Landolt Visual Acuity Research Articles

Visual perceptual learning modulates microsaccade rate and directionality

Microsaccades, incessant “fixational eye movements” (< 1°), are an important window into cognitive functions. Yet, its role in visual perceptual learning (VPL)–improvements in visual discrimination due to practice–remains practically unexplored. Here we investigated whether and how microsaccades change in VPL. Human observers performed a Landolt acuity task for 5 consecutive days and were assigned to the Neutral or Attention group. On each trial, two peripheral Landolt squares were presented briefly along a diagonal. Observers reported the gap side of the target stimulus. Training improved acuity and modified the microsaccade rate; with training, the rate decreased during the fixation period but increased during the response cue. Furthermore, microsaccade direction during the response cue was biased toward the target location, and training enhanced and sped up this bias. Finally, the microsaccade rate during a task-free fixation period correlated with observers’ initial acuity threshold, indicating that the fewer the microsaccades during fixation the better the individual visual acuity. All these results, which were similar for both the Neutral and Attention groups and at both trained and untrained locations, suggest that microsaccades could serve as a physiological marker reflecting functional dynamics in human perceptual learning.

Simultaneous perception of prosthetic and natural vision in AMD patients

Loss of photoreceptors in atrophic age-related macular degeneration (AMD) results in severe visual impairment. Since the low-resolution peripheral vision is retained in such conditions, restoration of central vision should not jeopardize the surrounding healthy retina and allow for simultaneous use of the natural and prosthetic sight. This interim report, prespecified in the study protocol, presents the first clinical results with a photovoltaic substitute of the photoreceptors providing simultaneous use of the central prosthetic and peripheral natural vision in atrophic AMD. In this open-label single group feasibility trial (NCT03333954, recruitment completed), five patients with geographic atrophy have been implanted with a wireless 2 x 2 mm-wide 30 µm-thick device, having 378 pixels of 100 µm in size. All 5 patients achieved the primary outcome of the study by demonstrating the prosthetic visual perception in the former scotoma. The four patients with a subretinal placement of the chip demonstrated the secondary outcome: Landolt acuity of 1.17 ± 0.13 pixels, corresponding to the Snellen range of 20/460–20/565. With electronic magnification of up to a factor of 8, patients demonstrated prosthetic acuity in the range of 20/63–20/98. Under room lighting conditions, patients could simultaneously use prosthetic central vision and their remaining peripheral vision in the implanted eye and in the fellow eye.

Exogenous attention facilitates perceptual learning in visual acuity to untrained stimulus locations and features.

Visual perceptual learning (VPL) refers to the improvement in performance on a visual task due to practice. A hallmark of VPL is specificity, as improvements are often confined to the trained retinal locations or stimulus features. We have previously found that exogenous (involuntary, stimulus-driven) and endogenous (voluntary, goal-driven) spatial attention can facilitate the transfer of VPL across locations in orientation discrimination tasks mediated by contrast sensitivity. Here, we investigated whether exogenous spatial attention can facilitate such transfer in acuity tasks that have been associated with higher specificity. We trained observers for 3 days (days 2–4) in a Landolt acuity task (Experiment 1) or a Vernier hyperacuity task (Experiment 2), with either exogenous precues (attention group) or neutral precues (neutral group). Importantly, during pre-tests (day 1) and post-tests (day 5), all observers were tested with neutral precues; thus, groups differed only in their attentional allocation during training. For the Landolt acuity task, we found evidence of location transfer in both the neutral and attention groups, suggesting weak location specificity of VPL. For the Vernier hyperacuity task, we found evidence of location and feature specificity in the neutral group, and learning transfer in the attention group—similar improvement at trained and untrained locations and features. Our results reveal that, when there is specificity in a perceptual acuity task, exogenous spatial attention can overcome that specificity and facilitate learning transfer to both untrained locations and features simultaneously with the same training. Thus, in addition to improving performance, exogenous attention generalizes perceptual learning across locations and features.

Habitual higher order aberrations affect Landolt but not Vernier acuity.

