Comparing clinical tests of visual loss in cataract patients using a quantification of forward light scatter

Evaluation value of subjective visual quality examination on surgical indications of the early cataracts based on objective scatter index values

Aim

To evaluate the subjective visual functions of early cataracts patients and assess their surgical indications.

Methods

Eyes were separated into a control group (Group A without cataract) and two early cataracts groups (Group B with 2.0 ≤ OSI < 3.0 and Group C with 3.0 ≤ OSI < 4.0). The objective scatter index (OSI), modulation transfer function cut-off frequency (MTF cut-off), and Strehl ratio (SR) values were applied to measure objective visual functions. The contrast sensitivity (CS) and scores of the questionnaires (QOL and VF-14) characterized subjective visual functions. Above visual functions were compared among three groups. Postoperative visual functions in Group B and C were analyzed to assess the outcome of surgery.

Results

Ninety two subjects (126 eyes) were included in the study. All objective visual function in Group B were significantly better than Group C (all P < 0.01), but worse than Group A (all P < 0.01). Except for 1.5 c/d CS, subjective visual function in Group A were significantly better than Group B and C (all P < 0.05), but there was no significant differences between Group B and C. As for eyes that underwent surgery in Group B and C, all visual functions significantly improved after surgery (P < 0.05), except for 1.5 c/d CS in Group C. There were no significant differences among the three groups after surgery.

Conclusion

The subjective visual function can be impaired in early cataracts patients with OSI < 3.0, whose objective visual functions were statistically better than patients with OSI ≥ 3.0. These patients can benefit equally from surgery as patients with OSI ≥ 3.0. Subjective visual functions can be used as surgical indications for these patients.

The significance of changes in pupil size during straylight measurement and with varying environmental illuminance

PURPOSE

In this work, we investigated the pupillary conditions during straylight measurement, and the potential effect this might have on the measured straylight.

METHODS

Five young (26-29-years-old) and 15 older (50-68-years-old) individuals participated in this study. First, the pupil diameter of both eyes was measured at three room illuminances. Next, straylight was assessed at two room illuminances. Simultaneously, the change in pupil size of the fellow eye was registered by a camera.

RESULTS

Pupil size decreased with room illuminance and with age (both p<0.05). The dependency of pupil size on age decreased as room illuminance increased (0.018mm/year at 4 lux, 0.014mm/year at 40 lux, and 0.008mm/year at 400 lux illuminances). However, during straylight measurement, pupil sizes hardly differed between 4 and 40 lux illuminances. Respective pupil sizes corresponded with 399 and 451 lux adaptation on average. No statistically significant difference was found between the straylight under the two illuminances with average R2=0.85, p<0.05.

CONCLUSION

We conclude that the illuminance of the examination room during straylight assessment does not affect the outcome in normal eyes. In fact, under mesopic and scotopic conditions, the luminance of the test field is so much higher than that of the room so that it determines the pupil size. Regardless of the lighting level, straylight measured in a laboratory, is valid for photopic pupils at an adaptation level corresponding with about 400 lux room illuminance.

Ocular Straylight: A Determinant of Quality of Life in the Elderly?

Intra-ocular straylight can cause decreased visual functioning, and it may cause diminished vision-related quality of life (VRQOL). This cross-sectional population-based study investigates the association between straylight and VRQOL in middle-aged and elderly individuals. Multivariable linear regression analyses were used to assess the association between straylight modeled continuously and cutoff at the recommended fitness-to-drive value, straylight ≥ 1.4 log(s), and VRQOL. The study showed that participants with normal straylight values, straylight ≤ 1.4 log(s), rated their VRQOL slightly better than those with high straylight values (straylight ≥ 1.4 log(s)). Furthermore, multivariable regression analysis revealed a borderline statistical significant association (p = .06) between intra-ocular straylight and self-reported VRQOL in middle-aged and elderly individuals. The association between straylight and self-reported VRQOL was not influenced by the status of the intra-ocular lens (natural vs. artificial intra-ocular lens after cataract extraction) or the number of (instrumental) activities of daily living that were reported as difficult for the elderly individuals.

History of ocular straylight measurement: A review

The earliest studies on 'disability glare' date from the early 20(th) century. The condition was defined as the negative effect on visual function of a bright light located at some distance in the visual field. It was found that for larger angles (>1 degree) the functional effect corresponded precisely to the effect of a light with a luminosity equal to that of the light that is perceived spreading around such a bright source. This perceived spreading of light was called straylight and by international standard disability glare was defined as identical to straylight. The phenomenon was recognized in the ophthalmological community as an important aspect of the quality of vision and attempts were made to design instruments to measure it. This must not be confused with instruments that assess light spreading over small distances (<1 degree), as originating from (higher order) aberrations and defocus. In recent years a new instrument has gained acceptance (C-Quant) for objective and controllable assessment of straylight in the clinical setting. This overview provides a sketch of the historical development of straylight measurement, as well as the results of studies on the origins of straylight (or disability glare) in the normal eye, and on findings on cataract (surgery) and corneal conditions.

