Troubleshooting bifocals and Market Availability in Nepal
Bifocals in Anisometropia
Prismatic Effect in Bifocal
Bifocal Prescription
Bifocals in High Astigmatism
Toric IOLs were developed to reduce astigmatism and improve spectacle independence for patients with cataracts and astigmatism. The document summarizes the history, design, and clinical outcomes of toric IOLs. A meta-analysis found that patients receiving toric IOLs were more likely to achieve good visual acuity without glasses compared to patients receiving non-toric IOLs or relaxing incisions. While toric IOLs are generally effective, predicting the exact amount of post-operative astigmatism remains challenging due to factors like IOL rotation and variability in surgically induced astigmatism. New technologies aim to improve the accuracy of toric lens alignment and outcomes.
This document provides guidelines for prescribing glasses in children. It defines various refractive errors such as myopia, hyperopia, and astigmatism. It recommends fully correcting refractive errors over ±4 diopters as these can cause amblyopia. For lower refractive errors, it recommends considering the child's age and visual needs. Anisometropia over 1.5 diopters should also be corrected. Special cases like accommodative esotropia may require bifocals. The goal of treatment is to provide a clear retinal image while maintaining proper accommodation and convergence.
The document describes the use of various Pentacam maps and indices for screening patients for keratoconus, including:
1) The standard 4-map composite report, keratoconus map, Holladay report, and Belin/Ambrosio Enhanced Ectasia Display.
2) Key features to examine on each map include anterior and posterior elevation maps, pachymetry maps, curvature maps, and indices values.
3) The Belin/Ambrosio Enhanced Ectasia Display aims to improve sensitivity by calculating an "enhanced" best fit sphere reference surface that excludes the thinnest corneal region, highlighting differences between normal and ectatic corneas.
Soft Contact Lenses: Material, Fitting, and EvaluationZahra Heidari
Soft contact lenses are made from various materials like silicone and hydrogels, with advantages like comfort and easier fitting but disadvantages like potential for complications. The document discusses the history and evolution of contact lens materials, characteristics of different lens types, factors to consider for patient fitting like base curve and power selection, and how to evaluate fit and make modifications if needed. Proper patient selection and evaluation is important for successful fitting of soft contact lenses.
This document discusses toric intraocular lenses (IOLs) for correcting astigmatism during cataract surgery. It provides details on the evolution of toric IOL designs from early PMMA lenses that often rotated, to current acrylic models with improved stability. Precise keratometry measurements and accounting for surgically induced astigmatism are important for toric IOL power calculations. The document outlines the toric IOL implantation procedure and factors affecting postoperative rotation. Toric IOLs can provide high levels of spectacle independence when used appropriately in patients with regular corneal astigmatism over 1.5 D.
Troubleshooting bifocals and Market Availability in Nepal
Bifocals in Anisometropia
Prismatic Effect in Bifocal
Bifocal Prescription
Bifocals in High Astigmatism
Toric IOLs were developed to reduce astigmatism and improve spectacle independence for patients with cataracts and astigmatism. The document summarizes the history, design, and clinical outcomes of toric IOLs. A meta-analysis found that patients receiving toric IOLs were more likely to achieve good visual acuity without glasses compared to patients receiving non-toric IOLs or relaxing incisions. While toric IOLs are generally effective, predicting the exact amount of post-operative astigmatism remains challenging due to factors like IOL rotation and variability in surgically induced astigmatism. New technologies aim to improve the accuracy of toric lens alignment and outcomes.
This document provides guidelines for prescribing glasses in children. It defines various refractive errors such as myopia, hyperopia, and astigmatism. It recommends fully correcting refractive errors over ±4 diopters as these can cause amblyopia. For lower refractive errors, it recommends considering the child's age and visual needs. Anisometropia over 1.5 diopters should also be corrected. Special cases like accommodative esotropia may require bifocals. The goal of treatment is to provide a clear retinal image while maintaining proper accommodation and convergence.
The document describes the use of various Pentacam maps and indices for screening patients for keratoconus, including:
1) The standard 4-map composite report, keratoconus map, Holladay report, and Belin/Ambrosio Enhanced Ectasia Display.
2) Key features to examine on each map include anterior and posterior elevation maps, pachymetry maps, curvature maps, and indices values.
