Spherical Refractive Error Research Articles

Hemidivisional vector planning to reduce and regularize irregular astigmatism by laser treatment

PurposeTo demonstrate how hemidivisional vector planning of refractive laser treatments of astigmatism can be used to directly address idiopathic corneal irregular astigmatism that has an asymmetrical, non-orthogonal bow tie topography appearance.DesignCase study.MethodsThe cornea is conceptually divided into two hemidivisions along the flat meridian of the corneal topographic astigmatism (CorT), which means that each hemidivision will approximately correspond to one lobe of the asymmetric, non-orthogonal topographic bow tie. An astigmatism reduction treatment can then be planned separately for each hemidivision using the vector planning technique, based on both its two hemidivisional CorT measures and common manifest refractive cylinder. The remaining irregularity is then regularized, and the junctional zone smoothed across the flat meridian. The final intended treatment thus combines hemidivisional astigmatism reduction and regularization of the corneal astigmatism and spherical refractive error in one treatment application. This could be applied to LASIK, PRK, SMILE, and Transepithelial PRK procedures using Designer Cornea® software.ResultsA theoretical treatment profile is derived from an actual example of a cornea with idiopathic asymmetric non-orthogonal astigmatism. The three steps of the derivation are as follows: (i) astigmatism reduction through the use of the vector planning technique; (ii) regularization, and (iii) smoothing across the hemidivisional midline.ConclusionsHemidivisional vector planning treatments could potentially both reduce and regularize asymmetric non-orthogonal astigmatism. These treatments can be systematically customized to account for qualitative and quantitative differences between the two corneal hemidivisions at the same time as correction of coexistent myopia or hyperopia.

Preliminary Evaluation of a Smartphone App for Refractive Error Measurement.

PurposeThe purpose of this study was to evaluate the potential feasibility of using a smartphone app in myopia screening.MethodsThe app estimates myopic refractive error by measuring the far point distance for reading three 20/20 Tumbling E letters. In total, 113 myopic subjects with astigmatism no greater than −1.75 diopters (D) were enrolled from 5 sites. The mean age was 22 ± 8.5 years. The app measurement was compared with noncycloplegic subjective refraction measurement or autorefractor if subjective refraction was not available. In addition, 22 subjects were tested with the app for repeatability.ResultsFor 201 eyes included, the range of spherical equivalent refraction error was 0 to −10.2 D. The app measurement and clinical measurement was highly correlated (Pearson R = 0.91, P < 0.001). There was a small bias (0.17 D) in the app measurement overall, and it was significantly different across the 5 sites due to different age of subjects enrolled at those sites (P = 0.001) – young adults in their 20s were underestimated the most by 0.49 D, whereas children were overestimated by 0.29 D. The mean absolute deviation of the app measurement was 0.65 D. The repeatability of multiple testing in terms of 95% limit of agreement was ±0.61 D.ConclusionsOverall, the app measurement is consistent with clinical measurement performed by vision care professionals. The repeatability is comparable with that of some autorefractors. Age-associated human factors may influence the app measurement.Translational RelevanceThe app could be potentially used as a mass screening tool for myopia.

Accuracy of Toric Intraocular Lens Axis Alignment Using Manual Slit Lamp Method and CALLISTO Eye Image-Guided System