Investigation of the effect of simulated lens yellowing, transparency loss and refractive error on in vivo resonance Raman spectroscopy

PURPOSE

To separately investigate the impact of simulated age-related lens yellowing, transparency loss and refractive error on measurements of macular pigment (MP) using resonance Raman spectroscopy.

METHODS

Two healthy young subjects with clear media underwent Raman spectroscopy under the following conditions: age-related lens yellowing was simulated using seven broad-band yellow filters with transmittance at 488 nm ranging from 0.54 to 0.90; cataract was simulated using five white filters of increasing opacity (scatter filters), the transmittance of which ranged from 0.42 to 0.86, each of which reduced peak contrast sensitivity by approximately 0.1 log units over the previous filter. Refractive error up to +6.25 D was achieved using soft contact lenses.

RESULTS

The Raman signal declined steadily to an average value of 43% of the starting value with the densest yellow filter in place. The white scatter filters produced a progressive linear reduction in signal resulting in almost complete signal loss with the densest filter. Refractive error resulted in an initial slight improvement in Raman count up to a value of +2.00 D followed by a decline thereafter.

CONCLUSIONS

These results imply that lens yellowing and increasing scatter has an influence on the Raman signal and suggest that studies using this technology to estimate MP levels in older populations should carefully account for the status of the lens.

The effect of simulated lens yellowing and opacification on blue-on-yellow acuity and contrast sensitivity

Short-wavelength-sensitive (SWS) resolution acuity has been reported to be limited by the density of the responding ganglion cells for people without appreciable age-related lenticular change. This study measured the robustness of SWS-cone acuity and contrast sensitivity (CS) to simulated lens yellowing and opacification. Resolution acuity at 8 deg eccentricity proved robust to significant amounts of yellowing and remained lower than detection acuity, indicating that the resolution continued to be limited by ganglion cell density. Both the detection and resolution CS functions were affected by simulated lens yellowing, except for resolution close to the CS cut-off. For simulated opacification, only dense opacity significantly affected performance. SWS resolution acuity and CS close to the resolution limit are resistant to moderate simulated age-related lens changes and continue to be mediated by the density of the responding ganglion cells, indicating important clinical potential to measure SWS neural losses of vision in older subjects.

Effects of cataract type and location on visual function: the Blue Mountains Eye Study

PURPOSE

To measure the effect of cataract type, severity and location on presenting, and best-corrected visual acuity, contrast sensitivity, and glare disability.

METHODS

In all, 3654 (82.4% participation rate) eligible noninstitutionalised residents aged 49 years or older, living in two postcode areas of the Blue Mountains, Australia, received detailed eye examinations including visual acuity, contrast sensitivity, and glare disability testing. Data from right eyes were analysed using multiple regression modelling.

RESULTS

The effect of age on visual acuity and contrast sensitivity only became evident in persons aged at least 60 years. Cataract severity was inversely related to visual acuity and contrast sensitivity. Late posterior subcapsular cataract caused the greatest reduction in visual acuity. Early grade cataract caused significant reduction in contrast sensitivity at intermediate and high spatial frequencies, but late grade cataract reduced contrast sensitivity across all spatial frequencies. There was insufficient study power to detect consistent significant effect of cataract on glare disability tests or cortical cataract location on visual function.

CONCLUSIONS

Age at least 60 years, cataract type, and cataract severity were principal determinants of visual acuity and contrast sensitivity in this study. Axial and superotemporally located cortical cataract had the greatest effect on visual function tests.

The assessment of lens opacities in clinical practice: results of a national survey

AIM

To investigate the examination of lens opacities in routine ophthalmic clinical practice.

METHOD

A questionnaire survey was mailed to 703 consultant ophthalmologists in the UK. The surgeons were asked which lens feature(s) they assessed in their clinics when deciding whether to offer cataract surgery.

RESULTS

489 replies were received. A broad range of lens opacities was assessed, with differences between surgeons for some opacities with high prevalences in the population, particularly cortical opacities. Many (74% of 467) surgeons assessed one or more lens opacities (anterior subcapsular cataract, vacuoles, water clefts, coronary flakes, focal dots, retrodots, fibre folds) which may be visually important but which have received relatively little attention by researchers.

CONCLUSIONS

Some classes of lens opacity which are traditionally measured by researchers may be ignored in clinical practice and opacities which are traditionally ignored by some researchers are regarded as clinically important by a substantial number of surgeons.

