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PubMedDate not supplied

Effectiveness of LASIK to correct refractive error after penetrating keratoplasty.

OBJECTIVE: Refractive errors may invalidate the good results of penetrating keratoplasty (PK). The Authors evaluate the effectiveness of excimer laser in situ keratomileusis (LASIK) in the correction of refractive error after PK. MATERIALS AND METHODS: Four patients, a 26-year-old woman, a 54-year-old man, a 19-year-old man, and a 51-year-old woman, showed refractive errors: -11 = -4.5 x 85 ; -8, -4.5 = -11 x 95 ; and -4.5 = -4 x = 1200, with a clear graft at least 20 months after penetrating keratoplasty secondary to keratoconus. However, they underwent the LASIK procedure with a nasal-hinged flap of 160 um. No sutures were placed. RESULTS: At follow-up, 24, 18, 12, and 12 months, respectively, the graft remained clear and the endothelial cells were unchanged. The uncorrected visual acuities were 20/50, 20/25, 20/50, and 20/25, respectively with an unchanged best corrected visual acuity (20/20) for all patients. No significant complications were observed. CONCLUSIONS: LASIK procedure seems to be an effective technique to correct refractive error after successful penetrating keratoplasty.

Adult↗
PubMed2005

Interpreting the multifocal visual evoked potential: the effects of refractive errors, cataracts, and fixation errors.

AIM: To understand how refractive errors, cataracts, and fixation errors affect multifocal visual evoked potential (mfVEP) responses. METHODS: Monocular mfVEP responses were obtained using a pattern reversal dartboard display. For the control condition, visual acuity was corrected to > or =20/20 and foveal fixation was maintained. The right eye was tested under the following conditions: simulated refractive error, simulated cataract, steady eccentric fixation, and unsteady fixation. RESULTS: No subject demonstrated significant abnormalities under control conditions. For the simulated refractive error condition, significant centrally located abnormalities were seen for all subjects. For the simulated cataract condition, significant abnormalities were found for three subjects. The steady eccentric fixation condition yielded abnormalities in both eyes for all subjects while the unsteady fixation condition yielded significant central abnormalities in the tested eye. With eccentric and unsteady fixation conditions, all subjects had at least one sector with a waveform polarity reversal. CONCLUSIONS: While the mfVEP is a useful tool for identifying local optic nerve damage or ruling out non-organic aetiology of visual field defects, factors such as uncorrected refractive errors, cataract, eccentric fixation, and unsteady fixation can produce apparent field defects on the mfVEP. With care, these problems can be correctly identified.

Adult↗
PubMed1999

Model of human refractive error development.

PURPOSE: To construct a model of refractive error development that can account for the different interactive mechanisms and time courses of refractive error in the hyperope (HYP), emmetrope (EMM), early-onset myope (EOM), and late-onset myope (LOM) over the first 30 years of life. METHODS: First, a baseline short-term (1 mo.) simulation of a previously developed nearwork-induced transient myopia (NITM) model was performed under both far- and near-viewing paradigms to obtain the critical relationships between AErms and refractive error for the four refractive groups. Then, two control pathways were added to the NITM model. The genetically-controlled pathway was associated with the long-term growth of the cornea, lens, and the eyeball. The environmentally-controlled pathway was associated with retinal-defocus during nearwork, wherein the root mean square (rms) of the accommodative error (AE) above a threshold level resulted in an increase in axial length of the eyeball. The thresholds for defocus-induced axial length change were empirically determined to correspond to the differential susceptibility in the four refractive groups. The combination of effects from the two pathways produced the overall refractive error. The relationship between AErms and refractive error was combined with the two control pathways for the long-term simulations (30 yrs: the initial 15 yrs using a far-viewing paradigm followed by an additional 15 yrs using a near-viewing paradigm) to quantify refractive error development as related to daily nearwork activity in the four refractive groups. RESULTS: All refractive groups began early in life with a genetically-determined hyperopic refractive error. The HYP had the lowest susceptibility or highest threshold to retinal defocus effects, and remained at a hyperopic level. The EMM exhibited a relative myopic shift in the first 2 years to become and remain at emmetropia. In the myopic groups, the EOM exhibited both a genetically-controlled component (starting 2 years of age) and a defocus-induced component (starting at 15 years of age), whereas the LOM manifested only a defocus-induced factor (starting at 15 years of age) in the development of myopia. In addition, simulations indicated that emmetropization occurred only for "induced" refractive error that was less than 0.5 D, which was consistent with the non-monotonic relationship between AErms and refractive error, wherein the minimum AErms occurred at 0.5 D. CONCLUSIONS: The model showed that both genetic and defocus-induced environmental factors play important roles in the development of refractive error in the different refractive groups. The model also provides a framework for further detailed quantitative analysis of the processes of refractive error development and emmetropization.

