Glare and contrast sensitivity testing in cataract patients

Photophobia and disability glare in adult patients with Marfan syndrome: a case-control study

PURPOSE

The aim of the present study was to investigate photophobia and disability glare in adult patients with Marfan syndrome (MFS).

METHODS

In this case-control study, 44 patients with MFS (87 eyes) were compared to 44 controls (88 eyes), who were matched for age and sex. The subjects were asked to grade their photophobia and glare using 10-cm visual analogue scales (VAS), which were marked with 'never' at zero and 'always' at 10 -cm. In addition, disability glare was measured with C-Quant straylight meter.

RESULTS

The patients with MFS had significantly higher VAS scores than the controls in four out of seven statements related to photophobia and glare. When including cataract, spherical equivalent, iris colour, axial length and corneal curvature, three of the seven statements were still significantly different between the two groups. The mean straylight values were 1.29 ± 0.03 log(s) in the MFS group and 1.01 ± 0.03 log(s) in the control group (p < 0.001, mixed model). These differences remained significant after adjusting for cataract, spherical equivalent, iris colour, axial length and corneal curvature.

CONCLUSION

Patients with MFS reported more photophobia and had a higher straylight value than the control group. Awareness of these findings of more photophobia and glare in the MFS patients is important when counselling and treating these patients.

Responses of turkey vultures to unmanned aircraft systems vary by platform

A challenge that conservation practitioners face is manipulating behavior of nuisance species. The turkey vulture (Cathartes aura) can cause substantial damage to aircraft if struck. The goal of this study was to assess vulture responses to unmanned aircraft systems (UAS) for use as a possible dispersal tool. Our treatments included three platforms (fixed-wing, multirotor, and a predator-like ornithopter [powered by flapping flight]) and two approach types (30 m overhead or targeted towards a vulture) in an operational context. We evaluated perceived risk as probability of reaction, reaction time, flight-initiation distance (FID), vulture remaining index, and latency to return. Vultures escaped sooner in response to the fixed-wing; however, fewer remained after multirotor treatments. Targeted approaches were perceived as riskier than overhead. Vulture perceived risk was enhanced by flying the multirotor in a targeted approach. We found no effect of our treatments on FID or latency to return. Latency was negatively correlated with UAS speed, perhaps because slower UAS spent more time over the area. Greatest visual saliency followed as: ornithopter, fixed-wing, and multirotor. Despite its appearance, the ornithopter was not effective at dispersing vultures. Because effectiveness varied, multirotor/fixed-wing UAS use should be informed by management goals (immediate dispersal versus latency).

Reduced Contrast Sensitivity Function in Central and Peripheral Vision by Disability Glare

Various glares can decrease visual performance and cause discomfort, thus increasing drivers' risk for traffic accidents in real life. The current study aimed to systematically investigate glare sensitivity in the central and peripheral visual fields by measuring contrast sensitivity function (CSF) under nonglare, steady glare, and transient glare conditions. Nine observers with normal visual acuity in the dominant eye were enrolled. The CSF in central and peripheral vision (the 5° upper left visual field) was measured in a mesopic environment while the stimulus was displayed under three conditions: nonglare, steady glare, and transient glare. An orientation identification task was used to obtain the CSF. After the experiment, the observers were asked to report their level of discomfort in the presence of the glare. The area under the log CSF (AULCSF) and cut-off spatial frequency served as indicators of visual performance. In agreement with previous studies, both steady and transient glare reduced the AULCSF and cut-off frequency. However, the AULCSF and cut-off frequency were reduced more for central vision than for nearly peripheral vision. In addition, the extent of the decreases in the AULCSF and cut-off frequency was greater for steady glare than for transient glare; in contrast, more discomfort was associated with transient glare than steady glare.

Visual field shape and foraging ecology in diurnal raptors

Birds, particularly raptors, are believed to forage primarily using visual cues. However, raptor foraging tactics are highly diverse — from chasing mobile prey to scavenging — which may reflect adaptations of their visual systems. To investigate this, we studied the visual field configuration of 15 species of diurnal Accipitriformes that differ in such tactics, first focusing on the binocular field and blind area by using a single traits approach, and then exploring the shape of the binocular field with morphometric approaches. While the maximum binocular field width did not differ in species of different foraging tactics, the overall shape of their binocular fields did. In particular, raptors chasing terrestrial prey (ground predators) had a more protruding binocular field and a wider blind area above the head than did raptors chasing aerial or aquatic prey and obligate scavengers. Ground predators that forage on mammals from above have a wide but short bill — which increases ingestion rate — and large suborbital ridge to avoid sun glare. This may explain the protruding binocular field and the wide blind area above the head. By contrast, species from the two other groups have long but narrow bills used to pluck, flake or tear food and may need large visual coverage (and reduced suborbital ridges) to increase their foraging efficiency (e.g. using large visual coverage to follow the escaping prey in three dimensions or detect conspecifics). We propose that binocular field shape is associated with bill and suborbital ridge shape and, ultimately, foraging strategies.

