Optometric practice 1

DR. Ann Benedicto O.D. at ISOPTIK

Basic Examinations of screening for ocular disease and visual defects:

A. External Examination of eyes consists of inspection of the eyelids, surrounding tissues and palperal fissure. The conjunctiva and sclera can be inspected by having the individual look up, and shining a light while retracting the upper or lower eyelid. The cornea and iris may be similarly inspected.

Visual Acuity is the eye's ability to detect fine details and is the quantitative measure of the eye's ability to see an in-focus image at a certain distance. This is often measured with a Snellen chart. The terms 20/20 or 6/6 are derived from standardized objects that can be seen by a person of normal vision at the specified distance. For example, if one can see at a distance of 20 ft an object that normally can be seen at 20 ft, then one has 20/20 vision. If one can see at 20 ft what a normal person can see at 40 ft, then one has 20/40 vision. Put another way, suppose you have trouble seeing objects at a distance and you can only see out to 20 ft what a person with normal vision can see at 200 ft, then you have 20/200 vision. The 6/6 terminology is more commonly used in Australia and Europe, and represents the distance in meters.

Eye test chart - Is made up of various sized letters, numbers and pictures to determine Visual acuity - the ability to see with glasses or contact lenses. Eye testing charts are essential to determine where your vision lies.

The optometrist eye testing room has undergone many changes over the years.

Gone are the days of a box on wall containing letters illuminated from behind. Although some older optical clinics still use this type of eye chart. The modern testing room will either consist of a projector of an eye test chart onto a wall plate or state of art LCD using a mirror.

A patient taking the test covers one eye, and reads aloud the letters of each row, beginning at the top. The smallest row on the eye test chart that can be read accurately indicates the patient’s visual acuity in that eye.

Modern testing room with projector chart on a wall plate and digital phoropter

What is 20/20 vision?

In the UK they work in Metric compared to Feet in the USA. In Metric Acuity, 20/20 equals 6/6. The conversion is that 20 feet equals approximately 6 meters (actually 6.096).

What do all the numbers mean?

In order to make comparisons visual acuity achieved is expressed as a fraction - the standard chart distance is six meters, normal acuity is designated 6/6, and other acuities are expressed as ratios

Visual acuity - what does the minus and plus mean on the prescription record?

Optometrist want to record the best Visual acuity line read, adding minus for incorrect letters read out or plus a few extra letters on the next line is seen. E.g. 6/10-2 missed to letters on this line or 6/6+2 read a couple of lines from next lineWhat about patients who don’t know the alphabet?

Some eye test charts use a series of “Es” facing different directions; his/her objectives are to identify the directions of the letters for people who can’t read. For children the optometrist selects pictures of common everyday objects. E.g. dog, car, duck, flower.

C. Pupil function includes inspecting the pupils for equal size (1mm. or less of difference may be normal), regular shape, reactivity to light, and direct and consensual accommodation. A swinging - flashlight test may also be desirable if neurologic damage is suspected. This is the most useful clinical test available for the assessment of optic nerve anomalies. This test detects the Marcus Gunn pupil - both pupils constrict when one is exposed to light. As the light is being moved from one eye to another, both eyes begin to dilate, but constrict again when light has reached the eye. This is also referred as afferent pupil defect.

If there is an afferent defect in the left eye, both pupils will dilate when the light is shining on the left eye, but both will constrict when it is shining on the right eye. If there is an efferent defect in the left eye, the left pupil will remain dilated regardless of where the light is shining, while the right pupil will respond normally. If there is a unilateral small pupil with normal reactivity to light, it is unlikely that a neuropathy is present. However, if accompanied by ptosis of the upper eyelid, this may indicate Horner's syndrome. If there is a small, irregular pupil that constricts poorly to light, but normally to accommodation, this is an Argyll Robertson pupil.

Credit: Fotosearch

D. Ocular Motility should always be tested, especially when patients complain of double vision. This is assessed by having the patient move his/her eye quickly to a target at the far right, left, top, and bottom. Poor ability of the eyes to jump from one place to another may impinge on reading ability and other skills.

Slow tracking or pursuits are assessed by the follow my finger test in which the examiner's fingers trace an imaginary double - H, which touches upon the eight fields of gaze. These test the inferior, superior, lateral, and medial rectus muscles of the eye, as well as superior and inferior oblique

Examiners tracing an imaginary double H

E. Visual Field (Confrontation) Testing consists of confrontation field testing in which each eye is tested separately to assess the extent of the peripheral field. To perform the test, the individual occludes one eye while fixated on the examiner's eye with the non occluded eye. The patient is asked to count the fingers that are briefly flashed in each of the four quadrants. This finger is referred to the wiggly finger test because it represents a rapid and efficient way of answering the same question: is the peripheral visual field affected?

Common problems of the visual field include Scotoma (area of reduced vision), hemianopia (half of visual field lost), Homonymous quadrantanopia, and bitemporal hemianopia.

