Ten Key Elements of a Diabetes-Related Eye Examination

Arguably, the most important aspect of any medical examination is the history that is obtained, and this holds true for ocular evaluations of people with diabetes. Understanding a person's duration of diabetes, current use of medications, glycemic stability and variability, and A1C and/ or time-in-range targets will give the examiner an idea of the person's potential for developing DRD.

In addition, establishing a timeline of any visual changes will help direct the exam, timing of treatment, and schedule for return appointments. It is important to understand that DRD is often asymptomatic until later stages of disease, and obtaining regular eye exams will aid in early diagnosis and help to protect eyesight. Depending on the findings of initial eye exams, ECPs may recommend more frequent exams or may refer people to a retinal specialist. American Diabetes Association guidelines for the timing of diabetes-related eye exams are shown in Table 1. (16)

The best uncorrected and corrected vision in each eye is typically measured at distance and up close in a dark-adapted room using a high-contrast test object known as an eye chart. Pinholes or more formal refraction can determine whether there is a refractive error limiting vision and the best possible visual acuity with new lenses.

A determination that a person has 20/20 vision means the person sees the same optotypes at 20 feet that a person with ideal vision would see at 20 feet. For people with decreased visual acuity—for example, to 20/80—what they can see at 20 feet is the same as what a person with ideal vision could see at 80 feet. People who are unable to see the largest (20/400) optotype are checked for their ability to count fingers, determine hand motion, or detect the presence or absence of light.

Dramatic fluctuations in blood glucose levels may cause a person's vision to change and are one of the ways ECPs can determine that a person has diabetes.

Pupils are evaluated in dark- and light-adapted states for reactivity, size, and symmetry of shape. A significant difference is >0.4 mm between the two pupils and is known as anisocoria. The etiology of anisocoria includes Horner syndrome, in which the smaller pupil is found on the affected side, oculomotor nerve (cranial nerve [CN] III) palsy on the side of the larger pupil, or simply physiologic anisocoria (25).

Analysis for a relative afterent pupillary defect is performed by using the swinging flashlight test. When a light is shined in the normal eye, both eyes briskly constrict. With unilateral optic nerve dysfunction, when the light is “swung” to the affected eye, the pupils “escape,” or dilate, because there is relatively decreased perceived light signal intensity. When the pupillary response is asymmetrical, a determination of whether the defect results from an abnormality of the afterent (optic nerve) or efferent (oculomotor nerve) pathway is necessary (26).

Pupil abnormalities are common among people living with diabetes because of diabetes-related autonomic neuropathy and ocular ischemia, which may cause pupils to dilate poorly and not properly react to light.

Extraocular motility (EOM) is checked by having the person maintain fixation on a test object and evaluating how the eyes move in the six cardinal directions of gaze, while looking for any difference between the two eyes. Over- or under-actions of ocular movement are recorded on a scale of 1–4 and are documented in each direction.

In people with diabetes, a benign cause of abnormal EOM may be a rare and often temporary CN palsy resulting from hyperglycemia, neuronal ischemia, and inflammation. Understanding the innervation of the EOM can help to identify which CN is responsible for abnormalities in EOM function. CN IV innervates the contralateral superior oblique muscle, which is responsible for intorsion and depression. CN VI innervates the ipsilateral lateral rectus muscle, which is responsible for abduction. CN III innervates the remaining ipsilateral extraocular muscles, including the inferior rectus, medial rectus, superior rectus, and inferior oblique, as well as the levator palpebrae, the main muscle that elevates the upper eyelid (27).

Intraocular pressure (IOP) is the fluid pressure inside the eye and is measured by instilling a drop of topical anesthetic (proparacaine) into the person's eye and placing the applanator against the center of the cornea. The internal pressure of the eye will resist and can be recorded in millimeters of mercury (mmHg). Normal pressure is between 12 and 22 mmHg.

Elevation of IOP is a potential sign of glaucoma, and diabetes and DRD modestly increase the risk for glaucoma. For this reason, a detailed examination of the optic nerve during ophthalmoscopy (described below) and additional testing may be required.

