Biometry of the crystalline lens in early-onset diabetes

Modelling ocular ageing in adults with well-controlled type I diabetes

Purpose

To develop a paraxial eye model based on a previously collected cohort of adults with well-controlled type 1 diabetes mellitus (DM1) and a limited range of refractive errors.

Methods

The study used the previously published biometric data of 72 participants (Age: 41.5 ​± ​12.4 years) with DM1. Measurements included objective refraction, anterior and posterior corneal radii of curvatures, and internal distances. Moreover, phakometry was used to determine the lens radii of curvature and lens equivalent indices, from which the lens powers were calculated. A multivariate linear regression was performed for each biometric parameter with respect to current age (Age), the time since the onset of diabetes (Tdb), and current levels of glycated hemoglobin (HbA1c). The vitreous chamber depth was determined from other distances, and lens equivalent index was chosen to balance the models. These were compared with an existing model for non-diabetic eyes.

Results

Some dependent parameters were not affected by the independent variables (spherical equivalent, anterior corneal radius of curvature, central corneal thickness), some were affected by time since onset (the lens radii of curvatures, anterior chamber depth) and others were affected by both age and time since onset (posterior corneal radius of curvature, lens thickness, axial length). None of the dependent parameters were affected by current levels of HbA1c.

Conclusions

The proposed model accurately describes the age-related changes in the eyes of people with DM1. In this description the age of diabetes onset plays an important role, especially if the diabetes onset occurred during childhood.

Force of lifelong crystalline lens growth: chronic traumatic mechanical insult to the choroid

PURPOSE

To calculate the forces applied to the uvea and retina as a result of lifelong crystalline lens growth.

DESIGN

Retrospective study.

SETTING

MRI Research, Inc., Middleburg Heights, Ohio; Institute of Ophthalmology and Visual Science UMDNJ-New Jersey Medical School, Newark, New Jersey; USC Psychology University of Southern California, Los Angeles.

METHODS

Magnetic resonance images were acquired from 15 phakic/pseudophakic eye pairs in patients with cataract (ages 46 to 83 years). Choroidal lengths were measured. The forces required to produce differences between phakic/pseudophakic choroidal lengths were calculated.

RESULTS

The length of the choroid is greater in the phakic eye compared with the corresponding pseudophakic eye (n = 15), and this difference increases with age (P = .00006; power = 0.99). The corresponding choroidal strain also increases with age (P = .00003, power = 0.99) as do the forces required to produce such a change in choroidal length (P = .000008, power = 0.99).

CONCLUSIONS

The authors theorize that lifelong crystalline lens growth applies a chronic, traumatic, mechanical insult to the uvea and retina. This previously unknown, ever-increasing, force appears to stretch the choroidal tissue and may be an intraocular pressure-independent modifiable risk factor for retinal disease. Implications exist for understanding the pathophysiology of retinal diseases in the aging eye that are often comorbid with cataracts, for example, glaucoma, macular degeneration, and diabetic retinopathy.

Calculation of intraocular lens power and to determine the relationship between ocular biometry and severity of diabetic retinopathy in patients with type II diabetes mellitus

Purpose:

To calculate the intraocular lens power and to determine the relationship between ocular biometry and severity of diabetic retinopathy (DR) in patients with type II diabetes mellitus.

Methods:

The study group included 150 type II diabetic subjects with DR. The control group consisted of 150 type II diabetic subjects having no DR. Axial length (AL), corneal power, and anterior chamber depth were measured using LenStar. DR and diabetic macular edema were classified according to International DR Classification. Crystalline lens power was calculated using Barrett Universal II formula. AL to corneal radius ratio was calculated. Chi-square test was used for categorical variables.

Results:

In multivariate logistic models adjusting for age, sex, glycosylated hemoglobin, duration of diabetes, Mean age of patients in the study group was 62.45 ± 4.85 years, whereas in the control group, it was 63.37 ± 7.29 years. Of the eyes with DR, 117, 76, 69, and 38 had mild NPDR, moderate NPDR, severe NPDR, and PDR, respectively. The difference in the mean duration of diabetes mellitus and glycosylated hemoglobin in both study and control groups was found to be statistically significant. A progressive decrease in the mean AL and the anterior chamber depth was observed with increasing severity of DR, and difference was statistically significant. There was a progressive increase in intraocular lens power with increasing severity of DR, and difference was found to be statistically significant.

Conclusion:

In persons with diabetes mellitus, globe elongation plays quite an important role in protective effects against DR, with contribution from intraocular lens power and other refractive components.

Implementation and evaluation of a team approach to managing diabetes mellitus and diabetic retinopathy in the South African district health system

Background: Diabetic retinopathy (DR) screening programmes have been developed and implemented in different countries based on availability of resources. Most protocols developed for DR have been solely dedicated to DR screening without involving systemic screening.Aim: To implement and evaluate a DR screening model utilising a team of healthcare practitioners (HCPs) to manage diabetes mellitus (DM) to reduce DR progression.Setting: Primary healthcare clinics and Voortrekker hospital in Waterberg district of Limpopo province.Methods: A cross-sectional study was conducted, in which a total of 107 patients with DM from seven clinics consented to participation. A proposed DR screening model was implemented where patients with DM were screened for systemic complications at clinics and referred to Voortrekker district hospital for retinal photography. Questionnaire responses evaluated the success of the screening process and operational challenges.Results: From the study population, 32 (29.1%) were male and 75 (70.1%) were female. The mean age of patients was 63.7 years with a mean weight of 80.69 kg. The mean duration of DM was 9.26 years and the mean haemoglobin A1c (HbA1c) level was 9.7%. From the 47 patients who had visual acuity less than 6/9, 74.5% had refractive error. About 10% (9.4%) had DR or diabetic macular oedema (DME) and 38.3% had other lesions. Referral to an ophthalmologist was necessary in 36.5% of cases.Conclusion: The implementation of a team approach to co-manage DM and DR utilising the developed protocol improved the quality of care for patients with DM in the district health system.

