Biometry is used to measure the eye to determine the correct intraocular lens power for cataract surgery. It involves measuring the corneal power with keratometry and the eye length with axial length measurement. The optimal method is optical biometry which measures both simultaneously while allowing the patient to fixate, improving accuracy. Special cases like high myopia, prior refractive surgery, or pathology require adjusted measurement techniques or formulas to calculate the lens power accurately.
Scleral contact lenses , types, uses in various ocular conditions.
An in-depth and unbiased details of these lenses as a therapeutic and also as a drug - delivery system in modern ophthalmology.
A must read for all Ophthalmologists and Optometrists.
Scleral contact lenses , types, uses in various ocular conditions.
An in-depth and unbiased details of these lenses as a therapeutic and also as a drug - delivery system in modern ophthalmology.
A must read for all Ophthalmologists and Optometrists.
introduction into Biometry and it's formulas.pptxQusaiAbusleem1
Biometry is the practice of applying mathematics to biology .
With regard to ophthalmology , there are several biometric systems used for making precise measurements of ocular structures : ultrasound (A- and B-scan , pachymeter) , low coherence interferometry (OCT) , laser interferometry (IOL Master , Lenstar)
These systems are used in measurement of axial length ,keratometry , pachymetry , and retinal thickness , among other things .
The term biometry , as it relates to ophthalmology , typically refers to preoperative measurements made for IOL calculations.
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.
A scan biometry | How to Use A-scan? Types of A-Scan Biometry?Naeem Ahmad
A-SCAN BIOMETRY | What is A-Scan Biometry? How To Use It?
A-scan is the short form of amplitude scan.
This eye ultrasound gives details about the length of the eye.
A-Scan is an essential diagnostic tool used in ophthalmology.
The measurement of the eye’s axial length through an A-scan is necessary for placing an intraocular lens (IOL, artificial lens) during cataract surgery.
The total refractive power of the emmetropic eye is approximately 60D. Of this power, the cornea provides roughly 40D, and the crystalline lens 20 diopters.
When a cataract is removed, the lens is replaced by an artificial lens implant. By measuring both the length of the eye (A-scan Biometry) and the power of the cornea (keratometry).
It may also be used to assess vision abnormalities and other diseases involving the eye such as tumors.
A-scan techniques are based on the principles of ultrasonography. Sound travels in a wave pattern. For a sound to be heard by the human ear, the frequency must be between 20 and 20,000 Hz (20 kHz).
For an eye examination through A-scan, an ultrasound of frequency of around 10 MHz is used.
Prix Galien International 2024 Forum ProgramLevi Shapiro
June 20, 2024, Prix Galien International and Jerusalem Ethics Forum in ROME. Detailed agenda including panels:
- ADVANCES IN CARDIOLOGY: A NEW PARADIGM IS COMING
- WOMEN’S HEALTH: FERTILITY PRESERVATION
- WHAT’S NEW IN THE TREATMENT OF INFECTIOUS,
ONCOLOGICAL AND INFLAMMATORY SKIN DISEASES?
- ARTIFICIAL INTELLIGENCE AND ETHICS
- GENE THERAPY
- BEYOND BORDERS: GLOBAL INITIATIVES FOR DEMOCRATIZING LIFE SCIENCE TECHNOLOGIES AND PROMOTING ACCESS TO HEALTHCARE
- ETHICAL CHALLENGES IN LIFE SCIENCES
- Prix Galien International Awards Ceremony
Acute scrotum is a general term referring to an emergency condition affecting the contents or the wall of the scrotum.
There are a number of conditions that present acutely, predominantly with pain and/or swelling
A careful and detailed history and examination, and in some cases, investigations allow differentiation between these diagnoses. A prompt diagnosis is essential as the patient may require urgent surgical intervention
Testicular torsion refers to twisting of the spermatic cord, causing ischaemia of the testicle.
Testicular torsion results from inadequate fixation of the testis to the tunica vaginalis producing ischemia from reduced arterial inflow and venous outflow obstruction.
