Age Related Macular Degeneration (ARMD)

 

It is a degenerative diasease of retina(Macular region). Usually happens to older people(age more than 50 yrs). 

Symptoms:

1) Problem in Face Recognition

2) Reading & driving problem

3) Blank areas in the central part of the field of vision

Types: There are 2types of Macular Degeneration-

1) Dry ARMD: Very common form, approx 80% of the ARMD happens in dry form. 

2) Wet ARMD: This is less common, approx 20% of the ARMD happens in wet form. It has more severe effect than dry form.

Risk Factors in ARMD:

• Cardiovascular disease
• Family history of ARMD
• High saturated fat diet
• Hypertension
• Obesity
• Smoking

Treatment: There is no effective treatment for dry ARMD except, the provision for Low Vision Aids. Though dietary supplements containing antioxidant vitamins, lutein and zeaxanthin may reduce the risk of dry ARMD progressing to the more severe stage of the wet ARMD. LASER treatment for wet ARMD to prevent further progress of the disease.

Prevention: 

• Healthy diet
• Regular exercise
• Use Blue Light Protection Ophthalmic Lens
• Wear Sunglass
• Yearly eye check up by an Ophthalmologist or Retina Specialist after 50yrs of age

Relationship between Visual Functions & Driving Performance

Good Vision → Safe Drive → Save Life

Driving Performance ∝ Visual Functions

80% of the information we received from the environment is visual and rest 20% through non-visual such as ears, skin etc. The commonest visual function tests that are performed at clinics and hospitals are: Visual Acuity, Visual Field, Colour Vision and Contrast Sensitivity.

Different testing procedures and standard is followed by different countries at the time of issuing a Driving Licence. In India, visual acuity and peripheral field of vision(side vision) is tested for driving licence. In other countries more rigorous examinations are used to assess visual functions, such as measurements of visual field, dark adaptation, stereopsis and glare recovery.

There are several factors affecting driver behaviour such as-

• Vision
• Fatigue
• Alcohol
• Vehicle Visibility
• Road Lighting
• Motor Co-ordination
• Accident Proneness
• Attention

Good visual acuity allows the driver more time to react against obstacles and signs, where as a driver with poor visual acuity requires the obstacle to be closer before its significance can be appreciated, leaving less time to react. He or she must be more alert, and will therefore fatigue faster.

Colour vision defects may be hazardous if they cause confusion between red, green and amber colour signal lights. According to Coles and Brown, a red colourblind person requires about 4times the normal intensity to see a red light.

Good peripheral vision is essential as significant increase of traffic day by day.

Stereopsis is important for judging the nearby vehicles.

Many drivers complain about glare during night driving. This is mainly due to dirt & scratches on the windscreen causing scattering of light.

Glare recovery time(the recovery time of retinal sensitivity) not only increases with age but also with the use of tinted spectacles or windscreen.

Alcohol impairs mental efficiency and slows the response to a hazardous situation. It also can cause diplopia(double vision) and blurring of vision.

Precautions to be taken by the Driver: 

1. First time spectacles or contact lens user should be well adjusted before start driving
2. Thick rim frames should be avoided as it may restrict peripheral vision(rimless frame is ideal)
3. Lenses of the spectacles should be high impact resistant(eg- polycarbonate and MR8)
4. If bifocals are required  they should be dispensed with the smallest possible bifocal segment. Progressive lenses are ideal for driving
5. Tinted spectacles should not be worn for night driving

 

Blindness

The term 'Blindness' means inability to perceive light. So, from a practical point of view, a person is said to be blind when he can not perform ordinary work.

In India, economically blind persons are those who, with both eyes open, can not count fingers beyond 3metres in broad daylight.

Major Causes: 

• Cataract
• Refractive Error
• Corneal Opacity

There are 8 million blind & 54 million partially-blind persons in India.

Causes of Blindness according to Age-group: 

1. Infants & Pre-school Age: Congenital cataract & glaucoma
2. School Going Age: Congenital & developmental anomalies, xerophthalmia, trauma
3. Adult Life(20-50yrs): Myopia, neurological disease, industrial injuries
4. Late Adult Life(50-70yrs): Cataract, glaucoma & diabetes
5. Elderly Persons(Above 70yrs): Cataract, glaucoma & Age Related Macular Degeneration

Prevention: In India, 80% of blindness is preventable or curable, but the problems are ignorance, superstition, poverty, illiteracy etc. Some preventive measures are as follows:

• Always use own towel or handkerchief
• Properly clean hands before touching to the eyes
• Try to avoid Kajal or Surma unless prescribed by eye doctor
• Use safety goggles during Diwali or Dussehra or within industrial working environment
• Retinal health check up once in every two years
• Yearly power check up 

Rehabilitation: 20% of blindness is incurable. These persons have to rehabilitated and trained properly so that they can earn their livelihood. Governments & Social Welfare Organizations should take proper initiative regarding education, training & rehabilitation for all blind persons in India so that they feel privileged. 

Visual Perception

Visual perception is the ability to perceive our surroundings when light falls on the retina. These are 4types:

1) Light Sense

2) Form Sense

3) Sense of Contrast

4) Colour Sense

Light Sense: It is the ability to perceive variations in the degree of light. This is assessed in 2ways:

A) Light Minimum

B) Light Difference or Differential Light Threshold

A) Light Minimum: Light minimum is the minimum amount of light energy which, when projected on the retina, causes a visual sensation. 

It varies greatly with the degree of adaptation of the eye at the time of observation. When the eye is dark-adapted(adaptation in dim light), the light minimum is very small as compared to when it is observed in a light-adapted(adaptation in bright light) eye.

