Objective line spread function measurements, Snellen acuity, and LOCS II classification in patients with cataract

Wavefront aberrations and retinal image quality in different lenticular opacity types and densities

To investigate wavefront aberrations in the entire eye and in the internal optics (lens) and retinal image qualities according to different lenticular opacity types and densities. Forty-one eyes with nuclear cataract, 33 eyes with cortical cataract, and 29 eyes with posterior subcapsular cataract were examined. In each group, wavefront aberrations in the entire eye and in the internal optics and retinal image quality were measured using a raytracing aberrometer. Eyes with cortical cataracts showed significantly higher coma-like aberrations compared to the other two groups in both entire eye and internal optic aberrations (P = 0.012 and P = 0.007, respectively). Eyes with nuclear cataract had lower spherical-like aberrations than the other two groups in both entire eye and internal optics aberrations (P < 0.001 and P < 0.001, respectively). In the nuclear cataract group, nuclear lens density was negatively correlated with internal spherical aberrations (r = −0.527, P = 0.005). Wavefront technology is useful for objective and quantitative analysis of retinal image quality deterioration in eyes with different early lenticular opacity types and densities. Understanding the wavefront optical properties of different crystalline lens opacities may help ophthalmic surgeons determine the optimal time to perform cataract surgery.

Monitoring and Morphologic Classification of Pediatric Cataract Using Slit-Lamp-Adapted Photography

Purpose

To investigate the feasibility of pediatric cataract monitoring and morphologic classification using slit lamp–adapted anterior segmental photography in a large cohort that included uncooperative children.

Methods

Patients registered in the Childhood Cataract Program of the Chinese Ministry of Health were prospectively selected. Eligible patients underwent slit-lamp adapted anterior segmental photography to record and monitor the morphology of their cataractous lenses. A set of assistance techniques for slit lamp–adapted photography was developed to instruct the parents of uncooperative children how to help maintain the child's head position and keep the eyes open after sleep aid administration.

Results

Briefly, slit lamp–adapted photography was completed for all 438 children, including 260 (59.4%) uncooperative children with our assistance techniques. All 746 images of 438 patients successfully confirmed the diagnoses and classifications. Considering the lesion location, pediatric cataract morphologies could be objectively classified into the seven following types: total; nuclear; polar, including two subtypes (anterior and posterior); lamellar; nuclear combined with cortical, including three subtypes (coral-like, dust-like, and blue-dot); cortical; and Y suture. The top three types of unilateral cataracts were polar (55, 42.3%), total (42, 32.3%), and nuclear (23, 17.7%); and the top three types of bilateral cataracts were nuclear (110, 35.8%), total (102, 33.2%), and lamellar (34, 11.1%).

Conclusions

Slit lamp–adapted anterior segmental photography is applicable for monitoring and classifying the morphologies of pediatric cataracts and is even safe and feasible for uncooperative children with assistance techniques and sleep aid administration.

Translational Relevance

This study proposes a novel strategy for the preoperative evaluation and evidence-based management of pediatric ophthalmology (Clinical Trials.gov, NCT02748031).

Spherical aberration reduction in nuclear cataracts

PURPOSE

To measure higher-order aberrations (HOAs) in nuclear cataracts and to investigate spherical aberration changes with nuclear cataract progression.

METHODS

A total of 102 eyes of older subjects (>50 years) were classified based on the nuclear opalescence (NO) grading of the Lens Opacities Classification System III: Group 1 (< NO2, 35), 2 (NO2, 23), 3 (NO3, 23), and 4 (≥ NO 4:21 eyes). Wave front measurements were performed with a Hartmann-Shack aberrometer. To investigate lenticular spherical aberration, HOAs were examined in 28 eyes before and after phacoemulsification, followed by insertion of an aberration-free intraocular lens. The relationship between lens opacity grade and ocular and lenticular spherical aberrations were investigated.

