Retinoscopy in infancy: cycloplegic versus non-cycloplegic.
The patient views a distance target (four-six metres) so that accommodation is presumed to be static and in a relaxed condition. The fixating eye (contralateral to the one being examined) should be adequately "fogged" with a positive lens (resulting in an "against" movement seen on the retinoscopy swipe).1 For children, maintaining fixation at this distance can be difficult and new computerised test charts generally provide dynamic and more interesting targets to view than a standard spotlight (Figure 1) to help with this. It is also possible to download a number of videoclips, especially cartoons, with different animations. Practitioners should also consider not using a phoropter or trial frame when conducting retinoscopy on a very young child, as this can be intimidating for the child. It is preferable to use single trial lenses or a lens rack. Speed during retinoscopy is essential when performing this technique in young children, especially as they maintain fixation only for very short periods of time. In cases of fluctuation of accommodation, the practitioner should follow the "with" movement, ignoring the occasional "against" movements seen.
[FIGURE 1 MITTED]
Yeotikar et al. (2) evaluated the difference in refractive error in non-strabismic children between the ages of seven years and 16 years, using static retinoscopy under two conditions--first by fogging the contralateral eye with a positive lens and second with cycloplegia using cyclopentolate 1%. The study found that the average difference in refractive error between these two conditions was only 0.29DS more hypermetropic with cyclopentolate, highlighting the accurate results that can be obtained when there is adequate accommodative control during static retinoscopy. Furthermore, Chan and Edward (3) suggested a calculation which can be used to match the dry retinoscopy result to that which would be obtained using cyclopentolate 1%, in children between three and a half to five years of age. The astigmatic component is kept the same whilst the spherical component found in both meridians is multiplied by 1.45 and a value of 0.39D is added. However, this depends on an accurate static retinoscopy result having been obtained.
The Mohindra technique, also known as near retinoscopy or near monocular retinoscopy, carries the main advantage of being child-friendly and requiring less co-operation from the child. (4) In this case, the stimulus is the dimmed light source of the retinoscope in a darkened room. The darkness of the room will facilitate the child to keep their attention on the retinoscope's light. The retinoscope is held at a distance of 50cm (errors in distance are not clinically relevant), with hand-held trial lenses used to find the neutral point. The accommodation activity during the examination is small and the same in both eyes. It is important during the examination to keep the light of the retinoscope on the child's pupil (to see the retinal reflex) for only a short period of time so as not to stimulate accommodation; subsequently the optometrist's attention should be focused on the pupil, watching for maximum dilation (indicating no accommodation). (5) The procedure should be carried out with one eye occluded, preferably by the parent, while the other eye is evaluated. However, Wesson et al. (6) confirmed that there is no substantial difference in the result if binocular fixation is allowed (Figure 2); indeed this can be useful if the infant is resistant and becomes agitated with occlusion. Several people advocate neutralisation of the two principal meridians of the eye separately, using loose spherical trial lenses. However, Saunders and Westall (7) confirmed that the accuracy of the technique can be improved using a combination of spherical and cylindrical lenses instead. Once the retinoscopy result is obtained, the refractive error was originally calculated by adding -1.25DS to the gross finding. (8,9) Saunders and Westall (7) have reported that the accuracy can be improved if -0.75DS is added instead, for children aged between zero to two years, and -1.00DS added for those children over two years of age. They also affirmed that the result achieved by the Mohindra procedure in children between six months and four years of age is similar to wet retinoscopy (using cyclopentolate 1%--see later), with a difference of only 0.50DS. Others have reported similar results, (10) and certainly no differences greater than 1.00DS, (11) whilst similar results were also obtained for children with Down's syndrome (12) and even in adults. (13) The Mohindra technique is useful for practitioners in Europe who are not permitted to used cycloplegic agents, (14) whilst there are benefits for conducting frequent follow-up assessments without repeated use of cycloplegic agents. (15) One must remember, however, that the accuracy of results will naturally depend on the practitioner's experience. (16)
[FIGURE 2 OMITTED]
