A-scan biometry ophthalmology residency viva questions axial length IOL power calculation

https://eyewiki.org/Biometry_for_Intra-Ocular_Lens_(IOL)_Pow…

A-scan biometry viva questions ophthalmology immersion vs contact technique spike pattern errors

ls -la /home/daytona/workspace/ 2>/dev/null || echo "workspace not found"

mkdir -p /home/daytona/workspace/ascan-viva && python3 -c "from reportlab.lib.pa…

~/ascan-viva/build_pdf.py

from reportlab.lib.pagesizes import A4
from reportlab.lib import colors
from reportlab.lib.styles import getSampleStyleSheet, ParagraphStyle
from reportlab.lib.units import mm, cm
from reportlab.platypus import (
    SimpleDocTemplate, Paragraph, Spacer, Table, TableStyle,
    HRFlowable, PageBreak, KeepTogether
)
from reportlab.lib.enums import TA_CENTER, TA_LEFT, TA_JUSTIFY
from reportlab.pdfgen import canvas
from reportlab.platypus import BaseDocTemplate, PageTemplate, Frame

OUTPUT = "/home/daytona/workspace/ascan-viva/AScan_Viva_StudyGuide.pdf"

# ── Colour palette ──────────────────────────────────────────────────────────
NAVY       = colors.HexColor("#0D2B55")
TEAL       = colors.HexColor("#1A7A8C")
GOLD       = colors.HexColor("#E8A020")
LIGHT_BLUE = colors.HexColor("#D6EAF8")
LIGHT_TEAL = colors.HexColor("#D0EDE9")
LIGHT_GOLD = colors.HexColor("#FEF3DC")
WHITE      = colors.white
DARK_GREY  = colors.HexColor("#333333")
MID_GREY   = colors.HexColor("#666666")
LIGHT_GREY = colors.HexColor("#F5F5F5")
RED_HL     = colors.HexColor("#C0392B")
GREEN_HL   = colors.HexColor("#1E8449")

W, H = A4

# ── Styles ───────────────────────────────────────────────────────────────────
styles = getSampleStyleSheet()

def S(name, **kw):
    return ParagraphStyle(name, **kw)

cover_title = S("CoverTitle",
    fontSize=32, fontName="Helvetica-Bold", textColor=WHITE,
    alignment=TA_CENTER, leading=40, spaceAfter=8)

cover_sub = S("CoverSub",
    fontSize=16, fontName="Helvetica", textColor=LIGHT_BLUE,
    alignment=TA_CENTER, leading=22, spaceAfter=4)

cover_badge = S("CoverBadge",
    fontSize=12, fontName="Helvetica-Bold", textColor=GOLD,
    alignment=TA_CENTER, leading=18)

sec_header = S("SecHeader",
    fontSize=14, fontName="Helvetica-Bold", textColor=WHITE,
    alignment=TA_LEFT, leading=18, spaceBefore=4, spaceAfter=4)

q_style = S("Question",
    fontSize=11, fontName="Helvetica-Bold", textColor=NAVY,
    alignment=TA_LEFT, leading=15, spaceBefore=6, spaceAfter=3)

a_style = S("Answer",
    fontSize=10, fontName="Helvetica", textColor=DARK_GREY,
    alignment=TA_JUSTIFY, leading=14, spaceAfter=4,
    leftIndent=12)

bullet_style = S("Bullet",
    fontSize=10, fontName="Helvetica", textColor=DARK_GREY,
    alignment=TA_LEFT, leading=14, leftIndent=20, spaceAfter=2,
    bulletIndent=8)

highlight_style = S("Highlight",
    fontSize=10, fontName="Helvetica-Bold", textColor=RED_HL,
    alignment=TA_LEFT, leading=14, leftIndent=12, spaceAfter=3)

mnemo_style = S("Mnemo",
    fontSize=10, fontName="Helvetica-Oblique", textColor=GREEN_HL,
    alignment=TA_LEFT, leading=14, leftIndent=12, spaceAfter=3)

table_hdr = S("TableHdr",
    fontSize=9, fontName="Helvetica-Bold", textColor=WHITE,
    alignment=TA_CENTER, leading=12)

table_cell = S("TableCell",
    fontSize=9, fontName="Helvetica", textColor=DARK_GREY,
    alignment=TA_LEFT, leading=12)

table_cell_c = S("TableCellC",
    fontSize=9, fontName="Helvetica", textColor=DARK_GREY,
    alignment=TA_CENTER, leading=12)

note_style = S("Note",
    fontSize=9, fontName="Helvetica-Oblique", textColor=MID_GREY,
    alignment=TA_LEFT, leading=13, leftIndent=12)

