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Lenses in ophthalmology

lenses in ophthalmology

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Lenses in ophthalmology

  1. 1. LENSES IN OPHTHALMOLOGY Dr. Reshma Peter
  2. 2. LENS FOR FUNDUS EXAMINATION
  3. 3. Indirect fundus biomicroscopy  Examination of the retina by Slit lamp and Volk double aspheric lenses is called indirect fundus Biomicroscopy LENS NON – CONTACT CONTACT CONVEX LENS CONCAVE LENS +60D +78D +90D HRUBY LENS GOLDMANN 3 MIRROR LENS MODIFIED KOEPPE’S LENS INDIRECT LENS +30D +40D +14/+ 15D
  4. 4. ADVANTAGES 1. Larger field of retina visible 2. Lesser distortion of image of retina 3. Easier to examine , if patient ‘s eye movements are present and with high spherical or astigmatic refractive errors 4. Easy visualization of retina anterior to equator , where most retinal holes and degenerations exist 5. It gives a 3D stereoscopic view of the retina wth considerable depth of focus 6. Useful in Hazy media because of its bright light and optical property DISADVANTAGES 1. Magnification in indirect ophthalmoscopy is 5 times 2. Impossible with very small pupils 3. Patient usually more uncomfortable with intense light and scleral indentation 4. Reflex sneezing on exposure to bright light 5. Requires extensive practice in technique
  5. 5.  Volk's 60D,78D and 90D fundus lenses with slit lamp indirect ophthalmoscopy as a standard diagnostic procedure for comprehensive fundus evaluation.  Double aspheric lenses  Optics of indirect fundus biomicroscopy is similar to that of indirect ophthalmoscopy.  Image formed is real, inverted, laterally reversed.
  6. 6. Technique  The patient’s pupil may be dilated and background lights dimmed as for direct ophthalmoscopy.  Patient is positioned comfortably at the slit lamp.  The slit lamp viewing piece and the light column are kept at an angle of 90 degrees.  Set illumination angle coaxial with the slit lamp-viewing system  The illumination is kept low, the slit beam at a width of 2-3 mm and length of 5-10mm
  7. 7.  Magnification preferably set at 10× initially or 16 x  The beam is focused onto the patient’s pupil and the +78 or +90 D condensing lens aligned at around 5-10 mm from the patient’s cornea.  The slit lamp is then pulled backwards gradually towards the examiner until the fundal glow is visualised  Reflections can be reduced by slightly tilting the lens  As with indirect ophthalmoscopy, the image from a non-contact Volk Lens slit lamp biomicroscopic examination is inverted and laterally reversed.  To view peripheral retina, ask patient to look into appropriate positions of gaze as with standard indirect ophthalmoscopy
  8. 8.  Magnification= power of eye x magnification of slit lamp power of lens Eg . Magnification of + 90 D = 60/90 x 10 = 7.6  Thus magnification is inversely proportional while, Field of view is directly proportional to the power of the lens. Stereopsis = magnification / 4 . Field of view = (D.P. of the lens x 2 )
  9. 9. Principle of Indirect Ophthalmoscopy  To make the eye highly Myopic by placing a  strong Convex lens in front of it.
  10. 10. +90 D lens  The original Volk 90D lens started the slit lamp examination.  relatively wide field of view with a good resolution  Real inverted image  General diagnosis and small pupil examinations.  It features a small 26mm diameter ring is ideal for dynamic fundoscopy.  The Volk 90D has very good small pupil capabilities, making it ideal for a quick look at the posterior pole.  Working distance from the cornea is 6.5mm.
  11. 11. 60D  High Magnification Views of the Posterior Pole.  High magnification lens for detailed optic disc and macula imaging.  Ideal diameter for use in the orbital area.  ( Its 31mm diameter allows a wide field of view and facilitates  easy handling within the orbital area.)  • Working distance from the cornea is 11mm.
  12. 12. 78D The Double Aspheric 78D is an excellent general diagnosis .  Ideal balance of magnification and field of view.  Working distance from the cornea is 7mm.
