The differing impact of induced astigmatic blur on crowded and uncrowded paediatric visual acuity chart results

Comparative Analysis of Tolerance to Experimentally Induced Astigmatism with Three Types of Multifocal Intraocular Lenses

Purpose

The effect of residual astigmatism and its axis on distance and near visual acuities (VAs) with multifocal intraocular lenses (IOLs) has not been studied extensively. This study compared the tolerance to experimentally induced residual astigmatism among bifocal, trifocal, and extended depth-of-focus (EDOF) IOLs.

Patients and Methods

This retrospective, comparative study included 70 eyes of 70 patients implanted with bifocal, trifocal, or EDOF IOLs. Distance and near VAs were assessed with experimentally induced astigmatism by placing positive cylindrical lenses in increments of 0.50 diopters to 2.00 diopters at 90° and 180° axes over the best distance correction.

Results

Both distance and near VAs worsened with increasing magnitudes of experimentally induced astigmatism except in the EDOF group, in which the near VA remained within a clinically acceptable limit, ie, within one line from the best corrected VA under all ranges of experimentally induced astigmatism. Furthermore, the EDOF group showed the highest astigmatic threshold for losing VA lines following experimental astigmatic induction at both distance and near. The distance VA was generally better at with-the-rule (WTR) than against-the-rule (ATR) astigmatism for all three IOL groups. On the other hand, the near VA was generally better at WTR than ATR astigmatism in the bifocal group, comparable between WTR and ATR astigmatism in the trifocal group, and generally better at ATR than WTR astigmatism in the EDOF group.

Conclusion

The EDOF IOL demonstrated the highest tolerance to experimentally induced astigmatism at both distance and near. VA was generally less affected by WTR astigmatism than ATR astigmatism, especially at distance. We proposed the residual astigmatism thresholds for clinically acceptable VA reduction in all three IOL groups.

Discrimination of paediatric acuity test optotypes by 6-year-old children

PURPOSE

To compare the discrimination performance of 6-year-old children for optotypes from six paediatric visual acuity tests and to fit Luce's Biased Choice Model to the data to estimate the relative similarities and bias for each optotype.

METHODS

Full data sets were collected from 20 typically developing 6-year-olds who had passed a vision screening. They were presented with single optotypes labelled 6/12 at a distance of 9 m and were asked to identify the optotype using a matching task containing all optotypes from the relevant test. The data were combined to form a confusion matrix for each test and a biased choice model was fitted to the data.

RESULTS

Median correct performance varied from 40% to 100% across optotypes, with the HOTV test having the highest values. Estimates of the similarity of each pair of optotypes indicated equal values for all pairs in the Landolt C, HOTV, Lea numbers and Tumbling E tests. The values differed for the picture tests, that is Lea Symbols and Allen figures. The estimates of bias for each individual optotype also indicated different values with the picture tests.

CONCLUSIONS

Previous studies of the threshold acuity of young children and adults have indicated differences in acuity estimates across paediatric tests. A recognition acuity task typically requires resolving the difference information between optotypes. The performance of the 6-year-olds here reveals variance in similarity and bias values for picture tests, particularly for the Allen figures when compared with the Lea Symbols. Ideally, this analysis should be performed when designing new tests, and these results motivate progression from the use of current picture tests to well calibrated letter or number tests at the earliest possible age.

Factors associated with reduced visual acuity in myopes with and without ocular pathologies after optical correction

PURPOSE

Considering that a certain proportion of high myopes have reduced visual acuity even after full optical correction, this study aimed to investigate the association between various refractive error components (sphere, cylinder and axis orientation) and reduced visual acuity in individuals with low to high myopia with and without pathologic myopia lesions.

METHODS

We analysed data from randomly selected eyes of 11,258 individuals with myopia (mean ± SD spherical equivalent (SE) -3.2 ± 2.9D; range: -0.5D to -21.5D). In total, 10,528 individuals had no pathologic myopia lesions. Sphere, cylinder and SE refraction were classified into mild, moderate and high categories. Astigmatism was defined as with-the-rule, against-the-rule or oblique based on the axis orientation. Reduced best-corrected visual acuity was defined as ≥0.18 logMAR. Logistic regression was performed to test factors associated with reduced visual acuity with and without pathologic myopia lesions.

RESULT

Overall, 6.4% (N = 720/11,258) of myopes had reduced best-corrected visual acuity. High sphere (≤-6.0D; Odd ratios [OR]: 16.1; 95% CI: 2.1-126.5), high cylinder (<-2.0 DC; OR: 2.5; 95% CI: 1.8-3.4), against-the-rule (OR: 1.5; 95% CI: 1.1-2.0) and oblique astigmatism (OR: 1.6; 95% CI: 1.2-2.1) were significantly (p ≤ 0.008) associated with reduced visual acuity in the absence of pathologic myopia lesions. Both moderate SE and high myopic SE were also associated with reduced visual acuity. In the presence of pathologic myopia lesions, tessellated fundus (OR: 6.9; 95% CI: 3.5-14.1), chorioretinal atrophy (OR: 7.7; 95% CI: 2.6-19.9) and choroidal neovascularisation (OR: 37.4; 95% CI: 3.3-419.3) were significantly (p ≤ 0.003) associated with reduced visual acuity.