def P(text, style=a_style): return Paragraph(text, style)
def Q(text): return Paragraph(f"Q: {text}", q_style)
def A(text): return Paragraph(text, a_style)
def B(text): return Paragraph(f"• {text}", bullet_style)
def HL(text): return Paragraph(f"⚠ {text}", highlight_style)
def MN(text): return Paragraph(f"💡 {text}", mnemo_style)
def SP(h=4): return Spacer(1, h*mm)
def HR(): return HRFlowable(width="100%", thickness=0.5, color=colors.HexColor("#CCCCCC"), spaceAfter=3)

def section_banner(title, color=NAVY):
    tbl = Table([[Paragraph(title, sec_header)]], colWidths=[W - 2*cm])
    tbl.setStyle(TableStyle([
        ("BACKGROUND", (0,0), (-1,-1), color),
        ("TOPPADDING", (0,0), (-1,-1), 6),
        ("BOTTOMPADDING", (0,0), (-1,-1), 6),
        ("LEFTPADDING", (0,0), (-1,-1), 10),
        ("RIGHTPADDING", (0,0), (-1,-1), 10),
        ("ROUNDEDCORNERS", [4,4,4,4]),
    ]))
    return tbl

def qa_box(question, answer_elements, bg=LIGHT_TEAL):
    """Wraps a Q+A block in a coloured box."""
    inner = [P(f"<b>Q: {question}</b>", q_style)] + answer_elements
    tbl = Table([[inner]], colWidths=[W - 2*cm])
    tbl.setStyle(TableStyle([
        ("BACKGROUND", (0,0), (-1,-1), bg),
        ("TOPPADDING", (0,0), (-1,-1), 6),
        ("BOTTOMPADDING", (0,0), (-1,-1), 6),
        ("LEFTPADDING", (0,0), (-1,-1), 8),
        ("RIGHTPADDING", (0,0), (-1,-1), 8),
        ("BOX", (0,0), (-1,-1), 0.5, TEAL),
        ("ROUNDEDCORNERS", [4,4,4,4]),
    ]))
    return tbl

def make_table(headers, rows, col_widths=None):
    data = [[Paragraph(h, table_hdr) for h in headers]]
    for row in rows:
        data.append([Paragraph(str(c), table_cell_c) for c in row])
    if not col_widths:
        col_widths = [(W - 2*cm) / len(headers)] * len(headers)
    tbl = Table(data, colWidths=col_widths)
    style = [
        ("BACKGROUND", (0,0), (-1,0), NAVY),
        ("ROWBACKGROUNDS", (0,1), (-1,-1), [WHITE, LIGHT_GREY]),
        ("GRID", (0,0), (-1,-1), 0.4, colors.HexColor("#BBBBBB")),
        ("TOPPADDING", (0,0), (-1,-1), 5),
        ("BOTTOMPADDING", (0,0), (-1,-1), 5),
        ("LEFTPADDING", (0,0), (-1,-1), 6),
        ("RIGHTPADDING", (0,0), (-1,-1), 6),
        ("VALIGN", (0,0), (-1,-1), "MIDDLE"),
    ]
    tbl.setStyle(TableStyle(style))
    return tbl


# ── Page decorators ──────────────────────────────────────────────────────────
def draw_cover(c, doc):
    c.saveState()
    # Navy background
    c.setFillColor(NAVY)
    c.rect(0, 0, W, H, fill=1, stroke=0)
    # Gold accent bar top
    c.setFillColor(GOLD)
    c.rect(0, H - 16*mm, W, 16*mm, fill=1, stroke=0)
    # Teal accent bar bottom
    c.setFillColor(TEAL)
    c.rect(0, 0, W, 12*mm, fill=1, stroke=0)
    # Decorative circles
    c.setFillColor(colors.HexColor("#163A6E"))
    c.circle(W - 50, H - 80, 110, fill=1, stroke=0)
    c.circle(40, 100, 70, fill=1, stroke=0)
    c.restoreState()

def draw_page(c, doc):
    c.saveState()
    # Top stripe
    c.setFillColor(NAVY)
    c.rect(0, H - 12*mm, W, 12*mm, fill=1, stroke=0)
    # Bottom stripe
    c.setFillColor(TEAL)
    c.rect(0, 0, W, 8*mm, fill=1, stroke=0)
    # Page number
    c.setFillColor(WHITE)
    c.setFont("Helvetica", 8)
    c.drawCentredString(W/2, 2.5*mm, f"A-Scan Biometry Viva Guide  |  Page {doc.page}")
    # Header text
    c.setFont("Helvetica-Bold", 8)
    c.setFillColor(GOLD)
    c.drawString(1*cm, H - 8.5*mm, "A-SCAN BIOMETRY")
    c.setFillColor(WHITE)
    c.setFont("Helvetica", 8)
    c.drawRightString(W - 1*cm, H - 8.5*mm, "Ophthalmology Residency Viva")
    c.restoreState()


