Primary Eye and Vision Care

Primary Eye and Vision Care encompasses a range of services aimed at maintaining optimal eye health, including regular eye examinations, vision correction, and management of ocular diseases.

• refers to the first level of contact between individuals and the health system for eye and vision-related needs.

  • Prevention

  • Early detection

  • Basic management

  • Referral of complex cases

Epidemiology

• Prevalence - total number of cases (old + new) in a population at a given time

• Incidence - number of new cases during a specific period

• Morbidity - frequency of disease in a population

• Mortality - frequency of deaths caused by a disease in a given population over a certain timeframe.

• Endemic Disease - Disease consistently present in a region (ex. Trachoma in poor rural communities in Africa)

• Epidemic - Sudden increase in disease occurrence (e.g., viral conjunctivitis outbreaks)

• Pandemic - Worldwide spread of disease (ex. COVID-19, Myopia)

The most common cause of visual impairment worldwide

• Uncorrected Refractive Error

Leading cause of blindness worldwide

• Cataract

Leading cause of reversible blindness worldwide

• Cataract

Leading cause of irreversible blindness

• Glaucoma

Leading cause of childhood blindness in developing countries

• Vitamin A deficiency (Xerophthalmia)

Most common preventable infectious blindness

• Trachoma

Prevention and Control of Eye and Vision Anomalies

Important Approaches Related to Disease Progression

Levels of Prevention

Primary Prevention

Actions aimed at preventing eye diseases before they occur

Examples;

• UV protection

• Nutrition (Vitamin A)

• Health Education

Secondary Prevention

Early detection and treatment of disease

Examples:

• Vision screening

• Glaucoma screening

• Diabetic Retinopathy screening

Tertiary Prevention

Reducing complications of established disease

Examples:

• Cataract surgery

• Retinal surgery

• Vision rehabilitation

Levels of Eye Health Care

Primary

First point of contact in the health system

Services:

• Vision screening

• Refraction and prescription of glasses

• Ocular health education

• Referral of complex cases

Key role:

• Detection

• Prevention

• Referral

Secondary

Specialized care provided at the district or provincial hospital

key roles:

• Specialized Diagnosis and Management

Tertiary

Highest level of specialized care

Service: Complex eye surgeries

Key Role:

• Advanced Treatment

Refractive Status

signifies the relation of the refracting system of the eye to its axial length by indicating the focal length of the eye or the position of its principal focus as compared to the position of the retina, with positive accommodation inactive

Optic Constants

Index of Refraction

Ametropia

• Axial

• Refractive

Hyperopia

• Hypermetropia

• Kastner - first person to mention the condition of farsightedness

• Donders - use the term hypermetropia

• Helmholtz - use the term hyperopia

S/sx

• BOV at near

• Eye Strain

• HA after close work

• Squinting at near

• Diplopia at near

• Eye fatigue

Degree

• Low hyperopia - +2.00 or less

• Moderate hyperopia - +2.25-+5.00

• High hyperopia- +5.00 and up

Sorsby’s Classification

• Correlation hyperopia- includes up to +6.00

• Component hyperopia- includes above +6.00

Treatment

• Prescription glasses

• Contact lenses

• LASIK

Myopia

• Hypometropia (Donders)

• Aristotle - credited with being the first to distinguish myopia

• Galen - Join “myein”(to close) and “op” (eye)

Causes

• Genetics

• Lack of vitamins

• Lack of outdoor activities

Symptoms

• Headaches

• Rubbing the eyes

• Squinting

• Tiredness when playing sports

• Holding objects close to the face

Degree

• Low myopia -3.00D and below

• Moderate -3.25-6.00

• High -6.00D and above

Sorsby’s Classification

• Correlation myopia- includes up to -6.00

• Component myopia- includes above -6.00

Treament

• Specialized Contact Lens

• Eyeglasses with a special lens design

• Atropine

• Outdoor time

Myopia Control Strategies

Clinical Examination SOP

• History Taking

• Visual Acuity

• Refraction (Cycloplegic)