  13. 13. Advantages : 1.Stereoscopic ,3 dimensional view of the retina-Binocular viewing through the slit lamp. 2.Better image achieved when viewing through media opacities - Cataract. 3.Allows for manipulation of image- Slit lamp magnification& filters. 4.Image size less affected by patient refractive error.
  14. 14. Hruby lens  Plano-concave lens with diopteric power of -58.6D, which neutralises the optical power of the eye (+ 60 D)  To be placed 10-12 mm in front of patient’s cornea.  Image formed : virtual, erect image 18mm in front of patient’s retina
  15. 15. Disadvantages  Low magnification 5-8 degrees (just about 1 disc diameter)  Small field , cannot visualise beyond the equator  Precise patient fixation required  Hence it is not ideal for screening posterior fundus
  16. 16. INDIRECT OPHTHALMOSCOPE LENSES BIO condensing lenses (Hand held lenses )  biconvex, aspheric designs with one surface more curved than theother.  Less curved surface toward patient’s eye (silver).  The hand-held lens acts both as:- 1. A condensing lens for the illuminating system. 2. A lens for forming an inverted image of the retina in space.
  17. 17.  The technique is called Indirect because the fundus isseen through a condensing lens.  The image is formed close to the principle focus of the lens, between the lens and the observer.  The condensing lens is a powerful convex lens (the usual power used is +14, + 20,and + 33 D )  The power of the condensing lens determines:-  Retinal Magnification  Field of view  Stereopsis.
  18. 18. +30 D lens  The high dioptric power lens (30D) has the highest magnification :-  Least magnification of the retina, 60/30 = 2.  Stereopsis is half that of the normal, 2/4= 1/2  Field of view is generally the largest = (60 degrees, 30 x 2 ).  used to obtain a panoramic view when detail and stereopsis are not as important , and used with small pupil.
  19. 19. +20 D lens  The middle dioptric power lens of (20D).  The retinal magnification = 60/20 = X3  The stereopsis is 3/4 that of the normal.  The field of view is 40 degrees (20x2 ).  20D lens most widely used, since it provides an adequate field of view, stereopsis and magnification.
  20. 20. +15 D lens  The low dioptric power lens of 14 or 15D.  The retinal magnification = 60/15 = X4.  The stereopsis is full ( 4/4 ).  The field of view is 30 degrees (15x2 ).  most useful for detailed view of the macula or optic disc or for determining elevation of the retina in shallow retinal detachment.
  21. 21. Contact lens biomicroscopy of fundus Combines stereopsis, high illumination, and high magnification with advantages of slit beam A. Modified Koeppe’s lens B. Goldmann’ s three mirror contact lens C. Wide field (panfundoscopic) indirect contact lenses
  22. 22. Modified Koeppe’s lens  posterior fundus contact lens  Used to examine the posterior segment  Virtual and erect image
  23. 23. Goldmann’ s three mirror contact lens  Central contact lens with 3 mirrors placed in the cone, each with different angles of inclination 1. central contact lens for posterior pole and vitreous 2. Mirror inclined at 73 ° - area around posterior pole 3. Mirror inclined at 67 ° - equatorial fundus 4. Mirror inclined at 59 ° - anterior peripheral fundus including ora serrata and pars plana  Virtual , erect image
  24. 24. TECHNIQUE 1. Dilate pupils 2. Instil topical anaesthetic drops 3. Insert coupling fluid into cup of contact lens but do not overfill 4. Ask patient to look up , insert inferior rim of the lens into lower fornix and press it quickly against the cornea 5. Always tilt illumination column except when viewing 12 o’ clock position in the fundus (ie, with the mirror at 6 o’clock) 6. When viewing different positions of peripheral retina, rotate axis of beam so that it is always at right angles to the mirror
  25. 25. 6. To visualize entire fundus, rotate lens for 360 degrees using the 59, 67 and 73 degrees tilted mirrors to give views of the peripheral retina, the equatorial fundus and the area around the posterior pole, respectively 7.To obtain a more peripheral view of the retina, tilt the lens to the opposite side and ask the patient to move the eyes to the same side. Eg-to obtain a more peripheral view of 12 o’clock position (with mirror at 6 o’clock), tilt the lens down and ask the patient to look up 8. Examine the vitreous cavity with central lens, using a horizontal and a vertical slit – beam and then examine posterior pole
  26. 26. Wide field (panfundoscopic) indirect contact lenses  Field view upto 130 degrees  For fundus examination and laser photocoagulation  Inverted image
  27. 27. LENS FOR GONIOSCOPY
  28. 28. PRINCIPLES AND OPTICS • Critical angle for the cornea-air interface is approximately 46 degrees. •Total internal reflection prevents direct visualization of angle in nearly all eyes. •The incident angle of light- reflected from angle is greater than the critical angle at the cornea–air interface.