# ── Build document ────────────────────────────────────────────────────────────
doc = BaseDocTemplate(OUTPUT, pagesize=A4,
    leftMargin=1*cm, rightMargin=1*cm,
    topMargin=1.5*cm, bottomMargin=1.5*cm)

cover_frame = Frame(0, 0, W, H, id="cover", leftPadding=0, rightPadding=0,
                    topPadding=0, bottomPadding=0)
body_frame  = Frame(1*cm, 1.5*cm, W - 2*cm, H - 3*cm, id="body")

cover_template = PageTemplate(id="Cover", frames=[cover_frame], onPage=draw_cover)
body_template  = PageTemplate(id="Body",  frames=[body_frame],  onPage=draw_page)
doc.addPageTemplates([cover_template, body_template])

story = []

# ═══════════════════════════════════════════════════════════════════════════════
# COVER PAGE
# ═══════════════════════════════════════════════════════════════════════════════
story.append(Spacer(1, 55*mm))
story.append(Paragraph("A-SCAN BIOMETRY", cover_title))
story.append(Spacer(1, 4*mm))
story.append(Paragraph("Viva Study Guide", cover_sub))
story.append(Spacer(1, 8*mm))
story.append(Paragraph("Ophthalmology Residency Exam Preparation", cover_badge))
story.append(Spacer(1, 14*mm))

# Quick-reference box on cover
cover_qr_data = [
    [Paragraph("KEY NUMBERS TO REMEMBER", ParagraphStyle("ch", fontSize=10, fontName="Helvetica-Bold", textColor=NAVY, alignment=TA_CENTER))],
    [Paragraph(
        "Normal AL: <b>24 mm</b>  |  Phakic velocity: <b>1555 m/s</b>  |  Aphakic velocity: <b>1532 m/s</b><br/>"
        "AL error impact: <b>2.5–3 D / mm</b>  |  K error impact: <b>1 D / D</b><br/>"
        "Contact spikes: <b>5</b>  |  Immersion spikes: <b>6</b>  |  Sulcus ACD reduction: <b>0.25 mm</b>",
        ParagraphStyle("cv", fontSize=10, fontName="Helvetica", textColor=DARK_GREY,
                       alignment=TA_CENTER, leading=17))],
]
cover_tbl = Table(cover_qr_data, colWidths=[14*cm])
cover_tbl.setStyle(TableStyle([
    ("BACKGROUND", (0,0), (-1,0), GOLD),
    ("BACKGROUND", (0,1), (-1,1), WHITE),
    ("BOX", (0,0), (-1,-1), 1.5, GOLD),
    ("TOPPADDING", (0,0), (-1,-1), 8),
    ("BOTTOMPADDING", (0,0), (-1,-1), 8),
    ("LEFTPADDING", (0,0), (-1,-1), 12),
    ("RIGHTPADDING", (0,0), (-1,-1), 12),
    ("ROUNDEDCORNERS", [6,6,6,6]),
]))
story.append(cover_tbl)
story.append(Spacer(1, 18*mm))
story.append(Paragraph("28 High-Yield Questions  |  7 Topics  |  Clinical Pearls", cover_sub))

# Switch to body template
from reportlab.platypus import NextPageTemplate
story.append(NextPageTemplate("Body"))
story.append(PageBreak())


# ═══════════════════════════════════════════════════════════════════════════════
# SECTION 1: PHYSICS & PRINCIPLES
# ═══════════════════════════════════════════════════════════════════════════════
story.append(section_banner("SECTION 1 — Physics & Principles", NAVY))
story.append(SP(4))

# Q1
story.append(KeepTogether([
    Q("What is the fundamental principle of A-scan ultrasonography?"),
    A("A-scan uses <b>10 MHz</b> high-frequency sound waves. The probe emits a pulse that "
      "reflects off each acoustic interface in the eye (cornea, anterior lens, posterior lens, retina). "
      "Time-of-flight is converted to distance:"),
    A("<b>Distance = Time × Velocity / 2</b>"),
    A("Result is a 1-D amplitude display — reflecting surfaces appear as vertical spikes. "
      "'A' = <i>Amplitude</i> modulation."),
    SP(3),
]))