Aims: Image-guided systems are the gold standard for determining toric intraocular lens (IOL) axis alignment. However, their high cost prevents widespread use of these systems. As an alternative, a simpler and affordable method could be performed manually using a slit-lamp biomicroscope. This study aims to compare the accuracy of manual toric IOL axis marking using a slit-lamp compared to the CALLISTO eye image-guided system.&#x0D; Study Design: Prospective comparative&#x0D; Methods: In this prospective study, toric IOL axis alignment of 42 eyes with cataract and coexisting corneal astigmatism were evaluated using manual slitlamp method and CALLISTO eye image-guided method. Preoperative and postoperative uncorrected visual acuity, best corrected visual acuity, amount of spherical and astigmatic refractive errors, and postoperative IOL axis alignment were evaluated. Intraclass correlation of the manual method was calculated and the difference of IOL axis alignment to the image-guided method was compared.&#x0D; Results: Toric IOL implantation reduced the amount of astigmatic refractive error from -1.63 ± 0.65 D to -0.50 ± 0.19 D in the image-guided group and from -1.93 ± -0.90 D to -0.87 ± 0.26 D in the manual slitlamp group. As many as 90.5% of eyes in the image-guided group and 81.0% of eyes in the manual slitlamp group reached the target induced astigmatism (p=0.38). Manual axis marking showed intraclass correlation of 99.3%. However, when the manual method was compared to the image-guided method a mean difference in axis alignment of 10.98o (95% confidence interval: 9.32o - 12.63o) was observed.&#x0D; Conclusions: Alignment of toric IOL axis using the manual method demonstrated a consistent result; yet producing a considerable difference to the result of the image-guided method.

18-month results of double-fanged 5-0 polypropylene suture transscleral bag fixation in subluxated cataracts.

To evaluate the stability and efficacy of the double-flanged 5-0 polypropylene suture to fixate subluxated cataracts at 18 months and the possible complications of this new technique. This technique uses a 5-0 polypropylene monofilament to create two flanges with a thermocautery, for fixation of a capsular tension segment to the sclera to fix the subluxated capsular bag. This technique was implemented in 17 eyes requiring intraocular lens implantation in a setting of zonular dialysis due to trauma, Marfan syndrome, microspherophakia, idiopathic disease, and post-phacoemulsification status. Follow-up of the patients occurred at 18 months. Best-corrected visual acuity improved significantly from 0.85 to 0.39 (logMAR), whereas the spherical and cylindrical refractive errors and intraocular pressure remained stable from preoperation. No suture photodegradation or pseudophacodonesis were detected. The double-flanged 5-0 polypropylene suture transscleral bag fixation technique has shown favorable long-term outcomes in terms of bag intraocular lens/complex fixation and stability. In eyes with zonular weakness or dialysis, this technique appears to be a safe and knotless option for cataract surgery.

Post-operative outcomes of small-incision lenticule extraction in patients with moderate to high astigmatism.

Purpose:To evaluate the visual outcomes of patients who underwent small-incision lenticule extraction (SMILE) for the treatment of myopic astigmatism with high cylinders (>2.5 diopters, D).Methods:Forty-two eyes of myopic astigmatism with a spherical error of magnitude between − 0.5 and − 6.0 Ds, cylindrical error of − 2.5 to − 4.5 Dcyl were included in the retrospective study. All patients were tested preoperatively and on days 1, 10, and 30 for uncorrected distance visual acuity, manifest refraction, and corrected distance visual acuity. Additional preoperative assessments were done including measurement of corneal thickness, corneal topography, and examination for ocular surface disease. All procedures were performed by a single experienced surgeon. VisuMax laser system (Carl Zeiss Meditec AG, Jena, Germany) was utilized for all the corrective refractive procedures.Results:Forty-two eyes were included. The logarithm of the minimum angle of resolution Uncorrected distance visual acuity (UDVA) was 1 ± 0.25 preoperatively and 0.00 ± 0.00 on postoperative day 30. There was no loss of corrected distance visual acuity (CDVA) lines.Conclusion:SMILE is a successful procedure in the treatment of both myopic spherical and cylindrical refractive errors including high cylindrical errors >-3 to − 4.5 Dcyl.

Perfecting Laser Treatment for Regular and Irregular Astigmatism

Perfecting the treatment of regular and irregular astigmatism using laser-assisted in situ keratomileusis, photorefractive keratectomy, and small in situ lenticule extraction is possible by reducing and regularizing the asymmetric, non-orthogonal corneal shape while correcting spherical refractive error. Such perfecting treatment may be achieved by conceptually dividing the cornea into two hemidivisions and applying vector planning to optimally customize each half of the cornea to the minimum regular astigmatism possible. This innovative treatment could improve best-corrected visual acuity and minimize aberrations.