TuebingenCSTest - a useful method to assess the contrast sensitivity function

Since contrast sensitivity (CS) relies on the accuracy of stimulus presentation, the reliability of the psychophysical procedure and observer's attention, the measurement of the CS-function is critical and therefore, a useful threshold contrast measurement was developed. The Tuebingen Contrast Sensitivity Test (TueCST) includes an adaptive staircase procedure and a 16-bit gray-level resolution. In order to validate the CS measurements with the TueCST, measurements were compared with existing tests by inter-test repeatability, test-retest reliability and time. The novel design enables an accurate presentation of the spatial frequency and higher precision, inter-test repeatability and test-retest reliability compared to other existing tests.

Performance of a differential contrast sensitivity method to measure intraocular scattering

Increased intraocular scatter degrades quality of vision, especially in the presence of glare sources. Standard tests, such as visual acuity, are not well suited to capture this condition. There are specific methods to measure intraocular scatter, but require dedicated instruments. In this work, we propose a method to estimate the amount of scatter by combining to sequential measurements of the contrast sensitivity function for two conditions, with and without a glare source. We applied the approach in a group of young subjects with no know ocular pathology fitted with photographic diffusing filters. The straylight estimates were compared with those provided by two alternative techniques, one based on the compensation comparison method and the other the optical integration. The results obtained with the three approaches were in a good agreement, demonstrating the feasibility of the proposed method.

Vision in avian emberizid foragers: maximizing both binocular vision and fronto-lateral visual acuity

Avian species vary in their visual system configuration, but previous studies have often compared single visual traits between 2-3 distantly related species. However, birds use different visual dimensions that cannot be maximized simultaneously to meet different perceptual demands, potentially leading to trade-offs between visual traits. We studied the degree of inter-specific variation in multiple visual traits related to foraging and anti-predator behaviors in nine species of closely related emberizid sparrows, controlling for phylogenetic effects. Emberizid sparrows maximize binocular vision, even seeing their bill tips, which may enhance the detection of prey and facilitate food handling. Sparrows have a single retinal center of acute vision (i.e., fovea) projecting fronto-laterally (but not into the binocular field). The foveal projection close to the edge of the binocular field may shorten the time to gather and process both monocular and binocular visual information from the foraging substrate. Contrary to previous work, we found that species with larger visual fields had higher visual acuity, which may compensate for larger blind spots (i.e., pectens) above the center of acute vision, enhancing predator detection. Finally, species with a steeper change in ganglion cell density across the retina had higher eye movement amplitude likely due to a more pronounced reduction in visual resolution away from the fovea, which would need to be moved around more frequently. The visual configuration of emberizid passive prey foragers is substantially different from that of previously studied avian groups (e.g., sit-and-wait and tactile foragers).

Cataracts among adults aged 30 to 49 years: a 10-year study from 1995 to 2004 in Korea

Purpose

To investigate the long-term characteristics of cataracts among adults aged 30 to 49 years in Korean over a span of 10 years.

Methods

Subjects between the ages of 30 to 49 years who underwent cataract surgery at St. Mary's Hospital from 1995 to 2004 (n = 976) were included. Patients with a history of ocular trauma, uveitis, other ocular or systemic diseases, and congenital cataracts were excluded. Additional information including type of lens opacity, urban/rural region, and pre- and postoperative visual acuities were analyzed. Lens opacity grading was conducted using Lens Opacity Classification System III. The Cochran-Armitage proportion trend test was used to analyze vision changes with the passage of time.

Results

Among the patients who had undergone cataract surgeries, 8.8% (976 / 11,111) met the inclusion criteria. The mean age was 41.7 ± 5.45 years. Gender breakdown of the patient population included 79.0% male and 21.0% female. In terms of home environment, 60.9% were from an urban region and 39.1% from a rural region. Opacity type included anterior polar (AP), posterior subcapsular (PSC), AP and PSC, cortical, and nuclear in 35.7%, 35.1%, 7.0%, 6.0%, and 5.4% of patients, respectively. At a 2-month postoperative follow-up appointment, 92.7% of patients showed a best-corrected visual acuity of more than 20 / 40.

