Visual Acuity Charts and Optotypes

Dear everyone, 

I would like to open up a discussion about how VA Charts and Optotypes can be represented in SNOMED CT.

Background: I have recently joined a team that would like to improve the openEHR Visual Acuity Test Archetype.
Our goal is to and to try and align the archetype and a FHIR Observation profile with one another (Prototype here), ideally to facilitate 1:1 mapping between their elements. 
This will likely require us to keep the different concepts involved in VA testing in seperatent coded elements, so that they can be flexibly recombined (as we do in real life).

Problems: Lots of different types of VA charts and other methods to display optotypes (Projectors, Digital Displays) have entered the market in the last decades.
This means that the same optotypes are often used across different methods of presentation (Chart/Near Card/Projector/Display), especially when using digital devices.
Currently, the charts and optotypes involved in VA testing are partly represented as physical objects as children of (400912000 | Visual acuity test equipment), and partly as Procedures as Children as (36228007 | Ophthalmic examination and evaluation (procedure)),
I Think  there are several areas for Improvement: 
1. The more modern methods of displaying Optotypes (Projectors, Digital Displays) are missing,
2. There is no family of terms for Optotypes, which would be needed to be able to code them independently of the presentation method used.  
3. Some procedure terms reference things that may be better classified as physical objects (285805006 | Cardiff acuity cards (procedure) ) 
3. Some of the terms used have lost their specificity as their use has changed over time. (ETDRS)

Example: While it used to be the case that "ETDRS Chart" was a term that was specific for one of these Charts which all used Sloan Letter Optotypes, the term "ETDRS" is now just used as a trademark to sell logarithmic VA Charts with all sorts of different Optotypes, which were not used in the original ETDRS Study. All of these optotypes are also used by digital displays or projectors. Just to illustrate that we need some way to independently represent Optotypes themselves as , non-physical "things" indepentend of the type of chart they are shown on. 

Proposal: 

Italic: moved
Bold: New

I hope this way of proposing changes is helpfull for discussion, i could move it to an excel sheet if you wish: 

Charts and other Physical objects: 
Changes: 
1. Include Digital Visual Acuity Chart Displays, Visual Acuity Chart Projectors are physical objects, in 400912000 | Visual acuity test equipment (physical object).
2. For some of the Visual acuity test equipment, a family structure may be beneficial. 

3. While I would think it would be optimal not to reference any Optotypes (like HOTV) at this point at all, but don't think it will do harm to keep them. 

4. Term "Potential Acuity Meter" is ambiguous, as it may either refer to any type of device that measures potential acuity, or or more specifically to the Guyton and Minkowski Potential Acuity Meter.

Parent: 400912000 | Visual acuity test equipment (physical object).
Children:

• Accommodative rule (physical object)

• Visual Acuity Chart Projector (physical object)

• Digital Visual Acuity Chart Display (physical object)

• Near card (physical object)

  • HOTV cards (physical object) {or maybe deactivate, as it mixed optotype and card concept?}

  • Allen cards (physical object) {or maybe deactivate, as it mixed optotype and card concept?}

•       Potential acuity measurement device (physical object)

  • Laser inferometer (physical object)

  • Guyton and Minkowski Potential Acuity Meter (physical object) {more specific}

  • Handheld Retinometer

•       Visual acuity chart (physical object)

  • Snellen chart (physical object) {Widespread use, usually implies use of Snellen Letter Optotype ?}

  • LogMAR Visual Acuity Chart (physical object)

    • Early Treatment of Diabetic Retinopathy Study visual acuity chart (physical object)

      • ETDRS Original Series Chart 1 (physical object)   

      • ETDRS Original Series Chart 2 (physical object)

      • ETDRS Original Series Chart R (physical object)

      • ETDRS Revised Series Chart 1 (physical object)

      • ETDRS Revised Series Chart 2 (physical object)

      • ETDRS Revised Series Chart 3 (physical object)

    • Bailey-Lovie Visual Acuity Chart

  • Golovin-Sitsev table (physical object) {apparently widely used in post-Soviet States}

  • Monoyer Visual Acuity chart (physical object) (from France, also used in italy, i think the optotypes may be non-standard)

• Preferential Looking Test Cards (physical object)

  • Cardiff preferential looking test acuity cards (physical object) { specify PLT use, move from procedures?}

  • Keeler preferential looking test acuity cards (physical object) {specify PLT use, move from procedures?} 

  • Teller preferential looking test acuity cards (physical object) {specify PLT use, move from procedures?}
    
    

Optotypes: 

Here is my current collection of Optotypes which I think we may want to consider, I linked some resources where available: 

I am uncertain as to which category these would best belong to, as they are not physical objects (esp. when displayed digitally) 
I was wondering which may be most suitable, because there does not relly seem to be a category for symbols: 
- Observable Entity? (they are some sort of entities and certainly are observable) 
- Procedure? as in the act of displaying a type of optotype to the patient being a procedure?
or maybe even as a group of "Special concepts"?

Proposed family structure: 
(Those with uncertain amount of use are shown in brackets)

• Optotype

  • Letter Optotype

    • Sloan Letter Optotype 

    • Cyrillic Letter Optotype

    • Snellen Letter Optotype

    • HOTV Letter Optotype

    • LVRC Letter Optotype

    • (1968 British Letter Optotype)

    • 2003 British Letters

    • (European-Wide Letter Optotype)

  • Number Optotype

    • Precision Vision Number Optotype

    • Lea Number Optotype

  • Orientation-Type Optotype

    • Landolt C Optotype

    • (Sjogren's Hand Optotype)

    • Tumbling E Optotype

  • Pictogramm Optotype

    • Lea Symbol Optotype

    • Kay Pictures (move from 278211009 | Printed material (physical object) 

    • Allen Pictures

    • Auckland Optotypes

    • Amsterdam Picture Optotypes

I think it would be usefull to use this structure, because there may be instances where the precise type of optotype is not known, only the fact that it is a number optotype. 

I hope that this is helpful for a start, but I sure that there are some more optotypes in use worldwide, especially in regions which don't use the latin alphabet. 

I would be very gratefull for everyone's thoughts on this!

Lars