  29. 29. L i < L r light rays are refracted at the contact lens-air interface light rays are reflected by a mirror light rays leave the lens at nearly right angles at the contact lens-air interface Total internal reflection is overcome by eliminate the cornea-air interface by Goniolenses in DIRECT method contact lenses –-to examine the anatomy of the angle Gonioprisms/mirror and viscous coupling solution or tears in INDIRECT method As the index of refraction of a contact lens approaches that of the cornea, there is minimal refraction at the interface of these two media, which eliminates the optical effect of the front corneal surface. Thus light rays from the anterior chamber angle enter the contact lens and are then made to pass through the new contact lens-air interface
  30. 30. METHODS  Three primary methods:  Indirect gonioscopy: Using mirrors,the angle is examined with reflected light  Indentation (dynamic) gonioscopy  Direct gonioscopy: look directly at the angle with lenses.
  31. 31. GONIOPRISMS(Indirect) GONIOLENSES(Direct) Requiring coupling agents Not requiring coupling agents 1.Goldmann single mirror gonioprism 2.Goldmann 2 mirror gonioprism 3.Goldmann 3 mirror gonioprism 4.Allen Thorpe gonioprism 1.Zeiss 4- mirror Gonioprism 2.Posner Gonioprism 3.Sussman lens 4.Tokel Gonioprism 5.Ritch Trabeculoplasty laser lens 1.Koeppe Goniolens 2.Huskins Barkans lens 3.Thorpe Goniolens 4.Swan Jacob ‘s lens 5.Richardson Shaffer’s Goniolens 6.Worth goniolens 7.Sieback goniolens
  32. 32. GONIOPRISMS Requiring coupling agents 1.Goldmann single mirror gonioprism Prototype diagnostic gonioprism  Mirror inclined at 62 degrees from plano front surface  Needs to be rotated 3 times to examine the whole angle  Mirror Height -12 mm  Central well diameter -12 mm  Posterior Radius of curvature -7.38 mm 2.Goldmann two mirror gonioprism  Both mirrors inclined at 62 degrees  Needs to be rotated once to examine whole angle
  33. 33. 3.Goldmann three mirror gonioprism A. Gonioscopy mirror: Inclination of 59 degree  Smallest  Dome shaped upper border  Broad area of contact with cornea (12 mm)may artificially close the angle under pressure B. Equatorial mirror: Inclined at 67 degrees  Largest  Oblong shaped  Examine Pars plana of ciliary body Posterior pole to the equator C. Peripheral mirror: Inclined at 73 degrees  Intermediate size  Square shaped  Examine from equator to ora serrata
  34. 34. 4.Allen Thorpe gonioprism  4 prisms instead of mirrors  Allows examination of whole angle without rotating the prisms  Suspended by a frame
  35. 35. Advantages of Goldmann gonioprisms  Easy to use  Excellent view  Peripheral retina can be seen  Stabilizes the globe Can be used in Argon Laser trabeculoplasty
  36. 36. Disadvantages of Goldmann gonioprisms  Only 1 mirror for gonio-has to be rotated by 360 degrees  Cannot be used for indentation  In case of 3 mirror lens, broad area of contact with cornea may cause artefactual closure of angle Curvature of lens > cornea Coupling material required Blurs vision and fundus Field charting ,direct and indirect ophthalmoscopy cant be done immediately after use
  37. 37. GONIOPRISMS Not requiring coupling agents 1.Zeiss 4- mirror Gonioprism  4 identical mirrors angled at 64 degrees  On an UNGER HOLDER  Small area of contact with the cornea (9mm) Indentation gonioscopy can be performed
  38. 38. Zeiss 4- mirror Gonioprism ADVANTAGES DISADVANTAGES • Easy to perform • All 4 quadrants visible at same time • Rotation of 11 degrees covers area between the mirrors • Indentation gonio • Coupling material not required, thus fundus viewing and photography possible • Difficult to master • Does not stabilise the globe • May open the angle artefactually If pressure is applied