To assess whether the eye's optical imperfections are relevant for hyperacute vision, we measured ocular wave aberrations, visual hyperacuity, and acuity thresholds in 31 eyes of young adults. Although there was a significant positive correlation between the subjects' performance in Vernier- and Landolt-optotype acuity tasks, we found clear differences in how far both acuity measures correlate with the eyes' optics. Landolt acuity thresholds were significantly better in eyes with low higher order aberrations and high visual Strehl ratios (r2 = 0.22, p = 0.009), and significantly positively correlated with axial length (r2 = 0.15, p = 0.03). A retinal image quality metric, calculated as two-dimensional correlation between perfect and actual retinal image, was also correlated with Landolt acuity thresholds (r2 = 0.27, p = 0.003). No such correlations were found with Vernier acuity performance (r2 < 0.03, p > 0.3). Based on these results, hyperacuity thresholds are, contrary to resolution acuity, not affected by higher order aberrations of the eye.

Stereopsis in end-stage renal disease (ESRD)

We investigated an effect of end-stage renal disease (ESRD) on the visual system by measuring the ability of 21 patients to perceive depth in the random dot stereograms and circles of the Randot Test. To control for other factors which might influence performance on the tests of stereopsis, patients were compared with healthy controls matched for age, years of education, IQ, and general cognitive ability. Vernier acuity (thought to reflect mainly central processing) and Landolt acuity (more sensitive to retinal and optical abnormalities) were also measured, but the study did not include a formal ophthalmological examination. All controls could perceive depth in random dot stereograms, whereas 9/21 patients could not. Patients who could perceive depth had worse stereoacuity than did their matched controls. The patient group as a whole had worse Vernier and Landolt acuities than the controls. The stereoblind patient subgroup had similar Vernier acuity to the stereoscopic subgroup, but worse Landolt acuity, and was more likely to have peripheral vascular disease. We conclude that ESRD had affected structures both within the eye, and within the visual brain. However, the similarity of Vernier acuity and difference of Landolt acuity in the stereoblind and stereoscopic patient subgroups suggest that the differences in stereoscopic ability arise from abnormalities in the eyes rather than in the brain.

Long-Term Results of Amniotic Membrane Transplantation for Partial Limbal Deficiency

To evaluate the long-term efficacy of amniotic membrane transplantation as a treatment option in cases with partial limbal deficiency. Sixteen eyes of 14 patients with partial limbal deficiency underwent amniotic membrane patch (AMP) or amniotic membrane graft with patch (AMGP) following keratectomy for conjunctivalization of the cornea. The average follow-up period was 52 months. We evaluated the mean corneal epithelialization time, visual acuity improvement, complications, and recurrence rate after the surgery. Eleven eyes underwent AMP, and the remaining 5 eyes received AMGP. All eyes eventually attained corneal reepithelialization. The mean time to reepithelialization was not significantly different between the AMP group (9 days) and the AMGP group (27 days). At the final follow-up visit, improved Landolt visual acuity was observed in 6 of the 11 eyes in the AMP group and in 2 of the 5 eyes in the AMGP group. No intraoperative complications were observed. However, 6 eyes in the AMP group and 3 eyes in the AMGP group had a recurrence or developed a persistent epithelial defect after mean durations of 21.2 and 17.7 months, respectively. Both AMP and AMGP appear to be effective in attaining corneal reepithelialization, but neither could provide stable, clear corneal epithelialization in the long term.

The relation of functional visual acuity measurement methodology to tear functions and ocular surface status

To investigate the relation of functional visual acuity (FVA) measurements with dry eye test parameters and to compare the testing methods with and without blink suppression and anesthetic instillation. A prospective comparative case series. Thirty right eyes of 30 dry eye patients and 25 right eyes of 25 normal subjects seen at Keio University School of Medicine, Department of Ophthalmology were studied. FVA testing was performed using a FVA measurement system with two different approaches, one in which measurements were made under natural blinking conditions without topical anesthesia (FVA-N) and the other in which the measurements were made under the blink suppression condition with topical anesthetic eye drops (FVA-BS). Tear function examinations, such as the Schirmer test, tear film break-up time, and fluorescein and Rose Bengal vital staining as ocular surface evaluation, were performed. The mean logMAR FVA-N scores and logMAR Landolt visual acuity scores were significantly lower in the dry eye subjects than in the healthy controls (p<0.05), while there were no statistical differences between the logMAR FVA-BS scores of the dry eye subjects and those of the healthy controls. There was a significant correlation between the logMAR Landolt visual acuities and the logMAR FVA-N and logMAR FVA-BS scores. The FVA-N scores correlated significantly with tear quantities, tear stability and, especially, the ocular surface vital staining scores. FVA measurements performed under natural blinking significantly reflected the tear functions and ocular surface status of the eye and would appear to be a reliable method of FVA testing. FVA measurement is also an accurate predictor of dry eye status.

