Snellen Visual Acuity Measurements Research Articles

Comparison of Snellen Visual Acuity Measurements in Retinal Clinical Practice to Electronic ETDRS Protocol Visual Acuity Assessment

Evaluate the differences between clinical visual acuity (VA) as recorded in medical records and electronic Early Treatment Diabetic Retinopathy Study (eETDRS) protocol VA measurements and factors affecting the size of the differences. Retrospective chart review. Study and fellow eyes of participants enrolled in DRCR Retina Network Protocols AC and AE (diabetic macular edema), and W (nonproliferative diabetic retinopathy) with clinical VA recorded within 3 months before the protocol visit. Differences and their association with patient and ocular factors were evaluated using linear mixed models with random effects for correlations within sites and participants. Difference between VA letter scores measured by eETDRS during a study visit versus measured by Snellen during a regular clinical visit (Snellen fraction converted to eETDRS). Data from 1016 eyes (511 participants) across 74 sites were analyzed. The mean VA measurements were 68.6 letters (Snellen equivalent 20/50) at the clinical visit and 76.3 letters (Snellen equivalent 20/32) at the protocol visit, with a mean (standard deviation [SD]) of 26 (21) days between visits. Mean (SD) protocol VA was better than clinical VA by 7.6 (9.6) letters overall, 10.7 (12.6) letters in eyes with clinical VA ≤ 20/50 (n= 376), and 5.8 (6.6) letters in eyes with clinical VA ≥ 20/40 (n= 640). On average, the difference between clinical and protocol VA was 1.3 letters smaller for every 1-line (5 letters) increase in clinical VA (P < 0.001). Mean (SD) differences by clinical correction of refractive error were 3.9 (9.0) letters with refraction, 6.9 (9.2) letters with glasses/contact lenses, 7.9 (11.5) letters with pinhole, and 9.8 (9.3) letters without correction (P= 0.06). On average, clinical Snellen VA is 1 to 2 lines worse than eETDRS protocol refraction and VA testing, which may partly explain why clinical practice does not always replicate clinical trial results. Eyes with lower clinical measurements and eyes tested without clinical refraction tended to have larger differences. Considering the potential discrepancies between clinical and protocol VA measurements, refracting eyes in the clinic may benefit patients when determining treatment plans and study referrals based on vision. Proprietary or commercial disclosure may be found after the references.

Comparison of sweep visual evoked potential of visual acuity and Snellen visual acuity in healthy and amblyopic children.

To evaluate the visual acuity of healthy and amblyopic children using sweep visual evoked potential and compare the results with those of Snellen visual acuity testing. A total of 160 children aged 6-17 years were included in the study. Of these, 104 (65%) were aged 7-17 years old, able to verbally communicate, and did not have any systemic or ocular pathology (Group 1). Group 2 included 56 (35%) children aged 6-17 years, able to verbally communicate, and had strabismus or anisometropic amblyopia whose best corrected visual acuity was between 0.1 and 0.8. All subjects underwent a detailed ophthalmological examination and sweep visual evoked potential measurement. Demographic characteristics, ocular findings, best corrected visual acuity, and sweep visual evoked potential results were recorded. In Group 1, the mean and maximum visual acuity values for sweep visual evoked potential were lower than the Snellen best corrected visual acuity (p<0.001, for both, respectively). Bland-Altman analysis revealed that in Group 1, the distribution of the differences between the Snellen best corrected visual acuity and mean sweep visual evoked potential visual acuity was ±0.11 logMAR, and the distribution of the differences between the Snellen best corrected visual acuity and maximum sweep visual evoked potential visual acuity was ±0.023 logMAR. In Group 2, the mean and maximum sweep visual evoked potential visual acuity were lower than the Snellen best corrected visual acuity (p<0.001 and p=0.009, respectively). Bland-Altman analysis revealed that the distribution of the differences between the Snellen best corrected visual acuity and mean sweep visual evoked potential visual acuity was ±0.16 logMAR, and the distribution of the differences between the Snellen best corrected visual acuity and maximum sweep visual evoked potential visual acuity was ±0.19 logMAR. Sweep visual evoked potential visual acuity measurements have comparable results with Snellen visual acuity measurements. This technique is an objective and reliable method for evaluating visual acuity in children.