3) The Belin/Ambrosio Enhanced Ectasia Display aims to improve sensitivity by calculating an "enhanced" best fit sphere reference surface that excludes the thinnest corneal region, highlighting differences between normal and ectatic corneas.
Soft Contact Lenses: Material, Fitting, and EvaluationZahra Heidari
Soft contact lenses are made from various materials like silicone and hydrogels, with advantages like comfort and easier fitting but disadvantages like potential for complications. The document discusses the history and evolution of contact lens materials, characteristics of different lens types, factors to consider for patient fitting like base curve and power selection, and how to evaluate fit and make modifications if needed. Proper patient selection and evaluation is important for successful fitting of soft contact lenses.
This document discusses toric intraocular lenses (IOLs) for correcting astigmatism during cataract surgery. It provides details on the evolution of toric IOL designs from early PMMA lenses that often rotated, to current acrylic models with improved stability. Precise keratometry measurements and accounting for surgically induced astigmatism are important for toric IOL power calculations. The document outlines the toric IOL implantation procedure and factors affecting postoperative rotation. Toric IOLs can provide high levels of spectacle independence when used appropriately in patients with regular corneal astigmatism over 1.5 D.
In this Presentation we learn about :-
1.What is Subjective Refraction.
2.Why we should relax the accommodation.
3.Outlines of Subjective Refraction.
4.Different Techniques or Instruments.
5.Determining Near Addition.
6.The Final Prescription.
7.References.
National Ocular Biometry Course (NOBC) 2015 An echoslide presentation Anis Suzanna Mohamad
This powerpoint presentation is basically about ocular biometry. Echo presentation is one of the method to deliver infomation that obtain from the course we attend to other staff in our Ophthalmology Department.
1) Toric IOLs are used to correct corneal astigmatism during cataract surgery. They have a cylindrical optic to neutralize corneal astigmatism.
2) The material and design of toric IOLs affect their postoperative rotational stability, with acrylic IOLs showing the highest stability. Larger diameter and loop haptic designs also increase stability.
3) Proper patient selection, preoperative measurements, surgical technique, and IOL alignment are important for achieving optimal visual outcomes with toric IOL implantation. Accurate axis alignment is critical to achieve the intended astigmatic correction.
This document discusses different types of intraocular lenses (IOLs) used to correct presbyopia. It begins by explaining that monofocal IOLs only correct far vision and do not provide near vision correction without glasses. It then describes multifocal IOLs, including bifocal and trifocal lenses, which aim to provide both near and far vision corrections simultaneously. The document discusses key principles and technologies used in multifocal IOLs, specifically refractive lenses with multiple zones, diffractive lenses using interference patterns, and apodized diffractive lenses. It provides details on specific IOL models and compares technologies between traditional bifocal, trifocal, and newer trifocal lenses.
Real pediatric refraction and spectacle power prescriptionSrijana Lamichhane
This document discusses pediatric refraction and spectacle prescription. It begins with background information on the development of the eye in childhood and importance of early detection and management of refractive errors. It then covers topics such as age groups in pediatrics, emmetropization, objectives of pediatric refraction, challenges, changes in refractive error with age, types of pediatric refraction including near retinoscopy, static retinoscopy, and cycloplegic refraction. Cycloplegic refraction is emphasized as the standard approach, with discussion of indications, principles, drugs used, and example calculations.
Accommodative and multifocal intraocular lensesBijan Farpour
This document discusses accommodative and multifocal intraocular lenses (IOLs) that are surgically implanted to replace the eye's natural lens and help restore vision and the ability to focus at different distances. It provides information on how the eye works, common refractive errors, the IOL procedure, types of IOLs including multifocal and accommodative IOLs, risks and considerations, and whether refractive surgery is right for a given patient.
This document discusses biometry techniques used for precise intraocular lens (IOL) power calculations. Keratometry and axial length measurements are essential but prone to errors. Manual keratometry uses fixed or variable object sizes while automated keratometry uses reflected images. A-scan ultrasound can overestimate axial length due to corneal compression. Immersion and optical biometry are more accurate. IOL power formulas continue improving but require adjustments for high myopia, silicone oil, pediatric or post-surgical eyes. Accurate biometry is critical for optimal IOL calculations and patient outcomes.
