Eye Disorders

Human vision is dependent on the successful interaction of optical
structures in the eye. When these structures malfunction, many
eye disorders occur. The key to the treatment and resolution of
these eye disorders is early detection through regular eye exams
and prompt consultation with an ophthalmologist when
problems occur.

Refractive Errors

The cornea is the clear front part of the eye. It is like a window that
controls and focuses the light coming into the eye. If the cornea has
an irregular shape, the light does not focus properly. Everything
looks blurry. These eye disorders are called refractive errors.

Classification

• Myopia( nearsightedness) — Clear vision close up but blurry in
  the distance
• Hypermetropia( farsightedness) — Clear vision in the distance
  but blurry close-up
• Presbyopia — Inability to focus close up as a result of ageing
• Astigmatism — Focus problems caused by the cornea

Hypermetropia and Presbyopia

Rays of light reflected off objects in front of the eye are focused behind
the retina as shown. Such persons can see well in the distance provided
they are young and the refractive error is not large. Hypermetropia
actually forms a stage in the normal development of the eyes. At birth,
practically all eyes are hypermetropic to the extent of 2.5 to 3.0 Diopters
and as the growth of the body proceeds, the length of the eye increases,
until adolescence is passed. So eye should theoretically be “normal” in
size and refraction. Hypermetropia, therefore, represents an imperfectly developed eye when it persists in adult life.

Causes

Hypermetropia

1. The eyeball is shorter than it should be.
2. The corneal may be flatter than it should be (curvature hypermetropia).
3. Change in the refractive index of the crystalline lens of the eye(cataract)
4. Injury to the eye with dislocation of the crystalline lens of the eye.

Presbyopia

1. After or near 40 years of age.
2. Age-related loss of accommodation due to decreased elasticity of the crystalline lens surface.

Symptoms and signs

Hypermetropia

1. Eye-strain
2. Watering
3. Redness of the eyes
4. Headaches in the later part of the day.
5. Convergent squint (young children )

Presbyopia

1. Blurring of text, especially after some time.
2. Difficulty in reading/writing and doing near work.

Myopia

The person affected is able to perform near work without correction,
and has difficulty defining distance objects. Rays reflected off an object
in front of the eye focusing in front of the retina.

Causes

• Increased length of the eyeball.
• Increase in the curvature of the cornea or the surfaces of the
  crystalline lens.
• Cataract
• Divergent squint(children)

Symptoms and signs

• Can not see distant objects
• The child makes too many mistakes copying things from the
  blackboard.

Astigmatism

Rays of light reflected off objects in front of the eye are focused differently
on the retina of the eye because more than one focal point exists.

Causes

• Distortion of the corneal surface in one or multiple planes
• The error of curvature(vertical curvature is greater than
  the horizontal )
• Error of centring
• The error of refractive index.
• Injuries to the eyes
• Surgeries to the eyes.

Symptoms and signs

• Headaches
• Low vision
• Reduced vision for distance and near
• Watering
• Redness
• Foreign body sensation in the eyes as the day progresses
• Running together text while reading
• Can not see well distant or near objects (more so the difficulty
  is with distant objects)
• Compensatory tilt in the head posture

Treatment

Hypermetropia

• A convex lens in eyeglasses
• Contact lens
• Refractive Surgery(LASIK)

Myopia

• A concave lens in eyeglasses
• Contact lens
• Refractive Surgery
• Lens implants(special rigid contact lenses to flatten the cornea)
• Pin-hole glasses(low myopia)

Presbyopia

• Reading glasses
• Bifocals glasses
• Contact lenses
• Monovision LASIK
• Intraocular Lenses

Astigmatism

• Gas permeable lens (make the surface of the eye spherical)
• Soft toric contact lens
• Eyeglasses(cylindrical lens power)

Cataract

A cataract results when the normally transparent lens of the eye
clouds, blurring vision. Most cataracts are age-related,
advancing slowly and progressively until functional blindness occurs.

Cataracts can be successfully treated through a surgical procedure
that removes the damaged, natural eye lens and replaces it with a
permanent, intra-ocular lens implant. The procedure has over a
90 per cent success rate. After refractive errors, cataracts are the
most common eye disorders.

