Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 26  |  Issue : 2  |  Page : 104-110

Sonographic evaluation of lens thickness in diabetes mellitus in a Nigerian tertiary hospital


1 Radiology Department, Ekiti State University Teaching Hospital, Ado-Ekiti, Ekiti State, Nigeria
2 Radiology Department, Obafemi Awolowo University Teaching Hospitals Complex, Ile-Ife, Osun State, Nigeria
3 Endocrinology Department, Obafemi Awolowo University Teaching Hospitals Complex, Ile-Ife, Osun State, Nigeria
4 Ophthalmology Department, Obafemi Awolowo University Teaching Hospitals Complex, Ile-Ife, Osun State, Nigeria
5 Nephrology Unit, Ekiti State University Teaching Hospital, Ado-Ekiti, Ekiti State, Nigeria
6 Radiology Department, Ladoke Akintola University Teaching Hospital, Osogbo, Osun State, Nigeria

Date of Web Publication13-Feb-2019

Correspondence Address:
Dr. Anthony A Thomas
Radiology Department, Ekiti State University Teaching Hospital, Ado Ekiti, Ekiti State
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njo.njo_8_18

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  Abstract 


Objectives: To noninvasively evaluate the lens thickness in type 2 diabetic patients using ultrasound, and to correlate age, disease duration, fasting blood sugar (FBS), and proteinuria with lens thickness. Materials and Methods: The study was performed in Obafemi Awolowo University Teaching Hospital Complex, Ile-Ife, a secondary and tertiary referral center. The study population consisted of 100 type 2 diabetic patients with age and sex-matched controls. Antero-posterior lens thickness, age, duration of diabetes, FBS, and proteinuria were assessed. Results: The lens was thicker in the diabetic group than in the controls (3.76 ± 0.45 versus 3.56 ± 0.34 mm; P = 0.001). There was a positive correlation between patient’s age and lens thickness (r = 0.533, P = 0.001 for the controls; and r = 0.335, P = 0.001 for diabetics). There were no significant correlations between lens thickness with duration of diabetes, proteinuria, or FBS. Conclusion: The lenses of type 2 diabetes were thicker than those of the control patients.

Keywords: Blood sugar level, diabetes mellitus, duration DM, lens thickness, proteinuria


How to cite this article:
Thomas AA, Ayoola OO, Ikem R, Onakpoya TH, Dada AS, Bello T. Sonographic evaluation of lens thickness in diabetes mellitus in a Nigerian tertiary hospital. Niger J Ophthalmol 2018;26:104-10

How to cite this URL:
Thomas AA, Ayoola OO, Ikem R, Onakpoya TH, Dada AS, Bello T. Sonographic evaluation of lens thickness in diabetes mellitus in a Nigerian tertiary hospital. Niger J Ophthalmol [serial online] 2018 [cited 2023 Feb 6];26:104-10. Available from: http://www.nigerianjournalofophthalmology.com/text.asp?2018/26/2/104/252186




  Introduction Top


Diabetes mellitus (DM) affects hundreds of millions of people worldwide, resulting in considerable morbidity and mortality. The global prevalence was estimated to be 2.8% in 2000 and is expected to reach 4.4% by 2030.[1] Its prevalence in Nigeria is 3.9%, whereas that of type 2 DM was reported to be 4.7% in Ibadan.[2]

DM is a systemic condition affecting numerous organs including the eyes. In developed countries, diabetic eye disease represents the leading cause of blindness in adults under 75 years.[3] Persons who have diabetes are at an increased risk for impairment due to diabetic retinopathy, glaucoma, and cataracts.[4],[5] In Nigeria, eye complications observed include background retinopathy, cataracts, advanced eye disease, legal blindness, and laser photocoagulation.[6] Overall, individuals with diabetes are 25 to 30 times more likely to progress to blindness than individuals without diabetes of similar age and gender.[5]

It is well known that the human lens continues to grow throughout life and that it becomes more convex and thicker with age.[7],[8] The thickness of the lens is about 4.0 mm in adult and increases slowly to 4.75 to 5.0 mm in extreme old age.[4] In patients with DM, the lens has been reported to become even thicker and more convex with age, compared with that of healthy patients.[9],[10],[11] In addition, a direct association has been suggested between lens swelling and cataract formation in diabetic patients.[5] After adjusting for the effect of age, the independent effect of the duration of DM per year on the lens thickness was more than 70%.[9],[10]

