Indian Journal of Ophthalmology

: 1995  |  Volume : 43  |  Issue : 4  |  Page : 181--184

Colour of the nucleus as a marker of nuclear hardness, diameter and central thickness

Vamsi Krishna Gullapalli, Praveen R Murthy, KR Murthy 
 From Prabha Eye Clinic and Research Centre, Bangalore, India

Correspondence Address:
Vamsi Krishna Gullapalli
From Prabha Eye Clinic and Research Centre, Bangalore


Hundred and thirty patients, aged above 40 years, with senile cataract were examined. Age and colour were selected as the probable preoperative indicators of nuclear hardness. The lens material collected after manual extracapsular extraction was washed and the nucleus isolated. The diameter and central thickness of the nucleus were measured; the mean diameter and mean central thickness were 7.13 mm 0.76 and 3.05 mm 0.48, respectively. The hardness of the nucleus was measured with a lens guillotine designed by us. Regression analysis was applied to the parameters measured and these were compared with the colour and age. The parameters measured had the following relationship: Colour vs hardness (r value = 0.7569) (p < 0.001) Colour vs diameter (r value = 0.3962) (p < 0.001) Colour vs central thickness (r value = 0.4785) (p < 0.001) Age vs hardness (r value = -0.0499) (p > 0.05) Age vs diameter (r value = 0.0987) (p > 0.05) Age vs central thickness (r value = 0.1700) (p > 0.05) The values showed that colour had a statistically significant relationship with all the 3 parameters (p < 0.001), while age had no significant relationship with the same parameters. The results indicated that colour can be used more reliably to predict physical characteristics of the cataractous lens nucleus, the preoperative knowledge of which would help the surgeon in planning small-incision surgery including phacoemulsification.

How to cite this article:
Gullapalli VK, Murthy PR, Murthy K R. Colour of the nucleus as a marker of nuclear hardness, diameter and central thickness.Indian J Ophthalmol 1995;43:181-184

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Gullapalli VK, Murthy PR, Murthy K R. Colour of the nucleus as a marker of nuclear hardness, diameter and central thickness. Indian J Ophthalmol [serial online] 1995 [cited 2023 Apr 1 ];43:181-184
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Full Text

Postoperative astigmatism is a deterrent for patient satisfaction in cataract surgery. In an attempt to minimise astigmatism, various newer techniques of cataract surgery, such as small-incision surgery, sutureless surgery and phacoemulsification have been devised. Information about nuclear hardness, diameter and central thickness, if available, makes the planning and execution of such techniques more rational.

Heyworth et al[1] have identified colour and age as major markers of nuclear hardness. Pau[2] has found that brown or black colouration is related to maximum hardness but maximum hardening is not restricted to brown or black colouration. In a Japanese study[3] of hydrodissected human lenses, the mean diameter and mean central thickness were found to be 6.43 mm and 2.93 mm, respectively; a positive correlation between age and central thickness and a weak correlation between central thickness and hardness of the nucleus.

As of now, there has been no study of these measurements in the Indian population. None of the studies highlight the predictive values for nuclear hardness, diameter and central thickness based on the colour and age.

The present study is an attempt to find a mathematical correlation between the preoperative markers (colour and age) and physical characteristics (parameters) of the nucleus. A total of 130 patients with senile cataract were examined preoperatively and the lenses harvested at surgery were assessed, and the data obtained were correlated.


A total of 130 patients with senile cataract, aged above 40 years, and scheduled for cataract extraction were included in the study. Diabetics were included in the study but patients with complicated, traumatic and steroid-induced cataracts were excluded.

After dilating the pupil with atropine 1%, homatropine 2% and phenylephrine 10%, the patients were examined with a slit-lamp biomicroscope and the colour of the nucleus was graded arbitrarily as follows: 1+ = yellow/grey; 2+ = light brown; 3+ = brown; 4+ = dark brown; 5+ = black.

After the lens was extracted by the extracapsular technique, the cortical matter and epinucleus were washed with Ringer's lactate solution, running through an infusion line from an effective height of 120 cm through a 20-gauge needle. The colour gradation was reconfirmed by examining the washed nucleus under white light of the operating microscope. The greatest and the least diameters were measured to an accuracy of 0.5 mm by employing a transparent scale and the average was calculated. The central thickness was measured with a screw gauge to an accuracy of 0.01 mm.

