RETINAL CONDITIONS

Once a person gets older it is natural for his eyesight to deteriorate and to need reading glasses. However, there are also some specific eye conditions that can affect older people (not only, but mainly): cataracts, glaucoma, macular degeneration and diabetic retinopathy, which are the most common causes of poor sight.

Cataracts is described as a cloudily on the eye' lens, which lies behind the pupil and is responsible to focus the light rays on to the retina at the back of the eye. With the cataract, light is prevented from reaching the retina, resulting in a fuzzy picture. Many factors can be involved in the origin of cataracts, for instance, congenital, age related, as the result of an eye injury, conditions such as diabetes, or long-term use of some drugs (e.g., corticosteroids).

Glaucoma is a health condition characterized by damage on the optic nerve, in a gradual process that results in a loss of peripheral vision, typically associated with a higher than normal pressure within the eye (Intraocular Pressure – IOP) .

Macular Degeneration is an eye condition that affects the central (reading) part of sight and the most common cause of poor eyesight in people aged over 60. Even not leading to a complete sight loss, in many cases it is difficult or impossible to treat. It is characterized by a failure on the functioning of photoreceptor cells in the macula, the most developed part of the retina, made up of millions of light-sensitive cells [Walters, 2006].

Diabetic Retinopathy is a sight-threatening, chronic ocular disease that affects almost all patients with diabetes mellitus. It is characterized by a gradually and progressive alteration in retinal microvasculature, leading to areas of retinal nonperfusion, increased vasopermeability and uncontrolled neovascularization [Aiello, 1998].

DIABETES AND DIABETIC RETINOPATHY

Diabetes mellitus is a public health worldwide problem! It is a metabolic disorder characterized by the presence of hyperglycaemia due to defective insulin secretion, insulin action or both. Based on the World Health Organization (WHO) criteria, diabetes is diagnosed by means of a venous plasma glucose concentration superior to 11.1mmol/l, two hours after the ingestion of a 75-g glucose tolerance test. Estimated to affect ≈171 million people in 2000, this number is projected to rise to 366 million in 2030. Depending on the type of the disease a patient is more likely to develop Diabetic Retinopathy [Wild, 2004].

There are two forms of diabetes mellitus recognized. Type 1, formerly called juvenile-onset or insulin-dependent diabetes, is characterized for the destruction of beta-cell, leading to absolute insulin deficiency. Type 2, previously called adult onset or noninsulin-dependent diabetes, is characterized by an insulin secretory defect that leads to relative insulin deficiency, being this, the reason why many of patients with type 2 diabetes take insulin. During pregnancy there’s also the risk of develop diabetes, mainly due to the changes in metabolic control [Aiello, 1998], [WHO, 2005].

Patients with Type 1 diabetes should have an ophthalmic examination 3 to 5 years after the diagnosis of the pathology. On the other hand, patients with Type 2 should be referred for ophthalmologic examination at the time of diagnosis. Patients with diabetes that are planning to get pregnant should have an ophthalmologic exam prior to conception and another one during the first trimester. Women who develop gestational diabetes do not require ophthalmologic exam, once these individuals are not at risk of developing Diabetic retinopathy during pregnancy [AAO, 2008].

More than 75% of patients who have diabetes mellitus for more than 20 years will develop some form of retinopathy. Diabetic retinopathy correlates with the duration of diabetes, so, with the increasing life expectancy, diabetic retinopathy and the consequent blindness will tend to increase. According to the WHO, Diabetic Retinopathy is responsible for 4.8% of the 37 million cases of blindness throughout the world [Aiello, 1998], [WHO, 2005].

Estimates are that 90-95% of patients suffering from diabetes are type 2. Due to this disproportional distribution of the different types of the disease, even type 1 diabetes being related to more frequent and severe ocular complications, patients with type 2 diabetes comprises a substantial proportion of patients with visual impairment due to Diabetic Retinopathy.

Correlating two important risk factors, duration and type of diabetes, some statistic could be getting into account: after 5 years, approximately 25% of type 1 patients will develop Retinopathy; this percentage rises to 60% and 80% after 10 and 15 years, correspondingly. For the other sample of patients, type 2 diabetes, more than 60% of patients will develop Diabetic Retinopathy over time of the disease [WHO, 2005].

