Albinism
Albinism is a genetic condition with a characteristic phenotype (physical appearance), owing to the absence or reduction of pigmentation in the skin, eyes and hair.
It is an extremely rare metabolic condition, owing to a defect in the gene which is in charge of the synthesis and distribution of melanin.
Albinism is rare throughout the world: just 1 in every 20,000 people suffer from this condition. It affects all races in the same degree. A person with albinism is usually characterised by having white or light gold hair, very pale or pink-tinged skin, and violet or pinkish eyes, although this is only observed when light hits their eyes, reflecting blood vessels from a lack of pigmentation.
Albinism can cause a deficit in pigmentation in the retina, iris and choroid (vascular layer of the eyeball). This can cause the pupil to appear a deep red shade, and the iris to have a light grey-blue or violet tone.
The fovea, which is the area of the retina with the sharpest vision, can be underdeveloped because of the lack of pigment, which can limit visual function.
Individuals with albinism can also suffer a lack of binocular vision, owing to a defect in the crossing of the fibers of the optic nerve, and subsequent connection to the brain.
A lack of pigmentation can cause some problems like:
• Visual acuity reduction from 20/60 to 20/400.
• Nystagmus: irregular and rapid side to side eye movement
• Squints: crossed or uncoordinated eyes.
• Photophobia: sensitivity to bright or shining lights
Normally, the appearance of the person gives way to the detection of the condition. This is confirmed by a thorough examination by a qualified ophthalmologist, and by a genetic study together with the family history.
For more information:
Asociación de Ayuda a las Personas con Albinismo, ALBA (Assistance for Persons with Albinism): www.albinismo.es
Aniridia
Anirida is a congenital disease of a genetic origin. Although the word “anirida” literally means “lack of iris”, it is in fact a disease in which various structures of the eye play a part.
Generally, it is bilateral and incomplete as in the majority of cases there is an incipient iris which has not completely developed.
Anirida is produced by a lack of development in the eyeball during pregnancy because of a genetic mutation (pair 13 of the 11th chromosome) affecting the PAX6 gene which is responsible for the formation of the eye as well as other structures. For this reason, it can sometimes be associated with malformation in other organs of the body.
The first symptom to be detected is light sensitivity, as well as a lack of development of the retina and optic nerve, causing low visual acuity. This is usually of 20% or less.
People with aniridia may also have other visual problems:
• Nystagmus: constant, involuntary eye movement.
• Glaucoma: intraocular pressure which can cause permanent damage to the optic nerve.
• Cataracts: opaqueness of the lens.
• Keratopathy: alterations in the cornea, caused by a lack of limbal stem cells.
Aniridia can be isolated or as part of a syndrome, of which the most common is WAGR Syndrome (Wilm’s tumour, aniridia, genito-urinary alterations and learning difficulties / mental retardation).
There is no treament or cure for aniridia, although some of the accompanying symptoms can be alleviated. Patients require frequent control and visits to ophthalmologists and GPs.
For more information:
Asociación Española de Aniridia (Spanish Aniridia Assocation): Web
Age-related Macular Degeneration (AMD)
Age-related Macular Degeneration is the primary cause of visual loss in the Western world in patients aged over 50. It is a degenerative disease that affects the macula, the area of the retina specialised in detailed vision, which allows us to read, or recognise faces.
There are many subcategories of AMD, but basically there are two main forms: wet (exudative) or dry (atrophic).
Wet AMD is the least frequent (around 15%), but it is the form with the most rapid progression. It requires immediate treatment to avoid a total irreversible destruction of central vision in a short period of time (weeks or months). It produces hemorrhage and leaks within the layers of the retina, caused by anomalies in small blood vessels invading the retina from the choroid. These destroy the neural arquitecture of the macula, producing a loss of vision right in the centre of the field of vision.
The disease usually starts in one eye, but eventually affects both. For this reason, it is possible that a patient may not realize they have a problem unless they cover the healthy eye for some reason. They may notice in this case that lines are distorted in the affected eye (metamorphopsia).
In recent years, there have been very significant advances in the treatment of wet AMD, which have given new hope in preserving the sight of patients.
The foremost treatment attempting to control wet AMD uses antiangiogenic drugs, via intraocular injections in the vitreal cavity. This drug works by blocking the molecule which causes the development and progression of neovascular membranes in wet AMD: the vascular endothelium growth factor (VEGF). This treatment will stop the illness in 3 out of 4 cases, and improve in 1 out of 3. In certain resistant cases, other alternative treaments should be tried, such as laser coagulation (either direct or veins), photodynamic therapy and, in some cases, combination of treatment with vitreoretinal macular microsurgery.
