Diabetes-Induced Retinal Ischemia

Diabetes is a disease in epidemic proportion in the United States.  In 2012, it is estimated that approximately 26 million people in the United States are diabetic and another 79 million are pre-diabetic.  Dramatic increases in disease prevalence are expected.  In addition to the significant array of systemic complications associated with diabetes, ocular complications are common.  Diabetic changes in the retina occur 60% of the time in diabetics presenting with more than a 10 year history of the disease.  This increases to 80% at 15 years with 25% developing proliferative changes at this point.  

The role of the primary eye care provider cannot be over-emphasized in the management of the diabetic patient.  As the ocular findings are simply a manifestation of what is happening everywhere in the vascular system, primary care physicians and endocrinologists managing the systemic disease are always very interested in the patient’s ocular health.  Timely communication regarding the ocular findings is good medicine.

Clinical Presentation

• 54-year-old black woman presents for her scheduled diabetic retinopathy surveillance examination
• She reports a subjective decrease in vision since her last visit six months earlier 

Conclusion

Diabetics with mild to moderate retinal pathology can present with a wide array of symptoms from none at all to moderate vision loss.  While diabetes can cause changes in refractive error, this is usually reserved only for patients with wildly uncontrolled blood sugar.  Optometrists and ophthalmologists should be aware of all the ocular complications that can be associated with diabetes.

History of Present Illness

• Associated signs and Symptoms: reading vision worse
• Location: night vision is overall worse
• Duration: at least the past three months
• Quality: vision is worse in dimmer light
• Context: decreased vision is more noticeable when driving 
• Severity: mild
• Timing: getting progressively worse 
• Modifiers: none

Review of Systems

The patient reported diabetes diagnosed 22 years prior, hypertension and depression. She was taking Mavik (tranolalin) for her hypertension but was controlling her diabetes with diet and exercise.  She did state she took diabetic medication in the past but none in the past five years.  She did not know her last HbA1c but monitors her blood sugar every week or so.  She reported it was “controlled” with most readings around 250mg/dL.  The patient had a normal body habitus.  All other medical history was unremarkable.

Past, Family and Social History

• Non-contributory

Best Corrected Distance Visual Acuity

• 20/30 in the right eye
• 20/25 in the left eye

Normal Examination Findings

• Mental status
• General medical observation 
• External examination
• Adnexal examination
• External ocular examination with biomicroscopy

RAPDx Expanded Pupil Diagnostics 

Pupillary reactivity testing using a RAPDx automated pupillographer was abnormal.

• A relative afferent pupillary defect was detected in the left eye
• Index-of-defect number was 0.38 for the amplitude of the pupillary response in the left eye
• Number is calculated by determining the log difference in amplitude between the pupillary responses
• Numbers above 0.30 are considered abnormal
• Higher the number, the more likely pathology is present in the neural light reflex pathway

Intraocular Pressure Measurement

• 14mm Hg in the right eye
• 15mm Hg in the left eye

Ophthalmoscopy

• Long-standing diabetes with ophthalmic manifestations
• Postoperative – laser surgery for diabetic macular edema in both eyes
• Cotton-wool spot on the superior vascular arcade in the left eye

Clinical Diagnosis

Clinical diagnoses are determined based on the knowledge obtained from the patient’s medical history and from the results of the eye examination alone, without the benefit of diagnostic tests or procedures. 

The patient’s clinical diagnoses is mild nonproliferative diabetic retinopathy based on the following clinical findings:

• Appearance of the retina
• Patient’s medical and ocular history

Treatment Plan

To gather the clinical information required to manage the diabetic changes, a diagnostic and treatment program is initiated.

• Determination of different types of diagnoses
• Selection of one or more treatment options

Several macular diseases have clinical signs that mimic the appearance of diabetic retinopathy.  Optometrists and ophthalmologists should keep in mind that retinal vascular presentations can be the result of systemic co-morbidities, especially diabetic and hypertensive complications.