The associations of lens power with age, axial length and type 2 diabetes mellitus in Chinese adults aged 50 and above

Background

To investigate the associations of lens power with age, axial length (AL), and Type 2 diabetes mellitus (DM) in Chinese adults aged 50 and above.

Methods

Random clustering sampling was used to identify adults aged 50 years and above in urban regions of Shanghai. The participants underwent a comprehensive ophthalmic examination including subjective refraction, autorefraction, and IOL-Master. The crystalline lens power was calculated using Bennett’s formula.

Results

A total of 4177 adults were included. A linear decrease in lens power was observed both with age and with AL, followed by a stop of lens power loss after the age of 70 or when AL ≥ 25 mm, respectively. Participants with Type 2 DM presented higher lens power (0.43 diopter (D), p < 0.001) and thicker lens thickness (0.06 mm, p < 0.001). In multivariate regression models, there was a positive correlation between lens power and Type 2 DM when age < 75 years (p < 0.001) or AL < 25 mm (p < 0.001) after adjusting for other factors, while no significant association was found in participants aged ≥ 75 years (p = 0.122) or with AL ≥ 25 mm (p = 0.172).

Conclusions

The lens power in adults aged 50 and above exhibited two stages with age and with AL. Type 2 DM caused an increase in lens power, which was not seen in participants aged ≥ 75 years or with AL ≥ 25 mm.

Safety and efficacy of a standardized intracameral combination of mydriatics and anesthetic for cataract surgery in type-2 diabetic patients

Background

Cataract surgery in diabetics is more technically challenging due to a number of factors including poor intraoperative pupil dilation and a higher risk of vision threatening complications. This study evaluates the safety and efficacy of an intracameral combination of 2 mydriatics and 1 anesthetic (ICMA, Mydrane) for cataract surgery in patients with well-controlled type-2 diabetes.

Methods

Post-hoc subgroup analysis of a phase 3 randomized study, comparing ICMA to a conventional topical regimen. Data were collected from 68 centers in Europe and Algeria. Only well-controlled type-2 diabetics, free of pre-proliferative retinopathy, were included. The results for non-diabetics are also reported. The primary efficacy variable was successful capsulorhexis without additional mydriatic treatment. Postoperative safety included adverse events, endothelial cell density and vision.

Results

Among 591 randomized patients, 57 (9.6%) had controlled type 2 diabetes [24 (42.1%) in the ICMA Group and 33 (57.9%) in the Topical Group; intention-to-treat (ITT) set]. Among diabetics, capsulorhexis was successfully performed without additional mydriatics in 24 (96.0%; modified-ITT set) patients in the ICMA Group and 26 (89.7%) in the Topical Group. These proportions were similar in non-diabetics. No diabetic patient [1 (0.5%) non-diabetics] in the ICMA Group had a significant decrease in pupil size (≥3 mm) intraoperatively compared to 4 (16.0%; modified-ITT set) diabetics [16 (7.3%) non-diabetics] in the Topical group. Ocular AE among diabetics occurred in 2 (8.0%; Safety set) patients in the ICMA Group and 5 (16.7%) in the Topical Group. Endothelial cell density at 1 month postoperatively was similar between groups in diabetics (P = 0.627) and non-diabetics (P = 0.368).

Conclusions

ICMA is effective and can be safely used in patients with well-controlled diabetes, with potential advantages compared to a topical regimen including reduced systemic risk, better corneal integrity and reduced risk of ocular complications.

Trial registration

The trial was registered at (reference # NCT02101359) on April 2, 2014.

Patient-specific determination of change in ocular spherical aberration to improve near and intermediate visual acuity of presbyopic eyes

The purpose was to determine the optimum negative spherical aberration induction required to improve near and intermediate visual acuity (VA) of presbyopic eyes. A total of 174 normal and diabetic (no retinopathy) presbyopic eyes (age ≥ 40 years) were measured with visual adaptive optics simulator (Voptica, Spain). First, baseline uncorrected VA and aberrations were measured. VA at 40 cm (near), 80 cm (intermediate) and distance was measured. Then, a negative spherical aberration (SA) was added to baseline ocular SA, and VA at all targets was reassessed after correction of distance refractive error. Clinically, baseline SA and root mean square of higher order aberrations were similar between the normal and diabetic presbyopic eyes. Baseline VA of the diabetic eyes at near and intermediate was better than the same of normal eyes (P = 0.001). After SA change, VA at near and intermediate of both normal and diabetic presbyopic eyes improved. However, fewer diabetic eyes needed higher SA change than normal eyes (P = 0.03). The corresponding trends with change in VA at near and intermediate were also similar between the normal and diabetic eyes. Patient-specific modulation of ocular SA to improve near and intermediate VA in a large cohort of eyes was successful in improving VA, sometimes even distance VA.

Refractive Changes Associated with Diabetes Mellitus

BACKGROUND AND METHODS

Diabetes mellitus is the most prevalent endocrinedisease in developed countries. In people with diabetes in addition to visionloss caused by diabetic retinopathy transient visual disturbances may occurfrequently caused by refractive changes. These changes in refraction are associated with variations in blood glucose levelsbut the underlying mechanism is still not fully understood. A systematic reviewwith a comprehensive literature search was performed in order to clarify the underlyingmechanisms regarding the connection of glycaemic control and refractive shift.

RESULTS

Some studies have shown that increasedblood sugar leads to a myopic shift whilst others demonstrated that this changeis in a hyperopic direction. Changes in visual acuity in patients with diabetescould be an indicator of inadequate metabolic control or even the first sign ofdiabetes mellitus.

CONCLUSION

This reviewgives a brief overview of current research regarding potential mechanisms ofglycemic control influence on refractive error. The aim isto emphasizethe importance ofunderstanding the relationship ofblood glucose concentration and refractive changes as one of thecommon but overlooked diabetic complications.

