following eight groups according to their refractive error (spherical power [D]) at 12 years of age: +1 D, 0 D, -1 D, -2 D, -3 D, -4 D, -5 D, and -6 D. Mean progressions of myopia in these students were as follows: for the +1 D group, -0.14 D/year; for the 0 D group, -0.25 D/year; for the -1 D group, -0.37 D/year; for the -2 D group, -0.40 D/year; for the -3 D group, -0.29 D/year; for the -4 D group, -0.25 D/year; for the -5 D group, -0.14 D/year; and for the -6 D group, -0.22 D/year. Boys and girls demonstrated a statistically significant difference in mean changes in refractive errors at the 6-year follow-up examination: the mean change in refractive error was -1.41 +/- 1.25 D for boys as compared with -1.03 +/- 1.07 D for girls (unpaired Student's t-test, P < 0.0001). Our results demonstrated an early age at onset for myopia and a recent increase in the proportion of myopic students. Further studies are needed to shed light on the extent to which myopia is caused by environmental factors, because it is through these factors that the prevalence rate may be affected.

Adolescent↗

Interventions to retard myopia progression in children: an evidence-based update.

TOPIC: To evaluate the efficacy of interventions such as eyedrops, bifocal lenses, or contact lenses in retarding the progression of myopia in myopic children. CLINICAL RELEVANCE: Myopia is a common ocular disorder, and high myopia (myopia at least -6.0 diopters) is associated with potentially blinding conditions. At present, there are no general guidelines on interventions that may decrease myopia progression in children, but some interventions such as contact lenses are offered on an ad hoc basis. METHODS OR LITERATURE REVIEWED: English and non-English language articles published from 1968 to 2000 were retrieved using a keyword search of MEDLINE, Embase, Cochrane Library, and Science Citation Index databases. Randomized controlled trials with comparisons of the effectiveness of interventions to decrease myopia progression in myopic children were reviewed. RESULTS: Ten clinical trials of different interventions to retard myopia progression were reviewed, including three trials that evaluated atropine and one trial that evaluated soft contact lenses. Atropine eye drops of 0.5% concentration were effective in clinical trials, but no significant effect was found for tropicamide or timolol eyedrops. Five of the six trials on bifocal spectacle lenses with various additions failed to show significant retardation, and results of the remaining trial were barely significant (P = 0.047). A trial of soft contact lenses failed to show significant effects. CONCLUSIONS: The latest evidence from randomized clinical trials does not provide sufficient information to support interventions to prevent the progression of myopia. Long-term large-scale double-masked randomized clinical trials, including cycloplegic refraction, are needed before any recommendations about interventions in clinical practice to prevent high myopia in myopic children are considered.

Atropine↗

Laser in situ keratomileusis for the correction of myopia and myopic astigmatism.

PURPOSE: To evaluate the efficacy, safety, predictability, and surgically induced astigmatism (SIA) of laser in situ keratomileusis (LASIK) for the correction of myopia and myopic astigmatism. SETTING: Department of Ophthalmology, National Taiwan University Hospital, Taipei, Taiwan. METHODS: This retrospective study comprised 69 eyes that had LASIK to correct myopia and 74 eyes that had LASIK to correct myopic astigmatism. The excimer laser keratectomy was performed using a Summit Apex Plus machine. Refraction, visual acuity, and computerized corneal videokeratography data from the preoperative and postoperative examinations were collected. The astigmatic change was calculated by the Alpins vector analysis method. RESULTS: The preoperative spherical equivalent at the glasses plane in the myopia and myopic astigmatism groups was -8.08 diopters (D) and -9.73 D, respectively. At 6 months, the spherical equivalent and residual corneal astigmatism were -0.25 D and 0.85 D, respectively, in the myopia group and -0.71 D and 0.82 D, respectively, in the myopic astigmatism group. In the myopia group, 88% of eyes were within +/-1.0 D of the intended myopia correction and in the myopic astigmatism group, 85% were within +/-1.0 D of the targeted spherical equivalent and 90% were within +/-1.0 D of the intended astigmatism correction. The uncorrected visual acuity was 20/40 or better in 94.1% of eyes in the myopia group and 92.5% of eyes in the myopic astigmatism group. The SIA magnitude was 0.66 D with the axis randomly distributed in the myopia group. The mean astigmatism correction index was 0.97, the mean magnitude of error was 0.13 D +/- 0.62 (SD), and the mean angle of error was -3.70 +/- 13.73 degrees in the myopic astigmatism group. CONCLUSION: Laser in situ keratomileusis had similar predictability, safety, and efficacy in the treatment of myopia and myopic astigmatism. The astigmatism correction was effective, but the results suggest that subjective astigmatism of less than 1.0 D need not be treated with the Summit Apex Plus laser.