Accommodation, Ocular↗
PubMed2002

Development of refractive errors into old age.

PURPOSE: To evaluate refractive errors in older adults. METHODS: The distribution of refractive error components was evaluated in a sample of 569 older adults including 171 participants over the age of 80 years. The mean age was 75.2 years with a range from 59 to 106 years. Emphasis was placed on modern methods of analyzing astigmatic refractive errors, which convert cylindrical refractive errors into primary and oblique components. RESULTS: The known increase in hyperopia after maturity continues into old age. The primary negative astigmatic component increases dramatically in prevalence and amount after age 70 years, whereas the oblique component remains unchanged. Significant anisometropia is common in the oldest old, suggesting failure of emmetropization mechanisms with age. Substantial gender differences exist in refractive changes with age. CONCLUSIONS: The continuing changes in all components of refractive error into old age and the surprisingly high prevalence of large amounts of astigmatism and anisometropia emphasize the importance of regular refractive evaluations among the oldest old.

Aged↗
PubMed1997

Effect of contralateral fog during refractive error assessment.

BACKGROUND: When assessing refractive error using static retinoscopy, it is conventional to fog the contralateral eye by approximately 2.00 D to prevent a blur-driven accommodative response stimulating consensual accommodation in the tested eye. However, the effect of higher amounts of contralateral fog (e.g., in a moderate-to-high uncorrected myopic individual) during refractive error assessment is unclear. METHODS: We assessed the refractive state in 16 visually normal myopic subjects while fogging the contralateral eye between zero and 6.00 D, in 1.00 D increments. Retinoscopy was simulated by shining a streak retinoscope light into the right eye, while simultaneously measuring the refractive state of this eye objectively. RESULTS: No significant change in mean refractive state was observed for up to 5.00 D of contralateral fog. But, 6.00 D of contralateral fog produced a significant mean increase in the myopic direction of 0.13 D. Also, in three subjects, a myopic shift of approximately 0.60 D was recorded after the introduction of 6.00 D of contralateral fog. Nevertheless, the magnitude of these largest shifts in refractive error are still smaller than the previously reported degree of repeatability of static retinoscopy. CONCLUSIONS: Since large amounts of contralateral fog produced only small and clinically insignificant changes in the refractive state, the practitioner merely needs to ensure that the nontested eye is indeed fogged. The magnitude of fog present will have only a minimal effect on the final result.

Adult↗
PubMedDate not supplied

Combining refractive error and uncorrected visual acuity to assess the effectiveness of refractive corneal surgery.

Residual refractive error and uncorrected visual acuity are two frequently measures used to assess the effectiveness of refractive corneal surgery. Nordan and colleagues have suggested a Visual Function Index which combines these two measures in one quantitative measure. This article presents a Visual Function Score for radial keratotomy which includes a set of qualitative categories (excellent, good, fair, poor) and specifies the clinical values for refractive error and visual acuity in each category. There was substantial agreement among ophthalmologists who reviewed the category definitions, and we think that the Visual Function Score improves our ability to objectively assess surgical outcome. Application of the score to the Prospective Evaluation of Radial Keratotomy (PERK) Study data yielded closer agreement with refractive error results than with visual acuity values. The Visual Function Score lowered the classification of eyes that were hyperopic but had sufficient accommodation to overcome so that a high visual acuity result could be achieved. The inclusion of astigmatism values would be an important next step in the development of composite measures for the assessment of refractive surgery. In the future, a multifactorial index or score may be used to estimate the outcome of reported surgical procedures.

Adult↗
PubMed1993

Relation between the dark focus of accommodation and refractive error--a cycloplegic study.

We measured distance refractive error (Dist R), dark refractive error (Dark R), and cycloplegic refractive error (Cyclo R) in 196 subjects whose ages ranged from 4 to 17 years, using the Canon Autoref R-1. We defined the values of (Dark R--Dist R) as DFcus (Dist R) and those of (Dark R--Cyclo R) as DFcus (Cyclo R) in this study. Although DFcus (Dist R) was larger in less myopic and more hyperopic eyes similar to DFcus (Cyclo R), it was zero or plus in high hyperopic eyes, unlike DFcus (Cyclo R). We found Dist R was more strongly influenced by Cyclo R than was Dark R. It is not adequate to use Dist R as the far point for precise evaluation of the dark focus. We should use the difference between Dark R vs. Cyclo R as the true value of the dark focus of accommodation.

