SlideShare a Scribd company logo
Prepared by
Loknath Goswami
B.Sc Optom 2nd year
Prism
 A prism is an object made up of a transparent material like
glass or plastic that has at least two flat surfaces that form
an acute angle (less than 90 degrees)
 A traditional prism has two flat, nonparallel surfaces
 Parallel light entering the prism is bent towards the base
of the prism and leaves the back surface at an angle
 A prism is thicker at the base than at the apex. The larger
the prism, the thicker the base of the prism will be
Prism
APEX
BASE
DEVIATION
TOWARDS
THE BASE
Properties of prism
 Dispersion
 Deviation occurs towards the base
 Total internal reflection occurs in some specific prisms.
 Prism never change the vergence of light rays. A prism
does not magnify or minify the image.
Recumbent prisms
 Prisms which deviate the light by 90˚
 Right angle prisms and prisms used in recumbent
spectacles
History
 In 1935, Mr. Andrew McKie
Reid designed the ‘recumbent
spectacles’, as a visual aid for
patients suffering from spinal
lesions and other diseases who
were confined to the bed in a
supine position for weeks or
months
History
 The spectacle was made by
Messrs Hamblin of
Wigmore Street, London
and was shown for the first
time at the Oxford
Ophthalmological
Congress in July 1935
Recumbent spectacles
 Recumbent spectacles are equipped with reflecting prism
that enable a person lying flat on his or her back to see
straight ahead while looking straight up
 The spectacle consists of a pair of prisms mounted in a
frame which could either be worn over the patient’s own
glasses or the refractive prescription could be incorporated
in the frame
 These can be useful for those wishing to read while being
required to remain on their backs for long periods of time
 The prisms must be perfectly aligned, or diplopia occurs,
making wear impossible
Recumbent spectacles
Principle
 The prisms had an apical angle of 35 degrees and basal
angles of 70 and 75 degrees
 These angles were calculated such that a book held in the
normal position on the chest could be read by a person in
the supine position even though apparently looking at the
ceiling
 So, with the base of the prism facing the patient, the line
of vision through refraction and double internal reflection
within the prisms was bent almost 90 degrees
Optics
a 2 = 52˚
Optics
Recumbent spectacles
Advantage Disadvantage
 Help people to read in supine
position
 It is heavy and not much
comfortable
History
 In 1970, the optical sciences group of San Rafael,
California, developed a series of Fresnel Press-on prisms –
thin plastic membrane prisms ranging in powers from 0.5
to 30 prism diopters
History
 These prisms are an
adaptation of the hand-
ground lenses designed by
the French engineer and
physicist Augustine Fresnel
in 1821
 Fresnel’s lenses were
originally used for
lighthouse beacons.
Fresnel lens and Fresnel prism
Fresnel lens and Fresnel prism
Fresnel prism
 A Fresnel prism attempts to avoid thickness by building a
tower of small prism
 A Fresnel prism is only 1 mm thick
 The refraction depends on the apical angle
 The angle between the two surfaces remains constant
across the prism.
 E.g. 3M Press-on
3M Press-On
 Manufacturer: 3M
 Location: USA
 Material: PVC (Polyvinyl chloride)
 Thickness: 1mm
 Usable area: 65mm diameter
 Base is noted in one corner of the prism, if it is cut then
base may be found by running finger nail along prism side
Press-on prism availability
1∆, 2∆, 3∆, 4∆, 5∆, 6∆, 7∆, 8∆, 9∆, 10∆, 12∆,
15∆, 20∆, 25∆, 30∆, 35∆, 40∆
Optics
Optics
Fresnel prism trial sets
 Fresnel prisms trial optics are similar to traditional prism
trial optics(ring) found in trial ring sets.
 Thin and light weight (particularly in the higher diopter
powers)
 Raised edges around the Fresnel prism trial optic prevents
scratching of prism features when placed on flat surfaces
 Allows for accurate testing of large oculomotor
imbalances and allows patient opportunity to experience a
Fresnel prism
 Recommend for prism cover test
 Available in two, 7 ring sets: TS4000 & TS5000
 TS4000: 2∆, 3∆, 4∆, 5∆, 6∆, 8∆, 10∆
 TS5000: 12∆, 15∆, 20∆, 25∆, 30∆, 35∆, 40∆
TS4000 TS5000
A coin has two faces
Advantages
 It is very thin and extremely lightweight
 It is flexible and can be applied to an existing spectacle
lens
 It can be cut to any shape with scissors or a razor blade.
This means that it can be cut and applied to one sector of a
lens
 It can be applied or removed at anytime
Disadvantages
 Fresnel prisms look different
than conventional lenses. It
gives striated appearance (to
observers) of the grooves. The
striated appearance can be
improved to some extent by
use of a lightly tinted or
photochromic lens
 Fresnel prisms have a number
of small ledges, they are
harder to clean than
conventional lenses
 High-powered prisms will cause a slight decrease in visual
acuity
Visual acuity loss is due to scattering of light, caused
by the grooves. The scattering of light causes both a loss of
contrast and the presence of bothersome reflections. The
minimal acuity decrease through Fresnel prisms is less than
one line on a Snellen chart at a 90% contrast level compared
with acuity through conventional prism.
 The flexible static vinyl material that gives these lenses
the ability to be easily cut to custom shapes, unfortunately,
reduces the contrast of objects viewed through the lens
Chart photographed with and without a
40 diopter Fresnel press-on
When to prescibe
 When a prismatic component is to be included in a
patient’s prescription, the advantages and disadvantages of
press-on prisms should be carefully weighed to determine
the suitability of using press-on prism.
When are Fresnel prism used?
 High amount of prism
Fresnel prism is very
thin comparatively to the
conventional prism. So it is
useful for high amount of
prism Conventional prism
Fresnel prism
 Use and reuse
Fresnel prism lenses are
easy to apply and remove. They
may be used and reused. This is
helpful when determining how a
given prism amount will work
long term or for use during
visual training.
 Sectorial application
A partially paralyzed
extraocular muscle may result
in a different amount of prism
needed for different directions
of gaze. A Fresnel prism can be
cut to fit that particular lens
area. Prism is present only
where it is needed.
 Visual field defects
 A person may have a
visual field defect
 For example, the case of
bilateral hemianopia, the
right half of the visual
field is blind for both right
and left eyes.
 Fresnel prism can be applied to the right side of the both
lenses.
 In this instance, prism base direction would be base right.
 With prism in place, the wearer looks to the right but does
not have to turn the eyes as far to see an object in the right-
hand field of view
 Slowing of nystagmus
 Nystagmus is a defined as regular and rhythmic to-and-fro
involuntary oscillatory movements. Such movement is
involuntary and reduces vision.
 In some cases, nystagmus may slow when the person looks to
one side or the other
 For example, if the examiner sees that movement slows when
the person looks to the right, equal amounts of prism may be
applied to both lenses. The correct base direction would be
base left. Because the eyes turn toward the apex, prism base
left will keep the head pointed straight while the eyes turn to
the right. Since the eyes are turned to the right, nystagmus
slows.
How to apply a Fresnel prism to a
spectacle lens
 Firstly we have to determine correct base direction
 After that we have to take the carrier lens out of the
spectacle frame
 We have to place the Fresnel prism on the back of the
carrier lens with its smooth side against the carrier.
Making sure base direction is properly oriented and then
we have to mark the boundary
 With a razor blade, trim the Fresnel prism along the
marking
How to apply a Fresnel prism to a
spectacle lens
 Reinsert the carrier lens into the frame
 Wash both carrier and Fresnel prism with a weak solution
of lotion-free liquid detergent
 In a bowl of warm water, or under a stream of warm
water, apply the smooth side of the Fresnel to the carrier.
Work out any air bubbles that may be trapped between the
two surfaces
 Then we can give the lenses to the wearer, but have to
instruct the wearer to handle the lenses with care for 24
hours until drying is complete.
How to clean Fresnel prisms
 The manufacturer’s recommended method of cleaning
these lenses is to rinse under warm running water. If the
lenses have dirt in grooves, use a soft brush. Blot dry with
a soft, lint-free cloth. Hard contact lens cleaning solutions
have also been used to clean Fresnel optics.
How to clean Fresnel prisms
Finally, the right tool to clean your
Fresnel Optics. The secret is the
cloth, a lint-free micro fiber cloth
that can reach into the small deep
grooves of a Press-On Lens.
Use with the alcohol free lens
cleaner to remove finger prints,
oils, make-up and the daily dirt and
grime that can get onto your lens.
Costs $5.00
REFERENCES
 Troy E. Fannin, Clinical optics 1st edition, Pg No. 106-107
 System For Ophthalmic Dispensing-2nd edition, Clifford
W. Brooks , Irvin M. Borish, Pg No. 516-519, 536
 http://www.sciencephoto.com/media/117959/view
 http://study.com/academy/lesson/what-is-a-prism-
definition-refraction-quiz.html
 http://www.hemianopsia.net/the-fresnel-prism
 http://www.gcsescience.com/pwav32.htm
 http://bjo.bmj.com/content/94/5/535.full
For letting me speak here