Conclusions

Predominance of AP and PSC opacities as well as male patients was observed in this study population.

Optical functional properties of the Boston Keratoprosthesis

PURPOSE

To evaluate the optical characteristics of the Boston Keratoprosthesis (KPro), identify glare sources, evaluate possible glare control, and examine the benefit of implantation when the fellow eye has normal vision.

METHODS

Computed and optical-bench-measured point spread function (PSF) and glare sources were compared. A translucent plastic cornea was used to determine the impact of glare caused by scatter in the cornea and its control with a dark-iris tinted contact lens. The effect of glare in implanted eyes was measured with a brightness acuity test (BAT), with and without the dark-iris contact lens. Computed and measured visual fields were compared. Stereopsis was measured in patients with an intact fellow eye.

RESULTS

Computed and measured modulation transfer functions for the KPro were found to be very close to the diffraction limit. Both the model-eye measurements and patients' BAT glare responses identified that the hazy corneal graft surrounding the KPro is the main source of glare and can be controlled with a dark-iris contact lens. The lid effectively blocks the light that would be scattered in the hazy cornea of patients in whom the type II KPro was implanted. An intact fellow eye remains the dominant eye, with better acuity, and the KPro eye supports only minimal stereo ability and does not expand the binocular visual field.

CONCLUSIONS

Glare can be reduced significantly with the use of a contact lens with a dark iris. Implanting the KPro in a patient whose fellow eye has normal or near normal vision does not seem to improve visual function.

Association Between Visual Impairment and Patient-Reported Visual Disability at Different Stages of Cataract Surgery

PURPOSE

To evaluate the association between visual impairment (visual acuity, contrast sensitivity, stereopsis) and patient-reported visual disability at different stages of cataract surgery.

METHODS

A cohort of 104 patients aged 60 years and over with bilateral cataract was assessed preoperatively, after first-eye surgery (monocular pseudophakia) and after second-eye surgery (binocular pseudophakia). Partial correlation coefficients (PCC) and linear regression models were calculated.

RESULTS

In patients with bilateral cataracts, visual disability was associated with visual acuity (PCC = -0.30) and, to a lesser extent, with contrast sensitivity (PCC = 0.16) and stereopsis (PCC = -0.09). In monocular and binocular pseudophakia, visual disability was more strongly associated with stereopsis (PCC = -0.26 monocular and -0.51 binocular) and contrast sensitivity (PCC = 0.18 monocular and 0.34 binocular) than with visual acuity (PCC = -0.18 monocular and -0.18 binocular). Visual acuity, contrast sensitivity and stereopsis accounted for between 17% and 42% of variance in visual disability.

CONCLUSIONS

The association of visual impairment with patient-reported visual disability differed at each stage of cataract surgery. Measuring other forms of visual impairment independently from visual acuity, such as contrast sensitivity or stereopsis, could be important in evaluating both needs and outcomes in cataract surgery. More comprehensive assessment of the impact of cataract on patients should include measurement of both visual impairment and visual disability.

Principles of disability glare measurement: an ophthalmological perspective

Disability glare describes the loss of retinal image contrast as a result of intraocular light scatter, or straylight. It has increasingly important modern implications such as with cataract and refractive surgery or high-intensity lighting. However, its measurement has proven difficult despite many varying approaches. This article aims to explain the principles and problems associated with glare testing that are important for assessment and use of glare measures. After defining disability glare, this article discusses the importance of its measurement to current clinical practice. It explains the principles and mechanisms that underlie disability glare and its measurement. Finally, some examples of available glare tests are described to illustrate the principles discussed.

Rapid, objective detection of cataract-induced blur using a bull's eye photodetector

PURPOSE

To determine whether optical aberrations caused by cataract can be detected and quantified objectively using a newly described focus detection system (FDS).

SETTING

The Wilmer Opthalmological Institute, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.

METHODS

The FDS uses a bull's eye photodetector to measure the double-pass blur produced from a point source of light. To determine the range and level of focus, signals are measured with a series of trial lenses in the light path selected to span the point of best focus to generate focus curves. The best corrected visual acuity (BCVA), refractive error, lens photograph grades, and FDS signals were obtained in 18 patients scheduled to have cataract surgery. The tests were repeated 6 weeks after surgery.

