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(Investigative Ophthalmology and Visual Science. 2005;46:2071-2075.)
© 2005 by The Association for Research in Vision and Ophthalmology, Inc.
DOI:  10.1167/iovs.04-0890
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Impairment of Visual Acuity and Reading Performance and the Relationship with Cataract Type and Density

Eva Stifter,1 Stefan Sacu,1 Thomas Benesch,2 and Herbert Weghaupt1

1From the Departments of Ophthalmology and 2Medical Statistics, Medical University of Vienna, Vienna, Austria.


   Abstract
Top
 Abstract
Methods
 Results
 Discussion
 References
 
PURPOSE. To evaluate the association between the density of nuclear, cortical, and posterior subcapsular lens opacities and visual impairment in patients with cataract.

METHODS. In 80 patients, visual acuity and reading performance were evaluated 1 day before and 4 weeks after cataract surgery. Cataracts were categorized and graded according to the Lens Opacities Classification System (LOCS) III of nuclear color (NC), nuclear opalescence (NO), cortical (C), and posterior subcapsular cataract (P). A multiple linear regression analysis and partial correlation coefficients were calculated. Data were also checked for significant pre- and postoperative differences in visual performance related to cataract grading.

RESULTS. In the multiple linear regression analysis, significant associations were found between the improvement in visual acuity and reading performance after cataract surgery and the NC, NO, and P scores (P < 0.001); no significant association was found for the C score (P > 0.05). High partial correlation coefficients were found between the P score and the preoperative visual acuity (r = 0.6; P < 0.001), reading acuity (r = 0.74; P < 0.001), and maximum reading speed (MRS; r = –0.77; P < 0.001). Significant but lower partial correlation coefficients were found for the NO score. No significant partial correlation coefficients were found for the NC and C score. Significant pre- and postoperative differences in MRS were found in patients with P scores ≥3 or NO and NC scores ≥5, representing functionally relevant impairment.

CONCLUSIONS. A strong association was found between visual impairment in patients with cataract and the severity of posterior subcapsular cataract (PSC) and nuclear opacity. Particularly in patients with PSC, deficits in reading performance significantly increased. The functionally relevant deficits in patients with P scores ≥3 or NO and NC scores ≥5, should be carefully considered for planning cataract surgery or visual rehabilitation.

Opacities of the crystalline lens directly affect vision, causing functional impairment and visual loss in patients with cataract. For evaluating these deficits, ophthalmologists primarily concentrate on measuring distance visual acuity (VA).1 2

However, in a previous study evaluating the predictability of reading tests for the postoperative visual outcome of patients with cataract seeking surgery, it has been shown that cataractous lens opacities significantly influence reading performance, so that reading tests offer new interesting options for the clinical evaluation of visual performance and may even be used as a diagnostic test.3 Moreover, the standardized evaluation of reading acuity and speed is gaining more clinical attention, since a high correlation between functional vision and reading performance was found in patients with cataract.4

In consideration of these findings, the present study was designed to evaluate the association between the density of nuclear, cortical, and posterior subcapsular lens opacities and the impairment in VA and reading performance in patients with pure and mixed cataracts. For planning cataract surgery and visual rehabilitation, it would be helpful to identify the relationship between cataract morphology and functionally relevant visual impairments. This knowledge may considerably improve the evaluation of patients with cataract in clinical practice and research by defining which lens opacities can be considered relevant to the impairment of VA and reading performance.


   Methods
Top
 Abstract
 Methods
Results
 Discussion
 References
 
In this prospective clinical study, 95 consecutive patients with cataract were tested 1 day before and 4 weeks after uneventful cataract surgery. Six patients with advanced cataracts had to be excluded from the study examinations because they were unable to read the test sentences even at large print sizes. Nine patients were excluded because of macular changes determined at either the pre- or at the postoperative tests. Consequently, the measurements of 80 patients (47 women and 33 men) were analyzed for the present study. The patients’ mean age was 69.4 ± 10.8 years (Table 1) . In accordance with the Declaration of Helsinki, informed consent was obtained from all participants. All examinations were performed in only one eye of each patient (80 eyes of 80 patients).


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  		TABLE 1. Age and Cataract Grading Scores According to the LOCS III

 
Recruitment Criteria
Eighty patients with age-related cataract and normal macular function were tested 1 day before and 4 weeks after cataract surgery. Exclusion criteria were a history of ocular disease, intraocular surgery, laser treatment, glaucoma, diabetic retinopathy, amblyopia, and age-related macular degeneration (ARMD). All cataract surgeries were performed by one experienced surgeon (HW). A standardized small-incision phacoemulsification technique with an implantation of a monofocal intraocular lens (AcrySof MA 60 BM; Alcon Laboratories, Fort Worth, TX) was used in all cases.