# Q2 - Velocity table
story.append(KeepTogether([
    Q("What are the standard sound velocities used in A-scan biometry?"),
    SP(2),
    make_table(
        ["Medium", "Velocity (m/s)"],
        [
            ["Cornea + Crystalline lens", "1641"],
            ["Aqueous humour + Vitreous", "1532"],
            ["Normal phakic eye (average)", "1555"],
            ["Aphakic eye", "1532"],
            ["Pseudophakic eye", "1532 + IOL correction"],
        ],
        col_widths=[10*cm, 5.5*cm]
    ),
    SP(2),
    MN("Memory: 1641 (solid structures) → 1555 (phakic average) → 1532 (fluid/aphakic)"),
    SP(3),
]))

# Q3
story.append(KeepTogether([
    Q("Why does sound travel faster through the lens than vitreous?"),
    A("The crystalline lens is a denser, more solid structure. Acoustic velocity increases "
      "with the elasticity-to-density ratio of a medium. Greater molecular density and structural "
      "rigidity → faster sound propagation. Aqueous and vitreous are watery liquids — lower density."),
    SP(3),
]))

# Q4 - spike pattern
story.append(KeepTogether([
    Q("Describe the A-scan spike pattern in a normal phakic eye (contact method)."),
    A("<b>5 spikes</b> in the contact technique:"),
    B("1. Probe tip + Cornea (combined — single spike)"),
    B("2. Anterior lens capsule"),
    B("3. Posterior lens capsule"),
    B("4. Retina (steep 90° rise — most critical)"),
    B("5. Sclera / Orbital fat"),
    A("Ideal scan: all spikes at maximum amplitude, retinal spike steeply rising and "
      "clearly separated from scleral spike."),
    SP(3),
]))

# Q5 - immersion
story.append(KeepTogether([
    Q("How does the immersion technique differ from contact in terms of spike count?"),
    A("Immersion produces <b>6 spikes</b> because the probe does not touch the cornea — "
      "probe tip and cornea are now separate acoustic interfaces:"),
    B("1. Probe tip (in saline)"),
    B("2. Cornea (separate spike)"),
    B("3. Anterior lens"),
    B("4. Posterior lens"),
    B("5. Retina"),
    B("6. Sclera"),
    MN("Contact = 5 spikes. Immersion = 6 spikes. Extra spike = separate cornea."),
    SP(3),
]))

story.append(PageBreak())

# ═══════════════════════════════════════════════════════════════════════════════
# SECTION 2: CONTACT vs IMMERSION
# ═══════════════════════════════════════════════════════════════════════════════
story.append(section_banner("SECTION 2 — Contact vs Immersion Technique", TEAL))
story.append(SP(4))

story.append(KeepTogether([
    Q("What is the most common and most important error in contact A-scan biometry?"),
    A("<b>Corneal compression (applanation artifact)</b>. Even minimal probe pressure "
      "indents the soft cornea, causing:"),
    B("Falsely <b>shortened</b> axial length"),
    B("Shallower ACD on scan"),
    B("Leads to underpowered IOL → residual <b>hyperopia</b> postoperatively"),
    HL("Rule: Delete readings with unexpectedly shallow ACD even if spikes look good."),
    SP(3),
]))

story.append(KeepTogether([
    Q("By how much does immersion A-scan differ from contact A-scan for axial length?"),
    A("Immersion eyes measure <b>0.1–0.3 mm longer</b> than contact eyes. This is NOT an "
      "overestimation — it is the accurate value. Contact underestimates due to corneal indentation."),
    SP(3),
]))

story.append(KeepTogether([
    Q("What is the Prager shell and what does it do?"),
    A("A small scleral cup placed between the lids over the anesthetized eye, filled with saline. "
      "The A-scan probe is immersed in the fluid bath — avoids any corneal contact, eliminating "
      "compression artifact. Enables the immersion technique of biometry."),
    SP(3),
]))

# Comparison table
story.append(KeepTogether([
    Q("Compare contact vs immersion A-scan vs optical biometry."),
    SP(2),
    make_table(
        ["Feature", "Contact A-scan", "Immersion A-scan", "Optical Biometry"],
        [
            ["Corneal contact", "Yes", "No", "No"],
            ["Main error", "Compression", "None significant", "Dense cataract block"],
            ["Spikes", "5", "6", "N/A (laser)"],
            ["Technician skill", "High", "Moderate", "Low"],
            ["Accuracy", "Lowest", "Good", "Best"],
            ["Dense cataract", "Works", "Works", "May fail"],
            ["Silicone oil", "Error", "Error", "Unaffected"],
        ],
        col_widths=[4.5*cm, 4*cm, 4*cm, 3.5*cm]
    ),
    SP(3),
]))

story.append(KeepTogether([
    Q("List advantages of immersion over contact A-scan."),
    B("Avoids corneal compression → more accurate axial length"),
    B("Less technician-dependent, reproducible between operators"),
    B("Faster when proficient"),
    B("Preferred in soft eyes (low IOP) where compression is worst"),
    B("Gold standard for paediatric biometry under anaesthesia"),
    SP(3),
]))

story.append(PageBreak())