RESULTS

The mean FDS outcome measures improved after cataract surgery, with increased peak height (P=.001) and decreased peak width (P=.001). Improvement in signal strength (integral of signal within +/-1.5 diopters of the point of best focus) strongly correlated with improvement in peak height (R(2)=.88, P<.0001) and photographic cataract grade (R(2)=.72, P<.0001). The mean BCVA improved from 20/50 to 20/26 (P<.0001). The improvement in BCVA correlated more closely with FDS signal strength (R(2)=.44, P=.001) than with cataract grade (R(2)=.25, P=.06).

CONCLUSIONS

Improvement in FDS outcome measures correlated with cataract severity and improvement in visual acuity. This objective approach may be useful in long-term studies of cataract progression.

Clinical symptoms and visual outcome in patients with presumed congenital cataract

PURPOSE

To investigate clinical symptoms and visual outcome in patients who had presumed congenital cataract with visual acuity > or =20/200.

METHODS

Twenty-nine patients (50 eyes) ranging in age from 5-28 years were included in this study. Congenital cataract was diagnosed by patients' past history, previous medical records, and typical findings of congenital cataract. Inclusion criteria were patients with visual acuity measured by Snellen chart, best corrected visual acuity > or =20/200, and no eye or systemic diseases influencing visual acuity. Seven patients had unilateral cataracts and 22 patients had bilateral cataracts. Cataracts were nuclear in 29 eyes, anterior or posterior subcapsular in 12 eyes, and polar in 7 eyes. All patients underwent lens aspiration or phacoemulsification combined with posterior chamber intraocular lens (PC-IOL) implantation without performing intentional posterior capsulotomy and anterior vitrectomy.

RESULTS

The most common clinical symptom was visual disturbance followed by blurred vision, glare and knitting the brow, strabismus, and leukocoria. Comparison of calculated PC-IOL power showed a more significant myopic shift in unilateral cataract than in bilateral cataract. Postoperative best corrected visual acuity >20/25 was attained in 28 (65.1%) eyes with bilateral cataracts and 1 (14.3%) eye with a unilateral cataract.

CONCLUSIONS

Cataract surgery is effective not only in improving visual acuity but also in eliminating clinical symptoms. Delaying cataract surgery in early infancy should be considered to avoid intentional operative procedures in patients with bilateral congenital cataract preserving visual acuity >20/200.

Use of vision tests in clinical decision making about cataract surgery: results of a national survey

AIM

To provide information on the use of vision tests in clinical decision making about cataract surgery in the UK.

METHOD

A questionnaire survey was mailed to 703 consultant ophthalmologists.

RESULTS

A response rate of 70% was obtained. Monocular distance visual acuity was the only visual function that was tested routinely by all surgeons. Supplementary use of contrast sensitivity and glare testing was low. Many surgeons (35%) were willing to consider surgery at acuity levels better than 6/9 and a small but substantial number (12%) indicated that they did not use an acuity criterion. Being prepared to consider surgery at relatively good levels of acuity was not associated with more common use of other tests of vision.

CONCLUSION

Many UK surgeons are prepared to consider cataract extraction at relatively good levels of visual acuity and use other vision tests infrequently.

Functional complaints, visual acuity, spatial contrast sensitivity, and glare disability in preoperative and postoperative cataract patients

PURPOSE

To quantify cataract patients' functional visual complaints and correlate them with their objective glare disability and spatial contrast sensitivity (SCS) scores.

SETTING

Sir Mortimer B. Davis Jewish General Hospital. Montreal, Quebec, Canada.

METHODS

Thirty patients scheduled for cataract surgery with a visual acuity of 20/70 or better at the time of patient selection and no other ocular pathology were evaluated objectively and subjectively for visual function preoperatively and within 3 months postoperatively. Objective measures of SCS and visual acuity in the presence and absence of glare were obtained with the Optec 3000 vision tester. Subjective visual function was evaluated with the Activities of Daily Vision Scale (ADVS), a questionnaire that evaluates patients' visual function by assessing the degree of difficulty they experience in performing tasks involving distance vision, near vision, and glare conditions.

RESULTS

Preoperatively, patients had decreased visual acuity and SCS in the presence of glare. The ADVS scores were correlated with visual performance. Postoperatively, there was a statistically significant improvement in all dependent measures (i.e., visual acuity and SCS in the presence of glare) as well as in the subjective report of visual performance assessed by the ADVS.

