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Lens

A Lens is a conceptual piece of code packaged as a FHIR Library resource that encodes clinical or context-specific knowledge, applying transformation rules based on patient data.

Purpose​

Lenses determine how ePI content should be adapted for individual patients by:

  • Highlighting relevant sections
  • Collapsing irrelevant sections
  • Adding supplementary content
  • Enriching with interactive elements

Packaging​

FHIR Library Resource​

Lenses follow the Lens Profile:

  • JavaScript code encoded in Base64 (UTF-8)
  • Stored as Library.content.data
  • LEE decodes from Base64 → UTF-8 before execution
  • Contains metadata (author, version, purpose)

Creation Tool​

Packaged using the FHIR Lens bundler tool.

Execution Inputs​

Lenses receive three inputs from LEE:

  1. p(ePI): Semantically annotated ePI
  2. IPS: Patient clinical data
  3. PV: User context and preferences

Lens Operations​

Attention Detail Modification​

Using modifyCSSClass() LEE helper:

// Highlight sections relevant to patient conditions
modifyCSSClass("pregnancy-warning", "highlight");

// Collapse irrelevant sections
modifyCSSClass("pediatric-dosing", "collapse");

See Attention Detail Modification for details.

Adding Supplementary Content​

Using addNewContent() LEE helper:

// Add hyperlink to Supporting Material
addNewContent(
  "pregnancy-section",
  '<a href="/sm/pregnancy-guide">More information</a>'
);

// Embed video
addNewContent(
  "administration-section",
  '<video src="/videos/injection-technique.mp4"></video>'
);

Lens Logic Example​

// Check patient's IPS for pregnancy
if (ips.hasCondition("pregnancy")) {
  // Highlight pregnancy warnings
  modifyCSSClass("pregnancy-warning", "highlight");
  
  // Add relevant Supporting Material
  addNewContent("warnings", pregnancySupportMaterialLink);
  
  // Collapse non-relevant sections
  modifyCSSClass("breastfeeding-only", "collapse");
}

Regulatory Constraints​

Critical Limitation: Lenses cannot:

  • Remove original ePI content
  • Change approved text
  • Delete HTML elements

They can only:

  • Modify CSS classes for visual presentation
  • Add supplementary HTML elements

Performance Requirements​

Client-Side Execution​

  • Must run efficiently on patient phones
  • Lightweight algorithms only
  • No heavy computation

Server-Side Execution​

  • Must scale for many concurrent users
  • Fast response times required
  • Ephemeral (not cached)

Design Principle​

Rely on Preprocessors for heavy computation (NLP, semantic analysis). Lenses execute lightweight logic based on preprocessor annotations.

Lens Types​

  • Clinical Lenses: Based on medical conditions
  • Demographic Lenses: Age, gender-specific
  • Preference Lenses: Language, literacy level
  • Summary Lenses: Provide condensed views
  • Multimedia Lenses: Add rich media content