Hypertensive Retinopathy Common finding is changes in the caliber of the retinal vessels Lipid and exudative deposits are similar in appearance to those seen in early non-proliferative diabetic retinopathy Cotton-wool spots are seen in both hypertensive retinopathy and diabetic retinopathy Exudates are uncommon except in advanced disease presentation

Most patients with diabetic retinopathy experience mild to no symptoms unless macular edema is present.  Even then, mild macular edema can present with normal Snellen acuity.  Ring like exudation, often referred to as circinate retinopathy, is often associated with areas of capillary non-perfusion and indicative of more advanced disease progression.  Macular edema can occur at any stage of the disease, even in the absence of retinal hemorrhages and exudates.

The risk of progression to more advanced disease (pre-proliferative or proliferative) is variable but most influenced by the severity and control of the systemic diabetes and the duration of the diabetes.  Conversion to proliferative disease and the appearance of macular edema are the two most significant concerns in monitoring the diabetic patient.

Ordering Diagnostic Tests

The following diagnostic tests can help determine the severity of the diabetic retinal changes and help to monitor progression:

• Subjective refraction
• Fundus photography  
• Retinal laser scan
• Threshold visual field
• Color vision examination
• Electroretinography

The decision to order and perform additional testing is totally based on the concept of medical necessity which can only be determined by the examining optometrist or ophthalmologist.

Visual Field Examnination

• Automated threshold perimeters measure the visual field by plotting the threshold luminance value of the patient in various locations in the visual field
• The luminance of the light stimulus is represented by non-specific units of measurement called decibels (dB)
• Glaucoma produces several changes in the visual field, and one of these changes occurs as a widespread, non-descript loss of retinal sensitivity
• In Tranquair’s “Hill of Vision” concept, loss of retinal sensitivity represents a reduction in the height of the hill
• The diffuse loss of retinal sensitivity should be considered highly diagnostic of glaucoma when it is asymmetric and correlates with asymmetric changes in intraocular pressure or disc appearance
• In most cases, the loss of sensitivity occurs in characteristic patterns and locations (e.g., nasal step, arcuate scotoma, paracentral scotoma) that often correlate with changes in the optic nerve and/or retinal nerve fiber layer.

Retinal Laser Scan — Nerve Fiber Layer

• Measuring retinal thickness and detailed evaluation of the retinal anatomy is a means to evaluate overall retinal health
• The procedure can be accomplished with the Cirrus OCT manufactured by Zeiss Meditec

		Right Eye Diffuse fallout of RNFL temporally Cup-to-disc ratio = .55/.40 Shallow optic cup depth Abnormal TSNIT curve profile Left Eye Diffuse fallout of RNFL temporally Cup-to-disc ratio = .55/.50 Shallow optic cup depth Abnormal TSNIT curve profile
Retinal Laser Scan — Macula Right Eye Shallowing of the foveal depression Decreased retinal thickness at the macula OCT scan is consistent with diabetes-induced retinal ischemia

Electroretinography

• Electroretinography tesing evaluates the integrity of the retina
• The procedure can be accomplished using the NOVA-ERG Testing Device manufactured by DIOPSYS
• Specialized pattern electroretinogram (pERG) test uses a contrast-reversing pattern for the stimulus to produce information about ganglion cell function

Right Eye Normal waveform shape: Three equally-spaced wave peaks in a sinusoidal-shaped waveform Abnormal signal strength: Magnitude is less than 1.2 microvolts Normal Magnitude D value: Magnitude D is at least 40% of signal strength value Left Eye Abnormal waveform shape: Three equally-spaced peaks are not present Abnormal signal strength: Magnitude is less than 1.2 microvolts Abnormal Magnitude D value: Magnitude D is less than 40% of the signal strength value Both Eyes Clinically significant asymmetry ERG test results correlate with OCT test results

Color Vision Examination

An extended color vision examination measures the combined function of the retina, the optic nerve and the intracranial visual pathway and is used clinically to detect or monitor color vision loss due to disease at any of these locations. Extended color vision testing divides people into two groups.  