CONCLUSION

Spatial contrast sensitivity, glare disability, and the ADVS questionnaire should be considered as adjuncts to visual acuity testing in evaluating certain cataract patients.

Visual acuity versus letter contrast sensitivity in early cataract

Large and small letter contrast sensitivity and visual acuity were assessed in 37 elderly eyes (mean VA -0.01 logMAR, Snellen 6/6) and their lens opacities were categorised and graded using the LOCS III system. Large letter contrast sensitivity was often not reduced in cataract from age-matched normal values and provided limited information. Small letter contrast sensitivity was shown to be a more sensitive measure of early cataract than visual acuity and large letter contrast sensitivity. Its usefulness may be limited by its strong correlation with visual acuity (r2 = 0.70), which is the standard and traditional measure of vision in cataract.

An instrument for assessment of subjective visual disability in cataract patients

AIMS/BACKGROUND

The construction and validation of an instrument for the assessment of subjective visual disability in the cataract patient is described. This instrument is specifically designed for measuring the outcome of cataract surgery with respect to visual disability.

METHODS

Visually related activities thought to be affected by cataract were considered for the questionnaire. These were reduced by pilot study and principal components analysis to 18 items. A patient's assessment of his/her ability to perform each task was scored on a four point scale. Scores were averaged to create an overall index of visual disability, as well as subscale indices for mobility related disability, distance/lighting/reading related disability, and near and related tasks visual disability. The questionnaire, administered verbally is entitled "The Visual Disability Assessment (VDA)". Reliability testing included test-retest reliability, interobserver reliability (p, the intraclass correlation coefficient), and internal consistency reliability (Cronbach's alpha). Construct validation, the process for proving that a test measures what it is supposed to measure, included consideration of content validity, comparison with the established Activities of Daily Vision Scale (ADVS) and empirical support with factor analysis.

RESULTS

For the four indices, interobserver reliability varied from 0.92 to 0.94, test-retest reliability varied from 0.96 to 0.98, and internal consistency reliability varied from 0.80 to 0.93. The VDA compared favourably with the ADVS by correlation, but Bland-Altman analysis demonstrated that the two instruments were not clinically interchangeable. Factor analysis suggests that all test items measure a common theme, and the subgroupings reflect common themes.

CONCLUSIONS

The VDA is easy to administer because it has a short test time and scoring is straightforward. It has excellent interobserver, test-retest, and internal consistency reliability, and compares favourably with the ADVS, another test of visual disability. Factor analysis demonstrated that the 18 items measure a related theme, which can be assumed to be visual disability. The VDA is a valid instrument which provides a comprehensive assessment of visual disability in cataract patients and is designed to detect changes within a patient over time.

Glare disability and contrast sensitivity before and after cataract surgery

PURPOSE

To determine whether brightness-induced glare decreases spatial contrast sensitivity and visual acuity in preoperative cataract patients with functional visual complaints and to compare preoperative with postoperative results.

SETTING

Sir Mortimer B. Davis Jewish General Hospital, Montreal, Quebec, Canada.

METHODS

Twenty patients with a visual acuity of 20/70 or better at the time of chart selection and no other ocular pathology who were referred for cataract surgery were evaluated with the Optec 3000 vision tester to assess contrast sensitivity and visual acuity in the presence and absence of glare. Testing was done preoperatively and 1 and 3 months postoperatively.

RESULTS

An analysis of variance indicated that there were statistically significant double interactions between the preoperative/postoperative and glare/no-glare variables and between the preoperative/postoperative and spatial frequency variables. Postoperatively, visual acuity and contrast sensitivity improved to within normal limits. There were no statistically significant differences in visual acuity and spatial contrast sensitivity between 1 and 3 months postoperatively.

CONCLUSION

Spatial contrast sensitivity and glare testing provided objective assessment of patients who had good visual acuity yet also had functional complaints.

Management of cataract

Images

Effect of a cataract simulation on clinical and real world vision

AIMS/BACKGROUND

Many reports have indicated that some patients with cataract can retain good visual acuity but complain of significant visual problems. This is the first in a series of papers trying to determine what causes these symptoms and whether other clinical tests can predict the real world vision loss.

METHODS

The effect of a cataract simulation with a similar angular distribution of light scatter as real cataract on clinical (visual acuity, contrast sensitivity, and disability glare) and real world vision (face recognition, reading speed, and mobility orientation) was investigated.