More Related Content

What's hot

Rgp lens
Rgp lensRgp lens
AC/A
AC/AAC/A
AC/A
zarin45
 
Slit lamp (methods of illumination)
Slit lamp (methods of illumination)Slit lamp (methods of illumination)
Slit lamp (methods of illumination)
maclester manahan
 
Ophthalmic dispensing
Ophthalmic dispensingOphthalmic dispensing
Ophthalmic dispensing
Kewal Hirwani
 
Frame measurementsand markings
Frame measurementsand markingsFrame measurementsand markings
Frame measurementsand markings
OPTOM FASLU MUHAMMED
 
Retinoscopy @adi
Retinoscopy @adiRetinoscopy @adi
Retinoscopy @adi
Farhana Adi
 
Binocular refraction techniques, binocular balancing
Binocular refraction techniques, binocular balancing Binocular refraction techniques, binocular balancing
Binocular refraction techniques, binocular balancing
Mohammad Arman Bin Aziz
 
Review of geometric optics
Review of geometric opticsReview of geometric optics
Review of geometric optics
SalalKhan5
 
Schematic eye
Schematic eye   Schematic eye
Maddox rod, Maddox wing, Bagolini striated glasses, RAF ruler and Prism bar
Maddox rod, Maddox wing, Bagolini striated glasses, RAF ruler and Prism barMaddox rod, Maddox wing, Bagolini striated glasses, RAF ruler and Prism bar
Maddox rod, Maddox wing, Bagolini striated glasses, RAF ruler and Prism bar
Bhageesh Bhaskar
 
RGP Fitting
RGP Fitting RGP Fitting
RGP Fitting
emlctvla
 
Synaptophore
SynaptophoreSynaptophore
Synaptophore
Manjusha Lakshmi
 
Potential acuity meter
Potential acuity meterPotential acuity meter
Potential acuity meter
OPTOM FASLU MUHAMMED
 
Vergence
VergenceVergence
Vergence
Hossein Mirzaie
 
Synoptophore
SynoptophoreSynoptophore
Synoptophore
Nikhil Oza
 
Orthoptic instruments arya
Orthoptic instruments aryaOrthoptic instruments arya
Orthoptic instruments arya
arya das
 
Synaptophore in ophthalmology
Synaptophore in ophthalmologySynaptophore in ophthalmology
Synaptophore in ophthalmology
Dr.Juleena Kunhimohammed
 
Amsler grid
Amsler gridAmsler grid
Amsler grid
Suhail Wahab
 
Soft Contact Lens Fitting
Soft Contact Lens FittingSoft Contact Lens Fitting
Soft Contact Lens Fitting
Vishakh Nair
 
Trifocals
Trifocals Trifocals
Trifocals
Sanjana Chouhan
 

What's hot (20)

Rgp lens
Rgp lensRgp lens
Rgp lens
 
AC/A
AC/AAC/A
AC/A
 
Slit lamp (methods of illumination)
Slit lamp (methods of illumination)Slit lamp (methods of illumination)
Slit lamp (methods of illumination)
 
Ophthalmic dispensing
Ophthalmic dispensingOphthalmic dispensing
Ophthalmic dispensing
 
Frame measurementsand markings
Frame measurementsand markingsFrame measurementsand markings
Frame measurementsand markings
 