A healthy retina, which is the light-sensitive tissue at the back of the eye, is necessary for a good vision. Diabetic Retinopathy characterizes for the damage of the tiny retinal blood vessels. It has four stages:

1. Mild Nonproliferative Retinopathy: the earliest stage corresponds to the occurrence of microaneurysms (small areas of balloon-like dilations in the retina’s tiny blood vessels).
2. Moderate Nonproliferative Retinopathy: some blood vessels that support the retina are blocked.
3. Severe Nonproliferative Retinopathy: more blood vessels are blocked, depriving parts of the retina with their blood supply. These parts send signals to grow new blood vessels for nourishment.
4. Proliferative Retinopathy (PDR): at this advanced stage, the signals sent by the retina for nourishment prompt the growth of new blood vessels, which are abnormal and fragile. They grow along the retina and along the surface of the clear, vitreous gel that fills the inside part of the eye. That process is called neovascularization. At this stage vitreous and preretinal haemorrhage can also occur [AAO, 2008].

These new blood vessels do not cause symptoms or vision loss. However, since they have thin and fragile walls they can easily leak blood, that way severe vision loss and even blindness can occur. Usually, Diabetic Retinopathy affects both eyes.

These new blood vessels, consequence of the neovascularization, can cause vision loss in two ways:

• They can develop and leak fluid into the centre of the eye leading to a blurred vision, due to the fragility of their walls;
• Fluid can leak into the centre of the macula, where sharp and straight-ahead vision occurs. That situation leads to a blurred vision too, because fluid makes macula swell – macular edema. It can occur at any stage of Diabetic Retinopathy, although it is more likely to occur as the disease progresses [AAO, 2008].

DIAGNOSIS OF DIABETIC RETINOPATHY

Comprehensive eye exams can be performed to detect Diabetic Retinopathy.

Visual acuity test – Using eye chart test to measure how well a patient sees at various distances.

Tonometry – to measure Intraocular Pressure.

Eye exam – Diagnosis of diabetic retinopathy can be based in different exams:

• Slit lamp biomicroscopy - Uses an instrument that combines a low-power microscope and a light source that produces a narrow beam of light. Requires an appropriate lens and pupil dilation. It is currently accepted as a routine practice to detect Diabetic Retinopathy.
• Direct and indirect ophthalmoscopy - There are two main types of ophthalmoscopes, direct and indirect. Direct ophthalmoscopes are simple handheld ophthalmic instruments consisting of a concave mirror, a light source and an eye piece for the ophthalmic professional to perform the exam. Indirect ophthalmoscopes are divided into two subcategories including monocular and binocular indirect ophthalmoscopes. Monocular indirect ophthalmoscopes offer a high level of magnification and a wider field of view than a traditional ophthalmoscope, but only offer one view of the inside of the eye. Binocular indirect ophthalmoscopes project three elements into the eye, rather than one, allowing eye care professional to get a three dimensional overview on the interior of the eye which allows for a more detailed examination.
• Retinal Photography – There are two ways to perform this exam, by using mydriatic drops to dilate pupils or not. Despite this difference, the examination follows a common procedure. Drops are placed in patients’ eyes to dilate the pupils (only in the mydriatic option) and then the eye care professional uses a special magnifying lens to examine the retina and optic nerve for signs of damage or other eye problems. It is performed with a Retinograph, which provides images on the back of the eye using for that infrared light (the blood-filled capillaries absorb more of the infrared light than the surrounding tissue, leading to a variation in the intensity of the reflection, allowing a good image on the vasculature of the eye). The images, called retinographies, are taken with a photographic camera, so that they can be analyzed after the exam and saved for a latter report on the case [AAO, 2008].
• Optical Coherence Tomography (OCT) – Providing a high-resolution imaging on different structures of the eye, the OCT is extremely useful to quantify retinal thickness, which is an effective way to monitory macular edema. OCT measures the echo time delay and intensity of backscattered light (the approach is similar to ultrasound, but image is performed by measuring light rather than sound). Visible and near infrared beams of light are used in this non-invasive technique, which provides tomographic images [Fujimoto, 2008].
• Fluorescein Angiography – Even not being routinely indicated as a part of the examination of patients with diabetes, it is commonly used as a guide for treating CSME (Clinically Significant Macular Edema) or a mean to explain unpredictable decreased visual acuity. Injecting a fluorescence dye (e.g., Fluorescein, Green Indocyanine) in the arm of the patient, abnormal leakages on retina microvasculature can be detected [AAO, 2008].

