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Continuing our CET series looking at refraction techniques, Tina Patel begins a discussion on establishing the near addition. Module C37275, one distance learning point for optometrists and dispensing opticians
Over the course of an optometrist’s career, a large percentage of patients will present to the practice with symptoms of near vision difficulties. Information elicited from the patient prior to and during the eye examination will aid the optometrist in determining what the possible cause/s of near vision difficulties could be and whether they are related specifically to the onset of presbyopia.
Presbyopia
Presbyopia is an age-related, normal physiological condition that affects all people approximately from the age of 40. It results from the gradual decrease in accommodation associated with age. As the amplitude of accommodation reduces, the range of clear vision that a patient requires to perform near vision tasks may become inadequate.
The impact of this process varies from one person to another. Those who are involved in more frequent or more demanding near vision tasks are likely to have more difficulty.
A patient presenting for an eye examination may complain of symptoms of near vision difficulties that specifically relate to the onset of presbyopia, for example, eyestrain or blurred vision after prolonged periods of detailed near work; ‘needing longer arms and having to read further away’; having to increase the font/print size on phones/tablets/computers; inability to see fine details at the customary near working distance; increasing the near working distance to read small print comfortably; headaches after reading; having to take longer breaks after carrying out close work tasks or the myopic patient who needs to take their glasses off to read.
Often, and more intriguing, are the patients who present with symptoms that are non-specific, causing them a ‘problem’, but they are not sure what, how or why – for example, the first time presbyopic latent hyperope who ‘only ever used their glasses occasionally for reading but now feels that their near vision has deteriorated and needs to use their glasses more but the distance vision is also blurred’; patients who complain of an intermittent ‘distance vision’ blur after reading; patients who complain of double vision but not in the true sense, dizziness or drowsiness during and after reading; ‘tired eyes’ after reading and as a result not reading as much; having to have a brighter light source for reading; ‘watery eyes’ or ‘tearing’ after reading.
An optometrist, with experience, will become familiar with the varying presenting symptoms and will more than often than not, along with other clues and in the absence of any binocular vision anomalies or pathology, determine these symptoms to be associated with presbyopia.
Clues to presbyopia
Careful and detailed history taking, gaining knowledge of the patient’s near vision tasks and various elements of the subjective refraction will offer clues to aid the practitioner in identifying and establishing treatment options suited to the individual’s needs.
Patient history
- Patient’s date of birth – is the patient of a ‘presbyopic age’?
- Pre-screening tests (autorefraction) – is the patient hyperopic but has not worn glasses previously? Is the patient myopic and finding close work difficult with their glasses on?
- Presenting problem and main complaint – what is the patient’s primary complaint? Are they complaining of blurred vision, headaches, distance vision blur, occasional near vision blur especially in dim light, the small print is a problem or tired eyes after reading?
- Patient’s visual and ocular history – what is the patient’s current prescription, are they myopic, hyperopic, or emmetropic? Did they previously read without glasses but now find that difficult. Do they have any underlying binocular vision anomaly that may be causing the symptoms of near vision blur? Do they wear contact lenses and the near vision is now becoming difficult with the lenses, or conversely in the case of the high myopic patient, do they find the near vision with their contact lenses fine but difficult in their distance spectacles?
- Patient’s general health – are there any systemic conditions causing premature presbyopia, for example, diabetes, cardiovascular disease, neurological disorders or traumatic complications?
- Medication – is the patient taking any medication that may lead to premature presbyopia, for example, anti-anxiety drugs or antidepressants, antipsychotics?
- Patient’s occupation – does the patient carry out demanding near vision tasks, use a computer or equipment requiring good near sight, such as a microscope? Has the patient’s working environment altered, for example, moved from natural to artificial lighting, carrying out more near vision and computer tasks? Has the patient returned to studying and found their near vision more blurred?
- Patient’s hobbies – does the patient have a hobby that requires good near vision, for example needlework/sewing, painting, model making?