CONCLUSION

Even after full optical correction, both refractive components and pathologic myopia lesions can independently cause reduced visual acuity, regardless of the degree of myopia.

Laser keratomileusis in treatment of anisometropic amblyopia in adults

PURPOSE

To compare and evaluate improvement in corrected distant visual acuity (CDVA) between myopia and hyperopia after laser in situ keratomileusis (LASIK) in adult patients with anisometropic amblyopia.

MATERIALS AND METHODS

This prospective clinical study included 103 amblyopic eyes (103 patients), which underwent LASIK correction of refractive error from January 2013 to January 2018. Uncorrected distance visual acuity (UDVA), CDVA, spherical equivalent (SE), postoperative astigmatism, and intraocular pressure were evaluated at time points of 1, 6, and 12 months.

RESULTS

Patients were divided into two groups according to refractive error. Group 1: Forty-six patients with myopia and Group 2: Fifty-seven patients with hyperopia. Mean CDVA (logarithm of the minimum angle of resolution [logMAR]) preoperatively was 0.23 ± 0.16 in Group 1 and 0.40 ± 0.19 in Group 2. Postoperative CDVA (logMAR) was 0.17 ± 0.13 in Group 1 and 0.32 ± 0.17 in Group 2. There was statistically significant increase in UDVA (P < 0.0001) postoperatively and no change during the follow-up period of 12 months in both groups. Group 1 showed more expectable results, 95% of variability SE achieved was dependent on SE intended (R² = 0.95), while in Group 2, the percentage was slightly lower of expected 87% (R² = 0.87). There was statistical significance in respect of CDVA change postoperatively and preoperatively in both groups. Correlation factors are low, in Group 1 r = -0.53 and in Group 2 r = -0.39.

CONCLUSION

LASIK can improve CDVA in a considerable portion of amblyopic eyes, both myopic and hyperopic. Eyes with better initial CDVA and those with myopia were associated with greater improvement in postoperative CDVA.

Effect of simulated refractive error on adult visual acuity for paediatric tests

PURPOSE

Although vanishing optotype preferential-looking tasks are commonly used to measure visual acuity (VA), the relative sensitivity of these tests to refractive error is not well understood. To address this issue, we determined the effect of spherical and astigmatic simulated refractive errors on adult VA measures obtained using vanishing optotypes, picture optotypes and Sloan letters.

METHODS

VA was determined uniocularly for adults under conditions of spherical (0.0-3.0 DS; n = 23) and astigmatic (0.0-3.0 DC at 90° and 180°; n = 20) defocus using the Cardiff Acuity Test (vanishing optotypes), crowded linear Lea Symbols (picture-optotype recognition task) and the Early Treatment of Diabetic Retinopathy Study (ETDRS) letter chart.

RESULTS

The Cardiff Acuity Test over-estimated VA compared with the Lea Symbols and ETDRS charts in both focused and defocused conditions. The mean difference between the Cardiff Acuity Test and the ETDRS chart was 0.31 logMAR (95% limits of agreement (LOA) 0.10-0.52 logMAR) in focused conditions and 0.64 logMAR (95% LOA 0.25-1.05 logMAR) with 3D of spherical defocus. Defocus degraded VA on all charts, however there was a significant chart-by-defocus interaction whereby the Cardiff Acuity Test was more resistant to the effects of both spherical (P < 0.0001) and cylindrical (P < 0.001) optical defocus than the recognition acuity tasks at all defocus levels.

CONCLUSION

Although the Cardiff Acuity Test provides an easy method for VA measurement in infants and toddlers, there is a considerable overestimation of VA compared with recognition acuity tasks particularly in the presence of defocus. A simple correction factor (of for example three lines overestimate) cannot be applied to Cardiff acuity measures as there is increasing over-estimation of VA with increasing defocus. Infants with significant refractive error may fall within normal visual acuity ranges for the Cardiff Acuity Test.

Do picture-based charts overestimate visual acuity? Comparison of Kay Pictures, Lea Symbols, HOTV and Keeler logMAR charts with Sloan letters in adults and children

Purpose

Children may be tested with a variety of visual acuity (VA) charts during their ophthalmic care and differences between charts can complicate the interpretation of VA measurements. This study compared VA measurements across four pediatric charts with Sloan letters and identified chart design features that contributed to inter-chart differences in VA.