Accommodation, Ocular↗
PubMed1996

Clinical vision characteristics of the congenital achromatopsias. I. Visual acuity, refractive error, and binocular status.

Visual acuity, refractive error, and binocular status were determined in 43 autosomal recessive (AR) and 15 X-linked (XL) congenital achromats. The achromats were classified by color matching and spectral sensitivity data. Large interindividual variation in refractive error and visual acuity was present within each achromat group (complete AR, incomplete AR, and XL). However, the number of individuals with significant interocular acuity differences is very small. Most XLs are myopic; ARs show a wide range of refractive error from high myopia to high hyperopia. Acuity of the AR and XL groups was very similar. With-the-rule astigmatism of large amount is very common in achromats, particularly ARs. There is a close association between strabismus and interocular acuity differences in the ARs, with the fixating eye having better than average acuity. The large overlap of acuity and refractive error of XL and AR achromats suggests that these measures are less useful for differential diagnosis than generally indicated by the clinical literature.

Adolescent↗
PubMed2006

[The influence on the static visual field of peripapillary chorioretinal atrophy--relation to refractive error].

PURPOSE: To investigate the influence of refractive error on white-on-white perimetry(W-on-W) in myopic subjects according to the presence or absence of peripapillary chorioretinal atrophy (PPA). SUBJECTS AND METHODS: W-on-W perimetry was performed on 57 normal volunteers whose fundus photography was clear and the presence or absence of PPA was distinct. We divided the 57 normal volunteers into a PPA-positive group and a PPA-negative group, and investigated the influence of refractive error. RESULTS: Mean deviation (MD) reduction was significantly correlated with the degree of myopia in the myopic group, whereas there was no significant correlation with refractive error in the control group. In the myopic group, MD reduction was significantly correlated with the degree of myopia in the PPA-positive group, whereas there was no significant correlation between refractive error and MD in the PPA-negative group. In the control group, there was no significant correlation between refractive error and MD in either the PPA-positive group or the PPA-negative group. CONCLUSIONS: MD reduction was significantly correlated with the degree of myopia in myopic subjects, and was more remarkable in PPA-positive subjects.

Adult↗
PubMed2005

[Intraocular lenses for the correction of refraction errors. Part II. Phakic posterior chamber lenses and refractive lens exchange with posterior chamber lens implantation].

In this overview, the current status of intraocular lens surgery to correct refractive error is reviewed. The interventions are divided into additive surgery with intraocular lens implantation without extraction of the crystalline lens (phakic intraocular lens, PIOL) or removal of the crystalline lens with implantation of an IOL (refractive lens exchange, RLE). Phakic IOLs are constructed as angle-supported or iris-fixated anterior chamber lenses and posterior chamber lenses which are fixated in the ciliary sulcus. The implantation of phakic IOLs has been demonstrated to be an effective, safe, predictable and stable procedure to correct higher refractive errors. Complications are rare and differ for the three types of PIOL; for posterior chamber lenses these are mainly cataract formation and pigment dispersion. RLE is preferable in cases of high ametropia in which the natural lens has lost its accommodative effect. The main complications for myopic RLA include retinal detachment, while hyperopic refractive lens exchange may be associated with surgical problems in the narrower anterior eye segment.

Humans↗
PubMed2005

Optic disk size correlated with refractive error.

PURPOSE: To evaluate for which range of refractive error the optic disk size depends on, or is independent of, the refractive error. DESIGN: Clinical observational study. METHODS: The study included 1999 eyes of 1011 subjects with a mean refractive error of -0.97 +/- 2.72 diopters (range, -24.25 to +9.4 diopters). Optic disk photographs were morphometrically evaluated. RESULTS: The relation between optic disk area and refractive error showed a curvilinear shape, with a steep increase toward high myopia starting at -8 diopters, and a decrease toward high hyperopia starting at +4 diopters. CONCLUSION: The optic disk size depends on the refractive error with an increase in highly myopic eyes beyond -8 diopters and a decrease in highly hyperopic eyes beyond +4 diopters. Confirming histomorphometric studies, the limits of -8 diopters and +4 diopters may be discussed to refine the definitions of high hyperopia and high myopia.

Chronic Disease↗
PubMed2002

A survey of the prevalence of refractive errors among children in lower primary schools in Kampala district.