RESULTS

Mean spherical aberrations in groups 1, 2, 3, and 4 were 0.25 ± 0.10, 0.16 ± 0.13, 0.12 ± 0.15, and 0.10 ± 0.20 μm, respectively, and showed a significant difference with nuclear opacity grading (p = 0.001). The spherical aberration showed negative associations with nuclear opacity grading (r = -0.408, p < 0.001). The predominant change in HOAs after phacoemulsification was an increase in spherical aberration, and 86 % of lenticular spherical aberrations were presumed to have negative values. The lenticular spherical aberration was negatively correlated with nuclear opacity severity (r = -0.409, p = 0.031).

CONCLUSIONS

Ocular spherical aberration decreases with the progression of nuclear cataracts due to the negative correlation between lenticular spherical aberration and nuclear opacity severity.

Representing the retinal line spread shape with mathematical functions

OBJECTIVE

To report a mathematical function that characterizes the double-pass line spread function (LSF) of the human eye. Determining analytical functions that represent the double-pass LSF is important because it allows modeling the optical performance of the eye.

METHODS

Optical section retinal images, generated in normal human eyes using a modified slit-lamp biomicroscope, were analyzed to derive the double-pass LSF by plotting the intensity distribution of laser light reflected/ scattered from the vitreoretinal interface. Three mathematical functions (Lorentzian, Gaussian, exponential) were fitted to the double-pass LSF and the root mean square error (RMSE) was calculated to provide a measure of the goodness of fit.

RESULTS

The Lorentzian function provided the best representation of the double-pass LSF of normal human eyes. The full width at half maximum (FWHM) of the Lorentzian fitted curve was positively correlated with age, indicating that the double-pass LSF broadens with age. Furthermore, the goodness of fit of the Lorentzian function was significantly better in younger subjects as compared with older subjects, suggesting that the fitted function to the double-pass LSF may vary according to age.

CONCLUSION

The results demonstrate an age-related change in the double-pass LSF width and the goodness of fit of the Lorentzian function.

Evaluation of Optical Function Using a New Point Spread Function Analysis System in Cataractous and Pseudophakic Eyes: Preliminary Results

PURPOSE

To evaluate optical function in cataractous and pseudophakic eyes using the new point spread function (PSF) analysis system in a clinical setting.

METHODS

We applied this new analysis system in the study of two cataractous eyes and one pseudophakic eye of two patients. Using a PSF analyzer, double-pass PSF was measured directly for each subject, and the single-pass modulation transfer function (MTF) and single-pass PSF were calculated. The simulated retinal images of various sizes of Landolt's rings and their contrast characteristics were also calculated by the PSF analyzer.

RESULTS

The MTF and the contrast of the simulated retinal images degraded in cataractous eyes were compared with data for normal eyes; the degradation pattern depended on the opacification pattern. The MTF and the contrast of the simulated retinal images in the pseudophakic eye improved significantly compared with the cataractous eyes, although both values were lower in the pseudophakic eye than in young normal eyes.

CONCLUSIONS

Our data showed degradation of optical function in cataractous and pseudophakic eyes in comparison with optical function in young normal eyes. If further accumulations of PSF data are made, it may be possible to establish an objective standard by which to measure the progression of cataract, as well as an objective indication for treatment in the future.

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.

Case–control study of indoor cooking smoke exposure and cataract in Nepal and India

BACKGROUND

The prevalence of cataract is higher in developing countries, and in both developed and developing countries more females than males are blind from cataracts. Three epidemiological studies have associated indoor cooking with solid fuels (e.g. wood or dung) and cataract or blindness. However, associations in these studies may have been caused by unmeasured confounding.

METHODS

A hospital-based case-control study was conducted on the Nepal-India border. Cases (n = 206) were women patients, aged 35-75 years with confirmed cataracts. Controls (n = 203), frequency matched by age, were patients attending the refractive error clinic at the same hospital. A standardized questionnaire was administered to all participants. Logistic regression analysis involved adjustment for age, literacy, residential area, ventilation, type of lighting, incense use, and working outside.