The prevalence of testicular torsion in adult patients hospitalized with acute scrotal pain is approximately 25 to 50 percent
Ozempic: Preoperative Management of Patients on GLP-1 Receptor Agonists Saeid Safari
Preoperative Management of Patients on GLP-1 Receptor Agonists like Ozempic and Semiglutide
ASA GUIDELINE
NYSORA Guideline
2 Case Reports of Gastric Ultrasound
Report Back from SGO 2024: What’s the Latest in Cervical Cancer?bkling
Are you curious about what’s new in cervical cancer research or unsure what the findings mean? Join Dr. Emily Ko, a gynecologic oncologist at Penn Medicine, to learn about the latest updates from the Society of Gynecologic Oncology (SGO) 2024 Annual Meeting on Women’s Cancer. Dr. Ko will discuss what the research presented at the conference means for you and answer your questions about the new developments.
- Video recording of this lecture in English language: https://youtu.be/lK81BzxMqdo
- Video recording of this lecture in Arabic language: https://youtu.be/Ve4P0COk9OI
- Link to download the book free: https://nephrotube.blogspot.com/p/nephrotube-nephrology-books.html
- Link to NephroTube website: www.NephroTube.com
- Link to NephroTube social media accounts: https://nephrotube.blogspot.com/p/join-nephrotube-on-social-media.html
New Drug Discovery and Development .....NEHA GUPTA
The "New Drug Discovery and Development" process involves the identification, design, testing, and manufacturing of novel pharmaceutical compounds with the aim of introducing new and improved treatments for various medical conditions. This comprehensive endeavor encompasses various stages, including target identification, preclinical studies, clinical trials, regulatory approval, and post-market surveillance. It involves multidisciplinary collaboration among scientists, researchers, clinicians, regulatory experts, and pharmaceutical companies to bring innovative therapies to market and address unmet medical needs.
Explore natural remedies for syphilis treatment in Singapore. Discover alternative therapies, herbal remedies, and lifestyle changes that may complement conventional treatments. Learn about holistic approaches to managing syphilis symptoms and supporting overall health.
These lecture slides, by Dr Sidra Arshad, offer a quick overview of physiological basis of a normal electrocardiogram.
Learning objectives:
1. Define an electrocardiogram (ECG) and electrocardiography
2. Describe how dipoles generated by the heart produce the waveforms of the ECG
3. Describe the components of a normal electrocardiogram of a typical bipolar leads (limb II)
4. Differentiate between intervals and segments
5. Enlist some common indications for obtaining an ECG
Study Resources:
1. Chapter 11, Guyton and Hall Textbook of Medical Physiology, 14th edition
2. Chapter 9, Human Physiology - From Cells to Systems, Lauralee Sherwood, 9th edition
3. Chapter 29, Ganong’s Review of Medical Physiology, 26th edition
4. Electrocardiogram, StatPearls - https://www.ncbi.nlm.nih.gov/books/NBK549803/
5. ECG in Medical Practice by ABM Abdullah, 4th edition
6. ECG Basics, http://www.nataliescasebook.com/tag/e-c-g-basics
Flu Vaccine Alert in Bangalore Karnatakaaddon Scans
As flu season approaches, health officials in Bangalore, Karnataka, are urging residents to get their flu vaccinations. The seasonal flu, while common, can lead to severe health complications, particularly for vulnerable populations such as young children, the elderly, and those with underlying health conditions.
Dr. Vidisha Kumari, a leading epidemiologist in Bangalore, emphasizes the importance of getting vaccinated. "The flu vaccine is our best defense against the influenza virus. It not only protects individuals but also helps prevent the spread of the virus in our communities," he says.
This year, the flu season is expected to coincide with a potential increase in other respiratory illnesses. The Karnataka Health Department has launched an awareness campaign highlighting the significance of flu vaccinations. They have set up multiple vaccination centers across Bangalore, making it convenient for residents to receive their shots.
