Purpose
To investigate the relationship among Lens Opacities Classification System III (LOCS III) grading score, Visual Function Index-14 (VF-14) score, average lens density by the Pentacam Nucleus Staging system, and the objective scatter index measured by the Optical Quality Analysis System in age-related cataract patients.
Design
Prospective, single-center, cross-sectional study.
Methods
Thirty-six subjects (60 eyes) with age-related cataract were recruited. Subjects with any corneal anomaly potentially affecting intraocular scatter were excluded. The best-corrected visual acuity (BCVA), LOCS III nuclear opalescence score and cortical cataract score, VF-14 score, average lens density, and objective scatter index were obtained. Correlations among these parameters were analyzed.
Results
The LOCS III nuclear opalescence score was correlated with the BCVA (r = 0.438; P = .001), objective scatter index (r = 0.543; P < .001), and average lens density (r = 0.621; P < .001). The objective scatter index was also correlated with the BCVA (r = 0.779; P < .001) and the average lens density (r = 0.320; P = .013). The VF-14 score had the strongest correlation with the objective scatter index (r = −0.712; P < .001). The difference between groups with objective scatter index<3.0 and ≥3.0 was significant with regard to BCVA, average lens density, LOCS III nuclear opalescence score, and VF-14 score.
Conclusions
LOCS III grading remains an economical and effective method to assess lens opacities, especially in the formation of early cortex cataracts. The objective scatter index can be a useful parameter to objectively analyze the correlation between ocular examination findings and patient concerns. Furthermore, the objective scatter index scores ≥3.0 can be a possible objective cut-off for preoperative decision making.
Cataracts are a major cause of blindness worldwide, affecting almost 18 million people. Fortunately, the visual impairment caused by cataract is reversible in the majority of patients after surgery. Thus the assessment, grading, and classification of cataract stage and the evaluation of cataract progression are vital, as they will help both eye care providers and patients to decide the optimal timing of cataract surgery.
Currently, both subjective and objective methods are used to assess cataracts. The Lens Opacities Classification System III (LOCS III) is a subjective grading system that has good reproducibility in cataract grading, and is widely used in clinical practice and research studies. The Visual Function Index-14 (VF-14) is a patient’s-perspective questionnaire. It subjectively quantifies the visual impairments caused by cataract and evaluates the need for cataract surgery. It is available in several languages, including Chinese, and is reliable, valid, and responsive to clinical changes. One widely used objective method is Scheimpflug imaging, which assesses cataracts by analyzing lens density. Recently, another objective assessment of cataract that is based on recording and analyzing double-pass retinal images of a point source has been proposed. This method quantifies the combined effect of light scatter and optical aberrations in human eyes and provides parameters, including the objective scatter index and the modulation transfer function, that allow comprehensive assessment of the optical quality of the eyes.
To help clinicians select an appropriate way of assessing cataracts, we investigated the relationship among these 4 cataract assessment methods. Based on our data, we also provided evaluations on the merits of each one. These results will be especially useful for scheduling of potential surgical patients whose cataracts are in the early to moderate stages of development.
Methods
This was a prospective, single-center, cross-sectional study. A total of 36 subjects (60 eyes) with age-related cataract were recruited between November 4, 2013 and February 21, 2014 at The Eye Hospital of Wenzhou Medical University, Wenzhou, China. The average age was 65.8 ± 7.8 years, ranging from 42 to 80 years. A comprehensive eye examination was performed on each participant, including refraction, logMAR best-corrected visual acuity (BCVA), slit-lamp examination (SL115; Carl Zeiss, Oberkochen, Germany), fundus examination under dilation, and noncontact tonometry (TX-F; Canon, Tokyo, Japan). Inclusion criteria were age-related cataract patients without significant posterior subcapsular opacification or other ocular abnormalities. All subjects were free of any clinically detectable corneal disease such as keratoconus, corneal dystrophies, or corneal opacity, as assessed by detailed slit-lamp examinations. This study was approved by the Institutional Review Board of The Eye Hospital of Wenzhou Medical University and adhered to the tenets of the Declaration of Helsinki. Informed consent was obtained from all subjects.
Lens Opacities Classification System III Lens Grading
The opacity of each eye was assessed using the LOCS III standards under pupil dilation with 0.5% tropicamide and 0.5% phenylephrine hydrochloride eye drops (Zhuobian, Sinqi, China). A well-trained ophthalmologist graded every eye under slit-lamp examination by comparing nuclear opalescence, nuclear color, cortical cataract, and posterior subcapsular cataract to standard color photographic transparencies. The assigned score was graded to reflect the relative decimal position between 2 successive standards. Subjects with posterior subcapsular cataract were excluded, and only cortical and nuclear cataracts were evaluated. Nuclear opalescence (0.1–6.9) and cortical cataract (0.1–5.9) gradings were used to assess the independent effect of nuclear opalescence and cortical cataract on visual function.
Visual Function Index-14
The Chinese Revision Visual Function Index-14 was used in this study. All subjects completed this questionnaire that was administered by the same trained interviewer. The subjects were asked whether, even with glasses, they had any difficulty in doing the 12 vision-dependent activities (2 of 14 were eliminated in the Chinese Revision Visual Function Index-14). The subjects then rated the amount of difficulty they had with the activity owing to their vision on the scale “a little,” “a moderate amount,” “a great deal,” or “unable to do.” The item was excluded if patients were not able to do the activity for any reasons other than their vision. The questionnaires were scored as recommended by the developers, with higher scores representing better visual functioning.
