Ametropic Eye Research Articles

Refracting The Diseased Eye

Refractive error refers to ocular refractive status where images of objects of regard do not fall on the retina in a relaxed eye - the ametropic eye. Thus, objects are perceived as blur. Refractive error is an aberration in an otherwise normal physiological phenomenon and not a disease. Uncorrected refractive errors are the second most causes of blindness after cataract and the cause of almost half of visual impairment. Clinical refraction is a careful scientific procedure employed to correct refractive error. Given that refractive error is the most common reason patients present to the eye care practitioner, a lot of attention must be given to refraction. When an irreversible eye disease co-exist with refractive error, then correction of refractive error under this circumstance; refracting the diseased eye (RDE) become very challenging and painstaking. There will be likelihood of irregularities in the transparent refractive surfaces of the eye due to disease or surgery which make refraction difficult both for the patient and the examiner. Personal clinical experience of the author who is a low vision consultant and review of related literature from textbooks and journals are brought to bear in this article. This paper is a review of the RDE algorithm with delineation of these steps to enable an effective refractive endpoint for the eye with disease. The paper will enable young Optometrists to deal with refractive error masquerading irreversible eye disease. It is also an essential reading for the low vision Optometrist in mastering the art and science of low vision refraction.

Associations between anisometropia and depth of amblyopia in Benghazi, Libya

Abstract Background: Amblyopia is a disorder characterized by a decrease in the best-corrected visual acuity in one or both eyes with no clear structural anomalies or ocular pathology. There are three primary types of amblyopia: anisometropic, strabismic, and sensory deprivation amblyopia. Anisometropic amblyopia occurs in children having a difference in refractive error between the two eyes and occurs in the more ametropic eye. Furthermore, there is a strong association of anisometropia with strabismus. Aim: The study aimed to investigate the association between age, sex, laterality, and type of refractive error on the depth of anisometropic amblyopia. Settings and Design: This was a retrospective (observational) study. Data were analyzed using IBM SPSS 23.0 software. Materials and Methods: One hundred and nine patient's files with anisometropic amblyopia were investigated, who were followed in a pediatric eye clinic in Sohail Elatrash's eye hospital Benghazi, Libya, between January 2008 and December 2018. Results: There is no effect of the type of gender on the depth amblyopia with P = 0.57. Furthermore, there is no difference in the predominance of amblyopia between the right and left eye (P = 0.93). Age is correlated in a positive manner with the depth of amblyopia (P = 0.035). Conclusions: in our study, eye laterality and gender had no effect on the depth of anisometropic amblyopia. The age and the smallest amount of astigmatism difference between both eyes had a direct proportion on the depth of anisometropic amblyopia.

The limits of fixation-Keeping the ametropic eye on target.

Accurate positioning of the naked eye is a prerequisite in many ophthalmic measurement and intervention systems. In most of these procedures the eyeball is stabilized through fixation of a target. Fixation is initiated, as well as sustained by a whole set of oculomotor processes: saccadic movements and drift, as well as vergence. Target appearance influences sustained fixation, but the influence of target information on the initiation of fixation has not been evaluated in detail. The current study evaluates the accuracy of fixation initiation as well as sustained fixation under refractive error. Twenty-one ametrope subjects repeatedly fixated a laser speckle-based fixation target for an extended duration of 3 s. Fixational area, fixational saccade rate as well as fixational saccade amplitude were analyzed during two different time intervals, namely in fixation initiation and sustained fixation. Fixation initiation was evaluated within the first 500 ms of fixation, whereas sustained fixation was evaluated 1 s after the eyes were directed toward the fixation target. During fixation initiation, fixation accuracy decreased in comparison to sustained fixation; fixational saccades occurred more frequently, and with larger amplitudes. During sustained fixation, an impact of refractive error was shown. With increasing refractive error, fixational saccade amplitude and fixational saccade rate increased. Fixational area increased in high ametropia through larger and more frequent saccades, but at a rather moderate rate of 10 arcmin/diopter (dpt) radial increase.

Differential Experience-Dependent Plasticity of Form and Motion Mechanisms in Anisometropic Amblyopia.