Cataract is a global health problem and is considered as a major cause of visual impairment in diabetic patients. The prevalence of cataract-related blindness is 2% in people over 50 years of age,[12] and it accounts for 43% of all causes of blindness in Nigeria.[13] The incidence and progression of cataracts are elevated in patients with DM.[4],[14],[15] As a result of increasing numbers of type 1 and type 2 diabetics worldwide, the incidence of diabetic cataracts steadily rises. Although cataract surgery, the most common surgical ophthalmic procedure worldwide, is an effective cure, patients with DM have higher complication rates.[15]

Techniques for the evaluation of lens biometry include ultrasonography, Scheimpflug photography, partial coherence interferometry, and magnetic resonance imaging.[16],[17],[18]

Interestingly, ultrasound ocular biometry has been considered to be more precise and reliable than optical measurement, and therefore, it has been considered to be a reference standard for the in vivo biometric measurement of the human lens.[19] Ocular lens sonography is a fast and reproducible noninvasive imaging modality which is easy to learn and perform, radiation-free, and can precisely measure the lens thickness. The equipment required is widely available, portable, and cost effective.

To the best of the authors’ knowledge, there are no available studies evaluating lens thickness in diabetic patients in Nigeria. In addition, this study will also evaluate the effect of proteinuria on the lens thickness in diabetic patients, which no other study has performed. Therefore, this prospective case–control study will aid in evaluating the influence of diabetes on the lens thickness in the South-Western Nigeria, using a fast, noninvasive, radiation-free, and convenient method.


  Materials and Methods Top


This study was conducted in the Radiology Department of Obafemi Awolowo University Teaching Hospital Complex, Ile-Ife, from February 2014 to May 2016. Preceding the study, ethical approval from the institution ethical research committee was taken. Institutional review board approval of the institution was also obtained, and it was ensured that the study adheres to the tenets of declaration of Helsinki. A written informed consent was taken from all the patients involved in the study and confidentiality was maintained.

A total number of 100 type 2 diabetic patients, between 18 and 80 years of age, were consecutively recruited into the study from the endocrinology clinic of the hospital. Equal number of age and sex-matched controls that satisfy the inclusion and exclusion criteria were also consecutively recruited into the study from the general outpatient unit of the institution. The type 2 diabetics were defined as those whose age at onset was 18 years or more; they were mainly on oral hypoglycemic drugs. Controls were those who had no history of diabetes or impaired glucose tolerance, and a nonfasting blood glucose of less than 6.1 mmol/l.

An ophthalmologic examination was conducted on all patients by a consultant ophthalmologist. Those with cataract, glaucoma, prior history of surgery or trauma, on-going eye infection, chronic use of steroids, and wearers of contact lenses were excluded from the study. Fasting blood sugar (FBS) was also taken for the diabetics and their levels of proteinuria were assessed using a test strip (megro-Medi-Test Combi 3A). Significant proteinuria was taken as proteinuria of greater than or equal to “++” (“++” is equivalent to 250 mg/l on a test strip).

Lens thickness was measured using a B mode Ultrasound (Mindray Real time ultrasound model DC-7 with 6.5–12 MHz linear transducer, Shenzhen Mindray Bio-Medical Electronics Co., Ltd, Nanshan, Shenzhen, P.R. China). With the patients in the supine position, they were asked to look straight ahead with eyes closed. The linear probe was placed transversely on the upper eyelid. Depth and gain was adjusted to achieve acceptable resolution. Antero-posterior lens thickness was measured by placing the cursors on the outer part of the anterior and posterior capsules of the lens. Measurement was taken at the mid-portion of the lens where its thickness was maximum, as shown in [Figure 1]. To ensure the accuracy of the measurements and to reduce intraobserver error, lens thickness in both eyes was obtained three consecutive times and the mean value for each eye was obtained.
Figure 1 Sonographic measurement of lens thickness

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All the lens thickness measurements were performed by the same radiologist (the researcher). To ensure good reliability of the test, t-retest reliability test was performed under the following condition. The same ultrasound machine was used throughout the period of the research. The correlation coefficient between separate measurements of the lens thickness was >0.7.