The document discusses Pentacam corneal topography. Some key points:
- Pentacam uses Scheimpflug imaging to obtain images of the anterior segment and measure the shape of the cornea.
- It provides quantitative indices like simulated keratometry and maps of corneal power, elevation, and irregularity to evaluate corneal shape.
- Pentacam is useful for diagnosing conditions like keratoconus by detecting thinning, steepening, and irregularity. It can also evaluate outcomes of procedures like refractive surgery and intraocular surgery.
- Clinical applications include pre-op screening, surgical planning, contact lens fitting, and determining refraction.
This document discusses the purpose and process of a contact lens aftercare visit. The goals are to maintain good lens performance, check for eye health issues caused by contact lens wear, and address any discomfort or vision problems. The visit involves taking a case history, examining the eyes with and without lenses, reviewing care and maintenance, resolving any identified problems, and providing advice or treatment. Examinations check vision, comfort, lens fit, and eye health using tools like a slit lamp. Common problems addressed include blurry vision, redness, discharge, and discomfort, which can indicate issues like improper lens power or fitting, solution toxicity, or infections. The criteria for a successful visit are meeting wearing time and comfort expectations and achieving good vision
Artificial lenses implanted in the anterior or posterior chamber of the eye in the presence of the natural crystalline lens to correct refractive errors. Phakic IOLs an evolving technique in the field of refractive surgery for the correction of moderate to high refractive errors. Patients with high myopia (above -10 diopters) constitute only about 2% of the myopic population but 13-15% of patients presenting for refractive surgery belong to this group. The increased knowledge on anterior segment anatomy and availability of better imaging technologies along with improved IOL designs and surgical techniques have led to higher success rates with these lenses.
Compared to corneal refractive surgery , phakic IOLs compete favorably for the correction of high ametropias, with excellent predictability, efficacy, safety and quality of vision.
The document outlines the history of indirect ophthalmoscopy, beginning with early observations of the fundus in 1704. Hermann von Helmholtz introduced the first ophthalmoscope in 1850 using a candle for illumination. Theodor Ruete designed the first monocular indirect ophthalmoscope in 1852 using a concave mirror. Marc Antonie Giracid Tenlon invented the first binocular indirect ophthalmoscope in 1861. Over time, the sources of illumination improved from candles to gas lamps to the first use of an incandescent light bulb within an ophthalmoscope by William Dennet in 1885.
Photostress testing determines how quickly the photoreceptor cells in the retina recover after being bleached by a bright light. The test involves exposing one eye to a light for 10 seconds to bleach the photoreceptors, then timing how long it takes for the patient to read letters at a certain size after the light is removed. Recovery times longer than 50 seconds are considered abnormal and may indicate a macular disease. The test provides a measure of macular function by assessing how quickly the visual pigment can be resynthesized after being bleached.
The document discusses Florida laws and rules regarding optometric physicians. It provides information on the composition of the Florida Board of Optometry, their meeting dates and committee structure. It also summarizes the definitions of key terms in Florida law relating to optometry, such as licensed practitioner, certified optometrist, and rules around supervision. Finally, it discusses recent changes classifying optometrists as physicians by the Joint Commission.
This presentation describes indications of intrastromal corneal rings implantation in keratoconus cases and how they are beneficial even in advanced cases.
Scleral contact lenses have different zones that control their fit including an optic zone, base curve, transitional zone, and haptic zone. The sagittal depth and vault are important measurements for proper fit. Applying scleral lenses involves bubble and touch tests to assess fit while accounting for conditions like keratoglobus, graves ophthalmopathy, corneal scarring, epithelial defects, prior surgery, and Steven-Johnson Syndrome. Scleral lenses can successfully fit patients with many complex ocular conditions.
A Classroom presentation, showing the various types of slit-lamps, their parts, and other accessory instruments that can be used with it for enhanced optometric clinical examination.
Iol power calculation in pediatric patientsAnisha Rathod
- Many factors affect intraocular lens (IOL) power calculation in pediatric patients including age at surgery, laterality, amblyopia, axial length, keratometry, and expected myopic shift due to ongoing eye growth.
- Normal eye development involves rapid growth of the axial length and changes in lens power in the first years of life.
