The retina is a mosaic of 130 million nerve cells that are sensitive to light.

Each eye has about 125 million rods and 7 million cones.

In normal physical conditions the human eye can distinguish about 10,000 different colours.

The eyelid muscles allow us to blink about 20,000 times a day.

The eyeball has an anteroposterior diameter of 24 mm.

The width of our horizontal visual field is 200º, whereas the vertical is 130º in normal conditions.

The average distance between the eyes is between 5.5 and 6.5 cm.

The eyeball weighs about 7.5 grams.

It is rare for people to have eyes with different tones of colour or completely different colours. Normally, a difference in colour is a result of a disease.

The visual field is the space covered by the vision of the eye when it is static and viewing a fixed point. Typically, the perimeter of the visual field and sensitivity within the different areas of the perimeter are assessed.

Blood is responsible for taking oxygen to all parts of the body, even the most remote. However, the cornea does not have any blood vessels, so oxygen is taken directly from the air.

The best light for reading or working on a computer is incandescent light (not fluorescent tubes) that comes from behind and from the side of the individual, avoiding reflections on the paper or the monitor.

They are exercises that are performed for the re-education of binocular vision in the event of symptoms such as eyestrain, headaches, eye pain, burning, tearing, dizziness and nausea caused by excessive close-up use, such as reading, computer use, etc. They are carried out by a professional technician who specialises in the muscular and sensory aspects of vision. These disorders also occur in school-age children, with symptoms of travel dizziness, difficulties in interpreting texts, spaced reading and errors in copying (reversal of letters or numbers).

Pupils in dark eyes dilate more slowly than in lighter-coloured eyes.

An increase in eye pressure is a result of several factors which can be summarised as mechanisms that prevent intraocular fluid (aqueous humour) from being removed properly through the normal channel. This can be mild and chronic—chronic glaucoma—or sudden, due to other processes. The ophthalmologist has to examine the patient urgently, especially in the event of acute forms.

It depends on the mydriatic drug (drops to dilate the pupil) used. Typically, the drops used to perform a normal examination of the eye make the pupil dilate very quickly, in about 15 or 20 minutes, and the effect disappears in about an hour and a half. At other times, when it is necessary to perform a stronger dilation, another type of drop is used, causing the mydriasis to take longer to diminish (it is particularly used in children to measure their correction). In these cases, the effects can last a week.

Sunglasses are a protection with filter to ensure that less radiation reaches the eye. There is no real necessity to protect the eyes from the sun, but wearing sunglasses is more comfortable, as less light penetrates our optical system. What you should never do is look directly at the sun, because this would cause severe damage to the retina.

Operations that require precision are usually performed with a microscope. Almost all operations involving the eyeball, therefore, are performed with a microscope. Operations performed on the eyelids or tear ducts do not usually require a microscope.

Surgeons and theatre nurses use microscopes that can be viewed by three people at the same time. An assistant and a theatre nurse usually observe what is being done during an operation.

Different magnifications are used, and they typically range from 4.5x to 25x.

Yes, they can recline, move, etc., so anybody can undergo an operation.

It is the result of tear secretion and eyelid disorders that can cause redness, itching, burning, the sensation of a foreign body in the eye and eyestrain. Proper lubrication of the eye is achieved with a correct balance of good-quality tear production and the normal functioning of the eyelids. When this balance is broken or altered by external factors, tear production decreases, and there is a propensity for dry eye to develop.

Normal cellular aging in humans leads to reduced tear production. In fact, it is estimated that between the ages of 10 and 40, tear production is reduced by 50%. In addition, other common causes of dry eye are eye infections (conjunctivitis, corneal ulcers, etc.), external or environmental factors (sun, wind, chlorine, contact lenses, etc.) and certain medication. Cosmetics and cleansing creams can also cause irritation and disrupt tear production.

In situations where dry eye symptoms occur, such as contact with chlorine in swimming pools, exposure to the sun or wind, air conditioning and eye strain (reading, driving, etc.), eye drop use should be increased. If symptoms persist, however, patients should see an ophthalmologist to assess the possibility of using other treatments.

The symptoms of a detached retina are the presence of flashes of light (photopsia) or objects floating in the vitreous humour and, occasionally, a progressive shadow and loss of vision. It is important to contact your ophthalmologist as quickly as possible. It is not an emergency, but it needs to be operated on as soon as possible by a surgeon.

If a patient who has been operated on for cataracts or other intraocular processes suffers a severe loss of vision with noticeable eye redness and pain, he or she must go and see an ophthalmologist urgently and without delay, as the emergency could threaten the vision of the eye.

