Optotype Acuity Research Articles

Validation Study of VEP Vernier Acuity in Normal-Vision and Amblyopic Adults

Vernier displacement thresholds can be measured with swept-parameter visual evoked potentials (sVEPs) and may therefore be useful in pre- or nonverbal subjects. This study was conducted to test whether sVEP vernier thresholds are valid measures of the visibility of vernier offsets in two different settings. Vernier acuity thresholds were measured psychophysically and electrophysiologically using square-wave gratings containing vernier displacements modulated at 3.76 Hz. The detectability of the vernier alignment cue was degraded by introducing either gaps or standing offsets in the stimulus. These manipulations were performed in normal-vision observers. In a second experiment, psychophysical and sVEP vernier acuity were measured in amblyopic observers. sVEP thresholds and overall amplitudes in normal observers were strongly affected by the introduction of gaps or standing offsets, as were psychophysical thresholds. Psychophysical and sVEP vernier offset thresholds were significantly correlated in the amblyopic eyes, as were sVEP and optotype interocular threshold differences. sVEP amplitudes of patients with strabismus were lower than those of patients with anisometropic amblyopia, even though optotype acuities were the same in the two groups. Vernier acuity thresholds derived from the sVEP tap mechanisms that are specific for the relative position of stimulus elements, and they correlate with perceptual visibility in normal and amblyopic observers. Because of this correlation and because sVEP thresholds can be measured without the need for instruction or behavioral responses, they may be useful in assessing visual function in pre- and nonverbal patients.

Treatment of capillary hemangiomas causing refractive and occlusional amblyopia

Capillary hemangiomas of the eyelid and orbit are treated when amblyopia secondary to anisometropic astigmatism or pupillary occlusion is present or when rapid growth of the hemangioma threatens to occlude the pupil. The goal of this study was to determine whether treatment of hemangiomas resolves or prevents occlusion or results in decrease in astigmatism. The records of 54 patients who underwent treatment for reduction in the size of a capillary hemangioma causing amblyopia or threatened amblyopia in two pediatric ophthalmology practices were reviewed. Twenty-eight patients were treated for amblyopia due to anisometropic astigmatism. The average amount of pretreatment astigmatism was 2.71 D, while the average amount of post-treatment astigmatism was 0.46 D. Fifteen of these patients could be tested for optotype visual acuity and all had vision acuity of 20/40 or better. Only 1 of the 15 patients treated for threatened occlusion of the pupil developed occlusion. Six of these patients cooperated with optotype visual acuity and all had vision acuity of 20/30 or better. Eleven patients were treated for pupillary occlusion. Occlusion resolved in all cases. Of the five patients treated for occlusion who cooperated with optotype visual acuity, two had a vision acuity of 20/100 or worse. Treatment to reduce the size of capillary hemangiomas results in resolution of occlusion, reduction in astigmatism, and prevention of pupillary occlusion. Those with occlusion are at higher risk for severe residual amblyopia and require prompt and definitive treatment.

Long-Term Visual Function and Relative Amblyopia in Posterior Persistent Hyperplastic Primary Vitreous (PHPV)

Background: Favorable results in the management of PHPV, made possible by improved surgical techniques, are described in the literature. However, the functional results are in general in the low-vision sector (rarely better than 0.025–0.1 maximum). Purpose: To introduce long-term acuity results and estimate the relative amblyopia in early operated PHPV. Material and Methods: Six patients suffering from PHPV of varying degrees (posterior polar cataract, posterior lenticonus, traction and malformation of the optic nerve head and macula region, persistent vitreous vessels) underwent pleoptic treatment after surgery (lentectomy in all, additional stalk-cutting in three cases) at the age of 3 to 7 months. The patients were followed up to age 7 to 12 years. Visual acuity was assessed by Landolt ring single and closely interspaced linear optotypes (C-Test developed by Haase/Hohmann). Results: Compliance with the amblyopia treatment was good in five patients. Visual acuity (VA) improvement in the affected eye could be seen up to early school age (6–8 years). Final VA outcome was 0.1 (minimum) to 0.7 (maximum) with single optotypes. VA for crowded optotypes was maximum 1 octave below single optotype VA. The visual development of the phakic eye was not delayed, i.e. not disturbed by long-term patching. Discussion: Compliance with amblyopia treatment and long-term visual acuity in the cases presented here are even more favorable than described in the literature. As the amount of crowding is small, we conclude that there is little relative (additional) amblyopia and that the functional outcome is limited only by the degree of ocular malformation. Surgical treatment in comparable cases is encouraged.

