A C T A O P k T H A L M O L O G l C A V O L . 5 7 1 9 7 3

VARIATIONS OF LENS THICKNESS IN RELATION TO BlOMlCROSCOPlC TYPES OF

HUMAN SENILE CATARACT

BY

A. BRUUN LAURSEN and H. FLEDELIUS

T h e results a r e reported of 3s ultrasonographic i n r i i r w mensurations of intraindividual differences in axial thickness between a cataractous lens in one eye and a bio~nicroscopically clear or slightly cataractous lens (incipient deep cortical opacity) in the other. Obviously intumescent cata- ractous lenses were excluded. In general. the cataractous lcns was / l i innrr than the contralateral clear or slightly cataractous lens. Large decreases in lens thickness appeared in lenses with the c.ci/~stilr- i i w r o/xrc. i l ic .v or posterior suhcapsular cataract (I’SC) + anterior cap- sular/subcapsular opacity (ACSCO). PSC was more closely correlated to lens thinning than was ACSCO. Nuclear cataract very often occurred in thin lenses. but did not appear to cause lens thinning / )or s c . Deep cortical opacity was not associated with lens thinning. T h e present results contributed to our argumentation that the decrease in lens thickness is due to a leak of lcns niaterial through the ’lens membrane’ beside a possible cessation of growth of the lens fibres.

K r y words: cataract, unilateral human scnilc - biomicroscopy - ultra- sonography - lcns thickness. intraindividual side dillerences in - opa- cities. capsule-near

It is the aitn of the present study to evaluate possible associations between biomicroscopical types of opacities in human senile cataractous lenses and ultrasonographically recorded variations in lens thickness (LT). In particular,

Received August 15, 19iX.

Acts oi~hthnl ii. I

1 I

A . Bruun Laursen and H . Fledelius

we were interested in clarifying whether anterior capsular/subcapsular opacity (ACSCO) - Bruun Laursen 1976, see ‘Mehods’ below - might be associated with L T changes, since ACSCO seems to be a biomicroscopical indicator of important biochemical changes during senile cataractogenesis in man. Thus, ACSCO in human senile cataract has been found to be associated with a) low ribonucleotide pools (Bruun Laursen 1976), b) an increase in lens sodium ion concentration, and c) a fall in lens potassium ion concentration (Klauber R. Bruun Laursen 1977).

The obvious macrosco/icnl characteristic of the cataractous lens is, of course, its opacification, but in addition many cataractous lenses are smaller (less voluminous) than clear lenses of coeval persons, as was first shown by Smith (1883). More recently, this has been confirmed through investigations into lens wet weights (Maraini & Mangili 1973) and by in vivo ultrasonic lens thickness mensurations (Babel et al. 1969; Delmarcelle & Luyckx-Bacus 1971). The latter authors further included optical pachymetry of the depth of the anterior chamber and roughly examined its possible relations to biomicroscopical types of cataract. They found that the thinnest lenses and the deepest chambers oc- curred when the lenses were totally opaque.

T o our knowledge, there have been no reports on the topic dealt with in the present paper: The possible associations between echographically recorded variations in ALT (the intraindividual side difference in lens thickness, in persons with unilateral cataract) and specified cataract morphology.

Material

38 consecutive patients aged 51-83 years with predominantly unilateral senile cataract were selected for the study. Excluded were patients with previous eye injuries or additional eye disease, diabetes mellitus, as well as patients receiving corticosteroid treatment. Excluded were also obvious cases of intumescent (Morgagni! cataract. These exclusions imply that our statements will be valid for non-intumescent cataracts only, and not for the full spectrum of human senile cataracts.

W e intended to include only strictly unilateral cases of senile cataract, but such a material is difficult to collect considering the above criteria of exclusion as well as the age of the patients. Even in a fellow eye with a visual acuity of 1.0 careful examination will, as a rule, reveal lens opacities in the age group under study. There were, however, 24 cases of str ic t ly mi lafera l senile cataract. The remaining 14 cases presented marked side differences concerning cataract morphology. In particular, we demanded that PSC and ACSCO be absent in the less affected lens. In general, this was affected by incipient deep cortical opacity only.

