Potential acuity meter results in cataract patients

Purpose : To determine the ability of the potential acuity meter (PAM) to predict potential visual acuity through lenticular opacities in a group of cataract patients without significant other ocular pathology. Methods : This prospective study undertook PAM measurements on each eye of 84 subjects during preoperative hospital visits to either A Scan or Primary Care clinics. PAM results were compared to best corrected visual acuity findings obtained at least 6 weeks post‐cataract extraction. Results : Comparison of PAM result to visual outcome showed poor correlation (rho = 0.41, P = 0.0005). Using predictive estimates, 49% of subjects’ PAM results underestimated visual outcome as determined by a difference of greater than 2 Snellen acuity lines in these results. Factors such as preoperative vision level, cataract type and pupil dilation did not significantly influence the predictive power of the PAM. Preoperative pinhole results were also correlated with visual outcome (rho = 0.42, P = 0.0006). Vison in the fellow eye of subjects with 6/9 or better was correlated to the PAM result indicating a moderate to good predictive power in ‘normal’ eyes. Conclusions : PAM results were considered to be poor for a clinical test. The results of this study indicate that this instrument has only a limited usefulness as part of the standard preoperative examination in patients undergoing cataract extraction.     

A comparison of visual function tests in eyes with maculopathy

Several recently developed tests of visual function, including the Potential Acuity Meter (PAM), laser interferometer (LI), white-light interferometer (WLI), blue field entoptic phenomenon, and focal electroretinogram (ERG) were compared in 81 eyes with clear media and known macular disease. The results indicate that the PAM, the LI, and the WLI overread relative to Snellen acuity. Laser interferometric acuity values differed from Snellen acuity by at least 1.5 octaves in approximately 40% of all eyes, regardless of stimulus size (2, 5, or 8 degrees). Similar results were obtained with the WLI. Agreement with Snellen acuity was better for the PAM, with 91% of eyes falling within 1.5 octaves of Snellen acuity. Blue field and focal ERG results were categorized as normal or abnormal. While not producing Snellen equivalents, abnormal results from the blue field and focal ERG corresponded with poor Snellen acuity (less than 20/40) in 65% and 91% of eyes, respectively. Assuming that media opacities do not prevent adequate retinal stimulation, the present results suggest that the PAM and focal ERG are the most reliable for evaluating macular function when maculopathy is present.     

The relationship between indoor and outdoor Snellen visual acuity in cataract patients

One hundred six cataractous eyes of 78 patients were evaluated to examine the relationship between indoor and outdoor Snellen visual acuity. While 81 of all cataractous eyes (76.4%) had Snellen visual acuities of 20/40 or better when tested indoors, only 33 eyes (31.2%) had 20/40 or better Snellen visual acuities when tested outdoors facing the sun. When tested indoors, only three eyes (2.8%) had Snellen visual acuities worse than 20/80, while 31 eyes (29.2%) had outdoor Snellen visual acuities worse than 20/80. Ten eyes (9.4%) had outdoor Snellen visual acuities worse than 20/200. Seventy-four eyes (69.8%) had outdoor visual acuities that were at least two Snellen lines worse than those measured indoors and 23 eyes (21.7%) had outdoor visual acuities that were at least five Snellen lines worse. The median difference between indoor and outdoor visual acuity was three Snellen lines. The need for increased precision in the ability to assess outdoor "real world" vision while in the ophthalmologist's examination room is discussed. Clearly, indoor Snellen visual acuity alone is insufficient to evaluate functional visual impairment in cataract patients.     

Eccentric visual acuity in patients with macular disease

A series of cards each containing a two dimensional array of identical Snellen "E's" was used to determine best eccentric visual acuity in patients with macular disease having Snellen visual acuity of 20/70 or worse. Each "full field E" card simultaneously presents the same letter to foveal and parafoveal areas. This test can therefore determine quickly if potentially useful vision is present in any area of the central visual field. In our study of 37 eyes, 70% demonstrated potential visual acuity at least two times better than visual acuity measured by conventional methods, and 20% demonstrated at least a fourfold improvement. This suggests that most patients with macular disease do not spontaneously employ their best remaining area of retina for fixation.     

小梁切除术后影响视力因素的临床分析

目的探讨青光眼患者小梁切除术术后影响视力的因素.方法回顾分析59例74只眼青光眼患者实施小梁切除术对视力的直接影响诸因素.并对视力较术前降低者展开讨论.结果术后视力改变程度59只眼(79.76%)不变和提高;15只眼(20.24%)降低.视力下降者年龄≤60岁者占26.7%,＞60岁者占73.3%.引起视力下降是综合因素,诸如瞳孔散大,晶状体混浊加重,晶状体前囊色素附丽,前房出血等.结论各类青光眼中慢性闭角型及老年伴有全身性疾病者手术后更具有发生视力下降的可能性,视力下降原因大多系多因素综合.     