PurposeWe measure neural responses associated with form and motion processing in children with anisometropia before and after treatment with spectacles and occlusion.MethodsIn this prospective, case-control treatment study, 10 children with anisometropia and amblyopia and 16 age-matched visually normal children participated. Steady-state visual evoked potentials (VEP) were recorded from electrodes over the occipital cortex. The visual stimulus comprised a horizontal bar grating into which Vernier offsets were introduced and withdrawn periodically at 3.75 Hz. The VEP amplitude at 3.75 Hz (first harmonic [1F]) and 7.5 Hz (second harmonic [2F]) were recorded to index the sensitivity of form/position-sensitive versus motion/transient-sensitive neural populations, respectively. Response amplitude at 1F and 2F were recorded over a series of 10 logarithmically spaced offset sizes before and after treatment. Main outcome measures are VEP amplitude versus displacement functions, interocular response amplitude differences.ResultsAfter relaxing into spectacles (minimally-treated state), form/position-sensitive responses in the dominant/less ametropic eye of the children with anisometropia were larger and responses in the more ametropic eye were smaller than those of controls. Motion-transient responses were equal to those of controls in the less ametropic eye, but were smaller than controls in the more ametropic eye. After treatment, responses did not differ from those of controls.ConclusionsForm and motion responses are differentially susceptible to neural deprivation via optical blur. Form responses are more plastic than motion responses in minimally-treated children with anisometropic amblyopia. Most treatment effects occurred above threshold range, suggesting some treatment effects are not detected clinically.

Ray-mapping based calculation of the intra-corneal wavefront and corneal ablation profile for ocular aberration corrections

We propose a ray-mapping based algorithm for the tissue ablation calculation to produce an optimum freeform anterior corneal surface that is responsible for the correction of ocular aberrations. With knowledge of the measured ocular wavefront and the anterior corneal surface, the numerical ray tracing method is used to calculate the intra-corneal wavefront and to generate the optimal corneal ablation profile determined by the accurate ray-mapping between the intra-corneal wavefront and the target ocular wavefront. This method is compared with the conventional wavefront-guided based algorithm for the ametropic eye models in theory, providing superior performance both in the aberration-free correction and the aberration selective correction.

Progression of High Anisometropia in Children.

To investigate the onset and rate of progression of high anisometropia in myopic children younger than 13 years. A retrospective study was performed on children with anisometropia younger than 13 years with myopia of more than 4.00 diopters (D) in the more ametropic eye and a difference in spherical equivalent refraction of 4.00 D between both eyes. All children had a complete ophthalmologic examination, including measurement of visual acuity and cycloplegic refraction every 3 to 6 months for at least 5 years. Change in the spherical equivalent and the cylindrical error for both eyes and changes in the difference in spherical equivalent refraction between both eyes were calculated for each patient at each visit. Linear, polynomial, logarithmic, and exponential fitting models were tested for both eyes and for the anisometropic difference between both eyes. The regression line with the greatest R2 value was considered best fit. Sixty-three patients fulfilled the inclusion criteria. The more ametropic eye grew in a regular fashion during the first 2 years of life, followed by a rapid decrease in the rate of growth to become almost stable after 4 years of age. The increase in myopia best fit a third-degree polynomial (cubic) model (R2 = 0.98). The less ametropic eye showed only a small increase in myopia during the follow-up period. The anisometropic difference between both eyes increased gradually during the first 2 years, then remained stable. High anisometropic myopia progresses rapidly in the first few years of life before becoming stable. [J Pediatr Ophthalmol Strabismus. 2017;54(5):282-286.].