The lens growth process

The factors that regulate the size of organs to ensure that they fit within an organism are not well understood. A simple organ, the ocular lens serves as a useful model with which to tackle this problem. In many systems, considerable variance in the organ growth process is tolerable. This is almost certainly not the case in the lens, which in addition to fitting comfortably within the eyeball, must also be of the correct size and shape to focus light sharply onto the retina. Furthermore, the lens does not perform its optical function in isolation. Its growth, which continues throughout life, must therefore be coordinated with that of other tissues in the optical train. Here, we review the lens growth process in detail, from pioneering clinical investigations in the late nineteenth century to insights gleaned more recently in the course of cell and molecular studies. During embryonic development, the lens forms from an invagination of surface ectoderm. Consequently, the progenitor cell population is located at its surface and differentiated cells are confined to the interior. The interactions that regulate cell fate thus occur within the obligate ellipsoidal geometry of the lens. In this context, mathematical models are particularly appropriate tools with which to examine the growth process. In addition to identifying key growth determinants, such models constitute a framework for integrating cell biological and optical data, helping clarify the relationship between gene expression in the lens and image quality at the retinal plane.

The influence of simulated cataract on retinal vessel oximetry measurements

Purpose

To assess the impact of human crystalline lens opacification and yellowing, similar to that observed in patients with cataracts, on retinal vessel blood oxygen saturation measurements using custom manufactured soft contact lenses.

Methods

Ten healthy, non‐smoking individuals were enrolled for this study. All subjects underwent digital blood pressure measurements, assessment of non‐contact intra‐ocular pressure, pupil dilation and retinal vessel oximetry using dual‐wavelength photography (Oximetry Module, Imedos Systems). To simulate lens changes, three different contact lenses were inserted, one to simulate opacities followed by two more lenses to simulate different levels of lens yellowing (Cantor & Nissel).

Results

The measurements obtained showed an opposite change in arterial and venous oxygen saturation and optical density ratio across conditions, resulting in a statistically significant difference in arterial minus venous oxygen saturation value (p = 0.003). However, this difference was only significant for the ‘opacity’ condition but not for the ‘yellowing’ conditions.

Conclusion

Lenticular changes such as cataracts can impact on spectrophotometric analysis in particular dual‐wavelength retinal vessel oximetry. Hence, lenticular assessment and cataract grading should be considered when assessing elderly individuals and patient groups developing cataract earlier in life such as those suffering from diabetes mellitus.

Straylight, lens yellowing and aberrations of eyes in Type 1 diabetes

Straylight, lens yellowing and ocular aberrations were assessed in a group of people with type 1 diabetes and in an age matched control group. Most of the former had low levels of neuropathy. Relative to the control group, the type 1 diabetes group demonstrated greater straylight, greater lens yellowing, and differences in some higher-order aberration co-efficients without significant increase in root-mean-square higher-order aberrations. Differences between groups did not increase significantly with age. The results are similar to the findings for ocular biometry reported previously for this group of participants, and suggest that age-related changes in the optics of the eyes of people with well-controlled diabetes need not be accelerated.

Biometry of eyes in type 1 diabetes

This is a comprehensive study of a large range of biometric and optical parameters in people with type 1 diabetes. The parameters of 74 people with type 1 diabetes and an age matched control group were assessed. Most of the people with diabetes had low levels of neuropathy, retinopathy and nephropathy. Marginal or no significant differences were found between groups for corneal shape, corneal thickness, pupil size, and pupil decentrations. Relative to the control group, the diabetes group demonstrated smaller anterior chamber depths, more curved lenses, greater lens thickness and lower lens equivalent refractive index. While the optics of diabetic eyes make them appear as older eyes than those of people of the same age without diabetes, the differences did not increase significantly with age. Age-related changes in the optics of the eyes of people with diabetes need not be accelerated if the diabetes is well controlled.

Optical quality of the diabetic eye: a review

Diabetes mellitus is a metabolic disorder characterized by the presence of chronic hyperglycaemia. Several structural, morphological, and physiological changes in each of ocular component have been described in detail during the past decades. Due to these abnormalities, the diabetic patient undergoes a degradation of the retinal image by an increase of higher ocular aberrations and ocular scattering coming from mainly tear film, cornea, and crystalline lens. This review aims to provide an overview of current knowledge about the effects of diabetes mellitus in these optical phenomena and its consequence on the visual quality of the diabetic patient.

The ocular biometric differences of diabetic patients

PURPOSE

To investigate the differences in ocular biometric and keratometric characteristics in comparison with biometric measurements using the noncontact optical low coherence reflectometer (OLCR) (Lenstar LS 900, Haag-Streit) on diabetic patients.

METHODS

The eyes of 170 patients were included in this study, including 81 diabetic and 89 nondiabetic subjects. Optical biometric measurements of diabetic and nondiabetic patients (between the ages of 25 and 85 years) who applied to the ophthalmology clinic were noted from March to June 2013. Detailed ophthalmologic examinations were done for every subject. Biometric measurements were done using the noncontact OLCR device.

RESULTS

Patient age ranged from 29 to 83 years. Subgroup analyses were done in diabetic patients according to their Hba1C levels. The minimum Hba1C value was 5.3, maximum was 12.4, and mean was 7.56 ± 1.48. The median duration of diabetes was 5 years (25th-75th percentile 3.00-11.75). Diabetic patients were found to have thicker lens and shallower anterior chamber in both eyes compared to nondiabetic control subjects. There were no statistical differences between the groups according to central corneal thickness, axial length, or keratometric values in both eyes. However, lens thicknesses were found to be thicker and anterior chamber depth values were found to be shallower in the diabetic group in both eyes.

CONCLUSIONS

It may useful to determine eyeglasses prescription, refractive surgery calculation, lens selection, and previous cataract surgery according to biometric measurements after the regulation of blood glucose.

