26/12/2021
More on Diabetes and the Eye.
The eye is a fascinating and intriguing structure. Sensitive and vital in our appreciation of life. Each eye serves as a window that brings to view the external environment in all its beauty and splendor. Anatomically the eye is likened to a ball, hence the term eyeball. It is not a regular globe or sphere. The diameter from front to back is longer than across. In front or as we say in medicine, anteriorly, is the “dark or black part” and we would also notice the “ white part. A good portion of the globe is situated within the bony skull in the orbital cavity. The very sensitive eyelids also help to protect the globe and ensure that tears is evenly distributed to keep the globe well lubricated and healthy. Openings and foramina within the orbital bones enable the globe to communicate through nerves and vessels with the immediate vicinity viz: the brain and vital supply vessels. Muscles anchored around the orbital bones and attached to the globe are useful for eye movement in direction of gaze, both eyes paired in correspondence to allow single vision with a significant appreciation of depth and position within space. Images formed by the eyes are transmitted via a
major central nerve directly into the brain feeding visual information to the brain for processing.
The “ dark or black part” of the eye on the front view, is the cornea which is transparent normally and resembles a watch glass The dark Iris behind the cornea gives it its color. A central opening called the pupil found in the iris allows light to pass into the eye. Behind the pupil lies the clear lens. The lens is situated between two major spaces, a smaller anterior chamber filled with a fluid called the aqueous humor and a larger posterior chamber filled with a gel-like substance like egg white, the vitreous humor. The eyewall consists of 3 layers, an outer sclera, and an inner retina. Between the two layers is the uveal tract which equally forms the iris earlier referred to. An intricate Neural sensory apparatus having gathered images from the eyes leaves the eye through the optic nerve at the rear of the eye on its way to the brain. Accessory structures around the eye play various roles e.g the lacrimals for tears, vessels for blood supply, muscles for movements and nerves for innervation, etc.
Diabetes Mellitus is a disease in which the body is unable to handle sugar leading to an increase of blood sugar levels above the acceptable range. The high sugar levels in the blood in this disease pose big challenges to the red blood cells and vessels primarily which in turn could affect the function of vital organs and tissues especially the eyes, kidneys, nerves, brain, heart, and limbs to mention just a few.
There are two types. Simply referred to as Type 1 and Type 2.
A chemical in the body called insulin normally regulates blood sugar levels. This chemical is produced in an abdominal organ called the pancreas.
Type 1 is also called Insulin Dependent Diabetes and Type 2 is known also as Non-Insulin Dependent Diabetes.
Blindness is more likely to occur in diabetics than in the normal population. The risk of blindness is as much as 25 times greater in diabetics.
Poor sugar control, duration of the disease, presence of uncontrollable hypertension, heart disease, kidney disease, and smoking can all predispose one to potentially blinding diabetic eye diseases.
Though The eye and its neighboring structures could all be affected by diabetes however we will consider the major two that are potentially blinding, cataracts, and severe retinal disease.
High glucose levels in the lens of the eye cause lens swelling and clouding which manifest as cataracts.
Preexisting age-related cataracts could also worsen in diabetics. One of the earliest signs of diabetic eye diseases is an alteration in vision. These alterations occur when the lens’s focusing ability is affected by high glucose induced changes in the metabolism within the lens.
Diabetic Retinopathy
Diabetic retina changes can be grouped into early Background changes, macular involvement, pre proliferative, and proliferative diabetic retina changes and depend on the stage of the pathology involved in the disease. The pathology disposes the retinal vessels to fluid leakages and occlusions that produce a wide range of signs and symptoms.
The symptoms may range from mild discomfort to blindness. Early detection is important to prevent diabetes-related blindness.
Such measures may involve better blood sugar control, multi-specialty consultations, control of hypertension, heart disease, kidney disease, certain risk factors, and the use of special substances e.g. anti-VEGF and or special high-intensity lights known as Lasers.
Cataract
The lens as earlier explained lies within the globe and is made up of protein. It is normally clear ( as clear as glass) when healthy. The lens functions more like the lens in a camera to focus the image on the retina at the back of the eye (see the diagram attached). This function of adjustment of focus is achieved by small muscles in the wall of the eyeball which connect to the lens through strand-like attachments called zonules ( see diagram).
Imagine the lens as a clear window. Images would appear clear once the window is clear. What do you think would happen once the window becomes cloudy? Yes, the image would become cloudy too.
The clouding of a normal lens from its clear transparent natural appearance would affect the image from clear to cloudy or smoky. That is cataract.
There are varying degrees of whitening or clouding of the natural lens in the evolution of cataracts hence often we refer to some cataracts as being immature, when still early, with varying degrees of vision or visual symptoms and mature, when fully covered or opaque, preventing any clear reasonable vision. Cataracts are potentially blinding if it occurs in both eyes.
When the cataract is immature, the symptoms could range from as little as glare to annoying distortions or even double vision. Some patients with immature cataracts may even surprisingly, notice an “improvement in their near vision”.
Patients complain of a painless slowly worsening, cloudy, or smoky diminishing vision in one or both eyes. The above symptom would exist alongside the symptoms of diabetes in this case.
The only definitive treatment for cataracts is currently surgery. Sometimes lasers and high technology machines, including huge operating microscopes are used to facilitate the removal of the cloudy lens and its replacement with an artificial clear synthetic lens called intra- ocular lens ( see image of an intraocular lens).
The artificial lens is most times implanted at the same position as the natural lens ( preferably) after extracting the diseased human lens through surgery.
Though we have various cadres of Eyecare workers ( e.g Ophthalmologists, Optometrists, Opticians, Ophthalmic Nurses, Community Eye workers, etc) and all professionals in their rights, ONLY THE OPHTHALMOLOGISTS are skilled and trained to carry out the surgery.
Your eye doctor when consulted will want to be sure that your signs and symptoms are compatible with a diagnosis of diabetes. Will run some investigations for further clarity. Will define the cause, the classification, complications if any. Cataract and retinal changes may coexist with other diabetic eye diseases or non diabetic eye problems or even other general systemic health problems and so it is equally important to document all these and rule out any that may need to be ruled out. Having done all of the above, the best treatment option for you is recommended bearing in mind your general health and any other coexisting eye pathologies
Clinical care would involve specialists in various fields to bring blood sugar under control and avoid complications.
Ensure that your eye care doctor carries out basic regular checks on your eyes which would include examination and photographs of the back of the eyes etc. and plan your subsequent care professionally.
The patient’s compliance with treatment and medical advice helps to improve care. `
