WordNet

to take an action to protect against future problems; "Count the cash in the drawer twice just to cover yourself"
clothe, as if for protection from the elements; "cover your head!" (同)wrap up
a recording of a song that was first recorded or made popular by somebody else; "they made a cover of a Beatles song" (同)cover version, cover song
fire that makes it difficult for the enemy to fire on your own individuals or formations; "artillery provided covering fire for the withdrawal" (同)covering fire
the act of concealing the existence of something by obstructing the view of it; "the cover concealed their guns from enemy aircraft" (同)covering, screening, masking
a false identity and background (especially one created for an undercover agent); "her new name and passport are cover for her next assignment"
make up for shortcomings or a feeling of inferiority by exaggerating good qualities; "he is compensating for being a bad father" (同)compensate, overcompensate
span an interval of distance, space or time; "The war extended over five years"; "The period covered the turn of the century"; "My land extends over the hills on the horizon"; "This farm covers some 200 acres"; "The Archipelago continues for another 500 miles" (同)continue, extend
hide from view or knowledge; "The President covered the fact that he bugged the offices in the White House" (同)cover up
protect by insurance; "The insurance wont cover this" (同)insure, underwrite
form a cover over; "The grass covered the grave" (同)spread over
act on verbally or in some form of artistic expression; "This book deals with incest"; "The course covered all of Western Civilization"; "The new book treats the history of China" (同)treat, handle, plow, deal, address
be responsible for guarding an opponent in a game
be sufficient to meet, defray, or offset the charge or cost of; "Is this enough to cover the check?"
help out by taking someones place and temporarily assuming his responsibilities; "She is covering for our secretary who is ill this week"
hold within range of an aimed firearm
invest with a large or excessive amount of something; "She covered herself with glory"
maintain a check on; especially by patrolling; "The second officer covered the top floor"
play a higher card than the one previously played; "Smith covered again"
protect or defend (a position in a game); "he covered left field"
provide for; "The grant doesnt cover my salary"
provide with a covering or cause to be covered; "cover her face with a handkerchief"; "cover the child with a blanket"; "cover the grave with flowers"
spread over a surface to conceal or protect; "This paint covers well"
undergo a test; "She doesnt test well"
any standardized procedure for measuring sensitivity or memory or intelligence or aptitude or personality etc; "the test was standardized on a large sample of students" (同)mental test, mental testing, psychometric test
the act of undergoing testing; "he survived the great test of battle"; "candidates must compete in a trial of skill" (同)trial
the act of testing something; "in the experimental trials the amount of carbon was measured separately"; "he called each flip of the coin a new trial" (同)trial, run
a hard outer covering as of some amoebas and sea urchins
put to the test, as for its quality, or give experimental use to; "This approach has been tried with good results"; "Test this recipe" (同)prove, try, try out, examine, essay
achieve a certain score or rating on a test; "She tested high on the LSAT and was admitted to all the good law schools"
determine the presence or properties of (a substance)
show a certain characteristic when tested; "He tested positive for HIV"
an artifact that covers something else (usually to protect or shelter or conceal it)
the act of protecting something by covering it
a natural object that covers or envelops; "under a covering of dust"; "the fox was flushed from its cover" (同)natural covering, cover
an examination of the characteristics of something; "there are laboratories for commercial testing"; "it involved testing thousands of children for smallpox"
the act of subjecting to experimental test in order to determine how well something works; "they agreed to end the testing of atomic weapons"
a polyhedron with two congruent and parallel faces (the bases) and whose lateral faces are parallelograms
optical device having a triangular shape and made of glass or quartz; used to deviate a beam or invert an image (同)optical prism