Computerized method to measure glare and contrast sensitivity in cataract patients

PURPOSE

To evaluate computerized methods for measuring glare sensitivity and visual acuity at 3 contrast levels in cataract patients.

SETTING

St. Erik's Eye Hospital, Stockholm, Sweden.

METHODS

In a prospective study, 25 consecutive cataract patients meeting the inclusion criteria were examined before and 12 weeks after cataract surgery. Measured were glare sensitivity and visual acuity at 3 contrast levels using the Opthimus Y-VA Contrast Sensitivity Test and Glare Test.

RESULTS

Preoperatively, all patients had impaired values compared with those in a group of age-matched normal volunteers (control group). Postoperatively, median values were similar to those in the age-matched control group in all parameters except glare sensitivity, which was significantly higher in the pseudophakic group (P = .03). Correlation coefficients between preoperative visual acuity and contrast sensitivity at 90%, 25%, and 10% were 0.50 (P = .01), 0.53 (P = .006), and 0.45 (P = .02), respectively, and between preoperative visual acuity and preoperative glare difference, 0.45 (P = .02). A significant correlation was found between age and visual acuity in the control group at all contrast levels: 90% (r = 0.61, P = .0018), 25% (r = 0.52, P = .01), and 10% (r = 0.42, P = .04). Median differences between Y-VA examinations (repeatability) were 0 LogMAR except between examinations 1 and 2 at the 25% contrast level, where it was 0.3 LogMAR.

CONCLUSION

The Ophthimus Y-VA Test and Glare Test were useful in the preoperative evaluation of patients with cataract and mild to moderate visual impairment.

Glare sensitivity and visual acuity after excimer laser photorefractive keratectomy for myopia

BACKGROUND

Following excimer laser photorefractive keratectomy (PRK), an increase in glare sensitivity and a reduction in contrast sensitivity can occur owing to changes in the cornea (structure and topography). In this study, an attempt was made to quantify and document objectively a change in those subjective perceptual factors.

METHODS

Snellen visual acuity and disability glare were measured with the Berkeley glare test preoperatively as well as 1, 3, 6, 9, and 12 months postoperatively, after excimer laser photorefractive keratectomy (PRK) on 32 myopic patients (46 eyes). During the postoperative progress checks, haze was graded and contrast sensitivity was measured with the Vistech chart. All the data were statistically analysed by multiple regression.

RESULTS

One year after PRK, a reduction in visual acuity (VA) measured with the low acuity contrast chart (10%) with and without glare could still be found, despite the fact that acuity measurements with a high contrast Snellen chart showed the same VA 6 months postoperatively as well as before the treatment. The lowest VA could be measured 1 month postoperatively; thereafter, the acuity increased despite the increase in haze that occurred during the first 3 months.

CONCLUSION

Disability glare and a reduction in contrast sensitivity could be observed in most patients after PRK treatment with the Meditec laser system with its scanning slit. The future will show if new technology and a broader flattening area of 6 to 7 mm can minimise these postoperative complications.

Contrast sensitivity in different types of early lens opacities

The purpose of the present study was to evaluate the relationship of various types of early lens opacities with contrast sensitivity at different spatial frequencies. The Lens Opacities Classification System II and Lensmeter 701 were used in the grading of the lens status. The contrast sensitivity was tested with the Vistech VCTS 6500 distance test with optimal correction of refractive errors. Data from 995 eyes were available for the present study. Contrast sensitivity decreased by increasing lens opacification graded with the Lens Opacities Classification System II and also by increasing Lensmeter 701 reading. When the statistical model was adjusted for age and best corrected visual acuity, nuclear opacities and nuclear colour were not associated with decreased contrast sensitivity, however, there was a weak, but statistically significant correlation between contrast sensitivity reduction and cortical opacities at high spatial frequencies, and between contrast sensitivity and posterior subcapsular opacities at low and medium spatial frequencies.

Measurement of glare sensitivity in cataract patients using low-contrast letter charts

The Committee on Ophthalmic Procedures Assessment of the American Academy of Ophthalmology suggested using low-contrast visual acuity measured before and after adding a glare source as a test for assessing overall visual disability from immature cataracts. We have developed a test that follows the Committee's three principles of design, and we report that the effect of glare on visual acuity is considerably greater for recognizing low-contrast letters than for recognizing high-contrast letters. The effect of glare on visual acuity increases progressively as letter contrast is reduced in the stages 96%, 50%, 25%, 11% and 4%. The 25% chart (and possibly the 11% chart) gives the most suitable sensitivity for eyes with immature cataracts. Age-related brunescence and aging itself do not necessarily produce high sensitivity to glare. Sensitivity to glare was markedly different in eyes with different kinds of cataract.

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.