> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/appertafoundation/openeyes/llms.txt
> Use this file to discover all available pages before exploring further.

# OphInBiometry Module

> Biometry measurements and IOL calculations for cataract surgery

# OphInBiometry - Biometry

The **OphInBiometry** module captures biometry measurements essential for intraocular lens (IOL) power calculation in cataract surgery. It integrates with biometry devices and provides comprehensive IOL calculation using multiple formulas.

## Overview

Biometry is a critical pre-operative investigation for cataract surgery, measuring:

* **Axial length (AL)**: Eye's front-to-back measurement
* **Keratometry (K)**: Corneal curvature in multiple meridians
* **Anterior chamber depth (ACD)**: Distance from cornea to lens
* **Lens thickness (LT)**: Crystalline lens measurement
* **White-to-white (WTW)**: Horizontal corneal diameter

These measurements enable accurate IOL power calculation for optimal post-operative refractive outcomes.

<Note>
  Accurate biometry is essential for achieving target refraction after cataract surgery. Modern optical biometry provides precision to within 0.01mm.
</Note>

## Core Element - Measurement

```php theme={null}
Element_OphInBiometry_Measurement extends SplitEventTypeElement
```

The biometry module uses a **split event type element**, providing separate data capture for left and right eyes.

### Measurement Properties

**Axial Length:**

* `axial_length_left`: Left eye AL (mm)
* `axial_length_right`: Right eye AL (mm)
* Typical range: 22-26mm
* High precision: ±0.01mm

**Keratometry:**

* Flat K (K1)
* Steep K (K2)
* Axis of steep meridian
* Average K (calculated)
* Delta K (K2 - K1, measures astigmatism)

**Additional Measurements:**

* Anterior chamber depth (ACD)
* Lens thickness (LT)
* Central corneal thickness (CCT)
* White-to-white diameter (WTW)
* Pupil diameter

**Lens Selection:**

* `lens_id_left`: Selected IOL for left eye
* `lens_id_right`: Selected IOL for right eye

### Data Sources

Biometry data typically comes from:

<CardGroup cols={2}>
  <Card title="Optical Biometry" icon="laser">
    Modern gold standard: IOLMaster, Lenstar, Argos - uses partial coherence interferometry or swept-source OCT
  </Card>

  <Card title="Ultrasound Biometry" icon="wave-square">
    Traditional A-scan ultrasound when optical methods fail (dense cataracts)
  </Card>

  <Card title="Keratometry" icon="circle">
    Manual keratometry or automated keratometry/topography for corneal measurements
  </Card>

  <Card title="Manual Entry" icon="keyboard">
    Direct entry of measurements from device printouts
  </Card>
</CardGroup>

## Device Integration

The biometry module supports integration with common biometry devices:

### Supported Devices

<Accordion title="IOLMaster Series (Zeiss)">
  **IOLMaster 500/700:**

  * Optical biometry using partial coherence interferometry
  * Non-contact measurement
  * Highly accurate axial length measurement
  * Integrated keratometry
  * WTW measurement
  * Data export via network or file

  **Integration Features:**

  * Direct device communication
  * Automatic data import
  * Quality control metrics
  * Multiple measurement averaging
</Accordion>

<Accordion title="Lenstar (Haag-Streit)">
  **Lenstar LS 900:**

  * Optical low coherence reflectometry
  * Comprehensive biometry package
  * Measures AL, ACD, LT, CCT, WTW, K
  * High repeatability
  * Integrated calculation platform

  **Import Capabilities:**

  * CSV file import
  * Network integration
  * Bilateral measurement support
</Accordion>

<Accordion title="Other Optical Devices">
  **Argos (Alcon Movu):**

  * Swept-source OCT biometry
  * Fast acquisition
  * Dense cataract capability

  **Aladdin (Topcon):**

  * Combination topographer and biometer
  * Placido disc topography
  * Optical biometry

  **AL-Scan (Nidek):**

  * Combination device
  * Optical and ultrasound modes
</Accordion>

<Accordion title="Ultrasound A-Scan">
  **Traditional Ultrasound:**

  * Contact or immersion technique
  * Used when optical methods fail
  * Requires skilled technique
  * Velocity assumptions critical
  * Manual data entry typically required

  **When Used:**

  * Dense brunescent cataracts
  * White cataracts
  * Posterior subcapsular plaques
  * Vitreous opacities
  * Corneal opacities
</Accordion>

### Data Import Workflow

<Steps>
  <Step title="Perform Measurement">
    Acquire biometry measurements on device (typically 3-5 readings per eye)
  </Step>

  <Step title="Device Quality Check">
    Review device quality metrics and measurement consistency
  </Step>

  <Step title="Export from Device">
    Export data via network, file, or prepare for manual entry
  </Step>

  <Step title="Create Biometry Event">
    In OpenEyes, create new biometry event for patient
  </Step>

  <Step title="Import or Enter Data">
    Import file or manually enter measurement values
  </Step>

  <Step title="Verify Import">
    Confirm imported values are correct and complete
  </Step>

  <Step title="Save Event">
    Save biometry event to patient record
  </Step>
</Steps>

## IOL Power Calculation

The module supports multiple IOL calculation formulas to determine optimal lens power.