Classification

• Subcapsular cataract (occurs at the back of the lens)
• Nuclear cataract (forms deep in the nucleus of the lens)
• Cortical cataract (occurs in the lens cortex)

Causes

• Ageing
• Diabetes
• Eye inflammation
• Eye injury
• Family history of cataracts
• High farsightedness
• Long-term use of corticosteroids (taken by mouth)
• Radiation exposure
• Smoking
• Surgery for another eye problem
• Too much exposure to ultraviolet light(sunlight)

Symptoms and signs

• Adult cataracts develop slowly and painlessly.
• Vision in the affected eye or eyes slowly gets worse.
• Mild clouding of the lens often occurs after age 60, but it may
  not cause any vision problems.
• By age 75, most people have cataracts that affect their vision.
• Being sensitive to glare
• Cloudy, fuzzy, foggy, or filmy vision
• Difficulty seeing at night or in dim light
• white, wedge-like opacities
• Double vision
• Loss of colour intensity
• Problems seeing shapes against a background or the difference
  between shades of colours
• Seeing halos around lights
• Decreased vision, even in daylight
• Frequent changes in eyeglass prescription

Investigations

• Standard eye examination
• Slit-lamp examination

Treatment

• Surgery

The main treatment for a cataract is surgery to remove it. If a cataract is not bothersome, surgery is usually not necessary

• Self-Care

• Better eyeglasses
• Better lighting
• Magnifying lenses
• Sunglasses
• Changes around the home (to avoid falls and injuries.)

Complications

• Permanent vision problems.
• Hyper-mature cataract

Prevention

1. Control cataract-causing diseases
2. Avoid exposure to causative factors
3. Wear sunglasses outside during the day(to filter out UV rays)
4. Stop smoking

Macular Degeneration

It occurs when the macula of the eye loses its proper structure. The blood
vessels and the proteins present in the body including cholesterol affect the eyesight of people suffering from this disease. Age-related macular
degeneration is the leading cause of blindness in most developed countries.

Causes    

• Damage to the area around blood vessels that supply
  the macula.
• Hereditary
• Caucasian race
• Cigarette smoking
• High-fat diet
• Female gender
• Obesity

Classification

• Dry macular degeneration

Occurs when the blood vessels under the macula become thin
and brittle. Small yellow deposits, called drusen, form. Almost
all people with macular degeneration start with the dry form.

• Wet macular degeneration

Occurs in only about 10% of people with macular degeneration. New
abnormal and very fragile blood vessels grow under the macula. This
is called choroidal neovascularization. These vessels leak blood and
fluid. This form causes most of the vision loss associated with
the condition.

Symptoms and signs

• Blurred vision
• Damaged central vision

1. objects look distorted and dim
2. colours look faded
3. blurred/dark spot gets larger and darker.
4. vision loss can occur very quickly 

• Can not read print or other details
• Can walk and perform most routine activities
• May need more light to read or perform everyday tasks.
• Straight lines appear distorted and wavy.
• Not able to recognize faces until they are close.
• Complete vision loss never occurs

Investigations

• Complete retinal check-up
• Fluorescein angiogram
• Fundus photography
• Optical coherence tomography (OCT)

Treatment

Once dry macular degeneration becomes advanced or severe, no treatment
can restore lost vision.

• Medicines

AREDS formula (vitamin C + beta-carotene+ zinc+copper), lutein,
zeaxanthin

• Laser photocoagulation
• Photodynamic therapy
• Anti-angiogenesis, anti-VEGF therapy
• Low-vision aids ( special lenses)
• Self-testing at home with an Amsler grid. Test each eye individually
  with the vision correction, you normally wear for reading.

Complications

Loss of vision

Prevention

• Don’t smoke
• Eat a healthy diet ( high in fruits and vegetables and low in animal fat)
• Exercise regularly
• Maintain a healthy weight

Glaucoma

Glaucoma is a disease of the optic nerve. If the aqueous humour does
not drain properly, the intraocular pressure builds, damaging the optic
nerve and causing blind spots to develop. When the entire nerve is
destroyed, blindness results. If glaucoma is detected and treated in
the early stages, loss of vision can be averted. Glaucoma is the most
common cause of blindness in the world.