USE OF A CARBONIC ANHYDRASE INHIBITOR IN X-LINKED RETINOSCHISIS: Effect on Cystic-Appearing Macular Lesions and Visual Acuity.

To evaluate changes in cystic-appearing macular lesions and visual acuity in patients with X-linked retinoschisis while being treated with a carbonic anhydrase inhibitor. A retrospective analysis of 68 eyes from 36 patients between the ages of 5 years and 61 years with X-linked retinoschisis were monitored while on a carbonic anhydrase inhibitor. Macular cystic-appearing lesions were monitored with optical coherence tomography. Snellen visual acuity measurements were converted to logarithm of the minimum angle of resolution equivalent Early Treatment Diabetic Retinopathy Study letters for analysis. Analyses for changes in both visual acuity and macular cysts included comparisons between treatment and pretreatment segments. Forty-five eyes (66%) had a reduction of their cysts while on a carbonic anhydrase inhibitor. Twenty eyes (29%) showed no cystic change, whereas 3 eyes (4%) demonstrated worsening of their cysts with treatment when compared with pretreatment. There was a statistically significant improvement in logarithm of the minimum angle of resolution visual acuity while on treatment relative to pretreatment (P < 0.0001). The estimated average Early Treatment Diabetic Retinopathy Study equivalent improvement was 0.09 (slightly less than one line on the Early Treatment Diabetic Retinopathy Study chart) with a 95% confidence interval of 0.08 to 0.11. Considering the entire 36 patients in this cohort, while statistically significant, the average improvement in visual acuity was modest. Nonetheless, in individual patients, the improvement was more substantial. Improvement in the extent of cystic macular lesions was observed in a high percentage of cases.

LASIK monocular en pacientes adultos con ambliopía por anisometropía

PurposeTo investigate the efficacy and safety of LASIK for the correction of anisometropic amblyopia in adult patients. MethodsA retrospective, case series. We found 12 amblyopic adult patients that underwent monocular LASIK for anisometropía in our Cornea and Refractive service. We evaluated the preoperative and postoperative refractive error, spherical equivalent (SE), uncorrected visual acuity (UCVA) and best corrected visual acuity (BCVA). Snellen visual acuity measurements were converted to LogMAR for statistical purposes. ResultsThe mean age was 31.92 (±12.13) years. The average preoperative SE in the treated eyes was -3.49 (±3.24), the average SE of the untreated eye was 0.25(±0.30). Preoperative UCVA was 1.12 (±0.3) and average preoperative BCVA was 0.31 (±0.1). All patients had LASIK with an average follow-up time of 19.1(6-74) months. The average postoperative SE decreased to -0.28 (±0.48). Five patients (42%) gained 1 line of vision, 1 (8%) patient gained 2 lines of vision, 1 (8%) patient gained 3 lines of vision and the rest (42%) remained unchanged compared to preoperative BCVA. Statistically significant differences were observed between the preoperative UCVA [1.12 (±0.3)] with the postoperative UCVA [0.27 (±0.1)](p=0.002, Z-Wilcoxon) and between the postoperative BCVA [0.23 (±0.12)] with the preoperative BCVA [0.31 (±0.1)] (p=0.014, Z-Wilcoxon). There were no complications related to the surgical procedures. ConclusionsMonocular refractive surgery in adult patients with anisometropic amblyopia is a safe and effective therapeutic option that offers a satisfactory visual outcome, preserving or even improving the preoperative BCVA.

