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PubMed1996

Reliability of refraction--a literature review.

BACKGROUND: The repeatability (reliability) of methods of measuring refractive error is an important consideration in patient management decisions and in research design and interpretation. Several papers on reliability of refraction have appeared in the literature. METHODS: Studies on the reliability of conventional clinical refraction, including repeated refractions by the same examiner (intraexaminer reliability) and comparisons of the results obtained by different examiners (interexaminer reliability), were reviewed. Studies comparing the results obtained by autorefractors and conventional subjective refraction were also reviewed. RESULTS: The intraexaminer reliability and interexaminer reliability of subjective refraction in most studies were close to 80 percent agreement within +/- 0.25D and 95 percent agreement within +/- 0.50D for spherical equivalent, sphere power, and cylinder power. The reliability of most autorefractors is similar to the reliability of conventional subjective refraction. CONCLUSIONS: The results of the reliability studies support Bannon's 1977 conclusion that conventional subjective refraction is reliable within 0.25 to 0.50D. Studies comparing objective autorefractors and conventional subjective refraction indicate that these autorefractors are satisfactory for a preliminary refraction but are not satisfactory as substitutes for conventional subjective refraction.

Humans↗
PubMed2006

In the absence of strabismus what constitutes a visual deficit in children?

AIM: To examine the range of monocular crowded logMAR acuity and cycloplegic refraction of children aged 3 years and 4 years without strabismus. METHODS: Data were collected prospectively. All children had full orthoptic and ophthalmic examination. Inclusion principally required the absence of strabismus, symptoms, and ocular pathology. Criteria were used to categorise the refraction findings as normal, borderline, or abnormal. RESULTS: 118 children aged 3 years (mean 3 years 6 months (SD 2 months) and 67 children aged 4 years (mean 4 years 4 months (SD 3 months) fulfilled the inclusion criteria. For the children with normal refraction, the mean monocular logMAR acuity was 0.200 (SD 0.09) for 3 year olds (n = 84) and 0.140 (SD 0.08) for 4 year olds (n = 45); the mean interocular acuity difference (IAD) was 0.03 (SD 0.06) for 3 year olds and 0.03 (SD 0.04) for 4 year olds. The 95% confidence limits were calculated for monocular acuity and IAD and compared to the acuity scores of the children with borderline (n = 17) and abnormal refractive error (n = 38). 15 borderline and 16 abnormal cases had a visual acuity within these limits. CONCLUSION: A wide range of refraction may be associated with a good level of visual acuity in children aged 3 years and 4 years.

Child, Preschool↗
PubMed1989

Optic disc photogrammetry: magnification factors for eye position, centration, and ametropias, refractive and axial; and their application in the diagnosis of optic nerve hypoplasia.

To determine if image magnification from ametropia or other factors required correction in the photogrammetric diagnosis of optic nerve hypoplasia, the following variables were studied using two standard 30 degrees field fundus cameras (Zeiss FF-3 and Kowa RC-2): (1) distance between the camera and the subject--variations in this distance do not change the image size; (2) decentration of the camera (i.e., decentration of the optic disc image within the field)--no effect was found using the Kowa camera, but in the Zeiss, a 2% (0.07 mm) increase in disc image size was found for each mm of optic disc decentration in the field; (3) ametropia, refractive experimental (induced in one subject with soft contact lenses, from +8.00 diopters (D) to -8.00D)--no significant change in image size was found (In addition, in 50 healthy adult eyes with various refractive errors, including ten with uncorrected aphakia, there was no significant difference found for the size of the optic nerve in different refractive ametropias. No correction factor was necessary for aphakia or for other refractive ametropias); and (4) ametropia, axial--axial myopia showed minor but significant magnification: a linear increase in the horizontal diameter of the optic disc image of 2% (0.07 mm) was found for each diopter of axial ametropia exceeding 3D. There was insufficient data for axial hyperopia. These magnification factors should be applied when measuring the optic disc on 35-mm transparencies to make a diagnosis of optic nerve hypoplasia.(ABSTRACT TRUNCATED AT 250 WORDS)

Aphakia↗
PubMed1987

Abnormal ocular head postures: Part I.