OPTOTYPE AND GRATING VISUAL ACUITY IN CHILDREN WITH VISUAL PERCEPTUAL IMPAIRMENT

Objectives: This study investigates whether the poorer visual acuity obtained with optotypes than with grating stimuli in children with cerebral visual impairment is related to the visual perceptual problems that frequently occur in this disorder. Since optotype acuity tasks require some shape perception visual perceptual problems could selectively affect the perception of these visually more complex stimulus.

Optotype and Grating Visual Acuity in Patients with Ocular and Cerebral Visual Impairment

To investigate the discrepancy between grating and optotype visual acuity in children with visual impairment due to brain and/or ocular abnormalities. Better eye acuity at 114 cm was studied in 81 patients (ages, 5-24 years) attending special schools for the visually handicapped. Fourteen patients had a brain abnormality, 48 had an ocular disorder, and 19 had both. Three acuity tasks were administered: detecting gratings in one of two positions, discriminating the orientation of single gratings, and discriminating the orientation of uncrowded Landolt-C optotypes. The three paradigms were similar in stimulus contrast, luminance, presentation mode, and psychophysical procedure. Overall, grating acuity was better than optotype acuity, and the disparity increased with poorer optotype acuity. The largest discrepancies occurred in patients with brain abnormality, but disparities were also large in patients with optic nerve disorder. In patients with ocular and brain abnormality, grating acuities were only mildly better and not different from patients with only ocular abnormality. Grating orientation and grating detection tasks yielded similar thresholds, except in patients with cerebral visual impairment and with optic nerve disorder, whose grating detection acuity was better than grating orientation acuity. Grating-to-optotype acuity superiority is typically large in visual disorders involving the brain. The closely matched test paradigms point to stimulus characteristics as the explanation. However, because the discrepancy decreased with grating orientation acuity instead of grating detection acuity, the complexity of the response required also plays a role.

Local and non-local deficits in amblyopia: acuity and spatial interactions

Amblyopic vision is thought to be limited by abnormal long-range spatial interactions, but their exact mode of action and relationship to the main amblyopic deficit in visual acuity is largely unknown. We studied this relationship in a group ( N = 59) of anisometropic ( N = 21) and strabismic (or combined, N = 38) subjects, using (1) a single and multi-pattern (crowded) computerized static Tumbling-E test with scaled spacing of two pattern widths (TeVA), in addition to an optotype (ETDRS chart) acuity test (VA) and (2) contrast detection of Gabor patches with lateral flankers (lateral masking) along the horizontal and vertical axes as well as in collinear and parallel configurations. By correlating the different measures of visual acuity and contrast suppression, we found that (1) the VA of the strabismic subjects could be decomposed into two uncorrelated components measured in TeVA: acuity for isolated patterns and acuity reduction due to flanking patterns. The latter comprised over 60% of the VA magnitude, on the average and accounted for over 50% of its variance. In contrast, a slight reduction in acuity was found in the anisometropic subjects, and the acuity for a single pattern could account for 70% of the VA variance. (2) The lateral suppression (contrast threshold elevation) in a parallel configuration along the horizontal axis was correlated with the VA ( R 2 = 0.7), as well as with the crowding effect (TeVA elevation, R 2 = 0.5) for the strabismic group. Some correlation with the VA was also found for the collinear configuration in the anisometropic group, but less suppression and no correlation were found for all the vertical configurations in all the groups. The results indicate the existence of a specific non-local component of the strabismic deficit, in addition to the local acuity deficit in all amblyopia types. This deficit might reflect long-range lateral inhibition, or alternatively, an inaccurate and scattered top–down attentional selection mechanism.