Retinoscopy @adi
Retinoscopy @adiRetinoscopy @adi
Retinoscopy @adi
 
Binocular refraction techniques, binocular balancing
Binocular refraction techniques, binocular balancing Binocular refraction techniques, binocular balancing
Binocular refraction techniques, binocular balancing
 
Review of geometric optics
Review of geometric opticsReview of geometric optics
Review of geometric optics
 
Schematic eye
Schematic eye   Schematic eye
Schematic eye
 
Maddox rod, Maddox wing, Bagolini striated glasses, RAF ruler and Prism bar
Maddox rod, Maddox wing, Bagolini striated glasses, RAF ruler and Prism barMaddox rod, Maddox wing, Bagolini striated glasses, RAF ruler and Prism bar
Maddox rod, Maddox wing, Bagolini striated glasses, RAF ruler and Prism bar
 
RGP Fitting
RGP Fitting RGP Fitting
RGP Fitting
 
Synaptophore
SynaptophoreSynaptophore
Synaptophore
 
Potential acuity meter
Potential acuity meterPotential acuity meter
Potential acuity meter
 
Vergence
VergenceVergence
Vergence
 
Synoptophore
SynoptophoreSynoptophore
Synoptophore
 
Orthoptic instruments arya
Orthoptic instruments aryaOrthoptic instruments arya
Orthoptic instruments arya
 
Synaptophore in ophthalmology
Synaptophore in ophthalmologySynaptophore in ophthalmology
Synaptophore in ophthalmology
 
Amsler grid
Amsler gridAmsler grid
Amsler grid
 
Soft Contact Lens Fitting
Soft Contact Lens FittingSoft Contact Lens Fitting
Soft Contact Lens Fitting
 
Trifocals
Trifocals Trifocals
Trifocals
 

Viewers also liked

Newer tests for glaucoma
Newer tests for glaucomaNewer tests for glaucoma
Newer tests for glaucoma
vaishusmail
 
Solid mensuration prism lecture
Solid mensuration prism lectureSolid mensuration prism lecture
Solid mensuration prism lecture
Denmar Marasigan
 
PRISM and Silverlight
PRISM and SilverlightPRISM and Silverlight
PRISM and Silverlight
mark mann
 
Prism Credentials 2012
Prism  Credentials 2012Prism  Credentials 2012
Prism Credentials 2012
Prism
 
Cardinal points
Cardinal pointsCardinal points
Cardinal points
Loknath Goswami
 
Embryology applied anatomy and physiology of lens
Embryology applied anatomy and physiology of lensEmbryology applied anatomy and physiology of lens
Embryology applied anatomy and physiology of lens
Laxmi Eye Institute
 
Orbit clinical round
Orbit clinical roundOrbit clinical round
Orbit clinical round
KafrELShiekh University
 
PACS lens AGS 2014 final
PACS lens AGS 2014 finalPACS lens AGS 2014 final
PACS lens AGS 2014 final
H. George Tanaka, MD
 
Eye, orbit, lacrimal apparatus
Eye, orbit, lacrimal apparatusEye, orbit, lacrimal apparatus
Eye, orbit, lacrimal apparatus
Dr.Faris Muhammed
 
pseudoexfoliative glaucoma
pseudoexfoliative glaucomapseudoexfoliative glaucoma
pseudoexfoliative glaucoma
Suresh Subramaniam
 
The watering eye
The watering eyeThe watering eye
The watering eye
Other Mother
 
Orbit
OrbitOrbit
3 4 cholinergic pharmacology younus h johan 2016
3 4 cholinergic pharmacology younus h johan 20163 4 cholinergic pharmacology younus h johan 2016
3 4 cholinergic pharmacology younus h johan 2016
younus johan
 
Optical Prisms
Optical PrismsOptical Prisms
Optical Prisms
Othman Al-Abbadi
 
Ocular Emergencies
Ocular EmergenciesOcular Emergencies
Ocular Emergencies
Azizul Islam
 
GLAUCOMA SYMPTOMS, RISK FACTORS, TREATMENT
GLAUCOMA SYMPTOMS, RISK FACTORS, TREATMENTGLAUCOMA SYMPTOMS, RISK FACTORS, TREATMENT
GLAUCOMA SYMPTOMS, RISK FACTORS, TREATMENT
MediFee
 
The Prism
The PrismThe Prism
The Prism
shwetalib
 
Evaluation of a glaucoma patient
Evaluation of a glaucoma patientEvaluation of a glaucoma patient
Evaluation of a glaucoma patient
Rashed-Ul-Hasan Rasu
 
Anatomy and embryology of crystalline lens DrBP
Anatomy and embryology of crystalline lens DrBPAnatomy and embryology of crystalline lens DrBP
Anatomy and embryology of crystalline lens DrBP
drbhushan17
 
Etiology of heterophoria and heterotropia
Etiology of heterophoria and heterotropiaEtiology of heterophoria and heterotropia
Etiology of heterophoria and heterotropia
Tukezban Huseynova, MD
 

Viewers also liked (20)

Newer tests for glaucoma
Newer tests for glaucomaNewer tests for glaucoma
Newer tests for glaucoma
 
Solid mensuration prism lecture
Solid mensuration prism lectureSolid mensuration prism lecture
Solid mensuration prism lecture
 
PRISM and Silverlight
PRISM and SilverlightPRISM and Silverlight
PRISM and Silverlight
 
Prism Credentials 2012
Prism  Credentials 2012Prism  Credentials 2012
Prism Credentials 2012
 
Cardinal points
Cardinal pointsCardinal points
Cardinal points
 
Embryology applied anatomy and physiology of lens
Embryology applied anatomy and physiology of lensEmbryology applied anatomy and physiology of lens
Embryology applied anatomy and physiology of lens
 
Orbit clinical round
Orbit clinical roundOrbit clinical round
Orbit clinical round
 
PACS lens AGS 2014 final
PACS lens AGS 2014 finalPACS lens AGS 2014 final
PACS lens AGS 2014 final
 
Eye, orbit, lacrimal apparatus
Eye, orbit, lacrimal apparatusEye, orbit, lacrimal apparatus
Eye, orbit, lacrimal apparatus
 
pseudoexfoliative glaucoma
pseudoexfoliative glaucomapseudoexfoliative glaucoma
pseudoexfoliative glaucoma
 