All patients exhibiting the various types of abnormal head postures of ocular origin that were seen during the last two years are presented in order to determine the relative frequency of the different causes of these postures, and the purposes they serve. The treatment modality and results are also discussed. The manuscript is divided into four parts: Part I, II, and III concern head postures in incomitant strabismus. In Part IV, head postures in Ciancia's syndrome, restrictions, and refractive errors are described.

Child↗
PubMed1990

Excessive loss of hyperopia. A presenting sign of juvenile aphakic glaucoma.

We present the cases of four patients in whom juvenile aphakic glaucoma developed. An excessive loss of hyperopia was the initial clinical sign that alerted us to the diagnosis of glaucoma. At the time of diagnosis, the mean refractive error of the six glaucomatous eyes in the four patients was +4.75 diopters (D) (range, -0.25 to +6.75 D). The mean change in refraction from time of cataract extraction to diagnosis of juvenile aphakic glaucoma was 17.00 D (range, 9.25 to 21.00 D). All aphakic patients in the private practice of one of us (B.J.K.) with a spherical equivalent of less than +8.00 D in either eye have glaucoma. The only exception are those patients with a coexisting condition predisposing them to myopia. We have found an excessive loss of hyperopia to be a useful sign in alerting the ophthalmologist to the diagnosis of juvenile aphakic glaucoma.

Aphakia, Postcataract↗
PubMed2004

Risk factors for treatment failure of anisometropic amblyopia.

PURPOSE: This study sought to explore factors which might predict the lack of vision improvement following therapy of anisometropic amblyopia. METHODS: We retrospectively reviewed the records of 104 children aged 3 to 8 years who had anisometropic amblyopia with a difference in the refractive power between the two eyes of at least 1 diopter, a difference in corrected visual acuity between the two eyes of at least 3 logMAR units, visual acuity in the amblyopic eye of 20/50 or worse, and no ocular structural abnormalities. Patients were treated with either patching or atropine penalization therapy. Patients with strabismus were included. Treatment failure was defined in two ways: (1) functional failure indicating a final visual acuity in the amblyopic eye worse than 20/40 and (2) relative failure indicating less than three lines of logMAR visual acuity improvement regardless of final vision. RESULTS: Failure risk factors were as follows: age above 6 at the onset of treatment (adjusted odds ratio [OR] (95% confidence limits [CL] = 4.69 [1.55, 14.2]), the presence astigmatism of more than 1.50 diopters in the amblyopic eye (adjusted [OR] (95% CL) = 5.78 [1.27, 26.5]), poor compliance with treatment (adjusted [OR] (95% CL) = 5.47 [1.70, 17.6]), and initial visual acuity in the amblyopic eye of 20/200 or worse (adjusted [OR] (95% CL) = 3.79 [1.28, 11.2]). Strabismus was not found to be a significant risk factor. Neither the type or amount of refractive error nor the difference in the refractive power between the two eyes was a significant risk factor for treatment failure. CONCLUSION: Eyes with poor initial visual acuity, the presence of significant astigmatism, and age over 6 years were less likely to achieve successful outcome. The clinical profile of patients with anisometropic amblyopia may be useful in predicting response to therapy, but compliance with treatment has a major effect on response to therapy.

Age Factors↗
PubMed2000

Correction of high astigmatism with astigmatic keratotomy combined with laser in situ keratomileusis.