To encourage widespread vaccination, the government is also collaborating with local schools, workplaces, and community centers to facilitate vaccination drives. Special attention is being given to ensuring that the vaccine is accessible to all, including marginalized communities who may have limited access to healthcare.
Residents are reminded that the flu vaccine is safe and effective. Common side effects are mild and may include soreness at the injection site, mild fever, or muscle aches. These side effects are generally short-lived and far less severe than the flu itself.
Healthcare providers are also stressing the importance of continuing COVID-19 precautions. Wearing masks, practicing good hand hygiene, and maintaining social distancing are still crucial, especially in crowded places.
Protect yourself and your loved ones by getting vaccinated. Together, we can help keep Bangalore healthy and safe this flu season. For more information on vaccination centers and schedules, residents can visit the Karnataka Health Department’s official website or follow their social media pages.
Stay informed, stay safe, and get your flu shot today!
Couples presenting to the infertility clinic- Do they really have infertility...Sujoy Dasgupta
Dr Sujoy Dasgupta presented the study on "Couples presenting to the infertility clinic- Do they really have infertility? – The unexplored stories of non-consummation" in the 13th Congress of the Asia Pacific Initiative on Reproduction (ASPIRE 2024) at Manila on 24 May, 2024.
Title: Sense of Smell
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
Learning Objectives:
Describe the primary categories of smells and the concept of odor blindness.
Explain the structure and location of the olfactory membrane and mucosa, including the types and roles of cells involved in olfaction.
Describe the pathway and mechanisms of olfactory signal transmission from the olfactory receptors to the brain.
Illustrate the biochemical cascade triggered by odorant binding to olfactory receptors, including the role of G-proteins and second messengers in generating an action potential.
Identify different types of olfactory disorders such as anosmia, hyposmia, hyperosmia, and dysosmia, including their potential causes.
Key Topics:
Olfactory Genes:
3% of the human genome accounts for olfactory genes.
400 genes for odorant receptors.
Olfactory Membrane:
Located in the superior part of the nasal cavity.
Medially: Folds downward along the superior septum.
Laterally: Folds over the superior turbinate and upper surface of the middle turbinate.
Total surface area: 5-10 square centimeters.
Olfactory Mucosa:
Olfactory Cells: Bipolar nerve cells derived from the CNS (100 million), with 4-25 olfactory cilia per cell.
Sustentacular Cells: Produce mucus and maintain ionic and molecular environment.
Basal Cells: Replace worn-out olfactory cells with an average lifespan of 1-2 months.
Bowman’s Gland: Secretes mucus.
Stimulation of Olfactory Cells:
Odorant dissolves in mucus and attaches to receptors on olfactory cilia.
Involves a cascade effect through G-proteins and second messengers, leading to depolarization and action potential generation in the olfactory nerve.
Quality of a Good Odorant:
Small (3-20 Carbon atoms), volatile, water-soluble, and lipid-soluble.
Facilitated by odorant-binding proteins in mucus.
Membrane Potential and Action Potential:
Resting membrane potential: -55mV.
Action potential frequency in the olfactory nerve increases with odorant strength.
Adaptation Towards the Sense of Smell:
Rapid adaptation within the first second, with further slow adaptation.
Psychological adaptation greater than receptor adaptation, involving feedback inhibition from the central nervous system.
Primary Sensations of Smell:
Camphoraceous, Musky, Floral, Pepperminty, Ethereal, Pungent, Putrid.
Odor Detection Threshold:
Examples: Hydrogen sulfide (0.0005 ppm), Methyl-mercaptan (0.002 ppm).
Some toxic substances are odorless at lethal concentrations.
Characteristics of Smell:
Odor blindness for single substances due to lack of appropriate receptor protein.
Behavioral and emotional influences of smell.
Transmission of Olfactory Signals:
From olfactory cells to glomeruli in the olfactory bulb, involving lateral inhibition.
Primitive, less old, and new olfactory systems with different path
2. Definition
• Biometry: measurement in relation to a biological structure.