RESULTS

The simulation had a relatively small effect on visual acuity (6/6 with the simulation), but much larger effects on contrast sensitivity and low contrast acuity with and without glare. The simulation had no effect on high luminance and high contrast real world tasks, such as mobility orientation in room light and optimal reading speed. A small, but significant deterioration was found for the slightly lower contrast task of face and expression recognition. However, under low luminance conditions, substantial defects in mobility orientation were obtained (despite 6/6 acuity).

CONCLUSIONS

Although the relative effect of the cataract simulation on acuity and contrast tasks is not typical of the average cataract, it can be found in those cataract patients with visual problems despite good visual acuity. This corroborates the suggestion that it is large amounts of wide angle light scatter (forward and/or backward) which are at least partly responsible for visual disability in cataract patients with good visual acuity. A patient's reported visual disability may depend on the percentage of time he or she spends under low contrast and/or low luminance conditions, such as walking or reading in dim illumination, and walking or driving at night, in fog, or heavy rain.

Visual function in pseudophakic eyes with poly(methyl methacrylate), silicone, and acrylic intraocular lenses

PURPOSE

To evaluate the quality of visual function after cataract surgery and intraocular lens (IOL) implantation with three lens materials.

SETTING

Klinik Dardenne, Bonn Bad Godesberg, Germany.

METHODS

In a prospective, randomized study, 55 patients having uncomplicated phacoemulsification received IOLs made of three materials: 16 received acrylic IOLs, 20 received silicone IOLs, and 19 received poly(methyl methacrylate) (PMMA) IOLs. Pseudophakic patients with accompanying eye diseases were excluded. Visual acuity, glare sensitivity, contrast sensitivity, and mesopic acuity were evaluated 6 weeks postoperatively.

RESULTS

Postoperatively, best corrected visual acuity was excellent in all three lens groups. Acuity under bright light conditions and contrast sensitivity were low in all groups; mesopic acuity was extremely low in 73% of patients. Glare and contrast sensitivity were significantly better with PMMA and acrylic IOLs.

CONCLUSION

The visual quality achieved in pseudophakic eyes with three different lens materials was lower than expected. The results of individual visual function tests were better for PMMA and acrylic IOLs than for silicone IOLs.

Contrast visual acuities in cataract patients. III. Changes of contrast acuity profiles in normal and pathological eyes

We compared pre- and postoperative visual acuities in 45 cataract patients without ocular pathology except lens opacity (group 1) and 20 patients with ocular pathologies and lens opacity (group 2) using Variable Contrast Visual Acuity Charts. Charts 1 and 4 have 90% contrast; chart 4 has white optotypes on a black background (reverse polarity), charts 2 and 3 have 15% and 2.5% contrast, respectively. The mean preoperative visual acuities of groups 1 and 2 measured with the high-contrast Landolt optotypes ranged from 0.02-0.80 and 0.22-0.40, respectively. Visual acuity improvements between the pre- and postoperative periods ranged from 1.37-1.61 and 0.52-1.24 octaves in groups 1 and 2, respectively, with the different charts. Visual acuity improvement was poorest with chart 3. The group 1 mean preoperative visual acuity measured with chart 2 was 1.11 octaves lower than with chart 1. In group 2, the visual acuity reduction was 1.81 octaves. The relation between the visual acuities measured with the high-contrast intermediate-contrast optotypes are important for predicting postoperative visual acuity improvement. An abnormal contrast acuity profile may indicate the presence of additional ocular pathologies.

Comparative study of intraocular lens implantation through 3.2- and 5.5-mm incisions

PURPOSE

To prospectively and comprehensively compare the clinical results of two small-incision cataract surgery procedures, silicone intraocular lens (refractive index of 1.46) implantation through a 3.2-mm incision and polymethylmethacrylate intraocular lens implantation through a 5.5-mm incision.

METHODS

Two hundred eyes with cataract randomly were assigned to either procedure. Except for incision size, identical surgical methods were used in every case. Data on uncorrected and corrected visual acuity, keratometry, corneal topography, flare-cell measurement, fluorophotometry, specular microscopy, glare disability measurement, and photographic examination of intraocular lens decentration were analyzed up to 6 months after surgery.

RESULTS

Eyes in the 3.2-mm incision group displayed significantly better uncorrected and corrected visual acuity in the early postoperative period, lower aqueous flare intensity and cell counts immediately after surgery, less operatively induced astigmatism throughout the study period, and less corneal topographic changes taken 3 months after surgery. No significant between-group differences were noted for other parameters. Complications in the two groups were few and comparable.