- Target postoperative refraction must account for this myopic shift and generally involves undercorrecting more in younger patients.
- Accurate biometry using immersion ultrasound or optical techniques is important to minimize errors from corneal compression.
- Formulas, IOL type and position can further influence outcomes.
Tints and filter for patients with low visionGauriChaudhary7
The document discusses various tints and filters that can help patients with low vision. It provides information on conditions like age-related macular degeneration, cataracts, glaucoma, diabetic retinopathy, retinitis pigmentosa, pathological myopia, and corneal dystrophy. For each condition, it recommends certain tints and filters that may help enhance contrast and reduce glare, such as amber, orange, grey, and green tints as well as filters like CPF and NoIR filters. The document provides details on the light transmission properties and benefits of different tint and filter options.
This document discusses comanagement of cataract surgery and premium intraocular lenses (IOLs) such as toric and multifocal IOLs. It provides guidance on criteria for ethical and legal comanagement including profitability. Reasons for comanaging with Visionary Ophthalmology include their reputation for excellent outcomes and being a leader in technology. The document reviews options for correcting astigmatism during cataract surgery such as toric IOLs. It discusses patient selection criteria and pearls for optimal results with toric IOLs including importance of accurate keratometry and marking the correct axis. The document also reviews multifocal IOL options and important tips for patient counseling, management of side effects
In this Presentation we learn about :-
1.What is Subjective Refraction.
2.Why we should relax the accommodation.
3.Outlines of Subjective Refraction.
4.Different Techniques or Instruments.
5.Determining Near Addition.
6.The Final Prescription.
7.References.
National Ocular Biometry Course (NOBC) 2015 An echoslide presentation Anis Suzanna Mohamad
This powerpoint presentation is basically about ocular biometry. Echo presentation is one of the method to deliver infomation that obtain from the course we attend to other staff in our Ophthalmology Department.
1) Toric IOLs are used to correct corneal astigmatism during cataract surgery. They have a cylindrical optic to neutralize corneal astigmatism.
2) The material and design of toric IOLs affect their postoperative rotational stability, with acrylic IOLs showing the highest stability. Larger diameter and loop haptic designs also increase stability.
3) Proper patient selection, preoperative measurements, surgical technique, and IOL alignment are important for achieving optimal visual outcomes with toric IOL implantation. Accurate axis alignment is critical to achieve the intended astigmatic correction.
This document discusses different types of intraocular lenses (IOLs) used to correct presbyopia. It begins by explaining that monofocal IOLs only correct far vision and do not provide near vision correction without glasses. It then describes multifocal IOLs, including bifocal and trifocal lenses, which aim to provide both near and far vision corrections simultaneously. The document discusses key principles and technologies used in multifocal IOLs, specifically refractive lenses with multiple zones, diffractive lenses using interference patterns, and apodized diffractive lenses. It provides details on specific IOL models and compares technologies between traditional bifocal, trifocal, and newer trifocal lenses.
Real pediatric refraction and spectacle power prescriptionSrijana Lamichhane
This document discusses pediatric refraction and spectacle prescription. It begins with background information on the development of the eye in childhood and importance of early detection and management of refractive errors. It then covers topics such as age groups in pediatrics, emmetropization, objectives of pediatric refraction, challenges, changes in refractive error with age, types of pediatric refraction including near retinoscopy, static retinoscopy, and cycloplegic refraction. Cycloplegic refraction is emphasized as the standard approach, with discussion of indications, principles, drugs used, and example calculations.
Accommodative and multifocal intraocular lensesBijan Farpour
This document discusses accommodative and multifocal intraocular lenses (IOLs) that are surgically implanted to replace the eye's natural lens and help restore vision and the ability to focus at different distances. It provides information on how the eye works, common refractive errors, the IOL procedure, types of IOLs including multifocal and accommodative IOLs, risks and considerations, and whether refractive surgery is right for a given patient.
This document discusses biometry techniques used for precise intraocular lens (IOL) power calculations. Keratometry and axial length measurements are essential but prone to errors. Manual keratometry uses fixed or variable object sizes while automated keratometry uses reflected images. A-scan ultrasound can overestimate axial length due to corneal compression. Immersion and optical biometry are more accurate. IOL power formulas continue improving but require adjustments for high myopia, silicone oil, pediatric or post-surgical eyes. Accurate biometry is critical for optimal IOL calculations and patient outcomes.
