Influence Of Refractive Error Research Articles

Ophthalmic fundus camera design based on freeform surface for reducing refractive error sensitivity

The eye has a remarkably complex structure and biomechanics. An imbalance between the forces acting on several muscles and the tissue properties may alter or even preclude vision. With the widespread use of electronics, refractive errors have become a common problem, making clear fundus imaging difficult. To overcome this challenge, freeform surfaces have emerged as a potential solution, enabling compact, low-cost, and user-friendly systems that are insensitive to refractive errors. We propose a fundus camera based on a freeform surface that can image the fundus without the influence of refractive errors. A special front lens was designed to image the pupil on a freeform lens that can realize phase modulation. The system performs well providing a field of view of 40∘ and a pupil diameter of 3 mm for refractive errors ranging from -5D to +5D. The volume of the system was less than 35 mm × 35 mm × 135 mm.

The effect of uncorrected ametropia on ocular torsion induced by changes in fixation.

Background and ObjectiveOcular torsion, the eye movements to rotating around the line of sight, has not been well investigated regarding the influence of refractive errors. The purpose of this study was to investigate the effect of uncorrected ametropia on ocular torsion induced by fixation distances.MethodsSeventy-two subjects were classified according to the type of their refractive error, and ocular torsion of the uncorrected eye was compared based on changes induced by different fixation distances. Ocular torsion was measured using a slit-lamp biomicroscope equipped with an ophthalmic camera and a half-silvered mirror.ResultsIn all groups, excyclotorsion values increased as the fixation distance decreased, but the myopia and astigmatism groups had larger amounts of ocular torsion than the emmetropia group. In addition, as the amount of uncorrected myopia and astigmatism increased, the amount of ocular torsion increased.ConclusionSince the amount of ocular torsion caused by a change to a shorter fixation distance was larger when the refractive error was uncorrected, we suggest that ametropia should be fully corrected in patients frequently exposed to ocular torsion due to changes in fixation distance.

Influence of refractive error on pupil diameters in highly myopic eyes with implantable collamer lenses.

To investigate the influence of refractive error on pupil diameters in highly myopic eyes with implantable collamer lenses. Shanghai, China. A prospective consecutive observational study. Sixty-six eyes of 66 patients that underwent ICL V4c implantation were included. Pupil diameters before and 1 week, 1 month, and 3 months after surgery were measured using an automatic pupillometry system (MonCv3; Metrovision, Pérenchies, France) under four standardized illumination conditions: 0, 1, 10, and 100 cd/m2. The correlations between changes in pupil diameter and spherical equivalent values and patient age were investigated. Based on preoperative spherical equivalent values, included eyes were divided into a high-myopia group (-6.3 to -9.9 D (diopters)) and a super-high-myopia group (-10 to -20 D). Pupil sizes remained unchanged after surgery in the high-myopia group and decreased at 1 and 10 cd/m2 in the super-high-myopia group. A between-group comparison showed that pupils were significantly smaller in the super-high-myopia group 1 week postoperatively under all illumination conditions and remained smaller at 1 month and 3 months under 1 and 10 cd/m2 lighting conditions. Preoperative spherical equivalent values were significantly correlated with the percent decrease in pupil diameter 1 week postoperatively under 0, 1, and 10 cd/m2 illumination conditions; the greater the degree of myopia, the greater the reduction in pupil diameter. Preoperative refractive error significantly affects pupil diameter in highly myopic eyes after implantable collamer lens implantation. Pupils of super highly myopic eyes remained smaller than preoperative levels under mesopic conditions after implantable collamer lens implantation.

Influence of refractive error on pupillary dynamics in the normal and mild traumatic brain injury (mTBI) populations

PurposeThere have been several studies investigating static, baseline pupil diameter in visually-normal individuals across refractive error. However, none have assessed the dynamic pupillary light reflex (PLR). In the present study, both static and dynamic pupillary parameters of the PLR were assessed in both the visually-normal (VN) and the mild traumatic brain injury (mTBI) populations and compared as a function of refractive error. MethodsThe VN population comprised 40 adults (22–56 years of age), while the mTBI population comprised 32 adults (21–60 years of age) over a range of refractive errors (−9.00D to +1.25D). Seven pupillary parameters (baseline static diameter, latency, amplitude, and peak and average constriction and dilation velocities) were assessed and compared under four white-light stimulus conditions (dim pulse, dim step, bright pulse, and bright step). The Neuroptics, infrared, DP-2000 binocular pupillometer (30Hz sampling rate; 0.05mm resolution) was used in the monocular (right eye) stimulation mode. ResultsFor the majority of pupillary parameters and stimulus conditions, a Gaussian distribution best fit the data, with the apex centered in the low myopic range (−2.3 to −4.9D). Responsivity was reduced to either side of the apex. ConclusionsOver a range of dynamic and static pupillary parameters, the PLR was influenced by refractive error in both populations. In cases of high refractive error, the PLR parameters may need to be compensated for this factor for proper categorization and diagnosis.