Comparing Treatment Options of Pterygium: Limbal Sliding Flap Transplantation, Primary Closing, and Amniotic Membrane Grafting

To compare 3 surgical treatment options of pterygium: limbal sliding flap transplantation, primary closing, and amniotic membrane grafting methods. Seventy-five patients with primary pterygium were included in the study. Snellen visual acuity measurement, grading pterygium, slit-lamp examination, keratometry, and anterior segment photography were performed preoperatively. Twenty-eight eyes of 28 patients (group 1) underwent limbal-conjunctival sliding flap transplantation, 22 eyes of 22 patients (group 2) underwent amniotic membrane grafting, and 25 eyes of 25 patients (group 3) underwent primary closing surgery. The patients were followed up on the first day and the first week after surgery and then at months 1, 3, 6, and 12. The mean size of the pterygium preoperatively was 3.58 ± 1.1 mm in group 1, 3.95 ± 0.90 mm in group 2, and 3.5 ± 0.87 mm in group 3. The mean follow-up time was 15.07 ± 13.8 months in group 1, 20.2 ± 6.7 months in group 2, and 28.04 ± 9.9 months in group 3. Grade 4 corneal recurrence rate in follow-up was 7.1% in group 1, 27.3% in group 2, and 56% in group 3 (p = 0.00). Mean recurrence times were 4.0 ± 1.7, 4.4 ± 3.3, and 4.4 ± 3.6 months according to groups 1, 2, and 3 (p = 0.963). After the surgery, corneal astigmatism decreased and keratometric values increased significantly in all the groups with no statistically significant difference between the groups (p>0.05). Limbal-conjunctival sliding flap transplantation is an efficient method to manage primary pterygium. It may be a safe and effective initial treatment option to reduce risk of recurrence and postoperative complications of pterygium surgery.

NOVEL METHOD FOR ANALYZING SNELLEN VISUAL ACUITY MEASUREMENTS

Most retrospective reviews convert Snellen visual acuity measurements obtained during routine clinic visits to logarithm of the minimum angle of resolution (logMAR) units so that statistical manipulations can be performed. However, visual acuity measurements expressed as logMAR units are not intuitively interpretable by clinicians. A more intuitive approach is presented here which uses the conversion of Snellen visual acuity fractions to Early Treatment Diabetic Retinopathy Study (ETDRS) letter scores for statistical manipulations. Snellen visual acuity measurements were converted to approximate ETDRS (approxETDRS) letter scores for statistical manipulations and then converted back to Snellen equivalent fractions. The formula to convert Snellen visual acuity measurements to approxETDRS letter scores is 85 + 50 x log (Snellen fraction), which may be rounded to the nearest letter. A linear relationship exists between true ETDRS letter scores, approxETDRS letter scores, and logMAR units. The interconversion between Snellen visual acuity measurements, logMAR units, and approxETDRS letter scores was prepared in a tabular form for easy reference. The same outcomes (in Snellen fractions) were obtained with statistical manipulation of either approxETDRS letter scores or logMAR conversions. Conversion of Snellen visual acuity fractions to approxETDRS letter scores for the purpose of performing statistical manipulations provides more readily interpretable outcomes compared with the current strategy of converting Snellen visual acuity fractions to logMAR units.

Near work, education, family history, and myopia in Greek conscripts

To investigate potential factors associated with the presence of myopia in a cohort of young adult men carrying out their military service in Greece. A nested case-control study of 200 conscripts (99 myopes and 101 non-myopes). The cohort consisted of approximately 1000 conscripts in compulsory national service. All cohort members had been screened for refractive errors by Snellen visual acuity measurement at presentation to military service; individuals not achieving visual activity 6/6 underwent noncycloplaegic refraction. The study sample consisted of the first 99 myopic and 101 nonmyopic conscripts who attended the study. In-person interviews of these 200 conscripts were conducted to obtain information on family history, occupation, level of education, near-work activities, and sleeping behaviour. chi(2) and Mann-Whitney tests were used as univariate analysis methods to identify the potential factors associated with the presence of myopia. Multiple logistic regression was used to estimate the adjusted relative risk of myopia. Univariate analysis showed that parental family history (P<0.001), older age (P<0.001), tertiary education (P<0.001), hours of reading per day (P<0.001), hours of computer use per day (P<0.001), and higher social classes (P<0.001) were associated with myopia. Sleeping in artificial or ambient light was not associated with myopia (P=0.75). Multiple logistic regression analysis showed that older age (OR=1.25, 95% CI 1.05-1.49), tertiary education (OR=12.67, 95% CI 3.57-44.88) and parental family history (OR=3.39, 95% CI 1.56-7.36) were independently associated with myopia. In young Greek conscripts, parental family history, older age, and education level are independently associated with myopia.