Anisometropia in Children from Infancy to 15 Years

To investigate anisometropia in children from age 6 months to 15 years. Children with refractions at 6 months (n = 1120), 5 years (n = 395), and 12 to 15 years (n = 312) were included in this study. All children were refracted in the laboratory by noncycloplegic retinoscopy. Myopes had spherical equivalent refraction (SER) of the less ametropic eye of less than -0.50 D, hyperopes had SER of the less ametropic eye greater than or equal to 1.00 D, and emmetropes had SER of the less ametropic eye from -0.50 to +1.00 D. The mean difference in refraction between the two eyes was similar at 6 months (0.11 D) and 5 years (0.15 D), increasing to 0.28 D at 12 to 15 years. Using a cutoff of 1.00 D SER for anisometropia, the prevalence was 1.96%, 1.27%, and 5.77% at 6 months, 5 years, and 12 to 15 years, respectively. At 12 to 15 years, the prevalence of anisometropia in the myopes was 9.64% and in the hyperopes was 13.64%, both significantly higher than that in the emmetropes (3.38%, P < 0.05). The degree of anisometropia at 12 to 15 years was significantly associated with the refractive error of the less ametropic eye at 12 to 15 years, with and without adjustment for relevant covariates (P < 0.05). Infants with significant astigmatism (cylinder power ≥ 1.00 D in one or both eyes) have an increased risk of anisometropia (P < 0.05). The prevalence of anisometropia increases between 5 and 15 years, when some children's eyes grow longer and become myopic. However, anisometropia was found to accompany both myopia and hyperopia, suggesting that other mechanisms in addition to excessive eye growth may exist for anisometropia development, especially in hyperopia.

The Accommodative Lag of the Young Hyperopic Patient

To determine the accommodative accuracy of infants and young children before they had had any form of clinical intervention or treatment, in an attempt to determine the difference between 'normal' and 'abnormal' visual experience for these individuals. Nott retinoscopy was performed on 111 subjects in binocular viewing conditions at a viewing distance of 50 cm. The target was a naturalistic cartoon image with a broadband spatial frequency amplitude spectrum. Accommodative accuracy was not related to age (4-90 months). In the group found to have no apparent clinical abnormality (n = 71), the mean lag in the more hyperopic meridian of the least ametropic eye was 0.34 diopters (D). When considering the group as a whole, those with less than approximately 4 D of hyperopia demonstrated similar lags, while those with higher hyperopia, amblyopia, or strabismus had more variable lags. An ROC analysis designed to detect hyperopia >5 D in any meridian, amblyopia and/or strabismus had an area under the curve of 0.90 (95% confidence interval [CI], 0.82 to 0.95), and for a lag criterion of 1.3 D had a sensitivity of 83.3% and a specificity of 96.5%. These data from a relatively small but broad sampling of age and clinical status suggest that clinically normal young infants and children with low amounts of hyperopia have similar lags of accommodation from the first few months after birth. Subjects with greater than 4 D of hyperopia, or amblyopia or strabismus, have more variable lags and therefore evidence of abnormal visual experience.

Independent and reciprocal accommodation in anisometropic amblyopia

Accommodation is considered to be a symmetrical response and to be driven by the least ametropic and nonamblyopic eye in anisometropia. We report the case of a 4-year-old child with anisometropic amblyopia who accommodates asymmetrically, reliably demonstrating normal accommodation in the nonamblyopic eye and antiaccommodation of the amblyopic eye to near targets. The abnormal accommodation of the amblyopic eye remained largely unchanged during 7 subsequent testing sessions undertaken over the course of therapy. We suggest that a congenital dysinnervation syndrome may result in relaxation of accommodation in relation to near cues and might be a hitherto unconsidered additional etiological factor in anisometropic amblyopia.

Amétropies en milieu scolaire primaire à Cotonou (Bénin)

Determine the epidemiologic aspects and the degree of severity of different refractive errors in primary schoolchildren. A prospective and descriptive study was conducted from 1 December 2005 to 31 March 2006 on schoolchildren ranging from 4 to 16 years of age in a public primary school in Cotonou, Benin. The refraction was evaluated for any visual acuity lower than or equal to 0.7. The study included 1057 schoolchildren. The average age of the study population was 8.5+/-2.6 years with a slight predominance of females (51.8%). The prevalence of refractive error was 10.6% and astigmatism accounted for the most frequent refractive anomaly (91.9%). Myopia and the hyperopia were associated with astigmatism in 29.4% and 16.1% of the cases, respectively. The age bracket from 6 to 11 years accounted for the majority of refractive errors (75.9%), without age and sex being risk factors (p=0.811 and p=0.321, respectively). The average vision of the ametropic eye was 0.61, with a clear predominance of slight refractive errors (89.3%) and particularly of low-level simple astigmatism (45.5%). The relatively low prevalence of refractive error observed does not obviate the need for implementing actions to improve the ocular health of schoolchildren.