The axial lengths of the eyes were used to exclude a possible source of error in the evaluation of ALT, namely a pre-existing anisometropia, now concealed behind

2

Variations of Lens Thickness in Cafarnct

opaque media. In fact, the axial lengths within the 38 pairs of eyes were almost identical, the median side difference being only 0.2 mm, and in all but 2 cases 2 0.4 mm.

Methods

Three classification systems were used (Bruun Laursen) based on slit lamp examina- tion and ophthalmoscopy according to a) Site(.s) of opocify within the lens, b) Extent of PSC (posterior subcafisular cataracf) and ACSCO c) An overall impression of the transparency of the lens.

a) Sites o f opacity 1) Anterior capsular/subcapsular opacity (ACSCO): whitish dots or an irregular

greyish coating apparently located in or immediately beneath the anterior lens capsule (Bruun Laursen 1976).

2) Posterior subcapsular cataract (PSC): posterior subcapsular tufaceous opacity. 3) Nuclear cataract: grey or brown opacity of the biomicroscopic lens nucleus

causing blurred insight to the posterior lens capsule and appearing as a disciform opacity on transillumination with the ophthalmoscope (mydriasis).

4) Cortical cataract: irregular or spoke-like anterior or posterior deep cortical opacities, apparently free of the lens capsule.

5) Totally opaque lenses: uniformly grey or brownish lenses, always with extensive ACSCO.

b) Exfent o f PSC and ACSCO, estimated as percentages of the visible parts of the anterior and posterior lens surfaces, respectively.

c) Lens transparency as estimated roughly on slit lamp and ophthalmoscopic exami- nations was recorded as:

Grade 0, quite clear. Grade 1, a high degree of transparency and a comparatively slight extension of

Grade 2, more severely affected immature cataract. Grade 3, total lens opacity. The above evaluations were, just as the following ultrasound mensurations, per-

formed in full mydriasis, after instillation of phenylephrine 10 O/n and cyclopentolate 0.5 O/n or tropicamide 1 "in.

Axial itltrasoitnd measitremenfs were performed with A-mode technique, as described by Fledelius (1976), and they were all carried out by him. Kretztechnik 7000, a 10 Mc ultrasonolux transducer and a Methocel-filled contact glass were used.

For the conversion from arbitrary apparatus units to lens thickness in mm we used the intralenticular ultrasound velocity of 1641 m/sec given by Jansson & Kock (1962) for clear lenses. The velocity in cataractous lenses has been found to be of the same order, 1629 m/sec (Coleman et al. 1975). The aberration being less than 1 per cent, we did not introduce this latter value in calculations for the cataractous lenses.

A pilot study was performed by Fledelius (quoted by Fledelius & Bruun Laursen 1978): 1) to control the US method, and 2) to estimate the level of intraindividual

the opacity.

3 I *

A . Briiitn Laiirsen and H . Fledeliiis

Median , ILT mm

L T differences (right-left) in a sample with healthy eyes. ,ILT values were - as expected - low, with a median value 5 0.1 mm.

Statistical comparisons between two types of lens opacity were carried out by means of the Mann-Whitney test and correlation analyses by means of the Spearman rank correlation analysis.

Range il L T mm

Table 1. Intraindividual side differences in lens thickness (3 LT) between a cataractous and a clear lens in 24 persons. arranged according to various biomicroscopic types. The individual opacities were compiled regardless of additional opacities in the same lenses. In a few cases the posterior cortex and the posterior capsule of immature cataractous lenses could not be evaluated. Abbreviations: PSC: posterior subcapsular

cataract. ACSCO: anterior capsularisubcapsular opacity. L T = lens thickness. See ‘Methods’.