Ocular Features of West Nile Virus Infection in North America: A Study of 14 Eyes

To present a case series of ocular findings of West Nile virus infection (WNVI) in North America. Retrospective, noncomparative, observational case series. All patients were referred to the authors for WNVI with ocular involvement between the years 2002 and 2005. Chart review was performed on all participants. All participants underwent complete ophthalmic evaluation during each examination, including best-corrected Snellen visual acuity measurement, tonometry, slit-lamp biomicroscopy of the anterior and posterior segments, and dilated fundus examination with indirect ophthalmoscopy. Fundus photography and fluorescein angiography were also performed on all eyes. Relevant ocular findings associated with WNVI were recorded and tabulated. The authors studied the characteristics, frequency, and locations of ocular lesions found in participants' eyes. There were 14 eyes (7 patients) with ocular West Nile virus lesions from 2002 to 2005. Average patient age was 58.4 years (range, 32-85 years). Ocular findings in descending order of frequency included multifocal chorioretinal target lesions in 12 eyes (85.7%), retinal hemorrhages in 7 eyes (50.0%), vitritis in 6 eyes (42.9%), chorioretinal linear streaks in 4 eyes (28.6%), perivascular sheathing and vasculitis in 4 eyes (28.6%), narrowed retinal vessels in 4 eyes (28.6%), disc edema in 4 eyes (28.6%), optic atrophy in 2 eyes (14.3%), vascular occlusion in 2 eyes (14.3%), and VIth nerve palsy in 1 eye (7.1%). Peripheral fundus lesions were found in all 14 eyes (100%), whereas posterior fundus lesions were found in 8 eyes (57.1%). Five patients (71.4%) were diabetic. Diabetic retinopathy was present in 7 eyes (70%). Multifocal choroiditis is the most common ocular manifestation associated with WNVI, with a typically benign clinical course. Less frequent ocular lesions, including optic neuritis and occlusive vasculitis, frequently induce persistent and likely permanent visual deficit. Diabetic patients and those older than 50 years of age are more vulnerable to the more severe features of WNVI, including more serious ocular lesions.

Transpupillary thermotherapy for chronic central serous chorioretinopathy

To determine whether transpupillary thermotherapy (TTT) causes resolution of neurosensory detachment associated with chronic central serous chorioretinopathy (CSCR). The study was a prospective interventional pilot study. All patients underwent Snellen visual acuity measurement (converted to LogMAR for analysis), slitlamp biomicroscopy, fundus examination, colour fundus photography, fluorescein and indocyanine green (ICG) angiography and optical coherence tomography (OCT). Follow-up was scheduled at 1, 2 and 3 months. Success was defined as resolution of neurosensory detachment on OCT at 3 months, and failure as persistence of the same. The primary outcome measure was resolution of OCT-measured neurosensory detachment and secondary outcome measure was change in visual acuity at the end of 3 months. Fourteen eyes of 13 patients were included in the study. Twelve patients were male. The left eye was affected in seven of 14 eyes. The patients' mean age was 42.7+/-4.5 years (range 38-54 years). TTT parameters were as follows: power 156+/-47.8 mW; spot size 2.2+/-1.1 mm; duration 39.6+/-7.5 s. Following treatment, complete resolution of neurosensory detachment on OCT was seen in nine eyes (64.3%) at month 1 (P=0.004) and 11 eyes (78.6%) at months 2 and 3 (P=0.001). Three eyes (21.4%) had persistent subretinal fluid at month 3. Eight eyes (52.7%) had >or=3 lines of improvement (two eyes: five lines and six eyes three lines) at the final visit. Transpupillary thermotherapy could be a therapeutic option in patients with chronic CSCR.