Control of accommodation in children of pre-school age is more commonly achieved by pharmacological means, using cycloplegic agents such as cyclopentolate and tropicamide; atropine can only be used by therapeutically qualified practitioners. All of these drugs are muscarinic receptor blockers, thus they work by blocking the muscarinic receptors in the ciliary body, which in turn prevents accommodation. A mydriatic effect is concurrently achieved by inhibiting muscarinic stimulation of the iris sphincter muscle. An ideal cycloplegic would have no ocular and systemic adverse effects. Also, it should produce a rapid onset of cycloplegia, blocking accommodation completely for an adequate period of time, before swiftly restoring accommodative ability. (17) Several studies have reported both ocular and systemic side effects (especially using atropine) in those children who have had a cycloplegic refraction, in addition to expected mydriasis and cycloplegia, as detailed later. (18)
Drug selection and instillation
Cycloplegia is an invasive technique which can be uncomfortable, or even distressing, for the child. This is notably so because the acidic pH of the cycloplegic agent leads to stinging on instillation. Some practitioners advocate the use of a local anaesthetic prior to instillation of the cycloplegic agent; proxymetacaine 0.5% is the drug of choice as it stings less than other topical anaesthetics. However, this is not always recommended due to the risks associated with an anaesthetised cornea. To facilitate the application of cycloplegics, cyclopentolate has been instilled in spray form onto the eyelashes and the closed upper lid. (19) Practitioners should also be conscious of their instillation technique, since different degrees of cycloplegia between the eyes can occur, especially if the child does not keep their eyes open wide enough and/or if there is significant post-instillation tearing (which is very likely). As such, practitioners can opt to instil the higher concentration of cycloplegic agent and/or instil further drops if regular review (eg, periodic measurement of the amplitude of accommodation) reveals differing levels of cycloplegia. Differences in the main cycloplegic agents are summarised in Table 1. The optometrist should select an appropriate agent considering factors such as the patient's age and whether they have dark, or light coloured, irides. Adequate cycloplegic effect could be achieved with tropicamide in a teenage patient suspected of having latent hypermetropia, for example, whereas cyclopentolate is likely to be required for an infant suspected of having an accommodative esotropia. Those with light coloured irides may exhibit an increased response to drugs as compared with darkly pigmented irides, and therefore a lower concentration/dose ought to be selected. Overdose of cycloplegic agent has to be avoided in children with Down's syndrome or those affected by cerebral palsy, trisomy 13 and 18, and other central nervous system (CNS) disorders. This is because toxicity increases in these people, especially children, which causes stimulation of the medulla and the cerebral centres, leading to hallucinogenic effects similar to those caused by LSD drugs. (20,21) These reactions generally occur within 20-30 minutes after administration. (22) Tropicamide 1% should be considered in these children as opposed to cyclopentolate.
Cyclopentolate 0.5% or 1.0% is commonly used by practitioners as the cycloplegic agent of choice for paediatric examinations. The cycloplegia achieved is not too deep, as compared with atropine, but it is quicker in onset, often achieved after 30 minutes from its administration. Recovery of accommodation is typically between six-12 hours after instillation whilst mydriasis resolves by 24 hours after instillation. Although full cycloplegia is achieved with atropine, the cycloplegic refractive results obtained with cyclopentolate are comparable in "normals", (23) high hypermetropic children (24,25) and also those children with strabismus. (26,27) For children under the age of three months, it is advised that two drops of cyclopentolate 0.5% are used as opposed to 1%.28 This is becasue drug absorption through the conjunctival epithelium and skin is more rapid in infants compared to adults, (29,30) due to immature metabolic enzyme systems in neonates and young children, which may prolong the effects of the drug. (31,32) The main side effects of cyclopentolate include incoherent speech, hallucinations and disorientation, psychosis and visual disturbances. (33,34)
This is an anti-muscarinic drug with short-lasting effect on the pupil (mydriasis) and on accommodation (cycloplegia) at the 1% concentration. Although tropicamide is mostly used for mydriasis, to examine the optical media and the ocular fundus, several studies have suggested that this drug can be used for a cycloplegic effect. (35) In particular, it is a cycloplegic agent that can at least detect latent hypermetropia, for example in school children, teenagers and those in their early 20s, with otherwise normal refractive status and/or with moderate hypermetropia, (36) as well as for children during the post-natal period. (37) In adult patients undergoing refractive surgery, a study showed no significant difference in cycloplegic refraction between tropicamide 1% and cyclopentolate 1%.38 In the same patients, however, the study showed that cyclopentolate was more effective than tropicamide in reducing accommodative amplitude in adult myopes (near-point testing).