Comparison of the potential acuity meter and pinhole tests in predicting postoperative visual acuity after cataract surgery

PURPOSE: To compare the accuracy of potential acuity meter (PAM) and pinhole (PH) tests in predicting visual acuity after cataract surgery. SETTING: Department of Ophthalmology and Visual Sciences, University of the Philippines, Philippine General Hospital, Manila, and Asian Eye Institute, Makati, Philippines. METHODS: This prospective study comprised 64 eyes with mild to moderate cataract that had uneventful phacoemulsification. The PAM and PH tests were performed to predict postoperative visual acuity. Best corrected visual acuity (BCVA) 4 weeks after surgery was compared with the predicted visual acuity. The number of lines of inaccuracy was calculated by subtracting the BCVA from the predicted visual acuity. The variables analyzed were type of predictive test and preoperative BCVA. The eyes were divided according to preoperative BCVA as follows: Group 1, 20/20 to 20/50; Group 2, 20/60 to 20/100; Group 3, 20/200 or worse. RESULTS: The PH predicted visual acuity was correct in 5% of eyes and the PAM predicted acuity, in 17%. The PH predicted acuity was accurate within 1, 2, and 3 lines of BCVA in 23%, 40%, and 54% of eyes, respectively, and the PAM predicted acuity, in 64%, 81%, and 92% of eyes, respectively. The mean number of lines of inaccuracy was significantly less with the PH than with the PAM (3.47 lines +/- 2.42 [SD] and 1.60 +/- 1.55 lines, respectively) (P=.0005). The mean lines of inaccuracy in Group 1 were 2.49 +/- 1.52 for the PH and 1.14 +/- 0.99 for the PAM (P=.027); in Group 2, 3.17 +/- 1.99 PH and 1.65 +/- 1.80 PAM (P=.642); and in Group 3, 6.58 +/- 3.03 PH and 2.67 +/- 2.10 PAM (P=.240). CONCLUSIONS: The PAM was more accurate than the PH in predicting visual acuity after cataract surgery. The accuracy of both tests decreased in patients with poorer preoperative visual acuity.     

原发性婴幼儿型青光眼视力影响因素分析

目的 探讨影响原发性婴幼儿型青光眼患者术后视力的主要因素。方法 收集手术治疗成功的原发性婴幼儿型青光眼患者23例40眼，记录矫正视力，分析视力的影响因素。结果 （1）本组病例中视力≥0．4者14眼，占35％，23眼为低视力眼，占57．5％，盲眼有3眼，盲目率7．5％；（2）经过多因素分析发现影响视力的主要因素是视神经损害，角膜损害（Haab纹），屈光不正和屈光参差。结论 影响原发性婴幼儿型青光眼患者视力的主要因素除了视神经损害以外还有角膜损害（Haab纹），屈光不正及屈光参差。改善视力预后的措施：在早期诊断，早期手术治疗的基础上，术后密切随访，及时发现和矫正屈光不正，以及采取积极的弱视治疗尤其重要。     

Visual acuity following treatment of bilateral congenital cataracts

Several studies have indicated that operation during the first months of life in children with dense congenital cataract improves the final visual acuity. In the current study seven otherwise healthy children operated on before the age of fifty-six days are compared with seven children operated on after the age of three months. The patients were followed by a team consisting of a paediatric ophthalmologist, a contact lens optician and an orthoptist. They were treated with contact lenses, spectacles with near addition and occlusion therapy when needed. Visual acuity was initially tested with preferential looking technique and later with Snellen optotypes. In the early treated group the visual development was almost normal with a final visual acuity of 20/20, while in the late treated group no patient obtained better visual acuity than 20/100. The findings indicate that dense congenital cataract should be treated before the age of three months.     

Relating vernier acuity and Snellen acuity in specific clinical populations

The relationship between vernier acuity and Snellen acuity in a group of cataract patients was examined. The vernier stimulus consisted of two small spots of light, vertically separated by a variable-sized gap. The Snellen stimulus was a standard projected Snellen chart. The form of the relation between vernier and Snellen acuity was found to depend upon the vernier gap size used. Specifically, when the smaller gaps of 4 or 8 min of arc are used, the two types of acuity are linearly related. When the gap is 16 or 32 min of arc, (or if best vernier performance irrespective of gap is considered) vernier acuity is related to Snellen acuity by a power function with an exponent less than one, within this clinical population. Thus, with increasing degrees of retinal image degradation caused by cataract, optimum vernier acuity is impaired at a slower rate than Snellen acuity. Our results in cataract patients are compared to results obtained by others within a population of strabismic and anisometropic amblyopes.     