Recognition versus Resolution: a Comparison of Visual Acuity Results Using Two Alternative Test Chart Optotype

Purpose To quantify the difference between recognition (letter) and resolution (Landolt) visual acuity (VA) in a group of normally sighted subjects. Is it reasonable to assume that the two acuity measures are clinically equivalent? Methods A pair of 6 m acuity test charts was produced: one comprised letters and the other Landolt broken rings. Construction of both charts conformed to the logMAR design format. Monocular VA was determined for the dominant eye of 300 screened and normally sighted optometric patients aged 16 to 40, each wearing an optical refractive (spectacle) correction. Results Letter acuity was superior to Landolt acuity ( P≤0.0001). The mean paired acuity difference was -0.041 logMAR (standard deviation 0.034): the 95% limits of agreement were ±0.067 logMAR units or ±3.3 chart optotype. Repeatability was high and similar for each chart type (±2.1 and ±2.4 optotype for letter and Landolt, respectively). Gender, test sequence, and laterality of the dominant eye (left or right) were each non-statistically significant variables. Conclusions For normally sighted subjects wearing an optimal refractive correction, a bias was recorded in favour of recognition over resolution acuity: the clinical difference amounted to approximately 40% of one logMAR chart line, with similar high repeatability for either chart optotype. We conclude that the assumption of clinical equivalence between letter and Landolt acuity is reasonable under optimum test conditions.

Functional Visual Acuity in Stevens-Johnson Syndrome

To evaluate the correlation of functional visual acuity (FVA) measurement with ocular surface findings in patients with Stevens-Johnson syndrome (SJS). Prospective comparative study. Sixty-nine eyes of 38 patients with chronic SJS assessed at the Tokyo Dental College, Tokyo Medical Center, and the Kyoto Prefectural University of Medicine, Department of Ophthalmology, Kyoto, Japan, were studied. Twenty eyes of 10 normal subjects and 40 eyes of 20 patients with Sjögren syndrome (SS) were also studied. Conventional Landolt visual acuity (VA) and FVA examinations and slit-lamp examinations were performed. FVA was measured continuously by the FVA measurement system during a 30-second blink-free period in one eye. The visual maintenance ratio (VMR) was calculated as follows: VMR = [(2.7 - FVA)/(2.7 - baseline VA)], where logarithm of minimal angle of resolution values of FVA were entered into the formula and 2.7 represented the lowest visual acuity in this series. Slit-lamp examinations, Schirmer test, and fluorescein vital stainings were also performed in all subjects. VMR was markedly lower in patients with SJS compared with patients with SS and controls. FVA values showed a relation with the presence of corneal opacity and vascularization. The FVA measurement system is not only a useful tool in the evaluation of dynamic VA changes, but also reflects the ocular surface clinical findings in SJS.

Visual Simulation of Retinal Images Through a Decentered Monofocal and a Refractive Multifocal Intraocular Lens

To evaluate the effect of decentration of a monofocal intraocular lens (IOL) and a refractive multifocal IOL on retinal image quality using a new visual simulation system. Using a new visual simulation system, we performed visual simulation of a monofocal and a multifocal IOL at 5, 4, 3, 2, 1, and 0.4 m with several decentered IOL positions from 0 to 1.0 mm through a 3- or 4-mm aperture using Landolt visual acuity (VA) charts. The VA was estimated under each condition from the simulated retinal image. With a monofocal IOL, the image was affected minimally by decentration at 4 and 5 m; at 2 and 3 m, the image contrast decreased slightly with increased decentration. With the multifocal IOL, some loss of image contrast developed at all distances compared with the monofocal IOL; however, the images of the Landolt's rings were still recognizable under all conditions. Our results suggest that up to 1.0 mm of decentration of a monofocal and multifocal IOL would not greatly affect the retinal image quality.

