Changes in light scatter and width measurements from the human lens cortex with age

Epinucleus Scraping: Safe New Phacoemulsification Technique for Rock-Hard Cataracts

Introduction:

Phacoemulsification of rock-hard cataracts is challenging because the leathery epinucleus at the posterior plate often found in such cataracts tends to prevent smooth dissection of the nucleus. We devised an Epinucleus scraping technique to overcome this problem.

Methods:

The epinucleus is initially stripped of the hard endonucleus using a new instrument. The isolated endonucleus can then be readily chopped and divided with a phaco chopper or in the usual manner.

Conclusion:

Phacoemulsification of rock-hard cataracts can be carried out safely and easily with epinucleus scraping technique.

On the contribution of the nucleus and cortex to human lens shape and size

BACKGROUND

The shape of the human lens changes from almost spherical at birth to ellipsoid due to a decrease in sagittal thickness and an increase in equatorial diameter during the first two decades of life. Both dimensions increase thereafter. This study was undertaken to determine the reason for the change.

METHODS

Published refractive index gradients, from 20 lenses aged from seven to 82 years, were used to calculate the protein contents of concentric shells of fibre cells in human lenses. The boundaries of nuclear cores containing from 2.5 to 45 mg, in 2.5 mg increments, were determined from the isoindicial shells. Cortex thickness was determined from the distance between the 30 mg nuclear boundary and the capsule.

RESULTS

The sagittal thickness of every nuclear core decreased until age 40 years and remained constant thereafter. Over the same time frame, the equatorial diameter of the cores containing up to 30 mg of protein increased, while those of cores larger than 30 mg decreased. The volumes of the cores decreased and their shapes changed from near spherical to spheroidal. Equatorial and sagittal cortex thickness increased linearly with age at 0.0082 mm per year. The anterior sagittal cortex was 0.23 mm larger than the posterior and the equatorial cortex was 0.62 mm greater.

CONCLUSIONS

Changes in lens shape observed during the first two decades of life are due to remodelling and compaction of the 30 mg nuclear core. Cortex growth is linear throughout life.

Age determination in dogs using ocular light reflection, dental abrasion and tartar

OBJECTIVE

The knowledge of an animal's age is important for disease probability, prognoses, or epidemiological questions, but unfortunately, it is often unknown for dogs in animal shelters. A simple estimating procedure is preferable being quick and easy to perform, even for non-veterinarians.

MATERIAL AND METHODS

In 295 dogs the dimension of light reflection (diameter in millimetres), visible on the posterior lens capsule using a penlight, the grade of dental abrasion and dental tartar were documented photographically and the exact weight and age in days were obtained. These photographs were evaluated blinded. The dogs were divided randomly into two groups. The first group was used to establish a model for age determination using linear and logistic regression models considering the documented parameters, which was then validated with the data of the second group.

RESULTS

The size of ocular light reflection and age correlated significantly (r = 0.781; p < 0.001; sy,x = 2.45 years [SD of y for given x]). The linear regression model gave the final equation: Estimated age [months] = 13.954 + 33.400 × lens reflection [mm] + 8.406 × dental abrasion [grade] + 8.871 × tartar [grade] with a standard error of estimation of 2.26 years.

CONCLUSION AND CLINICAL RELEVANCE

Age determination, even based on three parameters results in a large standard deviation making age estimation in dogs very crude.

The ageing lens and cataract: a model of normal and pathological ageing

Cataract is a visible opacity in the lens substance, which, when located on the visual axis, leads to visual loss. Age-related cataract is a cause of blindness on a global scale involving genetic and environmental influences. With ageing, lens proteins undergo non-enzymatic, post-translational modification and the accumulation of fluorescent chromophores, increasing susceptibility to oxidation and cross-linking and increased light-scatter. Because the human lens grows throughout life, the lens core is exposed for a longer period to such influences and the risk of oxidative damage increases in the fourth decade when a barrier to the transport of glutathione forms around the lens nucleus. Consequently, as the lens ages, its transparency falls and the nucleus becomes more rigid, resisting the change in shape necessary for accommodation. This is the basis of presbyopia. In some individuals, the steady accumulation of chromophores and complex, insoluble crystallin aggregates in the lens nucleus leads to the formation of a brown nuclear cataract. The process is homogeneous and the affected lens fibres retain their gross morphology. Cortical opacities are due to changes in membrane permeability and enzyme function and shear-stress damage to lens fibres with continued accommodative effort. Unlike nuclear cataract, progression is intermittent, stepwise and non-uniform.