Evaluating cataract surgery gains by assessing patients’ quality of life using the VF-7

Purpose To describe the development and performance of a questionnaire designed to measure functional impairment caused by cataract. Setting Department of Ophthalmology, Helsinki University Central Hospital, Helsinki, Finland. Methods The results of a visual-functioning index (VF-14) of 168 patients with first-eye cataract surgery were analyzed. Patients with significant comorbidity were excluded, leaving 142 patients for the final analysis. Snellen visual acuity measurements and complete preoperative and 4 month postoperative clinical status were performed by ophthalmologists. Outcome measures, including the VF-14, patient perception of trouble with vision, patient satisfaction with vision, and the cataract symptom score, were taken by nurses at the preoperative clinical examinations and at the 4 month postoperative visit. The Spearman rank correlation was used to determine which items of the VF-14 best correlated with a change in patient satisfaction. Results Seven items of the VF-14 that best correlated with patient satisfaction were selected for inclusion in a new 7-item index (the VF-7). Based on the Spearman rank correlation, the items from best to worst were nighttime driving; reading small print; watching television; seeing steps, stairs, or curbs; reading traffic, street, or store signs; cooking; and doing fine handwork. The correlation among changes in the VF-7 score and visual acuity in the operated eye was 0.17, while the correlation among changes in the VF-7 and patient satisfaction caused by cataract surgery was high (r = .56). Conclusion The VF-7 was a strong predictor of change in patient satisfaction caused by cataract surgery.

Small Incision Cataract Surgery and Placement of Posterior Chamber Intraocular Lenses in Patients With Diabetic Retinopathy

Diabetic patients undergoing cataract surgery have been demonstrated to have a guarded prognosis. Small incision cataract surgery has been postulated to cause fewer complications than other techniques of cataract extraction. We looked at small incision cataract surgery to see how diabetics fared. One hundred fifty-four eyes of diabetic patients were evaluated preoperatively through dilated fundus examination and Snellen visual acuity. The eyes then underwent small incision cataract surgery and were followed, undergoing periodic ophthalmoscopy, Snellen visual acuity measurement and additional postoperative therapeutic and surgical intervention. Final visual acuity improved by two Snellen lines or more in 61 out of 154 (40%) eyes. Final visual acuity worsened in 38 out of 154 (25%) eyes. Our results are similar to those reported for extracapsular surgery and phacoemulsification, suggesting that the prognosis is guarded for diabetics, even when undergoing small incision cataract surgery.

Computerized Topographic Analysis of the Healing Graft After Penetrating Keratoplasty for Keratoconus

After penetrating keratoplasty, visual rehabilitation can be slow and is largely a function of corneal surface configuration. Computerized topographic analysis allows the detailed study of corneal surface factors that determine the optical function of the graft. We performed a prospective, longitudinal study of eight patients with keratoconus by using computerized topographic analysis to determine the rate and pattern of postoperative surface normalization and stabilization. Study data included Snellen visual acuity, contrast sensitivity function, central keratometry, photokeratoscopy, and computerized topographic analysis. Data were collected preoperatively and at one week, one month, two months, three months, and six months postoperatively. Results demonstrate that the greatest configurational changes both topographically and functionally occur in the first month after keratoplasty. The computer-generated surface asymmetry index and the surface regularity index correlated well with improvement in Snellen visual acuity measurements. Contrast sensitivity function was depressed initially but improved to well above preoperative values by one month postoperatively and paralleled the improvement in the surface indices and visual acuity. The axis of astigmatism stabilized by one month postoperatively. Our data indicate that topographic analysis provides a good indication of the rate and course of optical stabilization during the early healing process after keratoplasty and correlates well with visual function in the otherwise normal eye.