Refractive Errors Flashcards
Refractive power of eyeball
+60(58.6)
What is near reflex or accommodation triad?
- Convergence of eyeballs by medial rectus
- Miosis by sphincter pupillae
- Accomodation by ciliary muscles-increase in Anterior curvature of lens.
Types of Myopia
- Axial-Path,Buphth,post staph
- Index-nuclear cataract
- Positional-ant dislocation/subluxation nd Weil march
- Curvatural-corneal or lens
Symptoms of myopia
- Defective far vision/near sightedness
2. Floaters(muscae volitantes)
Signs of eye in myopia
- Large eyeball-blue thin sclera
- Cornea-large
- AC-deep
- Exophoria
What is fundus?
View of all structures in the post segment 1.vitreous nd retina transparent 2.Choroid(red)
*viewed with ophthalmoscope.
Fundus signs in myopia
- Myopic temporal crescent around optic disc
- Optic disc tilted
- Lacquer cracks
- Foster fuch’s spots
- Posterior staphyloma
Overall appearance of fundus in myopia
Tessellated or Tigroid appearance d/t diffuse alterations in RPE
Other retinal findings in myopia
- Lattice degeneration
- Rhegmatogenous RD
- Retinal tears
- Vitreous deatchment - Seen as WEISS rings
Complications of path myopia
- RD
- Complicated cataract-post subcapsular
- Vitreous hmg nd choroid also hmg
- PAOG- more like an association
- Strabismus fixes convergence
Fundus signs nd complications are absent in?
Simple or developmental myopia
What are the zones of chorioretinal atrophy
2 zones:
- Alpha-always seen in glaucoma
- Beta-TMC
Laser surgeries in myopia
- Corneal based
- Radial keratotomy
- PRK with excimer laser
- LASIK with excimer or femto(upto -8₹
- Smile(upto -10D)
- Lens based
- Clear lens extraction-Fucala sx (for >-12D)
- ICL
Types of Hypermetropia
- Axial-Newborn,micro,nano
- Index-cortical sclerosis
- Positional-post dislocation
- Curvatural-cornea plana
- Aphakia
- Overcorrected Myopia in refractive Sx or Undercorrected IOL in cataract Sx
Symptoms of Hmt
- Defective near vision
2. Asthenopic symptoms(over active near reflex)
Signs of Hmt
- Small eyeball
- AC shallow
- ESOTROPIA
Fundus signs in Hmt
- Pseudopapillitis
2. Shot silk fundus
Complications of Hmt
- Recurrent styles,chalazia
- Accomodation convergent squint
- Amblyopia
- PACG- prevent mydriatic use in elderly hypermetropes
Management of Hmt
- Convex(+) sphere spectacles
- Contact lens-U/L Hmt
- Surgery-1.Cond keratoplasty-radiofreq,upto 3D
2. Thermal keratoplasty=THC-YAG laser
3. Hyperopic laser-upto +4D - Lens based-1.ICL upto +4D
2. Refractive lens exchange-mainly in presbyopes
What is astigmatism?
A cylindrical refractive error in which both the horizontal nd vertical meridians have different refractory power.
Types of regular astigmatism?
- Simple myopic
- Simple Hypermetropic
- Compound myopic
- Compound Hypermetropic
- Mixed
- With the rule
- Against the rule
- Oblique
Causes of astigmatism?
- Corneal
- Lenticular
- Retinal/Macular
Symptoms nd signs nd investigationsof regular astigmatism
- Asthenopia
- Elongation of objects
- Reading close to eyes
- Half closure of lids
- Head tilt
Ix
- Retinoscopy-2 diff refr powers in 2diff axes
- Keratometry-diff corneal curvatures in 2 principal meridians
- Astigmatic fan test
- Jackson cylinder test
Management of regular astigmatism
- Spectacles cylinder convex/concave
- Contact lens-rigid/soft/Toric
- Surgical-1.Astigmatic keratectomy(AK)
2. Limbal relaxing incisions(LRI)-upto +2D
3. Corneal “ “ (CRI)- “
4. PARK-photoastigmatic refractive keratotomy
5. Astigmatic LASIK-upto +5D
6. smile
Lens used in astigmatism
Convex-plus-steep axis
Concave= - =flat axis
Mx of post keratoplasty astigmatism
- Selective removal of sutures in steep meridians-1st performed
- Arcuate relaxing incisions along steep meridians-upto 4-6D
- Relaxing incisions comb with compression - upto 10D
- Corneal wedge resection with suture closure of wound in flat meridian.
- > 10D - LASIK
Symptoms nd signs of irregular astigmatism
- Defective vision
- Distortion of objects
- Polyopia
- Retinoscopy-irregular pupillary reflex
- Slit lamp-corneal irregularity
- Placido’s disc test-distorted circles(pg522)
- CCT-irregular corneal curvature
- Contact lens
- PTK with excimer laser
- Sx-Penetrating keratoplasty or DALK
Purkunje images
4 in normal eye
2 in aphakic eye
What is anisometropia?
How much diff causes diplopia?
Diff refractory power btw2 eyes
>2.5D nd >5% diff magnification causes diplopia.
*1D=2% magnification
Spectacles upto 4D
Contact lens for higher
IOL in aphakia, Refractive corneal Sx,PRL nd RLE(very high)
Early t/t to prevent amblyopia
What is aniseikonia?
Etiology?
Types?
Images projected to the visual cortex from 2 retinae are in unequal in size nd or shape
*Upto 5% well tolerated
Etio-Optical,Retinal,Cortical
2 types-1.Symmetrical= Spherical,Cylindrical
2.Asymmetrical =Prismatic-inc in 1 direction
Pin cushion-inc in 2 directions(high plus correction)
Barrel- decr in 2 directions(high minus correction)
Oblique distortion
What is presbyopia?
Condition of failing near vision d/t age related decrease in amplitude of Accomodation or Increase in punctuation proximum.
Near point 7@10 yrs
25@40 yrs
33@45yrs
Causes of presbyopia?
Age related-1.Changes in lens- decrease elasticity or increase sclerosis
2.Decreased ciliary muscle power
Premature causes-1.Uncorrected Hmt
2. Premature sclerosis
3. Chronic simple glaucoma
Presbyopic glasses guide
45 yrs=+1 to +1.25
50 yrs=+1.5
55 yrs=+2
60 yrs=+2. 5
Disadvantages of spectacles in aphakia
- High magnification-diplopia
- Spherical aberration-Pin cushion effect
- Prismatic aberration-Roving ring scotoma/Jack in box phenomenon
What is cycloplegia?
Causes?
Paralysis of Accomodation
- Drug ind-Atropine,HA
- Paralytic internal ophthalmoplegia
- Complete 3rd nerve paralysis
- Blurring of near vision
- Photophobia(glare)
- Decrease in near Point
Spasm of Accomodation?
Excess Accomodation
- Drug ind-strong miotics
- spont
Relaxed by atropine
