Glaucoma Workup Review: from A to OCT

Dr. Nathan Rains

Eye Center of Northern Colorado

What is Glaucoma?

3 million Americans have glaucoma

One of the leading causes of adult blindness

No symptoms until extensive peripheral vision loss (for most types of glaucoma)

“sneak thief of sight”

Chronic condition, no cure, just control

Control is lower eye pressures by

Eye drops, laser surgeries, or medical surgeries

What is Glaucoma?Prevalence

http://www.nei.nih.gov/eyedata/glaucoma.asp#1

What is Glaucoma? Definition

... optic neuropathy with associated visual function loss, with intraocular pressure (IOP) being one of the primary risk factors...

American Academy of Ophthalmology

Optic Neuropathy?

Pic 1: http://www.hopkinsmedicine.org/wilmer/glaucoma_center_excellence/book/chapter_what_is_glaucoma.html

Optic Neuropathy?

http://www.cehjournal.org/article/the-optic-nerve-head-in-glaucoma/

Goals of Glaucoma Testing

The ultimate goal of glaucoma testing is three fold: To Diagnose Glaucoma (probably the hardest step)

Is the test RELIABLE

Is the test REPEATABLE

To Determine its Severity

Suspect, mild, moderate, severe

Initiate treatment, set appropriate target pressures, etc.

To Monitor Progression

Glaucoma Testing

Tonometry Pachymetry Gonioscopy Tomography Perimetry *Biomicroscopy *Photography *Corneal Hysteresis *Ganglion Cell Complex

What is Tonometry?

The measurement of intraocular pressure (IOP) recorded in mmHg

Normal IOP – 10-20 mmHg (avg ~ 16mmHg)

Ocular hypertension - >20-22mmHg

Diurnal fluctuations – 4-6 mmHg

Pressure is highest at night, in the supine position (3 am)

Difference between eyes – 2-3 mmHg

>4-6 is suspicious

Only treatable measure of glaucoma

All medicine and surgery is geared to this one task, lower IOP

Tested at every examination and followup care

Diurnal Variation

http://www.eyecalcs.com/DWAN/pages/v3/v3c046.html

How is Tonometry MeasuredDigital Palpation

Tonometry InstrumentsIndentation – iCare & Tonopen

http://www.icaretonometer.com/rebound-technology/Good 38 sec video

Tonometry InstrumentsNon-Contact Tonometry

Advantages

No anesthesia

*No contact

Ease of use

Quick

Disadvantages

Patients 'love' to hate this test

Accuracy?

Tonometry Instruments Goldmann Applanation Tonometry

Gold standard

Accurate

Inexpensive

easy to use

Disadvantages

Anesthesia

still dependent on corneal properties

Tonometry Instruments

Take homes

Digital

basic, only detects extremely high pressures

Indentation

portable, cheap, supine

Non-contact tonometry

expensive machine, touchless, quick, patient discomfort

Applanation

gold standard, inexpensive, easy to use, less variability

Pachymetry

What is Pachymetry?

The measurement of corneal thickness, in microns (um)

Average CENTRAL corneal thickness ~ 555 um

In glaucoma, used as a risk factor in the development of glaucoma Ocular Hypertensive Treatment Study (OHTS)

CCT <555, high risk

CCT 555-585 no increased risk

CCT >585 low risk

Pachymetry and IOP correction table?

Theory

The thicker the cornea, the artificially high reading

The thinner the cornea, the artificially low reading

IOP correction table? 1975 study

Every 100um adjust by 7mmHg

17 other studies, all different IOP per 100um adjustment… no consensus

Reason Thickness of cornea is only one part of it:

Corneal properties (steep/flat, hysteresis (stiffness), etc.)

Center of cornea

Compare symmetry (>30, repeat)

LASIK/PRK?

Diseased Corneas?

Fuchs, keratoconus?

Used as a RISK factor

No universal agreement on IOP correction table to use

So, we do NOT adjust IOP measurement

Pachymetry Pearls

Goals of Glaucoma Testing

The ultimate goal of glaucoma testing is three fold: To Diagnose Glaucoma (probably the hardest step)

Is the test RELIABLE

Is the test REPEATABLE

To Determine its Severity

Suspect, mild, moderate, severe

Initiate treatment, set appropriate target pressures, etc.

To Monitor Progression

What is Glaucoma?By Type

Primary Open Angle Glaucoma Acute Angle Closure Glaucoma Pseudoexfoliative Glaucoma Pigmentary Glaucoma Normal/Low Tension Glaucoma Neovascular Glaucoma Congenital Glaucoma Traumatic Glaucoma Secondary Glaucoma And more… over 60 types...