This is a natural alkaloid extracted from the deadly nightshade (Atropa belladonna) plant. Its administration is justified in children of pre-verbal age or when other cycloplegic agents fail to produce a satisfactory level of cycloplegia. Atropine is administrated three times a day during the three days before the eye examination. Associated mydriasis decreases in two weeks after the refractive examination. This drug is an antagonist of the muscarinic acetylcholine receptors, thus it dampens mediation of the parasympathetic nervous system. As a result, systemic absorption of atropine can lead to difficulties with swallowing food (opposed effects of the vagus nerve), inhibition of the salivary glands leading to a dry mouth, and reduction of sweating. Atropine can also increase firing of the sino-atrial node (SA) and conduction through the atrio-ventricular node (AV) of the heart, leading to tachycardia. It also decreases bronchial secretions, which can make breathing difficult. Other side effects that have been reported include dizziness, nausea and sensation of being unbalanced and allergic reactions of the eyelids and conjunctiva. Atropine is able to pass through the blood-cerebral-barrier and alter the state of consciousness of the child. Therefore, in order to minimise the systemic absorption of atropine, the practitioner can gently press the punctum of both eyes and keep the patient's head tilted back. A recent study (39) compared the cycloplegic efficacy of homatropine 2% and atropine 1% in children between the ages of four and 10 years by retinoscopy and automated refraction. As expected, the study reported that homatropine produced a significantly lesser cycloplegic effect than atropine, with residual accommodation being greater (1.80 [+ or -] 0.40D with atropine vs 3.10 [+ or -] 0.50D with homatropine; p<0.001). Another study (40) compared the cycloplegic effect obtained at 90 minutes after administration of two drops of atropine 0.5% to that obtained after three times daily instillation of atropine 0.5% for three days, in strabismic children. It was found that although residual accommodation was greater at 90 minutes after instillation (1.00D) compared with three-day atropinization (0.50D), the former still allows a more rapid and less toxic assessment of refraction than the usual three-day dose.
Indications for cycloplegic refraction
There are several instances when a cycloplegic refraction is indicated, including:
* Hypermetropia over +5.00D
* Anisometropia more than 1.50D
* Suspect and/or manifest strabismus (especially esotropia)
* Family history of strabismus, high hypermetropia and amblyopia
* In the presence of unstable esophoria, pseudomyopia and asthenopia
* Poor cooperation/fixation of the child
* When the retinal reflex during retinoscopy changes motion or brightness due to dynamic accommodative status. There are also some instances where cycloplegic refraction is contraindicated, including:
* Cases where administration of cycloplegic agents will cause undue stress for the child, resulting in a complete lack of co-operation
* Risk of ocular and/or systemic side effects (which are more likely with atropine than cyclopentolate and tropicamide)
* Risk of developing acute angle closure glaucoma in those with a shallow anterior chamber (especially with cyclopentolate)
Conducting wet retinoscopy
Cycloplegic retinoscopy is carried out in a similar way to dry static retinoscopy. Despite pharmacological control of accommodation, some co-operation of the child is still required to keep fixation during the examination, so that off-axis aberrations do not distort the retinoscopic reflex. Zadnick et al. (41) found that the repeatability of retinoscopy under cycloplegia is poorer than noncycloplegic conditions, mainly due to the irregularity of the retinoscopic reflex through a dilated pupil. For this reason it is important for the practitioner to concentrate only on the central portion of the pupil, ignoring the movement seen in the peripheral annulus.
Objective automated refraction
When a cycloplegic retinoscopy result has been obtained, it can be useful to conduct objective automated refraction too, for comparison of the results. A study (42) comparing cycloplegic refraction measurements using the hand-held autorefractor (Retinomax), a table-mounted autorefractor (Canon FK-1) and streak retinoscopy in a large cohort of children between 24 and 72 months of age found no significant difference in the mean spherical equivalent (MSE) refractive error between the table-mounted autorefractor (1.03 [+ or -] 1.64D) and streak retinoscopy (1.09[+ or -]1.58D, p=0.66). However, the MSE using the hand-held Retinomax (0.80[+ or -]1.43D) was significantly different (p=0.0004) to streak retinoscopy. Astigmatism measured using the hand-held (-0.89 [+ or -] 0.51D) and table-mounted (-0.83 [+ or -] 0.61D) autorefractors were significantly greater than that obtained with retinoscopy (-0.58 [+ or -] 0.56D, p=0.0003). Therefore, practitioners should remember that autorefractometry and videorefractometry, although useful as a guide and screening tool, are not accurate enough to base actual prescribing decisions upon in preschool children. (42,43) Issues of ensuring correct fixation on the target tend to be the primary reason for the discrepancy, but even in co-operative older subjects, variable readings can be obtained from different autorefractor tools. (44-45) Dry autorefraction seems particularly inaccurate in hypermetropia (46) and astigmatism in children of preverbal age, (47) although hand-held autorefraction devices can evaluate astigmatism without administration of cycloplegic drugs, with the same repeatability as wet retinoscopy. (48) Wet autorefraction generally seems more accurate if it is compared to the subjective refraction under cycloplegia. (49) Practitioners should also remember that cycloplegic drugs might temporarily modify the structures of anterior chamber, inducing astigmatism or modifying an existing astigmatic ametropia. This could occur because there is a change in intraocular pressure (IOP) under cycloplegia, which alters the position of the crystalline lens from the normal corneal distance. These modifications have an effect on the refraction, but this is difficult to quantify in terms of refractive power. (50)
During the refractive assessment it is necessary to control and often inhibit accommodative function, especially in paediatric cases. This can be obtained using dry and wet techniques, both of which are appropriate for identifying the most appropriate correction. Although the refractive assessment should be carried out as naturally as possible, when the practitioner encounters uncooperative children or those with risk factors for binocular vision anomalies the refraction should be performed under cycloplegia. Tropicamide seems to be as effective as cyclopentolate for measurement of refractive error in most non-strabismic infants, particularly at the 1% concentration, so it should be considered more often in paediatric eye care in order to reduce the possibility of adverse reactions. Where there is suspicion of a binocular vision anomaly, cyclopentolate should be the agent of choice.