PURPOSE: To evaluate the efficacy, predictability, and stability of a combined procedure, arcuate keratotomy and laser in situ keratomileusis (LASIK), for the correction of high astigmatism. SETTING: Instituto de Microcirugía Ocular (IMO), Barcelona, Spain. METHODS: Fifteen eyes of 11 patients with naturally occurring astigmatism (NOA) (86. 66%) or surgically induced astigmatism (SIA) (13.34%) between -3.00 and -8.00 diopters (D) who had astigmatic keratotomy were studied. The patients had a secondary procedure, LASIK, to correct the residual refractive error. RESULTS: Mean baseline spherical equivalent refraction was -2.47 D +/- 3.69 (SD) and mean refractive cylinder, -4.59 +/- 1.66 D. Twelve months after LASIK, mean spherical equivalent was -0.09 +/- 1.50 D and the mean refractive cylinder, -1. 21 +/- 1.07 D. The mean cylindrical correction attempted in the NOA group was -4.05 +/- 1.19 D and in the SIA group, -7.00 +/- 1.41 D. Postoperatively, the values were -1.50 +/- 1.17 D and -1.62 +/- 0.17 D, respectively. Twelve months after LASIK, the uncorrected visual acuity (UCVA) was 0.5 +/- 0.1. The UCVA in the NOA group (0.50 +/- 0. 08) was better than in the SIA group (0.32 +/- 0.10). The efficacy index was 0.96 overall. Best corrected visual acuity deteriorated by 1 Snellen line in 1 case (6.6%) but improved by 1 and 2 Snellen lines in 4 cases (26.6%) and 2 cases (13.3%), respectively. All procedures were completed without adverse reactions intraoperatively or postoperatively. CONCLUSION: This combined technique was effective in the treatment of high astigmatism, with excellent results compared with the results of each procedure alone. Because of its high predictability, we strongly recommend the technique in cases with astigmatism higher than 3.0 D, particularly in those with astigmatism higher than 5.0 D.

Adult↗
PubMed1998

Secondary implantation of a double intraocular lens after penetrating keratoplasty.

Penetrating keratoplasty (PKP) patients often have severe, visually disabling refractive errors. Astigmatism can be addressed by refractive surgery; however, correcting hyperopia is more problematic. Although pseudophakic PKP patients can have a lens exchange, it can be traumatic in this population. In this pseudophakic PKP patient, I added a second posterior chamber intraocular lens, correcting the hyperopia and resolving visual complaints.

Astigmatism↗
PubMed1991

The reproducibility of biometry and keratometry measurements.

Axial length and corneal curvature are entered into formulae to calculate intraocular lens power for cataract surgery and the absolute measurement of fundus structures such as neuroretinal rim area in glaucoma. The reproducibility (coefficient of variation, CV) of biometry and keratometry was investigated by taking five measurements of thirty phakic eyes. Although both techniques were found to be highly reproducible (CV less than 1%), keratometry was the more so. However, a clinically significant difference was noted between the first and the mean of five readings for both biometry (0.15 +/- 0.05 mm) and keratometry (0.05 +/- 0.03). Taken together, these errors would result in a postoperative refractive error of 0.65D using the SRK formula. Measurement errors were just as likely to occur with short or long eyes. Similar results were found when the analysis was performed on three measurements of both axial length and corneal curvatures. We recommend taking the average of three biometry and keratometry readings to improve the reliability of the techniques, and to increase the accuracy of calculating intraocular lens power and fundus structure dimensions.

Biometry↗
PubMed1991

Opportunistic screening of visual acuity of elderly patients attending outpatient clinics.

A standard Snellen letter chart was used to screen the visual acuities of 202 elderly patients while they attended outpatients clinics. Patients overestimated the adequacy of their vision: only 34 patients reported inadequate vision while 72 had significant measured visual impairment. Of these, 30 patients had refractive errors and 42 primarily non-refractive problems. Thirty patients were examined by an ophthalmologist, of whom 24 had previously undiagnosed conditions. Eighteen patients had treatable conditions, predominantly cataracts and glaucoma. Ten patients with untreatable conditions had the benefit of a definitive diagnosis, most commonly of age-related macular degeneration, and an assessment of eligibility for registration of blindness. The routine assessment of elderly patients should include objective screening of their visual acuity.

Aged↗
PubMedDate not supplied

Refractive index of the crystalline lens in young and aged eyes.