The watering eye
The watering eyeThe watering eye
The watering eye
 
Orbit
OrbitOrbit
Orbit
 
3 4 cholinergic pharmacology younus h johan 2016
3 4 cholinergic pharmacology younus h johan 20163 4 cholinergic pharmacology younus h johan 2016
3 4 cholinergic pharmacology younus h johan 2016
 
Optical Prisms
Optical PrismsOptical Prisms
Optical Prisms
 
Ocular Emergencies
Ocular EmergenciesOcular Emergencies
Ocular Emergencies
 
GLAUCOMA SYMPTOMS, RISK FACTORS, TREATMENT
GLAUCOMA SYMPTOMS, RISK FACTORS, TREATMENTGLAUCOMA SYMPTOMS, RISK FACTORS, TREATMENT
GLAUCOMA SYMPTOMS, RISK FACTORS, TREATMENT
 
The Prism
The PrismThe Prism
The Prism
 
Evaluation of a glaucoma patient
Evaluation of a glaucoma patientEvaluation of a glaucoma patient
Evaluation of a glaucoma patient
 
Anatomy and embryology of crystalline lens DrBP
Anatomy and embryology of crystalline lens DrBPAnatomy and embryology of crystalline lens DrBP
Anatomy and embryology of crystalline lens DrBP
 
Etiology of heterophoria and heterotropia
Etiology of heterophoria and heterotropiaEtiology of heterophoria and heterotropia
Etiology of heterophoria and heterotropia
 

Similar to Recumbent prisms and fresnel prisms

FRESNEL PRISMS AND LENSES by optom. Jithin Johney
FRESNEL PRISMS AND LENSES by optom. Jithin JohneyFRESNEL PRISMS AND LENSES by optom. Jithin Johney
FRESNEL PRISMS AND LENSES by optom. Jithin Johney
backbenchersoptometr
 
Optometry instruments
Optometry instruments Optometry instruments
Optometry instruments
Muhammad Akbar Rashid Qadri
 
frenel & rotary prism PART 2.pptx
frenel & rotary prism PART 2.pptxfrenel & rotary prism PART 2.pptx
Lenses in ophthalmology
Lenses in ophthalmologyLenses in ophthalmology
Lenses in ophthalmology
Reshma Peter
 
lensesinophthalmology-171212163049 (1).pdf
lensesinophthalmology-171212163049 (1).pdflensesinophthalmology-171212163049 (1).pdf
lensesinophthalmology-171212163049 (1).pdf
DrSunandaMajumder
 
Special type of lenses
Special  type of lensesSpecial  type of lenses
Special type of lenses
OPTOM FASLU MUHAMMED
 
what is slit lamp Biomicroscopy | What is a slit lamp exam used for? |Differe...
what is slit lamp Biomicroscopy | What is a slit lamp exam used for? |Differe...what is slit lamp Biomicroscopy | What is a slit lamp exam used for? |Differe...
what is slit lamp Biomicroscopy | What is a slit lamp exam used for? |Differe...
Naeem Ahmad
 
laser lenses for retinal diseases
 laser lenses for retinal diseases laser lenses for retinal diseases
laser lenses for retinal diseases
nalini2218
 
Lenses of slit lamp biomicroscope & indirect ophthalmoscope.
Lenses of slit lamp biomicroscope & indirect ophthalmoscope.Lenses of slit lamp biomicroscope & indirect ophthalmoscope.
Lenses of slit lamp biomicroscope & indirect ophthalmoscope.
Ayat AbuJazar
 
Binocular Indirect Ophthalmoscopy
Binocular Indirect OphthalmoscopyBinocular Indirect Ophthalmoscopy
Binocular Indirect Ophthalmoscopy
abhishek ghelani
 
Objective refraction
Objective refractionObjective refraction
Objective refraction
sneha_thaps
 
Techniques of refraction is the process of calculation of glass power.
Techniques of refraction is the process of calculation of glass power.Techniques of refraction is the process of calculation of glass power.
Techniques of refraction is the process of calculation of glass power.
drbrijeshbhu
 
Trial box
Trial boxTrial box
Trial box
Swati Panara
 
Trial box
Trial boxTrial box
Trial box
vivek parmar
 
INDIRECT OPHTHALOMOSCOPE
INDIRECT OPHTHALOMOSCOPEINDIRECT OPHTHALOMOSCOPE
INDIRECT OPHTHALOMOSCOPE
Sheim Elteb
 
Spectacle prescription
Spectacle prescriptionSpectacle prescription
Spectacle prescription
Richa Naik
 
Refraction in different refractive errors and their Management
Refraction in different refractive errors and their ManagementRefraction in different refractive errors and their Management
Refraction in different refractive errors and their Management
DrArvindMorya
 
TRIAL BOX PPT.pptx
TRIAL BOX PPT.pptxTRIAL BOX PPT.pptx
TRIAL BOX PPT.pptx
LovelyWinsome
 
Slit lamp examination
Slit lamp examinationSlit lamp examination
Slit lamp examination
SIDESH HENDAVITHARANA
 
Ophthalmic prisms
Ophthalmic prismsOphthalmic prisms
Ophthalmic prisms
OPTOM FASLU MUHAMMED
 

Similar to Recumbent prisms and fresnel prisms (20)

FRESNEL PRISMS AND LENSES by optom. Jithin Johney
FRESNEL PRISMS AND LENSES by optom. Jithin JohneyFRESNEL PRISMS AND LENSES by optom. Jithin Johney
FRESNEL PRISMS AND LENSES by optom. Jithin Johney
 
Optometry instruments
Optometry instruments Optometry instruments
Optometry instruments
 
frenel & rotary prism PART 2.pptx
frenel & rotary prism PART 2.pptxfrenel & rotary prism PART 2.pptx
frenel & rotary prism PART 2.pptx
 
Lenses in ophthalmology
Lenses in ophthalmologyLenses in ophthalmology
Lenses in ophthalmology
 
lensesinophthalmology-171212163049 (1).pdf
lensesinophthalmology-171212163049 (1).pdflensesinophthalmology-171212163049 (1).pdf
lensesinophthalmology-171212163049 (1).pdf
 
Special type of lenses
Special  type of lensesSpecial  type of lenses
Special type of lenses
 
what is slit lamp Biomicroscopy | What is a slit lamp exam used for? |Differe...
what is slit lamp Biomicroscopy | What is a slit lamp exam used for? |Differe...what is slit lamp Biomicroscopy | What is a slit lamp exam used for? |Differe...
what is slit lamp Biomicroscopy | What is a slit lamp exam used for? |Differe...
 
laser lenses for retinal diseases
 laser lenses for retinal diseases laser lenses for retinal diseases
laser lenses for retinal diseases
 
Lenses of slit lamp biomicroscope & indirect ophthalmoscope.
Lenses of slit lamp biomicroscope & indirect ophthalmoscope.Lenses of slit lamp biomicroscope & indirect ophthalmoscope.
Lenses of slit lamp biomicroscope & indirect ophthalmoscope.
 