RESULTS

Compared with using a clean-burning-fuel stove (biogas, LPG, or kerosene), the adjusted odds ratio (OR) for using a flued solid-fuel stove was 1.23 [95% confidence interval (CI) 0.44-3.42], whereas use of an unflued solid-fuel stove had an OR of 1.90 (95% CI 1.00-3.61). Lack of kitchen ventilation was an independent risk factor for cataract (OR 1.96; 95% CI 1.25-3.07).

CONCLUSION

This study provides confirmatory evidence that use of solid fuel in unflued indoor stoves is associated with increased risk of cataract in women who do the cooking. The association is not likely to be due to bias, including confounding, and strengthens the findings of three previous studies. Replacing unflued stoves with flued stoves would greatly reduce this risk, although cooking with cleaner-burning fuels would be the best option.

INCIDENCE OF CATARACT EXTRACTION AFTER DIABETIC VITRECTOMY

PURPOSE

To determine the frequency of visually significant cataracts after vitrectomy for complications of diabetic retinopathy.

METHODS

We studied 40 patients and 56 concurrent control patients in a retrospective, consecutive, comparative case series in an institutional setting. Entry criteria included phakic patients with a clear lens or mild lens opacity undergoing anatomically successful diabetic vitrectomy, without lens removal at the time of vitrectomy, without intraocular gas or silicone oil use, and with at least 1 year of postoperative follow-up examination information. Two comparative phakic control groups with the diagnosis of macular hole or epiretinal membrane were selected, also with follow-up examination information of at least 1 year postoperatively. The occurrence of cataract extraction was the principal outcome measure. Its validity as a measure of cataract formation was evaluated by ascertainment of improved visual acuity after cataract extraction. A secondary endpoint analysis included eyes that needed cataract extraction at the final follow-up examination.

RESULTS

For the primary analyses (clear lens preoperatively), there were 26 patients in the study group, 38 in the macular hole control group, and 18 in the epiretinal membrane control group. The cumulative cataract extraction rates at 2 years were 15%, 66%, and 53% respectively. By using multivariate survival analysis, the patient age was an important factor, with a younger age associated with a lower rate of progression to nuclear sclerosis. After controlling for age, the difference in these three groups was still statistically significant. In the four patients with diabetes undergoing cataract surgery, the visual acuity improved at least two lines in only one of the eyes and did not change in three eyes. After expanding the outcome measures to include study patients with mild lens opacities at baseline or those judged to be in need of cataract surgery at the final follow-up examination, there was still a strongly statistically significant difference between the three groups.

CONCLUSION

The rate of cataract extraction after vitrectomy in patients with diabetes is lower than in patients without diabetes undergoing vitrectomy and suggests a lower rate of cataract formation. This inference should be considered when attributing subnormal vision in a patient who has had a diabetic vitrectomy to a cataract. This is especially significant because the risk ratio in patients with diabetes in general and in patients with a previous vitrectomy is likely less favorable compared with the general population.

Light scattering and optical aberrations as objective parameters to predict visual deterioration in eyes with cataracts

PURPOSE

To predict the visual deterioration of eyes with cortical (CC) or nuclear (NC) cataract from objective data on ocular higher-order aberration (HOA) and forward (FLS) and backward light scattering (BLS).

SETTING

Osaka University Medical School, Osaka, Japan.

METHODS

Twenty-two eyes with mild NC, 41 eyes with mild CC, and 11 normal eyes were examined. Higher-order aberrations were calculated with the Zernike polynomials up to the fourth order from the values obtained by wavefront analysis using the Hartmann-Shack aberrometer. Forward light scattering was calculated from the size of the aberrometer spot images for the central 4 mm, and backward light scattering (BLS) was calculated from the optical density of the Scheimpflug images. The relationship between the area under the log contrast sensitivity function (AULCSF) curve and HOAs, FLS, and BLS was examined.

RESULTS

Area under the log contrast sensitivity function was moderately correlated with the HOAs, FLS, and BLS. Multiple linear regression analysis revealed that the AULCSF was predicted by the linear combination of these variables (R(2)=.484, P<.001). Area under the log contrast sensitivity was predicted by BLS and HOA (R(2)=.555) in the NC group and by FLS and HOAs (R(2)=.540) in the CC group.