Gradients of refractive index in the crystalline lens and transient changes in refraction among patients with diabetes

Transient hyperopic refractive shifts occur on a timescale of weeks in some patients after initiation of therapy for hyperglycemia, and are usually followed by recovery to the original refraction. Possible lenticular origin of these changes is considered in terms of a paraxial gradient index model. Assuming that the lens thickness and curvatures remain unchanged, as observed in practice, it appears possible to account for initial hyperopic refractive shifts of up to a few diopters by reduction in refractive index near the lens center and alteration in the rate of change between center and surface, so that most of the index change occurs closer to the lens surface. Restoration of the original refraction depends on further change in the refractive index distribution with more gradual changes in refractive index from the lens center to its surface. Modeling limitations are discussed.

Measuring the refractive properties of the diabetic eye during blurred vision and hyperglycaemia using aberrometry and Scheimpflug imaging

PURPOSE

This study aimed to measure the refraction and geometry in the diabetic eye during the presence and absence of hyperglycaemia and blurred vision, using aberrometry and Scheimpflug imaging.

METHODS

Aberrometry and Scheimpflug imaging were used to examine ocular refraction and higher-order aberrations, as well as the shape of the cornea and the lens, in 25 patients with diabetes mellitus. From these parameters, the equivalent refractive index of the lens was calculated. Using paired t-tests, comparisons were made between a first series of measurements (Visit 1) taken in the presence of blurred vision and hyperglycaemia (> 10.0 micromol/l), and a second series of measurements (Visit 2) taken under normal conditions.

RESULTS

The mean difference in blood glucose between Visits 1 and 2 was 5.9 mmol/l (standard deviation [SD] 3.1) (p < 0.0001). Both small hyperopic and myopic shifts of equivalent refractive error (ERE) were found in nine patients (mean absolute difference ERE: 0.38 D [SD 0.12]; p = 0.02). Furthermore, higher-order aberrations (root mean square [RMS] error) were slightly increased in four patients (mean difference RMS error: 0.07 microm [SD 0.02]; p = 0.04) at Visit 1, compared to Visit 2. No significant changes were observed in the shape of the cornea or lens in any of the patients. No significant correlations were found between changes in blood glucose levels and the measured parameters in diabetic eyes.

CONCLUSIONS

The present study suggests that subjective symptoms of blurred vision during hyperglycaemia are not necessarily caused by changes in the refractive properties of the diabetic eye.

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.

Prevalence and associated factors of refractive errors among type 2 diabetics in Kinmen, Taiwan

PURPOSE

A community-based study was conducted to identify the extent of prevalence of refractive errors and their associated factors from among the Chinese type 2 diabetic population in Kinmen.

METHODS

A total of 547 patients (> 40 years old) with type 2 diabetes were examined with a complete eye screening tests including objective autorefraction. Spherical equivalent refractions of right eyes were reported. Data collected include age, gender, general medical information and serum biochemistry.

RESULTS

The mean refraction was -0.83 +/- 2.49 D. Prevalence rates were determined for myopia (44.1%), hyperopia (24.1%), high myopia (13.0%), and astigmatism (87.8%). Age is an important factor for all of the refractive errors. After adjustment for age, male gender and > 3 grade nuclear opacity appeared to be statistically significant factors for myopia. For hyperopia, > or =7% HbA1c was a significant associated factor, and for astigmatism, > or =200 mg/dl total cholesterol was the risk factor. Multiple linear regression showed that every increase of one year of age and one percent of HbA1c is associated with 0.04 D (p = 0.003) and 0.13D (p = 0.04) shift in hyperopia, respectively. Nuclear opacity with grade 3-4 and grade 5-6 will shift toward myopia of -0.72D (p = 0.02) and -5.34D (p < 0.0001) after adjustment for other risk factors.

CONCLUSIONS

This study provides epidemiological data on refractive errors in a Chinese diabetic population in Kinmen, Taiwan. The myopia prevalence is higher than the reported rates in the general population. This survey further confirmed that myopia is more prevalent than hyperopia in the diabetic population. Age and blood sugar shift the refraction toward hyperopia while nuclear cataract reverses it. Correction of refractive errors in the diabetics remained a challenge as not only spectacles but medical intervention is mandatory.

The influence of chronic diabetes mellitus on the thickness and the shape of the anterior and posterior surface of the cornea

PURPOSE

To determine the influence of diabetes mellitus (DM) type 1 and type 2 on the thickness, radius of curvature, power, and asphericity of the cornea.

METHODS

In this observational cross-sectional study, 102 patients with DM type 1, 101 patients with DM type 2, and 69 healthy subjects were measured by means of Scheimpflug imaging to determine central corneal thickness and the radius and asphericity of the anterior and posterior corneal surfaces. Corneal power was calculated from these parameters. Several systemic parameters (eg, duration of diabetes, glycated hemoglobin, blood glucose levels, and type of medication) and ocular comorbidity (eg, stage of retinopathy) were recorded.

RESULTS

Patients with DM type 1 and 2 had significantly smaller posterior corneal radii (P < 0.05) than those of healthy subjects (men: 6.49/6.48/6.64 mm; women: 6.36/6.30/6.49 mm). As a result, the optical power of the posterior corneal surface of the patients with diabetes differed from that of the healthy subjects (P < 0.01; men: DM, -6.2 D; healthy, -6.0 D; women: DM, -6.3 D; healthy, -6.2 D). However, corneal thickness, anterior radius and asphericity, and overall corneal power did not differ significantly between the groups. Furthermore, none of the systemic factors or ocular comorbidity had any influence on the corneal thickness or shape.

CONCLUSIONS

DM affects the posterior corneal radius, resulting in a small change in posterior corneal power. However, chronic DM does not seem to significantly influence the overall corneal power.