Estimation of Intraocular Lens Power Calculation Formula in Irregular Astigmatism With Normal Axial Length Eyes

Background and Objectives: We evaluated the intraocular lens power calculation (IOL) formulas in eyes with cataracts and irregular astigmatism who have undergone cataract surgery. Methods: In a retrospective case series, 50 eyes with cataracts and irregular astigmatism who underwent phacoemulsification with IOL implantation were assessed. The IOL power was determined using the data of the keratometry of IOL master-derived keratometry in five formulas: Haigis, Hoffer Q, Holladay 1, SRK2 and SRKT. One month after surgery, refractive error and visual acuity were assessed. Results: The Mean±SD age of participants was 66.10±6.57 years (ranged 32-83). The percentage of male and female subjects was 45.8% and 54.2%, respectively. The axial length was 19.00mm to 23.00mm, which is a normal range. The most and least used formulas were SRKT and Haigis, respectively. Astigmatism and spherical refractive errors before and after surgery had significant differences (P&lt;0.001). There was a decrease in astigmatism and hyperopic shift after surgery. Conclusion: SRKT is a suitable formula for this group of patients. According to a decrease in astigmatism and hyperopic shift, an improvement in visual acuity can be expected.

Comparison of subconjunctival microinvasive glaucoma surgery and trabeculectomy.

To assess surgical success and the post-operative development of intraocular pressure between XEN45® gelstent, Preserflo® MicroShunt and trabeculectomy with mitomycin C. Data from 105 eyes from 105 patients of matched cases with refractory open-angle glaucoma, who underwent surgery between January 2019, and August 2020, were evaluated. Patients underwent either stand-alone XEN gelstent insertion with Mitomycin C, stand-alone Preserflo with Mitomycin C or trabeculectomy with Mitomycin C. The primary outcome was the proportion of complete surgical success at 6 months post-operatively (i.e. intraocular pressure between 5mmHg and 18mmHg, no revision surgery, no loss of light perception and no post-operative pharmaceutical antiglaucomatous treatment). The reduction of intraocular pressure after 6 months, the classes of antiglaucomatous medication used post-operatively, best-corrected visual acuity, spherical refractive errors and astigmatism were assessed as secondary outcomes. We included 35 eyes in each group. After 6-month follow-up, complete success was 73.5% [95%-CI: 57.9%-89.2%] in the trabeculectomy group, 51.4% [95%-CI: 34.0%-68.8%] in the XEN group and 74.2% [95%-CI: 57.9%-90.5%] in the Preserflo group (p = 0.08). Regarding secondary outcomes, the reduction of intraocular pressure was 12.1 ± 7.9 mmHg in the trabeculectomy group and was thereby 5.8 [95%-CI: 2.2-9.6] mmHg greater compared with the XEN group (p < 0.001) and 4.8 [95%-CI: 0.9-8.7] mmHg higher than the Preserflo group (p = 0.01). No statistically significant differences were found between trabeculectomy, XEN45® gelstent implantation and Preserflo® MicroShunt implantation regarding surgical success after 6 months. Yet reduction in intraocular pressure was significantly higher in the trabeculectomy group. However, all three interventions resulted in sufficiently low post-operative intraocular pressure and may therefore be considered individually for glaucoma treatment.

Initial Power of Rigid Gas Permeable Contact Lenses in Patients with Keratoconus.

Purpose:To simplify the fitting process, this study was designed to predict the initial power of contact lenses using the regression model based on manual Javal keratometry data and refractive errors.Methods:In this retrospective study, 121 eyes of 69 patients with keratoconus (KCN) were fitted with a specific trial set of rigid gas permeable contact lenses based on the standard criterion of “three-point touch” over a 7-year period. Power of the cornea was measured using Javal keratometer. Refractive errors and over refraction of patients were diagnosed using Topcon autorefractometer (RM-A2000) and confirmed by Heine beta 2000 retinoscope.Results:The results of multiple linear regression showed the following equation: power of contact lens = −14.368 (constant of the final multiple regression model), +0.475 (spherical refraction), and +0.275 (flatter corneal power).Conclusions:The results of this study revealed that lens power has a significant relationship with the power of the flat corneal meridian and spherical refractive error in KCN patients. The obtained regression model can be used to shorten patients’ chair time and optometric examination for predicting the power of contact lens.