# ═══════════════════════════════════════════════════════════════════════════════
# SECTION 3: AXIAL LENGTH
# ═══════════════════════════════════════════════════════════════════════════════
story.append(section_banner("SECTION 3 — Axial Length & Normal Values", NAVY))
story.append(SP(4))

story.append(KeepTogether([
    Q("What is the average axial length of a normal adult phakic eye?"),
    A("Average: <b>24 mm</b> (range ~22–26 mm in emmetropia)."),
    A("Clinical significance: <b>Each 1 mm change in AL = ~2.5–3 D change in IOL power</b>. "
      "Effect is greater in short eyes than long eyes. AL is the single most important variable "
      "in IOL power calculation."),
    SP(3),
]))

story.append(KeepTogether([
    Q("What axial lengths define microphthalmos and high myopia?"),
    SP(2),
    make_table(
        ["Condition", "Axial Length"],
        [
            ["Nanophthalmos", "< 20 mm"],
            ["Microphthalmos (clinical)", "< 21 mm"],
            ["Short eye (formula caution)", "< 22 mm"],
            ["Emmetropia", "~24 mm"],
            ["Long eye (myopia prone)", "> 26 mm"],
            ["High myopia / staphyloma risk", "> 26–28 mm"],
        ],
        col_widths=[10*cm, 5.5*cm]
    ),
    SP(3),
]))

story.append(KeepTogether([
    Q("From where to where is axial length measured?"),
    A("From the <b>anterior corneal epithelial surface</b> to the "
      "<b>retinal pigment epithelium (RPE) at the macula (fovea)</b>. "
      "Alignment must be along the <b>visual axis</b>, not the optic nerve axis. "
      "Beam hitting the optic nerve → absent scleral spike (recognisable error pattern)."),
    SP(3),
]))

story.append(PageBreak())

# ═══════════════════════════════════════════════════════════════════════════════
# SECTION 4: IOL POWER CALCULATION FORMULAE
# ═══════════════════════════════════════════════════════════════════════════════
story.append(section_banner("SECTION 4 — IOL Power Calculation Formulae", TEAL))
story.append(SP(4))

story.append(KeepTogether([
    Q("Write the basic SRK formula. State its limitations."),
    A("<b>P = A − 0.9K − 2.5(AL)</b>"),
    A("Where: P = IOL power (D), A = A-constant, K = average keratometry (D), AL = axial length (mm)"),
    A("<b>Limitations:</b>"),
    B("1st-generation empirical regression formula — least accurate"),
    B("Inaccurate for extreme axial lengths (short/long eyes)"),
    B("Superseded by SRK II → SRK/T"),
    B("Use only for manual calculation when no software is available"),
    SP(3),
]))

story.append(KeepTogether([
    Q("Which IOL formula to use for short vs long eyes?"),
    SP(2),
    make_table(
        ["Eye Type", "Axial Length", "Recommended Formulae"],
        [
            ["Short", "< 22 mm", "Hoffer Q, Haigis, Hill-RBF, Kane"],
            ["Average", "22–26 mm", "SRK/T, Holladay 1, Haigis, any 3rd gen"],
            ["Long", "> 26 mm", "Barrett Universal II, Holladay, Haigis (optimised), Kane"],
        ],
        col_widths=[3.5*cm, 4*cm, 8*cm]
    ),
    SP(2),
    HL("Short eyes are MOST prone to unexpected mean spherical error after surgery."),
    SP(3),
]))

story.append(KeepTogether([
    Q("What is ELP and why is it the most critical variable in modern formulae?"),
    A("<b>Effective Lens Position (ELP)</b> = predicted distance from the anterior corneal surface "
      "to the principal plane of the implanted IOL."),
    A("All formulae try to optimize ELP prediction:"),
    B("3rd gen (SRK/T, Holladay 1, Hoffer Q): predict ELP from K + AL"),
    B("4th gen (Haigis, Holladay 2): add ACD, lens thickness, white-to-white"),
    B("5th gen (Barrett, Kane): AI/regression-enhanced ELP prediction"),
    SP(3),
]))

