Choroidal neovascularisationCNV

PDT,TTT,MPC

ALI . SALEHI MD

CNV is an important cause of visual

Impairment and may develop from more than 30 ocular diseases.

The most common causes of CNV are ARMD Pathologic myopia

ARMD Non neovascular (Nonexudative)

Neovascular (exudative)

The hallmark of nonexudative form is drusen.

The hallmark of neovascular is the presence of CNV.

Prevalence

Is the most common cause of irreversible visual loss in the world in individuals over 50 years of age (1.7%)

Age % of patients

65-75 10%

>75 30%

AMD is a major cause of visual impairment in the USA.

1.8 million Americans age 40 and older have advanced AMD and another 7.3 million people with intermediate AMD are at substantial risk for vision loss.

By 2020 there will be 2.9m people with advanced AMD.

Nonneovascular changes with AMD can increase a break in bruch’s membrane .

neovascular tissue from choriocapillaris to perforate the outer aspect of BM.

These new vessels are accompanied by fibroblasts

Fibrovascular complex Proliferates within the inner aspect of BM.

CNV in the fovea is the major cause of severe central visual loss , in AMD

FA pattern of CNV Classic CNV Occult CNV

o Classic CNV is an area of bright fairly uniform hyperflorscence identified in the early phase of the FA

That progressively intensifies and with

leakage of dye obscuring the boundaries

of this area by the late phases.

Occult CNV : (2Forms)

Fibrovascular PED

Late leakage of an undetermined source

3 terms are important :

Predominantly classic CNV

Minimally classic CNV

Occult CNV with no classic

Predominantly classic Lesions where the CNV occupies more

than 50% of the lesion , including contiguous blood , pigment, scar, and staining.

Minimally classic

When the proportion of classic CNV occupies between 1-49% of the entire lesion.

Occult with no classic CNV there is no classic CNV in the lesion( only

occult CNV)

Management of the neovascular form

of AMD

Laser photocoagulation (thermal laser)

Photodynamic therapy (PDT)

T.T.T (Transpupillary Thermo Therapy)

Antiangiogenic drugs (Avastin,Lucentice)

The benefits of laser (MPC)

therapy have been shown only

for classic CNV and the benefits

of PDT only for lesions that are

predominantly classic or purely

occult CNV.

Photocoagulation is used in the treatment of many retinal disease including:

1)Diabetic retinopathy2)CNV3)retinal vascular disease4)sickle cell retinopathy5)peripheral retinal tears

Until the year 2000 the only available treatment for the more aggressive, wet form of AMD was laser photocoagulation.

It was used only in those patients with small well-defined lesions located outside the fovea.

Laser light is mainly absorbed by 3 pigments

1)melanin2)hemoglobin3)xanthophyll

Melanin strongly absorbs all ultraviolet and invisible wavelengths.

Hemoglobin has strong absorption in the violet (420nm) and green(514nm) wavelengths.

Xanthophylls which is the pigment most densely distributed in the macular area absorbs the blue wavelength (460nm)

Laser application can affect tissue according to different interaction mode

1)Thermal (MPC,TTT)2)Ionizing (YAG Capsulotomy)3)Phothochemical (PDT)

Laser photocoagulation uses a thermal (heat-producing) laser beam to cauterize abnormal blood vessels in the retina.

( abnormal scotoma).

80-90% CNV due to AMD presents subfoveally that don’t benefit from MPC.

Laser photocoagulation is the

transfer of light energy into heat

energy wavelength extend from

400nm which is blue light to 800nm

which is the infrared wavelength.

A rise in temperature of about 10c to 20c will cause coagulation of the

ocular target tissue.The most common laser used for theseProcedure is argon green light source.

Patients with subfoveal lesion or

juxtafoveal lesion so close to the

foveal center that laser may

damage the center of vision,

needs to PDT

Photodynamic therapy with visudyne

(verteporfin):

PDT selectively closes CNV, halting the progression and size of CNV lesions while slowing the loss of VA

In 2001 the FDA also approved visudyne for the treatment of pathologic myopia and ocular histoplasmosis

PDT involves an IV injection of

visudyne a photosensitizer, light-

activated drug.

After infusion visudyne is selectively

activated by illuminating a light from

a non-thermal laser source at a

wavelength (689nm)

Photochemical effect (PDT) A chemical reaction can be made to

occur by intense laser energy if the energy of the photons is high enough

Energizing of photons increases with shorter wavelengths therefore ultraviolet light is more effective in producing photochemical reaction than is visible or infrared light.

The power of laser is not strong enough to cause any thermal damage to the retinal tissue.

Visudyne is a potent second-generation photosensitizer derived from porphyrin.

The molecule has along absorption wavelength with several peaks, including a strong absorption peak in the 688 to 692 nm region

Visudyne absorb light at wavelengths around 690nm (red light), which can penetrate blood , melanin and fibrotic tissue.

When visudyne is activated by light in the presence of oxygen, highly reactive , oxygen short-lived singlet and reactive oxygen radicals are generated.

Light activation of visudyne

Results in local damage to neovascular endothelium, resulting in vessel occlusion.

( Platelet aggregation, fibrin clot formation and vasoconstriction).

Visudyne is indicated : Predominantly classic subfoveal CNV due

to ADM Pathologic myopia POHS

The most frequently adverse events

(10-30% incidence) were :

Site reactions (extravasations-rash)

Blurred visionDecreased VAVisual field defect

Hyperthermia

Is the process whereby the laser causes an elevated tissue temperature above the normal 37c

But still avoids coagulation.

This temperature generally ranges between 42c and 52c.

At these temperature bimolecular undergo

changes that may result in significant

membrane alteration.

If this type of hyperthermia is maintained

for a period of time (20 seconds to 3 to 4

minutes) irreversible effects occur.

Hyperthermia--------T.T.T

T.T.T Is a technique in which heat is delivered to

the choroid and RPE through the pupil using a modified diode laser.

This laser technique contrast with the laser used in standard MPC in that T.T.T uses a lower power laser for more prolonged periods of time and is designed to gently heat the choroidal lesion, thus limiting damage to the overlying RPE.

The use of T.T.T to treat

Subfoveal CNVChoroidal melanomaRetinoblastoma

The goal is to stop the growth and

leakage of the new blood vessels and

preserve vision .

THE END