Median age

years

Type of opacity N

+PSC+ACSCO tPSC +ACSCO -ACSCO -1’SC

-PSC-ACSCO

Median mm

+ru’uclear opacity -Nuclear opacity

Range mm

+Deep cortical opacity -Deep cortical opacity

Ixns transparency

Grade 1

Grade 2

Grade 3 (total opacity)

-1.0 -0.5 -0.4

-0.25 -0.1 -0.1

-0.4 -0.3

-0.3

-0.4

-0.2

-0.7

-0.7

-0.4 - -1.6 -0.2 - -1.6 -0.1 --1.6

0 --0.6 0 --0.6

0 - -0.6

-0.1 --1.6

0 --0.6

0 --1.6

-0.2 - -1 .0

0 --0.6

-0.3 - -1.6

-0.4 - -1.4

L T of cataractous lenses

GX 5 64 8

68 7 64.5 10 67.5 8

66 7

4 .O 3.6 - 4.8 66.5 8 4.4 3.9-5.1 64 9

4.5 3.6 - 5.1 67 12

4.3 4.0 - 4.5 60 5

4.5 3.9 - 5.1 65 11

4.0 3.6 - 4.8 65.5 6

3.9 3.6 - 4.6 65 7

4

Vcirintions o/ Lens Thickness in Cntarnct

L T of cataractous lenses Median Range

.1LT 1 L T mm mm Median Range

Type of opacity

mm mm

Resu I ts

Median age N

years

In the following the results will be viewed from two aspects. First the intraindividual side differences in axial lens thickness (dLT) will

be given in relation to different types of lens opacity. This is done a) for the strictly unilateral cases (N = 24), Table I, Fig. 1) and b) for the combined group of unilateral + bilateral cases (N = 38, Table 11, Figs. 2 and 3).

Besides, the frequencies of the different kinds of lens opacity in immature cataractous lenses are shown in relation to intraindividual side differences in lens thickness (Tables 111 and IV), the material being roughly divided into a group of numerically high and a group of numerically low ALT values.

Table 11. Differences in intraindividual lens thickness (ALT) between a cataractous lens on one side and a clear or slightly cataractous lens (with only incipient deep cortical opacity) on the other side, again arranged according to biomicroscopic types. N = 3H.

See legend of Table I also (1 lens was inadvertently not graded).

+PSC+ACSCO +PSC 4 ACSCO -ACSCO -PSC -PSC-ACSCO

+Nuclear opacity -Nuclear opacity

Lens transparency

Grade 1

Grade 2

Grade 3 (total opacity)

-0.75 -0.4 - - l . 6 3.9 3.4 - 4.6

-0.6 -0.2 --1.6 4.0 3.4 - 4.6

-0.65 -0.1 --1.6 4.0 3.4 - 4.8

-0.2.5 0 - - 1 . 1 4.4 3.5 - 5.1

-0.1 0 --0.6 4.5 3.9 - 5. I

-0.15 0 --0.6 4.5 3.9 - 5.1

-0.6 -0.1 --1.6 4.0 3.4 - 4.8

-0.25 0 --0.6 4.4 3.9 - 5.1

-0.2 0 --0.6 4.5 3.9 - 5.1

-0.8 -0.3--1.6 4.0 3.4 - 4.8

-0.6 +0.1 --1.4 4.0 3.2 - 4.6

70 10

67 12

70 12

65.5 12

69 9

67.5 8

70 13

65 10

65.5 12

72 11

69 14

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A . Bruiin Laursen and H . Fledelitis

L T mm

5.0

L.0

3.0

50 55 60 65 70 75 80 85 YEARS Fig. 1 .

Ultrasonographically recorded intraindividual side differences in lens thickness (d LT) between a cataractous and a clear lens (N = 24) in relation to age. No significant correlation was found between age and the thickness of the clear lenses in the present age interval of 51-83 years (Spearman's rank correlation coefficient corrected for

ties = 0.38. 0.10 > P > 0.05). 0: clear lens; 0: cataractous lens.

The d L T values will be given with signs, as the L T value of the cataractous lens minus the LT value of the clear(er) lens. In most cases the sign is a minus, to signify a deficit in the thickness of the cataractous as compared with the clear(er) lens.