In practice:
• Biometry is the process of measuring the power of the cornea
(keratometry) and the length of the eye, and using this data to
determine the ideal intraocular lens power for cataract surgery.
Community Eye Health. 2006 Dec; 19(60): 70–71.
3. What is needed for biometry?
1. Axial length/ACD
2. Keratometry
3. A formula to calculate
the IOL power using the
above two.
Dc
DL
ACD
AL
Dc: Power of Cornea
DL: Power of Lens
ACD: Anterior Chamber Depth
AL: Axial length
7. Axial length: Principal of ultrasound
• Ultrasound echoes are reflected at
the interface of tissue with
different densities.
• Using the transit time between
transduction and receipt of the US
waves, the length of structures in
between the interfaces can be
calculated if the speed is known in
that structure.
8. Axial length: US contact A-scan
• Disadvantages:
• Compression of the cornea: thus
underestimates the axial length. This
will give a myopic surprise.
• Patient cannot fixate to align their
visual axis.
9. Axial length: Non-contact (immersion) A-scan
• Disadvantage:
• Still patient cannot fixate on a target
to align their visual axis.
• Requires a ”water bath” or
immersion shell
• Can miss the centre of the pupil but
is generally comparable to the optical
biometry.
However avoid compression.
10. Axial length: The optical method
• Uses light waves (780nm) instead of
Ultrasound waves.
• Partial coherence interferometry to
estimate the axial length.
11. Axial length: The optical method
• Advantages:
• More accurate: Patient can fixate
on a target and thus the “visual
axial length” is measured.
• No compression of the cornea.
• Measures the K values at the same
time.
• Disadvantages:
• Cannot penetrate dense opacities
(e.g. dense cataract).
12. US method
Regarding axial length: Unlike A-scan ultrasound, which reflects off the surface
of the retina, the IOLMaster beam passes through the translucent surface of
the retina and back further to the more opaque pigment layer. The computer
corrects for this difference, but because everyone has different tissue thick-
nesses, results from the IOLMaster and immersion ultrasound may be slightly
different.
In addition, the use of contact ultrasound will indent the cornea, thus decreas-
ing the distance between the cornea and the retina and artificially shortening
the axial length measured. Because of this, axial lengths measured on the IOL-
Master are almost always longer than those obtained through contact ultra-
sound.
Regarding corneal curvature: First, manual keratometry measures the corneal
curvature more peripherally—perhaps at 3.0 mm or 3.2 mm, depending on
your manual system—while the IOLMaster measures the more relevant central
curvature at 2.5 mm. Thus on a typical eye, IOLMaster K’s will be slightly
13. Conclusion for axial length
• Use optical biometry whenever possible
• In case of a dense cataract: It is best to use immersion US as opposed
to contact US.
14. What is needed for biometry?
1. Axial length
2. Keratometry
3. A formula to calculate the IOL power using the above two.
15. Keratometry
• Measure the power of the cornea
• The k-readings over the central 3mm zone is usually measured.
17. Keratometry
• Older machines measure only anterior corneal curvature (K-values)
• Assume a constant relationship between the anterior and corneal
curvature (Rpos/Rant: 82% and thus use n=1.3375)
• Newer technology also measures the posterior curvature and gives
more accurate net K. Important in toric iols, post refractive surgery
and keratoconus.
18. Conclusion for Keratometry readings
• If regular virgin cornea, use optical biometer K-readings.
• If keratoconus, refractive surgery, toric iol calculations best to use
total corneal power where the posterior corneal curvature is also
measured (using tomography, AS-OCT).
20. What is needed for biometry?
1. Axial length
2. Keratometry
3. A formula to calculate the IOL power using the above two.
21. IOL calculation formulas
In history, the formulas started as
theoretical formulas based on geometric
optics. However, there were problems:
1. Estimated lens position cannot be
determined from the pre-operative
anterior chamber depth.
2. The refractive index used to estimate the
corneal power from the anterior corneal
curvature is hypothetical.