Effects of varying illumination on ocular aberrations and aberration compensation before and after small incision Lenticule extraction: a prospective cohort study

BackgroundThere are few reports regarding the influence of varying illumination on the compensation effect before and after corneal refractive surgery. We aimed to evaluate the changes in refraction, higher-order aberrations, and aberration compensation between mesopic and photopic illumination before and after small incision lenticule extraction.MethodsIn this prospective cohort study, only the right eyes of patients who underwent small incision lenticule extraction for the correction of myopia and myopic astigmatism at the Tianjin Eye Hospital were included. Wavefront refraction and higher-order aberrations were measured preoperatively and 3 months postoperatively under mesopic and photopic illumination. Compensation factors were calculated as 1 − (aberration of the whole eye/aberration of the anterior corneal surface).ResultsForty patients undergoing small incision lenticule extraction were enrolled. All surgeries were completed without postoperative complications. Preoperatively, the eyes only had a statistically significantly higher (t = − 4.589, p < .001) spherical refractive error under mesopic vs. photopic illumination (median [interquartile range], − 6.146 [2.356] vs. − 6.030 [2.619] diopters [D]), whereas postoperatively, the eyes also exhibited statistically significantly higher (t = − 3.013, p = .005) astigmatism (− 0.608 [0.414] vs. − 0.382 [0.319] D). Differences in spherical refraction between the two illuminations were the highest in postoperative eyes (Δ > 0.5 D). Only postoperative eyes exhibited statistically significant elevations (t ≥ 4.081, p < .001) in higher-order aberrations under mesopic illumination, and only preoperative eyes exhibited statistically significantly enhanced (χ2 = 6.373, p = .01 for fourth-order and χ2 = 11.850, p = .001 for primary spherical aberrations) and decreased (χ2 = 13.653, p = .001 for horizontal trefoil) compensation factors under mesopic illumination.ConclusionsExaggerations in higher-order aberrations and myopic shift after small incision lenticule extraction became apparent under mesopic illumination. Slight undercorrection may have an enhanced effect under low illumination and may reduce night vision. The specific changes in compensation effects in preoperative eyes may improve optical quality under mesopic illumination. Postoperative eyes have reduced compensation ability, specifically for spherical aberrations, under mesopic illumination, which may diminish night vision. Further studies that include the measurement of subjective night vision parameters should be conducted.

Evaluate the Prevalence, Natural Course, and Final Visual Acuity in Patients with Stages III or IV of Diffuse Lamellar Keratitis Following Laser in Situ Keratomileusis

Background: And aim: The prevalence of DLK has been reported differently in different centers based onits severity. Hence, the aim of present study was evaluate the prevalence, natural course, and final visualacuity in patients with stages III or IV of diffuse lamellar keratitis following laser in situ keratomileusis.Methods: In the present descriptive study, 3941 eyes files from 2125 patients underwent LASIK surgery;were examined. All patients had a complete ophthalmologic examination before LASIK and had suitableconditions for LASIK.Result: Among the studied cases, 39 eyes (0.98%), out of 16 patients (0.75). The mean time intervalbetween LASIK and DLK diagnosis was 3± 2.4 days. A history of allergy was negative in all patients. Themean post-operative spherical refractive error in all eyes was in the range of 1 diopters and the averagecylindrical refractive error in 33 eyes was -0.66±1.2 diopters. The mean of final spherical refraction in34 eyes was 0.5±1.2 diopter and the mean of final cylindrical refraction in 35 eyes was -0.75±1.3 diopter.Severe turbidity at the flap surface in the first week decreased over time in all patients with stage III and IVDLK. So that only in four eyes (10.25%)Conclusion: The prevalence of stages III and IV in DLK is negligible compared to the large number ofLASIK procedures and all patients respond well to topical and systemic corticosteroid therapy.