影响原发性先天性青光眼手术后视力的原因分析

目的：探讨影响原发性先天性青光眼术后视力的原因及预防措施。方法：追踪检查５１只接受手术治疗后１０年以上的原发性先天性青光眼的眼压、视力、角膜及杯盘比值等的变化情况。结果：手术不成功的１２只眼视力全部在０．０５以下。手术成功的３９只眼视力在０．１至０．８以上，７只单眼发病者视力都在０．２以下；角膜直径大于１３ｍｍ的２７只眼中２１中眼有Ｈａａｂ线存在；杯盘比值大于０．２以上者１２只眼。结论：手术不成功     

Potential acuity pinhole: a simple method to measure potential visual acuity in patients with cataracts, comparison to potential acuity meter.

OBJECTIVE: To describe the potential acuity pinhole (PAP) test and compare its accuracy to the potential acuity meter (PAM) in predicting visual outcome after cataract surgery. STUDY DESIGN: Prospective case series. PARTICIPANTS: A total of 56 preoperative patients with cataracts participated. MAIN OUTCOME MEASURES: Accuracy of predicting postoperative distance visual acuity was measured. METHODS: Lines of inaccuracy were calculated by subtracting actual postoperative best-corrected distance visual acuity (BCVA) from predicted values. Variables analyzed were method of prediction, preoperative BCVA, and preoperative spherical equivalent. RESULTS: The PAP test predicted visual outcomes within 2 lines in 100%, 100%, and 56% of eyes with preoperative BCVA of 20/50 and better (group 1), 20/60 to 20/100 (group II), and 20/200 and worse (group III), respectively. The PAM predictions within 2 lines for the same groups were 42%, 47%, and 0%, respectively. Mean lines of inaccuracy of PAP predictions were 0.83, 1.11, and 3.50 lines for groups I, II, and III, respectively. Mean lines of inaccuracy for PAM predictions were 2.50, 2.68, and 6.22 lines for the same groups. Differences in lines of prediction between PAM and PAP were 1.67 (P = 0.004), 1.58 (P = 0.0002), and 2.72 lines (P = 0.0001) for groups I, II, and III, respectively. There was no statistically significant correlation between PAP predictions and preoperative myopic spherical equivalent. CONCLUSIONS: The PAP test is a simple, inexpensive, and relatively reliable method to estimate visual outcome after uncomplicated cataract surgery in eyes with no coexisting disease. It is less accurate in patients with preoperative BCVA worse than 20/200. It appears to be more predictive than PAM.     

Comparison of Snellen acuity and objective assessment using the spatial frequency sweep PVER

Background: We compared the vision objectively assessed by spatial frequency sweep pattern-reversal visual-evoked response (SPVER) with the Snellen acuity in patients. Methods: SPVER acuity and Snellen acuity were measured in 100 patients with various ocular pathologies, including macular diseases, diffuse retinal degeneration, optic nerve diseases, glaucoma, and high myopia. For SPVER, 10 sinusoidally modulated vertical gratings were presented as stimuli. The responses were averaged and displayed through the discrete Fourier transform on the monitor display. The PVER acuity was determined by extrapolating the SPVER amplitude-spatial frequency function to baseline. Results: Vision ranged from 20/15 to 20/400 with Snellen acuity, and from 20/25 to 20/190 with SPVER. The overall correlation between the two acuities wasr=0.666. The correlation varied fromr=0.895 in eyes with glaucoma tor=0.436 in eyes with optic nerve disease. Seventy-seven eyes (77%) had a visual acuity agreement of within 1.0 octave between the two measurements. Conclusion: The SPVER acuity and the Snellen acuity correlated to a certain degree. Discrepancies were found in certain diseases, with the highest disparity in patients with optic nerve disease. We conclude that the SPVER is effective in estimating vision objectively, particularly in patients in whom the standard Snellen test is impossible to perform or yields unreliable results.This study was presented in part at the American Academy of Ophthalmology Annual Meeting, San Francisco, November 1994     

The influence of cataract types on potential acuity meter results

The records of 100 patients who had cataract surgery were reviewed to compare preoperative potential acuity meter (PAM) results with postoperative visual acuity. A PAM acuity was obtainable in 95 patients. In 82 of the 95 patients (86%), the PAM levels were within three lines of the outcome. Potential acuity meter results substantially lower (less than or equal to four Snellen lines) than outcome generally occurred when posterior subcapsular (PSC) or PSC plus diffuse cortical or nuclear changes were present. We believe that the PAM projection can usually go around or through the nuclear sclerosis to give an accurate prediction. However, with PSC or mixed type, one may not always find a window in the cataract. Also, PSC or diffuse cortical cataracts may be particularly disruptive to the paracentral diffracted light that is an important factor in PAM acuity.     