A multifocal electroretinogram model predicting the development of diabetic retinopathy

The prevalence of diabetes has been accelerating at an alarming rate in the last decade; some describe it as an epidemic. Diabetic eye complications are the leading cause of blindness in adults aged 25-74 in the United States. Early diagnosis and development of effective preventatives and treatments of diabetic retinopathy are essential to save sight. We describe efforts to establish functional indicators of retinal health and predictors of diabetic retinopathy. These indicators and predictors will be needed as markers of the efficacy of new therapies. Clinical trials aimed at either prevention or early treatments will rely heavily on the discovery of sensitive methods to identify patients and retinal locations at risk, as well as to evaluate treatment effects. We report on recent success in revealing local functional changes of the retina with the multifocal electroretinogram (mfERG). This objective measure allows the simultaneous recording of responses from over 100 small retinal patches across the central 45 degrees field. We describe the sensitivity of mfERG implicit time measurement for revealing functional alterations of the retina in diabetes, the local correspondence between functional (mfERG) and structural (vascular) abnormalities in eyes with early nonproliferative retinopathy, and longitudinal studies to formulate models to predict the retinal sites of future retinopathic signs. A multivariate model including mfERG implicit time delays and 'person' risk factors achieved 86% sensitivity and 84% specificity for prediction of new retinopathy development over one year at specific locations in eyes with some retinopathy at baseline. A preliminary test of the model yielded very positive results. This model appears to be the first to predict, quantitatively, the retinal locations of new nonproliferative diabetic retinopathy development over a one-year period. In a separate study, the predictive power of a model was assessed over one- and two-year follow-ups. This permitted successful prediction of new retinopathy development in eyes with and without retinopathy at baseline. Finally, we briefly describe our current research efforts to (a) locally predict future sight-threatening diabetic macular edema, (b) investigate local retinal function change in adolescent patients with diabetes, and (c) better understand the physiological bases of the mfERG delays. The ability to predict the retinal locations of future retinopathy based on mfERG implicit time provides clinicians a powerful tool to screen, follow-up, and even consider early prophylactic treatment of the retinal tissue in diabetic patients. It also aids identification of 'at risk' populations for clinical trials of candidate therapies, which may greatly reduce their cost by decreasing the size of the needed sample and the duration of the trial.

Effect of glycemic control on refractive changes in diabetic patients with hyperglycemia

PURPOSE

To investigate the effect of intensive glycemic control on hyperglycemia- induced changes in refraction, corneal topography, lenticular and corneal thickness in diabetic patients.

METHODS

Eighteen diabetic patients with plasma glucose >300 mg/dl were enrolled in the study consecutively. Autorefraction, C-Scan corneal topography, Javal keratometry, corneal pachymetry and ultrasonic biometric measurements were carried out at presentation and after metabolic control of blood sugar (plasma glucose profile <200 mg/dl). One eye of each patient was selected randomly for statistical analysis.

RESULTS

Mean plasma glucose levels were 356.00 mg/dl before and 133.78 mg/dl after treatment. The median values of the autorefractometric measurements were - 0.125 D on admission and + 0.375 D at the second examination. The difference in the refraction was statistically significant (P = 0.022). Nine of 18 patients became hyperopic, 2 became myopic and 7 showed no change after treatment. There was a significant change in the corneal topographic keratometric measurements at the flattest corneal meridian after treatment (P = 0.037). After treatment no statistically significant changes were observed in the pachymetric corneal thickness, anterior chamber depth, biometric dioptric lens calculations and Javal keratometric data.

CONCLUSIONS

Hyperglycemia is the major cause of the transient refractive changes in diabetic patients. Following intensive medical treatment, a considerable number of patients tend to become more hyperopic compared with the hyperglycemic state. During the treatment period, changes in the corneal topographic parameters might be a potential source of error for keratorefractive and cataract surgery.

Effects of hyperglycaemia on ocular development in rabbit: refraction and biometric changes

AIM

To determine the effect of acute and chronic hyperglycaemia on the refraction and development of the rabbit eye.

METHODS

Ocular dimensions of five alloxan-induced hyperglycaemic and six control rabbits were measured over 9 weeks using A scan biometry. Refraction was measured using retinoscopy. The animals were 10 weeks of age at the start of the experiment.

RESULTS

The acute onset of hyperglycaemia was associated with a fast and stable 2 D hyperopic shift in refraction. Lens thickness increased during the first 2 weeks of hyperglycaemia, returned to near normal thickness after 3-5 weeks of hyperglycaemia and then decreased in thickness in the last 4 weeks of the study. The hyperopic refraction remained unchanged during changes in lens thickness. Nine weeks of hyperglycaemia was associated with a 25% reduction in the growth of both the globe and the lens and a 17% decrease in body mass compared with the controls.

CONCLUSION

The hyperopic refraction change of acute hyperglycaemia is likely to be because of a change in the refractive index of the cortical fibres of the lens and is the probable source of the fluctuating refraction seen in diabetic patients. Chronic hyperglycaemia reduced the axial development of the eye and is the probable source of the chronic hyperopic refraction seen in children with Type I diabetes.

Screening for sight-threatening diabetic retinopathy: comparison of fundus photography with automated color contrast threshold test

PURPOSE

To compare tritan contrast threshold (TCT) with fundus photography in screening for sight-threatening diabetic retinopathy (STDR), before significant visual loss.

DESIGN

Prospective, comparative study.

METHODS

A total of 510 consenting diabetic patients attending a hospital-based photographic screening clinic were recruited over a 2-year period. Exclusion criteria included visual acuity of worse than 6/9, previous photocoagulation, and a history of previous eye disease known to affect color vision. The automated TCT test was performed using a computerized cathode ray tube-based technique. Retinal photography was performed using a Polaroid mydriatic fundus camera with a 45 degrees field. Grading of diabetic retinopathy was carried out by an ophthalmologist using slit-lamp biomicroscopy and a 78-diopters lens. Assessments of sensitivity, specificity, and predictive values for both fundus photography and the TCT test were made.