Ocular Surface Findings in Hallopeau-Siemens Subtype of Dystrophic Epidermolysis Bullosa

This article describes the clinical features and long-term changes in corneal sensitivity, tear function, and impression cytology findings in a patient with recessive dystrophic epidermolysis bullosa (DEB). The patient underwent best-corrected Landolt visual acuity measurements, slit-lamp examinations, anterior segment photography, Schirmer test with anesthesia, tear film break-up time, corneal fluorescein and Rose-Bengal staining, assessment of corneal sensitivity, and conjunctival impression cytology at the initial and final visits. The patient had a recurrent corneal erosion in the right eye and a painful corneal blister with extensive superficial punctuate keratopathy in the left eye, which remained refractory to treatment with patching, lubricants, and antibiotic ointments for 10 weeks. The corneal disease in both eyes responded swiftly to topical fibronectin, topical nonpreserved tears, vitamin A ointment, and therapeutic soft contact lenses. Maintenance treatment was continued with preservative-free topical tear drops and vitamin A ointment. Corneal disease did not recur in the patient during the follow-up of 29 months. The mean corneal sensitivity and tear film break-up time were decreased initially in both eyes and attained normal values with treatment. Impression cytology revealed squamous metaplasia, loss of cellular cohesion, and total absence of goblet cells before treatment, all of which were observed to be normalized at the final follow-up. The ocular surface disease in DEB was characterized by low corneal sensitivity, disorder of tear quality, decreased cellular cohesion, squamous metaplasia of the conjunctiva, and goblet cell loss. Close follow-up for ocular complications in DEB is essential and a pathophysiology-oriented approach to the epithelial disease may not only provide rapid healing but might prevent recurrences as well.

Effect of preoperative tear function on early functional visual acuity after laser in situ keratomileusis

Purpose: To assess the effect of preoperative tear function on early changes in functional visual acuity (FVA) after laser in situ keratomileusis (LASIK). Setting: Minamiaoyama Eye Clinic, Tokyo, Japan. Methods: This prospective single-center study assessed the effect of preoperative and postoperative tear functions on FVA in 30 eyes of 15 patients who had LASIK. Functional visual acuity was defined as the binocular recognition acuity measured by the FVA tester (Wellsystem) during a 10-second, blink-free period. All patients had a Schirmer test with anesthesia and tear-film breakup time (BUT) measurements preoperatively and 1 day and 1 week after LASIK. Corneal topography and Landolt visual acuity and FVA measurements were performed before surgery and 1 day and 1 week after LASIK. Eyes with a Schirmer test reading less than 5.0 mm and a BUT less than 5 seconds were grouped as definite dry eye (DDE). Eyes with a normal Schirmer test score but a shortened BUT were grouped as probable dry eye (PDE). Results: In all patients, the best uncorrected Landolt visual acuity was 20/20 or better at the postoperative examination times. In the DDE group, the mean preoperative FVA declined from 1.2 to 0.75 ± 0.16 (SD) at 1 day and increased to 1.2 at 1 week. No change in FVA was observed postoperatively in the PDE group. Conclusion: Laser in situ keratomileusis patients with low basal tearing and full uncorrected distance Landolt acuity may experience a transient decrease in FVA that returns to baseline within 1 week.

