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LABORATORY TESTING IN PRIMARY CARE OPTOMETRY

LABORATORY TESTING IN PRIMARY CARE OPTOMETRY

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LABORATORY TESTING IN PRIMARY CARE OPTOMETRY

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  1. LABORATORY TESTING IN PRIMARY CARE OPTOMETRY Tammy P. Than, MS, OD, FAAO Carl Vinson VAMC Dublin, GA tammy.than@va.gov

  2. Microbiology

  3. Cultures and Sensitivities • Mandatory • central corneal ulcers • hyperacute conjunctivitis • ophthalmia neonatorum • membranous conjunctivitis • Parinaud’s oculoglandular syndrome • postoperative infections • Recommended • chronic conjunctivitis • unresponsive conjunctivitis • new practitioner

  4. Cultures and Sensitivities • specimen preparation is important • no anesthetic – if possible • sterile swab  plate onto culture media • culturette • media: • Thioglycolate broth • Blood agar • Chocolate agar • Saboraud’s agar

  5. Transport Media • Amies media without charcoal • Higher yield than other media • Comparable to plates

  6. In-Office Microbiology • Gram Stain • Gram (+) = purple • Gram (-) = pink • look at morphology • Cytology • PMNs = bacterial • lymphocytes = viral • eosinophils = allergic

  7. Diagnostic Imaging • plain film X-Ray • CT scan • MRI • 75 million in 2003 • Ultrasonography • Angiography • GDx, OCT, HRT • etc…

  8. Resources • Imaging of the Globe and Orbit: A Guide to Differential Diagnosis • Hosten and Bornfield • Publisher Thieme • http://www.med.harvard.edu/AANLIB/home.html • http://www.loni.ucla.edu/index.shtml

  9. X-Ray: The Basics • Incident X-Ray enters tissue • Beam is attenuated • Exit X-Ray leaves tissue exposes film • White areas = not exposed • Dark areas = film exposed • 3-D represented by 2-D • Black = air (no attenuation) • White = bone • Gray = soft tissue

  10. X-Ray: Types of Views • Skull / Sinus Series • Caldwell • Lateral • Waters • Chest • AP, PA, lateral • Spinal

  11. CALDWELL

  12. CALDWELL

  13. LATERAL

  14. LATERAL

  15. WATERS

  16. WATERS

  17. X-Ray Indications • Confirm the integrity of the orbit • Intraocular Foreign Body • Intraorbital Foreign Body • Trauma • muscle entrapment?

  18. X-Ray Indications • Sinusitis • R/O Orbital cellulitis • Horner’s syndrome • Uveitis • Ankylosing spondylitis • Reiter’s syndrome

  19. X-Ray: Contraindications • Pregnancy • Excessive Radiation Exposure • Rad = unit of absorbed energy in tissue • Gray (Gy) = 100 Rad • the “latest” unit • 1 Gy = 100 cGy • chest X-Ray is < 1 cGy • cancer treatment may be 6000 cGy • lens is most sensitive

  20. X-Rays • Pros • Inexpensive • Readily available • Rapid results • Cons • Radiation exposure • No information about soft tissue • 2-D interpretation can be difficult

  21. Case #1 • 17 YOM • Hit in eye x 1 day • + pain • +diplopia

  22. Work-Up • EOMs • Exophthalmometry • Crepitus? • Nerve sensation • IOP • Imaging

  23. Management • Nasal decongestants • Oral antibiotics • broad spectrum • e.g. Keflex 500 mg qid • Don’t blow nose! • +/- Sx in 1-2 weeks

  24. Other Considerations… • R/O Seidel’s sign • Anterior Segment Pathology • uveitis • corneal abrasion • subconjunctival hemorrhage • Commotio Retinae

  25. CT Scan: The Basics • Series of thin X-Ray sections • flat panel detectors may eliminate slices • Emitted X-Rays • Diode sensors • Computer reconstructs views

  26. CT Scan: The Basics • CT Numbers • density < water = negative CT# • density > water = positive CT# • “Windowing” • Gray Scale • White = bone • Black = air • Gray = brain

  27. CT Scan • Views • coronal • paranasal sinuses, orbital integrity • sagittal • chiasmal pathology • axial • orbital and visual pathways

  28. CT – The Exam • Specific protocols • orbital • chiasmal • brain • sinuses • Slice thickness and slice increment • Cranial • ~1 cm / no overlap • Orbital and Chiasmal • 3 mm with 2 mm between • allows overlap • Gantry • 10-20 minutes / scan