Dry AMD makes up the remaining 85% of cases. Although it is much more common and the visual impairment it causes is severe, it is often erroneously considered to be more benevolent than wet AMD. This is because its evolution is slower, over a period of several years.
In this type of macular degeneration, loss of visual acuity is slower, meaning that sufferers can be perceived to have apparently good central vision. In the case of reading, for example, a patient may see each of the letters clearly independently, but may not see the previous letter or the one after. In this manner, they are incapable of recognising the words to read.
Currently, there is no treatment for atrophic AMD, although research going on throughout the medical world is intense and promising. Even though there is no known method of preventing macular degeneration to an absolute degree, there are lifestyle factors which can increase or decrease your chances of developing the disease:
— Do not smoke.
— Maintain a healthy diet, rich in fruits and vegetables and low in animal fats.
— Undertake regular exercise
— Maintain a healthy weight.
Glaucoma
Glaucoma is a group of visual diseases which have in common the progressive degeneration of the optic nerve. One of the most common and well-known factors for which there is an available treatment is intraocular pressure (IOP).
The evolution of glaucoma is usually masked or latent, which means that most patients do not notice the visual loss until the illness is in an advanced state. If an early diagnosis is not given and an adequate treatment administered, it may produce irreversible visual loss. This is why regular eye exams are so important.
Diagnosis of glaucoma has to be carried out by an ophthalmologist with adequate technology. The following diagnostic tests are usually required:
• measurement of eye pressure (Tonometry).
• side or periphery vision examination (visual field test).
• inspection of the drainage angle of the eye (Gonioscopy).
• optic nerve inspection (Ophthalmoscope).
• measurement of the thickness of the cornea (Pachymetry).
Glaucoma is a chronic illness whose treatment currently centres on decreasing IOP and, depending on the disease progression, either administering appropriate drugs or taking a surgical route (or both).
For more information:
Asociación de Glaucoma para Afectados y Familiares, AGAG (Patients and families’ Glaucoma Association): www.asociaciondeglaucoma.es
Asociación Gallega de Glaucoma (Galician Glaucoma Association): http://www.asoglaucoma.info/asociacion/
High-Degree Myopia
Myopia is a defect in the refraction of the eye, in which images are focused in front of the retina instead of on it. This causes blurred vision of faraway objects, and optical correction is needed (eyeglasses or contact lenses) or surgery to achieve a correct vision. Low level, or simple, myopia is a very frequent alteration which requires the use of eyeglasses, nothing more.
However, when myopia is high (more than 6 dioptres) this is called high-degree myopia or pathological myopia. Unlike simple myopia, high-degree myopia is an ocular disease in which there is an excessive length to the eyeball which creates an anomalous stretch to all structures within the eye, particularly the retina which becomes thin, fragile and predisposed to alterations.
Having high-degree myopia does not just mean having many dioptres. Individuals with high-degree myopia also have a higher chance of suffering ocular complications. It is associated with a higher risk of cataracts, glaucoma or alterations in the back of the eye (choreoretinal atrophy, retinal degeneration, retinal detachment, alterations in the optic nerve head (optic disc) or macular degeneration). This risk increases the more elongated the eyeball. Although many of these complications have effective treatments, on occasions the consequences of these complications can severely affect the person with high-degree myopia. Early detection and treament of complications is fundamental in minimising harm.
For more information:
Asociación de Miopía Magna con Retinopatía, AMIRES (High-degree myopia and retinopathy association): www.miopiamagna.org
Diabetic Retinopathy
It is the most frequent vascular retinal disease. It comes about from damage produced in retinal blood vessels because of metabolic decompensation from diabetes. It can bring about a loss of vision, which in some cases can be very severe.
With elevated levels of glycemia, the walls of retinal blood vessels can change and become more permeable, allowing fluid to pass into extracelullar areas. In advanced cases, there can be a propagation of anomalous blood vessels which can bleed. The presence of blood in the vitreous (transparent gel which fills the eyeball) renders it opaque, causing a reduction in vision which often comes about extremely rapidly. It is often the case that a patient is not aware of the issue until the damage is severe.
Symptoms of diabetic retinopathy can be:
• Blurred vision and gradual vision loss.
• Patchy vision, or moving floaters
• Shadows or blind spots.
• Difficulties in seeing in the dark.
Patients with diabetes must maintain a strict watch on glycemia, blood pressure and plasma lipids. There are other factors which can negatively influence diabetic retinopthy such as obesity, smoking, and a sedentary lifestyle. Sufferers (more than 200 million people around the globe) should undertake regular retinal examinations, as generally diabetic retinopathy produces few symptoms until the damage is extensive.