### Calculation Formulas

<AccordionGroup>
  <Accordion title="SRK/T Formula">
    **Sanders-Retzlaff-Kraff Theoretical**

    **Characteristics:**

    * Theoretical vergence formula
    * Good for average eyes (AL 22-26mm)
    * Widely used and validated
    * A-constant optimized for each IOL

    **Best For:**

    * Standard axial lengths
    * Routine cataract surgery
    * General purpose calculation
  </Accordion>

  <Accordion title="Holladay Formulas">
    **Holladay 1 & 2**

    **Holladay 1:**

    * Surgeon factor (SF) personalization
    * Good accuracy for most eyes
    * Well-established formula

    **Holladay 2:**

    * Incorporates additional variables (ACD, LT, WTW, age, refraction)
    * Better for extreme eyes
    * Improved accuracy in long/short eyes
  </Accordion>

  <Accordion title="Haigis Formula">
    **Three-Constant Formula**

    **Features:**

    * Uses measured ACD (not predicted)
    * Three constants: a0, a1, a2
    * Particularly good for short eyes
    * Optimizable per surgeon

    **Advantages:**

    * Better for unusual axial lengths
    * Accounts for anterior chamber variation
    * Good for post-refractive surgery eyes
  </Accordion>

  <Accordion title="Barrett Universal II">
    **Modern Advanced Formula**

    **Characteristics:**

    * Incorporates AL, K, ACD, LT, WTW
    * Excellent for extreme axial lengths
    * Very accurate across all eyes
    * Continuously refined with big data

    **Best For:**

    * Long eyes (greater than 26mm)
    * Short eyes (less than 22mm)
    * High accuracy requirements
    * Modern practice standard
  </Accordion>

  <Accordion title="Hill-RBF Calculator">
    **Pattern Recognition Formula**

    **Method:**

    * Radial basis function algorithm
    * Pattern matching to large database
    * Self-validating with bounds checking
    * "Out of bounds" warning system

    **Use Cases:**

    * Unusual eye configurations
    * Cross-checking other formulas
    * When traditional formulas uncertain
  </Accordion>

  <Accordion title="Other Formulas">
    **Additional Options:**

    * **Hoffer Q**: Good for short eyes (less than 22mm)
    * **T2**: Modification of SRK/T
    * **Olsen**: Uses ray tracing
    * **Kane**: New generation AI formula
    * **Pearl-DGS**: Deep learning formula
    * **EVO**: Emmetropia Verifying Optical
  </Accordion>
</AccordionGroup>

### Formula Selection Guide

<CardGroup cols={3}>
  <Card title="Short Eyes (under 22mm)" icon="compress">
    * Barrett Universal II
    * Haigis
    * Hoffer Q
  </Card>

  <Card title="Average Eyes (22-26mm)" icon="arrows-left-right">
    * SRK/T
    * Holladay 1
    * Barrett Universal II
  </Card>

  <Card title="Long Eyes (over 26mm)" icon="expand">
    * Barrett Universal II
    * Haigis
    * SRK/T
  </Card>

  <Card title="Post-Refractive" icon="eye">
    * Haigis-L
    * Barrett True K
    * Specialized calculators
  </Card>

  <Card title="Toric IOLs" icon="rotate">
    * Barrett Toric
    * Holladay 2 Toric
    * Online calculators
  </Card>

  <Card title="Premium IOLs" icon="star">
    * Barrett Universal II
    * Formulas with high accuracy
    * Consider multiple formulas
  </Card>
</CardGroup>

### Target Refraction

Determining the desired post-operative refraction:

**Common Targets:**

* **Emmetropia (0.00)**: Distance vision priority, both eyes
* **Mini-monovision**: Dominant eye emmetropic, non-dominant eye -0.75 to -1.50
* **Full monovision**: Dominant eye distance, non-dominant eye -2.00 to -2.50
* **Myopia (-1.00 to -2.00)**: Patient preference, reduces presbyopic symptoms
* **Matching fellow eye**: Consistency with previous cataract surgery

**Considerations:**

* Patient occupation and hobbies
* Previous refractive history
* Fellow eye refraction (if already operated)
* Presence of macular disease (may prefer slight myopia)
* Patient preference and lifestyle