PrepTutorEJDIC

(…で)…‘の'『表面をおおう』,'を'包む,かぶせる《+『名』+『with』+『名』》 / (範囲が)…‘に'『及ぶ』,わたる,'を'取り扱う範囲に入れる / 〈ある距離〉'を'行く,進む(受動態にできない) / …‘に'保険を掛ける / …'を'報道する,取材する / 〈要塞・砲などが〉'を'制圧する / (ピストルなどで)〈人〉'を'ねらう《+『名』+『with』+『名』》 / (球技などで)〈相手〉の動きなど〉'を'ふせぐ;〈地域など〉'を'守る / (…の)代役をする,身代りをする《+『for』+『名』》 / 〈C〉『おおい』,包むもの,カバー;ふた / 〈C〉『表紙』 / 〈U〉隠れ場所,潜伏所 / 〈U〉姿を隠してくれるもの(暗闇,煙など) / 〈C〉(秘密を隠すための)見せかけ / 〈U〉(…の)保険《+『against』+『名』》 / 〈C〉封筒;(郵便小包などの)包装紙 / 〈C〉毛布,ふとん
(人の能力などの)『試験』,考査,テスト / (物事の)『試験』,検済,試錬,実験《+of+名》 / 化学分析;試薬 / =test match / …‘を'『試験する』,検査する / …‘を'化学分析する / (…の)試験を受ける,試験をする《+for+名》
〈U〉おおうこと;援護 / 〈C〉おおう物(布,ふた,屋根など)
プリズム(分光に用いる透明な三角柱) / (幾何で)角柱

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2017/06/16 09:19:34」(JST)

wiki en

The "prism cover test" (PCT), is an objective measurement and the gold standard in measuring strabismus, i.e. ocular misalignment, or a deviation of the eye.^[1] It is used by ophthalmologists and orthoptists in order to measure the vertical and horizontal deviation and includes both manifest and latent components.^[1] Manifest is defined by the eye deviating constantly or intermittently, where-as latent is where the deviation is normally controlled but becomes present when the eyes are dissociated.^[2] A PCT reveals the total deviation and cannot distinguish between latent and manifest strabismus as you are using an alternate cover test.

A number of different instruments are required when performing a PCT.

Play media

This video demonstrates what is involved when performing a prism cover test.

These include:

Horizontal and vertical prism bars (or loose prisms).^[1]
An occluder ^[1]
Near accommodative target. For example, near fixation stick ^[1]
Distance target.^[1] For example, most commonly a Snellen chart is utilised, however the LogMAR chart is preferred as it has letters of equal legibility, same numbers of letters on each row and uniform spacing between letters and rows^[3] This compared to the Snellen Chart which has ‘poor reproducibility and reliability’ ^[3]

In order to perform a PCT, you must first perform a cover test as this gives an estimation of the size of the strabismus, thus an approximate starting point on the prism bar.^[1] You can also get an indication of presence and type of strabismus by observing the patients’ eye and observing corneal reflections, also known as Hirschbergs.^[2] It also shows whether the patient has a manifest or latent deviation. If a manifest deviation is present, it reveals which eye has the deviation or if it is alternating between both eyes.^[1]

Indicated in

Patients with manifest and latent strabismus ^[1]
Patients with concomitant and incomitant deviations.^[1]
Horizontal and vertical deviations ^[1]
Patients with good fixation, visual acuity and cooperation ^[1]
For accurate (within two prism dioptres) numerical recording that will provide a point of reference for future consultations ^[1]
Monitoring the efficacy of various noninvasive treatments and also surgery interventions ^[1]

Not indicated in

Cyclotropias or torsional deviations ^[1]
Patients with eccentric fixation because the movement of the deviating eye stops when the stimulus falls on the eccentric retinal area used for fixation and not on the fovea ^[1]
Patients that do not have simultaneous perception ^[1]
Patients that have difficulty with nystagmus ^[1]
Unreliable deviations greater than eighty prism dioptres ^[1]

Advantages

Provides complete dissociation that gives the maximum angle of deviation ^[1]
Provides a comparison of distance and near deviations ^[1]

Disadvantages

Can not be used in all types of deviations as above in ‘Not indicated in’ ^[1]

Method

The prism cover test must be conducted at near (33 cm), at distance (6m) and if necessary at greater than 6 metres. Before commencing the test, ensure the patient is sitting upright with their chin and head straight. Patients with a head tilt (abnormal head posture) are ‘not formally controlled by using a bite bar or chin rest’ and are always tested with their head tilt and then without their head tilt ^[4]

The results leading on from the cover test will give you an indication of the type of deviation and which way you should hold your prism for the next stage of the test. Either BASE IN for an exodeviation (eye turned out), BASE OUT for an esodeviation (eye turned in), BASE UP for a hypodeviation (eye turned down) or BASE DOWN for a hyperdeviation (eye turned up).^[5]