Cataract Grading
One day before cataract surgery, the crystalline lens opacity was categorized and graded in mydriasis at the slit lamp with respect to nuclear opalescence (NO: 0.1–6.9) and nuclear color (NC: 0.1–6.9) and cortical (C: 0.1–5.9) and posterior subcapsular (P: 0.1–5.9) cataracts, using the reliable and validated Lens Opacities Classification System (LOCS) III.5 6 7 The grading was performed by one experienced examiner (ES). The LOCS III grading scores are given for the whole study population and the pure and mixed cataracts in Table 1 .

Visual Acuity
At both testing sessions, the best corrected VA was determined monocularly using the Early Treatment Diabetic Retinopathy Study (ETDRS) charts (Precision Vision) in logMAR (logarithm of the minimal angle of resolution) at a test distance of 4 m.2 All tests were performed at a constant luminance of 80 to 90 cd/m2.

Reading Performance
Reading ability was tested monocularly with the Radner Reading Charts8 at a reading distance of 32 cm. This German reading chart system was designed for the simultaneous determination of reading acuity and speed.8 9 10 In previous studies, a high test–retest and interchart reliability was evaluated for these standardized reading charts and the highly comparable test sentences.11 12 The best corrected reading acuity (RA) was set at the smallest print size the patient was able to read completely and was expressed in logRAD (logarithm of the reading acuity determination). Reading speed was calculated for each print size based on the number of words in a sentence and the time needed to read the sentence (words per minute; wpm). The maximum reading speed (MRS) was the best reading speed the patient achieved during the reading test. The critical print size (CPS) was defined as the smallest print size the patients could read at optimal reading speed.13 At both testing sessions, the examiner, who tested the patients’ VA and reading performance, was masked to the patients’ cataract grading scores. Different but equivalent reading charts were used at the two testing sessions to avoid memorization effects.

Statistical Analysis
Because the difference between post- and preoperative visual tests is representative of the gain in vision related to cataract surgery, a multiple linear regression analysis was performed for the pre- and postoperative differences in VA, RA, MRS, and CPS with the independent variables NC, NO, C, P, and age, using the stepwise-selection technique. Considering the interrelationships between the different types of opacity, partial correlation coefficients and the corresponding probabilities were calculated for each of the preoperative lens grading scores (NO, NC, C, and P) and the pre- and postoperative visual parameters (VA, RA, MRS, and CPS). The probabilities were all corrected for multiple testing, applying the Bonferroni-Holm step-down test ({alpha} = 0.05).14 15 Descriptive analyses were performed for the pure and mixed cataract groups, calculating mean, standard deviation, and 95% confidence limits. All calculations were performed on computer (SAS, ver. 8.2; SAS, Cary, NC).


   Results
Top
 Abstract
 Methods
 Results
Discussion
 References
 
The mean VA and reading parameters are given for both the pre- and the postoperative measurements in Table 2 . The postoperative measurements were comparable in all groups (P > 0.05).


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  		TABLE 2. Pre- and Postoperative Visual Acuity and Reading Parameters

 
Association between Cataract Type and Density and the Visual Improvement after Cataract Surgery: Multiple Linear Regression Analysis
The difference between post- and preoperative visual tests is representative of the gain in vision related to cataract surgery. Performing a multiple linear regression analysis, the influence of the NO, NC, and P cataract grading scores were found to be statistically significant for VA and all reading parameters. No significant influence was observed for the C score (P > 0.05). No significant influence of age was found.

Partial Correlation Coefficients between the Cataract Grading Scores and the Preoperative Visual Parameters
The partial correlation coefficients and corresponding probabilities are given in Table 3 . Significant partial correlation coefficients were found between the P scores and the VA and all reading parameters. The highest correlation coefficient was found for the MRS (r = –0.77; P < 0.001), revealing a strong association between reading speed and posterior subcapsular lens opacities. High correlation coefficients were also found between the P scores and the RA and the CPS. Statistically significant but lower correlation coefficients were found between the NO score and the VA and reading parameters (Table 3) . Regarding the NC and C grading scores, the partial correlation coefficients were not statistically significant for the VA or the reading parameters. Analysis of the associations between the cataract grading scores and the postoperative visual parameters showed no significant correlation coefficients for any of the cataract grading scores after adjustment for multiple testing (Table 3) .


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  		TABLE 3. Partial Correlation Coefficients between the LOCS III Lens Grading Scores and the Pre- and Postoperative Study Parameters

 
MRS Measurements in Relation to the Lens Grading Scores
Comparing the pre- and postoperative MRS measurements in relation to the NO scale, significant intertest differences were found for pure nuclear cataract with advanced NO scores ≥5 (Table 4) . At NO scores <5, no significant differences in MRS was found in the pure or the mixed nuclear cataract groups. Similar results were observed in relation to the NC scale (data not shown), in consequence of the high correlation of the nuclear cataract scores.


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  		TABLE 4. MRS in Words per Minute in Patients with Pure and Mixed Nuclear Cataracts

 
In the pure PSC group, significant differences in MRS were found in patients with P scores ≥3 (Table 5) . Similar results were found for the mixed nuclear-posterior subcapsular cataract group and the nuclear-cortical-posterior subcapsular cataract group.