Bruch membrane opening-minimum rim width and retinal nerve fiber layer thickness in myopic children

Background/objectivesIt is debatable whether the decrease of retinal nerve fiber layer (RNFL) thickness in myopic people under 18 years of age is due to insufficient measurement techniques or to real physical loss of retinal ganglion cells and axons. Hence, to better understand the relationship between the degree of myopia and the neuroretinal rim (NR), we aim to investigate the NR in the eyes of healthy myopic children using the novel measurement algorithms of spectral-domain optical coherence tomography (SD-OCT). Subjects/methodsThis prospective, cross-sectional study includes 378 left eyes of 378 (301 female) participants divided into three groups according to their spherical equivalent (SE) refractive error (RE) [Group-1(G1), -1.00 ≤ SE ≤ 1.00 diopters (D); Group-2 (G2), -4.00 ≤ SE < -1.00 D; Group-3 (G3), SE<-4.00 D]. All participants underwent a full ophthalmic examination, including biometric and pachymetric measurements. Standard peripapillary RNFL, as well as the novel algorithms, Bruch's membrane opening-minimum rim width (BMO-MRW), and RNFL acquired using the anatomic positioning system (APS-RNFL) were obtained by SD-OCT. Nasal, temporal, temporal-inferior, temporal-superior, nasal-inferior, nasal-superior sectors’ and their general (global) averages were recorded. Rim areas and disc sizes were measured via confocal scanning laser ophthalmoscopy. Global and the six sectors’ averages were recorded. ResultsG1 consisted of 141 subjects, G2 consisted of 89, and G3 consisted of 48. The sex distribution (p = 0.112) and mean age (p = 0.129) of the groups were similar. The mean global averages of the standard RNFLs were 96 ± 14.4 µ in G1, 93.8 ± 12.9 µ in G2, and 86 ± 11.8 µ in G3. The mean global averages of the APS-RNFLs were 103.9 ± 97 µ in G1, 103.3 ± 10.6 µ in G2, and 102 ± 10.6 µ in G3. The mean global averages of the BMO-MRW were 374.4 ± 57.7 µ in G1, 373.2 ± 62.2 µ in G2, and 351.9 ± 63.9 µ in G3. For the global averages, APS-RNFL and BMO-MRW did not detect any difference between the three groups (p = 0.563, p = 0.089, respectively), but the standard RNFL did (p < 0.001). Standard RNFL and APS-RNFL were found to be well correlated; however, the correlations between BMO-MRW and standard RNFL or APS-RNFL were either absent or very weak. All three methods showed weak but significant negative correlations with high myopic spherical RE, especially those in the standard RNFL. Moderately negative correlations were found between BMO-MRW and disc size in all sectors (highest in the nasal sector; r = -0.387, p < 0.001). However, there was almost no significant relationship between disc size and standard RNFL or APS-RNFL. Moderately significant negative correlations were observed between the groups categorically and standard RNFL in almost all sectors, while this was much less with APS-RNFL and was not observed in almost any sector with BMO-MRW. ConclusionsWhen evaluating the NR in healthy myopic children, it was found that, in particular, BMO-MRW and APS-RNFL are less effected by RE degree compared to standard RNFL. BMO-MRW and APS-RNFL should be used on these children to avoid the possible misdiagnosis of glaucoma.

Effect of Opposite Clear Corneal Incision (CCI) on Corneal Higher-Order Aberrations after Phacoemulsification