The document discusses Pentacam corneal topography. Some key points:
- Pentacam uses Scheimpflug imaging to obtain images of the anterior segment and measure the shape of the cornea.
- It provides quantitative indices like simulated keratometry and maps of corneal power, elevation, and irregularity to evaluate corneal shape.
- Pentacam is useful for diagnosing conditions like keratoconus by detecting thinning, steepening, and irregularity. It can also evaluate outcomes of procedures like refractive surgery and intraocular surgery.
- Clinical applications include pre-op screening, surgical planning, contact lens fitting, and determining refraction.
This document discusses the purpose and process of a contact lens aftercare visit. The goals are to maintain good lens performance, check for eye health issues caused by contact lens wear, and address any discomfort or vision problems. The visit involves taking a case history, examining the eyes with and without lenses, reviewing care and maintenance, resolving any identified problems, and providing advice or treatment. Examinations check vision, comfort, lens fit, and eye health using tools like a slit lamp. Common problems addressed include blurry vision, redness, discharge, and discomfort, which can indicate issues like improper lens power or fitting, solution toxicity, or infections. The criteria for a successful visit are meeting wearing time and comfort expectations and achieving good vision
Artificial lenses implanted in the anterior or posterior chamber of the eye in the presence of the natural crystalline lens to correct refractive errors. Phakic IOLs an evolving technique in the field of refractive surgery for the correction of moderate to high refractive errors. Patients with high myopia (above -10 diopters) constitute only about 2% of the myopic population but 13-15% of patients presenting for refractive surgery belong to this group. The increased knowledge on anterior segment anatomy and availability of better imaging technologies along with improved IOL designs and surgical techniques have led to higher success rates with these lenses.
Compared to corneal refractive surgery , phakic IOLs compete favorably for the correction of high ametropias, with excellent predictability, efficacy, safety and quality of vision.
The document outlines the history of indirect ophthalmoscopy, beginning with early observations of the fundus in 1704. Hermann von Helmholtz introduced the first ophthalmoscope in 1850 using a candle for illumination. Theodor Ruete designed the first monocular indirect ophthalmoscope in 1852 using a concave mirror. Marc Antonie Giracid Tenlon invented the first binocular indirect ophthalmoscope in 1861. Over time, the sources of illumination improved from candles to gas lamps to the first use of an incandescent light bulb within an ophthalmoscope by William Dennet in 1885.
Photostress testing determines how quickly the photoreceptor cells in the retina recover after being bleached by a bright light. The test involves exposing one eye to a light for 10 seconds to bleach the photoreceptors, then timing how long it takes for the patient to read letters at a certain size after the light is removed. Recovery times longer than 50 seconds are considered abnormal and may indicate a macular disease. The test provides a measure of macular function by assessing how quickly the visual pigment can be resynthesized after being bleached.
The document discusses Florida laws and rules regarding optometric physicians. It provides information on the composition of the Florida Board of Optometry, their meeting dates and committee structure. It also summarizes the definitions of key terms in Florida law relating to optometry, such as licensed practitioner, certified optometrist, and rules around supervision. Finally, it discusses recent changes classifying optometrists as physicians by the Joint Commission.
This presentation describes indications of intrastromal corneal rings implantation in keratoconus cases and how they are beneficial even in advanced cases.
Scleral contact lenses have different zones that control their fit including an optic zone, base curve, transitional zone, and haptic zone. The sagittal depth and vault are important measurements for proper fit. Applying scleral lenses involves bubble and touch tests to assess fit while accounting for conditions like keratoglobus, graves ophthalmopathy, corneal scarring, epithelial defects, prior surgery, and Steven-Johnson Syndrome. Scleral lenses can successfully fit patients with many complex ocular conditions.
A Classroom presentation, showing the various types of slit-lamps, their parts, and other accessory instruments that can be used with it for enhanced optometric clinical examination.
Iol power calculation in pediatric patientsAnisha Rathod
- Many factors affect intraocular lens (IOL) power calculation in pediatric patients including age at surgery, laterality, amblyopia, axial length, keratometry, and expected myopic shift due to ongoing eye growth.