RESULTS

Both the fundus photography and TCT test correlated significantly with the presence of STDR (P <.0001, chi(2) test). The TCT test yielded a sensitivity of 94% (95% confidence interval [CI], 73%- 100%) and a specificity of 95% (95% CI, 92%- 96%) for detection of STDR compared with a sensitivity of 88% (95% CI, 66%-97%) and a specificity of 95% (95% CI, 93%-97%) with fundus photography. Combined modality improved overall screening performance.

CONCLUSION

The TCT assessment is an effective and clinically viable technique, in comparison with fundus photography, to screen for STDR among a diabetic population. Additionally, our results also showed that combining the TCT test with fundus photography greatly increases the performance of screening for STDR.

Assessment of colour vision as a screening test for sight threatening diabetic retinopathy before loss of vision

AIM

To assess the effects of sight threatening diabetic retinopathy (STDR) on colour vision and to evaluate automated tritan contrast threshold (TCT) testing for STDR screening before significant visual loss.

METHOD

Patients were recruited from a hospital based photographic screening clinic. All subjects underwent best corrected Snellen visual acuity (BCVA) and those with 20/30 vision or worse were excluded. Automated TCT was performed with a computer controlled, cathode ray tube based technique. The system produced a series of sinusoidal, standardised equiluminant chromatic gratings along a tritan confusion axis. Grading of diabetic retinopathy was made by one of the team of experienced ophthalmic registrars (SpR) using slit lamp biomicroscopy and a 78D lens; HbA(1c) and urine albumin were also tested.

RESULTS

Patients with STDR had significantly worse TCT despite normal BCVA (p<0.0001). TCT yielded a sensitivity of 100% for detecting diabetic maculopathy and 94% for STDR with a specificity of 95%. Logistic regression analyses showed that TCT (p<0.001) and HbA(1c) (p<0.05) correlated significantly with the presence of STDR but duration of diabetes, urine albumin counts, and BCVA failed to show any significant correlation. No associations between TCT and duration of disease, TCT and HbA(1c), and TCT and urine albumin counts were found.

CONCLUSION

Tritan colour vision deficiency was observed in patients with STDR despite their normal BCVA. These results indicate that automated TCT assessment is an effective and clinically viable technique for detecting STDR, particularly diabetic maculopathy, before visual loss.

Analysis of nuclear fiber cell compaction in transparent and cataractous diabetic human lenses by scanning electron microscopy

BACKGROUND

Compaction of human ocular lens fiber cells as a function of both aging and cataractogenesis has been demonstrated previously using scanning electron microscopy. The purpose of this investigation is to quantify morphological differences in the inner nuclear regions of cataractous and non-cataractous human lenses from individuals with diabetes. The hypothesis is that, even in the presence of the osmotic stress caused by diabetes, compaction rather than swelling occurs in the nucleus of diabetic lenses.

METHODS

Transparent and nuclear cataractous lenses from diabetic patients were examined by scanning electron microscopy (SEM). Measurements of the fetal nuclear (FN) elliptical angles (anterior and posterior), embryonic nuclear (EN) anterior-posterior (A-P) axial thickness, and the number of EN fiber cell membrane folds over 20 microns were compared.

RESULTS

Diabetic lenses with nuclear cataract exhibited smaller FN elliptical angles, smaller EN axial thicknesses, and larger numbers of EN compaction folds than their non-cataractous diabetic counterparts.

CONCLUSION

As in non-diabetic lenses, the inner nuclei of cataractous lenses from diabetics were significantly more compacted than those of non-cataractous diabetics. Little difference between diabetic and non-diabetic compaction levels was found, suggesting that diabetes does not affect the degree of compaction. However, consistent with previous proposals, diabetes does appear to accelerate the formation of cataracts that are similar to age-related nuclear cataracts in non-diabetics. We conclude that as scattering increases in the diabetic lens with cataract formation, fiber cell compaction is significant.

The shape of the aging human lens: curvature, equivalent refractive index and the lens paradox

Scheimpflug slit images of the crystalline lens are distorted due to the refracting properties of the cornea and because they are obliquely viewed. We measured the aspheric curvature of the lens of 102 subjects ranging in age between 16 and 65 years and applied correction for these distortions. The procedure was validated by measuring an artificial eye and pseudophakic patients with intraocular lenses of known dimensions. Compared to previous studies using Scheimpflug photography, the decrease of the radius of the anterior lens surface with age was smaller, and the absolute value for the radius of the anterior and posterior lens surface was significantly smaller. A slight decrease of the posterior lens radius with age could be demonstrated. Generally, front and back surfaces were hyperbolic. Axial length was measured of 42 subjects enabling calculation of the equivalent refractive index of the lens, which showed a small, but highly significant decrease with age. These new findings explain the lens paradox and may serve as a basis for modelling the refractive properties of the lens.

Cataract surgery and pupil size in patients with diabetes mellitus

PURPOSE

Constriction of the pupil during phacoemulsification and intraocular lens (IOL) implantation in patients with diabetes mellitus was studied.

METHODS

Before surgery a combination of 0.75% cyclopentolate and 2.5% phenylephrine was applied topically to the eyes of 32 patients with diabetes mellitus and 25 age-matched controls. Epinephrine was mixed with buffered saline solution and used during the surgery. The surgical procedure included capsulorhexis, phacoemulsification in the posterior chamber and implantation into the capsular bag of a heparine surface-modified poly(methyl metacrylate) IOL with an optic diameter of 5.0 mm. The durations of phacoemulsification and the whole surgical procedure were recorded. Measurements of the horizontal pupillary diameter were taken before surgery, after phacoemulsification and at the end of the surgery.

RESULTS

There was no significant difference in pupil size between controls and the diabetic group before the operation. Surgically induced miosis after phacoemulsification and at the end of operation were significantly more pronounced in the diabetic group than in controls (p < 0.05) (p < 0.05). Phacoemulsification and the entire surgical procedure took significantly longer time when performed in the diabetic eyes (p < 0.05) (p < 0.05).