CONCLUSIONS

Loss of contrast sensitivity was predominantly due to BLS and HOA in eyes with NC and FLS and HOA in eyes with CC. Higher-order aberrations, FLS, and BLS, variables that are obtained objectively, can be used to predict quantitatively the visual deterioration in cataractous eyes.

Spatial visual filtering in diabetes mellitus

PURPOSE

To investigate spatial visual filtering in a group of diabetic patients and compare the results with those of a group of controls.

METHODS

The luminance threshold of a moving 2 degrees achromatic target, viewed against a 17 degrees achromatic background grating, was measured as a function of grating periodicity from 0.21 to 31.4 cpd in 22 diabetic patients and 12 controls, giving a response characteristic of the spatial function of a sustained-response type of visual channel. A previously published model of spatiotemporal filtering, integrating photoreceptor kinetics with difference-of-Gaussian circularly symmetric receptive fields, was used to analyse the data.

METHODS

The model gave a good fit to the data in the control group, with a mean central space constant of 0.046 degrees and centre:surround ratio of 1:5.2 and mean R(2)=0.78 (SD 0.12). The mean central space constant in the diabetic group was 0.051 degrees and the centre:surround ratio 1:4.2, although best fit was significantly worse, at R(2)=0.54 (SD 0.19), P=0.001. The best fit for diabetic subjects with grade 2 maculopathy was significantly worse than for those with no maculopathy ( P=0.03).

CONCLUSION

The study demonstrates a disruption of circularly symmetric centre-surround receptive field structure of the sustained-response channel in the diabetic retina to a degree that is consistent with the retinal level of anatomical change in diabetic maculopathy.

Wavefront analysis in eyes with nuclear or cortical cataract

PURPOSE

To compare the higher-order aberrations of the oculus (whole eye) and cornea in eyes with mild cortical or nuclear cataract and to estimate the effect of ocular higher-order aberrations on the loss of contrast sensitivity using wavefront analysis.

DESIGN

Observational case series.

METHODS

Six eyes of four patients with mild nuclear cataract, 18 eyes of 14 patients with mild cortical cataract, and nine eyes of nine normal patients were examined. Wavefront aberrations of the oculus and cornea for central 6 mm diameter were measured using the Hartmann-Shack (HS) aberrometer. Higher-order aberrations were calculated with Zernike polynomials up to sixth order. The relationship between average lens density (ALD) measured by the Scheimpflug camera and the ocular total higher-order aberration (OTHA) was investigated. The relationship between contrast sensitivity (CS) and the OTHA or ALD was also examined.

RESULTS

The OTHA was significantly larger in cataracts compared with normal subjects, while corneal total higher-order aberration did not differ between cataracts and normal subjects. The polarity of spherical aberration was negative in all eyes with nuclear cataract while positive in all eyes with cortical cataract. The correlation between ALD and OTHA was not significant in eyes with cataracts. The CS highly correlated with OTHA while it moderately correlated with ALD.

CONCLUSIONS

The HS aberrometer is useful to objectively evaluate the deterioration of images in eyes with mild cataract and it revealed that the polarity of spherical aberration was different between nuclear and cortical cataract. It was also suggested that in mild nuclear or cortical cataract, not only light scattering, but also optical aberration of the lens contributes to the loss of contrast sensitivity.

New objective classification system for nuclear opacification

We have developed an autonomous objective classification scheme for degree of nuclear opacification. The algorithm was developed by using a series of color 35-mm slides acquired with a Topcon photo slit-lamp microscope and use of standard camera settings. The photographs were digitized, and first, and second-order gray-level statistics were extracted from within circular regions of the nucleus. Classifications of severity were performed by using these features as input to a neural network. Training versus classification performance was tested by using photographs of different eyes, and test/retest classification reproducibility was evaluated by using paired photographs of the same eyes. We demonstrate good performance of the classifier against subjective assessments rendered by the Wilmer grading system [Invest. Ophthalmol. Visual Sci. 29, 73 (1988)] and markedly better test/retest reproducibility.