Vision and visual acuity
- Measuring the distance and near vision unaided and/or aided – what is the patient’s vision and visual acuity? Is there a reduction in the vision? Is there any pathology associated with this or is the cause due to an uncorrected refractive error? Is the patient a contact lens wearer who only wears contact lenses?
Refraction
- Examination and determination of the distance refractive error – what is the patient’s refractive error and how will this impact on the near vision? As discussed earlier in this series, objective refraction (near/dynamic retinoscopy) can be used to determine the amount of plus power needed at near. Is the patient myopic and therefore not yet conscious of their presbyopic prescription because they take their glasses off to read? Has the patient’s prescription previously been under corrected for adaptation/comfort purposes but increasing the prescription has highlighted the near vision difficulty? Is the patient a hyperope or emmetrope and therefore more likely to experience near vision difficulties? Due to lens effectivity, myopic patients tend to require a lower reading addition compared to the hyperopic or emmetropic patient.
Assessing the near addition/prescription
As previously discussed in this series, subjective routines can vary between practitioners and depend upon the patient. Careful and precise determination of the distance refraction/correction is very important as this forms the basis of the management of the presbyopia; the final near vision prescription is the sum total of the distance correction plus the near vision addition.
Always ensure you are explaining the test/procedure to the patient and what they may expect. Be clear and concise, know how to explain the test you are conducting and keep it simple. The steps of the routine refraction are outlined in Table 2.
Procedure for measuring the near addition/prescription
Various methods have been described for the assessment of the near vision addition. Common procedures include checking the near add empirically by age and working distance, which we will cover now. Other important assessments, such as confirming addition as a proportion of the amplitude of accommodation and consideration of the patient’s previous near vision prescription (along with other, less used, techniques such as balancing negative and positive relative accommodation and binocular cross cylinder) will be described in the penultimate article in this series next month.
The clinician should aim to simulate, as much as possible, the patient’s habitual viewing circumstances, such as lighting and working distance. Using illumination that is significantly greater than that in the habitual visual environment can cause an increased depth of focus and thereby provide a potentially misleading estimate of the accommodation.
- Ensure the distance vision is fully corrected and the results kept in the trial frame.
- Adjust the pupillary distance in the trial frame for near.
- Keep the room lights on and as natural as possible to the patient’s working environment. (Ask the patient what sort of light they read in eg natural, additional artificial light, dim light etc).
- Explain to the patient that you are going to be checking their reading prescription along with any additional prescription required for specific tasks for example the VDU, hobbies.
- Ask the patient to hold the reading chart at their ideal or required reading distance.
– Note and measure using a measuring tape the distance at which the patient is holding the reading chart.
– Beware of the first time/early presbyope who holds the chart much further away because this is where they have become accustomed to holding near print.
– Confirm that the working distance is indeed correct and where the patient wants to read at, making adjustments if necessary, so that the reading add/s may be determined accurately.
- Ask the patient the clearest print they can read on the near chart.
– This can indicate if the patient still has some useful accommodation, if they are a hyperope and using some accommodation or in the case of the myope if the reading vision had reduced with the distance correction in place.
- Age and working distance: Table 3 provides a preliminary guide to determine a patient’s reading addition for a working distance starting at approximately 40cm.
– Place the selected positive (+ve) lens binocularly in the trial frame and ask the patient what the clearest paragraph is that they can now see – aiming to read N5 assuming VA at distance is 6/6-6/9.
– Using the confirmation lenses (+/-0.25DS flippers), present +0.25DS binocularly over the selected reading add lens and ask the patient if the near print looks clearer and more comfortable or better without the lens. If the patient reports the print is clearer, remove the initial selected lens and replace with +0.25 stronger. Eg patient is 55 years old, initial selected lens = +2.00DS. Patient prefers +0.25DS binocularly, remove +2.00DS lens and replace with +2.25DS.
– With the new reading lens in place, present +0.25DS binocularly and ask if the print looks clear and more comfortable with the lens or better without. Continue to change the lens until the patient reports no difference or a blurring of the vision.