Gonioscopy

Obtain a view of the drainage angle formed between the eye’s cornea and iris

Aids in diagnosis and monitoring of glaucoma

Performed under slit lamp, with a gonio lens

Used in laser treatment of the angle (SLT – selective laser trabeculoplasty)

Gonioscopy

Gonioscopy.org Video Clip

Can’t See That Stupid Line

Normal angle

Pigmented Angle

http://www.academy.org.uk/tutorials/gongrade.jpg

Anterior Segment OCT

http://www.iovs.org/content/52/5/2095/F1.expansion.html

GonioscopyTake home

Helps diagnose and determine type of glaucoma

Check out gonioscopy.org

Glaucoma Testing

Tonometry Pachymetry Gonioscopy Tomography Perimetry *Biomicroscopy *Photography *Corneal Hysteresis *Ganglion Cell Complex

Optic Neuropathy?

http://www.cehjournal.org/article/the-optic-nerve-head-in-glaucoma/

Optical Coherence Tomography

Non-invasive, high resolution, imaging technology

Time Domain vs Spectral Domain

TD – 400 scans per sec, 10um

SD – 20,000-40,000 per sec, 3um

3-D reconstructions

AWESOME!

Scan types

Retinal (macular)

Optic Disc

http://www.docvadis.fr/aobeffroi/page/l_oeil_et_les_examens/les_machines_utilisees_par_l_ophtalmologiste/oct_ou_tomographie_en_coherence_optique.html

OCT Optic Disc

Scans the optic disc using a 6mm cube

Obtains Retinal Nerve Fiber Layer Thickness

Color codes a thickness map

‘hour glass’ appearance

Red (350um), to blue (0um)

Normative table

RNFL thickness

Symmetry

C/D ratio

Etc.

RNFL TSNIT Map

Quadrant and Clock Hour RNFL thickness chart

Normal OCT

OCT Optic DiscDiagnosing Glaucoma

Average RNFL

Symmetry

>20um difference is statistically significant

Quadrant RNFL layout

Inferior and Superior are the greatest indicators

Clock Hour RNFL layout

Inferior temp and/or superior temp thin

Lastly – does it correlate with the visual field

***structural loss precedes VF loss***

OCT optic discExample

OCT Optic DiscMonitoring Glaucoma

Average NFL

Symmetry

Progression Analysis

http://www.healio.com/ophthalmology/journals/osli/2011-7-42-4-supplemental/%7Bde06c09a-2d95-42f4-b403-2fc1fa6a3550%7D/clinical-use-of-oct-in-assessing-glaucoma-progression

Retinal Nerve Fiber Layer Anatomy

Carl Zeiss Webinar Photo – Effective Perimetry

Fibers

Make an arc

Do NOT cross horizontal axis

Temporal raphe

Defects on nerve are

opposite on fields

PerimetryAutomated Visual Field

Automated Perimetry for Glaucoma

Types of tests used

30-2, 24-2, and 10-2

Strategies used

SITA Standard, SITA Fast

Visual Field

Types: 30-2, 24-2, 10-2 1st number refers to the degrees AROUND

fixation Ex: 10-2 – 10 degrees around the fovea (20 degrees total)

2nd number refers to the protocol Protocol 1 – points directly on the horiz and vert axis

Protocol 2 – points directly above and below axis

Easier to interpret and used exclusively now

Points tested 30-2 – 6 degrees apart, total points 76, ~8 min per eye

24-2 – 6 degrees apart, total points 54, ~5 min per eye

10-2 – 2 degrees apart, total points 54

30-2 vs 24-2?

24-2 advantagesFaster time (~5 min per eye)Less variableSimilar results

30-2 advantagesMore degrees of field tested

May help detect/monitor neurological defects, ie. Idiopathic intracranial hypertension

SITA Standard vs SITA Fast

SITA Standard

Best threshold test

Better for early detection in glaucoma

More reliable, more sensitive

SITA Fast

Fast(er)

Can be used for screening purposes

More Variable, less sensitive (underestimates) scotomas

When to use 10-2 in Glaucoma?

Previously, used exclusively in severe peripheral field loss

24-2 not providing enough information to monitor progression, so 10-2 replaces 24-2

Recently, published in the JAMA Ophthalmology, January 2014, 10-2 VF testing was found to detect early glaucomatous defects missed on 24-2

Of 22 eyes tested as normal on 24-2 testing, 22.7% were abnormal in 10-2 testing

May use 10-2 in addition to 24-2

Automated PerimetryGlaucoma VF Types

Types

Nasal Step

Arcuate

Paracentral

Severity

Mild to Very Severe

http://www.medrounds.org/glaucoma-guide/2006/02/section-1-c-understanding-vision-loss.html

Visual FieldDiagnosing Glaucoma

Reliability Fixation losses, false positive, false negatives, etc.

Repeatability When there’s a defect, is it repeatable?

Three consecutive fields to reliably confirm glaucoma*

Global Indices GHT – glaucoma hemifield test

MD – Mean Deviation

PSD – Pattern Standard Deviation

VFI – Visual Field Index (percentage)

*Keltner et al. for the Ocular Hypertenstion Treatment Study Group, Arch Ophthalmol 123:1201 (2005)

Normal Visual Field

Visual Field - Glaucoma

Visual Field - Monitoring Progression

Visual Field/OCT Integration

Visual Field/OCT Integration

Glaucoma Workup Review

The End! Questions?