Types

• Open-angle (chronic) glaucoma, also called
  Angle-closure (acute) glaucoma
• Congenital glaucoma
• Secondary glaucoma

Causes

1. Open-angle glaucoma

• Hereditary
• African race

2. Angle-closure (acute) glaucoma

Dilating eye drops and certain medications

3. Congenital glaucoma

• Hereditary
• Abnormal development of the fluid outflow channels in the eye

4. Secondary glaucoma

• Drugs( corticosteroids)
• Eye diseases (uveitis)
• Systemic diseases

Symptoms and signs

1. Open-angle glaucoma

• Most people have no symptoms until they begin to lose vision
• Gradual loss of peripheral vision (tunnel vision)

2. Angle-closure glaucoma

• Symptoms may come and go at first, or steadily become worse
• Sudden, severe pain in one eye
• Decreased or cloudy vision
• Nausea and vomiting
• Rainbow-like halos around lights
• Red eye
• Eye feels swollen

3. Congenital glaucoma

• Symptoms are usually noticed when the child is a few months old
• Cloudiness of the front of the eye
• Enlargement of one eye or both eyes
• Red eye
• Sensitivity to light
• Tearing

Investigations

• Gonioscopy (use of a special lens to see the outflow channels of the angle)
• Tonometry test (to measure eye pressure)
• Optic nerve imaging (photographs of the inside of the eye)
• Pupillary reflex response
• Retinal examination
• Slit lamp examination
• Visual acuity
• Visual field measurement

Treatment

1. Open-angle glaucoma

• Eye drops
• Pills to lower pressure in the eye
• Laser treatment
• Surgery to open a new outflow channel.

2. Angle-closure glaucoma

• Drops, pills, and medicine IV( to lower pressure)
• Emergency operation( iridotomy)

3. Congenital glaucoma

Surgery( to open the outflow channels of the angle)                                       

Prevention

• Early diagnosis
• Careful management is the key to preventing vision loss.
• Everyone over age 40 should have an eye examination at
  least once every 5 years

Diabetic Retinopathy

Diabetic retinopathy is damage to the eye’s retina that occurs
with long-term diabetes

Causes

• Damage to blood vessels of the retina.
• More severe diabetes for a longer period of time

Classification

• Non-proliferative
• Proliferative

Symptoms and signs

• Blurred vision and gradual vision loss
• Floaters
• Shadows or missing areas of vision
• Difficulty seeing at night time
• No symptoms before major bleeding occur in the eye

Investigations

• Retinal photography
• Fluorescein angiography

Treatment

Treatment usually does not reverse the damage that has already
occurred, but it can help keep the disease from getting worse.

Medical

• Photo-coagulation

1. laser photo-coagulation is used to treat macular oedema.
2. Panretinal photo-coagulation treats a large area of the retina

• Vitrectomy( to repair retinal detachment)
• Drugs (to prevent abnormal blood vessels from growing)
• Corticosteroids (injected into the eyeball )  

Self-Care

• Make sure your home is safe so you do not fall
• Organize your home so that you can easily find what you need
• Get help to make sure you are taking your medicines correctly

Complications

• Blindness
• Glaucoma
• Retinal detachment

Prevention

• Tight control of blood sugar, blood pressure, and cholesterol
• Do not smoke.
• Avoid high-impact exercises, which can strain already
  weakened blood vessels in the eyes.
• Regular eye examination in case of–

1. Children older than 10 years who have had diabetes for 3 – 5
   years or more
2. Adults and adolescents with type 2 diabetes soon after diagnosis
3. Adolescents and adults with type 1 diabetes within 5 years
   of diagnosis

Strabismus

Strabismus is a physical defect. One or both of the eyes are
misaligned and point in different directions. One eye may look
ahead while the other eye points up, down, in, or out. Strabismus
is more common in children than in adults. It is more commonly
known as cross-eyed or wall-eyed.

Causes

• Weak eye muscles
• Graves’ disease
• Traumatic brain injury
• Stroke
• Cerebral palsy
• Guillain-Barre syndrome
• Diabetes
• Damage to the retina in children who are born
  prematurely
• Hemangioma near the eye during infancy
• Injuries to the eye
• Tumour in the brain or eye
• Vision loss from any eye disease or injury

Symptoms and signs

• The eyes do not move together and may appear
  crossed at times.
• The other eye will appear turned out, up, or down from
  wherever the first eye is focused.
• Depth perception loss
• Double vision
• Vision loss

Investigations

• Corneal light reflex
• Cover/uncover test
• Retinal exam
• Standard ophthalmic exam
• Visual acuity
• Neurological examination

Treatment

• Glasses
• For amblyopia, a patch is placed over the better eye. This forces
  the weaker eye to work harder.
• Eye muscle surgery
• Eye muscle exercises (help keep the eyes straight)
• Surgery(to straighten the eyes.)