Yes, it is an emergency, but relatively speaking, as it is possible to wait 3 or 4 days. It is necessary to examine the eye, because the symptom could indicate the onset of decompensation, which can cause severe loss of vision. This distortion is sometimes not due to decompensation, but it always needs to be confirmed.

Eye secretions are usually symptoms of external processes such as conjunctivitis or other infections or inflammation. They do not usually constitute a serious condition and can typically be treated with topical antibiotics.

The amblyopic eye has not developed vision correctly, but all eye structures are in good condition. Vision develops from birth, and the eye becomes increasingly more capable of perceiving objects, which is called visual acuity. The amblyopic eye does not develop visual acuity for various reasons. The eye is anatomically correct, i.e. its structures are normal, but vision has not developed.

There are several eye diseases that are linked to chromosomal inheritance and even the genetic defect is determined. Diseases of all parts of the eye can be inherited. The most common is retinitis pigmentosa.

Eye tumours can occur on any tissue, but the most common in adults is choroidal melanoma, a malignant tumour that can be treated with radiotherapy and other treatments with notable success. Malignant tumours can also appear on the conjunctiva, the lacrimal gland and the orbit. Benign tumours can also appear, but they can be easily dried out. In children a retinal tumour known as retinoblastoma can appear, which looks like a white pupil and must be treated as soon as possible, as it can be life-threatening if appropriate treatment is not performed.

It is important to know how old the patient is, because age affects the eye and determines the kind of pathology that can occur.

The most important thing for a patient to do is to heed the advice of the doctor in terms of the continued treatment. Patients often believe that they will forget to ask the doctor something important or they have to ask a lot of questions about the treatment. The doctor is fully aware of the patient’s situation and explains the treatment and how it can affect the patient’s life. It is, therefore, very important for the patient to focus on what the doctor says, the guidance he gives and the limitations that the patient could experience.

Most patients who suffer rejection of a corneal transplantation experience reduced vision. Other symptoms include the appearance of foreign bodies and being dazzled or bothered by light.

The patient should avoid strenuous activities and, in particular, avoid direct trauma to the eye.

Nowadays, there are several techniques. The most popular for small refractive errors, such as myopia, hyperopia and astigmatism, is LASIK. In special cases there are other options available: phakic lenses, crystalline extraction, intracorneal lenses or intrastromal rings.

The patient can generally have acceptable or near-maximum vision within a few hours. Occasionally, however, it can take up to a week for vision to improve.

For the first two weeks, in particular, the patient should avoid rubbing the eyes, going swimming in a public pool and using eyelid make-up.

In general, the patient can lead a normal life, unless there is gas inside the eye, in which case the patient should heed the advice of his doctor. Flying above 600–800 m and travelling over high mountain passes, either by train or car, should be avoided. If such needs arise, the ophthalmologist should be consulted.

Yes, as can all post-operative patients, irrespective of the pathology, provided that their physical condition permits and several days have passed since the operation.

Yes, any patient can wear tinted glasses to avoid discomfort from sunlight. The patient generally chooses the most appropriate filter, but it should be an approved model.

If there is no gas or silicone oil, the patient can sleep in any position. If there is no covering element (gas or silicone oil), the patient’s position is unimportant.

The head should normally be tilted forward so that the gas does not contact the front of the eye, but the surface of the back of the eye. The length of time that the head should be kept in this position depends on the quantity of gas given.

When they have very little gas, i.e. one fifth or less in the eyeball, they can travel by air without a problem. If, however, they have a larger amount, they cannot fly, because the change in air pressure makes the gas bubble expand, which can cause ocular hypertension and damage the optic nerve.

Yes, provided that the patient takes appropriate precautions to protect himself/herself from the light.

The time between photodynamic therapy treatments is three months. Occasionally, a patient can be re-treated if there is an early recurrence of subretinal neovascularisation.

A lot of research work in this field still needs to be carried out for stem cells to be applied to patients suffering from eye diseases, especially relating to the retina.

Age-related macular degeneration is one of the greatest challenges in ophthalmology today. We know that there are two types: the dry form and the wet form. The dry form is experienced by patients who are slowly losing their vision. It has been demonstrated that treatment with antioxidants and vitamins can reduce vision loss, although the slowing down of the process is not particularly spectacular. The wet form, which is so called because fluid is produced in the macula, is the most destructive, and current treatment involves the combining of photodynamic therapy, which started to be used some years ago, with other treatments, which has produced more positive results. Each year, new possibilities appear, which help in the fight against this disease.