Adult↗

Excimer laser photorefractive keratectomy for myopia: six-month follow-up.

In this study, 108 eyes of 62 patients had photorefractive keratectomy (PRK) with a 193 nm excimer laser to correct myopia. The eyes were assigned to one of three groups: low, moderate, or high myopia. Six months after PRK, 88.9% of eyes in the low myopia group, 90.0% in the moderate myopia group, and 23.8% in the high myopia group achieved an uncorrected visual acuity of 20/40 or better. In the low myopia group, 88.9% were within +/- 1 diopter (D) of attempted correction, as were 70.0% in the moderate group and 18.8% in the high myopia group. There were no significant complications. We conclude that excimer laser PRK appears to be a safe and relatively accurate procedure to correct low to moderate myopia but not high myopia because of regression over time.

Adult↗

Photorefractive keratectomy for astigmatism greater than -2.00 diopters in eyes with low, high, or extreme myopia.

PURPOSE: To assess the efficacy of excimer laser photorefractive astigmatic keratectomy (PARK) in correcting astigmatism of more than -2.00 diopters (D) in eyes with low, high, and extreme myopia. SETTING: Pusan National University Hospital, Pusan, Korea. METHODS: Eighty-five patients (110 eyes) whose spherical error ranged from -3.00 to -13.00 D and cylinder ranged from -2.00 to -5.50 D had PARK with a VISX Twenty-Twenty excimer laser; follow-up was 6 months. All cases of myopic astigmatism were treated using the elliptical method and multizone ablation technique. Eyes were divided into 3 groups: low myopia, less than 6.00 D (n = 47); high myopia, from 6.25 to 10.00 D (n = 43); extreme myopia, over 10.25 D (n = 20). Alpins vector analysis was used to calculate the astigmatic change. RESULTS: By vector analysis, the success rate of astigmatic correction was more predictable in the low and high myopia groups than in the extreme myopia group (P < .05). There was little improvement in astigmatism in the extreme myopia group. CONCLUSION: Using PARK to correct astigmatism greater than -2.00 D in eyes with myopia less than -10.00 D tended to result in undercorrection; astigmatic correction in eyes with myopia over 10.25 D was minimal.

Adult↗

Determinants of myopia among Omani school children: a case-control study.

BACKGROUND: Our aim was to determine risk factors for myopia in students of 10th grade of eight regions of Oman. METHODS: This was a case control study. Students of 10th grade with and without myopia were cases and controls respectively. In 2002 to 2003, their vision, refractive status, and physical measurements were recorded. The health records of all students were reviewed for their ocular and physical status in the 7th grade. The association of myopia to anthropometric variables, "Protein Energy Malnourishment" status, gender, history of myopia in parents and sibling, trachoma, and allergic conjunctivitis were analyzed. RESULTS: Myopia in students was significantly associated to myopia in parents [OR = 2.11 (95% CI 1.8-2.47)] and their siblings [OR = 2.87 (95% CI 2.45-3.35)]. Height was significantly higher in myopes compared to non-myopes both at the 10th and 7th grades. Weight and body mass index were greater in myopes than non-myopes only at 7th grade. Myopia in parents and siblings and female gender were predictors of myopia in the students. CONCLUSIONS: Hereditary and anthropometric factors seem to be associated with myopia in Omani children. The genetic etiology needs further confirmation.

Adolescent↗

The epidemiology of myopia.