Data collected were analyzed using statistical software (SPSS) for windows (SPSS Inc., Chicago, Illinois, USA) version 19.0. Categorical and numerical variables were analyzed with Chi-square and Student’s t-test, respectively. Comparison between the lens thickness among the case and control was performed with independent sample t-tests. analysis of variance (ANOVA) statistic was used to assess the association between lens thickness and degree of proteinuria. The relationship between lens thickness and other variables such as age, duration of diabetes, and FBS was determined with Pearson correlation. A P value less than 0.05 was considered as statistically significant.

Preliminary analysis was conducted, which shows that both right and left lenses were perfectly correlated (r = 0.981, P < 0.000 and r = 0.998, P < 0.000 for diabetics and controls, respectively); therefore, only right lenses were analyzed in the study.


  Results Top


Two hundred (n = 200) eyes were examined comprising 100 eyes of 100 diabetics and 100 eyes of 100 control patients. [Table 1] lists the baseline characteristics of both the diabetic and control group. There was no significant difference in age or gender between the groups. The mean age of the controls and diabetes were 56.79 and 57.29, respectively (P = 0.102).
Table 1 Baseline characteristics of both the diabetic and control group

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Diabetics had thicker lenses than the control patients, with the diabetics having a mean lens thickness (MLT) of 3.76 ± 0.45 mm, whereas the control patients had a MLT of 3.56 ± 0.34 mm (P = 0.001).

[Figure 2] demonstrates the level of proteinuria in the diabetic patients. The majority (98%) had no significant proteinuria (++).
Figure 2 Bar chart showing frequency distribution of proteinuria

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The lens thickness showed an increasing trend with increasing age [[Figure 3] and [Figure 4]], which was found to be significant (r = 0.533, P = 0.001 and r = 0.335, P = 0.001 for diabetics and controls, respectively).
Figure 3 Plot of correlation between lens thickness and age for diabetics

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Figure 4 Plot of correlation between lens thickness and age for the controls

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No significant correlation was seen between duration of DM and lens thickness (r = 0.149, P = 0.138) or between lens thickness and FBS (r = 0.063, P = 0.536), and there was no significant association between lens thickness and degree of proteinuria (r = 0.061, P = 0.546).


  Discussion Top


The aim of the present study was to investigate the effect of DM on the human crystalline lens in patients with type 2 DM and to compare them with those of healthy control patients. The crystalline lens accounts for about 20 D of the eye’s total refractive power.[20] Any change in the morphology of the crystalline lens in patients with DM is associated with alteration in the refractive status.[21]

Diabetic patients had significantly thicker lenses than the controls (3.76 ± 0.45 mm versus 3.56 ± 0.34 mm) (P = 0.001). This is in agreement with other studies, including previous ultrasound literature, which have reported a thicker lens in diabetics than in nondiabetics. An hospital-based study in Pokhara, Nepal, by Shrestha and Kaini[21] reported that diabetic patients had significantly thicker lenses than controls (4.33 ± 0.38 versus 4.05 ± 0.55 mm, P < 0.001). The higher values they got in their results is likely due to the effect of racial and ethnic differences in lens thickness.[22] In addition, Shrestha and Kaini[21] study was performed on type 1 diabetic patients.[9]

Sparrow et al.[10] also found that the lenses of diabetics were thicker than those of the controls, but stated that the impact of type 1 DM on the lens was two to three times greater than that of type 2 DM.

Raitelaitienė et al.[23] reported a MLT of 3.86 ± 0.6 mm for type 1 DM compared with a healthy group of similar age with MLT of 3.58 ± 0.18 mm (P < 0.05), whereas the MLT for type 2 diabetic group was 4.35 ± 0.59 mm compared with nondiabetic group of similar age with MLT of 4.22 ± 0.44 mm (P > 0.05). The greater lens thickness recorded by Raitelaitienė et al. for type 2 DM may be due to the fact that they recruited younger patients (16–35 years) for type 1 DM, whereas the patients recruited for type 2 DM study were older (40–75 years).