Atypical Fixation Preference with Anisometropia

To describe a child with hyperopia and anisometropia who manifests strabismus and amblyopia in the much less hyperopic eye. A 6-year-old child presented with a history of strabismus and refractive error since infancy, which has been treated with glasses and patching. The present examination revealed 3 D of hyperopic anisometropia, intermittent exotropia, and amblyopia. The strabismus and amblyopia occur in the less hyperopic eye. Ocular health assessment including optical coherence tomography was normal. After patching therapy, the vision improved in the amblyopic eye. Amblyopia and strabismus need not always occur in the more ametropic eye when accompanied by anisometropia.

Analysis the Necessary of Mydriasis with 1% Atropine Eye Oint under 12 Years Old Children

目的 了解托品酰胺滴眼液和1%阿托品眼膏散瞳对不同年龄屈光不正儿童的影响.方法对598例屈光不正儿童先液散瞳验光;再眼膏,散瞳验光,比较分析屈光度变化.结果①各年龄组用眼液与用眼膏散瞳前后球面镜、柱镜、等效球镜的屈光度比较眼膏散瞳后屈光度均高于眼液散瞳(p<0.05);②不同年龄组两种方法散瞳后的两两比较显示用眼膏散瞳验光比用眼液更能反映球镜、柱镜度数的真实变化.结论①用眼膏散瞳后验光的多项屈光指标均有显著性变化,球面镜度数绝大多数增高,等效球镜屈光度也增大;②在11岁以内年龄组,用眼膏散瞳后验光可以提高屈光不正的检出率,减低漏诊率,减少验光度数的误差。

Changes in refraction in anisomyopic patients

PURPOSE. The purpose of this study was to investigate the evolution of refraction and visual function in patients with myopic anisometropia. DESIGN. A retrospective study on a selected population. METHODS. Forty-six anisomyopic patients underwent a complete ophthalmologic examination (cycloplegic refraction, visual acuity, ocular movement and fundus examination). RESULTS. The results show two different patterns of changes in refraction between the two eyes; in the same patient, the less myopic eye tends to get more myopic, while the more ametropic eye shows a more stable refraction. Furthermore, a recovery of binocular vision and amblyopia can be obtained by occlusion and full-time refractive correction. CONCLUSIONS. The evolution of refraction seems to be different in eyes with anisometropia and it is still to be understood whether it is fixation or reduced fixation that leads to a myopic shift.

The challenge of fitting astigmatic eyes: Rigid gas-permeable toric lenses

It is generally acknowledged that rigid gas permeable lenses (RGP) afford superior visual correction of the ametropic eye compared with hydrophilic lenses. However, there are occasions when a spherical rigid lens will not provide an acceptable result in terms of fitting or vision on astigmatic eyes. In these instances a toric RGP lens will be required. This paper deals with the definitions, indications, fitting technique, calculations and designs relating to this modality of fitting. Whilst often perceived as a complex area within contact lens practice, the basic optics and fitting of toric RGP lenses is not overly difficult. A simple empirical means of fitting the lenses will be described which has a high ‘First-fi’ success rate.

New matrix formulation of spectacle magnification using pupil magnification. I. High myopia corrected with ophthalmic lenses

In this paper we have applied the matrix method to calculating spectacle magnification (SM) and relative spectacle magnification (RSM) for myopic eyes corrected with ophthalmic lenses (OLs). We have been able to obtain very simple expressions of the magnifications and analogous values to the ones obtained using other geometric methods. Through the paraxial 2 × 2 object—image matrix for spherical systems, we can calculate the correcting lens pupil matrix (ML) and the corrected ametropic eye pupil matrix (Mca). These two matrices, that is ML and Mca, directly provide the lateral magnification and the lens—eye system's image focal parameters that enable us to easily calculate SM and RSM. The magnifications have been calculated for the case of myopic eyes corrected with OLs, which shows the validity of this method since its results are similar to the ones obtained using other methods. The analysis of other correcting systems such as contact intraocular lenses will be presented in two associated papers (to be published as parts II and III of this review).