A comparison of atropine and patching treatments for moderate amblyopia by patient age, cause of amblyopia, depth of amblyopia, and other factors

Objective To assess whether the relative treatment effect of patching compared with atropine for moderate amblyopia varies according to patient age, cause of amblyopia or depth of amblyopia, and initial number of patching hours prescribed. Design Multicenter, randomized clinical trial. Participants Four hundred nineteen children younger than 7 years of age with amblyopia in the range of 20/40 to 20/100. Methods Patients were assigned randomly to receive treatment with either patching or atropine and followed up for 6 months. Primary outcome measure Single-surrounded HOTV optotype visual acuity in the amblyopic eye after 6 months. Results Improvement in the amblyopic eye visual acuity was slightly greater in the patching group compared with the atropine group in all subgroups based on patient characteristics. The relative treatment effect did not vary with age ( P = 0.84), cause of amblyopia ( P = 0.68), or baseline amblyopic eye acuity ( P = 0.59). Patients with acuity of 20/80 to 20/100 who were prescribed 10 or more hours a day of patching showed a more rapid improvement in acuity than did patients prescribed a lesser amount of patching ( P = 0.01) or than did patients in the atropine group ( P < 0.001), but by 6 months, the differences were not significant ( P = 0.47 and 0.15, respectively). Conclusions A beneficial effect of both patching and atropine is present throughout the age range of 3 to younger than 7 years old and the acuity range of 20/40 to 20/100. Patients with acuity of 20/80 to 20/100 improve faster when a greater number of hours of patching is prescribed, but by 6 months, the amount of improvement is not related to the number of hours of patching initially prescribed.

The pattern of visual deficits in amblyopia.

Amblyopia is usually defined as a deficit in optotype (Snellen) acuity with no detectable organic cause. We asked whether this visual abnormality is completely characterized by the deficit in optotype acuity, or whether it has distinct forms that are determined by the conditions associated with the acuity loss, such as strabismus or anisometropia. To decide this issue, we measured optotype acuity, Vernier acuity, grating acuity, contrast sensitivity, and binocular function in 427 adults with amblyopia or with risk factors for amblyopia and in a comparison group of 68 normal observers. Optotype acuity accounts for much of the variance in Vernier and grating acuity, and somewhat less of the variance in contrast sensitivity. Nevertheless, there are differences in the patterns of visual loss among the clinically defined categories, particularly between strabismic and anisometropic categories. We used factor analysis to create a succinct representation of our measurement space. This analysis revealed two main dimensions of variation in the visual performance of our abnormal sample, one related to the visual acuity measures (optotype, Vernier, and grating acuity) and the other related to the contrast sensitivity measures (Pelli-Robson and edge contrast sensitivity). Representing our data in this space reveals distinctive distributions of visual loss for different patient categories, and suggests that two consequences of the associated conditions--reduced resolution and loss of binocularity--determine the pattern of visual deficit. Non-binocular observers with mild-to-moderate acuity deficits have, on average, better monocular contrast sensitivity than do binocular observers with the same acuity loss. Despite their superior contrast sensitivity, non-binocular observers typically have poorer optotype acuity and Vernier acuity, at a given level of grating acuity, than those with residual binocular function.

Retinal illuminance and the dissociation of letter and grating acuity in age-related macular degeneration.

To report on the differential effect of retinal illuminance on letter and grating acuity. For 13 subjects with age-related macular degeneration (ARMD) and four subjects with normal vision, standard distance and near letter acuity, as well as grating acuity data were obtained at mesopic to high-photopic light levels. In general, both acuity forms improved with increasing light level, but not in proportion with one another. The ratio of letter/grating acuity separated the ARMD subjects into two subgroups, one with relatively low letter acuity scores for which the dissociation of the two acuity forms increased with retinal illuminance, and another with higher letter acuity values for which the ratio converged toward unity. These findings demonstrate that both letter and grating acuity increase with retinal illuminance and that equating grating acuity with optotype acuity is untenable in subjects with ARMD, irrespective of light levels. The latter conclusion is of importance whenever acuity is used as a criterion to classify the visually impaired with regard to their legal and social status.

