Visual Acuity
It is the relative ability of the visual organ to resolve detail that is usually expressed as the reciprocal of the minimum angular separation in minutes of two lines just resolvable as separate and that forms in the average human eye an angle of one minute
Visual acuity (VA) commonly refers to the clarity of vision. Visual acuity is dependent on optical and neural factors, i.e., (i) the sharpness of the retinal focus within the eye, (ii) the health and functioning of the retina, and (iii) the sensitivity of the interpretative faculty of the brain
Autorefractometer
An autorefractor or automated refractor is a computer-controlled machine used during an eye examination to provide an objective measurement of a person’s refractive error and prescription for glasses or contact lenses. This is achieved by measuring how light is changed as it enters a person's eye
Refraction
A refraction test is usually given as part of a routine eye examination. It may also be called a vision test. This test tells your eye doctor exactly what prescription you need in your glasses or contact lenses.
Normally, a value of 20/20 is considered to be optimum, or perfect vision. Individuals who have 20/20 vision are able to read letters that are 3/8 of an inch tall from 20 feet away.
If you don’t have 20/20 vision, you have what is called a refractive error. A refractive error means that the light is not bending properly when it passes through the lens of your eye.
Causes of refractive errors
The eye's ability to refract or focus light sharply on the retina is primarily based on three eye anatomy features
Eye length. If the eye is too long, light is focused before it reaches the retina, causing nearsightedness. If the eye is too short, light is not focused by the time it reaches the retina
Curvature of the cornea. If the cornea is not perfectly spherical, then the image is refracted or focused irregularly to create a condition called astigmatism.
Changes related to lens.
Cycloplegic Refraction
Cycloplegic refraction is a procedure used to determine a person's complete refractive error by temporarily aborting the activity of muscles that aid in focusing the eye. To bring this effect cycloplegic eye drops are used to stop the functioning of ciliary muscle of the eyes. The duration and level of this effect depends upon the drug used. The choice of the drug used is dependent on the age of the patient and disease present.
It is required in :
Refraction in children and young adults
Patient for refractive Surgery like LASIK, ICL etc
Squint and Lazy eye patients
Patients with asthenopic symptoms
Retinoscopy
Retinoscopy (Ret) is a technique to obtain an objective measurement of the refractive error of a patient’s eyes .The examiner uses a retinoscope to shine light into the patient's eye and observes the reflection (reflex) off the patient’s retina. While moving the streak or spot of light across the pupil the examiner observes the relative movement of the reflex or manually places lenses over the eye (using a trial frame and trial lenses) to "neutralize" the reflex. This method is specially useful in paediatric patients as well as eyes with media opacities where autorefractor readings are not possible.
NCT
Non-contact tonometry (or air-puff tonometry) uses a rapid air pulse to applanate (flatten) the cornea. Corneal applanation is detected via an electro-optical system. Intraocular pressure is estimated by detecting the force of the air jet at the instance of applanation.It is a fast and simple way to screen for IOP. Modern non-contact tonometers have been shown to correlate well with Goldmann tonometry measurements and are particularly useful for measuring IOP in children and other non-compliant patient groups
Slit Lamp Examination
A slit lamp is an instrument consisting of a high-intensity light source that can be focused to shine a thin beam of light into the eye. It is used in conjunction with a biomicroscope. The lamp facilitates an examination of the anterior segment of the human eye, which includes eyelid, sclera, conjunctiva, iris, natural crystalline lens and cornea . The binocular slit-lamp examination provides a stereoscopic magnified view of the eye structures in detail, enabling anatomical diagnoses to be made for a variety of eye conditions.
Posterior Segment evaluation by Slit Lamp: This technique is used to examine fundus (Retina and Optic nerve head) by using a slit lamp and specialized lenses. It gives a magnified and three dimensional view helpful to diagnose diseases of central retina and optic nerve.