Comparison of contrast sensitivity,visual acuity,and Humphrey visual field testing in patients with glaucoma

BACKGROUND: Despite their normal or near-normal Snellen visual acuity, patients with glaucoma often complain of "poor" vision. OBJECTIVE: To investigate the relationship between large-letter contrast sensitivity, high-contrast visual acuity, and visual field defects in patients with glaucoma who have 20/40 or better visual acuity. DESIGN :Prospective, cross-sectional case series. PATIENTS AND METHODS: We evaluated 250 eyes of 144 subjects from the Glaucoma Service at the University of Illinois at Chicago College of Medicine. Subjects with a diagnosis of glaucoma, suspected glaucoma, or ocular hypertension who met the 20/40 or better vision requirement were recruited. Visual acuity was measured using the rear-illuminated Lighthouse Visual Acuity Chart at 4 m. Contrast sensitivity was measured using the Pelli-Robson Chart in a front-illuminated box with even luminance across the chart. Visual fields of the patients were measured using the 24-2 full-threshold program on the Humphrey Visual Field Analyzer. RESULTS: A significant correlation (r = 0.57, P < 0.001, n = 127) was found between the visual field mean deviations and the contrast sensitivity scores. The correlation (r = -0.322, P < 0.001, n = 127) was less between the visual field mean deviation and the log MAR visual acuity values, as was the correlation between the contrast sensitivity scores and log MAR visual acuity values (r = -0.370, P < 0.001, n = 127). In the subgroup of patients with chronic open-angle glaucoma, the correlation between the mean visual field deviation and the contrast sensitivity score was higher at 0.689 (P < or = 0.001, n = 62). CONCLUSIONS: Reduced contrast sensitivity is significantly correlated with visual field losses in patients with glaucoma and a visual acuity of 20/40 or better. The study data support the conclusion that, compared with visual acuity, the disease process preferentially affects contrast sensitivity. In our previous work, contrast sensitivity was shown to be more related than visual acuity to real-world function in patients with early glaucomatous changes.     

10-Hz flash visual evoked potentials predict post-cataract extraction visual acuity

Cataract patients suspected of having disease which might interfere with good postoperative visual function were referred for evaluation. Monocular steady-state luminance visual evoked potentials (VEPs) were elicited with closed eyes at a stimulus rate of 10 flashes/sec. VEPs were rated as either normal or abnormal. Patients with normal VEPs were predicted to have an acuity of 6/15 (20/50) or better. Patients with abnormal VEPs were predicted to have acuities of 6/18 (20/60) or worse. Postoperative acuities were determined for all patients who underwent surgery and who had no intraoperative or early postoperative complications. The association of preoperative VEPs and observed postoperative acuities were quantitatively compared by a 2 × 2 contingency table for the 59 eyes which met these criteria. The chi-square was significant (p < 0.001). The overall accuracy of prediction was 76%. Accuracy was 80% for patients with a preoperative acuity of 6/60 (20/200) or better and 75% for those whose postoperative acuity was 6/120 (20/400) or worse. This difference was not statistically significant.Research supported by an unrestricted departmental grant from Research to Prevent Blindness, Inc.     

正视眼波前像差与低对比度视力相关性研究

目的 分析正视眼波前像差与低对比度视力的相关性.方法 对95例(95眼)健康正视眼用WASCA(wavefront supported corneal ablation)波阵面像差仪测眼波前像差,对瞳孔6 mm时第2,3,4阶像差的各项Zernike函数(C3-C14)进行分析.用多功能电子视力测量仪检测亮、暗环境中对比度为10﹪和5﹪时的裸眼视力和最佳矫正视力.用多元线性回归分析眼波前像差与各低对比度视力间的相关关系.结果 离焦像差(C4)与亮、暗环境中对比度为10﹪和5﹪时的裸眼视力间的直线相关关系有统计学意义(P＜0.01);水平彗差(C8)与亮、暗环境中对比度为10﹪和5﹪时的最佳矫正视力间的直线相关关系有统计学意义(P＜0.01).其余Zernike 函数与各低对比度视力间的直线相关关系均无统计学意义(P＞0.05).结论 正视眼的波前像差与低对比度视力有关,其中离焦像差与裸眼视力有关,水平彗差与最佳矫正视力有关.     