Oculographic and clinical characterization of thirty-seven children with anomalous head postures, nystagmus, and strabismus: The basis of a clinical algorithm

Background and Purpose: We studied children with nystagmus who also had anomalous head postures and strabismus to determine the etiology of the conditions and present a diagnostic clinical algorithm. Methods: The patients for this study were among the 560 patients evaluated in the ocular motor neurophysiology laboratory between the years 1991 and 1997. Clinical characteristics, infrared oculography data, and medical and surgical treatments were entered into a database for analysis. Oculography was performed on all patients according to a standard protocol, and data were stored and analyzed off-line. Etiology of anomalous head posture was determined with both clinical and oculography information. Results: Thirty-seven children are the subjects of this report. The etiology of anomalous head posture was a “gaze null” due to congenital nystagmus in 23 (62%) patients, an “adduction null” due to manifest latent nystagmus in 12 (32%) patients, spasmus nutans in 1 (3%) patient, and strabismus in 1 (3%) patient. The patients' ages ranged from 9 months to 12 years and averaged 4.4 years. Sixty-nine percent were male patients. Nineteen (63%) of 30 patients had abnormal recognition (linear optotype) acuity in at least 1 eye on monocular cover; the recognition remained abnormal in 5 (17%) of 30 patients under binocular conditions. Thirty percent of patients had amblyopia, 16% had some structural disease of the eyes, 22% had some systemic syndrome or abnormality, 57% had a significant refractive error, and 27% had some ability to fuse. Conclusions: The major etiology for anomalous head posture in these patients was to adopt a gaze null due to congenital nystagmus (62% of patients) regardless of the direction of their anomalous head posture or type of strabismus. Moving the fixing eye as the first step for the anomalous head posture, combined with moving the nonfixing eye for the resulting strabismus may help treat these patients. (J AAPOS 1999;3:25-32)

Assessment of visual acuity in children aged 1½-6 years, with normal and subnormal vision

The aim of the study was to assess different visual acuity tests in the age group 1½-6 years in 105 children with assumed normal vision, visual impairment due to ocular disease or strabismus. Acuity tasks for young children can be divided into three subtypes according to the kind of stimulus used. For "detection acuity", the stimulus should be detected or distinguished from the background, as assessed with the Stycar Rolling Balls. For "resolution acuity", the stimulus pattern should be resolved, as assessed with the Preferential Looking procedure (Teller Acuity Cards). For "recognition acuity", the stimulus must be recognized by the subject as assessed with the BUST-D symbol test, Sheridan Gardiner (S-G) single letters, LH single symbols and line tests, and also the HVOT test. Different acuity values were obtained with regard to detection, resolution and recognition acuities. Assessment with the Stycar Rolling Balls only gave a rough estimate of the visual function. There was an overestimation of the acuity values in all groups of children when using the Preferential Looking technique. Good agreement was found between the LH line and HVOT tests. The BUST-D test, S-G single letters, and LH single symbols gave slightly better acuity values than linear recognition tests. A "crowding ratio" was calculated by dividing the single optotype acuity by the linear acuity, and also by dividing the grating acuity by the optotype linear and single acuity. The crowding ratio varied in the individual children and in the different groups, being highest for strabismic amblyopia. The general conclusion is that reliable visual acuity measurements were not obtained until the visual acuity could be assessed with a recognition test using linear letters or symbols.

Visual Consequences for Children with Early Acquired Lesions to the Optic Radiation—Vision ‘without Seeing’

The brain lesion caused by perinatal hypoxic-ischemic events at gestational age 24 – 34 weeks has a typical anatomical pattern known as periventricular leukomalacia (PVL). PVL affects the corticospinal tracts, causing spastic diplegia and/or the geniculocalcarine tract, causing visual impairment. Computer tomography or magnetic resonance imaging are the methods of choice for diagnosing PVL. This lesion is the cause of visual impairment in 20% of all visually impaired children in a Swedish population of children born in 1989 – 1995. The visual deficit in PVL is characterised by decreased vision with crowding (an inability to resolve linear optotypes, while single optotypes of the same size may be identified) and visual field defects, further complicated by perceptual and cognitive problems. A relatively high single optotype acuity may lead to overestimation of visual function. Oculomotor impairments with strabismus and nystagmus are common findings. Colour vision is often preserved and used by the children as one of many strategies to sort out an otherwise chaotic visual world. Instead of looking, these children listen carefully, talk a lot and remember well, and sometimes use tactile information to solve visual tasks. They easily get lost in new surroundings and they recognise known faces among others only by the voice and the colour of the clothes. Reading is often difficult. This group of visually impaired children call for adaptation of education and habilitation to manage daily life, mobility, and reading.