BACKGROUND: When the ageing crystalline lens is modelled on the basis of a constant equivalent lens, the changes in ocular dimensions would lead to an increase in power of the order of two dioptres. A comparable increase in myopia is usually not evident with increasing age and this inconsistency has been referred to as the lens paradox. It has been proposed that this paradox can be resolved if the refractive index is modelled as a gradient refractive index. The purpose of this paper was to study differences in the equivalent, gradient and surface refractive index of the crystalline lens between a young and old age group. METHODS: Biometric data was collected for 96 subjects: 48 young adults with an age range 19 to 31 years (mean 22.10 +/- 2.93 years) and 48 old adults with an age range 49 to 61 years (mean 53.88 +/- 3.88 years). The equivalent refractive index was determined for each subject by paraxial ray tracing and a merit function based on refractive error and Purkinje image height. The refractive index gradient was determined by modelling the crystalline lens as a bi-elliptical iso-indicial structure in a three-surface Gullstrand-Emsley schematic eye and a merit function based on the surface power, the gradient refractive index power and the equivalent power of the lens. The central refractive index of the lens was assumed to be 1.406. RESULTS: The differences between the groups included a decrease in the mean equivalent refractive index from 1.427 +/- 0.007 to 1.418 +/- 0.006, an increase in surface refractive index from 1.386 +/- 0.007 to 1.394 +/- 0.006 with a concurrent change in the gradient refractive index profile. The refractive index changes maintained a constant mean lens power in each group. CONCLUSIONS: The so-called 'lens paradox' whereby an increase in the power of the crystalline lens does not lead to an increase in myopia is resolved by a decrease in the equivalent refractive index of the lens or when modelled as a gradient refractive index structure, by an increase in the surface refractive index and an associated change in gradient for an assumed central refractive index of 1.406.

Journal Article↗
PubMed1993

Ocular and vision defects in preschool children.

Ocular and/or vision defects are one of the commonest reasons for the referral of young children to hospital. In a survey of a birth cohort in one health district, 7.1% of children were diagnosed as having such defects by their fifth birthday; 2.1% were detected before the age of 2 years, and 5.1% between 2 and 5 years. Up to the age of 2 years, low birthweight children and those who require postnatal special care had a higher risk of having an ocular or vision defect diagnosed and were more likely to have serious visual impairment than other children. In contrast, between the ages of 2 and 5 years of age these high risk children showed no continuing increased risk of having a defect diagnosed, nor did they show any differences in the severity or type of vision defects compared with other children. Averaged over the years studied, the incidence of defects presenting to specialist eye clinics among all 2-5 year olds was 1.7%, higher than the 1.1% found for 0-2 year olds. This increase consisted primarily of children with refractive errors only.

Child, Preschool↗
PubMed2003

[Cataract extraction and intraocular lens implantation after high-risk penetrating keratoplasty].

OBJECTIVE: To study the indication and incision of phacoemulsification and intraocular lens (IOL) implantation after high-risk penetrating keratoplasty (PKP) and to evaluate the clinical results. METHODS: Twenty-six eyes of 25 patients who underwent high-risk PKP were treated with phacoemulsification and IOL implantation. The high-risk reasons included chemical burn of cornea, severe infective corneal perforation, total keratoplasty, diameter of the corneal graft larger than 8.5 mm, secondary keratoplasty and PKP combined with cataract extraction and anterior segment vitrectomy. Systemic and local steroid administration was given and surgical indication and incision were chosen according to the condition of the eyes. The mean interval time between PKP and IOL implantation was 11 months. Visual acuity, refractive status, central corneal endothelial cell density before and after IOL implantation (3 months) and allograft rejection were recorded. The mean follow-up after IOL placement was 17 months. RESULTS: Uncorrected visual acuity was 50/100 or better in 7 (27%) eyes and corrected visual acuity was 50/100 or better in 12 (46%) eyes. Fourteen (54%) eyes had refractive errors within 2 diopters. The mean refractive cylinders before and after IOL implantation were 5.70 D and 4.70 D, respectively (paired t test, t = 1.471, P = 0.154). The endothelial cell density before and after IOL implantation was 1883 cells/mm(2) and 1760 cells/mm(2), respectively (t = 1.934, P = 0.065) and the rate of endothelial cell loss was 6.5%. Only one graft rejection (4%) occurred 7 months after IOL implantation (anterior chamber IOL). CONCLUSION: It is safe and effective to perform phacoemulsification and IOL implantation after high-risk PKP when paying attention to the perioperative treatment and selecting the surgical indication and the position of the incision.