Steps: 1. The patient should be measured in primary position first and then in any other positions of gaze of concern. For near fixation, the patient should hold an accommodative target (fixation stick) at 33 cm, ensuring it is in line with their visual axis. By having the patient read out loud the letters at the top of the fixation stick, it is easy to ensure they are maintaining their accommodation.^[5]

2. The examiner then holds the prism bar over the patients deviating eye, starting at a small strength prism, however, if the deviation on the cover test appeared to be large, a larger strength prism may be used to achieve results quicker.

3. With the prism present, an alternate cover test is performed. It is important that an alternate cover test is performed correctly in order to ensure maximum dissociation as we are determining the total deviation size which includes both latent and manifest.^[5]

Note: It is important to ensure the patient maintains good fixation, by continuing to look at the near fixation stick.

4. As the alternate cover test is performed, the examiner watches the patients eye for movement. If movement is seen, the prism bar is moved to increase the power. If the ‘deviation exceeds 50 prism dioptres, such that a single prism bar cannot be used’, prisms can either be stacked or split ^[4]

5. Prism strength is increased until the eye under the prism produces no movement, meaning the deviation is neutralised.

6. To confirm neutralisation the next prism of increasing strength should produce a movement in the opposite direction indicating overcorrection.^[5]

7. Once the results for the near PCT have been recorded, the procedure should be repeated at 6m with the Snellen chart and if needed at greater than 6m by patient fixating out the window.

8. Continue the test until neutralisation has been established.

Recording

The PCT recordings assist in classification and diagnosis of specific strabismic conditions by comparing the size of the deviation from near to distance and also in other various positions of gaze.

When recording the results obtained on a PCT it must be noted:

If correction (glasses or contact lenses) was worn at the time of measurement
The fixation distance where the prism neutralised the deviation. That way we can gain an understanding as to whether it increases or decreases in size in different positions of gaze and therefore make a diagnosis of whether it is a concomitant or incomitant deviation.
The prism base utilised. For example, Base in (BI), Base out (BO), Base up (BU) or Base down (BD).
The angle of the deviation with the units in prism dioptres
Which eye is fixating and which eye is deviating
Whether the test was performed with or without an abnormal head posture

Examples of recording

               PCT cc  (D) 12 p.d BI  6 p.d BU (FL)        (N) 18 p.d BI  6 p.d BU (FL)

or

               PCT cc  (D) 12 p.d BI  R/L 6 p.d (FR&L)     (N) 18 p.d BI  R/L 6 p.d (FR&L)

Interpretation

In the first example, it has been noted that when conducting the PCT, this patient wore correction, was fixing left and has a twelve prism dioptre exotropia in the distance. At near they have a larger exotropic deviation measuring 18 prism dioptres. They also have a right hypertropia of six prism dioptres. This means that when the PCT was performed, the deviating eye was neutralised and no movement was seen at these points on the prism bar.

Considerations

Ensure prisms are held straight, if they are held off centre the power of the prism will not be accurate. There are two types of prisms, the first type is glass prisms which need to be held in the prentice position and the second type is plastic prisms that need to be positioned in the frontal plane.^[1]
Try to estimate the angle of deviation before placing the prism over the affected eye, this way time can be saved in busy clinics and especially with children who may have a short attention span.^[1]
In larger deviations when stacking prisms (see image for table of stacking prisms) or prism bars it may be easier to place one before each eye to better observe if there is any movement taking place ^[1]
The cover should be altered slowly enough to give the patient time to fixate accurately and avoid fusion by continued use of alternate cover test ^[1]
To control accommodation with a fixation target ensure it is maintained by asking the patient to identify the next letter ^[1]

