PRESENTED BY T.Muthuramalingam PRESCRIPTION WRITING PRESENTED BY T.Muthuramalingam

Introduction The final part of the clinical routine is to give the patient a prescription for spectacles. Clinical refraction should be done to provide best glass prescription. Mainly it include Objective refraction Subjective refraction Binocular balancing Near vision assessment

Objective refraction In objective refraction (retinoscopy), the examiner determines the type and degree of refractive error without active participation of patients. Retinoscopy is performed with the patient gazing at a distant object. Observe the movement of reflex (with or against) Neutralize the reflex using appropriate lens.(plus lens for with movement and minus lens for against movement) Lens which neutralize the reflex is the total refractive error of eye.

Subjective refraction The findings of retinoscopy should be checked subjectively. The most comfortable lenses should be prescribed to patients by trial and error method. The corrections of refractive errors determined by the objective technique are entered into the lens aperture of trial frame before eye.

Contd. Spherical lens are altered first. The lens which gives best vision is chosen. Then cylinder lens are altered to correct the remaining error. Verification of the axis is done by rotating the cylinder in 5-10deg. In either direction and asking whether the acuity improves

Supplementary test To verify the subjective refraction and to achieve best glass prescription supplementary tests are done. Some important tests are: Cycloplegic refraction Jackson cross cylinder Duochrome test Muscle balance Worth four dot test

Cycloplegic refraction The test is performed when abnormally accommodation is actively involved. (especially for children ) Cycloplegic eye drops (atropine, cyclopentolate and tropicamide) are instilled to achieve cycloplegia (paralysis) of ciliary muscles, which results in full relaxation of accommodation. It is recommended when patient have following situations:   Ø     Asthenopic symptom Ø      Hypermetropia Ø      Convergent strabismus Ø      Active accommodation  

Jackson cross cylinder The cross cylinder is a sphero-cylinder lens in which the power of the cylinder is twice the power of the sphere and of the opposite sign. It is used to refine power and axis of cylindrical power Axis check:  Position the cross cylinder axis 450 from the principal meridian of correcting cylinder Determine preferred flip choice Rotate the axis towards the corresponding axis of cross cylinder (plus cylinder axis rotated to + cylinder axis of JCC, minus cylinder axis rotated to - cylinder axis of JCC) Repeat until two flip choices are equal.   

Power check: Align JCC axes with the principal meridians of correcting cylinder Determine preferred flip choice Add or subtract cylindrical power according to the preferred position of cross cylinder Compensate for change in position of the circle of least confusion by adding half as much sphere in opposite direction.

Duochrome test Each eye is tested separately to find out if eye is over corrected or under corrected. It consist of letters in red and green color background. An emmetropic eye sees the letters on both sides of the chart to be of equal clarity, darkness and definition Over corrected of myopia green more clear. Over corrected of hypermetropia red more clear. Then fog and unfog so that both color seen equally clear or blurr.

Muscle balance Before final prescription is given it is important to test for the oculomotor balance both for near and distant vision with and without the correction. To find out the presence of any squint, convergence insufficiency fusional reserves. It include: Corneal reflex done by torch light. Ocular movement in all direction. Cover test. Accommodation and convergence by RAF ruler. Fusion with prism bar with base out.

Cover test RAF ruler Prism bar

Worth four dot test The test is done using red glass in right and green glass in left eye to find the presence of binocular single vision. It consist of four dots.one white,two red, one green. Interpretation: If two red is seen then left eye is suppressed. If three green is seen then right eye is suppressed. If five dots are seen then diplopia is present. If four dots with respective color are seen patients have no diplopia

Near vision assessment A suitable weakest convex lens addition should be made over the distant correction with which an individual can see clearly and binocularly at normal near distance should be prescribed. It should be performed on the basis of working distance, visual needs and age of the patients.

Binocular balancing test It is done To avoid the asthenopic symptoms due to unstable accommodation. To ensure the subjective finding include an over or under correction for the two eyes. It is carried by prism dissociation method.

Prism dissociation method. With the best correcting lens, both eyes are fogged with+1.0Ds and a vertical prism of 3 or 4 Δ BD OD and 3 or 4 Δ BU OS and ask the patient to see a single line. If the line is seen simultaneously with both eye then +0.25Ds is placed before one eye. BD prism will cause image to be higher (top)The image will be displaced towards the apex (point) of the prism ΔBU prism will cause image to be lower (bottom)

Contd. If the patient reports the top image clearer, add +0.25DS to the OD. If the patient reports the lower image clearer add +0.25DS to the OS and again asked the patient which image is clear. Remove prisms and take down binocularly to BCVA Do not add minus to the more blurry image, instead add plus to the clearer image Then bring patient down out of the fog by –0.25 steps until the BCVA is reached

Guide lines for prescribing the glass For myopia: Never over correct the myopia. Choose under correction for indoor profession Full correction for out door profession Complete correction of cylinder in low myopia. Under correction of cylinder in high myopia If more cylinder and less sphere, then give spherical equivalent in low myopia, and in high myopia under correct the cylinder. Above 3D cylinder check the keratometer.