Preliminary report: Examination of young children with Lea symbols

Lea symbols are highly sensitive for detection of amblyopia in cooperative patients. They are favorable for visual acuity assessment in childhood. Therefore, we assessed age-related normal values and interocular differences of Lea symbol visual acuity. We reexamined 50 out of 193 children aged 21 months to 7 years who came for a routine pediatric examination between January and November 1999. Lea symbol acuity (Lea Symbols Single Symbol Book (LS) and Lea 15-Line Folding Distance Chart (CLS)) and Landolt-C acuity (single (LC) and crowded with 2.6' inter-optotype distance (LC(2.6))) were measured. A three out of four criterion was used. Strabismus and any organic eye disease were excluded by orthoptic and ophthalmologic examination, consisting of biomicroscopy, ophthalmoscopy, retinoscopy or refractometry, cover test or Hirschberg test and Lang Stereotest. Only 26% of the parents (50 out of 193) accepted an examination in our hospital. In 35 (32) of the 50 children, visual acuity could be measured in both eyes separately with single (crowded) Lea symbols, while 26 (25) children could be examined in both eyes monocularly with the Landolt-C with single (crowded) optotypes. Except for one 3-year-old boy, all of the children older than 30 months could be tested with single Lea symbols. Lea acuity surpassed Landolt acuity. The difference was about 1.5 lines (1.5 dB) for both the single and the crowded optotypes. In 63% (69%) of the children who could be tested monocularly, LS acuity (CLS acuity) was higher than 0.8 (0.63). 89% (83%) of the children had an interocular difference of maximum 1 line for single (crowded) Lea symbols. The youngest child whose visual acuity could be assessed with Lea symbols was 23 months old. Almost every child older than 30 months could be tested with Lea symbols. Lea acuity higher than 1 and an interocular difference less than 2 lines is not suspect for amblyopia. Children with a difference of more than one line should be reexamined.

Preliminary report: Examination of young children with Lea symbols

BACKGROUND. Lea symbols are highly sensitive for detection of amblyopia in cooperative patients. They are favorable for visual acuity assessment in childhood. Therefore, we assessed age-related normal values and interocular differences of Lea symbol visual acuity. METHODS/PATIENTS. We reexamined 50 out of 193 children aged 21 months to 7 years who came for a routine pediatric examination between January and November 1999. Lea symbol acuity (Lea Symbols Single Symbol Book (LS) and Lea 15-Line Folding Distance Chart (CLS)) and Landolt-C acuity (single (LC) and crowded with 2.6' inter-optotype distance (LC 2.6 )) were measured. A three out of four criterion was used. Strabismus and any organic eye disease were excluded by orthoptic and ophthalmologic examination, consisting of biomicroscopy, ophthalmoscopy, retinoscopy or refractometry, cover test or Hirschberg test and Lang Stereotest. RESULTS. Only 26% of the parents (50 out of 193) accepted an examination in our hospital. In 35 (32) of the 50 children, visual acuity could be measured in both eyes seperately with single (crowded) Lea symbols, while 26 (25) children could be examined in both eyes monocularly with the Landolt-C with single (crowded) optotypes. Except for one 3-year-old boy, all of the children older than 30 months could be tested with single Lea symbols. Lea acuity surpassed Landolt acuity. The difference was about 1.5 lines (1.5 dB) for both the single and the crowded optotypes. In 63% (69%) of the children who could be tested monocularly, LS acuity (CLS acuity) was higher than 0.8 (0.63). 89% (83%) of the children had an interocular difference of maximum 1 line for single (crowded) Lea symbols. CONCLUSIONS. The youngest child whose visual acuity could be assessed with Lea symbols was 23 months old. Almost every child older than 30 months could be tested with Lea symbols. Lea acuity higher than 1 and an interocular difference less than 2 lines is not suspect for amblyopia. Children with a difference of more than one line should be reexamined.

Visual Function Following Congenital Cataract Surgery

To evaluate the results of congenital cataract extraction and postoperative visual function, we retrospectively reviewed the records of 95 patients who underwent pars plana (plicata) lensectomy or aspiration surgery. Forty-nine percent of the patients with bilateral aphakia and 25% with bilateral pseudophakia had a Landolt visual acuity of 0.5 or above at the final visit. The figures were 31% and 66% for patients with unilateral aphakia and pseudophakia, respectively. Eight patients (16.3%) with bilateral and 2 patients (5.8%) with unilateral cataract for whom contact lenses were prescribed after surgery attained fine stereopsis. Five of 8 patients (62.5%) with unilateral cataract who had intraocular lens implantation ended up with gross or fine stereopsis. We stress that very early surgery and optical correction in the sensitive period of binocular visual development should be instituted, especially in the presence of dense opacities. A good postoperative visual outcome can be achieved in patients undergoing late surgery if the opacities are light or partial in nature. We also reemphasize the importance of aggressive and diligent visual rehabilitation and occlusion therapy against amblyopia.