  39. 39. 2.Posner Gonioprism  Similar to Zeiss  Made of plastic instead of glass  Has a fixed handle
  40. 40. 3.Sussman lens Similar to Zeiss but has no handle 4.Tokel Gonioprism • Single mirror lens • Broader viewing area than Goldmann single mirror lens • Convex anterior face that provides slight magnification • For delivery of Laser to angle
  41. 41. 5.Ritch Trabeculoplasty laser lens  2 mirrors tilted at 59degrees to see inferior angle  2 mirrors at 64 degrees to view the superior angle  A convex button in front of a 59 degree mirror and a 64 degree mirror for extra magnification and laser treatment
  42. 42. GONIOLENSES Koeppe lens  Prototype diagnostic lens  Available in several sizes  Most commonly used lens for diagnostic direct gonio. Huskins Barkan lens  Prototype surgical goniolens  Used for Goniotomy Thorpe Goniolens Surgical and diagnostic lens for operating rooms
  43. 43. Swan jacob’s lens • Surgical goniolens • used in children Richardson Shaffer’s lens Small lens for use in infants Worth goniolens It anchors to the cornea by partial vaccum Sieback goniolens Tiny goniolens which floats on the cornea
  44. 44. 2 types of laser lenses are available to assist in slitlamp delivery of photocoagulation:  Plano-concave lenses  an erect image  high resolution of small retinal area.  mirrors angulated at 59 , 69 and 73 degrees  High plus power lenses(indirect lens) • an inverted image • mild loss of fine resolution • a wide field of view very suitable for PRP
  45. 45. LENS FOR LASERS
  46. 46. Common characteristics of laser lenses  Concave posterior surface conforming to the corneal curvature and a flat or convex anterior surface  Planar mirrors allowing observation of the anterior chamber angle or peripheral retina.  A prism to allow visualization of the mid-periphery of the retina.  A flange to stabilize the lens and prevent blinking  Knurled edge to facilitate lens manipulation.  Laser lenses generally consist of a conical PMMA or aluminium shell  Glass anterior surface, lenticular elements and mirrors.
  47. 47. Antireflection coatings  Usually applied to each optical surface in a laser lens that reduces reflected white light (from the slit lamp source) that could decrease contrast or the slit lamp image, and laser light (from the treatment beam) that could pose a potential hazard to an observer standing behind the laser operator.  The hazard distance is 7 meters for an uncoated lens and 1.6 meters for a coated lens.  Most laser lenses use broad-spectrum, multilayer, antireflection coatings that reduce reflected light between 400 nm and 700 nm from approx 4 % to < 1%
  48. 48. Mirror lenses  high magnification and high resolution  only a small part of the fundus or chamber angle can be viewed at any one time.  Therefore, the mirrors at various degrees of inclinations are necessary. e.g. Goldmann 3 mirror lenses. The image formed in the Goldmann 3 mirror lens is the mirror image of the area focused. Lenses without Mirrors  field of view may be increased to a variable extent by use of biconcave contact lenses based on the simple Goldman lens (without mirrors).  Another different way of increasing the field of view involves using contact lenses based on the EL Bayadi lens.Eg- Rodenstock Panfundoscope and Mainster lens  All wide-angle systems of this category are derived from the principle of indirect ophthalmoscopy  large and inverted field of view.  both the panfundoscope and the Mainster lenses produce inverted real images.