TREATMENT ON DIABETIC RETINOPATHY

After the detection of abnormal signs of the Diabetic Retinopathy, a treatment has to be followed. In general laser photocoagulation surgery is advised for patients with high-risk Proliferative Diabetic Retinopathy and for CSME, since both groups have better prognosis when treated. However, also in the earliest stages there are strong evidences that tight glycemic and blood pressure control (this last case is valid for patients suffering from hypertension in addition to diabetes) reduces the incidence and progression of Diabetic Retinopathy as well as the visual loss related to the pathology [AAO, 2008], [Mohamed, 2007].

CSME is treated with focal laser photocoagulation surgery. Hundreds of small laser burns are placed in the areas of retinal leakage surrounding the macula. These burns slow the leakage of fluid and reduce the amount of fluid in the retina.

During the first three stages of Diabetic Retinopathy, no treatment is needed, unless you have macular edema. Once a patient suffers from Proliferative Diabetic Retinopathy he/she should be treated with scatter (panretinal) laser photocoagulation surgery, which helps to shrink the abnormal blood vessels. About 1000 to 2000 laser burns are placed in areas of the retina away from the macula, causing the abnormal vessels to shrink. Scatter laser treatment may slightly reduce the colour and night vision. This procedure must be performed before bleeding of the new vessels. However, if the bleeding have already started and is severe, a vitrectomy may be needed.

A vitrectomy is performed under either local or general anaesthesia. A tiny incision is made in the eye. After that, a small instrument is used to remove the vitreous gel that is clouded with blood. The vitreous gel is replaced with a salt solution, because the vitreous gel is mostly water [AAO, 2008], [NEI, 2003].

Diabetic Retinopathy is the leading cause of preventable blindness in working adults [Mohamed, 2007]. However, an early detection followed by an effective therapeutic approach can prevent a fast development of the disease. Screening is an effective way of Detecting Diabetic Retinopathy as early as possible. Patients with diabetes should be monitoring, so that, eye threatening lesions as a consequence of the disease can be prevented, a therapeutic can be adjusted and many years of sight can be saved due to this preventable attitude.

BIBLIOGRAPHY

[AAO, 2008] American Academy of Ophthalmology Retina Panel. Preferred Practice Pattern© Guidelines. Diabetic Retinopathy. San Francisco, CA: American Academy of Ophthalmology; 2008. Available at: http://www.aao.org/ppp

[Aiello, 1998] Aiello L, Gardner T, King G, Blankenship G, Cavallerano J, Ferris F, Klein R, "Diabetic Retinopathy", Diabetes Care, 1998, volume 21, number 1, 143-156

[Fujimoto, 2008] Fujimoto J, "New growth for optical coherence tomography", OLE, May 2008, optics.org/ole

[Mohamed, 2007] Mohamed Q, Gillies M, Wong T, "Management of Diabetic Retinopathy", JAMA, 2007, volume 298, number 8, 902-916

[NEI, 2003] US DEPARTMENT OF HEALTH AND HUMAN SERVICES, National Institutes of Health, National Eye Institute, NIH Publication No: 06-2171, Revised 9/03

[Walters, 2006] Walters R, "Understanding your eyes: Cataracts, Glaucoma & Macular Degeneration", Family Doctor Books, 2006

[Wild, 2004] Wild S, Roglic G, Green A, Sicree R, King H, "Global Prevalence of Diabetes – Estimates for the year 2000 and projections for 2030", Diabetes Care, 2004, Volume 27, Number 5, 1047-1053

[Wilkinson, 2003] Wilkinson C, Ferris F, Klein R, Lee P, Agardh C, Davis M, Dills D, Kampik A, Pararajasegaram R, Verdaguer J and Global Diabetic Retinopathy Project Group, "Proposed international clinical diabetic retinopathy and diabetic macular edema disease severity scales", Ophthalmology, 2003, Volume 110, Number 9,1677-1682

[WHO, 2005] "Prevention of Blindness from diabetes mellitus", Report of a WHO consultation in Geneva, Switzerland, 9-11 November, 2005