- Normal eye development involves rapid growth of the axial length and changes in lens power in the first years of life.
- Target postoperative refraction must account for this myopic shift and generally involves undercorrecting more in younger patients.
- Accurate biometry using immersion ultrasound or optical techniques is important to minimize errors from corneal compression.
- Formulas, IOL type and position can further influence outcomes.
Tints and filter for patients with low visionGauriChaudhary7
The document discusses various tints and filters that can help patients with low vision. It provides information on conditions like age-related macular degeneration, cataracts, glaucoma, diabetic retinopathy, retinitis pigmentosa, pathological myopia, and corneal dystrophy. For each condition, it recommends certain tints and filters that may help enhance contrast and reduce glare, such as amber, orange, grey, and green tints as well as filters like CPF and NoIR filters. The document provides details on the light transmission properties and benefits of different tint and filter options.
This document discusses comanagement of cataract surgery and premium intraocular lenses (IOLs) such as toric and multifocal IOLs. It provides guidance on criteria for ethical and legal comanagement including profitability. Reasons for comanaging with Visionary Ophthalmology include their reputation for excellent outcomes and being a leader in technology. The document reviews options for correcting astigmatism during cataract surgery such as toric IOLs. It discusses patient selection criteria and pearls for optimal results with toric IOLs including importance of accurate keratometry and marking the correct axis. The document also reviews multifocal IOL options and important tips for patient counseling, management of side effects
What diagnostics you need for a successfull premium cataract surgery.
Tomey OA-200 and Casia2 biometry and other values for premium ophthalmic surgeon
Soon an english version
L'ortocheratologia è una tecnica di riduzione della miopia ottenuta mediante l'uso di lenti a contatto rigide. Le lenti modificano leggermente, rendendola meno curva, la prima superficie dell'occhio sulla quale le lenti stesse appoggiano.
contenuto a cura del Dott. Luca Avoni e di Pietro Gheller
Breve analisi rivolta a chi vuole correggere la presbiopia. La presbiopia, cioè non vedere più bene da vicino, si manifesta intorno ai 40 anni ed è necessario sottoporsi ad una visita oculistica specializzata.
3. Il risultato
refrattivo?
Mentre nelle prime estrazioni del cristallino il risultato era "ridare
la luce"
Mano a mano che si sono raffinate le tecniche chirurgiche e che
si sono ottimizzate le prime formule biometriche di calcolo il
risultato refrattivo è diventato sempre più importante
Anche il paziente è diventato sempre più esigente in termini di
risultati visivi
Abbiamo visto negli ultimi 20 anni, quello che era un intervento
di necessità, diventare un vero e proprio trattamento refrattivo
Questo ha portato a considerare il successo post-operatorio non
solo in termini di visus ma di qualità visiva
Non è importante andare a fuoco in fovea ma come si va
4.
5.
6. L'aberrazione sferica
SA neutra – tutta l'energia e l'immagine è focalizzata in
un solo piano per tutta l'estensione della zona ottica
analizzata – no profondità di fuoco e qualità massima di
visione
SA positiva/negativa – l'energia e i piani di fuoco sono
allungati in base alla zona ottica analizzata che
prendiamo in considerazine - profondità di fuoco a
discapito di una minore qualità di immagine
Considerando il movimento di restringimento pupillare
durante la visione da vicino, la SA negativa è quella
sicuramente più utile nel cercare di dare un'elongazione
di fuoco funzionale
Neutra
Positiva
Negativa
7. SA e IOL
monofocali
Molte aziende hanno introdotto IOL monofocali
con l'intento di annullare l'SA positivo corneale
propiro a favore della qualità del singolo fuoco
Altre hanno scelto una IOL ad SA neutra per non
incorrerere nella problematica di decentramento
possibile rispetto all'asse visivo e le aberrazioni
che questo indurrebbe
(appendice per i riferimenti)
12. Proporzione tra
addizionale e fuoco
per lontano
Chi fa il mi lavoro molto spesso
"omette" erroneamente i pregi e i difetti
delle IOL che vengono proposte
Anche la proporzione di superficie tra
addizionale e fuoco principale è
importante per la scelta della lente
14. Significato di diffrazione
La diffrazione, nella fisica, è un fenomeno associato alla deviazione della traiettoria di
propagazione delle onde quando queste incontrano un ostacolo sul loro cammino.