Methods

VA was determined for right eyes of 25 adults and 17 children (4–9 years of age) using Crowded Kay Pictures, Crowded linear Lea Symbols, Crowded Keeler logMAR, Crowded HOTV and Early Treatment of Diabetic Retinopathy Study (ETDRS) charts in focused and defocused (+1.00 DS optical blur) conditions. In a separate group of 25 adults, we compared the VA from individual Kay Picture optotypes with uncrowded Landolt C VA measurements.

Results

Crowded Kay Pictures generated significantly better VA measurements than all other charts in both adults and children (p < 0.001; 0.15 to 0.30 logMAR). No significant differences were found between other charts in adult participants; children achieved significantly poorer VA measurements on the ETDRS chart compared with pediatric acuity tests. All Kay Pictures optotypes produced better VA (p < 0.001), varying from -0.38 ± 0.13 logMAR (apple) to -0.57 ± 0.10 logMAR (duck), than the reference Landolt C task (mean VA -0.19 ± 0.08 logMAR).

Conclusion

Kay Pictures over-estimated VA in all participants. Variability between Kay Pictures optotypes suggests that shape cues aid in optotype determination. Other pediatric charts offer more comparable VA measures and should be used for children likely to progress to letter charts.

Crowded letter and crowded picture logMAR acuity in children with amblyopia: a quantitative comparison

Aims

Clinically, picture acuity tests are thought to overestimate visual acuity (VA) compared with letter tests, but this has not been systematically investigated in children with amblyopia. This study compared VA measurements with the LogMAR Crowded Kay Picture test to the LogMAR Crowded Keeler Letter acuity test in a group of young children with amblyopia.

Methods

58 children (34 male) with amblyopia (22 anisometropic, 18 strabismic and 18 with both strabismic/anisometropic amblyopia) aged 4–6 years (mean=68.7, range=48–83 months) underwent VA measurements. VA chart testing order was randomised, but the amblyopic eye was tested before the fellow eye. All participants wore up-to-date refractive correction.

Results

The Kay Picture test significantly overestimated VA by 0.098 logMAR (95% limits of agreement (LOA), 0.13) in the amblyopic eye and 0.088 logMAR (95% LOA, 0.13) in the fellow eye, respectively (p<0.001). No interactions were found from occlusion therapy, refractive correction or type of amblyopia on VA results (p>0.23). For both the amblyopic and fellow eyes, Bland-Altman plots demonstrated a systematic and predictable difference between Kay Picture and Keeler Letter charts across the range of acuities tested (Keeler acuity: amblyopic eye 0.75 to −0.05 logMAR; fellow eye 0.45 to −0.15 logMAR). Linear regression analysis (p<0.00001) and also slope values close to one (amblyopic 0.98, fellow 0.86) demonstrate that there is no proportional bias.

Conclusions

The Kay Picture test consistently overestimated VA by approximately 0.10 logMAR when compared with the Keeler Letter test in young children with amblyopia. Due to the predictable difference found between both crowded logMAR acuity tests, it is reasonable to adjust Kay Picture acuity thresholds by +0.10 logMAR to compute expected Keeler Letter acuity scores.

The influence on unaided vision of age, pupil diameter and sphero-cylindrical refractive error

BACKGROUND

The aim was to derive equations for the relationship between unaided vision and age, pupil diameter, iris colour and sphero-cylindrical refractive error.

METHODS

Data were collected from 663 healthy right eyes of white subjects aged 20 to 70 years. Subjective sphero-cylindrical refractive errors ranged from -6.8 to +9.4 D (mean spherical equivalent), -1.5 to +1.9 D (orthogonal component, J0 ) and -0.8 to 1.0 D (oblique component, J45 ). Cylinder axis orientation was orthogonal in 46 per cent of the eyes and oblique in 18 per cent. Unaided vision (-0.3 to +1.3 logMAR), pupil diameter (2.3 to 7.5 mm) and iris colour (67 per cent light/blue irides) was recorded. The sample included mostly females (60 per cent) and many contact lens wearers (42 per cent) and so the influences of these parameters were also investigated.

RESULTS

Decision tree analysis showed that sex, iris colour, contact lens wear and cylinder axis orientation did not influence the relationship between unaided vision and refractive error. New equations for the dependence of the minimum angle of resolution on age and pupil diameter arose from step backwards multiple linear regressions carried out separately on the myopes (2.91.scalar vector +0.51.pupil diameter -3.14 ) and hyperopes (1.55.scalar vector + 0.06.age - 3.45 ).

CONCLUSION

The new equations may be useful in simulators designed for teaching purposes as they accounted for 81 per cent (for myopes) and 53 per cent (for hyperopes) of the variance in measured data. In comparison, previously published equations accounted for not more than 76 per cent (for myopes) and 24 per cent (for hyperopes) of the variance depending on whether they included pupil size. The new equations are, as far as is known to the authors, the first to include age. The age-related decline in accommodation is reflected in the equation for hyperopes.