To measure the nuclear hardness, a lens guillotine was designed, which consisted of a metal frame, in which a wooden cross moved vertically [Figure:1]. To the cross was attached a safety razor fitted with a razor blade. The nucleus was placed on the base of the metal frame and the cross with the fixed blade was gently placed over it. A plastic cup was placed on top of the cross at the centre and into this Ringer's lactate solution was poured through an infusion line, with a 20-gauge needle fixed to it. As the weight increased, the blade cut through the lens nucleus. The end point of the infusion was the visual contact between the entire length of the blade and the base of the guillotine which would necessarily indicate the complete sectioning of the nucleus. The weights of the blade, razor, cross, and cup with water were measured. The force required to cut the nucleus was calculated and expressed in newtons (N). This guillotine could not measure hardness of lenses softer than 0.26 N, the force required to cut through a very soft yellow nucleus.


One hundred thirty patients with senile cataract were examined. Of these, 29 were diabetics. The age of the patients was above 40 years.

The mean values of the nuclear parameters increased with increasing colour grade [Table:1]. On the contrary, the mean values of the nuclear parameters did not show a consistent increase with increasing age [Table:2]. Similar results were obtained when the hardness of nuclei were compared for varying age groups for a given colour.

The data obtained were subjected to linear regression analysis and the results are shown in [Table:3]. Colour had a statistically significant (p < 0.001) relationship with all the three parameters, while age had no significant relationship with any of the parameters. There was also a significant relationship between central thickness and hardness of the nucleus.

The regression analysis yielded the following formulae:

Nuclear hardness = 0.256 x colour + 0.146 N (57.3%) {r value = 0.7569} (p < 0.001)

The above formula was plotted and compared with the mean nuclear hardness in different colour grades [Figure:2].

Nuclear diameter = 0.274 x colour + 6.556 mm (15.7%) (r value = 0.3962} (p < 0.001)

Central thickness of the nucleus = 0.209 x colour + 2.611 mm (22.9%) {r value = 0.4785} (p < 0.001)

The force required to cut the lens nucleus was plotted against the colour grades [Figure:2]. While the nuclear hardness increased with colour grade (r = 0.7569; p < 0.001), there was no clear relationship with age (r = 0.0499; p > 0.05).

The values within brackets indicate the percentage of variation of the outcome variable that can be explained by linear variation in colour. r (correlation coefficient) indicates the quantum of statistical relationship between the variable. r takes a value between -1 and +1.


Lens hardness increases with relative dehydration.[4] However, the relationship between relative dehydration of the lens and age is inconclusive. While some studies[5-7] have shown a positive correlation, others have not been able to show a significant relationship.

The results of our study indicate that age does not have any correlative value to the nuclear hardness and diameter, as indicated by r values of -0.0499 and 0.0987, respectively. However, its correlation with central thickness is of some significance (r value = 0.17).

The findings of this study indicate that colour is a better marker of nuclear hardness, diameter and central thickness. Although the exact cause for the nuclear colour change is not known, it is associated with an increase in water insoluble proteins, especially the urea-insoluble subfraction. It is believed that photo-oxidation of tyrosine and tryptophan might be responsible for the colour; the intensity of colour increasing with the accumulation of such products.[8] The accumulation of these aromatic amino acids is more in the nucleus. Pigmentation is part and parcel of the cataract process and is independent of age.[9]

The knowledge of the 3 parameters measured in our study would help in employment of a suitable technique during cataract extraction, especially that of the central thickness of the nucleus would be useful in trenching of the nucleus during phacoemulsification. In routine cataract extraction, the knowledge of the diameter and central thickness of lens nucleus would, in turn, indicate the length of the section required to express a particular nucleus depending on its colour. A slightly larger section would facilitate easy expression of the nucleus. This would thereby reduce the use of a very large section, and consequently reduce the degree of postoperative astigmatism.

In conclusion, our study shows that colour is a more reliable indicator of nuclear hardness than age.


The authors wish to thank Mr. M. Aswathnarayan, for making the lens guillotine and Mr. Vishwanath, Department of Preventive and Social Medicine, Bangalore Medical College, for advice on statistical analysis.


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