Quantitating nuclear opacification in color Scheimpflug photographs.

PURPOSE: To test the validity of the color component subtraction method, a new objective technique of measuring nuclear cataract, and to correlate the tangent values of the different degrees of nuclear opacities to their corresponding subjective nuclear cataract grading using the Lens Opacities Classification System II and to another objective method of measuring nuclear cataract. METHODS: Densitometries for red, green, and blue colors of the color Scheimpflug image were conducted simultaneously along the anteroposterior axis of the lens nucleus. The three color curves were subtracted from each other, giving rise to three subtracted curves: blue-red, green-blue, and red-green. This technique was applied to 99 color Scheimpflug photographs taken in 99 eyes of 51 patients with varying degrees of nuclear opacities. Using linear regression analysis, the regression coefficient obtained, called tangent value (TV), represents the degree of nuclear opacification. RESULTS: Higher tangent value indicated greater nuclear opacification and was associated with higher correlation coefficient. This was seen graphically as an increased steepness in the slope of the subtracted curve. Good correlation existed between the subjective nuclear opacity grading and the objective tangent value. When the tangent values were correlated to the mean density of the three original color curves, good correlation was present in red and green, but only fair for blue, where maximum light scattering occurs. CONCLUSIONS: These results support the validity of color component subtraction technique in measuring nuclear cataract. This technique provides quantitative measures of nuclear opacification, has good reproducibility, and is useful for monitoring nuclear cataract longitudinally.

Long-term nutrient intake and early age-related nuclear lens opacities.

OBJECTIVE: To assess the relation between usual nutrient intake and subsequently diagnosed age-related nuclear lens opacities. SUBJECTS: Four hundred seventy-eight nondiabetic women aged 53 to 73 years from the Boston, Mass, area without previously diagnosed cataracts sampled from the Nurses' Health Study cohort. METHODS: Usual nutrient intake was calculated as the average intake from 5 food frequency questionnaires that were collected during a 13- to 15-year period before the evaluation of lens opacities. The duration of vitamin supplement use was determined from 7 questionnaires collected during this same period. We defined nuclear opacities as a nuclear opalescence grade of 2.5 or higher using the Lens Opacification Classification System III. RESULTS: The prevalence of nuclear opacification was significantly lower in the highest nutrient intake quintile category relative to the lowest quintile category for vitamin C (P<.001), vitamin E (P =.02), riboflavin (P =.005), folate (P =.009), beta-carotene (P =.04), and lutein/zeaxanthin (P =.03). After adjustment for other nutrients, only vitamin C intake remained significantly associated (P =.003 for trend) with the prevalence of nuclear opacities. The prevalence of nuclear opacities was significantly lower (P<.001) in the highest vitamin C intake quintile category relative to the lowest quintile category (odds ratio, 0.31; 95% confidence interval, 0.16-0.58). There were also statistically significant trends of decreasing prevalence of nuclear opacities with increasing duration of use of vitamin C (P =.004 for trend), vitamin E (P =.03 for trend), and multivitamin (P =.04 for trend) supplements, but only duration of vitamin C supplement use remained significantly associated with nuclear opacities after mutual adjustment for use of vitamin E (P =.05 for trend) or multivitamin (P =.02 for trend) supplements. The prevalence of nuclear opacities was significantly lower (P =.004) for women who used a vitamin C supplement for 10 or more years relative to women who never used vitamin C supplements (odds ratio, 0.36; 95% confidence interval, 0.18-0.72). Plasma measures of vitamins C and E taken at the eye examination were also inversely associated with the prevalence of nuclear opacities. CONCLUSION: These results provide additional evidence that antioxidant nutrients play a role in the prevention of age-related nuclear lens opacities.

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.

Ray tracing error correction in ophthalmic optics.