## IOL Selection

### Lens Types

```php theme={null}
OphInBiometry_LensType_Lens
```

The module maintains a database of available IOL models:

<Accordion title="IOL Categories">
  **Monofocal IOLs:**

  * Single focal point
  * Optimized for distance vision
  * Reading glasses needed for near
  * Most predictable outcomes
  * NHS standard

  **Toric IOLs:**

  * Corrects astigmatism
  * Requires precise alignment
  * Stable rotation critical
  * Reduces spectacle dependence

  **Extended Depth of Focus (EDOF):**

  * Enhanced intermediate vision
  * Some near capability
  * Reduced halos vs multifocal
  * Good for computer users

  **Multifocal IOLs:**

  * Distance and near focal points
  * Reduced spectacle dependence
  * Potential for halos/glare
  * Patient selection critical
  * Private/premium option

  **Accommodating IOLs:**

  * Designed to change power
  * Variable effectiveness
  * Less common currently
</Accordion>

### Lens Properties

Each IOL model has specific characteristics:

* **A-constant** (or SF, ACD): Formula-specific constant for IOL power calculation
* **Power range**: Available powers (typically +5.0 to +30.0D)
* **Power steps**: Increments (0.50D or 1.00D)
* **Material**: Acrylic, silicone, PMMA
* **Haptic design**: Single-piece, three-piece
* **Optic diameter**: Typically 6.0mm
* **Overall diameter**: Typically 13.0mm
* **Incision size**: Required for insertion
* **Manufacturer**: Alcon, J\&J, Bausch & Lomb, Zeiss, Rayner, etc.

### Formulary Management

Institutions configure their available IOL inventory:

* Standard IOLs for NHS/routine cases
* Premium IOLs for private patients
* IOL constants optimized for local outcomes
* Preferred models by surgeon
* Stock management integration

## Clinical Workflow

### Pre-Operative Assessment

<Steps>
  <Step title="Indication for Surgery">
    Patient scheduled for cataract surgery during examination
  </Step>

  <Step title="Biometry Appointment">
    Patient attends for pre-operative biometry measurement
  </Step>

  <Step title="Measurement Acquisition">
    Technician/optometrist performs biometry on optical biometer
  </Step>

  <Step title="Data Import">
    Measurements imported into OpenEyes biometry event
  </Step>

  <Step title="IOL Calculation">
    System calculates IOL powers using configured formulas
  </Step>

  <Step title="Surgeon Review">
    Surgeon reviews calculations and selects target refraction and IOL
  </Step>

  <Step title="IOL Selection">
    Final IOL power and model recorded in biometry event
  </Step>

  <Step title="Integration with Operation Note">
    Biometry data available during operation note creation
  </Step>
</Steps>

### Integration Points

<CardGroup cols={2}>
  <Card title="Examination" icon="eye" href="/modules/examination">
    Cataract surgical management element references biometry status
  </Card>

  <Card title="Operation Booking" icon="calendar" href="/modules/operations">
    Biometry completion tracked as pre-operative requirement
  </Card>

  <Card title="Operation Note" icon="notes-medical" href="/modules/operations">
    IOL details auto-populate from biometry event
  </Card>

  <Card title="Surgical Whiteboard" icon="clipboard">
    Biometry completion status displayed on theatre board
  </Card>
</CardGroup>

## Special Situations

### Post-Refractive Surgery Eyes

Eyes with previous corneal refractive surgery (LASIK, PRK, RK) require special handling:

<Accordion title="Post-LASIK/PRK Challenges">
  **Problems:**

  * Standard keratometry inaccurate (measures front surface only)
  * IOL formulas assume normal cornea
  * Hyperopic surprise common if not adjusted

  **Solutions:**

  * **Historical method**: Use pre-refractive K and refractive change
  * **Contact lens method**: Over-refraction with contact lens
  * **Corneal topography**: Central K values or effective refractive power
  * **OCT-based**: Anterior segment OCT total corneal power
  * **Specialized calculators**: Barrett True-K, Haigis-L, Shammas
  * **Intraoperative aberrometry**: Real-time measurements
</Accordion>

### Dense Cataracts

Optical biometry may fail with very dense cataracts:

**Alternatives:**

* Attempt multiple measurements
* Immersion ultrasound A-scan
* Use fellow eye data (if applicable)
* Empiric IOL selection (if bilateral dense cataracts)

### Extreme Axial Lengths

**Short Eyes (under 21mm):**

* Risk of hyperopic surprise
* Use Hoffer Q, Haigis, or Barrett formulas
* Consider piggyback IOL if AL less than 17mm