  29. Contrast • Iodine • good agent for photoelectric capture • enhances visibility of vascular lesions • Administered IV (or intrathecal) • 1:40,000 incident of AE • BUN and Creatinine • NPO • Good medication hx • d/c Metformin (Glucophage) prior to procedure • CI is shellfish allergy

  30. BUN (Blood Urea Nitrogen) • actually performed on serum or plasma • 12% higher than blood • nitrogen portion of urea • urea is formed in liver from protein breakdown • filtered through renal glomeruli • small amount reabsorbed in the tubules • remainder excreted in urine • azotemia – elevated BUN • nonspecific • prerenal, renal, or postrenal

  31. BUN (Blood Urea Nitrogen) • must be compared over time or evaluated with other tests • renal function – also assess creatinine levels • fasting not required • Adult 5-20 mg/dL • >60 8-21 mg/dL • increased BUN • many conditions and many drugs • decreased BUN • alcohol abuse, diet lacking protein, liver destruction, late pregnancy

  32. CREATININE • product of anaerobic energy-producing creatine-phosphate metabolism in skeletal muscle • excreted by kidneys • increased levels indicative of decreased glomerular filtration rate • Avoid excessive exercise for 8 hours and avoid excessive red meat for 24 hours before testing

  33. CREATININE • Normal • females 0.5 – 1.1 mg/dL • males 0.6 –1.2 mg/dL • elderly – may be lower • Creatinine clearance, urine • 24 hour collection • Creatinine clearance, serum urine • 6, 12, or 24 hour collection • blood sample collected anytime during urine collection period

  34. CT Scan: Artifacts • Motion • Dental Fillings • Partial volume phenomenon

  35. CT Indications • bone imaging • calcification • blood detection • acute • meningiomas • when MRI contraindicated

  36. CT Contraindications • pregnancy • excessive radiation exposure • contrast contraindication • iodine sensitivity • shellfish allergy • kidney disease

  37. CT Scan • Pros • High diagnostic yield • Good for bone • Can reconstruct different views • Cons • Expensive • Human risk • Motion artifacts • Hard to ddx tumors

  38. MRI Unpaired protons (H) = tiny magnets • from water and fat • body is 63% hydrogen atoms • Disrupt with radio pulse • Protons return to original state • Release energy -> MRI

  39. MRI • Signal strength: proton density • Relaxation time: surrounding tissue • T1 weighted • Proton density • tissue composition • T2 weighted • Tissue differences • Intermediate • fat suppression

  40. MRI • White Matter and Fat • T1 = bright T2 = dark • Gray Matter and CSF • T1 = dark T2 = bright • Vitreous • T1 = dark T2 = bright • blood, air = black • EOMs and optic nerves = intermediate density

  41. MRI: The Examination • Gantry • Flux • 0.5 – 1.5 Tesla • Energy detected • Image reconstructed • 40 minutes • +/- gadolinium contrast • paramagnetic • highlights images of similar density

  42. MRI Indications • tumors • posterior visual pathway • brain stem • pituitary • infarcts • posterior fossa • MS

  43. MRI Indications • elevated optic nerve head(s) • unilateral proptosis • field loss • hemianopia • bitemporal • cranial nerve palsies

  44. MRI Contraindications • pregnancy • metallic FB • pacemakers • kidney disease • (if using contrast) • claustrophobia?

  45. Latest… • Short bore • high field • >1.5 Tesla • advantages of tunnel and open MRIs

  46. MRI • Pros • More accurate 3-D image • Good structural detail • No radiation • Cons • $$$ • Time consuming • Won’t show recent hemorrhage

  47. Case #3. • 46 YOWF • CC: Time to change her glasses • HabRx: • OD –4.25 DS • OS –5.00 DS • BVA • OD: -4.00 20/20 • OS: -0.25 20/20

  48. Other Imaging Tests…

  49. Magnetic Resonance Angiography (MRA) • Non-invasive method for investigation of blood vessels • Surgical planning • 3-D view • Picks up rapid blood flow • highly accurate for stenosis >50%

  50. Positron Emission Tomography (PET) • Biochemical and physiologic function – in vivo • Radioactive “Tracer” compound • Injected or inhaled • C, N, O, F • 18F labeled fluorodeoxyglucose • Image of brain activity