Changes in the internal structure of the human crystalline lens with diabetes mellitus type 1 and type 2

PURPOSE

To investigate the effect of diabetes mellitus (DM) type 1 and type 2 on the internal structure of the lens.

DESIGN

Observational cross-sectional study.

PARTICIPANTS AND CONTROLS

One hundred seven patients with DM type 1, 106 patients with DM type 2, and 75 healthy control subjects.

METHODS

Scheimpflug photography was used to image the lens of the right eye of 213 patients with DM and 75 healthy control subjects. The densitogram of the Scheimpflug image was used to indicate the nucleus and the different layers of the cortex of the lens. Lenses with cataract were excluded.

MAIN OUTCOME MEASURES

The size of the nucleus and the different layers of the cortex of the lens.

RESULTS

The nucleus and the different cortical layers of the DM type 1 lenses were significantly thicker compared with those of the control group (P<0.001). A significant association was found between the duration of DM type 1 and both the anterior and posterior cortex, its different layers, and the nucleus (P<0.001). The increase in the anterior and posterior cortex with the duration of DM was comparable with that of the nucleus. No important differences in the internal structure of the lens were found between the patients with DM type 2 and the control group.

CONCLUSIONS

Diabetes mellitus type 1 has a significant effect on the internal structure of the lens. The difference in effect of DM type 1 and type 2 on internal lens structure suggests an essential difference in pathogenesis. Furthermore, the results of the present study may indicate that the increase in the size of the lens with DM type 1 is the result of a generalized swelling of the lens, affecting all its different parts.

Effects of different degrees of cataract on the multifocal electroretinogram

AIM

To study the effect of different degrees of nuclear cataract on the multifocal electroretinogram (mfERG).

METHODS

mfERGs were recorded from 30 elderly subjects with very mild, mild, or moderate nuclear cataracts using a VERIS System (version 4.1). The subjects were divided into three groups (10 in each group) according to their degree of nuclear cataracts as classified according to the Lens Opacities Classification System III (LOCS III). No subjects had any significant eye disease or degenerative changes except for cataracts. The mfERG responses were grouped into six concentric rings for analysis. Both the N1 and P1 amplitudes and the latencies of N1 and P1 of first-order responses were used for analysis.

RESULTS

Amplitudes of N1 and P1 from the central retina (14 degrees) were significantly reduced in patients with mild or moderate cataract when compared with subjects with very mild cataract. However, there was no significant reduction of N1 and P1 amplitudes in the para-central retina (14-40 degrees). There was no difference in the latencies of N1 and P1 in these three groups of subjects.

CONCLUSIONS

The mfERG responses from the central retina (central 14 degrees) were affected by the severity of cataract, but responses from the paracentral retina (14-40 degrees) were not affected. This suggests that in interpreting the mfERG in subjects with mild or moderate cataract subjects some care should be taken as reduced amplitudes (N1 and P1) will be expected from the central retina.

Changes in the internal structure of the human crystalline lens with age and accommodation

Scheimpflug images were made of the unaccommodated and accommodated right eye of 102 subjects ranging in age between 16 and 65 years. In contrast with earlier Scheimpflug studies, the images were corrected for distortion due to the geometry of the Scheimpflug camera and the refraction of the cornea and the lens itself. The different nuclear and cortical layers of the human crystalline lens were determined using densitometry and it was investigated how the thickness of these layers change with age and accommodation. The results show that, with age, the increase in thickness of the cortex is approximately 7 times greater than that of the nucleus. The increase in thickness of the anterior cortex was found to be 1.5 times greater than that of the posterior cortex. It was also found that specific parts of the cortex, known as C1 and C3, showed no significant change in thickness with age, and that the thickening of the cortex is entirely due to the increase in thickness of the C2 zone. With age, the distance between the sulcus (centre of the nucleus) and the cornea does not change. With accommodation, the nucleus becomes thicker, but the thickness of the cortex remains constant.