Binocular Indirect Ophthalmoscopy
Binocular Indirect OphthalmoscopyBinocular Indirect Ophthalmoscopy
Binocular Indirect Ophthalmoscopy
 
Objective refraction
Objective refractionObjective refraction
Objective refraction
 
Techniques of refraction is the process of calculation of glass power.
Techniques of refraction is the process of calculation of glass power.Techniques of refraction is the process of calculation of glass power.
Techniques of refraction is the process of calculation of glass power.
 
Trial box
Trial boxTrial box
Trial box
 
Trial box
Trial boxTrial box
Trial box
 
INDIRECT OPHTHALOMOSCOPE
INDIRECT OPHTHALOMOSCOPEINDIRECT OPHTHALOMOSCOPE
INDIRECT OPHTHALOMOSCOPE
 
Spectacle prescription
Spectacle prescriptionSpectacle prescription
Spectacle prescription
 
Refraction in different refractive errors and their Management
Refraction in different refractive errors and their ManagementRefraction in different refractive errors and their Management
Refraction in different refractive errors and their Management
 
TRIAL BOX PPT.pptx
TRIAL BOX PPT.pptxTRIAL BOX PPT.pptx
TRIAL BOX PPT.pptx
 
Slit lamp examination
Slit lamp examinationSlit lamp examination
Slit lamp examination
 
Ophthalmic prisms
Ophthalmic prismsOphthalmic prisms
Ophthalmic prisms
 

More from Loknath Goswami

Pigment epithelial defect and intraretinal fluid
Pigment epithelial defect and intraretinal fluidPigment epithelial defect and intraretinal fluid
Pigment epithelial defect and intraretinal fluid
Loknath Goswami
 
Bandage Contact Lens
Bandage Contact LensBandage Contact Lens
Bandage Contact Lens
Loknath Goswami
 
Synoptophore and its parts
Synoptophore and its partsSynoptophore and its parts
Synoptophore and its parts
Loknath Goswami
 
Slit lamp biomicroscopy and illumination techniques
Slit lamp biomicroscopy and illumination techniquesSlit lamp biomicroscopy and illumination techniques
Slit lamp biomicroscopy and illumination techniques
Loknath Goswami
 
Retinoscope and retinoscopy
Retinoscope and retinoscopyRetinoscope and retinoscopy
Retinoscope and retinoscopy
Loknath Goswami
 
Tonometry and tonography
Tonometry and tonographyTonometry and tonography
Tonometry and tonography
Loknath Goswami
 
Keratometer and keratometry
Keratometer and keratometryKeratometer and keratometry
Keratometer and keratometry
Loknath Goswami
 

More from Loknath Goswami (7)

Pigment epithelial defect and intraretinal fluid
Pigment epithelial defect and intraretinal fluidPigment epithelial defect and intraretinal fluid
Pigment epithelial defect and intraretinal fluid
 
Bandage Contact Lens
Bandage Contact LensBandage Contact Lens
Bandage Contact Lens
 
Synoptophore and its parts
Synoptophore and its partsSynoptophore and its parts
Synoptophore and its parts
 
Slit lamp biomicroscopy and illumination techniques
Slit lamp biomicroscopy and illumination techniquesSlit lamp biomicroscopy and illumination techniques
Slit lamp biomicroscopy and illumination techniques
 
Retinoscope and retinoscopy
Retinoscope and retinoscopyRetinoscope and retinoscopy
Retinoscope and retinoscopy
 
Tonometry and tonography
Tonometry and tonographyTonometry and tonography
Tonometry and tonography
 
Keratometer and keratometry
Keratometer and keratometryKeratometer and keratometry
Keratometer and keratometry
 

Recently uploaded

Temple of Asclepius in Thrace. Excavation results
Temple of Asclepius in Thrace. Excavation resultsTemple of Asclepius in Thrace. Excavation results
Temple of Asclepius in Thrace. Excavation results
Krassimira Luka
 
Mule event processing models | MuleSoft Mysore Meetup #47
Mule event processing models | MuleSoft Mysore Meetup #47Mule event processing models | MuleSoft Mysore Meetup #47
Mule event processing models | MuleSoft Mysore Meetup #47
MysoreMuleSoftMeetup
 
How Barcodes Can Be Leveraged Within Odoo 17
How Barcodes Can Be Leveraged Within Odoo 17How Barcodes Can Be Leveraged Within Odoo 17
How Barcodes Can Be Leveraged Within Odoo 17
Celine George
 
What is Digital Literacy? A guest blog from Andy McLaughlin, University of Ab...
What is Digital Literacy? A guest blog from Andy McLaughlin, University of Ab...What is Digital Literacy? A guest blog from Andy McLaughlin, University of Ab...
What is Digital Literacy? A guest blog from Andy McLaughlin, University of Ab...
GeorgeMilliken2
 
skeleton System.pdf (skeleton system wow)
skeleton System.pdf (skeleton system wow)skeleton System.pdf (skeleton system wow)
skeleton System.pdf (skeleton system wow)
Mohammad Al-Dhahabi
 
Electric Fetus - Record Store Scavenger Hunt
Electric Fetus - Record Store Scavenger HuntElectric Fetus - Record Store Scavenger Hunt
Electric Fetus - Record Store Scavenger Hunt
RamseyBerglund
 
Stack Memory Organization of 8086 Microprocessor
Stack Memory Organization of 8086 MicroprocessorStack Memory Organization of 8086 Microprocessor
Stack Memory Organization of 8086 Microprocessor
JomonJoseph58
 
