Special Hospital Sveti Vid is a unique clinic in the region with a specialized retina department involved in handling diverse macular problems: diagnostics, therapeutical (PDT and conventional laser treatment, surgical treatment). In order to understand the function of this specific part of the human eye, an analogy with the photo camera is often made. Light passes thorugh the clear, transparent structures of the eye (cornea, lens, vitreous, which correspond to the optical media of the eye); the light beam is then refracted by the optical media and falls and focuses on the posterior part of the eye – retina. The retina acts as the film of the photo camera, it absorbs and transforms light into neural impulses that travel to the brain where the brain analyses them and creates consciousness/perception about the object being observed, what we call the picture of the object.
The part of the retina specialized for central vision and distinction of the smallest details is the MACULA or yellow spot. It is abundant with photoreceptors – specialized cells that receive the visual stimulus and transfer it by the nerve elements. The thick configuration of the receptors in the macula enables the sharpness of vision, detail distinction and distinction of faces, reading, writing, recognition of colors…
DEGENERATION OF THE MACULA (DM)
Degeneration of the macula is one of the crucial ophthalmologic problems of the modern age. It appears in several forms. The most common one is related to the old population and it is named age related macular degeneration /ARMD/. Fewer forms are seen in congenital degenerative progressive diseases /juvenile macular degeneration/ or in degenerative high myopia. The macula will suffer when the body undergoes systemic or infective diseases.
RISK FACTORS FOR MD
The risk of ARMD increases with age. Within population aged between 65 and 75 years, the risk is 10-20 percent. At the age of 75 to 85, the risk is 35 percent.
There is no doubt that genetic predisposition represents a risk factor. Children of ARMD patients have a greater risk of an earlier development of the disease.
Persons of light skin and those who extremely expose themselves to light, especially the blue part of the spectrum, are in the risk group. Therefore they are advised to wear sunglasses with a protective filter particularly out on the ocean or snow. The other risk factors are the risk factors for developing atherosclerosis: smoking, increased level of lipids in blood, deficiency of vitamins such as C, E, A.
Hypertension and cardiovascular disturbances may speed up the development of changes. Smokers whose close relatives developed macular degeneration have two times greater chance to develop it than those who do not smoke.
Damage to the macula will cause the disturbance of central vision without the possibility of correcting this disturbance with corrective lenses such as glasses, but with the preservation of peripheral vision and therefore the patient does not become completely blind as only his peripheral vision is preserved. Each patient ought to seek ophthalmologic help as soon as symptoms such as decreased contrast sensitivity, decreased visual acuity, distortion of visual pictures, appearance of spots in the central field of vision occur /central scotoma/.
Although ocurring in both eyes, this disease will not affect both eyes equally and therefore the “better” eye will compensate the decrease in vision and the patient will not be able to notice the initial changes of visual acuity in the first stages of the disease.
Since there is no physical pain involved in MD disease and in first stages only discreet changes in vision occur, it will be difficult to notice it binocularly, and therefore it is highly recommended to have regular ophthalmologic check-ups, each 6 months, or self-test at home /cover one eye at the time and look at the Amsler grid – a paper chart designed for this testing/. Noticing irregularities or blur in the center of the Amsler grid is an alarm to visit an ophthalmologist. Further development of macular degeneration means that visual acuity will continue to decrease to the point of inability to read.
CHANGES ON THE TISSUE LEVEL
The chorioidea or choroid coat is the vascular layer of the eye containing connective tissue located between the retina and the sclera. The innermost layer of the choroid is Bruch’s membrane or the basement membrane of the retinal pigment epithelium.
FORMS OF MACULAR DEGENERATION
Aging means a decrease in the number of the receptors and nerve cells of the retina, while the pigment epithelium underlying the retina has a function to “absorb” and dissolve the parts of dead cells. Eventually this ability will be exhausted and this will result in sediments of deposits /drussen/ that obstruct the exchange of nutrients between the choroid and the retina /dry form of macular degeneration/.
The detachment and destruction of the pigment layer means introduction into a more complex form of macular degeneration /atrophic form/ that results in the destruction of vision.
The body will try to “correct’ this defect creating new blood vessels /choroid neovascularization or CNV/ and this further will destroy the tissue balance. These are the characteristics of the “wet” form of macular degeneration. The tissue destruction occurs fulminantly and ends in scars with the absence of the functional tissue.
The dry form of macular degeneration is more frequent than the wet form /90 percent of MD patients suffer from the dry form/. There is always a possibility that the dry form will transform into the wet form of degeneration characterized by fudroajant loss of vision. Therefore it is of great importance to educate the patient to self-check visual function in order to detect the symptoms in time and start the treatment.
CNV occurs in 5-10 percent of population with degenerative nearsightedness. Due to the growth of the eye ball, the increase in axial length will result in thinning the eye ball protective coating and in the formation of “staphiloma” which are abnormal protrusions of the uveal tissue through weak points of the eye ball. This is a predisposition for CNV and possibility of the occurrence of holes and ruptures in the lower layer of the retina under the pigment epithelium.
Through these holes, newly formed poor quality choroid CNV blood vessels will invade and destroy the pigment and neuro-sensory apparatus of the retina causing the destruction of central vision that is irrecoverable and irreversible.
Until the appearance of PDT, there was no possibility to treat CNV in these eye conditions effectively.
The early recognition of the problem and earlier application of the therapy will reduce the risk of fudroajant irreversible loss of central vision.
The golden rule in diagnostics is fluorescein angiography. Filming the back of the eye – fundus after introducing the contrast intravenously /fluorescein/ will mark “the bloodstream” of the back of the eye and detect the defect zones by leaking the fluorescein dye through the wall of the blood vessel. That is how to differentiate two subforms of wet macular degeneration – occult and classic, each prognosing differently.
There is no specific treatment for the dry form of macular degeneration. Patients are advised: to use vitamins, ginko supplements, to abstain from smoking, protect themselves against the blue part of the spectrum. Aids such as loupes or telescopes can help. Training to work with tele-monitor systems, mobile as well as stationary, can be obtained in the SVETI VID center for low-vision.
Surgical implants of micro telescopes can help magnifying letters approximately 3-6 times more than the spectacles, but one should always consider that these are temporarily aids while the process of the disease is conserved in the present stadium of the disease. With a progressive decrease in visual acuity, the implanted telescope looses its power and sharpness and therefore its effectiveness as well.
Therapy for the wet form of macular degeneration/ Photodynamic therapy PDT
For this type of macular degeneration there is therapy called PDT- Photodynamic therapy. Its purpose is to conserve already diagnosed changes and prevent further destructive tendencies, therefore to CONSERVE the state of visual acuity. This is the way to treat subfoveal and juxtafoveal CNV, predominantly the classic type of CNV. The aim is to destruct newly formed blood vessels by a specific type of non-thermal laser and photosensitive substance – verteporfin. In the country, this therapy is available ONLY IN SVETI VID, where particular attention is dedicated to the problem of macular degeneration.
Classic laser photocoagulation has effect only in cases of peripheral localization, far away from the center of the macula. It is non-selective in reference to the tissue where it is applied in order to treat the aimed pathological zone, and it involves the functional part of the retina, leading to the partial fall of acuity.
SURGERY OF THE MACULA
A surgical approach that has been taking off in the last few years is the so called “translocation” of the macula. Actually, the whole of retina is rotated in such a way that the macula will “fall” exactly to the healthy preserved part of the pigment epithelium. This is a very complex surgery and requires additional surgery on the external eye muscles.