CONCLUSION

We conclude from these data that constriction of the pupil during cataract surgery is more pronounced in diabetic eyes as compared to controls.

Long-term influence of insulin dependent diabetes mellitus on refraction and its components: a population based twin study

AIM

To study whether refraction of the eye, or some of its components is influenced by duration of insulin dependent diabetes mellitus.

METHODS

From the young cohort of the population based Danish Twin Register, containing 20,888 twin pairs born between 1953 and 1982, all twin pairs having one or both partners affected with IDDM were searched. Autorefraction, autokeratometry, and ultrasonic biometric measurements were carried out on 45 twin pairs: 16 monozygotic (MZ) twin pairs, 14 dizygotic twin pairs of same sex (DZss), and 15 dizygotic twin pairs of opposite sex (DZos). To obtain an estimate of the influence of duration of diabetes, the intrapair differences in duration of diabetes were correlated with intrapair differences in refraction and each of its components.

RESULTS

Refraction was statistically significantly negatively correlated with duration of diabetes in the DZss group, and axial length correspondingly positively correlated. Surprisingly, refraction and axial length in the MZ group, adjusted for confounding factors, were correlated with diabetes duration in the opposite direction than in the DZss group, although not reaching statistical significance. Lens thickness was statistically significantly positively correlated with duration of diabetes in both MZ and DZ twins. Anterior chamber depth was negatively correlated with duration of diabetes in all the zygosity groups.

CONCLUSIONS

Studies of relations between refraction and duration of diabetes show diverging results. In the MZ group, a tendency to reduced axial length and corresponding hyperopia with increasing duration of diabetes was found. However, in the DZ group of same sex the opposite tendency was found. Increasing lens thickness and decreasing anterior chamber depth with increasing duration of diabetes have been confirmed in this study.

Correlation of lens thickness with blood glucose control in diabetes mellitus

The aim of this study was to verify if lens thickness in insulin-dependent diabetic patients is greater than in non-diabetics, and to establish which parameters affect the thickness of the lens age, diabetes duration, glycaemic control, insulin dose. Ultrasound biometry and blood glucose measurements were taken in 87 patients three times a day: fasting 2 and 4 h after lunch. The patient sample was divided into three groups: 30 with no retinopathy, 30 presented background retinopathy and 27 with proliferative retinopathy; 30 normal subjects with a similar age to the diabetic group, comprised the control group. No correlation was found between biometric values and blood glucose in the three groups (p < 0.05). A significant difference in lens thickness was found in the four groups, even after adjusting for age (p < 0.05). Significant differences in lens thickness were seen between proliferative retinopathy and the other groups, after adjusting for age and duration of diabetes (p < 0.05); lens thickness was shown to correlate with diabetes duration (p < 0.05).

Lens thickness and insulin dependent diabetes mellitus: a population based twin study

AIM

To investigate the relation between lens thickness and duration of insulin dependent diabetes mellitus (IDDM).

METHODS

From the new population based Danish twin register, containing 20,888 twin pairs born between 1953 and 1982 (inclusive), all twin pairs having one or both partners affected with IDDM were searched. Among the 45 twin pairs available for clinical eye examination there were 15 monozygotic pairs, 14 dizygotic pairs of same sex, and 16 dizygotic pairs of opposite sex. Lens thickness was measured by ultrasonography. Using a twin control design, the relation between lens thickness and duration of IDDM was assessed by estimating the correlation between the intrapair difference in lens thickness and the intrapair difference in diabetes duration.

RESULTS

In monozygotic twin pairs a statistically highly significant correlation between duration of diabetes and lens thickness was found (right eye: r = 0.88, p < 0.0001; left eye: r = 0.90, p < 0.0001). In dizygotic twin pairs of the same sex the correlations were r = 0.58 (p = 0.029) and r = 0.53 (p = 0.053) for right eye and left eye, respectively. For dizygotic twin pairs of opposite sex the correlations were r = 0.58 (p = 0.018) and r = 0.69 (p = 0.005) for right eye and left eye, respectively. The slope in regression analysis were similar for monozygotic twin pairs (0.025, common for both eyes) and dizygotic twin pairs grouped (0.024, common for both eyes).

CONCLUSIONS

There is a statistically significant positive correlation between duration of IDDM and lens thickness, as assessed by the twin control method. The higher correlation in monozygotic twins compared with dizygotic twins suggests that genetic factors play an additional role in the determination of lens thickness. The similar slopes in regression analysis indicate that the effect of diabetes duration on lens thickness is independent of zygosity.

Risk factors associated with contrast sensitivity loss in diabetic patients

BACKGROUND

Psychophysical tests in patients with diabetes mellitus reveal deficits of central vision before the development of overt retinopathy. We evaluated the contrast sensitivity thresholds in 30 patients with type II diabetes mellitus and without retinopathy, taking into account the crystalline lens density. Risk factors for contrast sensitivity deficits were investigated.

METHODS

Contrast sensitivity was compared in 30 aretinopathic diabetic patients and age-matched controls. Contrast thresholds were determined for stationary gratings at three spatial frequencies (6, 15, and 27 cycles/deg) and for mesopic (5 cd/m2) and low photopic (85 cd/m2) vision. Lens density was measured using a IntraOptics opacity lensmeter.

RESULTS

Significant contrast sensitivity losses at all three spatial frequencies were observed in low photopic and mesopic vision in diabetic patients. The optical density of the lens in the diabetic group did not differ from that in the controls. Contrast sensitivity deficits were positively correlated with patient's age, systolic blood pressure and nephropathy at all three spatial frequencies. No relationship between cardiovascular autonomic neuropathy and contrast sensitivity defects was observed.