**Long Eyes (over 26mm):**

* Risk of myopic surprise
* Barrett Universal II excellent choice
* Haigis also good option
* Consider IOL exchange strategy

### High Astigmatism

For corneal astigmatism >1.50D:

* Consider toric IOL
* Calculate cylinder power needed
* Plan IOL axis alignment
* Consider limbal relaxing incisions as alternative/adjunct
* Topography helpful for irregular astigmatism

## Quality Assurance

### Measurement Quality Checks

<CardGroup cols={2}>
  <Card title="Axial Length" icon="ruler">
    * SNR (signal-to-noise ratio) adequate
    * Multiple measurements agree (SD less than 0.05mm)
    * Value physiologically plausible (18-32mm)
    * Consistent with patient age and refraction
  </Card>

  <Card title="Keratometry" icon="circle">
    * Mires properly aligned
    * Measurements repeatable
    * Values physiologically normal (40-48D typically)
    * Consistent with topography if available
  </Card>
</CardGroup>

### Calculation Verification

**Cross-Check Methods:**

* Use multiple formulas
* Compare results across formulas
* Verify lens constants
* Check extreme values
* Review against clinical expectation

**Red Flags:**

* Large discrepancy between formulas (greater than 0.50D)
* Calculation outside expected range
* Unusual lens power for axial length
* Inconsistent with fellow eye

### Outcome Monitoring

**Post-Operative:**

* Record actual refraction achieved
* Calculate prediction error
* Optimize IOL constants over time
* Audit outcomes by surgeon
* Identify systematic biases

## Configuration

### Module Setup

```php theme={null}
'modules' => [
    'OphInBiometry' => [
        'class' => 'application.modules.OphInBiometry.OphInBiometryModule',
    ],
],
```

### IOL Formulary

Administrators configure:

* Available IOL models
* A-constants (or surgeon factors)
* Power ranges and steps
* Default selections
* Formula preferences

### Device Interfaces

Setup device integration:

* Network endpoints for biometers
* File import locations
* Data mapping configuration
* Quality control rules

## Best Practices

<CardGroup cols={2}>
  <Card title="Multiple Measurements" icon="repeat">
    Always obtain at least 3 measurements per eye and review consistency
  </Card>

  <Card title="Check Both Eyes" icon="eye">
    Measure both eyes even for unilateral cataract - helps verify plausibility
  </Card>

  <Card title="Quality Metrics" icon="star">
    Review device quality indicators - SNR, SD, alignment scores
  </Card>

  <Card title="Multiple Formulas" icon="calculator">
    Use at least 2-3 formulas and understand why they might differ
  </Card>

  <Card title="Document Target" icon="bullseye">
    Clearly record target refraction and rationale
  </Card>

  <Card title="Verify Before Surgery" icon="check">
    Final check of IOL selection on day of surgery
  </Card>
</CardGroup>

## Troubleshooting

<Accordion title="Optical Biometry Fails">
  **Causes:**

  * Dense cataract
  * Posterior subcapsular opacity
  * Corneal opacity
  * Poor patient fixation
  * Vitreous hemorrhage

  **Solutions:**

  * Multiple acquisition attempts
  * Optimize patient positioning
  * Different fixation target
  * Pupil dilation if PSC plaque
  * Resort to ultrasound A-scan
</Accordion>

<Accordion title="Formulas Give Different Results">
  **Understanding Differences:**

  * Normal to have 0.25-0.50D variation
  * Formulas optimize for different situations
  * Check if eye is unusual (very short/long)
  * Review formula suitability for case

  **Resolution:**

  * Use average of most appropriate formulas
  * Weight toward formula best for this eye
  * Document rationale for selection
  * Consider IOL exchange strategy if uncertain
</Accordion>

<Accordion title="Import Data Incorrect">
  **Check:**

  * Correct patient selected
  * Left/right eye mapping correct
  * Units correct (mm vs µm)
  * All fields populated
  * Device export settings

  **Fix:**

  * Re-export from device
  * Manual entry if import fails
  * Verify against device printout
</Accordion>

## Related Modules

<CardGroup cols={3}>
  <Card title="Examination" icon="eye" href="/modules/examination">
    Cataract assessment and surgical decision
  </Card>

  <Card title="Operations" icon="hospital" href="/modules/operations">
    Surgical documentation with IOL details
  </Card>

  <Card title="User Guide" icon="book" href="/user-guide">
    Biometry workflows and procedures
  </Card>
</CardGroup>

## Further Information

<CardGroup cols={2}>
  <Card title="IOL Constant Optimization" icon="sliders" href="/admin">
    Improving calculation accuracy over time
  </Card>

  <Card title="Device Integration" icon="network-wired" href="/admin">
    Configuring biometry device connections
  </Card>
</CardGroup>