For myopic anisometropia: BE. Low myopia:- less myopic eye full correction and more myopic eye slight under correction BE.high myopia:- never fully correct. keeping the near vision comfortable balance the two eye by slightly over correcting less myopic eye and under correction the more myopic eye to balance the prescription.

Hypermetropia : For first time wear initially under correct. Do not correct the latent hypermetropia. Do not over correct the facultative hypermetropia.

Astigmatism: (low < 0.5D, mod < 0.75 to 1.5D,high > 1.75D) In low astigmatism:- it can be ignored with horizontal and vertical axis, with oblique axis it can be corrected to relieve the symptoms of asthenopia. In moderate astigmatism:- it should be corrected optimally. If spherocylinder having high sphere then spherical equivalent can be used. In high astigmatism:- under correction of high cylinder

Format     Paulsamy m 226878 06/07/2006 56yrs +2 -1 90 6/6 +1.50 -1.0 90 6/6 add add + 2.50 Ds N6 +2.50 Ds N6 31mm 31mm 32mm 32mm    

Additional points to write in prescription Lens material: Glass plastics Lens design: Specially for Presbyopic patient Bifocal ( kryptok, executive, univis –D) PAL Vocational glasses( trifocal) Instruction to patients: Constant use Near vision only Vocational use Interpupillary distance: For near and distance

Interpupillary distance The distance between the center of pupil of one eye to the other eye. It is important for placement of optical centers of the eye glasses coincide with it, to prevent the unwanted prismatic effect produced by decentration. Measurement : By using ruler or optical ruler By instrument called pupilometer

Some examples… 1) R.E. = +2.0Ds 6/6 Age: 35/M L.E. = +10Ds 6/18 Occupation:Weaver Check diplopia Check binocular single vision Test binocular balance Diagnosis: Hypermetropic Anisometropia Treatment Contact lens Secondary IOL Spectacle correction Spectacle prescription R.E. +2.0DS 6/6, L.E. Secondary IOL or contact lens For near vision separate glass is advice

2) R.E. = 6/6 ( IOL) Age: 35/M Diagnosis: Antiometropia L.E. = - 3.0Ds 6/12 (IMC) Occupation:Agriculture Check binocular single vision Check diplopia Test binocular balance Alternative vision using Diagnosis: Antiometropia So need of glass

3) R.E. = - 2.0Ds 6/6 Age: 35/M L.E. = - 10Ds 6/12 Occupation:Field Work Check diplopia Check binocular single vision Test binocular balance Diagnosis: Myopic Anisometropia Treatment Lasik Contact lens Spectacle correction Spectacle prescription R.E. -2.0Ds 6/6, L.E.-5.0Ds 6/36 under correction in L.E.

4) R.E. = +2.0Ds 6/6 Age: 35/M L.E. = +4.0Ds 6/12 Occupation:Accountant Check diplopia Check binocular single vision Test binocular balance Diagnosis: Anisometropic Ambylopia Treatment Contact lens Spectacle correction Spectacle prescription R.E. +2.0Ds 6/6, L.E. +4.0Ds 6/12

5)R.E. = +1.0Ds 6/6 Age: 40/M L.E. = +1.0Ds 6/6 Occupation:Weaver add +1.0Ds Diagnosis:Hypermetropic with presbyopia Treatment Spectacle correction Spectacle prescription R.E.+1.0Ds 6/6, L.E. +1.0Ds 6/6 Bifocals is not necessary only distance vision glass is sufficient

6)R.E.= -3.0Ds/-4.0Dcylx90 6/12 Age:25/M L.E. = -4.0Ds/-6.0Dcylx90 6/12 Student Check diplopia Check binocular single vision Test binocular balance Keratometer Reading Diagnosis:myopic with astigmatism Treatment Lasik Contact lens Spectacle correction Spectacle prescription R.E. -3.0Ds/-4.0Dcylx90 6/12 L.E. -3.0Ds/-4.0Dcylx90 6/12

Points to remember Prefer is given to prescription in minus cylinder form unless vision is improves significantly with plus cylinder. If axis of cylindrical component is not vertical and horizontal, it is better to under correct astigmatic power. Prescription should be written clearly with correct sign and power. Prescription should not be over corrected. All the information given to patient should be written.

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