Ray tracing error correction (RTEC), a new method for various refractive calculations, is introduced. It consists of two procedures: (1) ray tracing that determines whether the ray originating from an infinite point focuses on the fovea and (2) error correction that varies the curvature of the different refractive surfaces according to an error correction formula when the ray is not focused at the fovea. These calculations are continued until the ray is focused at the fovea. The refraction of Gullstrand's schematic eye at relaxation and at accommodation, the desired postoperative corneal curvature for postoperative emmetropia after corneal ablation surgery, and the intraocular power of convex-plano, biconvex, and plano-convex intraocular lenses are presented.

New method of measuring nuclear cataract in color Scheimpflug photographs.

Based on the differential equation, a new method of measuring nuclear cataract in color Scheimpflug photographs was introduced. The densitometries for red, green and blue color were conducted simultaneously along the anteroposterior axis of the lens within the nuclear region. The 3 color components were subtracted from each other, yielding blue-red, green-red and blue-green curves which were linear within the nuclear region. The tangent values were calculated from the curves that correlate well with the degrees of nuclear cataract.

Subjective (LOCS II) versus objective (BGS) measures of cortical and subcapsular cataracts in retroillumination photographs.

96 black-and-white Neitz retroillumination photographs were graded subjectively using the Lens Opacities Classification System Version II (LOCS II). They were also measured objectively using the background subtraction (BGS) analysis. Subjective and objective BGS gradings were compared and showed good agreement (kappa = 0.78 for cortical and 0.78 for posterior subcapsular cataracts) and good correlation (correlation coefficient = 0.82 for cortical and 0.84 for posterior subcapsular cataracts; Spearman rank analysis).

Evaluation of lens opacities classification system III applied at the slitlamp.

The Lens Opacities Classification Systems (LOCS III) was developed and standardized using photograding. The purpose of this study was to assess the validity of LOCS III at the slitlamp and to compare slitlamp with photograding. To do so, two independent observers graded cataract at the slitlamp and in photographs from two sets of patients; the first set consisted of 205 eyes (193 acceptable photographs) and the second set of 51 eyes (51 photographs). The 95% tolerance limits (TL) for grading at the slitlamp ranged from 0.9 to 1.8 for the first set and 0.6 to 1.2 for the second (intraclass correlation coefficients 0.79 to 0.91 vs. 0.70 to 0.97, respectively). Specifically, there was a significant decrease in 95% TL for cortical and nuclear color. For the first set of photograding, the 95% TL were 0.3 to 0.6 between the two observers and 0.6 to 0.8 for the same observer at two different sessions. Similar results were found for photograding the second set. The 95% TL for comparing slitlamp and photograding were generally > 1.0. The results suggest that (1) LOCS III at the slitlamp has 95% TL only slightly worse than those for LOCS III photogradings; (2) LOCS III slitlamp grading for cortical and nuclear color improves with practice; and (3) the slitlamp and photographic gradings cannot be used interchangeably.

Quantitating cataract and nuclear brunescence, the Harvard and LOCS systems.

Subjective and objective systems are used to quantify cataract at The Center for Clinical Cataract Research. We have described each system and its use, presented data on reproducibility and validity, and for objective systems, demonstrated the correlation to the subjective grade of the cataract as defined by the Lens Opacities Classification Systems, Versions II and III (LOCS II and III). The subjective systems are used to classify nuclear color, nuclear opalescence, cortical cataract, and posterior subcapsular cataract. Reported kappa scores for LOCS II range from 0.85 to 1.0. Intraclass correlation coefficients for LOCS III (r1) range from 0.67 to 0.94. The computerized objective system are: (1) fast spectral scanning colorimetry (FSSC) for assessment of nuclear color (r1 = 0.96 to 0.98); (2) nuclear mean density (NMD) for assessment of nuclear opalescence (r1 = 0.97); and (3) percent area opacity (anterior = a; posterior = p) (OPAC-a and OPAC-p) for assessment of cortical and posterior subcapsular cataract (r1 = 0.92 to 0.96).