The various lens opacities were, of course, mingled in many combinations in our material, and it is, therefore, difficult to evaluate the association between the separate opacity and the corresponding ALT. However, this is attempted in Tables I-IV, in Figs. 2 and 3, as well as in our statistical calcula- tions. Thus, the ,4LT value of an immature cataractous lens with PSC (poste- rior subcapsular cataract), ACSCO (anterior capsular/subcapsular opacity), cor- tical, nnd nuclear opacities was used 5 times, namely each time each separate opacity was considered, regardless of the 3 additional opacities, and when the lens transparency was graded.

Fig. 1 shows the individual lens thicknesses (LT) of both eyes of the 21 patients with strictly unilateral cataract. A slight increase in L T with age possibly occurred for the clear lenses. However, the significance level was only 0.10 > P > 0.05.

Variations of Lens Thickness i n Cataract

A LT m m

- 1.0

- 0.8

- 0.6

- 0.4

- 0.2

e .

20 GO 60 80 100 O/o PSC Fig. 2.

The correlation between the extent of PSC (posterior subcapsular cataract) and dLT. i. e. the intraindividual difference in lens thickness between an immature cataractous lens on one side and a clear or slightly cataractous lens with incipient deep cortical opacity on the other side. Spearman’s rank correlation coefficient uncorrected for ties = 0.81, P < 0.001. N = 19. 5 lenses were cxcluded (compare Table 11), because

the extent of PSC could not be evaluated.

Site of opacity; degree of opacification

From Table I comprising the group of strictly unilateral cataracts it is obvious that the numerically highest median ALT values, i.e. the thinnest lenses, are associated with PSC + ACSCO (-1.0 mm, P < 0.02), with PSC (-0.5 mm, P<0.02) , and with grade 2 and 3 cataract (-0.7 mm in both instances, P < 0.05 and P < 0.01, respectively). The P-values refer to com- parisons with lenses without PSC or ACSCO, wiflzout PSC, and to grade 1 lenses, respectively.

The ALT values of immature cataractous lenses with ACSCO did not differ from those of immature cataractous lenses without this opacity. Nor was there any statistical difference in the strictly unilateral cases as for ALT values between immature cataractous lenses with and without nuclear opacity or with and without deep cortical opacity.

Isolated deep cortical cataract - the type that occurred in the clearer lens of the ‘almost’ unilateral cases - presented low ALT values, the median 1LT value for 7 pure cortical grade 1 lenses being -0.1 mm (range = 0 - -0.6

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A . Brurrn Lniirsen and H . Fledelius

- 0.2.:

A L T m m

0

t -

- l . L

- 1.0

0

ALT mm

I - 0.4

+PSC+ ACSCO

.

+nuclear opacity

Grade 1 +deep (grades

1+2 = cortical opacity 100 " 0 )

Tnble I l l . Distribution of various biomicroscopic lens opacities in numerically high (2 0.6 mm) and low (5 0.4 mm) values of intraindividual side differences in lens thickness (ALT) between a n immature cataractous lens and a clear lens in 1 7 persons. See Legend

of Table I also. Median LILT = -0.4 mm.

+PSC +ACSCO

~

N

2 0.6 GO O/o

5 0.4 18 O I o 80 O/o

36 O/o

GO 010

33 010

60 O/o 60 " l o 40 O I o 42 OIo 75 010 75 010

5 12

Variations o j Lens Thickness i n Cntarcict

+PSC+ +Nuclear +PSC +ACSCO opacity -ILTmm ACSCO

Grade 1 (grades

1+2 = N

I00 010)

mm, not specified in able 1) . On this background it was considered justifiable to pool the ‘strictly’ and the ‘almost’ unilateral cases, and the combined results are presented in Table 11.