Many people have reduced unaided vision because of myopia, a spherical error of refraction. The biological theory of myopia views myopia as the result of genetically determined characteristics of eye tissues, whereas the use-abuse theory views myopia as the result of habitual use of the eye at a near focal length, near-work. The use-abuse theory implies that myopia is preventable whereas the biological theory does not. Myopia varies over age, gender, race, ethnicity, level of education, social class and degree of urbanization. The explanation of the epidemiology of myopia in the use-abuse theory is that some types of people do more near-work than others. Using data from the Health Examination Survey of 12 to 17-year-olds conducted by the US Public Health Service from 1966--1970, this paper finds that the use-abuse theory can explain at least some of the variance of myopia and much of the socially patterned variance. This finding raises the possibility that at least some of the myopia extant in a population is preventable.

Adolescent↗

Relation between work and myopia in Singapore women.

BACKGROUND: Work and related activities may be connected to myopia development and progression. We investigated the relationship between working activities and the onset as well as worsening of myopia. METHODS: Information on the working status of the mothers of 374 children, the number of hours of close-up work activity, and whether the mother was short-sighted, was obtained by a face-to-face interview. In addition, a subsample of 84 mothers was interviewed over the telephone and asked whether the myopia occurred in adulthood and, if so, the age of cessation of myopia. RESULTS: The adjusted odds ratio for myopia in working women was 1.9 [95% confidence interval (CI) 1.2 to 3.2] and the adjusted odds ratio for high myopia (> -6.0 D) was 1.6 (95% CI 0.8 to 3.0). Women who were working also had higher rates of adult-onset myopia, odds ratio 4.4 (95% CI 0.9 to 21.2), and a later age of cessation of myopia than nonworking women. CONCLUSIONS: In our study, work was related to myopia in Singapore women. Work may be a surrogate for another risk factor, close-up work activities such as reading, writing, and computer use.

Adolescent↗

Adult onset myopia--oculometric features.

Adult onset myopia was investigated by ultrasound eye measurements and keratometry in 33 subjects (16 females, 17 males; age 32-62 years; age at myopia onset 18-50 years, mean value 26.2 years, SD 7.80). They were compared with 30 subjects (15 females, 15 males; age 29-62 years) with myopia onset age 4-16 years (mean value 11.1 years, SD 2.89). Excluded were subjects with cataract and corneal pathology. In the adult onset group, myopia ranged a little lower than in early onset myopia (mean values -3.24 and -4.91 D, respectively), but high myopia was encountered in both groups (peak values -10 and -10.5 D). In both groups axial elongation was the main oculometric event. There was no evidence of a corneal/lenticular background in adult onset myopia. In accord with the higher myopia in the early onset group the eyes were also larger (as for axial and vitreous length, mid lens depth) than in those of adult onset. Adult onset myopia being axial of nature, the findings confirm what has been suggested from recent reports by other authors: that the eye has a potential for re-starting growth, even years after the presumed normal ocular growth arrest during early teenage years.

Adult↗

Quality of life in myopia.

BACKGROUND: The safety and predictability of refractive surgery for all degrees of myopia is now becoming established. It is therefore appropriate to evaluate whether there is a patient driven demand for such treatments and, if so, to establish guidelines for its provision within the National Health Service (NHS). METHODS: A comparative study was designed to assess the effect of degree of myopia on quality of life ("high" (n = 30) -10.00D, worse eye; "moderate" (n = 40) -4.00 to -9.75D, worse eye; "low" (n = 42) <-4. 00D, worse eye) compared with a group of patients with keratoconus (n = 30) treated by optical correction. Data collection included binocular logMAR visual acuity, Pelli-Robson low contrast letter sensitivity, questionnaires to assess subjective visual function (VF-14) and effect on quality of life (VQOL), and semi-structured interviews. RESULTS: There were no significant differences in any of the measures between patients with a high degree of myopia and those with keratoconus, or between those with a low and those with a moderate degree of myopia. However, those with a high degree of myopia had highly significantly poorer logMAR, VF-14, and VQOL scores than those with low and moderate myopia (p<0.001). Interview data supported these findings with patients with a high degree of myopia and those with keratoconus reporting that psychological, cosmetic, practical, and financial factors affected their quality of life. CONCLUSION: Compared with low and moderate myopia, patients with a high degree of myopia experience impaired quality of life similar to that of patients with keratoconus. Criteria should therefore be identified to enable those in sufficient need to obtain refractive surgical treatment under the NHS.

Adolescent↗