story.append(KeepTogether([
    Q("What makes the Haigis formula unique?"),
    A("<b>Three IOL constants (a0, a1, a2)</b> instead of a single A-constant:"),
    A("<b>P = a0 + a1 × ACD (measured) + a2 × AL</b>"),
    A("Separates contribution of ACD from AL → superior for abnormal eyes. "
      "Allows personalised optimisation per surgeon per IOL."),
    SP(3),
]))

story.append(KeepTogether([
    Q("What is the A-constant? What factors affect it?"),
    A("IOL-specific empirical constant representing predicted IOL position (ELP). "
      "Provided by the manufacturer."),
    A("<b>Factors affecting it:</b>"),
    B("IOL design (single-piece vs 3-piece)"),
    B("IOL material (PMMA / acrylic / silicone)"),
    B("IOL position: sulcus → reduce ACD by <b>0.25 mm</b>; posterior iris fixation → further 0.25 mm"),
    B("Surgeon's own technique — should personalise using ≥ 20–50 own cases"),
    SP(3),
]))

story.append(KeepTogether([
    Q("How does a keratometry error compare to an axial length error in terms of IOL impact?"),
    SP(2),
    make_table(
        ["Error Source", "Magnitude", "IOL Power Impact"],
        [
            ["Axial Length error", "1 mm", "2.5–3 D"],
            ["Keratometry error", "1 D", "~1 D"],
        ],
        col_widths=[5*cm, 4*cm, 6.5*cm]
    ),
    SP(2),
    HL("Axial length error has 2.5–3× greater impact than keratometry error — most consequential mistake."),
    SP(3),
]))

story.append(PageBreak())

# ═══════════════════════════════════════════════════════════════════════════════
# SECTION 5: SPECIAL SITUATIONS
# ═══════════════════════════════════════════════════════════════════════════════
story.append(section_banner("SECTION 5 — Special Situations", NAVY))
story.append(SP(4))

story.append(KeepTogether([
    Q("How do you perform biometry in silicone oil-filled eyes?"),
    A("Silicone oil velocity (~980–1040 m/s) is far lower than normal vitreous (1532 m/s). "
      "A-scan significantly <b>overestimates</b> axial length (falsely long)."),
    A("<b>Solutions:</b>"),
    B("Use optical biometry (IOL Master) — unaffected by silicone oil"),
    B("A-scan: use silicone oil-specific velocity setting"),
    B("Apply Okulix calculation or correction: <b>CF = CT × (1 − 1532/vel)</b>"),
    HL("Silicone oil = use optical biometry as first choice."),
    SP(3),
]))

story.append(KeepTogether([
    Q("What are the pseudophakic A-scan correction factors for different IOL materials?"),
    A("Use aphakic mode (1532 m/s), then <b>add correction</b>:"),
    SP(2),
    make_table(
        ["IOL Material", "Correction to Add"],
        [
            ["PMMA", "+0.4 mm"],
            ["Acrylic", "+0.2 mm"],
            ["Silicone (high velocity)", "−0.4 to −0.8 mm"],
        ],
        col_widths=[8*cm, 7.5*cm]
    ),
    SP(2),
    A("Formula: <b>CF = CT × (1 − 1532 / velocity of material)</b>"),
    SP(3),
]))

story.append(KeepTogether([
    Q("How does aphakia affect A-scan biometry?"),
    B("Sound velocity = <b>1532 m/s</b> (no lens, all fluid)"),
    B("Two lens spikes are <b>absent</b>; single spike from anterior vitreous face / posterior capsule"),
    B("Biometer must be set to <b>aphakic mode</b>"),
    B("Immersion technique strongly preferred"),
    SP(3),
]))

story.append(KeepTogether([
    Q("How do you manage biometry after previous LASIK/PRK?"),
    A("Standard IOL formulas FAIL because:"),
    B("Keratometry underestimates corneal power (altered index of refraction assumptions)"),
    B("ELP prediction errors (formulae assume normal corneal shape)"),
    A("<b>Approaches:</b>"),
    B("Clinical history method: pre-LASIK refraction + K values"),
    B("Contact lens method: plano lens to derive true corneal power"),
    B("Haigis-L formula: statistical regression, no historical data needed"),
    B("Barrett True K / Masket formula"),
    HL("Always target mild myopia (−0.5 to −1.0 D) as safety buffer. Warn patient of refractive surprise."),
    SP(3),
]))

story.append(KeepTogether([
    Q("A contact lens wearer needs biometry. What precaution is required?"),
    B("Soft contact lenses: withhold for <b>≥ 1 week</b> before biometry"),
    B("Rigid gas permeable (RGP) lenses: longer period needed — corneal re-stabilisation"),
    B("Purpose: allow corneal curvature to return to natural state to avoid false K readings"),
    SP(3),
]))

story.append(PageBreak())