BIOLOGY NATIONAL EXAMINATION COUNCIL (NECO) 2024 PRACTICAL MANUAL.pptx
BIOLOGY NATIONAL EXAMINATION COUNCIL (NECO) 2024 PRACTICAL MANUAL.pptxBIOLOGY NATIONAL EXAMINATION COUNCIL (NECO) 2024 PRACTICAL MANUAL.pptx
BIOLOGY NATIONAL EXAMINATION COUNCIL (NECO) 2024 PRACTICAL MANUAL.pptx
RidwanHassanYusuf
 
Chapter wise All Notes of First year Basic Civil Engineering.pptx
Chapter wise All Notes of First year Basic Civil Engineering.pptxChapter wise All Notes of First year Basic Civil Engineering.pptx
Chapter wise All Notes of First year Basic Civil Engineering.pptx
Denish Jangid
 
The basics of sentences session 7pptx.pptx
The basics of sentences session 7pptx.pptxThe basics of sentences session 7pptx.pptx
The basics of sentences session 7pptx.pptx
heathfieldcps1
 
How to Predict Vendor Bill Product in Odoo 17
How to Predict Vendor Bill Product in Odoo 17How to Predict Vendor Bill Product in Odoo 17
How to Predict Vendor Bill Product in Odoo 17
Celine George
 
REASIGNACION 2024 UGEL CHUPACA 2024 UGEL CHUPACA.pdf
REASIGNACION 2024 UGEL CHUPACA 2024 UGEL CHUPACA.pdfREASIGNACION 2024 UGEL CHUPACA 2024 UGEL CHUPACA.pdf
REASIGNACION 2024 UGEL CHUPACA 2024 UGEL CHUPACA.pdf
giancarloi8888
 
Leveraging Generative AI to Drive Nonprofit Innovation
Leveraging Generative AI to Drive Nonprofit InnovationLeveraging Generative AI to Drive Nonprofit Innovation
Leveraging Generative AI to Drive Nonprofit Innovation
TechSoup
 
Bossa N’ Roll Records by Ismael Vazquez.
Bossa N’ Roll Records by Ismael Vazquez.Bossa N’ Roll Records by Ismael Vazquez.
Bossa N’ Roll Records by Ismael Vazquez.
IsmaelVazquez38
 
MDP on air pollution of class 8 year 2024-2025
MDP on air pollution of class 8 year 2024-2025MDP on air pollution of class 8 year 2024-2025
MDP on air pollution of class 8 year 2024-2025
khuleseema60
 
NEWSPAPERS - QUESTION 1 - REVISION POWERPOINT.pptx
NEWSPAPERS - QUESTION 1 - REVISION POWERPOINT.pptxNEWSPAPERS - QUESTION 1 - REVISION POWERPOINT.pptx
NEWSPAPERS - QUESTION 1 - REVISION POWERPOINT.pptx
iammrhaywood
 
Benner "Expanding Pathways to Publishing Careers"
Benner "Expanding Pathways to Publishing Careers"Benner "Expanding Pathways to Publishing Careers"
Benner "Expanding Pathways to Publishing Careers"
National Information Standards Organization (NISO)
 
Philippine Edukasyong Pantahanan at Pangkabuhayan (EPP) Curriculum
Philippine Edukasyong Pantahanan at Pangkabuhayan (EPP) CurriculumPhilippine Edukasyong Pantahanan at Pangkabuhayan (EPP) Curriculum
Philippine Edukasyong Pantahanan at Pangkabuhayan (EPP) Curriculum
MJDuyan
 
Data Structure using C by Dr. K Adisesha .ppsx
Data Structure using C by Dr. K Adisesha .ppsxData Structure using C by Dr. K Adisesha .ppsx
Data Structure using C by Dr. K Adisesha .ppsx
Prof. Dr. K. Adisesha
 
Jemison, MacLaughlin, and Majumder "Broadening Pathways for Editors and Authors"
Jemison, MacLaughlin, and Majumder "Broadening Pathways for Editors and Authors"Jemison, MacLaughlin, and Majumder "Broadening Pathways for Editors and Authors"
Jemison, MacLaughlin, and Majumder "Broadening Pathways for Editors and Authors"
National Information Standards Organization (NISO)
 

Recently uploaded (20)

Temple of Asclepius in Thrace. Excavation results
Temple of Asclepius in Thrace. Excavation resultsTemple of Asclepius in Thrace. Excavation results
Temple of Asclepius in Thrace. Excavation results
 
Mule event processing models | MuleSoft Mysore Meetup #47
Mule event processing models | MuleSoft Mysore Meetup #47Mule event processing models | MuleSoft Mysore Meetup #47
Mule event processing models | MuleSoft Mysore Meetup #47
 
How Barcodes Can Be Leveraged Within Odoo 17
How Barcodes Can Be Leveraged Within Odoo 17How Barcodes Can Be Leveraged Within Odoo 17
How Barcodes Can Be Leveraged Within Odoo 17
 
What is Digital Literacy? A guest blog from Andy McLaughlin, University of Ab...
What is Digital Literacy? A guest blog from Andy McLaughlin, University of Ab...What is Digital Literacy? A guest blog from Andy McLaughlin, University of Ab...
What is Digital Literacy? A guest blog from Andy McLaughlin, University of Ab...
 
skeleton System.pdf (skeleton system wow)
skeleton System.pdf (skeleton system wow)skeleton System.pdf (skeleton system wow)
skeleton System.pdf (skeleton system wow)
 
Electric Fetus - Record Store Scavenger Hunt
Electric Fetus - Record Store Scavenger HuntElectric Fetus - Record Store Scavenger Hunt
Electric Fetus - Record Store Scavenger Hunt
 
Stack Memory Organization of 8086 Microprocessor
Stack Memory Organization of 8086 MicroprocessorStack Memory Organization of 8086 Microprocessor
Stack Memory Organization of 8086 Microprocessor
 
BIOLOGY NATIONAL EXAMINATION COUNCIL (NECO) 2024 PRACTICAL MANUAL.pptx
BIOLOGY NATIONAL EXAMINATION COUNCIL (NECO) 2024 PRACTICAL MANUAL.pptxBIOLOGY NATIONAL EXAMINATION COUNCIL (NECO) 2024 PRACTICAL MANUAL.pptx
BIOLOGY NATIONAL EXAMINATION COUNCIL (NECO) 2024 PRACTICAL MANUAL.pptx
 