Impact of simulated hyperopia on academic-related performance in children

PURPOSE

To investigate the impact of simulated hyperopia and sustained near work on children's ability to perform a range of academic-related tasks.

METHODS

Fifteen visually normal children (mean [±SD] age, 10.9 [±0.8] years; 10 male and 5 female) were recruited. Performance on a range of standardized academic-related outcome measures was assessed with and without 2.50 diopters of simulated bilateral hyperopia (administered in a randomized order), before and after 20 minutes of sustained near work, at two separate testing sessions. Academic-related measures included a standardized reading test (the Neale Analysis of Reading Ability), visual information processing tests (the Coding and Symbol Search subtests from the Wechsler Intelligence Scale for Children), and a reading-related eye movement test (the Developmental Eye Movement test).

RESULTS

Simulated bilateral hyperopia and sustained near work each independently impaired reading, visual information processing, and reading-related eye movement performance (p < 0.001). A significant interaction was also demonstrated between these factors (p < 0.05), with the greatest decrement in performance observed when simulated hyperopia was combined with sustained near work. This combination resulted in performance reductions of between 5 and 24% across the range of academic-related measures. A significant moderate correlation was also found between the change in horizontal near heterophoria and the change in several of the academic-related outcome measures, after the addition of simulated hyperopia.

CONCLUSIONS

A relatively low level of simulated bilateral hyperopia impaired children's performance on a range of academic-related outcome measures, with sustained near work further exacerbating this effect. Further investigations are required to determine the impact of correcting low levels of hyperopia on academic performance in children.

The visual and functional impacts of astigmatism and its clinical management

PURPOSE

To provide a comprehensive overview of research examining the impact of astigmatism on clinical and functional measures of vision, the short and longer term adaptations to astigmatism that occur in the visual system, and the currently available clinical options for the management of patients with astigmatism.

RECENT FINDINGS

The presence of astigmatism can lead to substantial reductions in visual performance in a variety of clinical vision measures and functional visual tasks. Recent evidence demonstrates that astigmatic blur results in short-term adaptations in the visual system that appear to reduce the perceived impact of astigmatism on vision. In the longer term, uncorrected astigmatism in childhood can also significantly impact on visual development, resulting in amblyopia. Astigmatism is also associated with the development of spherical refractive errors. Although the clinical correction of small magnitudes of astigmatism is relatively straightforward, the precise, reliable correction of astigmatism (particularly high astigmatism) can be challenging. A wide variety of refractive corrections are now available for the patient with astigmatism, including spectacle, contact lens and surgical options.

CONCLUSION

Astigmatism is one of the most common refractive errors managed in clinical ophthalmic practice. The significant visual and functional impacts of astigmatism emphasise the importance of its reliable clinical management. With continued improvements in ocular measurement techniques and developments in a range of different refractive correction technologies, the future promises the potential for more precise and comprehensive correction options for astigmatic patients.

[Induced astigmatism after corneal suture removal after cataract surgery]

PURPOSE

To evaluate the time until astigmatic stabilization after corneal suture removal after cataract surgery.

METHODS

A prospective study was performed on 13 patients who had undergone cataract surgery by phacoemulsification with 2.4mm incision, for whom it was felt necessary to remove a corneal suture. A specular corneal topography was performed by OPD Scan before removal, immediately after, then 10, 20, 30 minutes and 15 days later. For each acquisition, the keratometric readings at the steepest (Kmax) and the flattest (Kmin) meridians (central at 1.15 mm from corneal center, intermediate at 2.30 mm and peripheral at 3.30 mm) and the amount of corneal astigmatism were measured.

RESULTS

Corneal topography of 13 patients was acquired. Mean age was 70 ± 12 years. Mean time after cataract surgery was 23 ± 14 days. The greatest change in Kmax occurred within the first minutes following suture removal for the central and intermediate cornea (mean variation of -4.38% and -4.59% of initial Kmax respectively, i.e. -2.04 D ± 3.14 D et -2.15 D ± 3.11 D) whereas it was observed between 0 and 10 minutes for the peripheral area (mean 1.57% of Kmax after suture removal i.e. 0.96 D ± 1.85 D). Mean change in corneal astigmatism between 30 minutes and day 15 was 0.08 D ± 0.31 D (3.6% of baseline). When suture removal was performed between 7 and 10 days postoperatively, mean change was 0.16 D ± 0.24 D, whereas it was 0.03 D ± 0.34 D when performed after four weeks.

CONCLUSION

Keratometric readings vary only slightly beyond the first 30 minutes after suture removal. These results suggest that the refraction could be accurately measured the same day as suture removal, with no additional follow-up absolutely necessary in order to prescribe the final spectacles.