# ═══════════════════════════════════════════════════════════════════════════════
# SECTION 6: ERRORS & QUALITY CONTROL
# ═══════════════════════════════════════════════════════════════════════════════
story.append(section_banner("SECTION 6 — Errors & Quality Control", TEAL))
story.append(SP(4))

story.append(KeepTogether([
    Q("List the sources of error in A-scan biometry."),
    A("<b>Technical errors:</b>"),
    B("Corneal compression (contact) → underestimates AL → hyperopic surprise"),
    B("Misalignment (off visual axis) → underestimates AL"),
    B("Sloped retinal spike (beam not perpendicular to macula)"),
    B("Beam directed at optic nerve instead of macula → absent scleral spike"),
    A("<b>Patient factors:</b>"),
    B("Poor fixation — dense cataract, nystagmus, macular disease"),
    B("Posterior staphyloma — variable readings from same eye"),
    B("Silicone oil in vitreous"),
    B("Previous corneal refractive surgery"),
    A("<b>Formula selection errors:</b>"),
    B("Wrong formula for extreme AL"),
    B("Unoptimised A-constants"),
    SP(3),
]))

story.append(KeepTogether([
    Q("What does the ideal retinal spike look like and why does it matter?"),
    A("The ideal retinal spike must:"),
    B("Rise <b>steeply at 90°</b> to the baseline"),
    B("Be at <b>maximum height</b>"),
    B("Be <b>clearly separated</b> from the scleral spike"),
    HL("A sloped retinal spike = off-axis measurement. That reading MUST be rejected — "
       "it represents a longer-than-true path through the vitreous."),
    SP(3),
]))

story.append(KeepTogether([
    Q("What is posterior staphyloma and why is it problematic for biometry?"),
    A("Posterior staphyloma is an outpouching of the posterior sclera seen in high myopia. "
      "The macula may be at the bottom of the staphyloma, resulting in:"),
    B("Multiple different axial length readings from the same eye"),
    B("Difficulty identifying the true macular point"),
    B("Optical biometry (IOL Master) is preferred as it targets the RPE directly"),
    B("A-scan: use the reading corresponding to the longest reproducible measurement"),
    SP(3),
]))

story.append(PageBreak())

# ═══════════════════════════════════════════════════════════════════════════════
# SECTION 7: CLINICAL VIVA SCENARIOS
# ═══════════════════════════════════════════════════════════════════════════════
story.append(section_banner("SECTION 7 — Clinical Viva Scenarios", NAVY))
story.append(SP(4))

story.append(KeepTogether([
    Q("A dense white cataract — contact A-scan gives AL = 21.8 mm. What do you do?"),
    HL("Red flags: dense cataract (poor fixation), very short AL, contact method used."),
    A("<b>Steps:</b>"),
    B("1. Repeat with <b>immersion technique</b> (Prager shell + saline bath)"),
    B("2. Measure fellow eye — bilateral AL should be within 0.3 mm"),
    B("3. Select formula for short eye: <b>Hoffer Q or Haigis</b>"),
    B("4. Target slight myopia (−0.5 D) to avoid aphakia from underpowered IOL"),
    B("5. If optical biometry was tried but failed: A-scan immersion is the gold standard backup"),
    SP(3),
]))

story.append(KeepTogether([
    Q("IOL Master K readings post-LASIK show 36.5 D. What is the concern?"),
    HL("Post-myopic LASIK: central ablation makes cornea flatter → IOL Master "
       "underestimates true corneal power using standard index (1.3375)."),
    A("<b>Approach:</b>"),
    B("Use Haigis-L or Barrett True K (no pre-LASIK data needed)"),
    B("If historical data available: clinical history method"),
    B("Target −0.5 to −1.0 D as safety buffer"),
    B("Counsel patient: higher risk of refractive surprise, possible piggyback IOL later"),
    SP(3),
]))

story.append(KeepTogether([
    Q("Why does optical biometry (IOL Master) fail in some cases and what is the backup?"),
    A("Optical biometry (partial coherence interferometry) uses laser — blocked by:"),
    B("Very dense posterior subcapsular cataracts"),
    B("Dense nuclear or cortical opacities where the signal cannot penetrate"),
    B("Corneal scarring / opacification"),
    A("<b>Backup:</b> Immersion A-scan ultrasonography — sound penetrates opaque media."),
    SP(3),
]))

story.append(KeepTogether([
    Q("A patient reports −6.0 D residual hyperopia after cataract surgery. "
      "What went wrong and how?"),
    A("Most likely cause: <b>corneal compression during contact A-scan biometry</b>. "
      "Compressed cornea → falsely short AL → IOL power calculated too low → "
      "insufficient refractive power implanted → hyperopic outcome."),
    A("Other possibilities: formula error for short eye, wrong A-constant, wrong IOL implanted."),
    B("Prevention: immersion A-scan or optical biometry; check fellow eye symmetry"),
    B("Management: spectacles, contact lens, IOL exchange, piggyback IOL, or LASIK correction"),
    SP(3),
]))