Abstract Background: Nowadays, care of a cataractous patient greatly exceeds surgical removal of the opacified lens. In a step foreword to welfare of the elderly, phacoemulsification can perform as a refractive tool, addressing both spherical and astigmatic refractive errors. Aim of Study: The aim of that work was to evaluate safety and effectiveness of OCCIs, as an innovative procedure for correction of corneal astigmatism, during phacoemulsification. Patients and Methods: The study assessed 64 patients, who underwent phacoemulsification. Pre-operative and post-operative corneal topography was done, documented and statistically analyzed for each patient. Results: The study revealed a decrease of pre-operative corneal astigmatism from a pre-operative mean of –1.78D to a post-operative mean of 1.09D in OCCI group and a decrease of pre-operative corneal astigmatism from a pre-operative mean of –1.71D to a postoperative mean of 1.29D in single incision group. Conclusion: The present study revealed that OCCIs with appropriate pre-operative corneal topography represent a real advance in the applications of refractive lenticular surgery. OCCIs provide an innovative technique for managing pre-operative, regular, corneal astigmatism. This is simple, easy to learn technique, with no extra instrumentation. The OCCIs in this study was safe, with no wound related complications. However, OCCIs require careful early post-operative care, due to their penetrating nature. Once the wounds are sealed, risk of further complications approaches zero. Further studies on that technique, employing different incision architecture are required to help development of nomograms correlating the incision length, width, age of the patient, and the amount of pre-operative corneal astigmatism to be corrected.

A Novel Use of Retinoscopy for the Evaluation of Binocular Balance of Spherical Refractive Errors

ABSTRACT Purpose Binocular balancing is an important component of refractive correction to avoid asthenopic complaints. Polaroid filters are commonly used for binocular balancing; they rely on subjective examination and cannot represent daily visual activities. We describe a new examination approach to evaluate binocular balance with retinoscopy, which is an objective examination method and does not require strict patient cooperation. Methods Healthy young individuals with refractive errors (under the age of 40) were included in this study. Each patient was examined by three different ophthalmologists in the same room at 20-min intervals. The first ophthalmologist performed refractive examination separately for each eye, the second physician used binocular balance tests with polaroid glasses, and the third physician practiced binocular balance test with retinoscopy. After completion of clinical examinations, autorefractometry was repeated with cycloplegia. The difference between the spherical equivalents (SE) of the eyes was calculated for each method and compared with the SE difference obtained by cycloplegic autorefractometry. The SPSS 21.0 software was used for the statistical tests. Results The study included 30 patients (16 males, 14 females) and the mean age of the patients was 21 ± 8.5 years (range 10–37 years). There was no significant difference between the four groups for the interocular difference of SE (Greenhouse–Geisser F = 1.390, p = 0.257). The highest correlation was found between the retinoscopic binocular balance technique and cycloplegic autorefractometry (r = 0.878, p < 0.001). In addition, the intraclass correlation coefficient and the 95% limits of agreement supported strong agreement. Conclusion Currently used binocular examination tests are subjective and some patients give inconsistent answers impairing the reliability of the outcome. These tests cannot be performed on patients with limited ability to cooperate. This study demonstrates that the use of retinoscopy in the evaluation of binocular balance delivers reliable results and is a low-cost, practical approach to address the above-mentioned problems.

The utility of a direct ophthalmoscope in estimating the magnitude of refractive error using a modification of the Brückner test

ABSTRACT Objective To evaluate the utility of a direct ophthalmoscope in detecting the type and magnitude of refractive error using a modified Brückner test. Methods In a prospective observational study, participants between the ages of 10 to 40 years underwent direct ophthalmoscopy by a single observer, using a modified interpretation of the Brückner test. The results were compared with the adjusted spherical equivalents obtained from retinoscopy (RSE), and subjective correction (SSE). The inter-test agreement, sensitivity, specificity, and predictive values were calculated. Results A total of 598 eyes were evaluated. In the eyes with a normal glow, the modified Brückner technique had a substantial degree of agreement when compared with techniques of retinoscopy, subjective refractive assessment in predicting the type of refractive error (κ > 0.75). In comparison with the SSE, the test was around 90% sensitive in detecting the presence of hyperopia and myopia of more than 2 diopters, if the upper or lower crescents respectively, were large enough to cross the midline of the pupil. Conclusion A direct ophthalmoscope is useful in diagnosing the presence and magnitude of spherical refractive errors. Clinical trial registration Clinical Trials Registry – India (CTRI) No.: CTRI/2018/09/015711; http://ctri.nic.in/Clinicaltrials/pmaindet2.php?trialid=24928&EncHid=&userName=refractive%20errors