Peripheral visual field

Confrontation visual fields can be measured by using the tester's finger movements as the stimulus or a white or black ball on a thin stick. The object or the fingers are moved forwards from behind the person's head and the person tells when (s) he sees the object or the fingers. A young child turns the eyes as soon as the stimulus is seen in the peripheral visual field.

The approximate place of the stimulus detection is recorded, e.g." 90 degrees to the right, and left, 60 degrees up and down". In a person whose right eye is blind and left eye has slightly constricted visual field the finding could be e.g."30R, 60L, 30U and 45D". Visual field defects can be hemianopias, half field defects in one or both eyes, on the same side (homonymous hemianopias) or on both temporal sides (bitemporal hemianopias) or - rarely - on both nasal sides (binasal hemianopias). They can be quadrantanopias, quarter of the visual field defects, again in one or both eyes. The defect can also be a ring scotoma, loss of visual function in the "midperiphery" of the visual field, i.e. not in the very periphery but around the central visual field.

F. Intraocular pressure (IOP) can be measured by Tonometry devices designed to measure the outflow (and resistance to outflow) of the aqueous humor from the eye. Diaton tonometry can measure IOP through the eyelid. Air Puff tonometer is used commonly by optometrists in their practice.

Non- contact tonometer – Air puff tonometer

A patient being tested for tonometry using the air puff tonometer.

G. Ophthalmoscopy may include visually magnified inspection of the internal eye structures and also assessment of the quality of the eye's red reflex. This allows the one to look directly at the retina and other tissue at the back of the eye. This is best done after the pupil has been dilated with eye drops. A limited view can be obtained through undilated pupil, in which case best results are obtained with the room darkened and the patient looking towards the far corner.

The appearance of the optic disc and retinal vasculature are the main focus of examination. Anomalies in the appearance of these internal ocular structures may indicate eye disease or condition.

A red reflex can be seen when looking at a patient's pupil through a direct ophthalmoscope. This part of the examination is done from a distance of about 50 cm and is usually symmetrical between the two eyes. Opacity may indicate a cataract.

H. Slit-lamp

Close inspection of the anterior eye structures and ocular adnexa are often done with a slit lamp machine. A small beam of light that can be varied in width, height, incident angle, orientation and color, is passed over the eye. Often this light beam is narrowed into a vertical slit, during slit lamp examination. The examiner views the illuminated ocular structures, through an optical system that magnifies the image of the eye.

This allows inspection of all the ocular media, from cornea to vitreous, plus magnified view of eyelids, and other external ocular related structures. Fluorescein staining before slit lamp examination may reveal corneal abrasions or herpes simplex infection. The binocular slit-lamp examination provides stereoscopic magnified view of the eye structures in striking detail, enabling exact anatomical diagnoses to be made for a variety of eye conditions.

Slit lamp instrument

I. Amsler grid, used since 1945, is a grid of horizontal and vertical lines used to monitor a person's central visual field. The grid was developed by Marc Amsler, a Swiss ophthalmologist. It is a diagnostic tool that aids in the detection of visual disturbances caused by changes in the retina, particularly the macula (e.g. macular degeneration), as well as the optic nerve and the visual pathway to the brain. In the test, the person looks with each eye separately at the small dot in the center of the grid. Patients with macular disease may see wavy lines or some lines may be missing.

Amsler grids can be obtained from an ophthalmologists or optometrists and may be used to test one's vision at home. The original Amsler grid was black and white. A color version with a blue and yellow grid is more sensitive and can be used to test for a wide variety of visual pathway abnormalities, including those associated with the retina, the optic nerve, and the pituitary gland.

Credit: Pub. Med Central (Amsler Grid chart)

J. Static retinoscopy is a type of retinoscopy used in determining a patient's refractive error. It relies on Foucault's principle, which basically states that the examiner should simulate the infinity to obtain the correct refractive power. Hence, a power corresponding to the working distance is subtracted from the gross retinoscopy value to give the patient's refractive condition, the working distance lens being one which has a focal length of the examiner's distance from the patient (e.g. +2.00 dioptre lenses for a 50 cm working distance). Myopes display an "against" reflex, which means that the direction of movement of light observed from the retina is a different direction to that in which the light beam is swept. Hyperopes, on the other hand, display a "with" movement, which means that the direction of movement of light observed from the retina is the same as that in which the light beam is swept.

Static retinoscopy is performed when the patient has relaxed accommodative status. This can be obtained by the patient viewing a distance target or by the use of cycloplegic drugs (where, for example, a child's lack of reliable fixation of the target can lead to fluctuations in accommodation and thus the results obtained). Dynamic retinoscopy is performed when the patient has active accommodation from viewing a near target.

Retinoscopy is particularly useful in prescribing corrective lenses for patients who are unable to undergo a subjective refraction that requires a judgment and response from the patient (such as children or those with severe intellectual disabilities or communication problems). In most tests however, it is used as a basis for further refinement by subjective refraction. It is also used to evaluate accommodative ability of the eye and detect latent hyperopia.

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