BACKGROUND: Refractive errors are a known cause of visual impairment and may cause blindness worldwide. In children, refractive errors may prevent those afflicted from progressing with their studies. In Uganda, like in many developing countries, there is no established vision-screening programme for children on commencement of school, such that those with early onset of such errors will have many years of poor vision. Over all, there is limited information on refractive errors among children in Africa. OBJECTIVE: To determine the prevalence of refractive errors among school children attending lower primary in Kampala district; the frequency of the various types of refractive errors, and their relationship to sexuality and ethnicity. DESIGN: A cross-sectional descriptive study. SETTING: Kampala district, Uganda PATIENTS: A total of 623 children aged between 6 and 9 years had a visual acuity testing done at school using the same protocol; of these 301 (48.3%) were boys and 322 (51.7%) girls. RESULTS: Seventy-three children had a significant refractive error of +/-0.50 or worse in one or both eyes, giving a prevalence of 11.6% and the commonest single refractive error was astigmatism, which accounted for 52% of all errors. This was followed by hypermetropia, and myopia was the least common. CONCLUSION: Significant refractive errors occur among primary school children aged 6 to 9 years at a prevalence of approximately 12%. Therefore, there is a need to have regular and simple vision testing in primary school children at least at the commencement of school so as to defect those who may suffer from these disabilities.

Age Distribution↗
PubMed2005

Refractive error in urban and rural adult Chinese in Beijing.

PURPOSE: To evaluate refractive error and its demographic associations in an urban and rural population in northern China. DESIGN: Epidemiological study. PARTICIPANTS: The Beijing Eye Study is a population-based cohort study in northern China including 4439 subjects. Excluding pseudophakic and aphakic patients, the present study involved 4319 subjects. It was divided into a rural part (1905 [44.1%] subjects) and an urban part (2414 [55.9%] subjects). Mean age was 55.85+/-10.33 years (range, 40-90). METHODS: Standardized ophthalmologic examination. For statistical analysis, the spherical equivalent was converted to binary variables, and logistic regression was used to investigate the association with continuous or categorical independent variables. MAIN OUTCOME MEASURE: Refractive error. RESULTS: Mean refractive error measured -0.33+/-2.22 diopters (D) (range, -20.88 to +7.88). Myopia of >-0.50 D, -1.0 D, >-6.0 D, and >-8 D, respectively, occurred in 22.9% (95% confidence interval [CI], 21.7-24.2), 16.9% (95% CI, 15.8-18.0), 2.6% (95% CI, 2.2-3.1), and 1.5% (95% CI, 1.1-1.9) of the subjects, respectively. Myopic refractive error was associated significantly with younger age (P<0.001), urban region (vs. rural region) (P<0.001), higher educational background (P<0.001), higher degree of nuclear cataract (P<0.001), decreasing uncorrected visual acuity (UCVA) (P<0.001), decreasing best-corrected visual acuity (BCVA) (P<0.001), and female gender (P<0.001). Prevalence of high myopia (myopic refractive error >-8 D) was associated with age (P<0.001), female gender (P = 0.020), urban region (P = 0.023), and lower BCVA (P<0.001). Mean anisometropia was 1.09+/-2.03 D (median, 0.38; range, 0-22.0). Prevalence of anisometropia of > or =1 D was associated significantly with age (P<0.001), refractive error (P<0.001), BCVA (P<0.001), and region (P<0.001). Mean astigmatic error measured 0.62+/-0.90 D (median, 0.25; range, 0-7.50). Astigmatism of > or =1 D was associated significantly with age (P<0.001), lower UCVA (P = 0.003), lower BCVA (P<0.001), urban area (P<0.001), and degree of cortical cataract (P = 0.027). CONCLUSIONS: As in other population-based studies on Chinese, myopia was more prevalent in younger subjects. Myopia was associated with urban region, educational background, female gender, decreasing visual acuity, and nuclear cataract. If longitudinal studies confirm the association of refractive error with age, refractive surgery may achieve emmetropia only for a limited time.

Adult↗
PubMed1993

Accommodative hysteresis of refractive errors in light and dark fields.

We investigated the accommodative hysteresis of the refractive error in the light and also in the dark in 19 healthy young women. We measured refractive error under light and dark conditions using the Nidek Autorefractometer AR 1600 with its target light on or off. Then we measured refractive error in the light and in the dark again after they performed nearwork. Post-task refractive error was measured after reading a magazine for 15 min wearing glasses -3.0 D over their distance correction. Nearwork produced a myopic shift of 0.21 D in the refractive error in the light but no shift in the refractive error in the dark. Refractive error in the dark increased significantly by the near task in eyes with more than 2.0 D of myopia, but it did not increase in eyes with less than 2.0 D of myopia. These apparent differences in the accommodative hysteresis are due to the different pre-task baseline values. If the post-task refractive error is evaluated with the same pre-task baseline value, the accommodative hysteresis does not differ among different refractive errors whether measured in the light or in the dark.