• Binocular Vision assessment

• Pupillary examination - photopic & mesopic condition

• Ocular Health assessment - SLE / IOP measurements

• Fundus evaluation

• Corneal topography

• A-scan (Axial length measurement)

Myopia Control with Optical Technology

• Tradition spectacles

• Next generation spectacles

  • DIMS Technology (Defocus Incorporated Multiple Segments)

    • Central zone 9mm diameter

    • Honeycomb-like multiple segments of lenslet with +3.50D adds

    • Almost 400 multiple defocus segments (33mm diameter)

    • Miyosmart from Hoya. Power up to -10.00, Cyl -4.00 D and 3 prism

    • Slow down the progression of myopia by an average of 60%

  • HALT Technology (Highly Aspherical Lenslet Target)

    • 11 rings of 1021 contiguous aspherical lenslets (1.12mm in dia) generate a volume of myopic defocus (VoMD)

    • Central clear zone of 9mm

    • The central area of the lens without lenslets and the areas in between the rings of lenslets provide distance correction

    • Stellest from Essilor. Power up to -10.00, Cyl -4.00 D and 2 prism

    • Slow down the progression of myopia by an average of 60%

  • CARE Technology (Cylindrical Annular Refractive Elements)

    • A central zone small enough to establish an effective functional zone projecting myopic defocus on the near periphery close to the fovea

    • 86% 10-12 yrs old, 63% 7-9 yrs old

    • Zeiss Myocare

  • DOT (Diffusion Optics Technology)

    • Contrast Theory for Myopia - Overstimulation of the retina from high contrast is associated with overstimulation of eye growth, thus instigating myopia progression

    • 5mm central zone

• Multifocal/multifocal-like contact lenses

  • SCL is increasingly used in myopia management

  • advised for children 8 years old and up

  • ADD power +1.50 to +2.50D (Majority 2.00)

  • Daily disposables are recommended

  • Power up to -12.00

• EDOF

  • center distance optics with ADD power placed immediately next to the central distance zone

  • creates a blur zone at the peripheral retina

  • Greater stereopsis and enhanced depth perception can be achieved with the lens

  • Seed 1-day pure EDOF

    • Daily

    • up to -12.00

    • ADD +0.75, +1.50, +2.25

• Ortho-k

  • Ortho - straight; Kerato - cornea; logy - knowledge

  • Reverse geometry gas-permeable lens

  • Flatten the central cornea to correct for myopia

  • Mid-peripheral Steepening

  • Indications:

    • Clear cornea, no surgery history

    • -1.00 to -8.00

    • up to -1.75 WTR, -0.75 ATR

    • 6 years above

    • Highly motivated patients

    • Can afford

    • MFSCL failure

Astigmatism

Thomas Young

• Had a crude measurement of his own astigmatism of about 1.75D

• The value remained when he immersed his head underwater

George Biddle Alry

• First to correct astigmatism by a spherocylindrical lens

John Green

• Produced the first distance test chart for astigmatism

• Including the clock dial

H. Knapp

• Credited for the first trial case with a cylindrical lens

• Suggested the method we use now for the location of the axis

Classification

Direct or WTR

• Curvature of the greatest power lies nearest to the vertical meridian (60-120)

Inverse/Perverse or ATR

• Curvature of the greatest power lies nearest to the horizontal meridian

Oblique

Symmetric

• The total of degrees between the two weakest or the two strongest is equal to 180

  • Homologous - if both, WTR

  • Heterologous - if both, ATR

Asymmetric

• when the two are not equal to 180

  • Homonymous - both are WTR, or both are ATR

  • Heteronymous - one eye is WTR, the other is ATR

Types

• Myopic

• Hyperopic

• Mixed

S/sx

• BOV

• Eye discomfort

• Squinting

Treatment

• PRK surgery

Presbyopia

• Presbys: old; ops: eye

• Hyperopes tend to become more presbyopic earlier than myopes due to depleted accommodation.on

• Caused by changes that occur in the lens’s elasticity, lenticular sclerosis, and loss of motor supply for the ciliary muscle