References

^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^aa Ansons, A. M., & Davis, H. (2014). Diagnosis and Management of Ocular Motility Disorders (4th ed.). pp. 104-105. London: Blackwell.
^ ^a ^b Ansons, A. M., & Davis, H. (2014). Diagnosis and Management of Ocular Motility Disorders (4th ed.). pp. 97. London: Blackwell.
^ ^a ^b Hussain, B., Saleh, G. M., Sivaprasad, S. and Hammond, C. J. (2006). Changing from Snellen to LogMAR: debate or delay?. Clinical & Experimental Ophthalmology, 34(1), 6–8. doi: 10.1111/j.1442-9071.2006.01135.x
^ ^a ^b Hohberger, G.G., Holmes, J. M., & Leske, D. A. (2008). Defining real change in prism-cover test measurements. American Journal of Ophthalmology, 145, 381-385. doi:10.1016/j.ajo.2007.09.012
^ ^a ^b ^c ^d Campos, E.C., & von Noorden, G.K. (2006). Binocular vision and ocular motility (6th ed.) (p.177) St Louis, Missouri: Mosby.

UpToDate Contents

全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.

1. 小児における斜視の評価およびマネージメント evaluation and management of strabismus in children
2. 小児における垂直斜視の原因 causes of vertical strabismus in children
3. 乳児や小児の視覚の発達と視力評価 visual development and vision assessment in infants and children
4. 小児における身体的診察：HEENT the pediatric physical examination heent
5. 小児における後天性斜頚 acquired torticollis in children

English Journal

Short prism adaptation test in patients with acquired nonaccommodative esotropia; clinical findings and surgical outcome.

Akbari MR1, Mehrabi Bahar MR1, Mirmohammadsadeghi A1, Bayat R1, Masoumi A2.
Journal of AAPOS : the official publication of the American Association for Pediatric Ophthalmology and Strabismus.J AAPOS.2018 Oct;22(5):352-355. doi: 10.1016/j.jaapos.2018.05.018. Epub 2018 Sep 15.
PMID 30227245

A Randomized Trial Comparing Bilateral Lateral Rectus Recession versus Unilateral Recess and Resect for Basic-Type Intermittent Exotropia.

Pediatric Eye Disease Investigator Group; Writing Committee, Donahue SP1, Chandler DL2, Holmes JM3, Arthur BW4, Paysse EA5, Wallace DK6, Petersen DB7, Melia BM2, Kraker RT2, Miller AM8.
Ophthalmology.Ophthalmology.2018 Sep 3. pii: S0161-6420(18)31552-5. doi: 10.1016/j.ophtha.2018.08.034. [Epub ahead of print]
PMID 30189281

Compared performance of Spot and SW800 photoscreeners on Chinese children.

Qian X1, Li Y2, Ding G1, Li J1, Lv H3, Hua N1, Wei N1, He L2, Wei L4, Li X1, Wang J5,6.
The British journal of ophthalmology.Br J Ophthalmol.2018 Jul 9. pii: bjophthalmol-2018-311885. doi: 10.1136/bjophthalmol-2018-311885. [Epub ahead of print]
PMID 29986946

Japanese Journal

Five-year follow-up of ocular deviation and stereopsis in bilaterally pseudophakic patients

干川里絵,伊藤美沙絵,清水公也,天野理恵,石川均
日本視能訓練士協会誌 41(0), 89-94, 2012
… Before surgery, at 1, 3 and 6 months and 1, 2, 3, 4 and 5 years after surgery, with corrected refractions ocular deviation was measured by alternate prism cover test and near stereopsis was measured by the Titmus stereo test. … Most of these patients had a preoperative near exophoria angle greater than 12 prism diopters (PD). …
NAID 130004552620

Frequency of appearance of high-frequency component of accommodative microfluctuation before and after prism adaptation in intermittent exotropia

藤井千晶,岸本典子,大月洋
日本視能訓練士協会誌 41(0), 77-82, 2012
… The frequency of appearance of the high-frequency component (HFC) of accommodative microfluctuation in intermittent exotropia was compared between before and after prism adaptation (PA). Subjects and Methods: … PA was performed based on the angle of deviation in distant vision measured in an alternate prism cover test. … Wilcoxon signed-rank test). Conclusion: …
NAID 130004552618

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Prism Cover Test - YouTube Prism Cover Test (PCT) - YouTube Prism and Cover Test / www.hawal-eg.com / الموقع المصري للحول - YouTube Prism cover test - Wikipedia Prism and Cover Test - YouTube Simultaneous Prism Cover Test (SPCT) - YouTube $Refraction$ Heterophoria