The significant differences appearing after statistical evaluation of the material presented in Table I reappear for the findings presented in Table 11. Besides, the induction in Table I1 of the 14 ‘almost’ unilateral cases resulted in additional statistically significant d L T differences. Thus, immature cata- ractous lenses with PSC + ACSCO (-0.75 mm, P < 0.01), with PSC (-0.6 mm, P < 0.01), with ACSCO (-0.65 mm, P < 0.02), with nuclear opacity (-0.6 mm, P < 0.02), with grade 2 cataract (-0.8 mm, P < 0.01), and lenses with grade 3 cataract (-0.6 mm, P < 0.05) had numerically higher ALT values - i. e. they were more thinned - than had lens pairs without these opacities. Again, for grade 2 and 3 lenses the P-values refer to comparisons with the ALT values of grade 1 lenses.

In the combined group the ALT values of immature cataractous lenses with PSC + ACSCO, PSC, ACSCO, nuclear cataract or grade 2 cataract did not differ significantly from the dLT values of totally opaque (= grade 3) lenses. The above characteristics are also obvious in Tables 111 and IV, which are divided by the size of d L T : Again, lenses with PSC + ACSCO, PSC, ACSCO, nuclear opacity, or grade 2 cataract dominate in the numerically high dLT group (higher degree of lens thinning), and correspondingly they are rare in the numerically low d L T group. Cortical cataract appears equally often in both groups (Table 111).

ACSCO has not been observed as an isolated apacity by the authors, neither in this material nor in other patients from the Eye Clinic. In particular, it is often combined with PSC: out of 11 immature cataractous lenses with ACSCO in which the posterior capsule could also be estimated 10 had PSC.

9

A . Brrrrrn Larirsen mid H . Fledeliris

As far as the o@cificntion of the immature cataractous lenses is concerned, nuclear cataract appeared to be more important than did deep cortical opacity. l h u s , nuclear cataract was found in only 2 out of 12 grade 1 lenses, in con- trast with 11 out of 11 grade 2 lenses (1 lens was inadvertently not graded). Among the latter 1 1 lenses a deep cortical cataract was unmistakable in 5 , slight only in 2 , and absent in 4.

Extent of PSC and ACSCO

Correlation analysis confirmed the aforementioned results. Positive correla- tions were found for the extents of PSC arid ACSCO on the one hand and the numerical size of d L T on the other. This means that the cataractous lenses were more thinned the higher the percentages of PSC and ACSCO were found to be (Figs.2 and 3).

Discussion

Associations between degree of lens thinning and biomicroscopic types of cataract

PSC and ACSCO appeared to be the most important opacities in this context. Above all, a high positive correlation was found between the extent of PSC

and the decrease in lens thickness. Next, ACSCO also showed a definitely positive correlation to the decrease in lens thickness, but this may, in part at least, be due to the common occurrence of PSC in lenses with ACSCO. Thus, the d L T differences between strictly unilateral cataracts with and with- out ACSCO proved to be insignificant.

Lens thinning was more pronounced in grade 2 cataracts (all of which presented nuclear opacity) than in grade 1 cataracts, which rarely presented nuclear opacity. This suggests an association of nuclear opacity with lens thinning. However, the following observation indicates that nuclear cataract does not cause lens thinning per se: The J L T difference between lenses with and without nuclear opacity was insignificant in the strictly unilateral cases.

Keeping constantly in mind the hazards connected with an approach so multifactorial as ours, we feel able to state that deep cortical opacity was not associated with the process of lens thinning.

Does a cessation of lens fibre growth or a real decrease in thickness of the

catatactous lens account for the side difference in lens thickness?

Biomicroscopically the ‘smaller lens of cataract’ has been ascribed to a thin- ning of the lens cortex (Goldmann k Favre 1961; Brown 1973), while the

10

Variations 01 Lens Thickness in Cntrircict

thickness of the nucleus of senile cataractous lenses appears to remain constant (Rodriguez-Caballero et al. 1973). The reason for the thinning of the cata- ractous lens has been claimed to be a cessation of the (ordinarily continuous) growth of the lens fibres (Goldmann k Niesel 1964), possibly setting in even before lens opacities become visible (Delmarcelle k Luyckx-Bacus 197 1).