La prima cose che ci viene in mente è: " ma anche nelle lenti precedenti avevamo dei fenomeni di
diffrazione". Si, anche nelle lenti che finora abbiamo definito refrattive abbiamo la deviazione della
traiettoria dei raggi (fuoco per lontano/vicino), anche il bordo pupillare produce diffrazione (disco di
Airy)
La vera differenza rispetto alle lenti prima definite refrattive è che qui, a "zona" avevamo un piano di
fuoco ora su tutta la zona analizzata abbiamo tanti piani di fuoco quanti ordini diffrattivi induciamo
Con questo tipo di tecnologia possiamo gestire i fuochi e l'apporto di luce in base alla zona ottica
della lente
15. Ordini diffrattivi
Ogni fenditura ha un fuoco e una ripartizione della
luce ben definita
Ogni fenditura in ogni caso genera ordini infiniti di
diffrazione multipli rispetto alla frequenza/lunghezza
d'onda di riferimento, e qui va a ricadere una piccola
porzione di luce che si disperde
16. Base e altezza
La base del triangolo della fenditura
rappresentano l'addizionale dove cadrà il fuoco
per vicino
L'altezza del triangolo della fenditura determina
la ripartizione della luce tra l'ordine di diffrazione
1 (vicino) e lo 0 (lontano)
Ogni ordine diffrattivo corrisponde a un piano di
fuoco
Una trifocale avrà 2 ordini diffrattivi
Più ordini diffrattivi più anelli e più effetti
collaterali
17. Quantità di anelli
diffrattivi
Il piatto ottico diffrattivo ha il vantaggio di determinare 2 o 3
piani di fuoco ben distinti
Rispetto a lenti concentriche reffrattive sono meno pupillo
dipendenti per quanto riguarda I piani di fuoco (possono dare
la trifocalità gia nei 2 mm di pupilla) però...
Ogni piano di fuoco che non è in uso crea degli anelli
disturbanti (sono gli anelli creati dalla diffrazione dei piani che
non sono a fuoco)
Gli effetti collaterali sono proporzionali al numero di anelli
diffrattivi
Questo è il motivo per il quale questo tipo di IOL preoccupa
nelle condizioni di scarsa luce (pupilla larga)
18. Visione in retina degli
anelli quando la IOL
corregge perfettamente
la lunghezza assiale
19. Evoluzione delle IOL
diffrattive
CONTRO mancanza di un
piano intermedio, solo
distante e vicino
• Alle trifocali con 15-29
anelli diffrattivi
• PRO piani di fuoco
lontano, intermedio e
vicino
• CONTRO presenza di
effetti collaterali maggiori
20. Importanza del
risultato refrattivo
Dall'immagine dei 3 punti di fuoco si capisce perchè è importante
il miglior risultato refrattivo possibile
Se il potere della IOL ci dà un risultato ipermetropico o miopico
questo risultato si ripercuote su tutti e 3 i piani di fuoco
Prende particolare importanza anche l'allineamento delle toriche,
un minimo decentramento produce un PSF scarso
21. IOL EDOF
La Symfony è considerata una IOL EDOF
In realtà la potremmo definire una IOL
bifocale, dove il piano di fuoco al posto di
essere per il vicino presenta una
addizionale bassa per l'intermedio
Quindi essendo solamente un ordine
difrattivo avrà pochi anelli e avendo
un'addizionale bassa saranno più distanti
fra di loro rispetto a una bifocale con fuoco
per vicino
Ha meno effetti collaterali sicuramente
rispetto alle trifocali ma manca di un fuoco e
anche se in minima parte può dare problemi
di aloni
22. EDOF
Definiamo il concetto di EDOF ( extended depht of focus)
Con questo termine negli ultimi anni abbiamo sentito dire tutto e il contrario di
tutto
E' una lente che "perdona di più"; E' una lente che non dà aloni e glare
Credo che ci sia la necessità di dare più chiarezza al concetto di EDOF
Questa caustica a mio avviso è il concetto
di elongazione di fuoco
Come abbiamo visto in precedenza la
larghezza dello "spot EDOF" definisce la
qualità visiva in quei punti
Più lunga è l'elongazione
di fuoco e più larga sarà
la banda di "Beam waist"
ovvero la larghezza del
piano di fuoco
23. Qualità del Beam
waist
Senza inoltrarsi nelle
formule espresse nell'immagine
bassa
Più la pupilla è piccola più "l'effetto
stenopeico" elonga la profondità di
fuoco e restringe la larghezza del
fascio
Più la lente è potente più efficacie
potrà essere l'elongazione di fuoco,
perchè l'occhio è più corto
warning
24. Non è tutto fantastico
Se questa è la lunghezza
focale della lente(dove c'è
una miglior qualità visiva)
• Questa è l'unica
parte sfruttabile di
elongazione di fuoco. E' la
parte che usiamo dall'infito
ad avvicinarsi
E' più difficile trovare una
refrazione realistica in un paziente
con un elongazone di fuoco ampia.