Visual fields are tested individually for each eye and represent the entire field of view that is seen with the person looking straight ahead. The simplest method of evaluating the areas of vision that are present or absent is confrontation visual field testing, which grossly determines peripheral vision. While maintaining central fixation, the person is asked to identify individual fingers that are presented in the periphery of each quadrant. If acuity is particularly poor, the person is asked to note the presence or absence of hand movement or a light that is presented in each quadrant. It should be noted that the documentation of visual field testing is recorded from the person's perspective, and areas of decreased or lost vision are represented as darkened areas.

Aside from the confrontational visual field testing, automated testing randomly evaluates points that can be used to document the central 10°, 24°, or 30° visual field. For individuals who are poorly attentive or have decreased vision <20/200, a Goldmann visual field allows an examiner to use test objects to map and record the visual field while ensuring the person's attention and fixation.

For individuals living with diabetes, visual field testing is useful for evaluating central macular and optic nerve function and monitoring for glaucoma, and repeat testing helps to determine stability or progression of the disease.

The external exam is an important evaluation in people with diabetes. Abnormalities of the position and symmetry of the eyelids and ocular alignment may be the first indication of CN dysfunction.

The lower position of the eyelid, known as ptosis, along with a deviation of the eye, could indicate a CN III palsy. In addition to eyelid symmetry and ocular alignment, a gross inspection of the sclera, conjunctiva, and iris can give insight into diabetes-related eye disease. Conjunctiva that are red and appear inflamed may be related to diabetes-related keratopathy (corneal disease) resulting from a decrease in corneal sensitivity. This condition may be an early or late sign of diabetes and is characterized by impaired innervation of the cornea that leads to decreased sensitivity difficulties with nonhealing corneal ulcers. A close inspection of the iris may reveal neovascularization of the iris (NVI), which occurs when new blood vessels grow in response to retinal ischemia. NVI is associated with more advanced disease known as proliferative diabetes-related retinal disease (PDR) and may cause spontaneous hyphema and neovascular glaucoma.

A sophisticated microscope known as a slit lamp allows the use of light at different angles, thicknesses, and intensities to magnify and evaluate three-dimensional ocular structures during the exam. When evaluating a person with diabetes, careful examination should be made of particular areas of interest, including of the lids, lashes, and lacrimal system to detect any abnormal anatomy, lesions at the lid margin, and loss of eyelashes. As mentioned earlier, it is important to evaluate the conjunctiva, sclera, and cornea for inflammation, masses, and foreign objects, as well as epithelial stroma or endothelial defects.

With the use of higher magnification and a narrow, oblique light, it is possible to see deeper structures of the eye, including the anterior chamber, iris, lens, and anterior vitreous. Red or white blood cells may be found in the anterior or posterior chambers, along with NVI and opacifications in the lens of people with DRD.

Fundoscopy is the most important method of determining the presence and level of DRD. Typically, once pupils are dilated, use of a direct ophthalmoscope, indirect ophthalmo-scope, or slit-lamp microscope will allow a highly magnified view of the posterior chamber, including the vitreous, retina, retinal blood vessels, and optic nerve.

When evaluating the optic nerve, special attention is given to looking for neovascularization, in addition to pallor, thinning, and the degree of symmetry in the optic cup-to-disc ratio. Close evaluation of the macula, retinal vasculature, and periphery in people with diabetes may reveal retinal hemorrhages, microaneurysms, hard exudates, DME, retinal ischemia (possibly seen as cotton wool spots), neovascularization, vitreous hemorrhage, and traction retinal detachment. Depending on the appearance of the retina, levels or stages of DRD can be determined.

ECPs use multiple imaging modalities to evaluate ocular function and anatomy. Apart from the physical examination, the additional tests described below may be required to guide classification and treatment options for DRD.

