MDA

[Torque2]

The EUOPS reference that 172 refers to is the latest legislation. Note there is now no requirement to add 50 ft for any reason. The table for calculating minimum RVR from DH refers specifically to a Constant Descent Angle Final Approach and as stated above if you for any reason don't do a CDFA then add the RVR supplements according to your approch category A,B,C or D).
It is different to the previous JAR rules. You can use most methods of finding distance from the threshold to calculate the constant descent angle ie: DME, GPS, IR's so no real reason not to do a CDFA.

Extract from our approach chrat provider Rules and Regs section EUOPS:

7.9.3 Non Precision Approach (NPA) (EU-OPS)
A Non-Precision Approach (NPA) operation is an instrument approach with a Minimum Decision Height or
Decision Height not lower than 250ft and an RVR/CMV of not less than 750m, unless accepted by the
authority.
⇒ Rules and Regulations General Information 7.9.6 System Minima vs. Facilities (EU-OPS Table 3),
7.9.4 Decision Height (DH) and Minimum Descent Height (MDH) for Cat 1, APV and NPA (EU-OPS)
Decision Height (DH)
An operator must ensure that the Decision Height (DH) to be used for an approach is not lower than:
• the minimum height to which the approach aid can be used without the required visual reference; or
• the OCH for the category of aircraft; or
• the published approach procedure decision height where applicable; or
• 200ft for Cat 1 approach operations; or
• the lowest decision height specified in the Aircraft Flight Manual (AFM) or equivalent document, if stated;
• the system minimum
⇒ Rules and Regulations General Information 7.9.6 System Minima vs. Facilities (EU-OPS Table 3)
whichever is higher.

Minimum Descent Height (MDH)
An operator must ensure that the MDH for an approach is not lower than:
• the Obstacle Clearance Height (OCH) for the category of aircraft; or
• the minimum descent height specified in the AFM if stated; or
• the system minimum
⇒ Rules and Regulations General Information 7.9.6 System Minima vs. Facilities (EU-OPS Table 3)
whichever is higher.

As far as EUOPS and circling goes here is an extract from our approach chart provider, Rules and Regs section:

7.10 Circling and Visual Approach (EU-OPS)
7.10.1 Minimum Descent Height (MDH)
The MDH for circling shall be the higher of:
• The published circling OCH for the aircraft category; or
• The DH/MDH of the preceding instrument approach procedure; or
• The minimum circling height indicated on the EU-OPS Table 10.
For more information refer to:
⇒ Rules and Regulations General Information 7.10.6 Minimum VIS and MDH for Circling vs. ACFT Category (EU-OPS Table 10)

7.10.2 Minimum Descent Altitude (MDA)
The MDA for circling shall be calculated by adding the published aerodrome elevation to the MDH, as determined under paragraph "Minimimum Descent Height (MDH)".
For more information refer to: ⇒ Rules and Regulations General Information 7.10.1 Minimum Descent Height (MDH)

These are all extracted from the EUOPS document and do not refer at any stage to having to add 50ft as previously.