New matrix formulation of spectacle magnification using pupil magnification. I. High myopia corrected with ophthalmic lenses

SummaryIn this paper we have applied the matrix method to calculating spectacle magnification (SM) and relative spectacle magnification (RSM) for myopic eyes corrected with ophthalmic lenses (OLs). We have been able to obtain very simple expressions of the magnifications and analogous values to the ones obtained using other geometric methods. Through the paraxial 2 × 2 object‐image matrix for spherical systems, we can calculate the correcting lens pupil matrix (ML) and the corrected ametropic eye pupil matrix (Mca). These two matrices, that is ML and Mca, directly provide the lateral magnification and the lens‐eye system's image focal parameters that enable us to easily calculate SM and RSM. The magnifications have been calculated for the case of myopic eyes corrected with OLs, which shows the validity of this method since its results are similar to the ones obtained using other methods. The analysis of other correcting systems such as contact intraocular lenses will be presented in two associated papers (to be published as parts II and III of this review).

Myopia among optometry students.

Four hundred forty-seven of five hundred beginning 2nd-year optometry students responded to a survey requesting them to report the equivalent sphere of the lenses neutralizing their most ametropic eye and, if myopic, the age at which they were first prescribed lenses. The population was 20% female, 80% male, and predominately Caucasian. The mean refractive status was -2.21 D with a range from -11.00 to +5.50 D. Seventy-five percent of the respondees were myopes. There was a clear relation between final amount of myopia and the age at which corrective lenses were first prescribed. New myopes did not seek care in equal numbers at each age, but instead clustered in three groups: ages 8 to 9 years, 12 to 13 years, and 19 years. Regression characteristics were different when myopes of 0.12 to 6.00 D were segregated from the total group, suggesting different rates of change, and, by implication, different populations within the group. Females tended to become myopic earlier. There were proportionately more high myopes among the females than among the males.

Distortion by ophthalmic lenses calculated at the farpoint sphere.

Distortion by ophthalmic lenses has generally been calculated with respect to an ideal flat image surface. This results in improper distortion values as the ideal image surface for the mobile eye is the farpoint sphere. Results of distortion calculations for lenses ranging from +20 to -24.65 D are given for point focal lenses (corrected for oblique astigmatism), Percival lenses (designed to place the circle of least confusion on the farpoint sphere), minimum astigmatism and minimum distortion lens forms. Distortion of point focal Ostwalt lenses of powers +6.60 to -24.65 D range from 4.45 to -28.31% when computed at the flat image surface. Referred to the farpoint sphere the corresponding distortion values are +0.85 to -13.54%. Similarly, the distortion of the minimum astigmatic forms of lenses ranging in power from +20 to +7 D are +27.31 to 4.64% at the flat image surface but decreased to +16.38 to 0.84%, respectively, at the farpoint sphere. If the rotations of the unaided ametropic eye that are required to fixate two points in the field are compared with the necessary rotations with a spectacle correction (+20 to -24 D), it is found that the corrected eye rotation errors at the flat image surface range from 14.87 to -4.53%, but drop to +0.87 to -1.88% when referred to the farpoint sphere. It is concluded that distortion at the farpoint sphere is a more valid measure of distortion for the mobile eye than the classical measurement of distortion. This has implications for the study of space perception through lenses.

Telescopic Magnification in Uncorrected Ametropia

SummaryTelescopic magnification for a distant object varies somewhat when the telescope is changed from its normal adjustment for an emmetropic eye, to an adjustment that will suit an eye with uncorrected ametropia. The separation of the two lenses in the telescope must be altered. A simple method is shown for calculating the change in the separation of the lenses and the change in the magnification which is produced when used by an uncorrected ametropic eye. The magnification is less in myopia and greater in hyperopia. Both angular and linear magnification are discussed.

Ocular Dioptrics and Lenses.

This book deals with the theory and practice of ophthalmic optics and the clinical management of errors of refraction. Beginning with the simple laws of refraction, the reader is carried through the mathematical and graphic reasoning and solution of the formulas for a simple refracting system, the commoner forms of ophthalmic lenses ; the correction of the ametropic eye and the imagery of the eye and a lens being described. There are a number of original diagrams. Although it is not so stated, the book is meant to be more in the nature of an essay than of a textbook. For while the author goes into considerable detail to explain mathematically the basic principles and fundamentals of optics, nevertheless there is no doubt that he takes it for granted that the reader is already familiar with the subject. In the opinion of the reviewer, it seems that a work of