Aging of the human lens: changes in lens shape at zero-diopter accommodation

Scheimpflug photographs of the zero-diopter-accommodated anterior segments of 100 human subjects, aged 18 to 70 yr and evenly spaced over this range, were digitized and analyzed to characterize lens and lens nucleus shape as a function of age by the Hough transform and other image analysis methods. Anterior and posterior lens surface curves exhibit a decrease in radius of curvature with increasing age, in qualitative but not quantitative agreement with the earlier observations of Brown [Exp. Eye Res. 19, 175 (1974)]. In contrast, the shape of the lens nuclear boundaries changes little with age. Overall lens volume at zero diopters increases with age, but the volume of the lens nucleus remains unchanged. The lens center of mass moves anteriorly with increasing age, as does the central clear region of the lens. Although these data sets were found to be more variable than those of Brown, the complementary variability of other factors, such as anterior chamber depth, for each subject leads to a very high statistical correlation between lens shape and lens location relative to the cornea. This supports the finding of previous work that image formation on the retina for a given individual results from the multifactorial balancing of related factors.

The development and maintenance of emmetropia

The human eye is programmed to achieve emmetropia in youth and to maintain emmetropia with advancing years. This is despite the changes in all eye dimensions during the period of growth and the continuing growth of the lens throughout life. The process of emmetropisation in the child's eye is indicated by a shift from the Gaussian distribution of refractive errors around a hypermetropic mean value at birth to the non-Gaussian leptokurtosis around an emmetropic mean value in the adult. Emmetropisation is the result of both passive and active processes. The passive process is that of proportional enlargement of the eye in the child. The proportional enlargement of the eye reduces the power of the dioptric system in proportion to the increasing axial length. The power of the cornea is reduced by lengthening of the radius of curvature. The power of the lens is reduced by lengthening radii of curvature and the effectivity of the lens is reduced by deepening of the anterior chamber. Ametropia results when these changes are not proportional. The active mechanism involves the feedback of image focus information from the retina and consequent adjustment of the axial length. Defective image formation interferes with this feedback and ametropia then results. Heredity determines the tendency to certain globe proportions and environment plays a part in influencing the action of active emmetropisation. The maintenance of emmetropia in the adult in spite of continuing lens growth with increasing lens thickness and increasing lens curvature, which is known as the lens paradox, is due to the refractive index changes balancing the effect of the increased curvature. These changes may be due to the differences between nucleus and cortex or to gradient changes within the cortex.

Aging of the human crystalline lens and anterior segment

Changes in the unaccommodated human crystalline lens were characterized as a function of subject age for 100 normal emmetropes over the age range 18-70 yr by Scheimpflug slit-lamp photography. With increasing age, the lens becomes thicker sagittally, but since the distance from the cornea to the posterior lens surface remains unchanged, this indicates that the center of lens mass moves anteriorly and the anterior chamber becomes shallower. Sagittal nuclear thickness is independent of age, but both anterior and posterior cortical thicknesses increase with age, shifting the location of the nucleus and the central sulcus in the anterior direction. The amount of light scattered by the lens at high angles, as represented by normalized and integrated lens densities from the digitized images, increases with increasing age in an exponential fashion. Similar relationships to age are observed for the major anterior zone of discontinuity (maximum density) and the central sulcus (minimum density). The relationships of these results to accommodation and presbyopia are discussed.

The zones of discontinuity in the human lens: development and distribution with age

Statistical analysis of Scheimpflug images from the crystalline lenses of 100 emmetropic human subjects ranging in age from 18 to 70 yr confirms that specific zones of discontinuity are a function of lens development and growth. At and beyond the age of 40 yr, as many as four sharply demarcated and complementary zones are seen within the anterior and posterior lens cortex. The locations of the inner edges of the anterior cortical zones of discontinuity were characterized relative to the central sulcus of the lens. Consecutively from the central sulcus, the distances were 1.094, 1.415, 1.695, and 1.994 (+/- 0.11 mm). Since nuclear thickness in the adult lens is age-independent and the rate of cortical growth has been characterized, the location of the inner margins of the zones are indicative of the age at which they originated; these ages were 4 (+/- 1 yr), 9 (+/- 2 yr), 19 (+/- 4yr), and 46 (+/- 10 yr). All of the zones become broader along the outer margin and more dense upon aging, with specific zones appearing to merge in older presbyopic lenses. While lens fetal nuclear transparency decreases with age, it does not feature zones of discontinuity; instead, symmetrically amorphous regions appear centrally in the anterior and posterior nucleus. This demonstration of the onset of specific zones of discontinuity in emmetropic individuals, at defined periods of lens growth that are synchronous the production of successively more complex lens sutures, strongly suggests a causal relationship between lens sutures and the zones of discontinuity.

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.