– If the patient reports no difference or a blurring of vision when +0.25DS is initially presented do not change the lens power; instead, present -0.25DS binocularly and ask if the print looks clearer and more comfortable with the lens or better without. If the patient reports the print is clearer, remove the initial selected lens and replace with -0.25DS weaker. Eg the patient is 55 years old, initial selected lens = +2.00DS. Patient prefers -0.25DS binocularly, remove +2.00DS lens and replace with +1.75DS.
– With the new reading lens in place, present -0.25DS binocularly and ask if the print looks clear and more comfortable with the lens or better without. Continue to change the lens until the patient reports no difference or a blurring of the vision.
i) Unlike in distance vision refraction where maximum postive/plus sphere is aimed for, the positive lens required to improve the reading vision should be kept to a minimum without compromising the patient’s required working distance and range.
ii) Increasing the reading addition will reduce the working distance.
iii) Ensure the patient is seeing the print ‘clearer’ and not just more ‘magnified’ or ‘bigger’.
– Check the near VA monocularly to ensure both eyes achieve equal acuity (in the absence of amblyopia or anisometropia).
– Once the final add has been determined, check the near range of vision attainable with this prescription. Ask the patient to bring the near chart towards them and report when the near print looks blurred and out of focus. Using a measuring tape, record this distance. Ask the patient if they carry out any near vision tasks closer than the distance measured. Now ask the patient to push the near chart away from them and report when the near print looks blurred and out of focus, using a measuring tape, record this distance. Ask the patient if they carry out any near vision tasks further than the distance measured.
i) If the patient is happy with the range of near vision measured and does not perform any tasks closer or further than the range measured, the final addition, working distance and range can be recorded.
ii) If the patient reports that they do require the print to be clearer at a range closer or longer than that measured, recheck the reading addition at the required distance and record the final prescription specifying the new add and working distance.
Eg Near add +2.00 DS @ 35cm range 35-50cm.
Intermediate add +1.50DS @ 55cm range 45-65cm VDU at 55cm.
Near add +2.50 DS @ 20cm range 20-30cm model making at 20cm.
- Increasing the reading addition will reduce the working distance and range of near vision significantly. Ensure the patient is happy with this and understands that the prescription may only be suitable for this specific purpose.
- Decreasing the reading addition for intermediate tasks, for example the VDU, will increase the working distance but may reduce the range of clear near vision limited to intermediate range only.
- For younger patients, aim to prescribe one reading addition that gives the longest range of near vision suitable for all their required working distances.
- For older patients, one or more reading addition may be required to cover the range of near vision suitable for their required working distances.
- Some patients may not like the idea of needing one or more reading add (ie more than one pair of glasses for differing ranges) and may therefore opt for the ‘best add’ covering the maximum working range for essential tasks and adjusting their working distance for the remainder of non essential near tasks.
? Tina Patel is an optometrist working in hospital and private clinics and is an examiner and assessor
Model answers
(The correct answer is in bold text)
1. Why do myopes require a lower reading add compared to hyperopes and emmetropes?
A. Due to the impact of base out prism
B. Lens effectivity at near means less accommodative effort is needed
C. Due to prescription adaptation
D. Due to contraction of the orbicularis muscle
2. What would be the initial tentative add for a 45 year old patient carrying out reading tasks at 30cm?
A. PLUS 0.50DS
B. PLUS 1.00DS
C. PLUS 1.50DS
D. PLUS 2.00DS
3. Distance vision blur relating to presbyopia is caused by?
A. A reduction in the amplitude of accommodation with viewing distance changes
B. Pupil constriction
C. Contraction of the orbicularis muscle
D. A slowed response of the lens-ciliary body during relaxation
4. Which of the following medications are likely to cause premature presbyopia?
A. Citalpram
B. Cetirizine
C. Caduet
D. Ciprofloxacin
5. Which of the following will not influence patient comfort with closer working distances relating to higher additions?
A. PD
B. Fusional reserves
C. Reduced lighting levels
D. Image size enlargement
6. Which of the following is most useful in determining the amount of plus power needed at near?
A. Static retinoscopy
B. Dynamic retinoscopy
C. Autorefraction
D. Cycloplegia