Our study does not support the theory of a cessation of lens fibre growth, a t least not as the only or main reason for the thinning of the cataractous lens. Clear lenses thicken 0.23 mm per decade in the age interval of 20-60 years (Weekers et al. 1973), and probably at a somewhat slower rate after the age of 60 years. Provided that the theoretic cessation of lens fibre growth was the only reason for lens thinning, some of our cataractous lenses should have stopped growing - in one eye only - already in early adolescence or childhood. Or, for our extreme ALT values, even before birth!

Furthermore, the so-called normal fellow eye in cases of unilateral pre- senile/senile cataract frequently develops a similar cataract (with PSC and/or ACSCO) in the course of a few years. In other words, the cataract of the first affected eye often remains unilateral for a limited period of time only. In such cases an intraindividual side difference in lens thickness - d L T - should, in fact, be minimal or absent, i f the ‘cessation of growth’ theory were the only valid one. The high ALT values of the present material indicate, therefore, that the thinning of the cataractous lens cannot be accounted for by a precocious arrest of lens fibre growth only.

All things considered, our carefully selected material of largely unilateral cataracts - the fellow eye serving as a control - strongly suggests a real decrease in k n s thickness in some biomicroscopical types of human senile cata- ract. In our opinion this is the most fruitful working hypothesis for further research.

Is the decrease in lens thickness caused by a leak of lens substance

Into the aqueous?

The most likely account for a decrease in lens size is an escape of lens material through a lens membrane. The membranes of the lens hypothetically comprise the capsule + the epithelium anteriorly and the lens capsule poste- riorly. In this context we would like to draw attention to Friedenwald’s (1930) studies. This author found evidence of an increase in permeability of the lens capsule after prolonged exposure of it to cataractous lens cortex. Later it has been suggested that proteins of low molecular weight leak from the lens to the aqueous during senile cataractogenesis (Mach 1963; Charlton k van Hey- ningen 1968; van Heyningen 1972). In accordance with this, Klauber 8: Bruun

1 1

A . Briliin Luicrscn rind H . Fledeliics

Laursen (1977) found low dry weight (= protein) percentages in totally opaque lenses. Since such lenses are small as compared with e. g. the thicker immature cataractous lenses, totally opaque lenses obviously contain less protein than do thick immature cataractous lenses.

We find it probable that the capsule-near opacities of ACSCO and, in par- ticular. PSC (only a single barrier posteriorly, the lens capsule) may be associated with an increase in lens ‘membrane’ permeability. T o our knowledge, however, no studies have been carried out so far on this topic.

Concluding Remarks

In summary, our concepts on the decrease in thickness of the biomicroscopic- ally prevailing types of human senile cataract (excluding intumescent lenses) are as follows:

1 ) In most cases the cataractous lens is definitely thinner than the clear lens of the fellow eye.

2) The intraindividual side difference in lens thickness (ALT) is associated with PSC (in particular) and ACSCO, and - to a minor extent - with nuclear opacity. Deep cortical cataract appears not to be associated with lens thinning.

3) The dLT is probably accounted for mainly by a real decrease in lens thickness and not only by a cessation of lens fibre growth.

4) The decrease in lens thickness may be accounted for by a leak of lens material through the lens ‘membranes’.

5) This leak of lens substance appears to be associated with the occurrence of the capsule-near o/mcities (PSC and ACSCO).

References

Babel J , , Psilas K. & Itin W. (1969) Mesures kchographiques de I’kpaisseur du cri- stallin dans les cataractes unilatkrales. In: Bock J. and Ossoinig K., Eds. Ultrci- sonographin Medicu. V o l . 2, pp. 547-555. Verlag der Wiener Medizinischen Akade- mie, Vienna (SIDUO 111).

Brown N. A. P. (1973) General discussion I. Lens change with age and cataract; Slit- image photography. In: Ciba Foundation Symposium 19 (new series) Ed. The Iiittnan lens-in relation to cataract, pp. 65-78. Associated Scientific Publishers, Amsterdam, London, New York.