Diabetic retinopathy can affect the macula (central part of the retina which is responsible for detail vision), or the periphery. Depending on which area is affected and the degree of advancement of the disease, eye specialists will choose different treament options, such as: photocoagulation with lasers, intravitreous injections or surgery (vitrectomy). Other sight complications associated with diabetes, like glaucoma or cataracts, will require specific treament.
For more information:
Federación de Diabéticos Española (Spanish Diabetics’ Federation): www.fedesp.es
Hereditary Retinal Distrophy
Retinitis Pigmentosa (RP)
Retinitis Pigmentosa is a group of degenerative and hereditary diseases of the retina which results in a poor function of the photorecptor cells, and the subsequent premature death of these cells. This is due to a genetic defect. Patients are born with the disease, but generally symptoms do not appear until they are in their twenties. The most frequent symptoms include night blindness, and a progressive reduction in the visual field until this reaches so-called tunnel vision. In advanced phases of the disease there is a also a loss of visual acuity, colour-blindness, loss of contrast, white-out or glare and, eventually, total blindness.
It is considered to be a rare disease because of its low prevalence, around 1 out of every 3700 people. RP is a complex and heterogenous pathology, both in its genetic origin and in its presentation and evolution in individual patients. There are currently more than 80 identified genes and hundreds of mutations which can produce Retinitis Pigmentosa. For this reason, obtaining a genetic diagnosis is not a simple task. Not only this, but with the currently identified genes, it is only possible to accurately diagnose around 60% of cases, meaning that there are most likely many genes and mutations still left undiscovered.
RP can present itself as an isolated condition or accompanied by extraocular syndromes (syndromic RP). The most common of these syndromes is Ushers, in which RP and deafness are present in different degrees. Ushers is one of the most common causes of deafblindness.
There is no treament or cure for RP, although there are promising lines of research in the fields of gene therapy and stem cells, offering some hope for the future. Some of the common complications which appear as RP progresses can be treated, such as Macular edema or Cataracts. Therefore, it is vital to have regular medical examinations with an expert ophthalmologist with experience in treating this pathology. It is also essential to protect RP eyes from light sources, especially blue and ultraviolet spectrum, which are the most damaging to the retina. It is recommended to use special filters, following the indications of an optician specialised in low vision.
For more information:
Asociación de Afectados por la Retinosis Pigmentaria en Gipuzkoa, Begisare: www.begisare.org
Asociación Retina Madrid- Fundación Retina España: www.retina.es
Asociación Retina Navarra: www.retinanavarra.org
Asociación Retina Asturias: www.retinosis.org
Federación Asociaciones Retinosis Pigmentaria España, FARPE: www.retinosisfarpe.org
Asociación de Sordociegos de España, ASOCIDE: www.asocide.org
Leber’s Congenital Amaurosis (LCA)
LCA is a congential distrophy of the retina which causes premature blindness. It is a genetically complex disease, inherited via the autosomal recessive route. There is currently a clinical trial with patients on gene therapy for LCA, caused specifically by the RPE65 gene. This gene is reponsible for a large percentage of LCA cases in Central and Northern Europe; however, in Spain the most frequent mutation is CRB1.
Stargardt’s Disease
Stargardt’s Disease is a hereditary retinal disease which affects the cone cells, and is characterised by macular degeneration (central area of the retina which has high sensitivity, and perceives fine details). Its prevalence is about 1 in every 10000 individuals approximately. In the majority of cases, there is a mutation in the ABCA4 gene, which is transmitted from parent to child via an autosomal recessive route. The onset of the symptoms occurs in childhood or during the teenage years. It begins with blurry central vision, blind spots (scotoma) in central vision, difficulty in adapting to low light situations and glare. In small children, typical macular lesions may not be present, even though sight loss occurs. This can slow down diagnosis. There is no treatment or cure currently, although promising research is happening.
However, it is important that Stargardt’s sufferers protect their eyes from sunlight using visors and glasses with special filters, as well as avoid the intake of Vitamin A supplements.
For more information:
Enfermedad de Stargardt (Stargardt’s Disease): stargardtpress.com
Other hereditary distrophies
There are numerous hereditary distrophies which affect the retina and other ocular structures, sometimes with very similar symptoms and clinical signs, making accurate diagnosis difficult. This is especially true in advanced phases of the diseases. Some of these are: Choroideremia, Rod-Cone Distrophy, Retinoschisis, Gyrate Atrophy, Bietti’s Crystalline Distrophy etc..
OTHER WEBSITES OF INTEREST
Asociación Acción Visión España: www.esvision.es
Asociación de afectados por Coroideremia: www.coroideremia.org
Asociación Gallega de Glaucoma: http://www.asoglaucoma.info