Accommodation, Ocular↗
PubMed1977

The Humphrey Vision Analyzer tm: reliability and validity of refractive-error measures.

Four subjective measures of the refractive error of 42 eyes (21 patients) were obtained by 2 examiners, one using a Humphrey Vision Analyzer TM and the other using a conventional refractor. Each examiner made 2 separate measures of each subject's refractive error, one without and one with an added cylindrical lens chosen at random from a predetermined set of powers and axes. The order of using the instruments and the added lenses was mixed. Measures of the refractive errors differed with the 2 instruments by approximately the same amount on average as did duplicate measures with either instrument. Refractive-error measures obtained with the 2 instruments are about as valid as they are repeatable.

Adult↗
PubMed2006

The correlation between migraine headache and refractive errors.

PURPOSE: A literature review reveals historical references to an association between migraine headache and refractive errors, but a lack of scientific evidence relating to these claims. METHODS: In a masked case-controlled study, we investigated the four aspects of refractive errors that have been implicated in the literature as correlated with migraine: spherical refractive error, astigmatic refractive error, anisometropia, and uncorrected ametropia. We also compared the calculated scalar value of refractive error, aided and unaided visual acuity, and spectacle use in migraine and control groups. We then investigated the relationship between refractive components and key migraine headache variables. RESULTS: Compared with the control group, the migraine group had higher degrees of astigmatic components of refractive error assessed both objectively (C, p = 0.01; C(0), p = 0.01; C(45), p = 0.05) and subjectively (C, p = 0.03; C(0), p = 0.03; C(45), p = 0.05), uncorrected astigmatic components of refractive error (C(0), p = 0.02; C(45), p = 0.04), and anisometropia (p = 0.06). CONCLUSIONS: Perhaps the historical literature is indeed correct that low degrees of astigmatism and anisometropia are relevant in migraine. Our most significant finding was of higher degrees of astigmatism in the migraine group. This study does indicate that people who experience migraine headaches should attend their optometrist regularly to ensure that their refractive errors are appropriately corrected.

Adult↗
PubMed2003

Refractive error blindness.

Recent data suggest that a large number of people are blind in different parts of the world due to high refractive error because they are not using appropriate refractive correction. Refractive error as a cause of blindness has been recognized only recently with the increasing use of presenting visual acuity for defining blindness. In addition to blindness due to naturally occurring high refractive error, inadequate refractive correction of aphakia after cataract surgery is also a significant cause of blindness in developing countries. Blindness due to refractive error in any population suggests that eye care services in general in that population are inadequate since treatment of refractive error is perhaps the simplest and most effective form of eye care. Strategies such as vision screening programmes need to be implemented on a large scale to detect individuals suffering from refractive error blindness. Sufficient numbers of personnel to perform reasonable quality refraction need to be trained in developing countries. Also adequate infrastructure has to be developed in underserved areas of the world to facilitate the logistics of providing affordable reasonable-quality spectacles to individuals suffering from refractive error blindness. Long-term success in reducing refractive error blindness worldwide will require attention to these issues within the context of comprehensive approaches to reduce all causes of avoidable blindness.

Amblyopia↗
PubMed1997

Prevalence and risk factors for refractive errors in an adult inner city population.

PURPOSE: To estimate the prevalence of refractive errors among adult black and white Americans and to identify risk factors associated with these refractive errors. METHODS: Refractive error was measured in a population-based sample of black and white adults age 40 or older residing in east Baltimore from 1985 through 1988. Aphakic eyes were excluded from analysis. RESULTS: The prevalence of myopia varied from 10.5% among black men 80 years and older to 42.1% among white women 40 to 49 years of age. Hyperopia ranged from 11.8% among black men 40 to 49 years to 68.1% among white men 80 years of age and older. Astigmatism ranged from 15.8% to 45.2%, and anisometropia ranged from 2.8% to 8.1%, depending on age, race, and gender. Black persons had less myopia, hyperopia, astigmatism, and anisometropia than did white persons. Myopia (< -0.5 diopter [D] spherical equivalent) declined with age, whereas hyperopia (> +0.5 D), astigmatism (> 0.5 D of cylinder), and anisometropia (> 1.0 D between eyes) increased with age. Myopia increased with increasing years of education, although this association was stronger for white persons than for black persons and among younger subjects. Hyperopia declined with increasing years of education, and this association was stronger among younger than older subjects. Education was not associated with astigmatism or anisometropia. CONCLUSIONS: Black persons had lower rates of refractive error than did white persons, except for hyperopia prevalence, which was comparable in black and white women. Refractive errors are common among adult inner city Americans, but rates vary substantially by age, race, gender, and education levels.

Adult↗