Diagnostic Tests


Dr Cronin uses the latest in networked high resolution and laser diagnostic imaging to ensure that any abnormalities in your eyes can be detected early and appropriate treatment started as soon as possible.  Some of the investigations and tests that you may required are explained below.

Ocular Coherence Tomography

OCT uses light that is reflected off the different layers of the retina to create an extremely high resolution image of the different structures of the eye.  It allows a clear view of microscopic detail that can be compared to previous or future scans to look for changes.  In the same way that a CT scan or an MRI produces cross-sectional images of other parts of the body, OCT produces similar images of the eye but in much higher detail.  With the most sophisticated ultra-high resolution OCT machines, microscopic details can be seen so that diseases are detected and treated early. 

OCT scans are used to look for and monitor diseases at the macula such as macular degeneration or diabetes.  They are also used for diagnosing and following glaucoma by assessing the thickness of the nerve layer at the back of the eye. 

Despite OCT scans being vital to giving you outstanding ophthalmic care, unfortunately they do not have a medicare rebate. 

 OCT of macular oedema

(An OCT of macular oedema in diabetes)

Heidelberg Retinal Tomography "HRT"

The HRT is a confocal laser scanning system that allows imaging of the cornea, optic nerve and retina.  It uses lasers to give different data to that given by OCT.  The HRT is one of the most accurate diagnostic tests that exists for glaucoma and its exquisite corneal confocal microscopy features make it indispensable in diagnosing the types of complex and rare corneal diseases that are often referred to Dr Cronin.  Confocal microscopy is so specialised and the machine so expensive, that very few textbooks and atlases exist.  Dr Cronin and the Prevent Blindness Foundation are working to create a free online atlas of conditions that can be diagnosed with this amazing piece of equipment.

The Queensland Eye Institute has one of the only HRT’s in Queensland to provide patients with world class care for glaucoma and corneal diseases.  Unfortunately medicare does not provide a rebate for HRT scans.  


HRT scan 

Corneal Topography /  Pentacam

This is a specialised piece of equipment for accurately mapping the shape of the cornea in diseases such as keratoconus.  The pentacam uses two high speed rotating cameras to enable analysis of the precise shape of the front and back surfaces of the cornea.  These measurements are used in the diagnosis and treatment of corneal pathology as well as to assist in choosing the correct intraocular lens in patients having cataract surgery.  

If you are being followed up for keratoconus, it is important that if possible, you avoid wearing your contact lenses for 1 week prior to the consultation.  This will ensure that the scan is not affected by any indentation from your contact lenses. 

Unfortunately medicare does not offer a rebate for Pentacam Corneal Topography. 

Pentacam topography
Topography report 

Visual Fields 

Your field of vision can be accurately mapped with an automated process called “computerised perimetry”.  Your visual field may be damaged in glaucoma, trauma and neurological diseases.  When combined with imaging data from HRT and OCT, this creates an extremely accurate picture of the health of the optic nerve and can detect any changes early so that treatment can be changed if required. 

Visual Field Analysis


Choosing the correct lens to place inside your eye during cataract surgery is vitally important for a good visual outcome.  To make this lens choice numerous parameters of your eye are measured with a laser.  A formula then calculates the correct lens to insert based on the extremely accurate measurements.  The IOL Master 500 used by Dr Cronin is the newest biometry machine available.  It utilises the Holliday 2 formula which is widely recognised worldwide as the most accurate way to calculate the correct customised lens for your eye.