CONCLUSION

Both procedures of small-incision cataract surgery offered satisfactory clinical results, but 3.2-mm incision cataract surgery allowed significantly earlier recovery of visual function and better preservation of corneal shape.

Glare sensitivity in early cataracts

In a previous study significant glare sensitivity (using Vistech MCT8000) was found only in patients with posterior subcapsular cataracts (PSC) beyond the very early (LOCS II grade 1) stage. The aim of the present study was to evaluate glare sensitivity in patients with early cataracts. The brightness acuity tester (BAT) was used with the Pelli-Robson chart on 50 patients with early cataracts (LOCS II grade 1 or 2) and on 14 normal volunteers. Only age and PSC were found to be associated with change in contrast sensitivity at high glare. Eyes with grade 1 PSC were not significantly different from eyes with grade 0 PSC after adjusting for age. Eyes with grade 2 PSC had significant glare effect compared with eyes having grade 0 PSC. Thus, glare sensitivity is associated only with early (grade 2) PSC. Other tests still need to be developed to assess visual function changes in patients with early cortical and nuclear cataracts.

Contrast sensitivity and visual acuity in patients with early cataracts

In a population of 188 nondiabetic patients with early cataracts or nuclear brunescence, we assessed the degree to which contrast sensitivity function (CSF) provided more information about a patient's visual disability than high contrast visual acuity measurements. Data collected included LOCS II cataract classification, Bailey-Lovie visual acuity (LogMAR score), Lotmar interferometric visual acuity (LI VA), and distance contrast sensitivity function (CSF) using the Vistech 6500. Generalized least squares regression models in which CS was the dependent variable and either LogMAR score or LI VA was among the independent variables were used to ascertain whether CSF provided additional information about visual disability to that provided by LogMAR score or LI VA. Contrast sensitivity function was decreased only by nuclear opalescence at high frequencies (12 to 18 cpd); for all other cataract types and nuclear color, CSF testing provided no more information about cataract-related visual loss than LI VA or LogMAR score. Measurement of CSF using the Vistech 6500 system in patients with early cataracts provides information on visual dysfunction beyond that provided by LogMAR score or LI VA only in patients with nuclear opalescence, and that may not be clinically significant.

Loss of contrast sensitivity in diabetic patients with LOCS II classified cataracts

Contrast sensitivity function (CSF) was assessed in a population of diabetics with moderate cataracts to determine if CSF testing provides more information about visual dysfunction than Snellen or Lotmar interferometric visual acuity. With the Lens Opacities Classification Systems Version II (LOCS II) of cataract classification it was possible to grade accurately the type and severity of cataract and nuclear brunescence. The presence of statistically significant relationships between increasing LOCS II classification (worsening cataract) and diminished function, even when the regression model was controlled for Snellen visual acuity, supports the thesis that CSF measurements do provide more information about cataract related visual loss than Snellen acuity alone. Statistically significant (p < or = 0.05) relationships existed between different morphological types of cataract, nuclear colour, and CSF at specific frequencies. The frequencies affected differed with cataract type or nuclear colour, and with distance and near CSF.

The morphology of cataract and visual performance

The various effects of cataract on vision are reviewed. The morphological types of senile cataract are classified into three basic categories: cortical spoke, nuclear and posterior subcapsular (PSC). The significant basic effect of cataract on the optical system of the eye is that of light scattering. Forward light scattering (light scattered towards the retina) accounts for reduced contrast sensitivity, for glare and for reduced visual acuity. Other effects of cataract are a myopic shift, a possible astigmatism change, monocular diplopia and polyopia, colour vision shift, reduced light transmission, and field of vision reduction. The effect of the various cataract morphologies on these functions is discussed. The nature of the effect varies with the degree of the cataract and with the cataract morphology. The assessment of a patient's visual disability is therefore not a simple task and cannot be based solely on the visual acuity nor on the objective measurement of the cataract.

