Loss of Vision in the Diabetic Patient: Reviewing the Causes

Objectives:To report on the ocular findings of diabetic patients, which may lead to decreased visual acuity.

Methods:A review of ocular findings in patients with DM in ophthalmic literature is done.

Conclusions:
Patients with DM develop ocular findings and complications as part of the disease. Co-management and routine comprehensive eye examinations in patients with Diabetes are needed to evaluate ocular manifestations and possible complications of the disease, and thus prevent vision loss.

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IntroductionDiabetes mellitus (DM) is a metabolic disorder characterized by hyperglycemia. Previous studies ¹ have shown that this increase in glycemia can produce structural, morphological and physiological changes in each of the ocular components, as in other organs of the human body.

Ocular complications can lead to degradation of the visual image that reaches the retina due to obstruction, alignment, aberration levels occurring in the tear film, cornea or lens. These in turn are the optical reasons for the quality of vision of the diabetic patient to decrease.

On the other hand, DM increases the risk of suffering from cataracts, glaucoma, diabetic retinopathy, among other eye problems. In fact, the main cause of eye disease is diabetic retinopathy because damage to small blood vessels of the retina occurs in diabetic patients.

To outline the causes, let's take a trip from the front to the back of the diabetic patient's eyes.

"Glycemia and a high glycosylated hemoglobin test are recognized as risk factors for developing cataracts in different layers of the lens, called cortical, nuclear or mixed cataracts "

EyelidsAdeoti and his colleagues ² found that the most common findings on the eyelids of the diabetic patient include: warts, poliosis and chalazions. It is also reported that diabetic patients can present edema of the eyelids, which should point to the primary doctor and endocrinologist about the possibility of fluid retention and kidney problem.

Masses and eyelid edema can obstruct vision, cause astigmatism and therefore, decrease vision in diabetic patients.

Extraocular muscles Adeotiand his colleagues ² showed that diabetic patients may present paralysis of some extraocular muscles. Paralysis of extraocular muscles leads to loss of alignment of the two eyes and as a consequence the patient has double vision. This impacts the vision and perception of depth. Adeoti ² says that about 2% of diabetics may have paralysis of the oculomotor nerve and that less than one percent may have paralysis of the fourth pair. The first would lead to a double vision in the horizontal plane: that is to say double vision of an object next to the other. The second produces vertical diplopia, where the patient sees the double image, one on the other.

In these patients the corresponding metabolic and neuroradiological studies must be done. I suggest the primary doctor stick an adhesive tape on the lens of the patient's overturned eye, to occlude the vision of that eye and avoid double vision.

Ojo SecoNajaki and colleagues ³ were able to demonstrate that patients with type 2 diabetes mellitus have a higher prevalence of dry eye than the general population. This happens especially in those patients who already have diabetic retinopathy.

An intact tear film is essential for good vision because the tear acts as a fluid lens in the eye. The change of light rays as they pass from the atmospheric air to the surface of the tear over the eye is the first refraction in the eye. It is said that the change from refractive means from air to tear, has a two-thirds effect of the refractive power of the eye.   Thus, a dry eye in the diabetic patient decreases the vision in these patients, in addition to the discomfort caused by the dryness and the ardor that this causes.

CorneaRosenberg and colleagues ⁴ reported that, in diabetic patients, scarring of corneal surface epithelium (outermost layer) is not optimal. This is important because much of the contemporary cataract surgery is done with a corneal incision. In addition, diabetic patients may present discomfort due to recurrent erosions of the corneal epithelium.

On the other hand, Dhasmana ⁵ and his collaborators have shown that diabetic patients have fewer endothelial cells (the innermost layer of corneal cells). These endothelial cells have a pump function to keep the cornea clear. This becomes important when the diabetic patient undergoes an intraocular surgery, since if the diabetic patient has fewer endothelial cells before surgery and lose more endothelial cells after cataract surgery. This has been documented in diabetic patients, by Schultz et al. ⁶ This loss of endothelial cells can lead to corneal edema, which in turn leads to loss of clarity of the cornea and, therefore, decrease in vision.

The Crystalline Lens and CataractHyperglycemia or changes in blood sugar levels often cause blurred vision. With high blood sugar levels, the concentration of sorbitol increases and the lens imbibes water. The thickening in the antero-posterior axis of the lens causes the patient to change the power of the lens and, therefore, to change the refraction. For example, the thickened lens puts the patient more myopic, and sees worse from afar.

Adeoti and colleagues ² reported that up to 65% of diabetic patients may have cataracts. The opacity of the lens of the eye, called the cataract, can cause vision loss in diabetic patients. In fact, in Latino patients ⁷ glycemia and a high glycosylated hemoglobin test are recognized as risk factors for developing cataracts in different layers of the lens, called cortical, nuclear or mixed cataracts. When the vision has diminished enough that the patient does not see or that the ophthalmologist can not see the fundus of the eye well to diagnose or treat diabetic retinopathy (to be discussed later), these patients would be advised to have cataract surgery .