Chapter wise All Notes of First year Basic Civil Engineering.pptx
Chapter wise All Notes of First year Basic Civil Engineering.pptxChapter wise All Notes of First year Basic Civil Engineering.pptx
Chapter wise All Notes of First year Basic Civil Engineering.pptx
 
The basics of sentences session 7pptx.pptx
The basics of sentences session 7pptx.pptxThe basics of sentences session 7pptx.pptx
The basics of sentences session 7pptx.pptx
 
How to Predict Vendor Bill Product in Odoo 17
How to Predict Vendor Bill Product in Odoo 17How to Predict Vendor Bill Product in Odoo 17
How to Predict Vendor Bill Product in Odoo 17
 
REASIGNACION 2024 UGEL CHUPACA 2024 UGEL CHUPACA.pdf
REASIGNACION 2024 UGEL CHUPACA 2024 UGEL CHUPACA.pdfREASIGNACION 2024 UGEL CHUPACA 2024 UGEL CHUPACA.pdf
REASIGNACION 2024 UGEL CHUPACA 2024 UGEL CHUPACA.pdf
 
Leveraging Generative AI to Drive Nonprofit Innovation
Leveraging Generative AI to Drive Nonprofit InnovationLeveraging Generative AI to Drive Nonprofit Innovation
Leveraging Generative AI to Drive Nonprofit Innovation
 
Bossa N’ Roll Records by Ismael Vazquez.
Bossa N’ Roll Records by Ismael Vazquez.Bossa N’ Roll Records by Ismael Vazquez.
Bossa N’ Roll Records by Ismael Vazquez.
 
MDP on air pollution of class 8 year 2024-2025
MDP on air pollution of class 8 year 2024-2025MDP on air pollution of class 8 year 2024-2025
MDP on air pollution of class 8 year 2024-2025
 
NEWSPAPERS - QUESTION 1 - REVISION POWERPOINT.pptx
NEWSPAPERS - QUESTION 1 - REVISION POWERPOINT.pptxNEWSPAPERS - QUESTION 1 - REVISION POWERPOINT.pptx
NEWSPAPERS - QUESTION 1 - REVISION POWERPOINT.pptx
 
Benner "Expanding Pathways to Publishing Careers"
Benner "Expanding Pathways to Publishing Careers"Benner "Expanding Pathways to Publishing Careers"
Benner "Expanding Pathways to Publishing Careers"
 
Philippine Edukasyong Pantahanan at Pangkabuhayan (EPP) Curriculum
Philippine Edukasyong Pantahanan at Pangkabuhayan (EPP) CurriculumPhilippine Edukasyong Pantahanan at Pangkabuhayan (EPP) Curriculum
Philippine Edukasyong Pantahanan at Pangkabuhayan (EPP) Curriculum
 
Data Structure using C by Dr. K Adisesha .ppsx
Data Structure using C by Dr. K Adisesha .ppsxData Structure using C by Dr. K Adisesha .ppsx
Data Structure using C by Dr. K Adisesha .ppsx
 
Jemison, MacLaughlin, and Majumder "Broadening Pathways for Editors and Authors"
Jemison, MacLaughlin, and Majumder "Broadening Pathways for Editors and Authors"Jemison, MacLaughlin, and Majumder "Broadening Pathways for Editors and Authors"
Jemison, MacLaughlin, and Majumder "Broadening Pathways for Editors and Authors"
 