Testing macular letter recognition ‐ reliability and influence of refraction errors

PurposeThe goal was the validation of the Macular Mapping Test (MMT) for clinical use. We studied its susceptibility to blur caused by refractive errors and its test‐retest reliability.MethodsWe tested letter recognition in 33 target locations in the central visual field (10° radius) at two contrast levels, 10 and 100 per cent. Healthy subjects were either young (mean: 25.7-years) or elderly (mean: 67.0-years). A third group (patients with age‐related macular degeneration, mean age: 76.4-years) were tested with their habitual optical correction and subsequently with optimal correction. The influence of refractive errors on performance was measured only for the healthy subgroups. All visual acuities were measured at 6.0 and 0.4 metres. Outcome measure was the ‘general field score’ (GFS), a single number expressing the overall level of letter recognition performance.ResultsThe general field score versus refractive error showed a mean loss of 3.9 points per dioptre and 5.9 points per dioptre in young subjects at 100 and 10 per cent contrast, respectively. In elderly subjects, mean losses were 2.6 points per dioptre and 5.5 points per dioptre for 100 and 10 per cent contrast, respectively. The general field score ratio (GFS at 10 per cent divided by GFS at 100 per cent) shows a decrease of eight per cent for the young group and 11 per cent for the elderly group.Performance increased after improvement of the refractive status in the AMD group: At 100 per cent contrast, the general field score increase from 21.5 to 24.1 (p < 0.008) was significant but not at 10 per cent contrast. Mean increase of acuity with the optimal correction was 0.32 to 0.46 decimal for distance (p = 0.018) and 0.28 to 0.44 decimal near (p = 0.018). Test‐retest reliability was good but dependent on contrast.ConclusionsAt both contrasts, performance declined with increasing blur caused by refractive errors. The slope of this decline is more pronounced at the lower contrast. In healthy subjects, optical blur beyond 1.00 D can cause significant performance losses.

Retinal Nerve Fiber Layer Thickness in Normal Chinese Students Aged 6 to 17 Years

We obtained retinal nerve fiber layer (RNFL) thickness measurements in normal Chinese students aged 6 to 17 years, and investigated the relationship between RNFL thickness and sex, eye laterality, age, axial length, and refractive error. A total of 4648 eyes in 2324 normal, randomly-selected Chinese students aged 6 to 17 years was examined in this study. The RNFL thickness was measured by optical coherence tomography. The effects of sex, eye laterality (left or right), age, refractive error, and axial length on RNFL thickness were assessed. The average age of the subjects was 12.82 ± 3.11 years. The global average RNFL thickness (±SD) was 106.89 ± 12.84 μm. The thickest RNFL measurements were found at the superior (133.22 ± 19.48 μm) and inferior (129.23 ± 20.30 μm) quadrants of the retina, followed by the temporal (93.58 ± 29.15 μm) and nasal (77.10 ± 14.89 μm) quadrants. In the 1529 participants aged 12 to 17, there were no significant differences in RNFL thickness values between the right and left eyes (P > 0.05); significant differences in RNFL were found only in the inferior and temporal quadrants of the retina in different sex groups (P < 0.05). Linear regression analysis revealed that the RNFL thickness values were correlated independently with axial length and refractive error (P < 0.05). For clinical assessment of RNFL thickness, the influence of refractive error and axial length should be taken into account.

Brain activation of eye movements in subjects with refractive error.

Recent functional magnetic resonance imaging (fMRI) studies have described reorganized activation of the oculomotor and visual cortex after focal brain lesions. These studies are based on comparison with healthy individuals who may have a very heterogenous refractive error. The influence of refractive error on the cortical control of an oculomotor task such as a prosaccade trial, however, is unknown. To investigate the influence of visual acuity on changes of cortical oculomotor control, we studied the representation of visually guided prosaccades in nine subjects with refractive error and 11 normally sighted subjects using fMRI. Correction of refractive error was not allowed during fMRI. Differences in activation between rest and saccades as well as between subjects with refractive error vs subjects with normal vision were assessed with statistical parametric mapping. In both groups, activation of a frontoparietal network was observed. Subjects with refractive errors showed increased activation compared to normally sighted subjects, with overactivation in bilateral frontal and parietal eye fields, supplementary eye fields, as well as in the bilateral extrastriate cortex. This group of subjects with refractive error showed increased activation in an extended oculomotor and visual network to maintain performance during simple prosaccades. This observation underlines the importance of using appropriate control groups in fMRI-studies after brain lesions.