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  		TABLE 5. MRS in Words per Minute in Relation to the P Score

 

   Discussion
Top
 Abstract
 Methods
 Results
 Discussion
References
 
In the present study, the association between the density of nuclear, cortical, and posterior subcapsular lens opacities and the impairment in VA and reading performance was evaluated for patients with pure and mixed cataracts, by using the reliable and valid Lens Opacities Classification System (LOCS) III.5 6 7

In the multiple linear regression analysis, significant associations with the pre- and postoperative improvement in VA and reading performance were found for the NC, NO, and P scores (P < 0.001). No statistically significant association was found for the C score (P > 0.05). In addition, partial correlation coefficients were calculated to show how the patients’ visual impairments raised with increasing cataract density. For the NO and the P scores, high correlation coefficients were found with the VA and all reading parameters (Table 3) . The highest correlation coefficient was found for the MRS, which significantly decreased with increasing P scores (r = –0.77; P < 0.001).

The MRS is a valid indicator of macular function and correlates stronger with functional vision than reading acuity or any other reading parameter.4 13 16 17 Thus, reading speed measurements are a valuable clinical measure to discover functional deficits.4

In the present study, a significantly reduced MRS was observed in patients with pure and mixed posterior subcapsular cataracts at P scores ≥3 (Table 5) . At P scores <3, however, the differences between the pre- and postoperative MRS measurements were not statistically significant (Table 5) . In nuclear cataracts, the MRS was significantly reduced at NO scores ≥5; at lower NO scores the pre- and postoperative MRS measurements were found to be comparable (P > 0.05; Table 4 ). These results define which lens opacities relevantly impair visual performance in patients with cataract, since the significant pre- and postoperative differences in MRS were found to be above the level for a "real change" in vision.9 11

Reading performance in patients with cataract with normal macular function has been evaluated,3 13 16 but based on the data of these studies, no reliable conclusions could be drawn about the relationship between the density of the different cataract types and the visual impairment. Mean lens grading scores were reported only in a descriptive way. In one previous study in which the predictability of reading tests for the postoperative visual outcome of patients with cataract was evaluated, the LOCS III lens grading scores were used for defining pure and mixed cataract groups.3 Focusing on intergroup differences, significant reading impairments were found in posterior subcapsular and dense nuclear cataracts, but an association between the lens opacities and visual impairment could be only assumed, without qualitatively or quantitatively characterizing the relationship between the density of the different cataract types and the visual performance. These clinically relevant conclusions are now given in the present study.

These findings, it may be suggested that cataract grading should be included into preoperative eye examinations, since significant visual impairment may be expected at P scores ≥3 or NO or NC scores ≥5. Differences between the cataract types influencing vision should be taken into consideration whenever discrepancies between the self-reported visual function and the clinical measures of visual performance make it difficult to decide whether cataract surgery is indicated. In ophthalmological research, these results have to be carefully considered whenever attempting to compare the visual performance of patients with cataract, because intergroup differences could be significantly biased.

The strong effect of PSC on reading performance might be explained by the typical morphology obscuring the eye’s nodal point and resulting in central visual loss. Another reason for the functional differences between the various cataract types may be the influence of the lens opacities on contrast sensitivity or glare disability.18 19 20 Recently, wavefront analyses have shown that the type of cataract also influences the polarity of spherical aberration.21 22 The polarity of spherical aberration was negative in eyes with nuclear cataract but positive in eyes with cortical cataract. These differences may relevantly influence visual performance.

In conclusion, in the present study we evaluated a strong association between the visual impairment and the type and severity of posterior subcapsular cataracts and nuclear opacity. The highest correlation coefficient was found for the MRS, which is closely related to functional vision.4 Reading speed was significantly impaired at P scores ≥3 or NO scores ≥5, representing a relevant functional deficit. Because official guidelines postulate that cataract surgery is indicated only in case of functional disability, the association between cataract type and density and visual impairment should be carefully considered in the clinical evaluation of patients with cataract.


   Footnotes
 
Supported by the Theodor-Körner-Fonds.

Submitted for publication July 27, 2004; revised October 27, 2004, and February 1, 2005; accepted February 18, 2005.

Disclosure: E. Stifter, None; S. Sacu, None; T. Benesch, None; H. Weghaupt, None

The publication costs of this article were defrayed in part by page charge payment. This article must therefore be marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Corresponding author: Eva Stifter, Department of Ophthalmology, Medical University of Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria; eva.stifter{at}meduniwien.ac.at.


   References
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 Abstract
 Methods
 Results
 Discussion
 References
 

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E. Stifter, S. Sacu, A. Thaler, and H. Weghaupt
Contrast Acuity in Cataracts of Different Morphology and Association to Self-Reported Visual Function
Invest. Ophthalmol. Vis. Sci., December 1, 2006; 47(12): 5412 - 5422.
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