Types

• Incipient - Earliest stage; 38-40 years old

• Functional - completely loses ability to focus on near objects; 45-50 years old.ld

• Absolute - 40 years old

• Premature - Earlier than normal age

• Nocturnal - Difficulty in dim light; any age

S/sx

• HA

• BOV

MFL

• Single lens

• Bifocals

• Trifocals

• Multifocals

Accommodation

Triad

• Constriction of pupils

• Convergence of eyes

• Contraction of ciliary muscle

Theories

Increased Tension Theory (Tscherning’s theory)

• states that during far vision (relaxed accommodation), the suspensory ligaments are lax, the lens is not in stress, and the flattened state of the lens is “natural.”

Decreased Tension Theory (Helmholtz theory)

• states that the suspensory ligaments upon the lens cause its flattened state, and during accommodation, the suspensory releases the tension, causing the lens to decrease its radius of curvature

Lenticular Changes

1. Radius of curvature of the anterior surface of the lens is decreased from 10mm to 5.33mm

2. anterior surface moves toward the cornea

3. thickness of the lens is increased

4. anterior chamber becomes shallower

5. radius of curvature of the posterior lens 6.0 to 5.33

6. In cases of aniridia, the equatorial diameter is decreased

7. The refracting power is increased from 19.11 to 33.06. This increases the total refraction power from 58.64 to 70.

Lag of accommodation on

• is the adjustment of the eye to focus from far to near

• Normal: 50-75D

Amplitude of accommodation

• is the maximum increase in optical power that an eye can achieve in adjusting its focus from far to near

Range of accommodation

• The range of distance over which an object can be accurately focused on the retina by accommodation of the eye

Formulas in Computing AA

• Hofstetter

  • Min = 15 - 0.25 (age)

  • Ave = 18.5 - 0.30 (age)

  • Max = 25 - 0.40 (age)

• Other solutions

  • AA for Emme = 1/PP

  • AA for Myope = PP-PR

  • AA for Hyperope = PP + PR

• AA = Gross #19 - #7

  • *non presbyope = increase 2.50

  • *presbyope = decrease 2.50

AC/A Ratio

• The measurement of the convergence induced by accommodation

Formulas

1. Gradient Method

   1. = 13B and 13B +1

2. Phoria Method

   1. AC/A = IPD (in cm) + (Near phoria - Far Phoria) / F

      1. Eso + sign, Exo - sign

      2. F = dioptric value of the working distance

Visual Acuity

Visual Senses

• Light Sens

  • Scotopic - night

  • Mesopic - middle

  • Photopic - daylight

• Form Sense (Visual Acuity)

  • Perceive the shape of objects

• Sense of contrast

  • ability to perceive light changes in luminance between regions that are not separated by a definite border

• Color Sense

  • distinguish different colors was excited by light of different wavelengths

Visual Acuity

• considered a measure of form sense, so it refers to the spatial limit of visual discrimination

• defined as the reciprocal of the min resolvable angle measured in minutes of arc

Components

• Minimum Visible (Detection)

  • smallest object or detail that can be detected by the eye, even if not clearly identified

• Resolution

  • the ability to distinguish fine details within an object, separating two points or lines as distinct

• Recognition

  • the ability to identify and assign meaning to visual stimuli

• Minimum Discriminable (Vernier Acuity or Hyperacuity)

  • the ability to detect small differences in size, position, or alignment between objects

Color Vision

• L-cones(long wavelength): Sensitive to red light

• M-cones(medium wavelength): Sensitive to green light

• S-cones(short wavelength): Sensitive to blue light

Major Tests

1. Ishihara Plates

• Uses pseudoisochromatic plates with colored dots forming numbers or patterns

2. Farnsworth D-15 Test

• Patient arranges 15 colored capes in order of hue

• Identifies moderate to severe color defects

3. Anomaloscope

• Patient adjusts a mixture of red and green light to match a yellow reference

• Gold standard for diagnosing red-green deficiency

4. Lantern Test

• a functional color vision assessment that uses a lantern device to project small apertures of colored lights (typically red, green, and white)

• to determine whether an individual can safely and accurately distinguish signal colors in occupational settings

Amsler Grid

Chart no. 2 (with X)

• used in cases where the central point is not seen

• The diagonal lines help to fix the center of the square despite a central scotoma.