Løgstrup et al.[24] also used ultrasonography to evaluate lens thickness in diabetics and reported a positive correlation between diabetes and lens thickness (r = 0.58, P = 0.018 and r = 0.69, P = 0.005 for right and left eyes, respectively).

Other studies including those of Wiemer et al.,[25] Suheimat et al.,[26] and Pope et al.[27] also agree on the profound impact of type 1 DM on the lens, but Wiemer et al. further stated that type 2 DM had very little effect on the different zones of the lens. As a result of this, they suggested that type 1 and type 2 DM have different underlying pathophysiologic mechanism.

The increase in the lens thickness in diabetic patients is due to over-hydration.[28] During the period of hyperglycemia, there is accumulation of glucose in the lens which gets converted to sorbitol which is further converted to fructose. These sugar alcohols tend to accumulate within the lens fibers, as they are poorly permeable through the lens membrane. This creates an osmotic gradient, resulting in the influx of water into the lens producing marked lenticular swelling.[29] It will also cause a change in solubility (precipitation) of lens proteins which can lead to metabolic cataract formation.[30]

Among the diabetes patients, there was no significant difference between right and left lens thicknesses. This was similar to what was reported in a study performed by Pierro et al.[11] which stated that there was no difference in lens thickness between the right and left eye.

In both studied groups (diabetics and controls), there was a positive correlation between patient’s age and lens thickness, though this correlation was stronger for the diabetic group than the controls. This result is similar to previous studies; Shrestha and Kaini[21] reported a significant correlation between lens thickness and age (P < 0.001, r = 0.651). Richdale et al.[31] in their study also reported an increase in lens thickness of 21 μm/year (r = 0.64, P < 0.01). Rosen et al.[32] also found a positive correlation between lens thickness and age (R2 = 0.48, P < 0.0001) mm/year. As both patients and the controls were of similar age groups, the thicker lens thickness in the diabetes could not have been as a result of aging alone, rather it showed that type 2 diabetes has significant impact on lens thickness.

This study showed no significant correlation between duration of DM and lens thickness. This result is similar to what was obtained by Sparrow et al.,[9],[10] which examined lens biometry by means of Scheimpflug photography, and digital imaging analysis in relation to early or late onset diabetes reported that lenticular biometry in type 1 diabetes showed abnormal lens growth with a powerful dependency on diabetic duration and patient age. In contrast, they found out that in type 2 diabetes, there was no such correlation between duration and lens biometry.

Shrestha and Kaini,[21] however, reported a significant correlation between lens thickness and duration of diabetes (P < 0.001, r = 0.468). Løgstrup et al.[24] also reported a positive correlation in their study for right (r = 0.58, P = 0.029) and left (r = 0.53, P = 0.053) eyes. This is likely due to the fact that their study were performed on type 1 DM.

No significant correlation was seen between lens thickness and FBS. This result was congruent with other reports which showed no significant impact of blood glucose level on the various lens parameters. Pierro et al.[11] correlated lens thickness with blood glucose control in diabetes but found no correlation between them. Shrestha and Kaini[21] also reported that FBS, postprandial blood sugar, and glycated hemoglobin had no significant influence on lenticular thickness.

There was no significant correlation between lens thickness and proteinuria. No comparative reference study was found for this result, but it showed that there was no significant relationship between lens thickness and presence or severity of diabetic nephropathy as measured by proteinuria. This may be due to the fact that majority of the patients recruited for this study did not have significant proteinuria.

In conclusion, the results of the present study showed that type 2 DM had a significant effect on the lens thickness. Aging was also an important parameter which is responsible for the increase in lens thickness. However, duration of diabetes, FBS, and diabetic nephropathy, as measured by proteinuria, had no significant influence on lenticular thickness.

It has been stated that once diabetic treatment begins, and blood glucose is under control, the lens resumes its normal thickness.[33] In addition, with improvement in blood sugar control, cataract may be reversible at the early stage in young diabetics.[34] Therefore, routine ocular ultrasound is essential to help early detection of lenticular thickness changes which may predispose to cataract formation and its attendant risk of visual impairment.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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