Factors Influencing Higher-order Aberrations in Young Myopes

Purpose : To investigate the effects of age, refractive errors, corneal refractive power, pupil diameter, and pupil center shift on high-order aberrations (HOAs) in young myopic eyes. Methods : The myopic eyes of aged 20 to 39 years who had no ophthalmologic diseases and refractive surgery were recruited. I-Profilerplus (Zeiss, Berlin, Germany) was used to measure HOAs and refractive errors, corneal refractive power, pupil diameter, and pupil shift, and factors affecting HOA were analyzed. Results : In young myopes, as the age increased, the total HOA was increased in the positive (+) direction (p<0.001), and the horizontal coma, vertical coma, and spherical aberration (SA) were increased in the negative (-) direction (all, p<0.001). As the equivalent spherical refractive errors increased in the negative (-) direction, the total HOA was increased in the negative (-) direction (p<0.001), and the SA was increased in the positive (+) direction (p=0.004). As the mean corneal refractive power increased, the total HOA and SA were increased in the negative (-) direction (p<0.001, p=0.025), and the horizontal coma and vertical coma aberration were increased in the positive (+) direction (p=0.001, p<0.001). As the pupil diameter increased, vertical trefoil and SA were increased in the positive (+) direction (all, p<0.001). As the pupil center shift increased toward the lateral, the horizontal coma aberration increased in the positive (+) direction (p=0.003), and as the pupil center shift increased toward the superior, the vertical coma aberration increased positive (+) direction (p<0.001). Conclusion : The ocular HOAs of the young myopes changes according to age, refractive error, corneal refractive power, pupil size, and pupil center shift and the results in this study would be cornerstones in designing lenses for spectacle and contact lens.

Flitcroft’s model of refractive development in childhood and the possible identification of children at risk of developing significant myopia

PurposeTo better understand juvenile myopia in the context of overall refractive development during childhood and to suggest more informative ways of analysing relevant data, particularly in relation to early identification of those children who are likely to become markedly myopic and would therefore benefit from myopia control. MethodsExamples of the frequency distributions of childhood mean spherical refractive errors (MSEs) at different ages, taken from previously-published longitudinal and cross-sectional studies, are analysed in terms of Flitcroft’s model of a linear combination of two Gaussian distributions with different means and standard deviations. Flitcroft hypothesises that one, relatively-narrow, Gaussian (Mode 1) represents a “regulated” population which maintains normal emmetropisation and the other, broader, Gaussian (Mode 2) a “dysregulated” population. ResultsAnalysis confirms that Flitcroft’s model successfully describes the major features of the frequency distribution of MSEs in randomly-selected populations of children of the same age. The narrow “regulated” Gaussian typically changes only slightly between the ages of about 6 and 15, whereas the mean of the broader “dysregulated” Gaussian changes with age more rapidly in the myopic direction and its standard deviation increases. These effects vary with the ethnicity, environment and other characteristics of the population involved. At all ages there is considerable overlap between the two Gaussians. This limits the utility of simple refractive cut-off values to identify those children likely to show marked myopic progression. ConclusionsAnalysing the frequency distributions for individual MSEs in terms of bi-Gaussian models can provide useful insights into childhood refractive change. A wider exploration of the methodology and its extension to include individual progression rates is warranted, using a range of populations of children exposed to different ethnic, environmental and other factors.

Effect of axial length and anterior chamber depth on the peripheral refraction profile.