• Follow the cross lines

Chart no. 3

• A chart with red on black to be used in cases of color scotoma,

• Red lines on a black background are very helpful in the diagnosis of optic nerve, chiasmal, or toxic amblyopia-related problems

Chart no. 4

• This chart, without lines, reveals only the scotoma; there is no form to be distorted.

Chart no. 5

• Chart with parallel lines. Must be looked at horizontally and vertically

• It shows metamorphopsia

Chart no. 6

• Another chart for metamorphopsia, which allows a more minute examination of distortion along the reading lines.

Chart no. 7

• This chart allows a more minute examination of the juxta-central area, where the rectangle with subdivided squares indicates the limits of the fovea.

• The same chart renders great service in cases of high myopia, when help is needed at the punctum remotum of the uncorrected eye.

Tonometry

The procedure performed to determine the IOP

Classification

• Direct

  • Indentation

    • It is based on the fundamental fact that a plunger will indent a soft eye more than a hard eye

    • The indentation tono in current use is Schiotz

    • It was devised in 1905, modified in 1924/1926

    • Procedure:

      • Patient should be anaesthetised with 4% lignocaine or 0.5% proparacaine

      • With the patient in the supine position, looking up at a fixation target, while examiners separate the lids and lower the tonometer plate to rest on the cornea so that the plunger is free to move

      • The 5.5gm weight is initially used

      • If the scale reading is 4 or less, additional weight is added

    • Advantages

      • simple technique

      • elegant design

      • portable

  • Applanation

    • Contact

      • Goldmann

        • Introduced by Goldmann in 1954

        • Based on Imbert-Fick law

          • P=F/A

        • Most popular and accurate tono

        • consists of a double prism

        • Technique:

          • Topical anesthetic

          • staining the tear film with fluorescein

          • The cornea and biprisms are illuminated with cobalt blue light

          • Biprism just touches the apex of the cornea

          • At this point, two fluorescent semicircles are viewed through a prism

        • Applanation force against the cornea is adjusted until the inner edges of the two semicircles just touch

        • Potential errors:

          • Px related

            • thin cornea

            • thick cornea

            • astigmatism

            • irregular cornea

          • Technical

            • tonometer is out of calibration

            • Repeated tonometer (up to 3 times only)

            • pressing on the eyelids or globe

            • squeezing of the eyelids

        • Advantages:

          • highly accurate

          • do not require supine position

        • Disadvantages

          • not portable

          • costly

          • reading error if there are scars on the cornea

      • Perkins

      • Pneumatic tonometer

      • Tono-pen

        • handheld Mackay Marg type tonometer

        • computerized pocket tonometer

        • converts IOP into electric waves

        • least accurate

    • Non-contact

      • Air-puff

        • In this, the central part of the cornea is flattened by a jet of air

        • Good for mass screening

        • no danger of contamination

      • Pulse Air

        • can be used in any position

• Indirect

  • Manometer

Vitamins Affecting Visual Health

Trachoma

• leading cause of infective blindness globally

• >150 million people have been affected

• associated with poor hygiene and inadequate sanitation

• Recent estimates shows 59 countries are endemic and India has high burden

• Egyptian ophthalmia, north western belt of India

Definition

• Chronic granulomatous kerato-conjunctivitis

• Caused by Chlamydia trachomatis (A,B,Ba,C)

• Mainly affects children at an early age who develop blindness later

• Cause of 3.6% of global blindness (WHO)

• Highly contagious

• Spread by transfer of conjunctival secretions through fingers, towels, flies etc.

Pathology

• C. Trachomatis - prokaryotic, obligatory intracellular parasite

• Halberstaedter-Prowazek including bodies - in

• NEED TO CHECK NOTES - KUWANG NI!!!!