Garcia-Serrano ⁸ and Suñer ⁹ have shown that after cataract surgery complications are likely in diabetic patients. For example, inflammatory signs, formation of fibrin deposits and synechia, uveitis, risk of pupillary block and rapid development of capsular opacification may appear in the anterior segment of these patients. In addition, surgery may accelerate the progression of retinopathy, macular edema ^10, or neovascular glaucoma, even in eyes that have received previous photocoagulation.

GlaucomaSeveral studies ¹¹ demonstrate that the duration of diabetes illness and uncontrolled blood glucose levels are associated with an increased risk for patients suffering from glaucoma ¹⁰ , including open-angle glaucoma. ¹² This is because diabetes and hyperglycemia are associated with elevations of intraocular pressure ¹¹ and glaucoma is an optic neuropathy that results in loss of vision and vision, the main risk factor being increased pressure in the eye.

Diabetic RetinopathyDiabetic retinopathy is the leading cause of blindness in diabetic Americans between the ages of 20 and 74 years. Interestingly, Varma and colleagues ¹³ showed that the prevalence of diabetic retinopathy (DR) is also high among Latinos. Overall, the occurrence of DR is proportional to the duration of disease and glycemic levels in diabetic patients.

Both patients with type 1 and type 2 diabetes are at risk for this ophthalmic complication of the disease. The problem is that the date of onset of the disease in patients with non-insulin dependent diabetes is often unclear. For this reason, diabetic retinopathy should be screened early in type 2 patients.

Diabetic retinopathy is caused by damage to the blood vessels of the retina, the layer that transforms images that enter and are refracted in the eye in nerve signals that are sent to the brain.

It is said that diabetic retinopathy has several stages divided into: nonproliferative and proliferative. Non-proliferative retinopathy is milder. Proliferative retinopathy ¹⁴ , as the word indicates, involves a proliferation of new blood vessels. That is why it is more serious and advanced. Fortunately it is less common.   

"Diabetic blisters can be on the back of the hands, fingers, feet and sometimes on the legs or forebones "

Symptoms of Diabetic RetinopathyVery often, diabetic retinopathy does not cause symptoms until the damage to the eyes is severe. This is because the damage can affect an important part of the retina before the vision is affected.

Symptoms of diabetic retinopathy include blurred vision, areas of vision loss, difficulty seeing at night. However, blurred vision may be due to macular edema, which occurs when blood vessels leak fluid, which should not occur, near the area of ​​the retina that provides the central acute vision (called the macula).

Blurred vision may also occur with a retinal detachment, sometimes caused by blood and fibrosis in the vitreous.

Tests and examsTo examine the retina of the diabetic patient, the ophthalmologist will examine the eyes. ¹⁵ After examining vision and intraocular pressure, mydriatic eye drops will be instilled to dilate the pupils of the eyes and examine the entire retina.

In the examination of the patient with early (non-proliferative) diabetic retinopathy, the doctor may observe: blood vessels with microaneurysms, blocked vessels, small retinal hemorrhages and fluid that escapes into the retina producing edema. It is possible that patients with nonproliferative diabetic retinopathy do not need treatment. However, an ophthalmologist trained to treat diabetic retinopathy should carefully monitor the condition.

If the patient has advanced (proliferative) retinopathy, the ophthalmologist may observe: new blood vessels in the optic nerve or in the retina, which may bleed because they are fragile. Once the ophthalmologist observes that new blood vessels are proliferating in the retina (called neovascularization) or macular edema develops, effective and rapid treatment is usually needed. The retina (an ophthalmologist sub-specialized in diseases of retina and vitreous) can order images such as: retinas photographs, optical coherence tomography ¹⁵ , ultrasound (if the blood in the vitreous does not allow visualization of the retina ) And fluorescein angiography (to see the vessels of the retina). ¹⁶

Treatment for Diabetic Retinopathy Treatmentfor diabetic retinopathy includes non-cutting surgery (which may be laser) and cutting surgery.

Laser (non-cutting) eye surgery creates areas of small ablations in the retina. This treatment is called photocoagulation. ¹⁸ It is used to prevent and treat the proliferation of abnormal blood vessels, to prevent the vessels from draining or to reduce the size of abnormal vessels.

Also you can use drugs ¹⁹ that are injected into the eyeball, which can help prevent the growth of abnormal blood vessels.

On the other hand, a surgery called vitrectomy is used in patients who have suffered bleeding inside the eye, in the so-called vitreous humor. Usually during the vitrectomy is added the intra-operative application of lasers. ²⁰ In addition, vitrectomy can be part of surgery to repair a detached retina.

ConclusionsGood glycemic control may help prevent ophthalmic complications in patients with diabetes. Effective co-management of diabetic patients, early detection of ocular manifestations and pathologies in such patients will help prevent the irreparable loss associated with complications of diabetes. Therefore, diabetic patients need to be referred by their primary physicians and specialists to the ophthalmologist for the latter to examine them. This will assess all the conditions that can afflict diabetic patients and that can potentially lead to loss of vision.