Adolescent↗
PubMed1988

Mathematical model of emmetropization in the chicken.

Recently a number of observations were made on refractive development in chickens and monkeys under various experimental treatments. Degradation of the retinal image by use of occluders produces myopia, although with a high variability in the individual refractions. This kind of image degradation myopia can be induced in the absence of accommodation and with the optic nerve sectioned. In chickens, recovery occurs both in normal birds and in operated birds in which accommodation has been eliminated by lesions in the Edinger Westphal nucleus. In addition, it was shown that, in the chicken eye, growth compensates for an imposed refractive error induced by spectacle lenses. A compensatory change in growth can also be induced in the absence of accommodation. Thus the role of accommodation in the refractive development must be explained. Here we develop a minimal model for regulation of eye growth that provides a possible explanation for all the above observations. A major conclusion is that the presence of two independent feedback loops must be assumed, one dependent on accommodation and one on a local mechanism detecting blur in the retina.

Accommodation, Ocular↗
PubMedDate not supplied

Persistence of diurnal fluctuation after radial keratotomy.

Three patients were examined before 8:00 AM and after 7:00 PM to determine diurnal changes in uncorrected visual acuity, refractive error, and average central keratometric power at 3 months, 4 years, and 6 years after radial keratotomy. The average absolute diurnal change in the spherical equivalent refraction increased over time: 0.26 diopters at 3 months, 0.75 D at 4 years, and 1.29 D at 6 years. Diurnal change in the absolute average keratometric values were not progressive: 0.35 D at 3 months, 0.27 D at 4 months, and 0.40 D at 6 years. Computer-assisted corneal topographic analysis demonstrated diurnal changes in the topography that may be subtle and not necessarily reflected in the average keratometry values. These limited data suggest that wound healing over several years may not restore stability to the cornea.

Adult↗
PubMed1989

Axial length and the average ophthalmologist--is biometry worthwhile?

The refractive predictability of 477 lens implants with powers calculated using biometric data and lens power formulas was reviewed and compared with postoperative refractions that would have been expected had standard power lenses been implanted. Eighty-nine percent of the calculated lenses were within 1.25 diopters and 98% were within 2.00 D of the desired refractions. Fifty-two percent and 73% of the standard lenses would have yielded these respective degrees of accuracy. Eyes grouped according to preoperative refractive error and those for which emmetropia or ametropia was predicted were similarly compared with similar results for all groups. The calculated lenses consistently provided better postoperative refractive predictability than could have been achieved with standard lenses.

Astigmatism↗
PubMed1978

Cycloplegics for refraction.

The actions and indications of cypcloplegics are presented along with recommended dosages and uses for clinical measures of refractive error.

Adult↗
PubMed1994

The effect of refractive blur on the detection sensitivity to light offsets in the central visual field.

Detection sensitivity to light decrements created on a cathode ray tube was measured along the nasal horizontal meridian of the central visual fields of 5 normal subjects. Decremental (light offset = negative contrast = dark-on-bright) static stimuli were presented at 6, 12, 18, 24 and 30 degrees eccentricity. Detection thresholds to rectangular stimuli of both 4 and 16 mm2 (Goldmann equivalent size III and IV, respectively) were determined with ascending staircase single-crossing technique under various Snellen visual acuity levels. Detection sensitivity diminished with increasing amounts of plus lens-induced refractive blur. One log unit decrease in visual acuity resulted in elevation of detection thresholds for an average of 3.8 contrast decibels (dB) using size III offset stimuli. The effect of blur was less with size IV offset stimuli which resulted in an average of 0.9 dB elevation in detection thresholds. The larger size decremental stimuli provided a wider dynamic range, less interindividual variation in stimulus visibility and more resistance to refractive error than those obtained with the smaller size stimuli.

Adult↗