• Lymphocytic infiltration of adenoid layer

• LEBER cells - necrosed and multinucleated giant cells

• Cicatricial bands - in late stages

Risk factors (6D)

• Dry

• Dusty

• Dirty

• Demographics

• Delayed access to health care

• Density

Transmission (5F)

• Fingers

• Flies

• Face

• Feces

• Formites

Predisposing Factors

• Age: more in infancy/childhood

• Sex: common in females

• Dry and dusty environments

• Low socioeconomic status, unhygienic conditions, and lack of sanitation

Spread of Infections

• Direct - contact with airborne or waterborne infections

• Vector - flies (Musca domestica)

• Material - example: sharing of towels

Clinical features

• Incubation period: 5 to 21 days

• Onset: subacute, but in massive outbreaks can be acute

• Symptoms: watering, foreign body sensation, redness, mucopurulent discharge, photophobia, blurring, mild pain

Signs

Conjunctiva

• Upper tarsal conjunctiva - mc affected, appears red velvety, congested

• Trachomatous follicle - essential lesion, up to 5mm size

• Scarring of conjunctiva

• Arlt’s line

• Limbal follicles

• Herbert pits - oval/pitted scars in limbus

Cornea

• Early - superficial keratitis on SLE(Fl Stain) in upper part due to erosion

• Later - trachomatous pannus, starts in upper half then spreads centrally to involve whole cornea

• Vascularisation - in between Bowman’s membrane and epithelium

• Pannus

  • progressive: vessels parallel, downwards, infiltration ahead of vessels

  • regressive

• KUWANG NOTES!!!!!!!!!!!!!!

Lids

• Edema

• Trichiasis

• Distichiasis

• Entropion

• Scarring

• Trachomatous ptosis

• stages   

  • active

  • cicatrical

WHO Classification (FISTO)

• developed for use by trained personnel other than ophthalmologists to assess the prevalence and severity of trachoma in population-based surveys in endemic areas

1. Trachomatous Follicular

   1. active disease

   2. five or more follicles in the upper tarsal conjunctiva

   3. MORE NOTES HERE

2. Trachoma Intense

   1. severe disease, needs urgent rx

   2. diffuse involvement of the tarsal conjunctiva, obscuring 50% or more of the normal deep tarsal vessels, papillae are present

3. Trachomatous Scarring

   1. Inactive infection

   2. Conjunctival scarring

   3. visible fibrous white bands on tarsal conjunctiva

4. Trachomatous Trichiasis

   1. at least one lash touching the globe

   2. needs corrective surgery

5. Corneal Opacity

   1. sufficient to blur details of at least part of the pupillary margin

McCallans Classification

Stage 1

• incipient trachoma/stage of infiltration

• hyperemia of palpebral conjunctiva & immature follicles

Stage 2

• stage of florid infiltration

• mature follicles, papillae, progressive panus

Stage 3

• cicatarizing trachoma, scarring

Stage 4

• healed trachoma, stage of sequelae

Diagnosis (must have at least 2 of the following)

• follicles on the upper tarsal conjunctivitis

• limbal follicles and sequelae (Herbert pits)

• typical tarsal conj scarring

• Vascular pannus is most marked on the superior limbus

Sequelae

• Lids - trichiasis, entropion, tylois, ptosis, madarosis

• Conjunctiva - concretions, pseudocysts, xerosis, symblepharon

• Cornea -

• asdasdasd

Differential Diagnosis

• allergic/vernal conjunctivitis

• bacterial conjunctivitis

• follicular conjunctivitis

Management

Treatment

• of active disease and sequelae

Prevention

• antibiotics

• oral: Azythromycin

• Topical: best for individual cases, cheaper, no systemic side effects

• Regimes: 1% tetracycline/erythromycin eye ointment QID for 6 weeks

• KUWANGGGG

SAFE STRATEGY was devised

• Surgery - correction of entropion, trichiasis rx: epilation, cryolisis

• Antibiotics

• Facial cleanliness

• Environmental improvements

Prophylaxis

• good personal hygiene

• health education

• Use of common towels is discouraged

• clean water supply for washing

• and others