DIAG: structure of eye

Like structure of a camera

Similarities: Lens = lens; Film - retina

• Accommodation

1. Camera: no presbyopia: decreased accommodation with age
2. Eye: presbyopia after age of 40

• Functional

1. Visual system not equal to camera
2. Perception >> Camera

SLIDE 3D pictures

• Normal binocular vision can see 'picture inside the picture'
• If not: abnormal vision, improper testing environment

• Tomorrow belongs to those who have the VISION today
• Vision > 90% of sensory input
• Blindness is one of the most fearful disabilities
• Increased need
• Information age
• Ageing population
• Not just life and death - quality enhancement

Ophthalmology is technology-driven

1. New technologies
2. New drugs
3. New operations

Laser

Assisted

In-situ

Keratomileusis

Marriage of

1. Precision of excimer laser technology
2. Control of wound healing by lamellar surgery (cornea as 5 layer, innermost is epithelial cells, cornea dissected into different lamina; tissue abrasion inside cornea instead on surface)

Process

1. Microcaritone to make cornea flap
2. Excimer laser to remove tissue and reshape cornea (30 sec - 2 min)
3. Put back cornea flap

• Cornea at pupil thickness 0.5mm
• Flap is 0.15mm (uneven, perforated flap)

• Macula = centre of retina; highest density of neuronal tissue
• Tangential force: split turns into hole; therefore relieve traction force by removing innermost layer of retina (internal limiting membrane) - traction totally relieved
• Absence of neurosensory retina tissue at the fovea, described 100 years ago
• Loss of tissue?
• Treatment was not feasible??
• ICG assisted ILM peeling

1. Surface anaesthesia - needleless
2. Phaco and foldable IOL - sutureless [wound is self-sealing; foldable intraocular lens]
3. Plus simultaneous correction of astigmatism - cannot form single point focus - therefore image split

• Make cornea more even in all meridians
• Ultrasonic probe softens hard nuclear component
• Insert stromal hydration to make wound more tight
• Whole procedure: 10-20 mins

• Incision & Curette for chalazion (small eyelid mass due to inflammation of a meibomian gland)

• Window of the eye
• Transparency
• Most important refractive structure (>40D) (40D = 4,000 degrees)
• Therefore, most refractive surgeries done on cornea
• Thickness: 0.5mm at the centre
• Refractive ability depends on

1. Curvature
2. Refractive index: tissue-air interface

Causes of opacity

• Degeneration
• Infection
• Inflammation
• Hereditary Dystrophy
• Trauma

• Start with conservative Tx - eg. Medication: infection from bacteria/ virus (ABX, anti-virals)

• 40 million blind people world-wide
• 10 million Cornea Blindness
• USA: >45,000 corneal grafts per year

• Therapeutic: remove cause of infection
• Optical: opacity, cannot see through
• Tectonic: risk of perforation, preserve integrity of eyeball
• Cosmetic: optic atrophy, but Pt doesn't want other people to know he cannot see

1. Corneal scar after infection and trauma
2. Corneal oedema after surgery (iatrogenic)
3. Failed graft
4. Keratoconus
5. Hereditary corneal dystrophies
6. Others

• In the past, >90% from Sri Lanka
• Demand >> Supply
• Many patients on the waiting list

• Few
• But: neurological diseases e.g. rabies (prevent cross-infection); diseases that may have infective origin; septicaemia (virus inside cornea)

• Lower limit: full term baby
• Upper limit: No

2 types of cornea implant:

1. Full-thickness
2. Lamellar

• Worries that recently deceased relative will not look good cosmetically
• No disfiguration because only remove corneal-scleral button
• Replace with a specially designed eye cap (with inverted hook)
• The only limitation: inadequate donor tissue
• Keep in mind when counselling potential donors

• Eye is opened: dangerous (accidentally exert pressure over eyeball)
• Suture tension must be even (astigmatism if not even)

1. Chemical injury
2. Ocular cicatricial pemphegoid
3. Steven Johnson Syndromes

• SC: given right environment, can develop into different cell types
• Limbus: zone between cornea and sclera; where SC are
• Transformation of conjunctival epithelial cells into cells biochemically and morphologically similar to corneal epithelium

• Conjunctival epithelial in-growth
• Persistent epithelial defect
• Chronic keratitis
• Keratinisation
• Vascularisation

Limbal Stem Cell Transplant

• Autograft: from one eye to other, same person, no rejection
• Allograft: from cadaver
• Survival rate increased

• Chemical burn
• Stevens-Johnson Syndrome
• Contact lens induced epitheliopathy
• Pterygium
• Ocular cicatricial pemphegoid
• Radiation keratopathy
• Ectodermal Dysplasia

Advances in therapy

1. Newer drug
2. Genetic

Diseases

• ARMD: age-related macular degeneration
• Myopia
• Glaucoma
• Retinitis pigmentosa

Transgenic animals

• Diagnosis
• Therapy

Advances in operations

• Intraocular telescope
• Micro-chips
• Surgery for presbyopia

• Family history
• Different prevalence in different cities USA: 25% prevalence
• HK: 50% prevalence

Treatment

• Prevention better than cure
• Anti-muscurinic agents: myopia due to elongation of eyeball on growth of scleral tissue; therefore atropine can inhibit scleral fibroblast proliferation (therefore decrease growth of sclera)
• Candidate gene will be found soon: which protein up- or down-regulated

• Commonest cause of visual loss in developed country
• Increasing importance in Hong Kong

1. High % population have myopia
2. Good family trees to follow

• Use of pre-laser photosensitising agent (Verteporfin)
• Reduce risk of vision loss in patients with subfoveal choroidal neovascularisation (CNV) due to AMD
• Illuminate retina with laser
• Laser light at 689 nm
• On-going study by large multi-centre clinical trials showed encouraging results
• Scar present: magnifying glass, telescope (make best use of residual visual functions)

• New type of miniature telescope
• Improve vision for patients with AMD who currently rely on low-vision aids
• Operation similar to that of cataract surgery
• Groove made on limbus
• 6.5mm Catactorexus performed
• Hydrodissection
• Emulsification
• Inject Helon
• Incision opened along 140 degree groove
• IMT insertion using Helon
• Lens does not touch endothelium
• Loops inserted into Lenticular bag
• Helon removed
• Peripheral iridectomy performed
• Nylon sutures to close incision

• No tilt
• No AP displacement
• After 3-4w: visual rehab, functional capabilities

• Quality is a journey, not a destination….
• Tomorrow does not just happen. It is MADE.
• Whatever imaginable is achievable
• Today's unthinkable, tomorrow's invention