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Module questions Course code: C-18551 O/D
PLEASE NOTE There is only one correct answer. All CET is now FREE. Enter online. Please complete online by midnight on May 4, 2012--You will be unable to submit exams after this date. Answers to the module will be published on www.optometry.co.uk/cet/exam-archive. CET points for these exams will be uploaded to Vantage on May 14, 2012. Find out when CET points will be uploaded to Vantage at www.optometry.co.uk/cet/vantage-dates
1. Which of the following statements is TRUE?
a) Atropine produces cycloplegia within 2-3 hours and recovery of accommodation in 2 days
b) Cyclopentolate produces cycloplegia within 30 minutes and recovery of accommodation in 12 hours
c) Homatropine produces cycloplegia in 20-30 minutes and recovery of accommodation in 24 hours
d) All of the above
2. Which pharmacological agent should be considered in a child with Down's syndrome?
3. When should Mohindra's retinoscopy technique be performed?
a) In all children
b) Only in children aged 7-10 years
c) Only in young children with moderate astigmatism
d) In pre-verbal children
4. How should Mohindra's retinoscopy technique be performed?
a) In darkness, fixation being on the retinoscope light, using hand held lenses
b) In room lighting, fixation being on a high contrast target at the retinoscope mirror
c) In darkness, fixation being on a spotlight at 6 metres, using hand held lenses
d) In room light, fixation being on a high contrast target at 6 metres, under cycloplegia
5. Which of the following statements regarding cycloplegic refraction is TRUE?
a) It should be considered in children with high hypermetropia or strabismus
b) It should be considered in every child at every sight test
c) Atropine is the cycloplegic of choice for a 5-year-old child
d) Objective automated refraction should be used for prescribing decisions
6. Which of the following is NOT a side effect of cyclopentolate?
a) Incoherent speech
d) Conjunctival hyperaemia
Fabrizio Bonci, Dip. Optom (ITA), MCOptom
Luigi Lupelli, Dip. Optom (ITA), FAILAC, FIACLE, FBCLA
Fabrizio Bonci is an optometrist and clinical research fellow at the division of clinical neuroscience and mental health, Imperial College, London, and the Faculty of Medicine, Charing Cross Hospital, London. Luigi Lupelli is an optometrist, professor in contact lenses at the Faculty of Science, Department of Physics, (Optics and Optometry) at the University of Roma Tre, Italy.
Table 1 Cycloplegic and mydriatic effects amongst the main cycloplegic drugs used in optometric practice Mydriasis Agent Concentration Max effect Recovery time Atropine 0.5-3.0% 1-2 hours 7-12 days Cyclopentolate 0.5-2.0% 30-60 min. 1 days Tropicamide 0.5-1.0% 20-40 min 6 hours Homatropine 2.0-5.0% 40-60 min. 1-3 days Scopolamine 0.25% 20-30 min 3-7 days Cycloplegia Agent Max Recovery effect time Atropine 60-180 min 6-12 days Cyclopentolate 25-75 min 6-12 hours Tropicamide 20-35 min 4-6 hours Homatropine 30-60 min 1-3 days Scopolamine 30-60 min 3-7 days
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|Title Annotation:||CONTINUING EDUCATION & TRAINING|
|Author:||Bonci, Fabrizio; Lupelli, Luigi|
|Date:||Apr 6, 2012|
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