3. The shape of the cornea and eye can be
altered by the surgery
22.
23. IOL calculation: Formulas
• The first regression formula was introduced by Sanders, Retzlaff and Kraff
(SRK I) in 1980s
P = A – 0.9K – 2.5AL
• Regression: Modification of formulas based on a large number of post op
refraction.
• Since then many generations of theoratical and regression formulas have
been introduced. SRK-T (T for theoratical) combined theoratical optics and
regression data. Ray tracing formulas (Oslen) are also now introduced.
25. SRK I formula
P = A – 0.9K – 2.5AL
P = Power of the lens for a particular target refraction
A = Constant relating to the lens design and their estimated position in
the eye.
K: Average corneal power
AL: Axial length.
27. Barret II and Hill-RBF work well for all AL
https://www.doctor-hill.com/iol-main/formulas.htm
28. Conclusion: formulas
• If AL <22mm use Hoffer Q
• If AL >22mm use SRK-T
OR
• Use Barret II universal or Hill-RBF for all AL
29. Example on how
to read IOLmaster
printout
Quality check:
Axial length
1) Composite SNR > 2
2) AL SD within 0.1
3) Inter-eye AL difference within 0.7
Keratometry
1) Make sure that not many X dots are
displayed.
34. Special cases: Short eyes
Problem:
• Inaccurate IOL calculations using some formulas.
Solution
• If Al < 22mm, Best to use Hoffer Q or Barret or Holladay II
36. Special cases: Long eyes
Problem:
• Overestimation of the “visual axial length” in staphylomatous eyes
Solution
• Best to use optical biometry with patient fixation on the target. However, may
not be possible if dense cataract.
37. Special cases: Dense cataract
Problem:
• The laser in optical biometry
will penetrate a dense cataract
Solution:
• Use US method to get a
reading of the AL and then
feed it into the optical
biometer.
38. Special cases: Regular astigmatism
Problem
• Patient might not attain
6/6 vision post op if
implanting a standard
monofocal lens.
Solution:
If corneal astigmatism is
0.75D, implant a toric IOL
39. Special cases: Irregular astigmatism
(Keratoconus)
Problem:
• Inaccurate K-readings by most devices. Can lead to upredictable post op surprise especially
hyperopic.
• Others: Irregular tear film, Long AL, deep AC, unpredictable ELP
Solution:
• If Kmax >55: Use standard Ks (because most devices are less repeatable and reliable) and
target for -1.5D post op refraction. Use SRK-T formula (most accurate and tend to have a
myopic error which counteract the hyperopic surprises).
• if Kmax <55: Use actual Ks (still the biometry prediction error is between -3 to +3D). Must
calculate the anterior and posterior corneal power without assumption. E.g. EKR-4.5 in
Pentacam with Hollday II or Barret True K formula (found online or in IOLmaster 700).
Br J Ophthalmol 2014; 98(3): 361-4.
40. Special cases: Refractive surgery
Problems:
• Instruments error:
• Most older devices (e.g. IOLmaster 500, lenstar, Placido devices) assume a constant
relationship between the anterior and posterior corneal curvature (Rpos/Rant: 82% and thus
use n=1.3375)
• Irregular corneal surfaces especially in decentered ablations, therefore wrong Ks.
• Formula error:
• ELP is estimated from the K values
Solution
• History or contact lens methods (old methods)
• Use actual posterior K values (obtained from Pentacam or IOLmaster 700).
Incorporate into the Holladay II or Barret true K formulas (calculators found
online at ASCRS, Barret-II suit)
41. Special cases: Silicone oil
Problem
• US waves travel slower in SO and thus
gives erranous long AL.
Solution
• AL x 2/3 (1000/1532 = 0.65)
• Optical biometer is not affected as SO
option is chosen.
42. Special cases: Macular pathology
Problem:
• Wrong AL if CME, RD, submacular hmg
(underestimated).
Solution:
• Always examine the retina!
• Newer devices (IOLmaster 700) give a
retinal image.