Visual Function following Unilateral Congenital Cataract Surgery

Purpose:The aim of this study was to evaluate the factors related to the postoperative visual prognosis in unilateral congenital cataracts.Methods:Pars plana lensectomy and anterior vitrectomy was carried out in 18 children with unilateral congenital cataract. All children received hard contact lens correction and occlusion therapy after surgery. Postoperative visual function was assessed by Landolt visual acuity (V/A) and Titmus® Stereo Tests.Results:Four patients in the good acuity group achieved a V/A of 1.0 and 14 patients in the poor acuity group had V/A ranging from 0.02 to 0.4. Age at surgery significantly related to the postoperative V/A in the poor group but not in patients with good acuity.Conclusion:We found that poor visual prognosis correlated with age at surgery performed after 3 months of age rather than with compliance to visual rehabilitation. Good visual prognosis in congenital cataract with early onset was attributed to very early surgery since a patient who had cataract extraction at 3 weeks of age attained a V/A of 1.0.

Objektive Noniussehschärfenprüfung bei Erwachsenen, Kindern und Kleinkindern - Möglichkeiten und Grenzen einer neuen Methode

Recently, a method of objective Vernier acuity testing using a modified Catford drum was presented. A tight correlation between the objective Vernier acuity and the Snellen acuity was reported (Hopkisson et al. 1991). In 41 cooperative patients with strabismic amblyopia and 20 normal subjects were compared the subjective Landolt acuity with the objective Vernier acuity and the individual interocular differences of the objective Vernier acuity. The Vernier method was then tested in 44 healthy 6- to 36-months-old infants. In 39 of the amblyopic and 15 of the normal subjects we compared the Landolt acuity with the grating acuity as measured with the Teller-acuity-card-test, and the interocular differences of the grating acuity. The Vernier target was a black line with an offset of one fifth of its thickness. In a distance of 1 m the offset appeared under visual angles of 15.9' to 0.3' corresponding to acuities of 0.06 to 3.2. The line was moving back and forth in its longitudinal direction. The objective Vernier acuity was defined by the smallest offset causing pursuit eye movements. Strabismic amblyopia was detected by the Vernier method with a sensitivity of 54%. In infants, however, the sensitivity would be less than 30%. In both eyes only 45% of the infants could be tested at all. The sensitivity of the Teller-acuity-card-test was 28%. Many cases of strabismic amblyopia will escape detection by the described method of Vernier acuity testing.

Cortical magnification and peripheral vision.

In a generalized form, the cortical magnification theory of peripheral vision predicts that the thresholds of any visual stimuli are similar across the whole visual field if the cortical stimulus representations calculated by means of the cortical magnification factor are similar independently of eccentricity. Failures of the theory in spatial vision were analyzed, and the theory was tested with five visual acuity tasks and two hyperacuity tasks. Almost all increases in thresholds with eccentricity were explained by the theory in five of these tasks, which included the two-dot vernier hyperacuity test, the measurement of visual acuities with gratings, the Snellen E test, and two acuity tests that required either separation between dots or discrimination between two mirror-symmetric forms. The two-dot vernier thresholds could be explained as a special case of orientation discrimination, and orientation discrimination at different eccentricities was in agreement with the cortical magnification theory. The increase of thresholds in peripheral vision was larger than predicted by the theory in the Landolt visual acuity and bisection hyperacuity tests, possibly because of retinal undersampling.

Toward the elimination of guessing bias in Landolt acuity testing.

A subjective guessing bias has been claimed to be present in association with visual acuity testing using the classic circular Landolt ring. A semiautomated visual test system has been described previously which uses an angular version of the broken ring. Evidence is presented here which indicates that this version of the test object overcomes the problem of guessing bias and thus might prove to be not only a preferred "standard" or reference optotype but also an acceptable clinical optotype in its own right.