Introduction
Pachychoroid Syndrome Pathophysiology:
- Whilst it isn't confirmed, 2 theories exist
1. Pachy vessels develop due to stretching of smooth muscles, causing fluid leakage from vessels. This along with oedema leads to pachychoroid thickening
2. Sympathetic stimulation causes a focal increase in the hydrostatic pressure of the choroid, dilating the vessels.
- Regardless, the vessels of Haller's layer becomes greatly enlargened, and the size of the choroid increases. This pushes the RPE up, and hence causes RPE disturbances regardless of onset, acute or chronic conditions.
Imaging is only achieved via enhanced depth imaging (EDI) on OCT
PPE:
- The RPE is still able to withstand pressure form the choroid, but the RPE elevation and pigmentary changes can be appreciated.
- Exacerbation will cause disease to progress
Dead Giveaways
The main giveaways are in the OCT, Fundus Autofluorescence and presence of PED
OCT:
Note RPE disturbances in the top image, and the PED in the bottom image. The choroid layer and the vessels are significantly larger than normal (191-350um)
There is additionally increased transmission of choroid at points of RPE disturbances.
PED or pigment epithelial detachment shows a separation of RPE from the Bruch's membrane, but it typically is not filled with fluid
FAF:
The pigment changes are slightly more obvious here The pigmentary changes from RPE is appreciated as areas of hypo-AF
Choroidal Angiography:
Shows the thick vessels on the en-face scan, which indicates the presence of pachychoroid spectrum.
diagnostic features
While the fundus photograph can sometime indicate PPE, it is very subtle and can be missed. On occasions however, pachydrusen can be seen, occuring with drusenal PED:
Shows subtle pigmentary changes around macula
If the RPE is exacerbated enough, PPE will progress to CSCR