The influence of refractive errors on IOP measurement by rebound tonometry (ICare) and Goldmann applanation tonometry

To evaluate the effect of refractive errors and central corneal thickness (CCT) on the measurement of intraocular pressure (IOP) by ICare rebound tonometer (RT), and its agreement with measurements by Goldmann applanation tonometer (GAT). Two observers measured the IOP by using RT and GAT in four groups of healthy volunteers with emmetropic (n = 78), hyperopic (n = 83), myopic (n = 87) and astigmatic (n = 79) eyes. Refraction was assessed by an autorefractometer. CCT was assessed by ultrasound pachymetry. In all groups, no significant interobserver difference was seen in IOP values detected by both tonometers (Wilcoxon signed-rank test not significant). In all groups, IOP values were higher as measured by RT than by GAT (paired t-test p = 0.000): mean RT-GAT difference was higher in myopic eyes (+1.6 +/- 1.8 mmHg), and it was less than 1 mmHg in the other groups. RT-GAT difference was correlated to the refraction (p < 0.001), and it was greater when an higher IOP was detected by RT (significant correlation between RT-GAT difference and IOP by RT, p < 0.001). Compared with GAT values, the IOP readings by RT were greater than 2 mmHg in respectively 17.9% (emmetropic), 13.3% (hyperopic), 34.5% (myopic) and 7.6% (astigmatic) of the eyes. With both tonometers, in all groups the IOP values were correlated with CCT (p < 0.05), but the discrepancy between RT and GAT values was not related to CCT. In all groups of subjects, higher IOP values were detected by RT; the IOP readings exceed the GAT values usually in a range of less than 1 mmHg, except when RT detects IOP >18 mmHg and generally in myopic eyes; RT-GAT discrepancy is related to the refractive error, but not to CCT.

Influence of scan radius correction for ocular magnification and relationship between scan radius with retinal nerve fiber layer thickness measured by optical coherence tomography.

To investigate how optical coherence tomography (OCT) modifies the preset scan parameters to correct the errors resulting from ocular magnification, the influence of examiner's final correction of those already modified parameters on retinal nerve fiber layer (RNFL) thickness measurements, the induced change on RNFL thickness measurements and RNFL estimated integrals (RNFL(estimated integrals)) by adjusting the actual scan radius during RNFL examinations performed by OCT. Thirty-five healthy patients underwent an RNFL examination by OCT four times using different scan radii. The first scan was performed with the preset circular scan diameter of 3.46 mm; the actual scan diameter was different, however, because it was modified by the OCT instrument. The second, third, and fourth scans were generated after readjusting the already modified scan diameter by the examiner to 3.46, 3.20, and 3.60 mm. The relationship of axial length and refractive error with the actual scan radius (with ocular magnification calculated by OCT), with the influence of the examiner's final correction on RNFL thickness measurements, with the relationship between scan radius with RNFL thickness measurements, and with RNFL(estimated integrals) were investigated. The actual scan diameter was found to be primarily determined by axial length (R = 0.97, P < 0.0001), but the influence of refractive error was small (R = -0.26, P = 0.067). Final correction of the actual scan radius by the examiner had a significant influence on RNFL thickness measurements (P = 0.025). RNFL thickness measurements obtained without correction of the actual scan radius for magnification were found to be inversely correlated with axial length (R = -0.54, P = 0.001), whereas no similar relationship was found when RNFL thickness measurements were obtained with correction (R = 0.21, P = 0.11). A reciprocal relationship between 1/scan radius with RNFL thickness measurements (they tended to be thinner as scan radii were increased) was found (R = 0.41, P = 0.169), but RNFL(estimated integrals) areas were found to be independent of the scan radius (P = 0.521). To increase the accuracy of RNFL thickness measurements, it will be appropriate for the examiner to manually correct the actual scan parameters to the desired or preset ones after their automatic modification performed by the OCT instrument. Keeping the actual scan radius constant for repeated exams is also recommended because RNFL thickness measurements were found to depend on scan size. Alternatively, RNFL(estimated integrals) could be used because they were found to be independent of the scan size.

A CENTRAL VISION SCOTOMETER

In case there is no opacity of the media of the eye, low central vision may be due to two causes : a refractive error or a centrally located defect in the sensorium. The separation of these two causes presents a somewhat difficult problem in diagnosis. Among the possibilities available the following may be noted: ( a ) An attempt may be made to improve vision by corrective glasses. ( b ) The eye may be refracted by one or more of the objective methods. ( c ) The influence of refractive errors may be reduced to a minimum by the use of a very small artificial pupil in close proximity to the cornea. ( d ) With the best corrective glass that can be obtained, an examination may be made for a central scotoma. In the instrument to be described, the following selection is made from these possibilities: The eye is rendered practically independent of refraction, and