  49. 49. Goldmann Lens  Single mirror inclined at 62 degrees or 3 mirror with gonio mirror at 59 degrees  Rotated 360 degrees to view angles structures  Flat ant surface  Erect virtual image near post surface of lens  Limited field of view without rotation
  50. 50. Yannuzzi fundus lens(Krieger lens )  modification of an earlier model developed by Krieger in 1966  designed to facilitate macular photocoagulation  concave corneal surface which is steeper and of greater diameter,  has a better optics than a simple Goldman fundus lens  allows posterior lens pressure to be transmitted to the sclera without distorting the cornea.  erect, virtual located in anterior vitreous humor.
  51. 51. Volk Area centralis lens  indirect contact lens  a good field of view 70/84 degrees  excellent magnification 1.06x.  Laser spot magnification is 0.94x.
  52. 52. Volk PDT lens  The field of view is 115/137 degrees  Image magnification is 0.67x.  Laser spot magnification is 1.5 x  allows treatment of CNVM upto maximum spot size of 6400um providing excellent visualization  comes standard with SupraCoat which covers the 689nm laser wavelength indicated in this type of procedure.
  53. 53. Volk Transequator lens  designed for focal laser therapy and mid-to-far peripheral fundus diagnosis.  unique optical design presents a realistic contour of the retinal concavity, offering an impressive wide-field of view of the entire posterior pole extending to the equator.  superior optics allow dynamic movement on the globe, therefore increasing its functional field of view.  The field of view is 110/132 degrees.  Image magnification is 0.70x.  Laser spot magnification is 1.44x.
  54. 54. Mainster  Introduced in 1986  more field of view (58% greater than Goldman) and a greater magnification.  Although the field of view is 14% less than the Panfundoscope, but the lateral and axial magnification are better which makes it useful for detecting retinal thickening.  It has a biconvex, aspherical anterior lens element and a concave lens element to fit the corneal curvature.  inverted, real image located in front of its biconvex aspheric anterior lens element
  55. 55. Common Features of Mainster and Panfundoscopic lens  Large areas of the fundus may be treated in PRP without lens rotation.  Visualization of the optic disc and macula during peripheral treatment prevents disorientation.  The experienced laser surgeon can achieve a more peripheral view by tilting the lens off-axis.  The field of view is increased in myopes and decrease in hyperopes and will lead to differences in how far peripherally laser photocoagulation can be applied.  Working distance on these lenses are greater.  Anterior segment irradiance becomes excessive with large spot sizes (1000μm) but should be acceptable at a spot size of 500μm.
  56. 56. Mainster Standard lens  for focal and grid laser treatment from the posterior pole to the midperiphery.  field of view is 90/121 degrees.  Image magnification is 0.96 x.  Laser spot magnification is 1.05x.  High resolution, high magnification of image allows appreciation of subtle intraretinal details and retinal thickening.  So, it is excellent for diagnosis and treatment of macular oedema, BRVO , CNVM in ARMD and presumed ocular histoplasmosis.
  57. 57. PRP Lenses Mainster wide field lens  This allows a very wide range of slit lamp magnification to be used.  It has excellent ophthalmic resolution and image binocularity is maintained across the entire field of view.  used for PRP in PDR  The field of view is 118/127 degrees.  Image magnification is 0.68x.  Laser spot magnification is 1.50 x.
  58. 58. Mainster Ultrafield PRP lens:  widest field of view available for PRP  It has a unique optical design to provide a clear, bright image across the entire field.  light- weight, has a secure fit flange for easy manipulation besides having a high efficiency laser light anti-reflective coating.  field of view is 165/180 degrees.  Image magnification is 0.51 x.  Laser spot magnification is 1.96x.