Bruun Laursen A. (1976) ,Concentrations of some ribonucleotides, L-lactate, and pyru- vate in human senile cataractous lenses with special reference to anterior capsular/ subcapsular opacity. Arta ophthul. ( K h h . ) 54, 677-692.

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Vuricitions o f Lens Thickness in Ccrtctrcict

Charlton J. & van Heyningen R. (1968) A n investigation into the loss of proteins of low molecular size from the lens in senile cataract. Ex!). Eye Res. 7, 47-55.

Coleman D. J., Lizzi F. L., Franzen L. A. & Abramson D. M. (1975) A determination of the velocity of ultrasound in cataractous lenses. In: Francois J. and Goes F., Eds. Ultrnsonogrnphy in Ophthnlniology. Bibl. Ophtltnl. 83, 246-251, Basel.

Delmarcelle Y. & Luyckx-Bacus J. (1971) BiomCtrie du segment antkrieur dans la cataracte senile. Act(/ oplrthnl. (Kbh.) 49, 454-466.

Fledelius H. (1976) Prematurity and the Eye. Ophthalmic 10-year follow-up of children of low and normal birth weight. Actn ophthnl. (Kbli.) Srrppl. 128. 35-46.

Fledelius H . & Bruun Laursen A. (1978) On Icns thickness in ccrfnrrrctotcs lenses. Read at the SlDUO VII Congress, Munster, Sept. 1978.

Friedenwald J. S. (1930) Permeability of the lens capsule with special reference to the etiology of senile cataract. Arch. Ophtlrnl. (Chicago) 3 , 182-193.

Goldmann H. & Favre M. (1961) Eine besondere Form praseniler Katarakt. Oplitltrrl- mologicn 141. 418-422.

Goldmann H. & Niesel P. (1964) Studien uber Abspaltungsstreifen und das Linsen- wachstum. Ophthnlmologiccr 147, 134-142.

Jansson F. & Kock E. (1962) Determination of the velocity of ultrasound in the human lens and vitreous. Actn ophthnl. (Kblt.) 30, 420-433.

Klauber A. & Bruun Laursen A. (1977) Relative contents of sodium, potassium, water, and dry matter in human senile cataractous lenses in relation to anterior capsular/ subcapsular opacity. Actn ophthnl. (Kbh.) 55, 789-799.

Mach H. (1963) Untersuchungen von Linseneiweiss und Mikroelektrophorese von was- serloslichem Eiweiss in Altersstar. Klin. Mbl. Airgenlieilk. 143, 689-710.

Maraini G. & Mangili R. (1973) Differences in proteins and in the water balance of the lens in nuclear and cortical types of senile cataract. In: Ciba Foundation Sym- posium 19 (new series) Ed. The hzinian lens - in relation to cataract, pp. 79-97. Associated Scientific Publishers, Amsterdam, London, New York.

Rodriguez-Caballero M. L., Gerhard J.-P. & Nordmann J. (1973) Le noyeau du cri- stallin humain 11. Son Cpaisseur. Arch. Ophtltnl. (Paris) 33, 425-428.

Smith P. (1883) Diseases of crystalline lens and capsule. Trans ophthnl. Soc. U.K. 3. 79-99.

van Heyningen R. (1972) The human lens I. A comparison of cataracts extracted in Oxford (England) and Shikarpur (W. Pakistan). E x p . Eye Res. 13, 136-147.

VJeekers R., Delmarcelle Y., Luyckx-Bacus J. & Collignon J. (1973) Morphological changes of the lens with age and cataract. In: Ciba Foundation Symposium 19 (new series) Ed. The lrzcmnn lens - in relation to catnrnct, pp. 25-40. Associated Scien- tific Publishers. Amsterdam, London, New York.

Authors’ addresses: A. Bruun Laursen, Eye Department 539, Hvidovre Hospital, Kettegird All6 30, 2650 Hvidovre, Denmark.

H. Fledelius, Eye Department 2061, Rigshospitalet, Blegdamsvej 9, 2100 Copenhagen 0, Denmark.

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