To evaluate the effect of axial length (AL) and anterior chamber depth (ACD) on peripheral refractive profile in myopic patients compared to emmetropic participants. This cross-sectional study was conducted in right eyes of 58 participants of whom 38 were emmetropic and 20 were myopic. Central and peripheral refraction were measured at 10°, 20°, and 30° eccentricities in nasal and temporal fields using an open-field autorefractor. The Lenstar LS900 was used to measure ACD and AL. The participants were divided into three groups of short (<22.5 mm), normal (22.5-24.5 mm), and long eye (>24.5 mm) according to AL and three groups of low ACD (<3.00 mm), normal ACD (3.00-3.60 mm), and high ACD (>3.60 mm) according to ACD. The mean age of the participants was 22.26±3.09y (range 18-30y). The peripheral mean spherical refractive error showed a hypermetropic shift in myopic and emmetropic groups although this shift was more pronounced in the myopic group. The results showed significant changes in the spherical equivalent, J0, and J45 astigmatism in all gazes with an increase in eccentricity (P<0.001). The pattern of refractive error changes was more noticeable in long and short eyes versus normal AL eyes. Moreover, the pattern of peripheral refractive changes was much more prominent in the high ACD group versus the normal ACD group and in the normal ACD group versus the low ACD group. Peripheral refraction changes are greater in participants with AL values outside the normal range and deeper ACD values compared to participants with normal AL and ACD.

Comparison between optical and digital blur using near visual acuity

In a low-cost laboratory setup, we compared visual acuity (VA) for stimuli rendered with Zernike aberrations to an equivalent optical dioptric defocus in emmetropic individuals using a relatively short observing distance of 60 cm. The equivalent spherical refractive error of + 1, + 2 or + 4 D, was applied in the rendering of Landolt Rings. Separately, the refractive error was introduced dioptrically in: (1) unchanged Landolt Rings with an added external lens (+ 1, + 2 or + 4 D) at the subject's eye; (2) same as (1) but with an added accommodation and a vertex distance adjustment. To compare all three approaches, we examined VA in 10 healthy men. Stimuli were observed on a PC CRT screen. For all three levels of refractive error, the pairwise comparison did not show a statistically significant difference between digital blur and accommodation-plus-vertex-distance-adjusted dioptric blur (p < 0.204). The best agreement, determined by Bland–Altman analysis, was measured for + 4 D and was in line with test–retest limits for examination in the clinical population. Our results show that even for a near observing distance, it is possible to use digitally rendered defocus to replicate dioptric blur without a significant change in VA in emmetropic subjects.

Abobotulinum toxin A for periorbital facial rejuvenation: impact on ocular refractive parameters

ABSTRACT Clinical relevance Botulinum toxin is commonly used for cosmetic facial rejuvenation and can result in pain at the injected site, bruising and ecchymosis, erythema and oedema, headache, diplopia, blurred vision, focal facial weakness. This study evaluates the impact of botulinum toxin on refractive error and binocular vision. Background Botulinum toxin (trade name: Dysport) is a neurotoxic protein which is made from a Gram‐positive anaerobic bacterium known as Clostridium botulinum. In this study, we aimed to evaluate the impact of Dysport injection on refractive error, near point of accommodation and convergence, and palpebral fissure height. Methods Twenty‐eight subjects were treated for facial wrinkles, using Dysport. A 500‐unit vial of Dysport was diluted with 2.5-ml preserved normal saline, and injected doses were 30-units for crow’s feet, six units for lower eyelid wrinkles, 25 to 50-units for glabellar lines (five points), and 20 to 40 for forehead creases on four points. The refractive error, near point of accommodation and convergence and palpebral fissure heights were assessed before and two weeks after injection. Results The participants comprised 23 women and five men at a mean age of 53.51 ± 14.1-years. The means of the equivalent sphere before and after injection were −0.07 ± 1.34 and −0.08 ± 1.35 (p = 0.36). The means of near point of accommodation monocularly before and after injection were 29.75 ± 6.16-cm and 26.75 ± 6.00, respectively. The means of near point of convergence before and after injection were 16.03 ± 5.27-cm and 15.55 ± 6.14, respectively (p = 0.30). The means of palpebral fissure height before and after injection were 10.33 ± 1.69-mm and 10.20 ± 1.46-mm, respectively. The changes in equivalent spherical refractive error, binocular near point of accommodation and convergence were not statistically significant. Conclusion Dysport injection for the correction of upper face animation lines, if performed at the appropriate sites and the appropriate concentration, has no significant impact on refractive error, near point of accommodation and convergence, and palpebral fissure height.