  59. 59. Rodenstock Panfundoscopic lens  Introduced in 1969 by Schlegel  used for PRP from the posterior pole to beyond the equator without the use of mirrors.  gives a panoramic view  inverted, real image located in its spherical biconvex anterior lens element.  Thus, the biomicroscope must be located further from the patient's eye than using a Goldman lens
  60. 60.  This low biomicroscopic magnification produces adequate magnification with a large field and acceptable depth of focus.  working field is 84% greater than a Goldman  lateral magnification is 24% lesser than a Goldman.  The spot size is 40% larger than the photocoagulator setting or twice large than the conventional contact lens. Disadvantage • it produces peripheral distortion. • It can produce marked laser beam astigmatism while treating the peripheral retina. • Reflexes compromise retinal image thereby causing oblong burns when treating through the periphery of the lens.
  61. 61. Volk Quadraspheric lens  The original 13 degree Quadraspheric introduced in 1989  preferred wide field fundus laser lens for diagnosis and treatment of the retina.  The 4 aspheric surfaces also employ high efficiency antireflection coatings thereby improving lens performance by reducing astigmatism across the entire field of view.  It also enhances visualization through a small pupil.  inverted and reversed image.  Its sleek 28.6mm diameter housing provides a definite advantage over competitive wide field lenses for peripheral retinal viewing, reflection displacement and ease of use.  The laser spot magnification is 1.97x  The image magnification is 0.51x.
  62. 62. Volk Super Quad 160 lens  offers the widest field of view.  ideal 0.5x image magnification  simultaneous visualization of the posterior pole to the peripheral retina providing a greater margin of safety even during extreme wide angle panretinal photocoagulation.  field of view is 160/ 165 degrees  Image magnification is 1.97x  laser spot magnification is 2.0x.  the ideal lens for visualization and treatment of PDR, ischaemic RVO and peripheral retinal holes and tears.  Laser beam transmission and fundus image quality are sharp and undistorted to the full extent of the viewing field.
  63. 63.  Volk has introduced two new high resolution (HR) lenses for laser photocoagulation – The HR Wide Field for Pan Retinal Photocoagulation (PRP) – The HR Centralis for focal and grid laser therapy  Both lenses feature double aspheric designs and high grade, low dispersion glass which gives superior imaging quality.  Both lenses may also be used as diagnostic lenses as well.  The lenses improve upon and replace the previous generation Superquad 160 and Area Centralis lenses.  Primary conditions diagnosed and treated are diabetic retinopathy and maculopathy.  Lenses can also be used to diagnose and treat other conditions such as retinal tears, breaks and holes.
  64. 64. HR Centralis Lens  Lens for detailed posterior pole examination and laser focal/grid treatment  Lens is an upgrade or replacement for: – Volk Optical Area Centralis – Ocular Mainster 1X Retina – Ocular Mainster Focal/Grid  better image quality and stereopsis at the extreme of the lens view  Specifications: FOV 74º, magnification 1.08x, laser spot 0.92x
  65. 65.  Enhanced double aspheric design eliminates distortion and improves stereopsis to the periphery of the view  Superior, high grade, low dispersion glass delivers unsurpassed resolution  Improved capability with pupils as small as 4mm  Reduced sized housing helps manipulation within the orbit
  66. 66. HR Wide Field Lens  Lens for extreme wide field examination and laser PRP treatment  Lens is an upgrade or replacement for: – Rodenstock pan fundus lens – Volk Optical Superquad 160 – Ocular Instruments Mainster PRP 165  better image quality at the extreme periphery of the lens view  Specifications: FOV 160º, magnification 0.5x,laser spot 2.0x
  67. 67.  Widest field of view and treatment area to the ora serrata  Superior, high grade, low dispersion glass design eliminates distortion at the extreme periphery  Much smaller and easier to manipulate within patient’s orbit  Short length of lens helps manipulate in front of laser
  68. 68. LENS FOR RETINAL SURGERIES
  69. 69. Contact Type :  VPFS ( Vitreous Panfundoscope)  CWF (Contact wide field System)  AVIS (Advanced Visual Instrument system)  ROLS (Reinverting Operating lens system)  Clarivit  HRX (Volk Optical) Non Contact Type :  BIOM (Binocular IDO) – (Oculus)  MERLIN –(Volk Optical )  EIBOS (Erect Indirect Binocular IDO)-  OFFISS (TOPCON)  RESIGHT (Carl Zeiss) - Peyman –Wessels-Landers
  70. 70. Hand Held Irrigating Contact lenses  Neutralize High Convergence of Corneal Curvature to focus on Retina , Vitreous.  3 types of Lenses:  Plano concave lenses with a view of 20 degrees  Biconcave lenses with view of 30 degrees  Prism lenses with meridonial view of 60 degrees
  71. 71. Hands Free Contact Lens (Landers System) OLIV-WF  Hands free contact lenses were introduced by Landers and co workers which were stabilized onto the cornea with the help of a sewn-on limbal ring (stainless steel )  Too tight – corneal folds,break suture midway of surgery  Too loose- decentration of lens  Bleeding can obscure view of surgeon.