Lens Density Measurement
The lens density of each participant was evaluated by the same examiner using a Scheimpflug imaging device (Pentacam HR; Oculus, Wetzlar, Germany) after pupil dilation with 0.5% tropicamide and 0.5% phenylephrine hydrochloride eye drops. Three successive measurements were performed in each eye using the 50-scan acquisition mode in a dark room. The acquisition with the best centrality of the 3 was selected and analyzed by the Pentacam Nucleus Staging software to evaluate lens density. The Pentacam Nucleus Staging gives the average lens density in 3 dimensions with a selected diameter of 4.0 mm. The software generated a nuclear cataract grade in 5 stages (Pentacam Nucleus Staging scores) based on the densitometry values in the 3 dimensions.
Optical Quality Analysis of Lens
The optical quality of each subject’s eyes was measured using the Optical Quality Analysis System II (Visiometrics S.L., Tarrasa, Spain). The measurements were taken with an artificial pupil diameter of 4.0 mm, set by the instrument, which is the standard size used in clinical double-pass studies. Astigmatism ≥−0.75 diopter was corrected by using external ophthalmic cylindrical lenses. The measurements were made in a dark room to assure that the natural pupil diameter was larger than 4.0 mm, eliminating the need for further dilation that could cause a shift in refraction. Three successive measurements were obtained for each eye by the same examiner. The mean value was used for each parameter.
The main parameter provided by the Optical Quality Analysis System II to assess cataract was the objective scatter index. It is defined as the ratio of the intensity at an eccentric location in the double-pass image and the central area (the peak). The objective scatter index can quantify the magnitude of the intraocular scattering, the main source of which is the cateractous crystalline lens. An elevated value of objective scatter index represents more intraocular scatter, and therefore more disturbance in vision. The modulation transfer function, which represents the loss of contrast in the retinal image at various spatial frequencies, can be used to objectively evaluate the visual quality. The modulation transfer function cut-off is the highest spatial frequency that the eye can detect. Therefore, higher cut-off frequencies were associated with better optical quality. The Strehl ratio is the ratio between the area under the modulation transfer function curve of the measured optical system and the aberration-free system, with a higher value representing better optical quality.
Statistical Analysis
All statistical analyses were performed using SPSS 16.0 (SPSS Inc, Chicago, Illinois, USA). All continuous variables were expressed as the means ± standard deviations. The normality of each variable was checked with the 1-sample Kolmogorov-Smirnov test. All variables were normally distributed except the Pentacam Nucleus Staging score. The relationship between each variable, including LOCS III grading (nuclear opalescence, cortical cataract), VF-14 score, objective scatter index, modulation transfer function cut-off, and the Strehl ratio was analyzed by the Pearson correlation test. Spearman correlation tests were used for determining the relationship of Pentacam Nucleus Staging scores with other variables. Partial correlation tests were used to evaluate the relationships among average lens density, LOCS III grading (nuclear opalescence, cortical cataract), VF-14 score, objective scatter index, and BCVA while controlling for age. Independent sample t tests were used for comparing the means of each parameter between each group. The level of significance was P < .05.
Results
For all 60 eyes, the mean value of BCVA was 0.19 ± 0.16; LOCS III nuclear opalescence score, 3.28 ± 0.49 (range, 2.5–4.7); cortical cataract score, 2.70 ± 1.12 (range, 1.0–4.9); average lens density, 10.61 ± 1.46; and objective scatter index, 4.41 ± 2.98. There were 57 LOCS III grading nuclear opalescence scores (95.0%) that were less than 4.0 and 54 cortical cataract scores (90.0%) that were less than 4.0.
Linear correlations were analyzed between the BCVA, LOCS III nuclear opalescence score, objective scatter index, average lens density, modulation transfer function cut-off, Pentacam Nucleus Staging score, and the Strehl ratio ( Table 1 ). The LOCS III nuclear opalescence score was significantly correlated with BCVA, objective scatter index, and the average lens density ( P ≤ .001 each), and with the modulation transfer function cut-off ( P = .014). The objective scatter index was significantly correlated with BCVA, modulation transfer function cut-off, and the Strehl ratio ( P < .001 each), and with the average lens density ( P = .013). The average lens density was significantly correlated with the BCVA and the Pentacam nucleus staging score ( P = .005 and P < .001, respectively).
| Comparisons | Correlation Coefficient | P Value |
|---|---|---|
| LOCS III NO score × BCVA a | 0.438 | .001 |
| LOCS III NO score × OSI | 0.543 | <.001 |
| LOCS III NO score × ALD | 0.621 | <.001 |
| LOCS III NO score × MTF cut-off | −0.315 | .014 |
| OSI × BCVA a | 0.779 | <.001 |
| OSI × MTF cut-off | −0.690 | <.001 |
| OSI × ALD | 0.320 | .013 |
| OSI × SR | −0.462 | <.001 |
| ALD × BCVA a | 0.360 | .005 |
| ALD × PNS score | 0.492 | <.001 |
a Partial correlation test was used while controlling for age.
The value of the VF-14 score was the same for each subject regardless of the difference in other parameters for each eye. The vision in the better eye usually suggested the visual limitation to perform daily activities, and the VF-14 score had stronger correlation with the better eye than with the worse eye. Therefore, the parameters of the better eye for each subject were selected for analysis. For all 36 subjects, the VF-14 score correlated with the BCVA (r = −0.645, P < .001; Figure , Top left), average lens density (r = −0.393, P = .018; Figure , Top right), LOCS III nuclear opalescence (r = −0.600, P < .001; Figure , Middle left), and modulation transfer function cut-off (r = 0.466, P = .004; Figure , Middle right), and strongly correlated with objective scatter index (r = −0.712, P < .001; Figure , Bottom left).