Acuity and contrast sensitivity in monkeys after neonatal intraocular lens implantation with and without parttime occlusion of the fellow eye: ∗Boothe RG, Louden TM, Lambert SR. Invest Ophthalmol Vis Sci 1996;37:1520–1531

The authors used a monkey model to evaluate intraocular lenses (IOLs) for the treatment of infantile cataract in humans. Specifically, they sought to assess the effectiveness of IOLs, with and without occlusion therapy, in preventing amblyopia.A diffuser contact lens was placed on one eye each of 11 neonatal monkeys to simulate an infantile cataract. A unilateral lensectomy, combined with the implantation of an IOL, was performed on the same eye 1 to 2 weeks after birth. Clear contact lenses were used to adjust the optical correction of the pseudophakic eyes to a near point, and opaque lenses were used to maintain daily part-time (70%) occlusion of the fellow eyes of half the subjects. Behavioral methods were used to assess grating acuity, optotype acuity (Landolt C), and contrast sensitivity.In five of the animals, complications that developed in the eye with the implant were severe enough to interfere with visual function. The authors present only behavioral outcomes obtained before or in the absence of surgical complications. In monkeys that underwent daily 70% occlusion, grating acuity in the pseudophakic eyes eventually matured to normal adult levels. Grating acuity was significantly poorer in animals with no occlusion therapy. Even in animals with normal grating acuity, assessments of optotype acuity revealed amblyopic deficits; contrast sensitivity was impaired as well at middle and low spatial frequencies.The current study demonstrates that if there are no complications secondary to surgery, normal grating acuity can be obtained in neonatal monkey eyes that undergo IOL implantation, optical correction of the pseudophakic eye to a near point, and 70% occlusion of the fellow eye. However, these good outcomes for grating acuity cannot be attained without occlusion therapy. In addition, optotype acuity and sensitivity to contrast always are impaired.

Measuring vernier acuity and motion perception with the parameter sweep VEP

The visual abilities of infants and small children, who are unable to communicate verbally, can be determined with "objective" visual acuity tests as, e.g., preferential looking (PL) or visual evoked potentials (VEP). Both methods provide an estimate of grating visual acuity, but are unable to determine optotype visual acuity. Grating acuity, however, is not an optimum indicator for visual performance, as it is less affected than optotype acuity by pathological changes. The diagnostic relevance of objective methods may be improved by testing visual functions that are more strongly degraded by a malfunction of the fovea than is grating acuity. Visual functions such as vernier acuity and relative motion sensitivity are potential candidates. Characteristic properties of vernier- and motion-VEP have been determined on adult subjects with a rapid-sweep-technique at various eccentricities. Both vernier and motion stimuli elicited VEP-responses at the 2nd harmonic (F2) of the stimulus frequency. A VEP-response at the fundamental frequency (F1) could be recorded with the vernier stimulus only. Foveal VEP-thresholds were very similar to psychophysical thresholds lying in the range from 11 to 25 arcsecs. The eccentricity dependence of the VEP-threshold recorded with vernier- and motion stimuli shows different cortical magnifications and supports the notion that the F1 response is related to the detection of the vernier offset, whereas the F2 response is generated by motion components of the stimuli. Vernier and relative motion-related VEP thresholds can be recorded with the steady-state VEP. They may provide more sensitive tests of foveal vision loss than grating visual acuity tests.

The course of myopia in children with mild retinopathy of prematurity

The courses of spherical equivalent in patients (n = 62) who had mild, non-cicatricial retinopathy of prematurity (ROP), and in those without a history of ROP (n = 25) were modeled as a linear function of age; an exponential model was also considered. A few (n = 5) without ROP have abnormal courses characterized by hyperopia in early infancy; none have poor acuity. Although the majority of patients with ROP have courses indistinguishable from those of term born controls, 27 (43.5%) have abnormal courses, most of which are toward myopia. Optotype acuities were significantly poorer among the ROP patients with abnormal than normal refractive courses. Thus abnormal refractive development and acuity deficits are associated in eyes that have had mild ROP.