• The first group consists of people with normal color vision and slight color deficiency
• The second group consists of people with moderate or severe color deficiency

One of the most common tests performed in clinical practice is the Farnsworth D15.  When performed on Konan Medical’s ColorDx software , the test is presented as fifteen colored bars and one fixed bar on an Android tablet. The hue of each bar has been chosen so that the adjacent bars have approximately equal hue differences.  When the bars are arranged in order, they form a hue circle.  As a result, errors in hue discrimination can be made across the hue circle.

Patients with normal color vision usually make no error but may make one or two minor transposition errors, as do those with mild color vision deficiency.  Patients with more advanced color deficiency make some or more of the following errors:

• They place colors that lie on the opposite side of the hue circle next to colors that lie on their confusion locus (e.g., diametrical errors)
• Two or more diametrical crossing errors indicates a “failed” test
• If diametrical crossing errors are made, the orientation of the crossing produces a diagnosis of protan, deutan, or tritan color vision deficiency

All of the diagnostic test results confirmed the initial diagnosis of moderate, non-proliferative diabetic retinopathy with clinically significant macular edema.

According to Current Procedural Terminology, when eye doctors perform ophthalmological examinations, the complexity of medical decision-making is not separated from the examining techniques used.  As a guideline to assist eye doctors in enhancing their medical decision-making skills, consider that the complexity of medical decision-making involves three components. 

The first component concerns the number of possible diagnoses and treatment options that must be considered. Many vascular and some non-vascular conditions can manifest with retinal findings similar to diabetic retinopathy.  These are listed in the Initial Diagnosis section.

The second component concerns the amount and complexity of medical records and diagnostic tests that have to be obtained, reviewed and analyzed.  In addition to an eye examination, this visit required the review and analysis of a subjective refraction, a retinal laser scan, a threshold visual field examination and fundus photography.

Third, the complexity of medical decision-making is affected by the risk of significant complications and/or morbidity associated with diabetic retinopathy and the risks involved in any treatment options.  This patient’s diabetic retinopathy was classified as a significant problem where the risk of total vision loss without treatment was significant and there was significant potential for other systemic co-morbidities.  In addition, coordination of care are essential elements of patients presenting with sight threatening disorder of this nature.

Treatment Guidelines

Management of diabetic retinopathy is mostly influenced by the stage of the presenting disease.  In most cases, diabetic retinal pathology has not progressed to the point where interventional treatment is required.  Most will require timely monitoring of the ocular complications and coordination of care with the patient’s primary care physician and/or endocrinologist. 

Specific to the diagnosis of diabetic retinopathy, the ETDRS study guidelines are still considered the preferred practice pattern for patients presenting with ocular complications from diabetes.  While not reviewed here in detail, up to the point of either severe pre-proliferative or proliferative findings or clinically significant macular edema, photodocumentation, imaging and careful monitoring of the condition is adequate.  The more severe the presentation, the more often progress evaluations should occur.  If the patient has proliferative disease, at significant risk for developing proliferative disease, or, has clinically significant macular edema per ETDRS guidelines, the patient should be referred to a retinal specialist for consideration of treatment.  Intravitreal VEGF drugs have become the most common initial treatment modality but focal and panretinal photocoagulation are still necessary components of treating proliferative disease.

Treatment Program

The patient was counseled strongly regarding her systemic disease and the resultant ocular complications.  The retinal presentation was documented by both photography and imaging.

Evaluation of the entire ocular system with consideration of the visual field results and clinical presentation, it was felt the night vision complaints were secondary to the damage done to her retina from the diabetes.  The patient was counseled regarding this finding and that no additional laser surgery or intraocular injections were necessary at this time.  The patient was asked to return for additional evaluation in four months.