Contrast visual acuities in cataract patients. II. After IOL implantation

Contrast visual acuities were measured in 100 eyes of 75 patients who attained a best-corrected visual acuity of greater than or equal to 0.8 (20/25) after intraocular lens (IOL) implantation. The variable contrast visual acuity chart (VCVAC), with three contrast levels of 90, 15, and 2.5% and reverse polarity of 90% contrast, was used to measure contrast visual acuities. The follow-up period ranged from 3 to 35 months (mean 7.41). The mean visual acuities measured with the 90, 15, and 2.5% charts were 0.92 (SD = 0.11), 0.59 (SD = 0.13), and 0.33 (SD = 0.14), respectively. The mean visual acuity measured with the 90% reverse polarity chart was 0.97 (SD = 0.11). The decreases in visual acuities compared with the 90% contrast were 0.64 and 1.48 octaves in the 15% and the 2.5% contrast charts, respectively. The pattern of the contrast acuity profile was comparable to normal subjects, but in 28 of 100 (28%) eyes, the visual acuities measured with the reverse polarity chart were slightly better than those measured with the standard 90% contrast chart, suggesting that the glare effect still exists after IOL implantation, though to a lesser degree than in cataractous eyes.

Measurement of glare disability using an automated perimeter

We have developed a new system to measure glare disability spatially and quantitatively using an Octopus 500E automated perimeter with an attached glare source. We describe the method used for measuring glare disability with this system and the results in cataracts and pseudophakia with and without various postoperative complications.

Contrast visual acuities in cataract patients. I. Comparison with normal subjects

Contrast sensitivity and glare sensitivity are often abnormal in cataract patients. However, despite significant subjective complaints, relatively good visual acuities often are obtained with high-contrast optotypes. Using Variable-Contrast Visual Acuity Charts (VCVAC), we measured visual acuities of 40 eyes of 24 normal subjects (visual acuity greater than or equal to 1.0) aged 41 to 72 years, and 40 eyes of 28 cataract patients (visual acuity greater than or equal to 0.6) aged 44 to 81 years. The VCVAC consists of 4 different charts (1-4). The contrast is 90% in charts 1 and 4, 15% in chart 2 and 2.5% in chart 3. Chart 4 is the reverse polarity of chart 1. The decrease of visual acuity compared with the high-contrast chart (chart 1) was larger in the cataract group with both in the 15% contrast (0.52 vs. 0.71 octave) and the 2.5% contrast (1.21 vs. 1.75 octaves). In cataract group, 23/40 eyes (57.5%) showed better visual acuity with chart 4 than that of chart 1. In addition to high-contrast optotypes, acuity measurements using intermediate- to low-contrast optotypes, combined with the reverse polarity chart, seem effective in analyzing the visual disabilities caused by early cataract.

Clinical and physical measurements of the cataractous lens

In connection with the clinical trial of an anti-cataract drug (Bendazac lysine) a number of examination methods were used to assess the progress of the cataract: slitlamp examination, visual acuity determination, and the measurement of the contrast sensitivity, light scatter in the eye and the autofluorescence and transmission of the lens. In this article the measurements of 43 patients (43 eyes) are presented, taken at the time that medication was started. In this way we can get an impression of the value of these measurements for the study of cataractous lenses. The contrast sensitivity of the cataractous eye is lowered for all spatial frequencies as compared with the normal population. Light scatter is greatly increased. The autofluorescent profile of the lens with nuclear cataract differs markedly from that of the lens with cortical cataract.

Comparing clinical tests of visual function in cataract with the patient's perceived visual disability

Conventional techniques for assessing the visual function of cataract patients include visual acuity (VA), contrast sensitivity (CS) and glare disability (GD). The extent to which these measurements provide accurate information about a patient's perceived visual disability is not known. In this study, binocular and monocular VA and CS and monocular GD measurements were made using commercially available techniques on 33 cataract patients. VA was measured using a Ferris-Bailey LogMAR chart and CS by the Pelli-Robson letter CS chart. Glare disability was measured using the Mentor Brightness Acuity Tester in conjunction with both the LogMAR and Pelli Robson charts. Each patient's perceived visual disability was quantified using a 20-point questionnaire about the effect of vision on everyday activities. There was little correlation between subjective visual disability and monocular or binocular VA measurements. Measurements of binocular CS, however, were highly correlated with the patient's perceived visual disability, particularly their subjective assessment of the effect of vision on their mobility-orientation. We suggest that binocular CS measurements using the Pelli-Robson chart provide useful additional information regarding the need for surgery in cataract patients.

Glare and mesopic vision before and after cataract surgery

Glare and mesopic vision were tested before and after cataract surgery in addition to the standard visual acuity measurement. Quantitative data on the amount of improvement in these functions are presented. Preoperatively, glare and mesopic vision were reduced to 20/200 or less in most patients. Postoperatively, a statistically significant improvement in the three visual functions measured was found in all five octaves of presurgical visual acuity.