Assessment of Vision: Distance, Near and Visual Fields

Assessment of Vision: Distance, Near and Visual Fields

Visual assessment is the first objective examination in most eye complaints. It establishes a baseline, detects asymmetry and helps localise disease to the optical media, retina, optic nerve or visual pathways. Distance and near acuity answer different questions; visual-field assessment detects missing vision that a patient may not notice.

Learning objectives

• Prepare a patient and test distance visual acuity accurately in each eye.
• Use correction, pinhole and low-vision notation appropriately.
• Assess near vision and recognise accommodation-related problems.
• Perform confrontation visual fields and understand their limitations.
• Explain Amsler-grid and formal perimetry principles.
• Document results clearly and identify emergency patterns.

1. Before testing

1. Explain the purpose, reassure the patient and check language, literacy, hearing and ability to respond.
2. Ensure good, even illumination without glare; place the correct chart at the prescribed distance.
3. Ask about glasses/contact lenses and test with usual correction first when relevant.
4. Test the right eye, then left eye, then both eyes; prevent peeking with an opaque occluder, not the patient’s fingers.
5. Do not press on the covered eye. Record whether the patient can identify optotypes, count fingers, detect hand movement or perceive light.
6. For acute disease, test before drops, patching or analgesia when clinically safe, and repeat after intervention if the situation changes.

2. Distance visual acuity

Snellen and logMAR concepts

Distance acuity is recorded as a fraction: the numerator is the testing distance and the denominator is the distance at which a standard eye can resolve the same optotype. A logMAR chart uses equal logarithmic steps and consistent letter spacing; it is often more precise for research and monitoring.

Procedure

1. Seat the patient at the chart’s calibrated distance, commonly 6 m where available; use the chart’s specified distance if different.
2. Ask the patient to keep both eyes open but occlude the non-tested eye completely without pressure.
3. Start with a line the patient can reasonably see, then proceed to smaller lines until errors occur. Encourage but do not coach.
4. Record the smallest line read according to local chart convention, including missed letters if the chart permits.
5. Repeat with usual correction and pinhole if reduced and if no contraindication; pinhole does not diagnose the cause by itself.
6. Test near vision separately, especially if the complaint is reading difficulty or distance vision is normal.

3. Pinhole interpretation

• Improvement suggests that refractive blur contributes to reduced acuity.
• No improvement may reflect corneal opacity, cataract, retinal/macular disease, optic-nerve dysfunction, amblyopia or poor technique.
• Pinhole is less useful in irregular astigmatism, dense media opacity or very low vision.
• A patient with sudden loss, pain, field defect or RAPD needs urgent evaluation regardless of pinhole response.

4. Measuring very poor vision

Do not convert CF, HM or PL into a falsely precise Snellen fraction. Record the method, distance, illumination and patient cooperation.

5. Near visual acuity

Near acuity tests the ability to resolve print at a specified distance, commonly around 35–40 cm, using a near card with standard notation such as N notation, Jaeger or equivalent. The patient should use near correction if normally worn.

1. Illuminate the card evenly without glare.
2. Hold it at the specified distance; do not let the patient bring it closer without recording the change.
3. Test each eye separately and then both eyes if useful.
4. Record the smallest line read and the correction used.

6. Visual-field assessment

The visual field is the total area visible while the patient fixates steadily. Testing each eye separately identifies monocular defects; testing both eyes helps understand functional impact. A patient may not notice a field defect because the brain fills in missing information.

Confrontation fields

1. Sit facing the patient at approximately the same eye level and ask the patient to fixate on your nose or a central target.
2. Test one eye at a time by having the patient cover the opposite eye without pressure; cover your corresponding eye.
3. Bring a finger or small target from the periphery toward the centre in each quadrant, comparing with your own field.
4. Ask when the patient first sees it and whether it is equally bright. Repeat with a red target when a subtle defect is suspected.
5. Map a defect by moving the target along different meridians; document central versus peripheral and the side/quadrant involved.

Limitations of confrontation

• It is a screening test and may miss small central, arcuate or early glaucoma defects.
• It depends on fixation, attention, the examiner’s own field and consistent target movement.
• Formal automated or kinetic perimetry is required for detailed diagnosis, monitoring, occupational decisions or unexplained field loss.

7. Amsler-grid assessment

An Amsler grid is a near central-field screen for metamorphopsia or scotoma. With reading correction, test one eye at a time at the specified distance while the patient fixates the central mark.

• Ask whether lines are straight, missing, blurred, wavy or different in size.
• Mark the location of distortion or missing areas; compare eyes.
• It is not a substitute for dilated examination or OCT. New distortion or a central scotoma requires prompt eye review.

8. Formal perimetry

Interpret reliability indices, fixation losses and false responses. A single unreliable field should not be labelled disease; correlate with optic-disc, retinal and neurological findings.

9. Common errors and how to prevent them

• Testing both eyes together and missing unilateral loss: always record right and left separately.
• Allowing peeking around an occluder: use an opaque occluder and avoid pressure.
• Incorrect chart distance or poor illumination: calibrate the room and follow the chart’s instructions.
• Failing to record correction/pinhole: state unaided, habitual correction and pinhole results.
• Calling “can read” normal: record the smallest line and errors.
• Ignoring language or literacy: use tumbling E, Landolt C, symbols or matching cards when appropriate.
• Overinterpreting a poor field: check fixation, attention, glasses, fatigue and reliability; repeat or arrange formal perimetry.
• Delaying urgent referral to complete all tests: stabilise, measure key functions and escalate first.

10. Emergency interpretation

11. Documentation template

12. Applied cases

13. Self-test

1. Why must acuity be tested one eye at a time?
2. What does pinhole improvement suggest?
3. How should CF, HM and PL be recorded?
4. What is the purpose of confrontation visual fields?
5. Why can a patient miss a field defect?
6. What does a central Amsler-grid distortion suggest?
7. Name three emergency causes of sudden visual loss.
8. When should formal perimetry be used?
9. Why must the occluder not press on the eye?
10. What information should accompany an urgent referral?

Answers

1. Binocular testing can hide unilateral loss; separate results reveal asymmetry and localise disease.
2. That uncorrected refractive blur contributes, but it does not exclude retinal/optic-nerve disease or emergency causes.
3. Method and distance: CF at 1 m, HM, PL positive/negative with projection if tested; do not invent a precise Snellen fraction.
4. Screen the peripheral field and identify gross retinal, optic-pathway or neurological defects.
5. The brain fills in missing information and the patient may compensate using the other eye or head movement.
6. Macular disease or central scotoma until assessed.
7. Retinal detachment/occlusion, optic neuropathy, acute glaucoma, severe trauma and stroke-related visual loss.
8. For suspected glaucoma/optic neuropathy/neurological defects, monitoring and unexplained or occupationally important field loss.
9. Pressure can injure a painful or open globe and may alter IOP or corneal findings.
10. Onset/last-known-well, laterality, acuity, pupils/RAPD, field, pain/trauma/contact lenses, examination, treatment and referral time/recipient.

Key takeaways

• Distance, near and field tests answer different questions; use them together.
• Record each eye, correction, pinhole, method and test conditions.
• New field loss, sudden acuity reduction and painful loss are emergencies.
• Confrontation is screening; formal perimetry and specialist examination are needed for detailed diagnosis.

References and further reading

• SlideShare: Vision assessment
• Merck Manual Professional: Evaluation of the ophthalmologic patient
• Merck Manual: The eye examination