# ═══════════════════════════════════════════════════════════════════════════════
# QUICK REFERENCE FLASHCARD TABLE
# ═══════════════════════════════════════════════════════════════════════════════
story.append(PageBreak())
story.append(section_banner("QUICK REFERENCE — High-Yield Numbers & Facts", GOLD))
story.append(SP(4))

qr_data = [
    [Paragraph("<b>Parameter</b>", table_hdr), Paragraph("<b>Value / Fact</b>", table_hdr)],
    [P("Normal adult axial length", table_cell), P("<b>24 mm</b>", table_cell)],
    [P("AL impact on IOL power", table_cell), P("<b>2.5–3 D per mm</b>", table_cell)],
    [P("K impact on IOL power", table_cell), P("<b>~1 D per 1 D</b>", table_cell)],
    [P("Sound velocity — phakic eye", table_cell), P("<b>1555 m/s</b>", table_cell)],
    [P("Sound velocity — aphakic eye", table_cell), P("<b>1532 m/s</b>", table_cell)],
    [P("Sound velocity — cornea + lens", table_cell), P("<b>1641 m/s</b>", table_cell)],
    [P("Contact A-scan spikes", table_cell), P("<b>5 spikes</b>", table_cell)],
    [P("Immersion A-scan spikes", table_cell), P("<b>6 spikes</b> (cornea + probe separate)", table_cell)],
    [P("Immersion vs contact AL difference", table_cell), P("<b>0.1–0.3 mm longer</b> on immersion (no compression)", table_cell)],
    [P("Sulcus ACD reduction", table_cell), P("<b>−0.25 mm</b> from in-bag value", table_cell)],
    [P("PMMA pseudophakic correction", table_cell), P("<b>+0.4 mm</b> from aphakic mode", table_cell)],
    [P("Acrylic IOL correction", table_cell), P("<b>+0.2 mm</b> from aphakic mode", table_cell)],
    [P("Silicone IOL correction", table_cell), P("<b>−0.4 to −0.8 mm</b> from aphakic mode", table_cell)],
    [P("Short eye formula choice (AL < 22 mm)", table_cell), P("<b>Hoffer Q, Haigis, Hill-RBF, Kane</b>", table_cell)],
    [P("Long eye formula choice (AL > 26 mm)", table_cell), P("<b>Barrett Universal II, Holladay, Haigis, Kane</b>", table_cell)],
    [P("Nanophthalmos", table_cell), P("<b>AL < 20 mm</b>", table_cell)],
    [P("A-constant unique to", table_cell), P("IOL design, material, position, surgeon technique", table_cell)],
    [P("Haigis formula constants", table_cell), P("<b>3 constants: a0, a1, a2</b>", table_cell)],
    [P("Soft CL: withhold before biometry", table_cell), P("<b>≥ 1 week</b>", table_cell)],
]
qr_tbl = Table(qr_data, colWidths=[8*cm, 7.5*cm])
qr_tbl.setStyle(TableStyle([
    ("BACKGROUND", (0,0), (-1,0), NAVY),
    ("ROWBACKGROUNDS", (0,1), (-1,-1), [WHITE, LIGHT_GOLD]),
    ("GRID", (0,0), (-1,-1), 0.4, colors.HexColor("#CCCCCC")),
    ("TOPPADDING", (0,0), (-1,-1), 5),
    ("BOTTOMPADDING", (0,0), (-1,-1), 5),
    ("LEFTPADDING", (0,0), (-1,-1), 7),
    ("RIGHTPADDING", (0,0), (-1,-1), 7),
    ("VALIGN", (0,0), (-1,-1), "MIDDLE"),
]))
story.append(qr_tbl)
story.append(SP(5))
story.append(P("Good luck in your viva! Review the high-yield numbers daily in the week before your exam.", note_style))

# ── Build ─────────────────────────────────────────────────────────────────────
doc.build(story)
print("PDF built successfully:", OUTPUT)

cd /home/daytona/workspace/ascan-viva && python3 build_pdf.py 2>&1

ls -lh /home/daytona/workspace/ascan-viva/AScan_Viva_StudyGuide.pdf

panophthalmitis case presentation clinical features management ophthalmology residency

https://eyewiki.org/Panophthalmitis