Common Investigations Your Eye Doctor May Ask You to Pay For!
Pachymetry:
Measurement of the thickness of the cornea – a test done to determine if your cornea is suitable for LASIK or collagen cross linkage procedure in patients with keratoconus or conical cornea
Keratometry:
Measurement of corneal curvature, usually done in the centre of the cornea. This measurement is handy to add to other measurements to calculate amount of LASIK laser required to bring your spectacle number to zero; also one of the measurements required to calculate the Intra-ocular lens power suitable for your eye in case you have a cataract.
AS-OCT:
Anterior Segment Optical Coherence Tomography. Something like a CT scan of the front portion of the eye. Comes in handy for a variety of diseases of the cornea and anterior segment
UBM – Ultrabiomicroscopy:
This is an ophthalmic ultrasound using a special probe, to view in detail structures in the anterior segment, up to and including the crystalline lens of the eye and an inserted IOL. Also useful to examine the angle of the eye (UBM Gonioscopy) to find out if it is narrow, closed or open. This may influence decision making about glaucoma surgery in some cases.
B-scan:
An ultrasound test to examine structures in the back of the eye, especially if the view of the back of the eye is hampered due to opacities in the normally clear media, such as a cataract or haemorrhage in the posterior compartment (vitreous haemorrhage), so that ophthalmoscopy examination is not possible. Also useful in lesions of the extra-ocular muscles and any space occupying lesions in the orbit, outside the eye.
A-scan:
Also called A scan biometry. In this the examiner determines the front to back measurement of the eye using ultrasound. He then feeds in the keratometry reading obtained from the keratometer. An inbuilt computer in the A- scan biometry machine, using one of several complex formulae, then calculate the power of the intra-ocular lens implant required for your eye
OCT:
Exactly like the AS-OCT talked about earlier; it gives you colour coded pictures of the back of the eye including individual layers of the retina. Therefore , if there is bleeding into the back of the eye or fluid collection in the retina, the OCT can tell you in which layer of the retina or whether it is just in front of or just behind the retina. It can also measure retinal thickness. This is helpful in planning treatment in conditions like diabetic macular oedema or monitoring efficacy of intravitreal injections given for wet age related macular degeneration.
Corneal Topography:
This gives you several ‘maps’ of the cornea; an invaluable tool in assessing suitability of the cornea for LASIK and useful in detection of keratoconus and in fitting of contact lenses. It provides information on the curvature of the cornea at various points of the cornea, the ‘power’ of the cornea etc.
Aberrometry:
This is often used by the LASIK surgeon in patients unhappy after a successful LASIK – it detects minute flaws called “higher order aberrations” in your eye’s optical system which prevents you from enjoying ‘super’ vision after LASIK. Some LASIK machines which are “wave-front guided” routinely use data from aberrometers to fine tune the LASIK treatment to reduce these aberrations post LASIK surgery.
Visual Field Analysis:
Mechanical devices that measured your field of vision were called perimeters. They have been largely replaced by Visual Field Analysers (VFA). These have inbuilt computers for storing and analysing your visual fields. They can compare fields done over a period and analyse whether the patient’s field is worsening or remaining the same. The routine test is a little cumbersome and requires your co-operation, lasting around 30-40 minutes, though for simple screening faster tests are available in the same machine. VFA is ordered in cases of glaucoma both for diagnosis and for judging efficacy of treatment. They are also invaluable in some neurological disorders causing drop in vision like in stroke etc.
Common Investigations of Your Eye – Part 2