  72. 72.  Plano concave lens – core vitrectomy Landers biconcave lens – visualization in air filled eye (90 D Lens – 25 deg angle field)  Machemers magnifying lens – surface details on posterior pole (28-30 deg angle field)  Peyman wide field lens –equatorial portion  Tolentino 20 degree prism – periphery  Tolentino 30 degree prism – extreme periphery
  73. 73. Disadvantages:  Limited field of view  Peripheral Retina seen only with Indentation  Lens alignment problems  Air Bubble/ Blood film coming beneath Lens System  Poor visualization in Small pupils and Fluid –gas exchange
  74. 74. OPTICS OF CONVENTIONAL VITREOUS SURGERY  A Plano-concave contact lens made of PMMA  Refractive index of 1.488 and a concave posterior surface radius of curvature of 7.7 mm is  Refractive power of the anterior surface 48.8 D to -14.5 D and the fundus is easily visualized
  75. 75. OPTICS OF CONVENTIONAL CONTACT LENSES  The first component (inferior lens) –acrylic contact lens concave posterior surface. Power of 4 D.  The second component (superior lens) –biconvex aspherical image-forming, high refractive index glass lens 0.5 mm anterior of the contact lens element and an effective power of 150 D in air.  Real, inverted, aerial retinal image anterior to the image forming lens system.
  76. 76. Optics in Air Filled Eye  Posterior surface of the lens becomes strongly refractive(64 D)  Total refractive power of the eye increases from 59 to 102 D  Field of View is 130 deg.  Microscope eye piece should be moved closer toPatients eyes.
  77. 77. Peyman-Wessels-Landers 132 D Upright Vitrectomy Lens  Wide field Upright images without invertor(Internalised prisms).  Operating Table mounted system  Can be attached to any microscope  When The OSVS-U132-2 used with the Ocular Peyman-Wessels-Landers 132 Diopter Upright Vitrectomy Lens (OUV-132-2), the system allows the surgeon to work in the vitreous with an upright, non- reversed image under panoramic viewing conditions
  78. 78. Resight 700 from Carl Zeiss  Can hold two lenses simultaneosuly  - 127 deg lens for Wide Angle field  - 60 deg lens for High resolution Macular lens
  79. 79. Contact Types  VPFS ( Vitreous Panfundoscope)  CWF (Contact wide field System)  AVIS (Advanced Visual Instrument system)  ROLS (Reinverting Operating lens system)
  80. 80. Contact Wide field lenses  Inverted image , Need of SDI  Field of View = 120-130 degree  Held by handle or Standard lens ring
  81. 81. Reinverting Operating Lens System  Single element reinverter prism design to correct the inverted image.  Super Macula lens -60 deg  Mini Quad lenses -127 deg  Mini Quad XL lenses – 134 deg  Dyna – 156 deg
  82. 82. High index corneal contact lenses  Form essential part of image capturing unit  Allow capturing of oblique rays emerging from peripheral retina  The changeable lenses (nose pieces )available to be attached to the image – capturing unit of Retcam II are as follows LENS FIELD OF VIEW ROP lens premature infants 130 degrees Standard children lens pediatric to young adult 120 degrees High magnification lenses Fine details 30 degrees 80 degree lens Higher contrast pediatric and adult imaging 80 degrees Portrait lens For external imaging

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