• Dark adaptation is delayed by prolonged exposure to bright light.
• Delayed dark-adaptation occurs in Retinitis Pigmentosa(degenerative disease of Retina) & in case of vitamin-A deficiency 

B) Differential Light Threshold: The smallest difference in light intensity that can be appreciated.

Form Sense: The ability to discriminate between the shapes of the objects. This can be assessed by Visual Acuity(resolving power of the eye)

Sense of Contrast: It is the ability to perceive slight changes in luminance between regions which are not separated by definite borders. 

Contrast Sensitivity is reduced in many ocular diseases such as Glaucoma, Macular disease, Cataract, Refractive errors etc. 

In case of poor contrast sensitivity, the person may face the following problems:

• Difficult to see facial expression
• Difficulty in navigating steps of the staircase.
• Problem in night driving

Colour Sense: It is the ability to distinguish among different colours. The appreciation of colours occur only in photopic vision(bright light vision). 

Optometric Abbreviation

AC- Anterior Chamber (between Cornea and Iris, filled with transparent liquid- Aqueous humour)

Acc- Accommodation(mainly occur in case of near vision)

ACT- Alternate Cover Test

Add- Addition (additional plus spherical power needed to improve near work)

AL- Axial Length

APCT- Alternate Prism Cover Test

APD- Afferent Pupillary Defect

ARMD- Age Related Macular Degeneration (usually occurred above 50 yrs age) 

BE- Both eyes

BVD- Back Vertex Distance (back surface of the spectacles to front surface of cornea)

CT- Cover Test

DC- Diptres Cylinder

DS- Dioptres Sphere

DV- Distance Vision

h/o- history of

IOL- Intra Ocular Lens (artificial lens which is implanted after cataract surgery)

IOP- Intra Ocular Pressure (fluid pressure inside the eye)

LP- Light Perception(it is measurement of visual acuity-when patient is unable to see hand movements)

LVA- Low Vision Aid(devices which improve visual performance)

NLP- No Light Perception(total blindness)

NPC- Near Point of Convergence

NV- Near Vision

OD- Doctor of Optometry ; Oculus Dexter (Right Eye)

OL- Oculus Laevus (Left Eye)

OS- Oculus Sinister (Left Eye)

OU- Oculus Uterque (Each Eye)

PD- Pupillary Distance(distance between centre of Right & Left pupil)

PERRLA- Pupils Equal, Round, Reactive to Light & Accommodation

PGP- Previous Glass Prescription

PL- Perception of Light

Px- Patient

RAPD- Relative Afferent Pupillary Defect

Rx- Prescription

SCL- Soft Contact Lens

Sx- Symptoms

TBUT- Tear Break Up Time

VA- Visual Acuity(spatial resolving power of the eye)

Ocular Injuries

Any kind of eye injury is known as Ocular Injury. The visual impairment as a result of an eye injury may vary from slight reduction in visual acuity to total blindness.

A) Mechanical Injuries-

1) Contusion Injuries: It may results from flying blunt objects(e.g. ⚽)

2) Perforation Injuries: It may results from sharp objects(e.g. 🖉)

B) Non-mechanical Injuries-

1) Chemical Injuries: Most of the chemicals are harmful to eyes. Ex- Acid, Alkali etc.

The severity of the burn depends on the concentration of the chemical, the exposure duration & the pH of the solution. All solutions are irritating to the eye, but is rarely serious if their pH is  ≥ 2.5 . Alkali burns are more severe than acid burns.

Apart from acids & alkalis there are few other chemicals like Organic Solvents(e.g. alcohol), Surfactants(e.g. soap), Irritants & Allergens(e.g. pollen) & Aerosols(e.g. deodorant) which are also harmful.

Ideal treatment is to neutralize the chemical. Immediate & prolonged irrigation with normal water should be carried out. 

2) Electrical Injuries: The main sources of electrical injuries are lightning & high voltage electrical appliances.

3) Radiation Injuries: The major natural source of electromagnetic radiation is sun. Fortunately, the atmosphere acts as a filter, absorbing a significant amount of the harmful radiation. The highest intensity of radiation that penetrates the atmosphere is in the visible range(400-800nm). The effect of radiation will depend upon the wavelength of the radiation & the photon energy.

• Long wavelength radiation has low photon energies. Infra-red radiation has 0.01 to 1 eV(electron volt) range

• Visible & short wavelength radiation have higher photon energies. For visible & UV radiation, the photon energy range is 1 to 4 eV.

4) Thermal Injuries: There are 2types of thermal injuries- flame( e.g. oven) & contact burns(e.g. molten metal).

All types of eye injuries- mandatory check up by an Ophthalmologist. 

Preventive Measures: A detailed history taking at the time of Vision test is very important. Few examples-

• Sportsperson- We will recommend Contact Lens or for Spectacles user high impact resistant lens material like MR8 /Polycarbonate 
• Two-wheeler Rider- Anti Reflection Coating lens to improve vision clarity by reducing unwanted light reflection. 
• Occupational (Mechanical Engineer)- Safety goggles is mandatory.

Also parents should educate their children regarding possible ocular hazards.

 

Colour Vision

 

Colour Vision is the ability to distinguish among different colours. The sensation of colour is subjective. Individuals are taught names for their colour sensations and subsequently use these names whenever the same sensation is obtained. By the age of 3 a child can correctly identify a colour. So, Colour Vision Test can be done at the age of 3.

There are 3 types of Photoreceptor cells in Retina-

1) Red Sensitive

2) Green Sensitive

3) Blue Sensitive

which combinedly perform the function of Colour Vision. 

In Colour Vision Deficiency(CVD) which is more commonly known as Colour Blindness, sensation of one or more primary colours(Red, Green & Blue) is either defective(anomalous) or absent(anopia).

Importance of Colour Vision:

Colour Vision defects can affect learning abilities and reading development. It also can limit career choices.