Proprio per questo le IOL EDOF
refrattive hanno difficoltà ad
ottimizzare le costanti per un
calcolo più accurato
Ma soprattutto bisogna tenere
in considerazione che a
pupilla stretta ci sono
solamente in gioco le
aberrazioni con cui la IOL
cerca di dare la profondità di
fuoco e questo potrebbe
penalizzare e non di poco la
visione del lontano
25. EDOF
Forse la EDOF più conosciuta fino a qualche mese
fà
Un idea molto interessante regolare le SA negative
e positive per avere un elongazione di fuoco
funzionale
I limiti possono essere le aberrazioni della cornea
che influiscono nel funzionamento della IOL stessa
La pupilla e la centratura rispetto all'asse visivo è
un altro elemento fondame ntale per la buona
visione
Ci sono molte variabili da considerare per l'effettiva
soddisfazione visiva del paziente
26. EDOF
In questo momento forse è la EDOF che è tra
le più impiantate in Italia
Zona centralissima "neutra" per visisone da
lontano e "ciambella" refrattiva per
elongazione di fuoco
27. Vivity
Nella immagine in alto si capisce che a
discapito del visus da lontano abbiamo,
rispetto alla versione mofocale, un
elongazione di fuoco
La "ciambella" intorno al centro della lente
serve a dare l'elongazione
Anche questa IOL come molte è sensibile
alla centratura rispetto all'asse visivo e la
qualità dell'immagine, specie per lontano, è
molto correlata all'apertura pupillare.
28. Non c'è una lente
Premium per tutte le
stagioni...
29. Esempi di aberrazioni con multifocali
EDOF refrattiva con
chiaro Beam waist largo
nel PSF
Stessa EDOF con correzione del
residuo refrattivo (sempre abbastanza
di difficile interpretazione) e PSF che
non si modifica di molto.
Questa è la massima ualità visiva
raggiungibile
Sempre la stessa lente
analizzando solamente i
2 mm centrali.
Come in un foro
stenopeico il PSF
migliora ma non così
tanto da rendere una
qualità visiva eccelsa
Analizzando la parte centrale la
refrazione è comunque miopica
creando possibili problemi per la
visione da lontano
30. Esempi di IOL multifocali
Lente trifocale a 25-29
anelli diffrattivi
PSF e MTF buoni
Nel complesso paziente
con una buona qualità
visiva
Stessa IOL ma come
abbiamo detto molte
slide prima, la perfezione
nel risultato refrattivo in
caso di IOL trifocali
diffrattive è molto
importante
La differenza rispetto alla
IOL di prima è che qui
correggendo sfero e cilindro
possiamo ottenere
un'ottimo risultato in termini
di qualità e di refrazione.
Non è possibile farlo con le
lenti EDOF refrattive
31. Lenti ibride
Il futuro delle lenti probabilmente tornerà a parlare
di diffrazione ma non più con la presenza di
moltissime incisure (anelli)
Probabile un ottica ibrida, dove accostare la
diffrazione alla refrazione per ottenre un buon
range di fuoco (vicino-intermedio-lontano) con
minore effetti collaterali possibili
Alcune aziende hanno già in commercio ottiche
ibride
Altre usciranno nei prossimi mesi
IOL con 1 solo ordine
diffrattivo per il vicino e
poche incisioni
Bottone centrale
iperprolato per
elongazione di fuoco a
dare un piano intermedio
continuo