Neodymium: YAG laser posterior capsulotomy: visual acuity outcome and intraocular pressure elevation

A Q-switched neodymium: YAG laser was used to perform 67 posterior capsulotomies in 67 patients. A clear visual axis was produced in all the eyes. The visual acuity improved by one or more Snellen lines in 90% of the eyes, and the final visual acuity was 20/40 (6/12) or better in 78% of the eyes. Cystoid macular edema developed in two patients after capsulotomy. Increases in intraocular pressure were most prevalent in the early postoperative period. No significant correlation was found between the acute pressure rise and the laser energy used, a previous history of glaucoma or the presence of an intraocular lens. After 6 months of follow-up none of the eyes showed a permanent pressure elevation.     

Estimating visual acuity by character counting using the Snellen visual acuity chart

PURPOSE: This study examines visual acuity estimation with character counting, which can be used in subjects with nonorganic visual loss. METHODS: The right eyes of 35 healthy subjects were fogged with plus lenses and tested with the Snellen visual acuity chart (Reichert 11180). Visual acuity and counting level were assessed under various degrees of fogging, up to a maximal fogged acuity of 20/200. Counting level was defined as the smallest line that subjects could count the number of characters correctly. For each counting level, the visual acuity that 95% of subjects could see equal to or better than was determined. RESULTS: A counting level of 20/10 estimates (ie 95% chance) a visual acuity equal to or better than 20/30. Counting levels 20/15, 20/20, and 20/25 estimate visual acuities of at least 20/50, 20/80, and 20/80, respectively. Counting levels 20/30-20/60 estimate a visual acuity of at least 20/200. CONCLUSIONS: Character counting appears to be a useful technique of obtaining a rough estimate of visual acuity in subjects unable to be tested by standard methods, such as those with non-organic visual loss.     

Grating acuity overestimates Snellen acuity in patients with age-related maculopathy

In foveally fixating patients resolution acuity is approximately the same when measured with a Snellen chart (Snellen acuity) or when estimated from the high frequency cutoff of the contrast sensitivity function (CSF) (grating acuity). In contrast, with peripheral viewing, normal patients have better grating than Snellen acuity. This suggests that grating acuity deteriorates less rapidly with eccentricity than does Snellen acuity. If patients with bilateral age-related maculopathy (ARM) fixate with a single, healthy peripheral-retinal locus, grating and Snellen acuities should be similar to those in the normal periphery. As expected from the normal data, grating acuity was better than Snellen acuity in all 19 patients with ARM. Although some showed acuities which were similar to those of the normal periphery, others had Snellen acuities that were even worse than predicted from the normal peripheral acuity. Possible explanations for the superiority of grating over Snellen acuity are discussed.     

Long-term visual prognosis in children after corneal transplant surgery for Peters anomaly type I

PURPOSE: To evaluate the long-term visual prognosis in children with corneal transplant surgery for Peters anomaly type I. DESIGN: Retrospective review of interventional case series. METHODS: Twenty-four children treated in a university-based practice were divided into two groups for analysis: a younger preverbal group and an older group of children three years of age or older. Children underwent corneal transplantation surgery (penetrating keratoplasty [PKP]) for Peters anomaly type I as infants (age range, two to 18 months). Visual acuity using Snellen or Allen charts and glaucoma and other complications were tabulated. RESULTS: Twenty-four patients had Peters anomaly; 16 had unilateral disease, eight had bilateral disease. Thirty eyes underwent PKP. Average age at PKP was five months. The mean follow-up from PKP to the most recent visit was 78.9 months. Fifteen eyes (50%) were treated for glaucoma. Five transplants (17%) had graft rejection episodes; two of these failed and were regrafted. Six eyes (20%) required cataract surgery. One eye had a retinal detachment. Currently, 27 eyes (90%) have clear grafts. In the younger group of children, five of six grafts are clear (83%). In the older group of 24 eyes of verbal children, seven eyes (29%) have visual acuity ranging from 20/20 to 20/50, six (25%) have visual acuity ranging from 20/60 to 20/100, nine (38%) have visual acuity ranging from 20/200 to counting fingers, and two eyes (8%) have visual acuity of hand movements. In this group, nine of 12 eyes without glaucoma had visual acuity better than 20/100; only four of 11 eyes with glaucoma were better than 20/100. CONCLUSIONS: Many children with PKP for Peters anomaly type I can experience good or functional vision in their operated eye. Children with glaucoma have a poorer visual prognosis.