Recumbent prisms and fresnel prisms

  • 2. Prism  A prism is an object made up of a transparent material like glass or plastic that has at least two flat surfaces that form an acute angle (less than 90 degrees)  A traditional prism has two flat, nonparallel surfaces  Parallel light entering the prism is bent towards the base of the prism and leaves the back surface at an angle  A prism is thicker at the base than at the apex. The larger the prism, the thicker the base of the prism will be
  • 4. Properties of prism  Dispersion  Deviation occurs towards the base  Total internal reflection occurs in some specific prisms.  Prism never change the vergence of light rays. A prism does not magnify or minify the image.
  • 5.
  • 6. Recumbent prisms  Prisms which deviate the light by 90˚  Right angle prisms and prisms used in recumbent spectacles
  • 7.
  • 8. History  In 1935, Mr. Andrew McKie Reid designed the ‘recumbent spectacles’, as a visual aid for patients suffering from spinal lesions and other diseases who were confined to the bed in a supine position for weeks or months
  • 9. History  The spectacle was made by Messrs Hamblin of Wigmore Street, London and was shown for the first time at the Oxford Ophthalmological Congress in July 1935
  • 10. Recumbent spectacles  Recumbent spectacles are equipped with reflecting prism that enable a person lying flat on his or her back to see straight ahead while looking straight up  The spectacle consists of a pair of prisms mounted in a frame which could either be worn over the patient’s own glasses or the refractive prescription could be incorporated in the frame  These can be useful for those wishing to read while being required to remain on their backs for long periods of time  The prisms must be perfectly aligned, or diplopia occurs, making wear impossible
  • 12. Principle  The prisms had an apical angle of 35 degrees and basal angles of 70 and 75 degrees  These angles were calculated such that a book held in the normal position on the chest could be read by a person in the supine position even though apparently looking at the ceiling  So, with the base of the prism facing the patient, the line of vision through refraction and double internal reflection within the prisms was bent almost 90 degrees
  • 13. Optics a 2 = 52˚
  • 15. Recumbent spectacles Advantage Disadvantage  Help people to read in supine position  It is heavy and not much comfortable
  • 16.
  • 17. History  In 1970, the optical sciences group of San Rafael, California, developed a series of Fresnel Press-on prisms – thin plastic membrane prisms ranging in powers from 0.5 to 30 prism diopters
  • 18. History  These prisms are an adaptation of the hand- ground lenses designed by the French engineer and physicist Augustine Fresnel in 1821  Fresnel’s lenses were originally used for lighthouse beacons.
  • 19. Fresnel lens and Fresnel prism
  • 20. Fresnel lens and Fresnel prism
  • 21. Fresnel prism  A Fresnel prism attempts to avoid thickness by building a tower of small prism  A Fresnel prism is only 1 mm thick  The refraction depends on the apical angle  The angle between the two surfaces remains constant across the prism.  E.g. 3M Press-on
  • 22. 3M Press-On  Manufacturer: 3M  Location: USA  Material: PVC (Polyvinyl chloride)  Thickness: 1mm  Usable area: 65mm diameter  Base is noted in one corner of the prism, if it is cut then base may be found by running finger nail along prism side
  • 23. Press-on prism availability 1∆, 2∆, 3∆, 4∆, 5∆, 6∆, 7∆, 8∆, 9∆, 10∆, 12∆, 15∆, 20∆, 25∆, 30∆, 35∆, 40∆
  • 26. Fresnel prism trial sets  Fresnel prisms trial optics are similar to traditional prism trial optics(ring) found in trial ring sets.  Thin and light weight (particularly in the higher diopter powers)  Raised edges around the Fresnel prism trial optic prevents scratching of prism features when placed on flat surfaces  Allows for accurate testing of large oculomotor imbalances and allows patient opportunity to experience a Fresnel prism
  • 27.  Recommend for prism cover test  Available in two, 7 ring sets: TS4000 & TS5000  TS4000: 2∆, 3∆, 4∆, 5∆, 6∆, 8∆, 10∆  TS5000: 12∆, 15∆, 20∆, 25∆, 30∆, 35∆, 40∆ TS4000 TS5000
  • 28. A coin has two faces
  • 29. Advantages  It is very thin and extremely lightweight  It is flexible and can be applied to an existing spectacle lens  It can be cut to any shape with scissors or a razor blade. This means that it can be cut and applied to one sector of a lens  It can be applied or removed at anytime
  • 30. Disadvantages  Fresnel prisms look different than conventional lenses. It gives striated appearance (to observers) of the grooves. The striated appearance can be improved to some extent by use of a lightly tinted or photochromic lens  Fresnel prisms have a number of small ledges, they are harder to clean than conventional lenses
  • 31.  High-powered prisms will cause a slight decrease in visual acuity Visual acuity loss is due to scattering of light, caused by the grooves. The scattering of light causes both a loss of contrast and the presence of bothersome reflections. The minimal acuity decrease through Fresnel prisms is less than one line on a Snellen chart at a 90% contrast level compared with acuity through conventional prism.  The flexible static vinyl material that gives these lenses the ability to be easily cut to custom shapes, unfortunately, reduces the contrast of objects viewed through the lens
  • 32. Chart photographed with and without a 40 diopter Fresnel press-on
  • 33. When to prescibe  When a prismatic component is to be included in a patient’s prescription, the advantages and disadvantages of press-on prisms should be carefully weighed to determine the suitability of using press-on prism.
  • 34. When are Fresnel prism used?  High amount of prism Fresnel prism is very thin comparatively to the conventional prism. So it is useful for high amount of prism Conventional prism Fresnel prism
  • 35.  Use and reuse Fresnel prism lenses are easy to apply and remove. They may be used and reused. This is helpful when determining how a given prism amount will work long term or for use during visual training.
  • 36.  Sectorial application A partially paralyzed extraocular muscle may result in a different amount of prism needed for different directions of gaze. A Fresnel prism can be cut to fit that particular lens area. Prism is present only where it is needed.
  • 37.  Visual field defects  A person may have a visual field defect  For example, the case of bilateral hemianopia, the right half of the visual field is blind for both right and left eyes.
  • 38.  Fresnel prism can be applied to the right side of the both lenses.  In this instance, prism base direction would be base right.  With prism in place, the wearer looks to the right but does not have to turn the eyes as far to see an object in the right- hand field of view
  • 39.  Slowing of nystagmus  Nystagmus is a defined as regular and rhythmic to-and-fro involuntary oscillatory movements. Such movement is involuntary and reduces vision.  In some cases, nystagmus may slow when the person looks to one side or the other  For example, if the examiner sees that movement slows when the person looks to the right, equal amounts of prism may be applied to both lenses. The correct base direction would be base left. Because the eyes turn toward the apex, prism base left will keep the head pointed straight while the eyes turn to the right. Since the eyes are turned to the right, nystagmus slows.
  • 40. How to apply a Fresnel prism to a spectacle lens  Firstly we have to determine correct base direction  After that we have to take the carrier lens out of the spectacle frame  We have to place the Fresnel prism on the back of the carrier lens with its smooth side against the carrier. Making sure base direction is properly oriented and then we have to mark the boundary  With a razor blade, trim the Fresnel prism along the marking
  • 41. How to apply a Fresnel prism to a spectacle lens  Reinsert the carrier lens into the frame  Wash both carrier and Fresnel prism with a weak solution of lotion-free liquid detergent  In a bowl of warm water, or under a stream of warm water, apply the smooth side of the Fresnel to the carrier. Work out any air bubbles that may be trapped between the two surfaces  Then we can give the lenses to the wearer, but have to instruct the wearer to handle the lenses with care for 24 hours until drying is complete.
  • 42.
  • 43. How to clean Fresnel prisms  The manufacturer’s recommended method of cleaning these lenses is to rinse under warm running water. If the lenses have dirt in grooves, use a soft brush. Blot dry with a soft, lint-free cloth. Hard contact lens cleaning solutions have also been used to clean Fresnel optics.
  • 44. How to clean Fresnel prisms Finally, the right tool to clean your Fresnel Optics. The secret is the cloth, a lint-free micro fiber cloth that can reach into the small deep grooves of a Press-On Lens. Use with the alcohol free lens cleaner to remove finger prints, oils, make-up and the daily dirt and grime that can get onto your lens. Costs $5.00
  • 45. REFERENCES  Troy E. Fannin, Clinical optics 1st edition, Pg No. 106-107  System For Ophthalmic Dispensing-2nd edition, Clifford W. Brooks , Irvin M. Borish, Pg No. 516-519, 536  http://www.sciencephoto.com/media/117959/view  http://study.com/academy/lesson/what-is-a-prism- definition-refraction-quiz.html  http://www.hemianopsia.net/the-fresnel-prism  http://www.gcsescience.com/pwav32.htm  http://bjo.bmj.com/content/94/5/535.full
  • 46. For letting me speak here