Fundus photography (Figure 1 A) involves a wide-angle, high-resolution photograph taken of the structures in the posterior chamber of the eye, including the macula, optic nerve, retinal vasculature, and peripheral retina. Images can be recorded and used for patient education, and grading of ultra-widefield retinal imaging is often used to stage and follow DRD. Comparing photos over time allows ECPs to determine disease severity and monitor progression.

Fluorescein angiography (Figure 1 B) is a procedure used to diagnose and monitor the severity of DRD and usually takes place after fundus photography. During fluorescein angiography, a nurse injects a vegetable-based dye known as fluorescein into a vein in the person's hand or arm, where it enters the circulation. As the fluorescein passes through the retinal and choroidal vasculature, a series of timed photographs are taken to document and evaluate the circulation in the retina, optic nerve, and choroid.

In eyes with DRD, the vasculature is abnormal and may show areas of nonperfusion, leakage, or staining of fluorescein dye from blood vessels; with more advanced disease (i.e., PDR), new blood vessels may be detected. Thus, the results of this study are used to determine whether additional monitoring, intravitreal injections, or laser procedures may be needed.

Some individuals may experience nausea and, occasionally, vomiting during this procedure. Localized skin irritation and yellowing may occur if the dye leaks around the injection site. For several hours after fluorescein is injected, the skin may turn yellow, but this effect disappears as the fluorescein is renally cleared. Urine may be orange/ yellow for a day or two after the test as well.

It should be noted that fluorescein is safe for people with renal impairment. Allergic reactions to fluorescein are rare and may include a rash or hives that respond to antihistamines. Rarely, anaphylaxis can occur and can be life-threatening.

Optical coherence tomography (OCT), as shown in Figure 1 C, uses light waves and a computerized camera to take cross-sectional images of the retina. This procedure allows for interpretations of retinal thickness, which is important for documenting the presence or absence of DME.

OCT angiography (OCTA) uses motion contrast instead of fluorescein and creates volumetric scans that can be segmented to specific depths. In eyes with advanced DRD, OCTA images may demonstrate abnormalities in the choriocapillaris and retinal vasculature. This study can also provide valuable insight into the presence of microaneurysms, capillary tortuosity and dilation, enlargement of the foveal avascular zone, and vascular remodeling.

In eyes with advanced DRD, when direct visualization of the posterior segment is limited, it is possible with B-scan ultra-sonography (Figure 1 D) to determine the presence of blood in the vitreous cavity, fibrosis, and retinal traction, in addition to a detached retina. Recorded images help to document these conditions and can be used for patient education.

Although diabetes-related eye evaluations are safe and noninvasive, it is helpful to prepare people regarding what to expect before, during, and after their screening eye exams. Health care professionals are encouraged to share the following tips with their patients with diabetes.

Before the exam:

• Bring all glasses and/or contact lenses you wear, along with sunglasses for afterward.

• Expect to have a dilated exam that will cause blurred vision for a few hours.

• Make a list of any questions you have about diabetes and your vision.

During the eye exam:

• Expect to have periods of waiting during the exam. Dilation and testing can often take several hours.

• Bring a source of quick-acting carbohydrates to correct any episodes of hypoglycemia that may occur during the exam.

• Although near vision may be difficult after dilation, bringing a book or magazine may help to pass the wait time before dilation.

After the exam:

• Ask for a report of the exam to be sent to your primary care provider and/or endocrinologist, and keep a copy for your own records.

• Schedule a return visit based on the absence or presence and stage of DRD found during the exam.

• It is best to ask someone to drive you after the exam or to wait until the dilation has worn off before driving yourself.

Editorial and project management services were provided by Debbie Kendall of Kendall Editorial in Richmond, VA.

Dualities of Interest

B.A.C. is a consultant for Genentech and Regeneron. S.A.R. is a speaker for Allergan, Inc., and VSP Vision Care. No other potential conflicts of interest relevant to this compendium were reported.

Author Contributions

All authors researched and wrote their respective sections. Lead author T.W.G. reviewed all content and is the guarantor of this work.