CONCLUSIONS

These data suggest that contrast sensitivity deficits in diabetic patients without retinopathy are not solely explained by a diabetes-induced increases in lens optical density. Abnormalities of the retina or its neural connections occurring before the onset of clinically detectable retinopathy may be involved. Risk factors for these deficits are advanced age, high systolic blood pressure, and nephropathy.

Massive proliferation of lens epithelial remnants after Nd-YAG laser capsulotomy

Eight eyes exhibited massive proliferation of lens epithelial remnants following Nd-YAG posterior capsulotomy. All eyes had pre-existing retinal pathology. Six had undergone vitrectomy (four for proliferative diabetic retinopathy) before extracapsular cataract extraction with posterior chamber intraocular lens implantation. The other two eyes had familial exudative vitreoretinopathy or retinopathy of prematurity, respectively. Five eyes required removal of the lens proliferations via a pars plana approach. High levels of growth factors in the posterior segment associated with proliferative disorders of the retina may play a role in lens cell proliferation.

Effect of diabetes associated increases in lens optical density on colour discrimination in insulin dependent diabetes

Optical density (OD) of the crystalline lens has been shown in non-diabetics to increase linearly with age over the first five decades and at an increased rate thereafter; in insulin dependent diabetic (IDDM) patients, lens OD increases with age and with duration of diabetes at a rate similar to that in non-diabetics over the age of 60 years. Recently, it has been established that colour discrimination is abnormal in a majority of young patients with uncomplicated IDDM and angiographically normal retinas. Colour discrimination loss was attributed to functional abnormalities in the retina or neural pathways; yet the possibility exists that increases in lens OD may account for part or all of the colour discrimination loss in IDDM. In the present study, colour discrimination was compared in aretinopathic IDDM patients and age-matched controls, and then in a group of aretinopathic IDDM patients individually matched to controls with respect to lens OD. Colour discrimination was significantly worse in diabetic patients than in age-matched controls, and was significantly worse when diabetic patients were compared with controls matched for OD. The magnitude of the difference in 100 hue error score between diabetic patients and OD matched controls was, however, considerably less than the difference between diabetic patients and age-matched controls. These data suggest that colour discrimination loss in aretinopathic IDDM patients cannot be explained solely on the basis of diabetes induced increases in lens OD, but must involve abnormalities of the retina or its neural connections.

Estimation of the thickness of the crystalline lens from on-axis and off-axis Scheimpflug photographs

Measurement of human lens biometry directly from Scheimpflug images of the anterior ocular segment may be impossible when pupil size precludes an adequate Scheimpflug view of the posterior lens surface. The authors describe a simple and accurate geometric method of overcoming this problem by estimating the true lens thickness from pairs of on-axis and off-axis Scheimpflug images. The method is validated and the variability of the estimate is quantified. This new method has utility in the study of lens biometry in subjects with large lenses whose pupils cannot be adequately dilated.

The lens in diabetes

This paper reviews the changes which occur in the human lens in diabetes. They include refractive changes and cataract and age-related increases in thickness, curvatures, light scattering, autofluorescence and yellowing. The incidence of cataract is greatly increased over the age of 50 years, slightly more so in women, compared with non-diabetics. Experimental models of sugar cataract provide some evidence for the mechanism of the uncommon, but morphologically distinct, juvenile form of human diabetic cataract, where an osmotic mechanism due to sugar alcohol accumulation has been thoroughly studied in diabetic or galactose-fed rats. The discrepancy between the ready accumulation of sugar alcohol in the lens in model systems and the very slow kinetics of aldose reductase (AR) has not been satisfactorily explained and suggests that the mechanism of polyol formation is not yet fully understood in mammalian systems. The activity of AR in the human lens lies mainly in the epithelium and there appears to be a marginal expectation that sufficient sorbitol accumulates in cortical lens fibres to explain the lens swelling and cataract on an osmotic basis. This is even more so in the cataracts of adult diabetics, which resemble those of age-related non-diabetic cataracts in appearance. The very low levels of sorbitol in adult diabetic lenses make an osmotic mechanism for the increased risk of cataract even less likely. Other mechanisms, including glycation and oxidative stress, are discussed. The occurrence of cataract is a predictor for increased mortality in the diabetic.

Biometry of the crystalline lens in late onset diabetes: the importance of diabetic type

Lenticular and anterior chamber biometry were studied in non-cataractous eyes by means of Scheimpflug photography and digital image analysis. The study population consisted of 91 late onset diabetic subjects and 115 non-diabetic controls. Anteroposterior axial lens thickness, cortical thickness, nuclear thickness, anterior clear zone thickness, anterior chamber depth, and anterior and posterior lenticular curvatures were assessed. Age played an important role in determining lens biometry in all subjects, and small but significant differences were found between late onset diabetics and non-diabetics. In the late onset diabetic subgroup, apart from age, diabetic retinopathy was the only significant parameter found which determined lens biometry. These biometric findings in late onset diabetes are in marked contrast to the large overall effect of diabetes and the powerful effect of diabetic duration which we previously reported in early onset diabetes. Further analysis of the data from our previous study has been provided, which clearly demonstrates differences between the impact of early and late onset diabetes on the biometry of the anterior ocular segment.

Biometry and auto-fluorescence of the anterior ocular segment in diabetics with and without autonomic neuropathy: a case control study

The biometry and auto-fluorescence of the anterior ocular segment were examined in a case control study of two populations of diabetics. Cases, with diabetic autonomic neuropathy, and controls without neuropathy (forty in each group) were selected from a community based diabetic population and matched individually for age, sex, and type of diabetes. Scheimpflug and auto-fluorescence anterior segment photography were performed and analysed by digital image analysis in a masked fashion. There were differences between the groups in axial lens thickness, front radius of curvature of the lens, anterior chamber depth and lenticular auto-fluorescence. These findings are discussed in the context of the known association between autonomic neuropathy and narrow angle glaucoma, and possible common mechanisms of tissue damage in diabetes.