Visual acuity vs letter contrast sensitivity in retinitis pigmentosa

This study examined the quantitative relationship between foveal visual acuity and contrast sensitivity for large-letter optotypes in a group of patients with retinitis pigmentosa (RP), in order to asses more completely the extent of foveal vision loss in this group of hereditary retinal dystrophies. High-contrast visual acuity and large-letter contrast sensitivity were measured with a computer-based testing system and with commercially available letter charts (Lighthouse Distance Visual Acuity Test; Pelli-Robson Contrast Sensitivity Chart). Findings from 20 patients with typical RP or Usher syndrome were compared with those from 15 age-similar control subjects with normal vision. On both the computer-based test and the chart tests, the patients with RP showed approximately equal reductions in visual acuity and large-letter contrast sensitivity. However, intersubject variability among the normal controls was greater for contrast sensitivity than for visual acuity on both test protocols. As a result, the patients with RP required a greater reduction in contrast sensitivity than in acuity to exceed the normal range, indicating that visual acuity was the more sensitive index of the loss of foveal visual function.

Small and large field grating acuity versus recognition acuity in different groups of amblyopic patients

Grating acuity was tested in 74 subjects with different amblyopia and five patients with pathological morphological findings, reducing visual acuity. Recognition acuity was tested with Landolt C single symbol and close inter-space 2.6 min. of arc. Grating acuity was tested with the Teller Acuity Cards with large (12.5 cm × 12.5 cm) and small (6.25 cm × 6.25 cm) test fields. Reduction of field size did not cause any significant difference. Patients with strabismic or strabismic and anisometropic amblyopia did not show a close correlation of recognition acuity with grating acuity. Stimulus deprivation amblyopia showed a good correlation between grating acuity (large and small field) and Landolt single optotype acuity. In children at risk for amblyopia, a difference in favour of large field gratings was found for both eyes (risk and non-risk eye) in the lower visual acuity group (identical with the lower age group). Better grating acuity for large fields seems to reflect an early stage of the visual development rather than that it is indicative for amblyopia.

Natural course of visual functions in the Bardet-Biedl syndrome.

To determine the course of visual functions in patients with Bardet-Biedl syndrome. The 21 patients with Bardet-Biedl syndrome seen at Children's Hospital, Boston, Mass, had optotype and grating acuities and dark-adapted thresholds measured over time. Their ages at first visit ranged from 2 weeks to 23 years (median age, 6 years). The courses of the visual functions were analyzed with a random-effects model. Substantial declines in visual functions were found. On average, grating and optotype acuities declined 0.09 log units (roughly 1 line) per year, and thresholds increased about 0.19 log units per year. The rates at which these visual functions were lost and the predicted level of the visual functions at ages 11 to 12 years (the mean ages of measurement) varied among individuals. The visual prognosis for children with Bardet-Biedl syndrome is poor. The course of both central and peripheral visual functions is variable.

Binocular enhancement of visual acuity

Using a computerized test system, we compared binocular and monocular visual optotype acuity, varying both contrast and contrast disparity between the two eyes. When contrast was the same in the two eyes, binocular acuity was better than best monocular acuity by an average of 0.045 log minimum angle of resolution, or 11%. When contrast differed in the two eyes, binocular acuity in most but not all cases was still better than the monocular acuity of the eye that received the higher contrast. This binocular advantage became smaller but remained significant as contrast disparity became larger. These results are most simply explained by threshold contrast summation of high-spatial-frequency letter components.

Visual Acuity Measurements by Swept Spatial Frequency Visual-Evoked-Cortical Potentials (VECPs): Clinical Application in Children with Various Visual Disorders

Previous studies have indicated that visual acuities of normal infants can be estimated with good accuracy using swept spatial frequency visual-evoked-potentials (VECPs). In this report we describe acuity measurements obtained with this technique from 304 examinations performed on 135 children having various visual disorders. When possible, two or more different stimulation frequencies (8, 12, 15 or 24 contrast reversals/sec) were used in each patient, and three to eight sweep VECPs were obtained from each patient under each simulation and recording condition. High correlation coefficients (0.94 - 0.96) between the acuity estimated on each patient from either the single sweep giving the best visual acuity (BSS) or from vector averages (VeA) of the EEG data obtained from several sweeps confirmed previous findings in normal infants. We also found high correlation coefficients among BSS recorded at different temporal frequencies (0.79-0.97) and among comparisons of BSS or VeA acuity to optotype visual acuity (0.6-0.89). Children with clinically undetectable optokinetic responses showed lower visual acuity estimated by BSS than those who demonstrated optokinetic nystagmus. We conclude that the sweep VECP is a valid method, giving estimates of acuity which correlate well with optotype acuity and correspond well to other clinical findings, and that it can be useful in the clinical management of nonverbal patients.