Patients can notice small floating objects, which are capsular remains in the vitreous space, but after a few days they normally disappear. Photocoagulation with YAG laser is applied to the capsule holding the artificial intraocular lens, which over time becomes opaque, resulting in the patient losing vision. Photocoagulation with YAG laser is painless and quickly achieves visual improvement.

It is much more likely for haemorrhages to occur after surgery, especially if a vitrectomy has been performed, in the case of patients with diabetic retinopathy. This is due to the vessel walls being extremely fragile in these patients and more prone to bleeding.

In general, the patient should continue taking the prescribed medication until he or she is examined again by the specialist. Occasionally, the duration of the treatment is already determined. If in doubt, the patient should consult the specialist to find out when to stop taking the medication.

It is to ensure that the patient loses as little visual acuity as possible.

The patient should stay out of the light and remain in semi-darkness for 48 hours. During this time, he or she can watch TV, but only with glasses provided by the clinic. After this time, we recommend that the patient stays out of the sun for a week.

If it is the first time, we do not recommend it, because of the small risk of visual acuity loss associated with the treatment itself. From the second session, if no complications have arisen, the treatment can be performed on both eyes on the same day.

Occasionally, the treatment can be brought forward if the angiography shows that the subretinal membrane has been reactivated.

Ocular occlusion is used to make the diseased eye work harder by patching the healthy one, as in amblyopia. The intensity of the patching of the good eye to develop the vision of the amblyopic eye depends on the degree of vision and the age of the patient.

It is prescribed in cases of subretinal neovascularisation, which is a degenerative disease that develops secondary to various kinds of eye diseases, particularly AMD and myopia. Irrespective of the underlying pathophysiology, retinal neovascularisation can lead to severe and irreversible central vision loss. Photodynamic therapy is also currently being performed in some cases of diffuse posterior epitheliopathy, which is a degenerative disease of the retinal pigment epithelium in the macular area.

Photodynamic therapy acts directly against the subretinal neovascularisation, trying not to cause damage to the supra-adjacent sensory tissue—in this case the retina—, as the therapy only acts at membrane level, leaving the retina virtually untouched, hence the advantage of this type of treatment over conventional argon laser treatment.

Yes, after any eye operation, although it is advisable to wait several days for the scars to heal. It normally takes ten to twelve days to return to a normal life. It is always best to consult the doctor to find out about the risk factors.

All eye operations can be carried out at any time during pregnancy. However, if surgery is optional and there is no risk to the eye, it is advisable for the patient to wait until after birth for the sake of comfort and because some refractive surgery can vary when performed on pregnant patients.

Enucleation is the complete removal of the eyeball, leaving only the eye muscles intact.

Evisceration is the removal of all ocular tissue, leaving only the sclera (the outer wall) intact. The cavity can then be filled with material to simulate the eye and a prosthesis fitted to the surface so that it has the same appearance as the other eye. Evisceration can be performed in many cases, except in tumours or when the sclera is severely damaged.

It is a diagnostic technique to determine pathological and abnormal structures in the blood vessels and the different layers of the retina. It can be used in cases of macular degeneration, diabetic retinopathy, vasculopathy and many other macular disorders.

Angiography is a technique used to delineate retinal or choroidal cases. Different contrasts are used, usually sodium fluorescein or indocyanine green. The scan is also useful for the diagnosis of other retinal diseases, such as pigment epithelium. In general, angiography is used to study many retinal diseases and their diagnosis.

The most important is to ensure that the patient is not allergic to the substances to be injected.

It is not counterproductive for any eye treatment.

Indocyanine green angiography is a technique used in some cases of AMD and serves to define the neovessels and, occasionally, to diagnose other diseases. Fluorescein angiography is the standard technique for studying blood vessel diseases and the retina in general.

Fasting is not necessary in either case, although it is not advisable to perform any contrast techniques after a heavy meal.

It is a grid of straight horizontal and vertical lines with a central point, used as a tool to detect visual disturbances in patients with scotoma or other anomalies.

Occasionally, young patients with visual defects cannot follow the class normally, as they have difficulty seeing objects from a distance. This can cause the child to be distracted and lose concentration and interest in continuing with his or her studies. It is, therefore, very important for all children who are underachieving at school to have an eye examination to rule out this possibility.

Obviously, if there is a vision problem, at any age. During their schooling it is obligatory for all children to be examined at the age of four or five to determine their visual ability.

Accommodation normally needs to be paralysed by applying drops before the eye test can be performed.